School Science Lesson
Topic16b
2024-06-20
Amino acids, amides. amines, peptides. proteins
(topic16b)
Contents
16.3.0 Amides
16.8.0 Amines
16.1.0 Amino acids
16.5.0 Reactions of esters
16.4.0 Oleoresins, balsams, "gums"
16.7.0 Peptides
16.6.0 Proteins
16.1.1 Alitame
16.1.2 Alkylamides
16.1.3 Betaines
16.1.4 Butanedioic acid (succinic acid)
16.1.5 Butanoic acid (butyric acid)
16.1.6 Chlorogenic acid
16.1.7 Choline
16.1.8 Ethanoic acid, (acetic acid), ionization reaction
16.1.9 Ethyl acetoacetonate
9.1.10 Glycaemic index (GI)
16.2.2 Glycoproteins and glycolipids
16.2.3 Isohumulone
16.2.4 Lactic acid
16.2.5 Lactones
16.2.6 Lectins
16.2.7 Methanoic acid, ionization reaction
16.2.8 Pentanoic acid (valeric acid)
16.3.1 Prions, "Mad cow disease"
16.7.1 Propanoic acid, (propionic acid), ionization reaction
16.7.2 Rubbing alcohol, surgical spirit
Experiments
16.3.2 Extraction of caffeine and benzoic acid from cola
16.3.3 Phenolphthalein
16.3.4 Food colouring liquids and detergent
16.3.5 Iron from breakfast cereal
16.3.6 Laundry starch
16.3.7 Prepare amyl acetate (pear oil)
16.3.8 Prepare egg recipes
16.3.9 Reactions of esters
16.4.1 Prepare ethyl chloride, chloroethane
16.4.2 Prepare ethyl acetate (ethyl ethanoate)
16.4.3 Prepare ethyl butyrate (pineapple oil)
9.1.8 Prepare ferric tannate with tea leaves
16.4.5 Prepare fruit salts, health salts
16.4.6 Prepare jelly with fresh and tinned pineapple
16.4.8 Prepare methyl chloride gas
16.4.9 Prepare methyl salicylate, oil of wintergreen
16.5.1 Prepare protein solutions
16.5.2 Prepare wood gas and wood tar by heating sawdust
16.5.3 Reactions of benzene
16.5.4 Reactions of urea
16.5.5 Tests for calcium
16.5.6 Tests for cigarette smoke
16.5.7 Tests for nitrogen content in food, Kjeldahl method
16.5.8 Tests for pectin in jelly and jam
16.5.9 Tests for the toxic effect of drugs on water flea, Daphnia pulex
16.6.1 Tests for trimethylamine fish smell
16.6.2 Wheat gluten and laundry starch
16.7.29 Toxic effect of drugs on water fleas, Daphnia
16.7.3 Yeast, fermentation, brewing, beer
16.1.0 Amino acids
1. Amino acids have two functional groups, a carboxylic acid group, (-COOH), and a primary amine, (-NH2).
α-amino acids have the formula NH2CRHCOOH
NH2CRHCOOH + NH2CRHCOOH --> NH2CRHCONHCRHCOOH + H2O
amino acid + amino acid--> dipeptide + water
Amino acids are water-soluble organic compounds and are the primary products of nitrogen anabolism in plants.
Amino acids use peptide bonds to join and form short chain peptides and long chain polypeptides, e.g. proteins.
Only 20 of the hundreds of plant amino acids are known.
The primary protein amino acids, are used by all organisms in the formation of peptides and proteins.
However, animals cannot synthesize all the 20 amino acids.
2. Amino acids
From "Peptide Guide", by Oleg Larin (D. Mendeleev University of Chemical Technology of Russia).
Most amino acids have the structure R-CH(NH2)COOH, with R = hydrogen or an organic group, aliphatic, aromatic or heterocyclic.
The α-amino acids in peptides and proteins (except proline), have:
* a carboxylic acid group -COOH, and an amino group -NH2, H3N+-), with these groups attached to the same carbon atom, the α-carbon atom,
* and an R-group (an organic group or H), that distinguishes one amino acid from another.
Amino acids have two functional groups, 1. a carboxylic acid and 2. a primary amine.
In strong acids, the H2N group accepts a proton to form a positive ion.
In strong alkalis, the -O-H group loses a proton to form a negative ion.
The carboxylic acid group tends to lose a proton to act as an acid.
-C=O(OH) <=> -C=O-O- + H+
The amine group tends to accept a proton to act as a base.
H-NH- + H+ <=> H-N+-H2-
So amino acids act as zwitterions, i.e. have both a positive and negative charge, but an overall neutral charge
HN+H2RCHC=OO-.
3. The 7 types of amino acids
See diagram 16.3.6.0.1 Amino acids, Types 1 to 4
Type 1. Amino acids with aliphatic R-groups, e.g. alanine, glycine, isoleucine, leucine, valine
Type 2. Non-aromatic amino acids with hydroxyl R-groups, e.g. serine, threonine
Type 3. Amino acids with sulfur-containing R-groups, e.g. cysteine, methionine
Type 4. Acidic amino acids and their amides, e.g. aspartic acid, 2-aminopentanedioic acid, asparagine, glutamic acid, glutamine.
See diagram 16.3.6.0.2 Amino acids, Types 5, 6 and 7, Imino acid proline
Type 5. Basic amino acids arginine, lysine, histidine
Type 6. Amino acids with aromatic rings phenylalanine, tyrosine, tryptophan.
Type 7. Imino acids proline, C5H9NO2.
4. Amino acid nomenclature
1. The table below contains the trivial name of the L or D or DL-amino acid, e.g. Alanine, the IUPAC 3-letter code, e.g. Ala, the systematic name, e.g. 2-Aminopropanoic acid, and the formula, e.g. CH3-CH(NH2)-COOH.
The ten essential amino acids, marked with *, must be in the diet, because they cannot be synthesized.
Also, plant proteins may not contain sufficient lysine and tryptophan in the diets of strict vegetarians.
Carboxylic acids (fatty acids), R-(COOH)n, contain the group -CO.OH, i.e. -COOH, carbonyl group attached to a hydroxyl group, are weak acids.
An anion formed from carboxylic acid is called a carboxylate.
Methanoic acid (formic acid), HCOOH
Ethanoic acid (acetic acid), CH3COOH
Propanoic acid (propionic acid), CH3CH2COOH
Butanoic acid (butyric acid), C3H7COOH
Pentanoic acid (valeric acid), CH3(CH2)COOH
Butanedioic acid (succinic acid) CH2)2(COOH)2
The symbol Asx denotes Asp or Asn.
5. Numbering of carbon atoms in amino acids
In acyclic amino acids, the carbon atom of the carboxyl group next to the carbon atom carrying the amino group is numbered 1.
The carbon atoms in proline are numbered as in pyrrolidine, the nitrogen atom being numbered 1, and proceeding towards the carboxyl group.
The carbon atoms in the aromatic rings of phenylalanine, tyrosine and tryptophan are numbered as in systematic nomenclature, with 1, (or 3 for tryptophan), designating the carbon atom bearing the aliphatic chain.
6. The 20 important naturally-occurring amino acids
They are all α-amino acids, because the amine group is on the carbon atom next to the -CO2H group.
The general formula is N2HRCHC=OOH.
+ = essential amino acid, must be in the diet.
Alanine, Ala, C3H7NO2, 2-aminopropanoic acid, CH3-CH(NH2)-COOH
Arginine, Arg, C6H14N4O2, L-arginne, 2-amino-5-guanidinopentanoic acid, H2N-C(=NH)-NH-[CH2]3-CH(NH2)-COOH, +
Asparagine, Asn, C4H8N2O3, L-asparagine, 2-amino-3-carbamoylpropanoic acid, H2N-CO-CH2-CH(NH2)-COOH
Aspartic acid, Asp, C4H7NO4, L-aspartic acid, 2-aminobutanedioic acid, HOOC-CH2-CH(NH2)-COOH
Cysteine, Cys, C3H7NO2S, L-cysteine, 2-amino-3-mercaptopropanoic acid, HS-CH2-CH(NH2)-COOH
Glutamic acid, Glu, C5H9NO4, L-glutamic acid, 2-aminopentanedioic acid, HOOC-[CH2]2-CH(NH2)-COOH
Glutamine, Gln, C5H10N2O3, L-glutamine, 2-amino-4-carbamoylbutanoic acid, H2N-CO-[CH2]2-CH(NH2)-COOH
Glycine, Gly, C2H5NO2, 2-aminoethanoic acid, CH2(NH2)-COOH
Histidine, His, C6H9N3O2, L-histidine, 2-amino-3-(1H-imidazol-4-yl)-propanoic acid, +
Isoleucine, Ile, C6H13NO2, L-isoleucine, 2-amino-3-methylpentanoic acid, C2H5-CH(CH3)-CH(NH2)-COOH, +
Leucine, Leu, C6H13NO2, L-leucine, 2-amino-4-methylpentanoic acid CH3)2CH-CH2-CH(NH2)-COOH, +
Lysine, Lys, C6H14N2O2, L-lysine, 2, 6-Diaminohexanoic acid, H2N-[CH2]4-CH(NH2)-COOH
Methionine , C5H11NO2S, L-methionine, Met, 2-amino-4-(methylthio)butanoic acid, CH3-S-[CH2]2-CH(NH2)-COOH, +
Phenylalanine, Phe, C9H11NO2, L-phenylalanine, 2-amino-3-phenylpropanoic acid, C6H5-CH2-CH(NH2)-COOH, +
Three forms, D-phenylalanine, L-phenylalanine, and DL-phenylalanine, but only L-phenylalanine is an essential amino acid.
Proline, Pro, C5H9NO2, L-proline, Pyrrolidine-2-carboxylic acid, proline CH2)3NHCHCOOH, (a cyclic "imino" acid!)
Serine, Ser, C3H7NO3, L-serine, amino-3-hydroxypropanoic acid, HO-CH2-CH(NH2)-COOH
Threonine, Thr, C4H9NO3, L-threonine, 2-amino-3-hydroxybutanoicacid, CH3-CH(OH)-CH(NH2)-COOH, +
Tryptophan, Trp, C11H12N2O2, L-tryptophan, 2-amino-3-(lH-indol-3-yl)-propanoic acid, C11H12N2O2, +
Tyrosine, Tyr, C9H11NO3, L-tyrosine, 2-amino-3-(4-hydroxyphenyl)-propanoic acid, C9H11NO3
Valine, Val, C5H11NO2, L-valine, 2-amino-3-methylbutanoic acid CH3)2CH-CH(NH2)-COOH, +
16.3.0 Amides
An amide has the functional group C=ONH2.
