Organic and Biological Chemistry

1. Organic and Biological Chemistry 4.10 Triglycerides

2. Triglycerides • Fats and oils from plants and animals • Tri-esters of propan-1,2,3-triol (glycerol) • Three long straight chain carboxylic acids (fatty acids) form ester linkages with each glycerol molecule

3. Carboxylic acid Propan-1,2,3-triol Triglycerides

6. Triglycerides • Fatty acids contain an even number of carbon atoms (between 12 and 20). The carbon chain can be saturated or unsaturated. • If there is more than 1 double bond the molecule is referred to as polyunsaturated • Naturally occurring tri-esters of propan-1,2,3-triol generally will contain three different fatty acids

7. Examples of Fatty Acids

8. Oleic Acid

9. Olive Oil

10. Triglycerides can be hydrolysed to produce glycerol and three fatty acid molecules. In biological organisms that can utilise triglycerides for energy this reaction is catalysed by lipase enzymes In the laboratory concentrated acid or alkali combined with heating can be used to break down the triglyceride Triglycerides

11. Triglycerides • The state of an edible fat or oil at room temperature can be used to determine its source. • Edible fats are solids at 25oC and generally are obtained from land animals • Edible oils are liquids at 25oC and are obtained from plants or marine animals

12. Triglycerides Melting points of fats and oils • As the length of the carbon chain increases so does the tm increase, due to increased dispersion forces. • As the degree of unsaturation increases (i.e. number of C=C bonds increases) the tmdecreases. The molecules can’t pack together as closely and so don’t solidify • Fat contains a greater percentage of saturated fatty acids than unsaturated fatty acids and as a result it is solid at room temperature • Oils contain a greater percentage of unsaturated fatty acids and are liquids

14. Reactions of Triglycerides • The degree of unsaturation of a triglyceride can be determined by its reaction with bromine or iodine • This is referred to as an Addition reaction • The orange colour of the bromine disappears as the reaction occurs. (The products are colourless) • To enable the bromine to mix with the triglyceride both the bromine and triglyceride are dissolved in a non polar solvent (cyclohexane)

15. Reactions of Triglycerides • By titrating a standard solution of bromine (burette) with a known volume of a standard solution of fat or oil the degree of unsaturation can be measured. • The greater the amount of bromine required the greater the degree of unsaturation. • The end point is indicated by the first permanent orange colour in the flask.

16. Reactions of Triglycerides Iodine number • The degree of unsaturation of a fat or oil is often described in terms of the iodine number • The iodine number is the mass of iodine that reacts with 100g of the fat or oil • The greater the iodine number the greater the degree of unsaturation Olive oil Iodine Number =75–94 (virgin and refined)

17. Reactions of Triglycerides • Liquid oils can be converted to solid fats by catalytic hydrogenation • The vegetable oil is heated with hydrogen gas under pressure in the presence of a nickel catalyst. These conditions increase the rate of reaction. • Sufficient hydrogen is added to produce a product that is solid at room temperature

18. Organic and Biological Chemistry 4.11 Carbohydrates

19. Carbohydrates • General formula is usually CxH2yOy • This can often be written as Cx(H2O)y • Carbohydrates are polyhydroxyaldehydes or polyhydroxyketones or compounds that produce these when hydrolysed • Can be monosaccharides, disaccharides or polysaccharides depending on the number of simple sugars in the molecule

20. Monosaccharides • Monomers • General formula CxH2xOx where x = 3 to 8 • Water soluble (Hydrogen bond with water) • Simple sugars eg. Glucose, Fructose • Solids at room temperature • Sweet

21. Glucose • C6H12O6 • Can exist as a chain or ring structure • These structures are in equilibrium in aqueous solution α-D-Glucose D-Glucose

23. Glucose • In the chain form the aldehyde can be oxidised by Tollen's reagent forming the silver mirror and the carboxylate ion but there is no reaction with the ring form • This reaction causes the equilibrium to favour the formation of the chain structure

24. Disaccharides • Two monosaccharides per molecule • Formed by a condensation reaction (eliminating water) • Can be hydrolysed to form monosaccharides • Water soluble compounds (Hydrogen bond with water)

25. Maltose Sucrose Lactose

26. Polysaccharides • Large polymers of monosaccharides • Formed by condensation reaction and broken down to monosaccharides by hydrolysis • (C6H10O5)n +½nH2O ½nC12H22O11 polysaccharide disaccharide • C12H22O11 + H2O  2C6H12O6 disaccharide monosaccharide • Overall • (C6H10O5)n + nH2O  nC6H12O6

27. Polysaccharides • Insoluble in water. Although hydrogen bonding can occur the large molecular size prevents mixing with water • Will absorb water

28. Polysaccharides Cellulose • Structural material in plants • Made up of approx. 3000 glucose units • Straight chain polymer

29. Polysaccharides Starch • Made up of amylose 250-2000 glucose units in a straight chain and amylopectin which contains hundreds of thousands of glucose in a branched chain structure.

30. Amylose Amylopectin

31. Polysaccharides Glycogen • Storage molecule for glucose in liver and muscle • Branched chain polymer