The Behavior of NH3+ Torsional Vibration in Amino Acids: A Raman Spectroscopic Study

André Luís De Oliveira Cavaignac,Ricardo Jorge Cruz Lima,Paulo Tarso Cavalcante Freire

doi:10.3390/cryst9100517

André Luís De Oliveira Cavaignac, Ricardo Jorge Cruz Lima + Show 1 more

Open Access

https://doi.org/10.3390/cryst9100517

Copy DOI

Abstract

In this work we present the continuation of studies carried out on the changes of geometric parameters of the hydrogen bonds in amino acid crystals subjected to temperature or pressure variations. Changes in geometric parameters of the hydrogen bonds are correlated with the temperature behavior of the Raman wavenumber of NH3+ torsional band. Now four monocrystals, L-valine, L-isoleucine, taurine, and L-arginine hydrochloride monohydrate, are studied. Temperature evolution of the Raman wavenumber of NH3+ torsional band, with positive slope (dν/dT = 0.023 cm−1/K) of L-isoleucine, can be related to the stability of the crystal structure and the hydrogen bonds strengths on heating due to different temperature lattice parameters variation.

Highlights

A hydrogen bond (HB) is a highly directional interaction notably responsible for molecular conformation, aggregation, and ordering states of a vast number of complex biological molecular systems
Freire et al [4], using Raman spectroscopy to study the torsional vibration of ammonium group, suggest the effect of high pressure on the HB in L-alanine crystal can be seen as a change in the geometry of the bond originated by a deviation of the linearity, instead of being due to the decreasing of its length
NH3 + torsional vibration recorded at low temperature for the four crystals (VAL, ISO, TAU, and arginine hydrochloride monohydrate (AHM))

Summary

Introduction

A hydrogen bond (HB) is a highly directional interaction notably responsible for molecular conformation, aggregation, and ordering states of a vast number of complex biological molecular systems. Changes in geometric parameters of the HB can be induced by pressure or temperature variation, as the Coulombic interaction between the protons and acceptor atoms is relatively weak compared to intramolecular covalent bonds. This effect is observed in protein dynamics at high pressure [1] and the temperature dependence of the hydrophobic interaction in protein folding [2]. The study of the stability mechanism of the molecular systems subjected to temperature or pressure variation can be related to changes in geometric parameters of the HBs. Amino acid crystals, small model organic molecules linked in the solid structure through complex. Funnell et al [3], in the state-of-the-art experimental approaches using high-pressure single-crystal X-ray and neutron powder diffraction measurements in crystals of deuterated L-alanine, confirmed those results providing a complete picture of the effects of pressure on Crystals 2019, 9, 517; doi:10.3390/cryst9100517 www.mdpi.com/journal/crystals

Methods

Results

Conclusion