The -OH in a carboxylic acid is replaced by an -NH2 group.
RC=O(OH) + NH3--> RC=ONH2 + H2O
carboxylic acid + ammonia--> amide + water
Methanamide, HCONH2, CH3NO, formamide, amide of formic acid, HCOOH
Ethanamide, CH3CONH2, C2H5NO, acetamide, amide of acetic acid, CH3COOH
Propanamide (propionamide), CH3CH2CONH2, C3H7NO, amide of propanoic acid (propionic acid), CH3CH2COOH
Butanamide (butyramide), CH3CH2CH2CONH2, C4H9NO, amide of butyric acid (butanoic acid), CH3CH2CH2COOH
"oic amide", e.g. propane C3H8, so CH3CH2CONH2 is propanoic amide, propanamide.
Methylethanamide, CH3CONHCH3, smells like a mouse!
So the molecules RC=ONR2, where C=O refers to a carbonyl group, are called amides, not amines.
Also, if an N-H group has been replaced by an N-M group, (M = metal), are also called amides.
Amide linkage (peptide linkage) : -C=O-NH-
Amide suffix: -oic, or -amide
Cyclic amides: Lactams
List of amides: 1.6
Amides group: -CONH2, or RCONH2: 16.1.5.6.
Lactams
Cyclic amides are called lactams, e.g. the beta-lactam 2-Azetidinone, C3H5NO
Lactams (-NH(CO-), caprolactam (6-hexanelactam C6H11NO: 16.3.4.0.3.
16.4.0 Oleoresins, balsams, "gums"
1. Oleoresins are prepared from common spices dissolved in alcohols or hydrocarbons, in contrast to essential oils obtained by steam distillation.
Oleoresins are like the concretes obtained especially from flowers used for perfumes.
Oleoresins from gymnosperm trees are made from the nonvolatile diterpene residue called rosin.
2. Incenses
Incenses containing strong-scented oleoresins, e.g. frankincense, myrrh.
3. "Natural lacquer"
"Natural lacquer"poison ivy, and shellac form from resinous excretions of the lac insect, (Tachardia lacca).
4. Amber resin
Amber resin is made of nonvolatile | Terpenes | from subterranean deposits of resin from pine trees, a yellow, translucent, fossilized vegetable resin, (Hymenaea courbaril).
5. Phenolic resins
Phenolic resins of hashish the pure resin of marijuana, contain volatile monoterpenes and sesquiterpenes + phenolic cannabinoids, e.g. psychoactive δ-tetrahydrocannabinol (THC), an alcohol.
16.5.0 Reactions of esters
Esters, derivatives of fatty acids (RCOOR'), Esters group (-COOR), Suffix (-oate)
See diagram 16.5.1.0 Esters
Esters (RCOOR', R(C=O)OR') (-oate), derivatives of fatty acids ethyl ethanoate (ethyl acetate) CH3COO(C2H5),
H3C=OOCH2CH3, [glyceride (acyl glycerol), fatty acid ester of glycerol HOCH2CH(OH)CH2OH.
Esters include
* Methyl butanoate (methyl butyrate) apple or pineapple, C5H10O2
* Ethyl methanoate (ethyl formate), rum smell, raspberry taste, in ants and bee stingers, C3H6O2
* Ethyl butanoate (ethyl butryate, butyric ether), pineapple oil, C6H12O2
* Pentyl ethanoate, pentyl acetate, amyl acetate, banana essence, pear oil, isoamyl acetate, isopentyl acetate, C7H14O2, [CH3COO(CH2)4CH3]
* Methyl salicylate, oil of wintergreen, C8H8O3
* Melissyl palmitate, beeswax, C15H31COO(C30H61
Experiments
Hydrolysis of esters
See diagram 16.5.3 Hydrolysis of esters
1. Add acid to an ester.
The H+ of the acid catalyses the hydrolysis.
CH3COO(C2H5 + HOH (H2O) --> CH3COOH + C2H5OH
2. Add alkali to an ester.
This is called saponification, because the reaction is used to prepare soap.
CH3COO(C2H5 + NaOH--> CH3COONa + C2H5OH
3. Reaction of esters with water
* Reaction with water - acid catalyst
Esters react with water at room temperature, in the presence of a strong acid catalyst, to form an equilibrium mixture of carboxylic acid, alcohol, ester and water.
RC=O-OR' + H2O [with H+ catalyst] <=> RC=O-O-H + R'-O-H
ester + water <=> carboxylic acid + alcohol
* Reaction with water - base catalyst
See diagram 16.5.4 Reaction of esters with water, NaOH catalyst
Esters react with water at room temperature, in the presence of a base catalyst, e.g. sodium hydroxide, to form an alcohol and the salt of the acid, so the equilibrium moves to the right as the acid is removed from the reaction.
16.6.0 Proteins
Protein is a "macronutrient, ", i.e. the body needs large amounts of it.
Unlike fat and carbohydrates, the body does not store protein, so has no reservoir to draw on when it is needed.
The basic structure of protein is a chain of amino acids.
Of the 20 amino acids the human body needs to make proteins, the body itself produces only 12 amino acids.
Proteins, peptides, and amino acids are used to make:
* Structural proteins for the body and its organs and tissues
* Enzymes for catalysts in biochemical reactions
* Hormones, e.g. insulin to regulate the blood sugar level
* Antibodies to protect from viruses and bacteria
* Intermediates in complex reactions, e.g. ornithine [H2NCH2CH2CH2CH(NH2)COOH].
Structural forms of proteins
* Primary proteins with a straight chain of amino acids
* Secondary proteins with a helical coil of amino acids stabilized by hydrogen bonds
* Tertiary proteins with folding and looping of a coiled polypeptide stabilized by hydrogen bonds
* Quaternary proteins with four joined tertiary proteins, e.g. haemoglobin.
1. Fibrous proteins and globular proteins
Fibrous proteins are usually insoluble in water and form long coiled strands, e.g. keratin, collagen, actin, myosin, fibrin.
* Collagen is an insoluble fibrous protein in connective tissue, e.g. tendons, skin, bone.
* Keratin, C47H77N13O15, contains the cysteine molecule formed by oxidation between sulfhydryl groups, -SH, of two cysteine molecules to form disulfide bonds, -S-S-, for strong proteins as in hair.
See diagram: Keratin.
2. Globular proteins are usually water-soluble, e.g. enzymes, antibodies, haemoglobin, casein, albumin, insulin.
3. Proteins lose their structure and coagulate when heated above 50oC, or are acted on by acids or alkalis, e.g. egg white.
Such proteins lose their biological function, i.e. become denatured.
Peptides and polypeptides are polymers of the 20 α-amino acids are listed below.
Other amino acids with special functions occur in the mammal body free or in combined states, i.e. not associated with peptides or proteins.
Some α-amino acids listed below have functions other than forming peptides and proteins, e.g. tyrosine is used to form thyroid hormones.
Proteins are amphoteric
Amino acids are amphoteric in that they contain both acidic and basic groups in their molecules.
Proteins dissolve in alkalis and in concentrated solutions of acids.
In alkaline solutions proteins are negatively charged.
In strongly acid solutions proteins are positively charged.
They are uncharged at the isoelectric point and are precipitated.
At pH higher than the isoelectric point, a protein acts as an acid.
At pH lower than the isoelectric point the protein acts as a base.
When acting as an acid a protein forms a fast colour with a basic dye, e.g. methylene blue.
When acting as a base, a protein reacts with an acid dye, e.g. eosin.
Experiment
To show the amphoteric nature of a protein, prepare four test-tubes, two containing eosin, and two containing methylene blue.
1. Add a white feather or white wool to each test-tube.
Add 3 drops of acetic acid to one eosin solution and 3 drops of concentrated ammonia solution (ammonium hydroxide), to the other eosin solution.
Leave to stand for five minutes.
Wash the feather or wool and note the fast dyeing in the eosin and acid solution.
The protein acted as a base in the presence of the acid, and reacted with the acid dye eosin.
2. Add 3 drops of acetic acid to one of the methylene blue solutions and 3 drops of concentrated ammonia solution (ammonium hydroxide), to the other methylene blue solution.
Leave to stand for five minutes.
Wash the feather or wool or feather and note the fast dyeing in the alkaline solution.
The protein acts as an acid in alkaline solution and reacts with thebasic dye methylene blue.
16.7.0 Peptides
16.3.6.0.3 Peptide bond
1. Peptides are formed when two amino acids are joined by a peptide bond
Compounds formed by the linkage of amino acids in amide linkages are called peptides, NH2-CH-R
Two amino acids can form a dipeptide, three amino acids can form a tripeptide, about 50 amino acids can form a polypeptide, and more than 50 amino acids can from a protein molecule.
However, when a protein or polypeptide is boiled in 6 M hydrochloric acid for a long period, all the peptide linkages are hydrolysed and all the original amino acids can be recovered as separate molecules.
2. Polypeptides are polyamides formed from the same or different amino acid monomers.
A protein is a large polypeptide.
The dipeptide unit still has -NH2 and -COOH groups, so it can continue to react to form polypeptides by condensation polymerization.
However, polypeptides are usually composed of many different amino acids.
16.7.29 Toxic effect of drugs on water fleas, Daphnia
Be careful! Children must not taste the test solutions!
Young children may be distressed by the sight of Daphnia struggling under the influence of these substances.
However, such a sight can send a powerful deterrent message about substance abuse.
Collect Daphnia in spring from ponds or purchase from goldfish supply shops.
1. Prepare the following test solutions in test-tubes
1.1 Use 10 mL coffee from a coffee cup containing 1 teaspoon of coffee powder, or the usual way you make coffee (active ingredient caffeine).
1.2 Use 10 mL cooking sherry, 17% alcohol / volume active ingredient.
2. Stir the following substances into 10 mL water at 37oC
2.1 Use 300 mg aspirin tablet, active ingredient acetylsalicylic acid,
2.2 Use 1 g pipe tobacco or the contents of discarded cigarette butts, active ingredient nicotine,
2.3 Use 1 Benadryl allergy caplet, active ingredient diphenhydramine.
3. Use an eye dropper to transfer a Daphnia to 5 test-tubes containing 10 mL pond water.
Transfer
1, 2, 3, 4 drops of test solution into test-tubes 1, 2, 3, 4.
