4.8 Amides 1

Amides 2 Amide functional group

Amides Possible under high temp for extended time to prepare amide from a carboxylic acid and an amine or ammonia (condensation) RCOOH + NH 3  RCOO – NH 4 + RCOO – NH 4 +  +H 2 O 3

Amides RCOOH + RNH 2  RCOO – + RNH 3 + RCOO – RNH 3 +  +H 2 O Amides are produced by the reactions of acid halides, acid anhydrides or esters with amines or ammonia 4

5 Lidocaine Prilocaine

Amides Hydrolysis of amides will occur with extended refluxing under acid or alkaline conditions Under acid conditions the amide will hydrolyse to form the carboxylic acid and protonated amine RCONRH + H + + H 2 O  RCOOH + NH 3 R + Under alkaline conditions the products are the carboxylate ion and an amine RCONRH + OH –  RCOO – + NH 2 R 6

4.9 Proteins 7

Proteins: Amino acids 8 Amino acids have both an Amino and a carboxyl functional group R group which varies giving 20 different natural amino acids Simplest is Glycine where R= H acid amino General Form

9 Proline Histidine Methionine

Proteins : Amino acids 10 + − Amino acids can self ionise to form a ZWITTERION by transferring a proton from the carboxyl group to the amine group The molecule does not have an overall charge

Proteins: Formation Proteins are polyamides formed when amino acids (monomer) covalently bond with each other to form large molecules The link between the amino acids is referred to as a peptide link or peptide bond (amide group) The reaction is a condensation reaction which is catalysed by enzymes Proteins are also referred to as polypeptides (long chain molecules with many peptide links) Proteins don’t have a repeating unit as the R groups vary along the polypeptide 11

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Proteins: Types of Bonding Primary (covalent bonds) form the chains Primary (ionic and covalent bonds) and secondary interactions between chains and secondary interactions within chains affect the shape of the protein 13

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Proteins: Secondary interactions Hydrogen bonding can occur between peptide links both within a protein chain and between protein chains Hydrogen bonding can occur between polar R groups on protein chains Hydrogen bonds will also form between the polypeptide and water molecules 15

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Proteins Hydrogen bonding (and other secondary interactions) within and between polypeptide chains results in each protein having a specific structure. This structure is unique to the protein and is necessary for the protein to carry out its biological function. 17

Proteins Within the structure of proteins are active sites which “fit” specific molecules. If the structure of a protein is changed in any way by the disruption of the secondary interactions then the active sites will be changed and will no longer fit the specific molecules. 18

Proteins If this occurs the protein is said to be denatured. Consequently the protein loses its ability to perform its biological function. Enzymes are proteins Their ability to biologically catalyse reactions is affected if their spatial arrangement is disrupted 19

Proteins Changes in pH Alters ionic bonding between NH 3 + and COO – groups Acid: Converts ionic carboxylate ions to carboxylic acids RCOO – + H +  RCOOH Alkali: Converts protonated amines to amine groups RNH OH –  RNH 2 This disrupts bonds between side groups destabilising the protein structure. 20

Proteins Temperature Proteins work effectively within a limited temperature range. Raising a protein to 50 o C or above disrupts secondary bonds destabilising the structure. 21