Empirical equations for predicting 13C chemical shifts in nuclear magnetic resonance spectra of certain types of amino acids

Abstract

13C chemical shift data were obtained for amino acids related to glycine which had the following types of substituents on C-2: alkyl, branched chain alkyl, ω-amino alkyl, and ω-guanido alkyl. Such data were obtained for aqueous solutions at a pH between the pK values of the carboxyl and 2-amino groups (zwitterion form). The data were subjected to graphical and statistical analysis to obtain separate predictive equations for C-1, C-2, and other carbon atoms. Data for the change in chemical shifts on titration with acid were also obtained to aid in 13C assignments and to elucidate configuration.