Properties of Amino Acids High melting points,over 200C More soluble in water than in ether. Larger dipole moments than simple acids or simple amines. Less acidic than most carboxylic acids, less basic than most amines. pK2=10 H3N-CH-C-O pK,=12 R 三> Chapter 24 11
Chapter 24 11 Properties of Amino Acids • High melting points, over 200C. • More soluble in water than in ether. • Larger dipole moments than simple acids or simple amines. • Less acidic than most carboxylic acids, less basic than most amines. H3 N CH R C O O + _ pKa = 10 pKb = 12 =>
Structure and pH 0.5 1.5 ←HN-CH2-C-O anionic above pH 9.6 pKa2=9.6 0 Isoelectric point =6.0 HN-CH2-C-O- zwitterionic near the isoelectric point 0 pKa1=2.3 H:N-CH2-C-OH cationic below pH 2.3 0.5 1.5 => Equivalents of OH added 12 Copyright 2005 Pearson Prentice Hall.Inc
Chapter 24 12 Structure and pH =>
Isoelectric Point pH at which amino acids exist as the zwitterion (neutral). Depends on structure of the side chain. Acidic amino acids,isoelectric pH ~3. Basic amino acids,isoelectric pH ~9. Neutral amino acids,isoelectric pH is slightly acidic,5-6. => Chapter 24 13
Chapter 24 13 Isoelectric Point • pH at which amino acids exist as the zwitterion (neutral). • Depends on structure of the side chain. • Acidic amino acids, isoelectric pH ~3. • Basic amino acids, isoelectric pH ~9. • Neutral amino acids, isoelectric pH is slightly acidic, 5-6. =>
Electrophoresis power supply Beginning cathode anode wet with pH 6 buffer solution streak containing Ala,Lys,Asp power supply End cathode anode Asp-moves toward the positive charge = Ala does not move Lyst moves toward the negative charge Copyright 2005 Pearson Prentice Hall,Inc
Chapter 24 14 Electrophoresis =>
Reductive Amination This method for synthesizing amino acids is biomimetic,mimics the biological process. React an a-ketoacid with ammonia,then reduce the imine with H2/Pd. Racemic mixture is obtained. ● Use enzyme catalyst to obtain pure L form N一H NH2 R-C-COOH exccss NH3 R一C一COO-+NH R-CH-COO Pd a-ketoacid imine a-amino acid Copyright 2005 Pearson Prentice Hall,Inc. => Chapter 24 15
Chapter 24 15 Reductive Amination • This method for synthesizing amino acids is biomimetic, mimics the biological process. • React an -ketoacid with ammonia, then reduce the imine with H2 /Pd. • Racemic mixture is obtained. • Use enzyme catalyst to obtain pure L form. =>