An Empirical Potential Function of α-Glycine Derived from Infrared Spectroscopic Data of D-, ¹³C-, ¹⁵N-, and ¹⁸O-Labeled Species

Abstract

The infrared spectra (4000-100 cm " 1) of the a-form crystal of glycine (NH 3 -CH, -COO ") and of thirteen isotopic modifications comprising D, 13C, 1SN, and O were measured at 80 and 290 K. Excellent resolution was reached at the low temperature. In the low temperature spectra the fine structure of the nearly degenerate NH3 and ND3 antisymmetric deformational modes and the C02-torsional bands in the vicinity of 200 cm-1 for each of the isotopic molecules, which in the low-frequency region are strongly overlapped by a number of lattice modes, clearly showed up. Based upon the frequency data of the 14 isotopic analogs and the precisely known structure of the molecule, a normal coordinate analysis was carried out. 307 observed frequencies were utilized to derive a new empirical valence force field reduced to a set of 50 force constants by a number of restrictive assumptions. The resulting force field reproduced the 307 frequencies with a root-meansquare deviation of 3.32 cm-1. This force field emphasizes the importance of interaction force constants of the in-plane C 02-rocking and C 02-deformational coordinates with the CH2-twisting coordinate, which can come form a significant deviation of this molecule from an ideal Cs-symmetry. The composition of normal vibrations from generally accepted local-symmetry coordinates is given in terms of the potential energy distribution (PED). The PED results indicate that almost all the normal modes below 1600 cm' 1 are extensively intermixed group modes, thus precluding a simple normal vibrational decription. Interestingly the PED description for several vibrations associated with the NHj -CH2 -C fragment exhibits strong mixing between quasi-,4' symmetric and -A" antisymmetric coordinates with respect to a pseudo molecular symmetry (CCN) plane in this molecule.

Theoretical Prediction of Vibrational Spectrum of N-Glycylglycine Hydrochloride: An ab Initio Study

“…Both of the ρ(N + H 3 ) modes are predicted at 1155 and 1126 cm -1 and are observed at 1135 and 1117 cm -1 in the GGH spectra, 1158 and 1100 cm -1 in the zwitterion, and 1130 and 1090 cm -1 in the GGMH. In many amino acids these ρ(N + H 3 ) modes appear as two closely spaced bands around 1100−1150 cm -1 . , …”

Vibrational spectra and assignments of histamine dication in the solid state and in solution

“…Primary amine hydrochlorides usually give one or two bands between 1100 and 1200 cm 1 which disappear upon N-deuteration, 24 arising at wavenumbers lower than 800 cm 1 . They correspond to the ammonium rocking vibrations, and have been well studied for solid amino acids 28,29 and other molecules with the ionized ammonium group. For this molecule they have been assigned at 1149 and 1110 cm 1 in the infrared spectrum and at 1150 and 1109 cm 1 in the Raman spectrum.…”

Thoughts on uncitedness: Nobel laureates and Fields medalists as case studies

“…Therefore, in such cases, bulk solvent effect should be treated with geometry optimization in solvent media. Experimental study of IR and Raman spectra of glycine in solution are limited 35. A theoretical study by Bonaccorsi et al 34 using the continuum model with a small basis set and partial geometry optimization led to the conclusion that the zwitterionic form of glycine in aqueous medium is more stable than the canonical form.…”

“…A theoretical study by Bonaccorsi et al 34 using the continuum model with a small basis set and partial geometry optimization led to the conclusion that the zwitterionic form of glycine in aqueous medium is more stable than the canonical form. Also full geometry optimization study of the glycine zwitterion in aqueous solution has been carried out using the Onsager's continuum model 19–36. However, as the Onsager's model is highly approximate and treats the solute only as a dipole, it is not suitable to study solvation of a general solute reliably.…”