Put no test solution in the control test-tube.
4. Use a microscope to observe movement, heart rate and gill movement of Daphnia in the control test-tube.
5. Use test-tubes 1 to 4 to record the least number of drops of test solution to kill the Daphnia.
Tobacco causes quick death at the lowest doses.
Alcohol first slows the heartbeat rate, then is lethal at higher doses.
Aspirin and allergy capsules are lethal at the highest doses.
Coffee causes "racing" of the heart, heart palpitations, but is not lethal.
6. Repeat the experiment with the following
6.1 Decaffeinated coffee,
6.2 Red wine 12.5% alcohol / volume,
6.3 100 mg low dose "baby" aspirin,
6.4 "Lite" low nicotine cigarettes.
6.5 "Red Bull" sports drink contains caffeine.
The Daphnia are easy to keep, easy to study, and inexpensive.
However, be cautious when interpreting your results, because what happens when Daphnia are exposed to caffeine may or may not have similarities to what happens when humans drink coffee.
7. Study the effect of salt concentration on the size of Daphnia.
16.8.0 Amines
Amines have the functional group C2H5NH2
Amines are produced by the decay of organic matter, ammonia-derivative organic compounds of nitrogen where one or more hydrogen atoms has been replaced by a hydrocarbon radical, an alkyl or aryl group.
Amines are organic derivative of ammonia, NH3, where one, two or three hydrogen atoms are replaced by alkyl groups as a primary amine, secondary amine or tertiary amine, e.g. trimethylamine CH3NCH3CH3.
Amines usually act as weak bases that form ammonium salts that are more soluble in water than the original amine, e.g. cough medicine, may contain the cough suppressants dextramethorphan hydrobromide or the decongestant, expectorant, pseudoephidrine hydrochloride and ephedrine.
Amines, RNH2 (amino, -NH2), amine, e.g. methylamine, CH3NH2
Amines, aliphatic amines (RNH2-, R = alkyl group).
Primary amine, methylamine, CH3N2 Secondary amine, dimethylamine, (CH3)2NH Tertiary amine, trimethylamine, N(CH3)3
16.1.1 Alitame
Alitame is an artificial sweetener that is 2, 000 times as sweet as sugar.
It is a protein and a dipeptide, from 2 amino acids - aspartic acid and phenylalanine.
It suitable for people with genetic disorder phenylketonuria (PKU).
It has a good taste and less aftertaste than Aspartame.
It is suitable as part of a diabetic diet and is not harmful to teeth.
Due to high costs production has recently ceased.
Sold as "Aclame".
Not yet approved in the USA, Approved in the EU as E956.
Approved in Mexico, China and Australia.
16.1.2 Akylamides
See diagram 16.3.18 Akylamides.
Akylamides, R1-C=O-N-R2, can be used to mask unpleasant tasting substances.
Akylamides include | Capsaicin | Diynoic acid isobutylamide | Sanshool amide C16H25NO | Spilanthol | tetraenoic acid.
Also, akylamides occur in Echinacea purpurea, purple coneflower, Asteraceae.
Capsaicin: 17.1.0
Sanshool, fatty amide, alpha sanshool, C16H25NO It occurs in Sichuan peppercorn, "ma", Zanthoxylum simulans, Rutaceae, It causes tingling buzzing, numbing sensation of the lips, because it affects D-afferent nerve fibres, light touch receptors called Meissner receptors, in the lips
Spilanthol, fatty acid amide, C14H13)NO, effect on mouth like local anaesthetic in Syzygium species
Acmella oleracea, toothache plant, Asteraceae.
16.1.3 Betaines
Neutral chemical compound, positive ammonium or phosphonium cation and negative carboxylate group, a zwitterion.
* Trimethylglycine (TMG), Glycine betaine, Oxyneurine, Lycine, (often called "Betaine"), C5H11NO2, (derived from glycine + three methyl groups), sweet crystalline quaternary ammonium salt, methylating agent, transmethylating metabolic intermediate, first isolated in sugar beet (Beta vulgaris subsp. vulgaris), also Betaine Hydrochloride, crystalline alkaloid, used as a gastric acidifier supplement.
* Homostachydrine
Homostachydrine, (S)-Homostachydrine, Pipecolic acid betaine, C8H15NO2, is an ammonium betaine, in green coffee beans.
Robusta and Arabica species, have heat stability so are used to determine coffee content in roasted coffee blends and coffee consumption. in human serum and urine, in Medicago sativa (alfalfa) seeds and leaves, in Achillea millefolium (yarrow), in fruits, seeds, and leaves of orange, lemon, and bergamot
16.1.4 Butanedioic acid
Butanedioic acid, HOOCCH2CH2COOH, succinic acid, spirit of amber, colourless crystals, citric acid cycle, in two colourless crystalline forms, the cis from is maleic acid and the trans form is fumaric acid.
They are used to make synthetic alkyd thermoset resins.
It occurs in sugar cane juice, castor oil plant and animal tissues as an intermediate stage of the Krebs cycle.
16.1.5 Butanoic acid
Butanoic acid, C3H7COOH, butyric acid, n-butyric acid (use < 10 mL), harmful by all routes
Butanoic acid, C3H7COOH, butyric acid, is in the form of two isomers, normal butyric acid (n-butyric acid), and isobutyric acid.
The n-butyric acid is a thick liquid with a rancid butter odour and occurs in rancid butter and human sweat.
It is used to prepare flavour and perfume esters, e.g. methyl butanoate, (rum odour), ethyl butanoate (pineapple odour).
It is a weak acid, Ka = 1.5 × 10-5.
16.1.6 Chlorogenic acid
Chlorogenic acid C16H18O9, (CGA), ester of caffeic acid, C9H8O4, and quinic acid, C7H12O6, (contains no chlorine!), an hydroxycinnamic acid, antioxidant ester, food additive, in torch ginger (Etlingera elatior), in bamboo, in Phyllostachys edulis, in heather Calluna vulgaris, in prunes, in peach, in green coffee beans.
16.1.7 Choline
See diagram 16.3.3.0 Lipids (choline)
Choline, C5H14NO, CH2OHCH2N(CH3)3OH, amino alcohol, is found in egg yolk, liver, kidney, soya beans, peas, and whole grain wheat.
Choline is an amino alcohol, a component of phospholipids, a water soluble essential lipid in cell membranes, associated with vitamin B complex.
Human milk and bovine milk is very rich in choline, but baby feeding formulas derived from soy must have lower total choline concentrations.
16.1.8 Ethanoic acid, (acetic acid), ionization reaction
Ethanoic acid, CH3COOH, is prepared by destructive distillation of wood, oxidation of ethanol, synthesized from ethyne. (acetylene).
Acetic acid is a weak acid and is used as a preservative.
Vinegar, prepared by fermentation of fruit juices, e.g. grape juice and cider, contains 3 to 6% acetic acid.
Ionization reaction, Ka = 1.76 × 10-5
CH3COOH + H2O <--> H3O+ + CH3COO-
The oxidation of ethanol under reflux with an acidified dichromate solution can be extremely vigorous so make sure that no undissolved chromate or dichromate salt is present.
Add acidified dichromate solution drop-by-drop and with vigorous mixing before heating.
16.1.9 Ethyl acetoactonate
ethyl ethanoate + sodium ethoxide --> ethyl acetoacetonate (3-oxobutanoate).
CH3COCH2COO(C2H5 (acetoacetic ester), (hydrolysis + acid) --> acetoacetic acid (3-oxobutanoic acid), CH3COCH2COOH, (unstable beta-keto acid),
CH3COCH2COOH --> CH3COCH3 + CO2
acetoacetic acid --> acetone + carbon dioxide.
16.2.2 Glycoproteins and glycolipids
Glycoprotein, Mucous glycoprotein, C28H47N5O18, conjugated protein-carbohydrate compounds, e.g. mucins, mucoid, and amyloid glycoproteins. If the sugars are bound to proteins they are called glycoprotein or if bound to fats they are called glycolipids.
Glycoproteins are the proteins covalently attached to carbohydrates, e.g. glucose, galactose, lactose.
Glycolipids are carbohydrate-attached lipids.
Their role is to provide energy and also serve as markers for cellular recognition.
Collectively they are called glycoconjugates of which 11 % of the human body is composed.
Glycoproteins are the most common conjugated proteins.
Glycoproteins are proteins with covalently attached sugar units, i.e. complex polypeptides + polysaccharides chains.
They are protective agents and lubricants and are often found in cell walls.
There are two main types:
1. O-linked glycans have N-acetylgalactosamine attached to the O-terminus of a threonine or serine residue.
2. N-linked glycans have N-acetylglucosamine bonded to the amide nitrogen of an asparagine molecule.
N-acetylglucosamine is a glucose molecule bonded to an amine group bonded to a hydroxyl group.
Glycoproteins on erythrocytes control interaction of blood group substances with antibodies.
They are involved in cell recognition in T-cells, HIV Aids, blood cell antigens, antibodies and pollen recognition.
Laminins are cross-shaped glycoproteins in extracellular matrix of animals and plants.
16.2.4 Lactic acid
Lactic acid, 2-hydroxypropanoic acid, C3H6O3
It occurs as an hygroscopic clear liquid or crystals.
It forms in cells at end stage of glucose metabolism in absence of oxygen and accumulates after strenuous exercise to cause cramp, "stitch", in the diaphragm solar plexus.
It is manufactured by bacterial fermentation of sugars, or by heating glucose with certain concentrations of caustic potash solution.
Lactic acid bacteria convert sugars into lactic acid, so are used in pickling, but also it can cause food spoilage, e.g. souring of milk by Lactobacillus acidophilus.
Streptococcus mutans causes tooth decay and it needs both glucose and fructose from the breakdown of sucrose in food and soft drinks to produce plaque and lactic acid.
Lactobacillus (over 120 species) converts lactose to lactic acid, in decaying plant substances, is benign in vagina and intestines.
It is used as a leavening agent to make fermentation products.
Lactobacillus bulgaricus is used to produce yoghurt, kimchi, curds, ferments glucose and lactose to produce lactic acid.
Experiment
Lactic acid with potassium carbonate
The earliest leavening agent was potassium carbonate from wood ash, potash, that was used to react with lactic acid in a soured dough.
