CHEM1004 Lecture Notes - Lecture 34: Chief Operating Officer, Diglyceride, Acid Dissociation Constant
Chemistry of Fatty Acids and Lipids
Chemistry of Fatty Acids and Lipids:
• Lipid - all material extractable from living systems by organic solvents
• Classification based on solubility properties - considerable structural diversity
• Examples
o Fatty acids
o Triglycerides
o Phospholipids
o Cholesterol
o Bile acids
o Steroids
o Vitamins A, D, E, K
Fatty Acids:
• Saturated
o Most common - palmitic acid (16:0)
o Systematic name - hexadecanoic acid
o Numbering starts at carboxyl end
o Carbon immediately adjacent to carboxyl group is the alpha carbon
o Methyl end is commonly referred to as the omega terminus
o Also common
• Myristic acid (14:0)
• Stearic acid (18:0)
• Unsaturated
o Cis double bonds in nearly all naturally occurring fatty acids
o Most common - oleic acid (18:1[9])
o Oleic acid - omega-9 fatty acid
• First double bond is 9 carbon in from omega end
o Polyunsaturated fatty acid
• Linoleic acid (18:2[9,12]) - omega-6 fatty acid
• Linolenic acid (18:3[9,12,15]) - omega-3 fatty acid
• Arachidoic acid (20:4[5,8,11,14]) - omega-6
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o When there is more than 1 double bond in an unsaturated fatty acid, they are
always 3 carbons apart
o Humans cannot synthesise omega-6 and omega-3 fatty acids - need them in diet
o Can synthesise omega-9 fatty acids
Properties of Fatty Acids:
• Amphiphilic
o Both hydrophobic (hydrocarbon chain) and hydrophilic (carboxyl group)
o Behaviour influenced by length of hydrocarbon chain
o Short chain - soluble in water
o Medium-long chain - insoluble (low pH)
• Carboxyl group dissociated at physiological pH
o pKa = 5
o -COO- - stronger interaction with water than -COOH
o Low pH, palmitic acid almost insoluble
o pH = 7, palmitic acid - palmitate, moderately soluble
• Melting temperature depends on double bonds and chain length
o Increasing chain length - increase in melting point
o Increasing (cis) double bonds - decrease in melting point
• Fatty acids usually have an even number of carbons
o Degraded in 2C units (b-oxidisation)
o Synthesised in 2C units (from acetate groups)
Behaviour of Fatty Acids in Aqueous Solution:
• At neutral pH
• FA form monolayer at the air-water interface
• FA form micelles in bulk solution - micelles form when [FA] > critical micellar
concentration
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Document Summary
Lipid - all material extractable from living systems by organic solvents: classification based on solubility properties - considerable structural diversity, examples, fatty acids, triglycerides, phospholipids, cholesterol, bile acids, steroids, vitamins a, d, e, k. Coo- - stronger interaction with water than -cooh: low ph, palmitic acid almost insoluble, ph = 7, palmitic acid - palmitate, moderately soluble, melting temperature depends on double bonds and chain length. Increasing chain length - increase in melting point. Increasing (cis) double bonds - decrease in melting point. Fatty acids usually have an even number of carbons: degraded in 2c units (b-oxidisation, synthesised in 2c units (from acetate groups) Behaviour of fatty acids in aqueous solution: at neutral ph. Fa form micelles in bulk solution - micelles form when [fa] > critical micellar concentration. Triglycerides (triacylglycerols): major storage form of fat, comprise 3 free fa esterified to glycerol, react to form ester linkage - fa"s link to oh group.
