Triglycerides

Organic and Biological Chemistry 4.10 Triglycerides1

Stage 2 Chemistry Lecture 17: Topics 4.10, 4.1126/07/2012TriglyceridesFats and oils from plants and animalsTri-esters of propan-1,2,3-triol (glycerol)Three long straight chain carboxylic acids (fatty acids) form ester linkages with each glycerol molecule

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Stage 2 Chemistry Lecture 17: Topics 4.10, 4.11226/07/2012Triglycerides3

Propan-1,2,3-triol

CarboxylicacidStage 2 Chemistry Lecture 17: Topics 4.10, 4.11326/07/20124

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Stage 2 Chemistry Lecture 17: Topics 4.10, 4.11526/07/2012TriglyceridesFatty 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 polyunsaturatedNaturally occurring tri-esters of propan-1,2,3-triol generally will contain three different fatty acids

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Stage 2 Chemistry Lecture 17: Topics 4.10, 4.11626/07/2012Examples of Fatty Acids7

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Oleic Acid

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Olive Oil

Stage 2 Chemistry Lecture 17: Topics 4.10, 4.11926/07/2012Triglycerides

10Triglycerides 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 enzymesIn the laboratory concentrated acid or alkali combined with heating can be used to break down the triglyceride

Stage 2 Chemistry Lecture 17: Topics 4.10, 4.111026/07/2012TriglyceridesThe 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 animalsEdible oils are liquids at 25oC and are obtained from plants or marine animals

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Stage 2 Chemistry Lecture 17: Topics 4.10, 4.111126/07/2012TriglyceridesMelting points of fats and oilsAs 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 tm decreases. The molecules cant pack together as closely and so dont solidifyFat contains a greater percentage of saturated fatty acids than unsaturated fatty acids and as a result it is solid at room temperatureOils contain a greater percentage of unsaturated fatty acids and are liquids

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Stage 2 Chemistry Lecture 17: Topics 4.10, 4.111326/07/2012Reactions of TriglyceridesThe degree of unsaturation of a triglyceride can be determined by its reaction with bromine or iodine

14 This is referred to as an Addition reactionThe 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)Stage 2 Chemistry Lecture 17: Topics 4.10, 4.111426/07/2012Reactions of TriglyceridesBy 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.

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Stage 2 Chemistry Lecture 17: Topics 4.10, 4.111526/07/2012Reactions of TriglyceridesIodine numberThe degree of unsaturation of a fat or oil is often described in terms of the iodine numberThe iodine number is the mass of iodine that reacts with 100g of the fat or oilThe greater the iodine number the greater the degree of unsaturation16Olive oil Iodine Number =7594 (virgin and refined)

Stage 2 Chemistry Lecture 17: Topics 4.10, 4.111626/07/2012Reactions of TriglyceridesLiquid oils can be converted to solid fats by catalytic hydrogenationThe 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 temperature17

Stage 2 Chemistry Lecture 17: Topics 4.10, 4.111726/07/2012Organic and Biological Chemistry 4.11 Carbohydrates18

Stage 2 Chemistry Lecture 17: Topics 4.10, 4.1126/07/2012CarbohydratesGeneral formula is usually CxH2yOyThis can often be written as Cx(H2O)yCarbohydrates are polyhydroxyaldehydes or polyhydroxyketones or compounds that produce these when hydrolysedCan be monosaccharides, disaccharides or polysaccharides depending on the number of simple sugars in the molecule19

Stage 2 Chemistry Lecture 17: Topics 4.10, 4.111926/07/2012MonosaccharidesMonomersGeneral formula CxH2xOx where x = 3 to 8Water soluble (Hydrogen bond with water)Simple sugars eg. Glucose, FructoseSolids at room temperatureSweet20

Stage 2 Chemistry Lecture 17: Topics 4.10, 4.112026/07/2012GlucoseC6H12O6Can exist as a chain or ring structureThese structures are in equilibrium in aqueous solution

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D-Glucose

-D-Glucose

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Stage 2 Chemistry Lecture 17: Topics 4.10, 4.112226/07/2012GlucoseIn 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

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This reaction causes the equilibrium to favour the formation of the chain structureStage 2 Chemistry Lecture 17: Topics 4.10, 4.112326/07/2012DisaccharidesTwo monosaccharides per moleculeFormed by a condensation reaction (eliminating water)Can be hydrolysed to form monosaccharidesWater soluble compounds (Hydrogen bond with water)

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Sucrose Lactose Maltose

Stage 2 Chemistry Lecture 17: Topics 4.10, 4.112526/07/2012PolysaccharidesLarge polymers of monosaccharidesFormed by condensation reaction and broken down to monosaccharides by hydrolysis(C6H10O5)n +nH2O nC12H22O11 polysaccharide disaccharideC12H22O11 + H2O 2C6H12O6 disaccharide monosaccharideOverall(C6H10O5)n + nH2O nC6H12O6

26Stage 2 Chemistry Lecture 17: Topics 4.10, 4.112626/07/2012PolysaccharidesInsoluble in water. Although hydrogen bonding can occur the large molecular size prevents mixing with waterWill absorb water

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Stage 2 Chemistry Lecture 17: Topics 4.10, 4.112726/07/2012PolysaccharidesCelluloseStructural material in plantsMade up of approx. 3000 glucose unitsStraight chain polymer

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Stage 2 Chemistry Lecture 17: Topics 4.10, 4.112826/07/2012PolysaccharidesStarchMade 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.29

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Amylose

AmylopectinStage 2 Chemistry Lecture 17: Topics 4.10, 4.113026/07/2012PolysaccharidesGlycogenStorage molecule for glucose in liver and muscleBranched chain polymer

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