2C3H6O3 + K2CO3 --> 2(K(C3H5O3 + H2O + CO2
lactic acid + potassium carbonate--> potassium lactate + water + carbon dioxide.
16.2.5 Lactones
Lactones are cyclic closed ring esters, a ring of two or more carbon atoms and a single oxygen atom with a ketone group at one of the atoms adjacent to the other oxygen, (–(C=O)–O–).
Lactones in natural products are used in the flavours and fragrance industry and may have antioxidant, antimicrobial and anticancer properties.
Lactones form from dehydration of lactic acid, 2-hydroxypropanoic acid.
See diagram 16.3.18 Lactones.
16.2.5.1 1. Angelica lactone
Angelica lactone, a-angelica lactone, C5H6O2, white crystals, is a food grade flavour ingredient, cancer chemopreventative in the digestive system, sweet nutty coconut odour, with a sweet creamy taste.
16.2.5.2 2. Atractylenolide II lactone
See diagram 16.3.18 Lactones - Atractylenolide II.
Atractylenolide II lactone, C15H20O2, sesquiterpenoid, anti-inflammatory, bone formation It occurs in Atractylodes macrocephala rhizome.
16.2.5.3 3. Butenolide lactone
Butenolide lactone, C4H4O2, 2-furanone, 2-butenolide, 2(5H)-Furanone
It occurs in Streptomyces and Picea species
. The 4-Hydroxy-2-butenoic acid gamma-lactone is used as a food additive.
16.2.5.4 4. Butylphthalide lactone
See diagram 16.3.18 Butylphthalide.
Butylphthalide lactone, C12H14O2, 3n-butylphthalide, 3-Butyl-1(3H)-isobenzofuranone, NPB, in celery smell and taste
It is used to treat disorders of nervous system.
It occurs in dill and is used in trials studying the prevention of renarrowing of blood vessels.
16.2.5.5 5. Decanolactone
See diagram 16.3.18 Lactones - Decanolactone.
Decanolactone, C10H18O2, 5-Hexyloxolan-2-one, γ-decalctone, gamma-decanolactone, 4-hexylbutanolide, peach flavour
It occurs in coconut milk, sherry, white wine, mango, cassava, loganberry, plum, used in flavourings.
Gamma-Decalactone; 706-14-9; 4-Decanolide; Gamma-Decanolactone; 2(3H)-Furanone, 5-hexyldihydro-; 5-hexyldihydrofuran-2(3H)-one
16.2.5.6 6. GBL, gamma-butyrolactone
See diagram 16.3.18 Lactones - GBL lactone.
GBL, gamma-butyrolactone, 4-butyrolactone, C4H6O2, γ-butyrolactone, is a naturally occurring colourless oily liquid with a characteristic pleasant odour.
It is used as a pharmacological agent and solvent stain remover and stripper, (including "Superglue").
It is a furan with a carbonyl thereby forming a cyclic lactone.
It is a an endogenous compound made from gamma-aminobutyrate and precursor of gamma-hydroxybutyrate.
GBL can be converted to the hypnotic drug GHB, γ-hydroxybutyric acid, which is illegal in many countries.
6.2.5.7 7. Gluconolactone, C6H10O6
E575, glucono δ-lactone, acidity regulator, raising agent, with no known adverse effect after consumption.
16.2.5.8 8. Mellitoxin, Hyenancine, (4-Hydroxytutin), C15H18O7, sesquiterpene lactone, poisonous, toxic to central nervous system
It causes honey poisoning in honey-dew, the excretion of the passion vine hopper, Scolypops australis. from leaves of the tutu plant, Coriaria arborea
It occurs in Taxicodendrum globosum
16.2.5.9 9. Phthalides lactone
Phthalides lactone, C8H6O2, base of more complex chemicals including the following: 16.1.5.13, 16.1.5.14, and 16.1.5.15):
16.2.5.1010. Protoanemonin lactone
See diagram 16.3.18 Lactones - Protoanemonin lactone
Protoanemonin lactone, CH4O2, anemonol, ranunculol, lactone of 4-hydroxy-2, 4-pentadienoic acid, toxin in Ranunculaceae, formed in wounded plant from glucoside ranunculin C11H16O8 and may cause itch, rashes or blistering.
16.2.5.11 11. Sedanolide lactone
See diagram 16.3.18 Lactones - Protoanemonin lactone
Sedanolide lactone, C12H18O2, neocnidilide, tetrahydrophthalide compound It occurs in celery smell and taste, celery oil and coriander.
16.2.5.12 12. Sotolone lactone
See diagram 16.3.18 Lactones - Sotolone
Sotolone lactone, sotolon, caramel furanone, sugar lactone, C6H8O3, 3-Hydroxy-4, 5-dimethyl-2(5H)-furanone, flavouring compound It occurs in raw cane sugar, mature sake, coffee, fenugreek, lovage, wines, strong aroma as in fenugreek, maple syrup, caramel.
16.2.5.13 13. Spironolactone
See diagram Spironolactone
Spironolactone (Aldactone) C24H32O4S, synthetic 17-lactone corticosteroid, which decreases reabsorption of sodium and water and decreases the secretion of potassium, inhabits the effect of aldosterone, anti-androgen activity, treats heart failure, hair loss, male baldness and acne, and possibly reduces Alzheimer's disease and dementia.
Spironolactone acts by antagonism of aldosterone in the distal renal tubules.
It is used mainly in the treatment of refractory oedema in patients with congestive heart failure, nephrotic syndrome, or hepatic cirrhosis.
It is used in treatments of hirsutism and acne, but these treatments can lead to adverse effects.
Spironolactone is an aldosterone antagonist.
Spironolactone has antihypertensive, and antiandrogen activities.
Spironolactone competitively inhibits adrenocortical hormone aldosterone activity in the distal renal tubules, myocardium, and vasculature.
This agent may inhibit the pathophysiologic effects of aldosterone produced in excess by various types of malignant and benign tumours.
14. Tetrachlorophthalide, gamma-lactone
See diagram Tetrachlorophthalide
Tetrachlorophthalide, 4,5,6,7-Tetrachlorophthalide, Rabcide, "phthalide", (C8H2Cl14O2) is a 2-benzofuran, a propan-1-ol, a gamma-lactone, a tetrachlorobenzene, organic heterobicyclic compound
It is a melanin synthesis inhibitor, antifungal agrochemical, used as a fungicide to control rice blast, but is not approved for use within the European Union.
15 Tutin, gamma-lactone
Tutin, Tutine, Tutu, Toot poison, C15H18O6, poisonous, causes convulsions, toxic honey poisoning
It occurs in tutu plants, Coriaria species, in New Zealand and South America, Mediterranean region.
16.2.6 Lectins
1. Lectins are a kind of defensive plant protein in seeds which protect them against common pests, sometimes described as "built-in insecticides".
Lectins are sugar binding proteins, obtained mainly from the seeds of legumes, which bind specifically to certain sugars or saccharide residues causing agglutination of particular cells.
Seed lectins are toxic to humans only when the seed is eaten raw, but may be denatured by cooking for about 20 minutes.
Lectins occur in most types of beans, e.g soybeans, grains, dairy products, potato, tomato, eggplant and pepper
Dairy lectins have been implicated in juvenile onset type I diabetes.
Wheat lectins have been implicated in juvenile nephropathy.
Lectins from soy, peanut, wheat germ, milk, nightshades, have caused damage to gut lining, joints, kidney, pancreas and brain.
Lectins found in peanut oil have been implicated in atherosclerosis.
The reaction between the agglutinin and the cell membrane causes alteration of the cell function thus producing the toxic effect.
Lectins in plants bind glycoproteins on the surface of cells
Lectins in animals also bind of soluble extracellular and intercellular glycoproteins.
Lectins in the immune system may recognize carbohydrates found exclusively on pathogens.
Lectins are used in resaerch to to clump red blood cells according to blood group and to stimulate mitosis.
Lectins include the following:
Abrin
Concanavaline A
Hemagglutinins
Ricin
Soybean lectin
Trichosanthin
Viccia cracca lectins
2. Abrin
Abrinin is an extremley toxic toxicalbumin, a ribosome-inactivating protein in seeds of Jequirity pea.
Abrin, as a white yellow powder, is an extremely toxic plant protein that inhibits synthesis of proteins, causes allergic reactions and may be fatal if absorbed through abraded or wounded skin.
Albrin (ABR) may cause death of certain cancer cells.
3. Concanavaline A
Concanavaline A, C10H13N5O4, carbohydrate-binding protein
It occurs in Canavalia
Its useful chemical properties and carbohydrate binding properties are used in research on organic substances.
It is now sold by chemical suppliers.
4. Hemagglutinins
Hemagglutinins (haemagglutinins), cause agglutination of red blood cells.
Lectin hemagglutinins, phytohemagglutinins (PHA), occur in many types of bean, but the highest concentration is in red kidney beans, Phaseolus vulgaris, which may cause intestinal problems, diarrhoea and vomiting.
The disorder is unpleasant, but not toxic.
These beans must be first soaked and cooked in boiling water for at least 10 minutes.
Cooking in less than boiling water may increase the toxicity of the beans!
5. Ricin
Ricin is a poisonous glycoprotein in the seeds of Ricinus communis (Castor bean).
It is one of the most toxic substances known, and there is no antidote for ricin.
However, ricin is water-soluble, so it should not be present in castor oil expressed from the castor bean.
If castor bean seed seeds are chewed or swallowed, ricin may prevent protein synthesis, although some ricin is inactivated in the stomach.
Castor bean seed contains type 2 types of disulfide-linked chains of ribose-inactivating protein, RIP.
Ricinus communis agglutinin (RCA) It occurs in two forms designated RCA60 and RCA120 according to their mol. wt. of approx. 60, 000 and 120, 000 respectively:
* RCA120, also referred to as RCAI is an agglutinin and has an affinity for terminal beta-D-galactosyl residues.
Ricin toxic A chain, N-glycoside hydrolase, Ricinus communis agglutinin, RCAI, contain amino acids causes red blood cells to agglutinate and burst by haemolysis.
* RCA60, also referred to as RCAII or Ricin D is extremely toxic, inhibits protein synthesis and has an affinity for N-acetyl-D-galactosamine.
Ricin toxic B chain, lectin, many amino acids, RCAII, Ricinus communis agglutinin II is an extremely toxic glycoprotein consisting of two disulfide-linked chains.
The B chain can bind to cell surfaces via galactose or N-acetylgalactosamine residues of membrane glycoconjugates and facilitates the transport of lectin to the cell.
