Infrared spectrum analysis of the dissociated states of simple amino acids
Date
2014
Authors
Sebben, D.A.
Pendleton, P.
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Journal article
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Spectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy, 2014; 132:706-712
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In this work, we present detailed analyses of the dissociation of dilute aqueous solutions of glycine and of lysine over the range 1 < pH < 12. Using appropriate spectrum subtraction methods, we obtained ATR-IR spectra of the solvated species as a function of pH. Discernible changes in the ionic species were identified in the absorption region between 1800 and 1100 cm -1. By applying peak deconvolution techniques to the spectra, we correctly interpret the apparent peak shift from 1615 to 1600 cm 1 as being due to the receding NH+3 asymmetric deformation alongside the appearing COO- asymmetric stretching. The effect of aqueous solution environment was also investigated in terms of 10 and 100 mmol/L NaCl. Salt solution spectra at each pH were also subtracted from each solution phase spectrum. Analysis of the deconvoluted peak areas due to C=O and COO at pH ranges < 4.5 and those due to NH2 and NH+3 for pH > 8 resulted in consistent pKa values for the amino acids.
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Copyright 2014 Elsevier BV