title: Infrared spectrum analysis of the dissociated states of simple amino acids.
abstract: 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 NH3+ 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 CO and COO- at pH ranges<4.5 and those due to NH2 and NH3+ for pH>8 resulted in consistent pKa values for the amino acids.
authors.affiliation: School of Pharmacy and Medical Sciences, University of South Australia, Adelaide, SA 5000, Australia.
authors.forename: Damien
authors.initials: D
authors.lastname: Sebben
authors.affiliation: School of Pharmacy and Medical Sciences, University of South Australia, Adelaide, SA 5000, Australia. Electronic address: p.pendleton@unisa.edu.au.
authors.forename: Phillip
authors.initials: P
authors.lastname: Pendleton
mesh_terms: D005998:Glycine / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D007477:Ions; D008239:Lysine / Q000737:chemistry*; D009994:Osmolar Concentration; D012965:Sodium Chloride / Q000737:chemistry; D012996:Solutions; D012997:Solvents / Q000737:chemistry; D017550:Spectroscopy, Fourier Transform Infrared
chemical_list: D007477:Ions; D012996:Solutions; D012997:Solvents; D012965:Sodium Chloride; D008239:Lysine; D005998:Glycine
keywords: ATR-IR; Amino acids; Glycine; Lysine; Solution spectroscopy