The A chain is incapable of entering the cell and is thus not toxic.
Ricin could be used in chemical warfare and in 1978, Bulgarian Georgi Markov died when injected with ricin from a poisoned umbrella tip.
Ricin may cause death of certain cancer cells, because RCAI-specific cell surface glycoproteins may cause metastasis in breast cancers.
The ricin toxins are mostly stable to proteolytic enzymes and so are not destroyed when taken orally. 6. Soybean lectin
Soybean agglutinin, SBA, 2 pairs of chains, A and B, agglutinates cells, in Glycine max (soyabean).
7. Trichosanthin
Trichosanthin, lectin, protein, ribosome-inactivating protein, toxic, single polypeptide chain of 220 amino acid residues
It is used to treat HIV-AIDS, and as an abortifacient.
It occurs in Chinese medicine herb, tian hua fen, abortifacient, in Trichosanthes kirilowii, (snake gourd), beta-trichosanthin in Trichosanthes cucumeroides.
8. Viccia cracca lectins
One chain lectin, Viccia cracca Gal/NAc lectin, blood group A specific
Two chain lectin, Viccia cracca Man/Glc lectin, blood group ABO non-specific.
16.2.7 Methanoic acid, (formic acid), ionization reaction
Formic acid, HCOOH, is a colourless, corrosive liquid with a pungent odour, prepared by passing carbon monoxide and steam under pressure over a hot catalyst.
Ionization reaction, Ka = 1.8 × 10-4
HCOOH + H2O <--> H3O+ + HCOO-.
16.2.8 Pentanoic acid, valeric acid
Pentanoic acid (valeric acid), Valeric acids are in the form of four isomers:
1. n-valeric acid, pentanoic acid, CH3(CH2)COOH, a colourless liquid used in perfume.
2. iso-valeric acid, 3-methyl butanoic acid CH3)2=CHCH2COOH,
3. methylethylacetic acid, 2-methyl butanoic acid CH3(C2H5)CHCOOH,
4. pivalic acid, 2, 2-dimetyl propanoic acid (CH3)3CCOOH.
Valeric acids have unpleasant odours, but valerian herb, which contains them, has a pleasant odour, Valeriana fauriei (V. officinalis var.angustifolia, var.latifolia), valerian, European v., Belgian v., fragrant v., Japanese v., kesso root, Valerianaceae
Valeriana wallichii, Indian valerian, Valerianaceae.
16.3.1 Prions, "Mad cow disease"
A prion is a protein with an abnormal tertiary structure that may force normal proteins to fold abnormally and destroy brain tissue.
They may be transmitted by eating infected brain tissue in animal feed or humans to cause spongiform encephalopathies diseases, e.g. scrapie and BSE (Bovine Spongiform Encephalopathy) in sheep, Mad Cow Disease in cows, and CJD (Creutzfeldt-Jacob Disease), Kuru, (Alpers Syndrome), laughing disease in humans.
In mammals, the only prion protein is PrPSc, misfolded conformer of the cellular prion protein PrPC, found in the body, mainly in the central nervous system.
PrPSc has multiple states, from small soluble oligomers to long, insoluble amyloid fibrils, depending on the stage of disease.
Perhaps it is the soluble oligomers, not the amyloid fibrils, that cause toxicity and pathogenesis.
The prion protein interacts with amyloid beta, one of the key proteins underlying Alzheimer's disease.
16.7.1 Propanoic acid, (propionic acid), ionization reaction
It is a naturally occurring, colourless, pungent fatty acid.
Sodium and calcium salts are used to inhibit mould in animal feed and bread, e.g. calcium propionate, food additive E282, preservative, anti fungal mould inhibitor
Ionization reaction, Ka = 1.34 × 10-5
CH3CH2COOH <--> H3O+ + CH3CH2COO-
The anions, CH3CH2COO-, are called propionates, (propanoates).
16.7.2 Rubbing alcohol, surgical spirit
Rubbing alcohol, (CH3)2CHOH, is usually isopropanol (isopropyl alcohol, 2-propanol.
However, in some countries, "rubbing alcohol" is a specified mixture of ethanol and water.
Surgical spirit is a methylated spirit, i.e. ethyl alcohol, denatured with methyl alcohol to prevent its use as an alcoholic beverage.
Different brands of "surgical spirit" may also contain other liquids.
It is used to clean body surfaces before surgery.
However, some people use the term "surgical spirit" for isopropanol.
16.7.3 Yeast, fermentation, brewing, beer
Yeast, Dried yeast (active granules), baker's yeast, living yeast
See diagram 16.1.1.2.2 Humulone
1. To make whisky, barley is soaked in water then allowed to germinate until roots and shoots form.
During this germination enzymes are produced that can convert starch to fermentable sugars.
The germinated grain (green malt), is then dried over a smoky peat fire to stop further germination.
The malt is ground to form grist that is mixed with hot water then put in a large container, a mash tun, for further germination to form a weak alcoholic solution, to be distilled into casks to form whisky.
The taste of whisky comes mainly from the smoke of the peat fire.
2. "Dried yeast" (active granules), baker's yeast, living yeast, contain "bakers' yeast", an emulsifier, e.g. emulsifier 491, potato flour and a vegetable gum, e.g. 414.
3. In sauerkraut manufacture, lactic acid bacteria convert sugar in cabbage into 2-hydroxypropanoic acid, (lactic acid).
4. Fermented fish sauce, garum, made usually from anchovies, tuna, eel and mackerel, was popular during the Roman empire and is still made in Vietnam and other Asian countries.
5. Beer is made from a malted grain, barley, wheat or rye.
Malt is made by allowing a grain to germinate, then dried.
During germination enzymes, e.g. alfa-amylase and beta-amylase, converts starch in the grain to sugar.
The malt is crushed then the grist is mixed with heated water, mashing.
The mashing allows enzymes to break down starch into sugars, e.g. maltose, activates beta-glucanase to breaks down beta-glucans and activate proteinases to break down proteins.
The colour of beer comes from the use of roasted malt and unmalted grains.
During the mashing process, enzymes present in the grain convert starches to sugars.
The "head" on beer contains proteins.
Later, the mash temperature is raised to deactivate enzymes.
After the mashing, the liquid, now called wort, is strained from the grains.
The wort is boiled with hops to end enzymatic processes, precipitate proteins, isomerize hop resins, concentrate and sterilize the wort.
The hops add flavour, aroma and bitterness to the beer.
The wort is filtered then yeast is added to convert the sugars from the malt into alcohol, carbon dioxide by fermentation or glycolysis.
Later the beer is cooled, yeast removed, the beer is left to "lager" or rest.
Ales Ales are more fruity and aromatic with a richer, creamier feel in the mouth.
Ales range in colour from very pale to black opaque.
Lagers are brewed at a lower temperature when the yeast sinks to the bottom.
Lagers are left at a cold temperature to produce a cleaner style of beer with fewer aromatics.
Nowadays most beers are lagers, e.g. Pilsner, originally made in Pilsen, Czech Republic.
Beers brewed around Brussels, Belgium, lambic beers, are fermented by wild yeast strains from near the Zenne river.
The bitter taste comes from the alpha acids, e.g. cis- and trans-isohumulone, in the resin glands of hops flowers used during the boiling of the wort.
Early "hoppng" increases bitterness.
Late "hopping" increases aromatic tastes.
Traditional ale is made from malted barley, hops, yeast and water.
16.2.3 Isohumulone, C21H30O5
In beer, 1,1-dimethyl allyl + amino acid (containing S) + (riboflavin, vitamin B2, as catalyst)-->3-methyyl-2-ene-1-thiol
Isohumulone gives the "skunky" smell of beer left in the sun or not kept in brown bottles.
Isohumulones are bitter acids from Hops, (Humulus lupulus)
16.3.2 Extraction of caffeine and benzoic acid from cola
16.3.33 Purine derivatives, True alkaloids
Caffeine
1. Isolation of caffeine
Add 2 g of sodium carbonate to 50 mL of a cola (kola), drink in a 1 litre conical flask.
Add 50 mL of dichloromethane (methylene chloride), and swirl gently for five minutes.
Do not shake.
Transfer into a separating funnel and leave to settle for 10 minutes.
Drain the lower methylene chloride layer into a 250 mL conical flask.
Add 50 mL more dichloromethane to the separating funnel and enclose with a stopper.
Carefully invert the separating funnel 3 times to allow any remaining caffeine to be extracted into the dichloromethane layer.
Again drain the lower methylene chloride layer into the 250 mL conical flask.
Add 5 g of anhydrous magnesium sulfate to remove the water when it forms insoluble hydrated magnesium sulfate.
Filter the now clear dichloromethane through cotton wool pad into a 250 mL beaker.
Evaporate the dichloromethane on a water bath in a fume cupboard or distil it off to recover the solvent.
Weigh the remaining precipitate.
Test the precipitate by putting a small amount on a watch glass and mix with 3 drops of concentrated hydrochloric acid.
Be careful! Add small crystals of potassium chlorate.
Mix with a glass rod and evaporate to dryness on a water bath in a closed fume cupboard.
Leave the watch glass to cool then moisten the residue with 2 drops of 2 M ammonia solution.
The residue turns purple.
2. Isolation of benzoic acid
Pour half a drink-can of lemonade is poured into a 1 L conical flask and add 2 drops of dilute hydrochloric acid.
Add 50 mL dichloromethane then swirled gently for five minutes.
Pour into a separating funnel and leave to allowed to settle for 5 minutes.
Drain the solvent layer into a 100 mL beaker and leave to evaporate in a fume cupboard.
A residue of benzoic acid remains.
16.3.3 Phenolphthalein
See diagram Phenolphthalein.
Phenolphthalein, C20H14O4, weak acid, former laxative, was prepared from phthalic anhydride, C6H4(CO)2O.
It is a yellow-white to pale orange fine crystalline powder, odourless, tasteless, acidic in water, used as an acid-base indicator in acid-base titrations, colourless to pH 8.5, pink to red above pH 9, but colourless if large amount of alkali.
It is used as a cathartic medicine stimulating the intestinal mucosa and constricting smooth muscles, but a suspected carcinogen.
16.3.4 Food colouring liquids and detergent
Use a dish of milk, three food colour liquids and a little detergent.
Put two drops of three different food colouring liquids into the three corners of a dish of milk.
Quickly add two drops of detergent into the fourth corner and observe.
