Glutamic acid optical rotation

The a-carbon of glutamic acid is chiral. A convenient and effective means to determine the chemical purity of MSG is measurement of its specific rotation. The specific optical rotation of a solution of 10 g MSG in 100 mL of 2 A/HQ is +25.16. Besides L-glutamic acid [56-86-0] D-glutamic acid [6893-26-1] and the racemic mixture, DL-glutamic acid [617-65-2] are known. Unique taste modifying characteristics are possessed only by the L-form. 

To answer this question, Goodman and his team synthesised by classic techniques a series of polypeptides of y-methyl-L-glutamate ranging from 3 to 11 units all composed of the same enanthiomorphic form of the amino-acid residues (73). The specific optical rotation of a polymeric molecule involving asymmetrical centres is enhanced by its... 

Wilson and Cannan (18) reported detailed observations on the equilibrium and velocity constants in the glutamic acid—pyrrolidone carboxylic acid system in dilute aqueous solution. They found that the conversion of glutamic acid to pyrrolidone carboxylic acid follows the equation for a reversible first-order reaction. The equilibrium constant and the rate at which the equilibrium is achieved depend on the pH of the solution and the temperature. In neutral solutions, the equilibrium favors almost complete conversion of glutamic acid to pyrrolidone carboxylic acid however, the rate of the reaction is very slow and thus only 1% conversion occurs after 2-3 hr at 100°. In weakly acid (pH 4) and alkaline (pH 10) solutions, the conversion of glutamic acid to pyrrolidone carboxylic acid is much faster and about 98% conversion occurs in less than 60 hr. In strong acid (2 N HC1) and base (0.5 N NaOH) the conversion of pyrrolidone carboxylic acid to glutamic acid proceeds rapidly and virtually to completion. Other studies have shown that the conversion of glutamic acid to pyrrolidone carboxylic acid can be carried out within 2 hr at 142° with little alteration of optical rotation (80). 

When azobenzenes are attached to polypeptides, photochromic reactions of azobenzenes can induce the change in helical properties of the polypeptides, which may be detected by CD spectrum as well as optical rotation. For 4-phenylazophen-ylamine-condensed poly(y-glutamic acid) A-9 containing up to 80 mol% of 4-phenylazophenylamide side chain, UV irradiation in organic solvents, such as... 

Fig. 15. Rotatory artifacts that simulate Cotton effects at an absorption band. The dependence of the rotatory artifact on absorbance of p-cresol solutions placed in series with the same poly-L-glutamic acid solution is shown. The concentration of p-cresol was adjusted to give the total absorbance of chromophore plus polypeptide background that appears with each curve. The rotator, poly-L-glutamic acid, was at concentration of 0.5% at pH 7.0 in a 10-cm cell. The rotations are those actually observed, a, in degrees. The rotatory dispersion at Am 2 coincides almost exactly with that for the polypeptide alone, so that it has been omitted from the figure. At Am 4, an interference filter, /, with maximum transmission between 280 and 285 m/i, was placed in the optical path. The absorption spectrum, in arbitrary units, is typical of p-cresol plus poly-L-glutamic acid background. The emission spectrum is represented in arbitrary units, uncorrected for detector response. (Urnes et al., 1961a.)...

In the polymerization of the mixture of R and S antipodes of valine NCA (8, R = CH(CH3)2) initiated by butylamine in N,N-dimethylformamide and in 1,2-dichloroethane, the optical rotation of the polymer in trifluoroacetic acid scarcely varied at any conversion as shown in F. 18 (52), in clear contrast to the cases of alanine NCA and -y-benzyl glutamate NCA. Fi re 18 im dies that the content of antipodal residues of the polymer chains is constant throughout the reaction. As seen in F. 19, the plot of the optical rotation of the polymer against the S content of feed monomer gives a strait line, independent of the conversion, a fact which confirms that the S content of the polymers is equal to that of the feed monomers, even at half conversion. 

The helix-coil transition in the copolymer clearly shows that the glutamic acid residues form the dominant helix (Table VII). There is no helix formation at alkaline pH owing to the lysine residues either by polarization of fluorescence or by optical rotation measurements in fact, both p and [ql]d decrease. The degree of polarization at pH 4 can be 85% reduced by 9M urea in both poly Glu97Lys3 and poly Glu63Lys37 (No. 3) this reflects destruction of the glutamic acid helix. 

Sachs, H. The optical rotation and some reactions involving a- and y-peptides of glutamic acid and alanine. Dissertation, Columbia University, 1954, iv + 55 pp. University Microfilms. Ann Arbor, Michigan, Publication No. 8818. 

Fig. 3.19 Theoretical and experimental comparison of the heUx-coil transition of poly-y-benzyl-L-glutamate in dilute solution of an ethylene dichloride-dichloroacetic acid mixture. The experimental points are the optical rotation [ao] plotted as a function of the temperature T minus the transition temperature T. The solid curves represent the best fit of theory for samples of various degrees of polymerization n. (From Zimm, Doty and Iso (79))...

The mixture of amino acids released by complete hydrolysis of lipopeptin A was fractionated by ion-exchange chromatography. Each amino acid was isolated and the optical rotation determined. Two moles of L-aspartic acid and 1 mole each of L-glutamic acid, L-serine, l-threonine, N-methyl-L-phenylalanine, L-threo-p-hydroxyglutamic acid and N-methyl-L-aspartic acid were obtained. 

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