A critical study of the amino acids was undertaken in an effort to discover the particular groups whose linkage is weakened by the absorption of light energy of different frequencies.The present paper deals with substances whose constitution varies in the number of substituent groups, CH2, COOH, or SH, with consequent symmetry, or asymmetry in their spatial configuration.Our results show that t,otal absorption of light of short wavelengths occurs in all these substances, and selective absorption in the case of symmetrically formed molecules.The amino acids used were HCl solutions of alanine (CH2.CHNH2.COOH), cysteine (HS .CH2.CHNH2.COOH), aspartic acid (HOOC .CH2 + CHNHz .COOH), glutaminic acid (HOOC .CH2 + CH2.CHNHz.COOH), and cystine (HOOC .CHNH2.CH2+S.S. CH2.CHNHz .COOH).For purposes of comparison butyric acid (CH3.CH2.CH2.COOH) and succinic acid (HOOC .CH2 * CH2.COOl!I) were included in the investigation.The ultraviolet oabsorption spectra had been previously studied to about 2100 A. for alanine (l-3), aspartic acid (4), glutaminic acid (l), cystine (1, 3), butyric acid (5), and succinic acid (5).In the present study complete absorption spectra have been obtained from 6000-1850 A., as stated in the preliminary reports made on our results (6, 7).The same experimental procedure, described in a previous paper (3), was used in the visible and ultra-violet regions, and the molecular absorption coefficients were obtained.
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Anslow et al. (1932) studied this question.