Look for common features, especially patterns that are seen when this experiment is least or most active.
Later, another drop of detergent can be added.
16.3.5 Iron from breakfast cereal
Magnetic stirrers, "Scientrific", (Commercial)
Powdered iron is added to breakfast cereal to "fortify" it.
We can digest some of it when the iron filings are oxidized in the stomach and later absorbed by the small intestine.
Iron is necessary for production of haemoglobin.
During production of the cereal in the factory very tiny particles of food grade iron are added to the dry cereal.
The A steelworks could make a small nail from the iron in your body.
Experiments
1. Crush a cup of breakfast cereal into a fine powder with a mortar and pestle.
Put the crushed cereal in a plastic bag and add hot water.
Stroke the bag with a strong magnet, e.g. a neodymium magnet used in electronics, towards one corner of the bag.
The black fur in the corner of the bag is iron.
Do not touch the cereal with the strong magnet.
2. Put a cup of cereal in a food blender.
Add hot water to submerge all the cereal.
After 20 minutes, hold a magnet to the side of the blender and turn it on.
See the iron deposit in the blender next to the magnet.
3. Crush a serving of dry breakfast cereal, e.g. corn flakes, add water and stir in a magnetic stirrer for 10 minutes.
Observe iron powder sticking to the magnetic follower.
Calculate the concentration of iron in the cereal, e.g. "Special K" 20 mg per 100 g dry cereal.
4. Float flakes of breakfast cereal in water in a Petri dish on an overhead projector.
Use a strong magnet to pull the flakes across the dish.
5. Attach magnetic tape to a wooden ice cream stick and wrap it in a plastic bag.
Crush fortified cereal in a plastic bag, pour it into a bowl and cover it with warm water.
Stir the cereal with the ice cream stick and observe the iron particles sticking to the plastic bag around the ice cream stick.
6. Crush a cup of breakfast cereal into a fine powder with a mortar and pestle.
Pour the powder on a piece of paper.
Move a magnet under the piece of paper and note any movement of the fine powder.
2. Laundry starch
Make a suspension of laundry starch, (C6H10O5)n +H2O.
The starch breaks up, but does not dissolve.
Boil the suspension.
The starch turns from chalk white to nearly water white, because boiling burst the starch grains and let the starch out.
The starch is now more soluble and more digestible.
16.3.7 Prepare amyl acetate, (pear oil)
Amyl acetate ester, CH3COO(CH2)4CH3, isoamyl acetate, pentyl acetate n-amyl acetate, n-pentyl acetate, has "banana" odour, but some people cannot smell its banana apple smell, possibly for genetic reasons.
Amyl acetate, (pear oil, pentyl ethanoate, CH3COO(C5H11), has the odour of bananas or pears.
Mix 5 mL of ethanoic acid (acetic acid), 3 mL of pentan-1-ol (amyl alcohol, n-pentyl alcohol, C5H11OH, and 1 mL of sulfuric acid in a test-tube.
Heat the test-tube gently and note the odour of the ester produced by the reaction.
Amyl alcohol, C5H12O, CH3(CH2)3CH2OH, pentan-1-ol, n-amyl alcohol, normal amyl alcohol, 1-pentanol
amyl alcohol (l) + acetic acid --> amyl acetate (banana or pear oil).
16.3.8 Prepare egg recipes
See: 9.4 Egg structure
1. Scrambled eggs
The white of an egg, the albumen, contains globular proteins called albumin proteins, which also carry substances in the human blood. The texture of egg yolk and egg white, albumen, is because of the dissolved globular proteins with outer electrical charges that attract water molecules and prevent other proteins from clumping them together.
However, when egg are heated, as in making scrambled eggs, the globular proteins unravel, denature, exposing the inner charges on the proteins causing the S-H groups on the amino acid cysteine to oxidize and form covalent disulfide bonds, disulfide bridges.
So the scrambled egg becomes hard and loses water.
2. An eggbeater forms foam better at room temperature than when chilled.
If beaten too much, the foam breaks and becomes liquid.
Add sugar and cream of tartar to stabilize the egg foam.
Add fat to cause the foam to collapse.
3. Heat the white albumen of an egg.
Observe how it turns from slimy watery white to chalk white in a firmly cooked egg.
The protein loses surrounding water and shrinks.
The reaction is irreversible.
You cannot dissolve the solid egg white in water.
4. Proteins can be denatured by heat or weak acid solutions that destroy the hydrogen bonds and cause tertiary proteins to uncoil, e.g. vinegar, acetic acid, can "cook" an egg white, albumen, without heat.
5. Egg in a cake mix
Use a cake recipe that requires use of one egg.
Use the same recipe for making four cakes, but with no egg, one egg, two eggs and three eggs.
Eat the four cakes and describe the taste and texture of each cake.
6. Make custard
Whisk together 2 egg yolks, 2tsp cornflour and 2tbsp sugar until well combined. Heat 1 cup of the milk and 1/2 tsp vanilla until warm, but not hot. Remove from the heat and add the milk to the egg mixture. Tip the mixture back into the warming saucepan and whisk constantly until boiling. Take off the heat and whisk until the custard is thick enough to coat the back of a spoon. If you cook custard at too high or too low a temperature it becomes either watery or curdled.
7. Mix oil and water then shake.
The oil and water separates and settles according to the different densities.
Add a surfactant and shake.
An emulsion forms.
If the surfactant is egg yolk, i.e. lecithin, the emulsion is salad dressing.
Beat the mixture hard to obtain small droplets so that the emulsion becomes mayonnaise.
8. Beat an egg yolk until it becomes thick.
Add lemon juice or vinegar.
Slowly add olive oil while stirring.
A stable emulsion forms.
9. Lemon juice does not dissolve fat, but lemon juice can hydrolyse tough fibres in meat to make it more tender.
16.3.9 Prepare esters
Prepare esters, organic acid + alcohol--> ester + water
RCO2H + R'OH <--> RCO2R' + H2O
carboxylic acid + alcohol <--> ester + water
( For -->, reaction needs a dehydrating agent present.)
See diagram 16.5.3 Prepare esters
1. Add drops of concentrated sulfuric acid then heat the test-tube gently in hot water.
Note the odour of the ester, e.g. pentyl ethanoate smells of apricots and octyl acetate smells of oranges.
2. Add five drops of ethanoic acid (glacial acetic acid), to five drops of ethyl alcohol (ethanol) with one drop of concentrated sulfuric acid as a catalyst.
Heat the test-tube gently.
Note the fruity odour of ethyl acetate and the sharp odour of acetic acid.
This is a reversible reaction so it forms an equilibrium mixture of reactants and products.
The carboxylic acid and the alcohol react to form an ester and a molecule of water is eliminated
alkanol + alkanoic acid <--> ester + water (H+ catalyst)
R1COOH + R2OH <--> R1COOR2 + H2O
organic acid + alcohol <--> ester + water
CH3COOH + C2H5OH <--> CH3COO(C2H5) + H2O
ethanoic acid + ethanol <--> ethyl ethanoate + water
(acetic acid + ethyl alcohol <--> ethyl acetate + water)
This reaction is a nucleophilic substitution reaction.
16.4.1 Prepare ethyl chloride, chloroethane
Ethyl chloride C2H5Cl, alkyl halide, colourless flammable gas at room temperature and pressure, ether-like odour, burning taste
It burns with a smoky, green flame to form hydrogen chloride
It reacts violently with oxidants, alkaline metals, calcium, magnesium, aluminium powder, and zinc, reacts with water or steam to produce fumes of hydrogen chloride.
See diagram 1.13 Smelling a gas
Pour ethyl alcohol or methylated spirit into a test-tube.
Note the odour.
Test the liquid with litmus paper.
No colour change occurs.
Add dilute hydrochloric acid.
Heat the mixture gently by putting the test-tube in hot water.
Smell any gas coming from the test-tube.
Be careful! Do not inhale gases directly from the test-tube.
Fan the gas towards the nose with the hand and sniff cautiously.
If no odour is detected, move closer and try again.
Cool the mixtures and add drops of concentrated sulfuric acid.
Heat the mixture gently by putting the test-tube in hot water.
Note the sweet "ethereal" smell.Be careful! Smell for not more than one second.
The gases may cause general anaesthesia.
The heated sulfuric acid acts as a catalyst.
HCl (aq) + C2H5OH (l) --> C2H5Cl (g) + H2O (l)
hydrochloric acid + ethanol--> ethyl chloride + water.
16.4.2 Prepare ethyl acetate
Alcohols react with organic acids to produce esters and water.
Esters are non-electrolytes, so they must be heated to speed the reaction.
Sulfuric acid is used for a dehydrating agent and catalyst to join the other portions of the reactant alcohol and acid to produce the ester.
Ethyl ethanoate (ethyl acetate, acetic ether CH3COO(C2H5), is a colourless liquid with a fruity smell used as a solvent for lacquers and paints.
Esters of low molecular mass have fruity smells and are found in flavours and perfumes.
The semi-structural formula is R1COOHR2.
R = alkyl groups, e.g. R1 = CH3 and R2 = C2H5.
When you heat a mixture of ester and water it produces a mixture of alkanoic acid and alkanol in an equilibrium mixture.
1. Repeat the above experiment with two drops of glacial ethanoic acid, (acetic acid), in place of the ethanol.
Connect a delivery tube from the test-tube to a solution of limewater.
Test for carbon dioxide during the reaction.
The odour of acetic acid disappears.
The reaction produces ethyl acetate.
2. Mix 2 mL ethyl alcohol with 3 mL acetic acid in a test-tube.
Add 3 drops concentrated sulfuric acid.
Heat the mixture gently by immersing the test-tube in hot water.
Cautiously note the odour of the ethyl acetate produced and compare it with the odours of ethyl alcohol and acetic acid.
Ethyl acetate has a fragrant odour different from the wine-like odour of ethyl alcohol and the sharp odour of acetic acid.
[heated with sulfuric acid] ethyl alcohol (l) + acetic acid (aq) --> water (l) + ethyl acetate (aq).
16.4.3 Prepare ethyl butyrate, (pineapple oil)
Ethyl butyrate, ethyl butanoate, C6H12O2, butyric ether, an ester, flavouring ingredient, colourless liquid, odour of pineapples, in many fruit, e.g. apple, banana, less dense than water, insoluble in water
Mix in a test-tube 1 mL of concentrated sulfuric acid and 2 mL of ethanol.
