Lipids

Lipids Types of Lipids Fatty Acids Fats, and Oils Chemical Properties of Triglycerides

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Types of Lipids • Lipids with fatty acids Waxes Fats and oils (trigycerides) Phospholipids Sphingolipids • Lipids without fatty acids Steroids 2

Fatty Acids • • • •

Long-chain carboxylic acids Insoluble in water Typically 12-18 carbon atoms (even number) Some contain double bonds corn oil contains 86% unsaturated fatty acids and 14% saturated fatty acids 3

Saturated and Unsaturated Fatty Acids Saturated = C–C bonds Unsaturated = one or more C=C bonds COOH palmitic acid, a saturated acid COOH palmitoleic acid, an unsaturated fatty acid 4

Structures Saturated fatty acids • Fit closely in regular pattern COOH COOH COOH

Unsaturated fatty acids H • Cis double bonds

H C C

cis double bond

COOH 5

Properties of Saturated Fatty Acids • Contain only single C–C bonds • Closely packed • Strong attractions between chains • High melting points • Solids at room temperature

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Properties of Unsaturated Fatty Acids • Contain one or more double C=C bonds • Nonlinear chains do not allow molecules to pack closely • Few interactions between chains • Low melting points • Liquids at room temperature

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Learning Check L1 How would the melting point of stearic acid compare to the melting points of oleic acid and linoleic acid? Assign the melting points of –17°C, 13°C, and 69°C to the correct fatty acid. Explain. stearic acid (18 C) saturated oleic acid (18 C) one double bond linoleic acid (18 C) two double bonds 8

Solution L1 Stearic acid is saturated and would have a higher melting point than the unsaturated fatty acids. Because linoleic has two double bonds, it would have a lower mp than oleic acid, which has one double bond. stearic acid mp 69°C oleic acid mp 13°C 9 linoleic acid mp -17°C

Fats and Oils Formed from glycerol and fatty acids O CH2 OH CH

OH

CH2

OH

glycerol

HO C O +

(CH2)14CH3

HO C (CH2)14CH3 O HO C

(CH2)14CH3

palmitic acid (a fatty acid) 10

Triglycerides (triacylglcerols) Esters of glycerol and fatty acids ester bonds O CH2

O

C

(CH2)14CH3 + H2O

O CH CH2

O O

C (CH2)14CH3 O C

+ H2O

(CH2)14CH3 +

H 2O 11

Learning Check L2 What are the fatty acids in the following triglyceride? O

CH2

O

C

(CH2)16CH3

O CH CH2

O O

C (CH2)7CH CH(CH2)7CH3 O C

(CH2)12CH3

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Solutions L2 What are the fatty acids in the following triglyceride? O Stearic acid

CH2

O

C O

CH CH2

(CH2)16CH3 Oleic acid

O

C (CH2)7CH CH(CH2)7CH3 O Myristic acid O C (CH2)12CH3 13

Properties of Triglycerides Hydrogenation • Unsaturated compounds react with H2 • Ni or Pt catalyst • C=C bonds

C–C bonds

Hydrolysis • Split by water and acid or enzyme catalyst • Produce glycerol and 3 fatty acids 14

Hydrogenation O CH 2

O

C

(CH 2)5CH CH(CH 2)7CH3

O CH CH2

O O

C (CH 2)5CH CH(CH 2)7CH 3 O C

+ 3 H2

Ni

(CH 2)5CH CH(CH 2)7CH 3

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Product of Hydrogenation O CH2

O

C

(CH 2)14CH 3

O CH CH2

O O

C (CH 2)14CH 3 O C

(CH 2)14CH 3

Hydrogenation converts double bonds in oils to single bonds. The solid products are used to make margarine and other hydrogenated items. 16

Hydrolysis Triglycerides split into glycerol and three fatty acids (H+ or enzyme catalyst) O

CH2

O

C

(CH2)14CH3

O CH CH2

O O

C (CH2)14CH3 O C

H

+

+3 H2O

(CH2)14CH3 CH2 OH CH

OH

CH2

OH

O +

3 HO C

(CH2)14CH3 17

Saponification and Soap • Hydrolysis with a strong base • Triglycerides split into glycerol and the salts of fatty acids • The salts of fatty acids are “soaps” • KOH gives softer soaps

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Saponification O CH2

O

C

(CH 2)16CH3

O CH CH 2

O O

C O C

(CH 2)16CH3 + 3 NaOH (CH2)16CH3

CH2 OH CH CH2

O

+OH + 3 Na O C (CH 2)14CH3 salts of fatty acids (soaps) OH 19

Learning Check L3 What are the products obtained from the complete hydrogenation of glyceryl trioleate? (1) Glycerol and 3 oleic acids (2) Glyceryltristearate (3) Glycerol and 3 stearic acids

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Solution L3 What are the products obtained from the complete hydrogenation of glyceryl trioleate? 2. Glyceryltristearate

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