Add 2 mL of n-butyric acid (butanoic acid, C3H7COOH
It smells like rancid butter.
Heat the test-tube gently and note the odour of the ester produced by the reaction.
ethyl alcohol + butyric acid --> ethyl butyrate (pineapple oil), condensation reaction.
16.4.5 Prepare fruit salts, health salts
Mix 0.45 kg icing sugar (fine sugar), 113 g cream of tartar, 113 g tartaric acid, 113 g carbonate of soda, 2 g Epsom salts.
Mix thoroughly and sift twice.
Put in glass jar and seal jar tightly.
Add one teaspoon fruit salts to 0.28 L water and drink without delay!
16.4.6 Prepare jelly with fresh and tinned pineapple
Jelly, "Jello", is not recommended with pineapple Ananas comosus, papaya Carica papaya, figs Ficus carica, guava Psidium guajava, kiwi fruit Actinidia chinensis, and ginger root Zingiber officinale, because they contain proteolytic enzymes that prevent the gelatine from setting.
Prepare two small jellies, one containing crushed fresh pineapple, the other containing crushed tinned pineapple.
Leave to set.
When the tinned pineapple jelly is firmly set, shake the jelly containing the fresh pineapple.
It has not set well, because the fresh pineapple contains enzymes that digest protein in the jelly.
The enzymes in the tinned pineapple have become inactive, because of heating and processing.
Fresh pineapple contains a powerful proteolytic enzyme called bromelase, but in tinned pineapple it is inactivated.
So a pineapple garnish for ham, gammon, should be made of fresh pineapple.
Fresh pineapple interferes with setting gelatine and whipped egg whites, because the enzyme is active.
16.4.9 Prepare methyl salicylate, (oil of wintergreen)
Methyl salicylate (oil of wintergreen, HO(C6H4COOMe, has the odour of "oil of wintergreen" and is used for liniments.
Add 1 g of salicylic acid to a mixture of 1 mL of methyl alcohol and three drops of sulfuric acid in a test-tube.
Heat the test-tube gently and note the odour of the ester produced by the reaction.
methyl alcohol + salicylic acid --> methyl salicylate (oil of wintergreen).
16.5.1 Prepare protein solutions
1. Shake the white of an egg in its own volume of water.
2. Squash peas in water, filter and use the filtrate.
3. Make a gelatine solution from a household "jelly" preparation
4. Collect solid proteins, e.g. hair, feathers.
16.5.2 Prepare wood gas and wood tar by heating sawdust
See diagram 16.10.4 Heating sawdust
1. When heating sawdust strongly in a hard glass test-tube, the gas coming out of the test-tube can be ignited.
This gas is called wood gas.
It contains carbon monoxide, hydrogen gas, methane, and other gases.
The oily dark brown liquid left in the bottom of the test-tube is called wood tar.
It contains wood alcohol, propanone (acetone), ethanoic acid (acetic acid), and other substances.
If sawdust is heated without any air, the residue will be wood charcoal.
Experiment
Fill a sidearm test-tube one half full of wood chips (or sawdust), and fit a one hole stopper with a delivery glass tube into the test-tube.
When heating, observe that the wood chips gradually become black and an oily dark brown liquid flows through the side arm of the test-tube.
Use a lighted match to ignite the gas coming out of the delivery tube.
The gas can burn steadily.
Note that the volume of the product is very small.
The residue is charcoal (carbon).
16.10.4.1 Distil wood (destructive distillation)
2. 16.10.4.1 Distil wood, (destructive distillation of wood)
Distil wood in a furnace.
Condense products in copper tubing to produce charcoal, pyroligneous acid, wood alcohol, acetone, acetic acid.
16.5.3 Reactions of benzene, C6H6
Pyrene, C16H10 (4 benzene rings), coal tar, toxic, in burnt barbecued food
Benzopyrene, C20H12, carcinogenic, lung cancer and throat cancers, in pitch, volcanoes, cigarette smoke, wood smoke, burnt barbecued food
See diagram 16.8.1 Benzene compounds.
Experiments
1. Add 1 mL bromine water to 5 drops of benzene in a test-tube.
The bromine water is not decolorized, unlike ethylene and acetylene with bromine water.
2. Put 5 drops of benzene in 2 test-tubes.
In one of the test-tubes add iron filings.
Add 3 drops of bromine water to each test-tube.
Hydrogen bromide forms in both test-tubes, but more in the test-tube containing the iron filings acting as a catalyst.
C6H6 + Br2 --> C6H5Br + HBr.
3. Add 5 drops of benzene to 1 mL of acidified potassium permanganate solution.
The permanganate solution decolorizes only when the mixture is heated.
The benzene is oxidized to lower molecular weigh molecules.
4. A reaction mixture of concentrated nitric acid and concentrated sulfuric acid in a Liebig condenser reacts with benzene at over 300 K in a nitration reaction to form nitrobenzene.
This reaction is an example of the substitution of a -NO2 group for a hydrogen atom in an arene ring.
The sulfuric acid in not included in the equation, because it acts as a sort of catalyst.
HNO3 + H2SO4--> NO2+ + H2O + 2HSO4-
C6H6 + NO2+ --> C6H5NO2 + H+
benzene + nitric acid--> nitrobenzene + water
C6H6 + HNO3 --> C6H5NO2 + H2O
Late in the reaction, 1,3-dinitrobenzene forms, C6H4(NO2)2, but on cooling to room temperature it separates as a solid from the liquid nitrobenzene.
16.5.4 Reactions of urea
1. Urea, CO(NH2)2, forms biuret, C2H5N3O2
Heat some crystals of dry urea slowly in a test-tube until the liquid that forms solidifies again as the white solid called biuret, NH2CONHCONH2.
Dissolve the biuret in water for use in the biuret reaction.
2NH2.CO.NH2--> NH2.CO.NH.CO.NH2 + NH3.
In the Biuret reaction, alkaline copper sulfate solution turns from blue to violet colour with compounds containing the amino group, -CONH.
This reaction is used as the biuret test for proteins to detect the peptide bond.
2. Reactions of urea with sodium hypochlorite
Dissolve crystals of urea in the minimum amount of water.
Add drops of sodium hypochlorite solution.
Nitrogen gas forms.
Carbon dioxide gas also forms, but it dissolves in the alkaline solution.
NH2.CO.NH2 + 3NaOCl--> N2 + 2H2O + 3NaCl + CO2.
3. Reactions of urea with nitrous acid
Add an equal volume of dilute hydrochloric acid to a saturated solution of sodium nitrite.
Cool under the tap.
When the effervescence has moderated, add drops of a solution of urea.
Nitrogen gas forms.
NH2.CO.NH2 + 2HNO2 --> 2N2 + CO2 + 3H2O.
4. Reactions of urea with soda lime
Heat a mixture of urea and soda lime.
Test the gas formed for ammonia.
NH2.CO.NH2 + 2NaOH --> 2NH3 + Na2CO3.
5. Hydrolysis of urea with urease
Urea + (urease catalyst)--> ammonia + carbon dioxide
If a solution of urea is first made slightly acidic using 0.1 M ethanoic acid, the ammonia produced as a result of enzyme activity will progressively neutralize the acid.
So if universal indicator is added, there will be a colour change as the reaction progresses.
Experiments
* Working concentrations suggested by the supplier 2 mL 0.1 M ethanoic acid, 10 drops of universal indicator, 5 mL urea (10%), 2 mL urease (5%).
* Dissolve urea crystals in water.
Add a tablet of urease or soya flour and keep at 40oC for a minute.
Test for ammonia.
The enzyme, urease, hydrolyses the urea.
NH2.CO.NH2 + H2O--> 2NH3 + CO2.
6. Urea acts as a base
Add an equal volume of concentrated nitric acid to a saturated solution of urea.
The white precipitate is urea nitrate NH2.CO.NH2.HNO3.
16.5.5 Tests for calcium
Test 1.
To 0.2 mL of a neutral solution containing a quantity of the substance to be examined equivalent to about 0.2 mg of calcium (Ca2+) per mL, add 0.5 mL of a 0.2% w / v solution of glyoxal-bis-(2-hydroxyanil) in 96% v / v ethanol.
Add to this mixture 0.2 mL of a 10.6% w / v solution of anhydrous sodium carbonate.
Shake this mixture with 2 mL of chloroform and add 2 mL of distilled water.
Shake the mixture again to allow the denser chloroform layer to separate from the aqueous layer.
A chloroform layer coloured red confirms the presence of calcium ions.
Test 2.
Dissolve 20 mg of the substance n 5 mL of 2M acetic acid.
Add 0.5 mL of a 5.3% w / v solution of potassium ferrocyanide, potassium hexacyanoferrate (II).
The solution remains mostly unchanged in clarity and colour.
Add 50 mg of ammonium chloride.
The formation of a white, crystalline precipitate confirms the presence of calcium ions.
16.5.6 Tests for cigarette smoke
Nicotine, C10H14N2
Burning, leaves of the tobacco plant give off smoke in which more than one thousand chemical substances have been identified.
These substances include tobacco tar, nicotine, carbon oxide and aldehydes considered harmful to human health.
Tobacco tar contains many kinds of carcinogens, e.g. benzopyrene.
Nicotine is similar to hydrocyanic acid in toxicity.
Excessive carbon oxide will weaken oxygen-carrying capacity of blood, and lead to an oxygen deficit in body tissues.
Experiment
Put 10 mL of 95% alcohol in a sidearm test-tube.
Fit a test-tube with a one hole stopper carrying a glass delivery tube.
Keep one end under the alcohol and close to the bottom of the test-tube.
Insert the other end of the delivery tube in a lighted cigarette.
Draw smoke down through the delivery tube into the alcohol solution by using an air extractor attached to the side arm of the test-tube.
Some substances, e.g. nicotine and benzidine, dissolve in the alcohol to make the colour of the solution change from colourless to yellow, and finally to brown, along with an increase in the number of lighted cigarettes.
16.4.8 Prepare methyl chloride gas
Pour 5 mL methyl alcohol and 5 mL ethyl alcohol into separate test-tubes.
Note their odours.
Drop small pieces of red and blue litmus paper into each liquid.
Add to each about 5 mL of dilute hydrochloric acid.
If you see no visible signs of reaction, warm each mixture gently by standing the tube in hot water for 5 minutes.
Cautiously smell any gas that may be coming from the test-tubes.
Be careful! Sulfuric acid is a corrosive chemical!
Cool the mixtures and add a few drops of concentrated sulfuric acid o each test-tube.
If you see no visible signs of reaction, warm each mixture gently by standing the tube in hot water for 5 minutes.
Cautiously smell any gas that may be coming from the test-tubes.
Avoid smelling for more than one second any gases liberated, since one of them can cause general anaesthesia when inhaled in sufficient quantity.
There is no apparent reaction when hydrochloric acid is mixed with either of the two alcohols.
But after heating the mixture with concentrated sulfuric acid, a reaction occurs, shown by the production of a gas with a sweetish "ethereal" smell.
[heated with sulfuric acid] methyl alcohol (l) + hydrochloric acid (aq) --> water (l) + methyl chloride (g).
16.5.7 Tests for nitrogen content in food, Kjeldahl method
(Johan Kjeldahl, 1849-1900, Denmark)
16.5.7 Tests for nitrogen content in food, Kjeldahl method
1. Be careful! Do this experiment in a fume cupboard.
Add 10 mL of concentrated sulfuric acid to 0.5 g of urea in a long necked flask (Kjeldahl Flask).
Add potassium hydrogen sulfate to raise the boiling point of the acid and complete the decomposition of the protein.
Boil in a fume cupboard for 10 minutes.
Leave to cool then add 100 mL water.
Add strong sodium hydroxide solution (30%), and anti-bumping granules.
Distil the mixture.
Test for ammonia in the distillate.
For volumetric titration, pass all the ammonia through 1 M acid solution.
The ammonia neutralizes some acid.
Titrate the acid left over with an alkali to find how much acid used by the ammonia.
2. Repeat the experiment with 5 g egg albumen (eggwhite).
H2SO4 (aq) + 2NH3 (g)--> (NH4)2SO4 (aq).
16.5.8 Tests for pectin in jelly and jam
1. To test whether fruit juice has enough pectin for jelly, stir together 5 mL (1 tsp) of fruit juice with 15 mL (1 tbsp) of methylated spirits.
If the juice forms one big clot, which can be picked up with a fork without breaking, it has sufficient pectin.
If the juice is low in pectin, several small clots will form.
This is a poisonous mixture, so do not taste it and discard it immediately after the test.
If fruit juice contains too much pectin, it flows slowly, so add sugar.
If the pectin is low, add apples, crabapple, chokecherry, which are high in pectin, to assure gelation.
Boil the juice to concentrate the pectin.
However, heating vigorously can break down the pectin with a loss of gelling power and flavour.
2. Test for pectin every minute.
Once the clot forms, add only 175 mL (3/4 cup) sugar for every 250 mL (1 cup) juice.
Measure fruit juice pH.
Best gelation occurs if pH is between 3.1 and 3.4.
If pH is too high, the jelly is watery and will not set.
3. To make pectin, combine 1 kg of sliced unpeeled crabapples and 750 mL of water.
Simmer 30 to 40 minutes, adding water as needed.
Drain and press through moistened cheesecloth.
To clear, heat the juice and pour through a moistened jelly bag.
If a good pectin clot is obtained, bring the juice to a boil and freeze the pectin for later use.
If a clot does not form, simmer gently to reduce the water content of the juice.
Usually, 1000 mL (4 cups) of homemade pectin replaces 85 mL of liquid pectin.
16.5.9 Tests for the toxic effect of drugs on water flea
Be careful! Children must not taste the test solutions!
Young children may be distressed by the sight of the water flea Daphnia pulex struggling under the influence of these substances.
However, such a sight can send a powerful deterrent message about substance abuse.
Collect Daphnia in spring from ponds or purchase from goldfish supply shops.
1. Prepare the following test solutions in test-tubes:
* Use 10 mL coffee from a coffee cup containing 1 teaspoon of coffee powder, or the usual way you make coffee (active ingredient caffeine).
* Use 10 mL cooking sherry, 17% alcohol / volume active ingredient.
2. Stir the following substances into 10 mL water at 37oC
* Use 300 mg aspirin tablet, active ingredient acetylsalicylic acid,
* Use 1 g pipe tobacco or the contents of discarded cigarette butts, active ingredient nicotine,
* Use 1 Benadryl allergy caplet, active ingredient diphenhydramine.
3. Use an eye dropper to transfer a Daphnia to 5 test-tubes containing 10 mL pond water.
Transfer 1, 2, 3, 4 drops of test solution into test-tubes 1, 2, 3, 4.
Put no test solution in the control test-tube.
4. Use a microscope to observe movement, heart rate and gill movement of Daphnia in the control test-tube.
5. Use test-tubes 1 to 4 to record the least number of drops of test solution to kill the Daphnia.
Tobacco causes quick death at the lowest doses.
Alcohol first slows the heartbeat rate, then is lethal at higher doses.
Aspirin and allergy capsules are lethal at the highest doses.
Coffee causes "racing" of the heart, heart palpitations, but is not lethal.
6. Repeat the experiment with the following:
* Decaffeinated coffee,
* Red wine 12.5% alcohol / volume,
* 100 mg low dose "baby" aspirin,
* "Lite" low nicotine cigarettes.
* "Red Bull" sports drink contains caffeine.
The Daphnia are easy to keep, easy to study, and inexpensive.
However, be cautious when interpreting your results, because what happens when Daphnia are exposed to caffeine may or may not have similarities to what happens when humans drink coffee.
7. Study the effect of salt concentration on the size of Daphnia.
16.6.1 Tests for trimethylamine fish smell
Trimethylamine
Proteins in raw fish are denatured by citric acid, lemon juice.
Freshly caught fish have no odour.
However, the end products of enzyme reactions accumulate when the fish is to give the characteristic fish smell.
If fish is not fresh, it give off trimethylamine, N(CH3)3, the source of fish smell.
The cooked fish is less tasty and the cooking smell is offensive.
Trimethylamine, CH3NCH3CH3, (TMA), volatile tertiary aliphatic amine, from food containing it or from precursors, e.g. (TMNO)
Trimethylamine, C3H9N
trimethylthamine-N-oxide, and L-Carnitine, C7H15NO3, an amino acid derivative.
In humans, ingested TMA may convert to TMNO by N-oxidation, but this process and its importance is not well understood, in 4-11-2016.
TMA is produced by bacteria in the human intestines, but it is broken down by oxidation in the liver.
The reaction requires a certain enzyme, but if people do not have the enzyme, due to a genetic fault, they may smell "fishy"!
They suffer from a metabolic disorder called Trimethylaminuria (TMAU).
They can be relieved of this embarrassing problem by avoiding foods rich in the amino alcohol choline.
Trimethylamine is found in beetroot and herrings, so some people say that beetroot has a "herring smell".
Experiment
Stopping fish smell when cooking fish
To stop fish smell, soak fish in soy bean paste or milk so that proteins in them absorb the smell.
Use ginger or green onion during cooking.
Lemon juice, vinegar, wine, and rice wine can neutralize fish fat, which contains trimethylamine.
Soak freshwater fish in vinegar water before cooking.
At the end of rigour mortis, bacterial action may decompose the fish protein and add to the offensive smell.
Fish should be eaten fresh and cooked for only a short time to denature tissue between the fibres and heat the fish to an acceptable temperature for eating.
16.6.2 Wheat gluten and laundry starch
Wheat gluten is a protein complex formed by kneading of the wheat flour dough proteins gliaden and glutenin.
Gliadin C29H41N7O9, is a simple protein, a prolamine, and is the toxic factor associated with celiac disease. Glutenin, is a protein aggregate, responsible for the strength and elasticity of dough. Gliaden is soluble in alcohol, but glutenin is not.
(Gluten is a combination of gliadin and glutenin proteins).
Experiments
1. Tie plain wheat flour in a fine cloth.
Bang it repeatedly in a dish of water.
Let the white suspension of starch settle in the dish and decant the water.
The sticky mass left in the cloth is mainly gluten and cellulose.
9.1.8 Prepare ferric tannate with tea leaves
Tannin is a mixture of organic chemicals related to polyhydroxy-benzoic acids.
Tannin has a bitter taste and is astringent, i.e. it contracts the mouth.
It is found in the bark and other tissues of many plants probably to control grazing.
It is used to prepare black ink and leather from animal hides.
Experiments
1. Add 200 g (2 tea bags) of dried tea to 250 mL of boiling water.
2. Add an unused pad of steel wool to 100 mL of vinegar, boil for 10 minutes, then strain through cotton wool in a filter funnel.
Leave to cool then add 1 mL of hydrogen peroxide solution to produce a brown red, indicating iron (III).
3. Add equal volumes of solution 1. to solution 2. to produce a black solution of ferric tannate.
2H+ + Fe --> Fe2+ + H2
2H+ + 2Fe2+ + H2O2 --> 2Fe3++ 2H2O
Fe3+ + tannic acid --> ferric tannate.
9.1.10 Glycaemic index (GI)
The glycaemic index is a ranking of carbohydrates based on their immediate effect on blood glucose (blood sugar), levels.
It compares foods gram for gram of carbohydrate.
Carbohydrates that breakdown quickly during digestion have the highest glycaemic indexes.
The blood glucose response is fast and high.
Carbohydrates that breakdown slowly, releasing glucose gradually into the blood stream, have low glycaemic indexes.
The theory behind low-glycaemic index diets is that rapidly digested, high-glycaemic index carbohydrates cause fluctuations in blood glucose (sugar) and insulin levels, contributing to hunger and preventing the breakdown of fat.
Glycaemia refers to the rise in blood sugar.
GI is a ranking of carbohydrates in food depending on their immediate effects on blood sugar levels.
Carbohydrates that breakdown rapidly during digestion and release glucose quickly into the blood have a high GI.
Carbohydrates with a low GI are called "smart carbs".
Low GI diets help people with type 1 and type 2 diabetes, pregnancy diabetes, overweight, excess abdominal fat, too high blood glucose levels, high levels of triglycerides and low levels of HDL cholesterol, ("good cholesterol").
GI values: High GI = 70+, Medium GI = 59-69, Low GI = <55.
Glycaemic load of a serving = (carbohydrate content in grams (g), X GI of the food) / 100,
So 1 glycaemic load unit has the effect of consuming one gram of glucose.
Experiment
Heat a mixture of starch and water by pouring boiling water on it while stirring.
The colour turns from chalk white to nearly water white, because the starch grains have burst and let the starch out.
This is similar to making the starch more soluble and more digestible.