Vibrational Spectroscopy of Homo- and Heterochiral Amino Acid Dimers: Conformational Landscapes.

Haolu Wang,Mohamad H Al-Jabiri,Matthias Heger,Yunjie Xu

doi:10.3390/molecules27010038

Abstract

The homo- and heterochiral protonated dimers of asparagine with serine and with valine were investigated using infrared multiple-photon dissociation (IRMPD) spectroscopy. Extensive quantum-chemical calculations were used in a three-tiered strategy to screen the conformational spaces of all four dimer species. The resulting binary structures were further grouped into five different types based on their intermolecular binding topologies and subunit configurations. For each dimer species, there are eight to fourteen final conformational geometries within a 10 kJ mol−1 window of the global minimum structure for each species. The comparison between the experimental IRMPD spectra and the simulated harmonic IR features allowed us to clearly identify the types of structures responsible for the observation. The monomeric subunits of the observed homo- and heterochiral dimers are compared to the corresponding protonated/neutral amino acid monomers observed experimentally in previous IRMDP/rotational spectroscopic studies. Possible chirality and kinetic influences on the experimental IRMPD spectra are discussed.

Highlights

IntroductionThe potential lethal consequence associated with chirality in pharmaceuticals has led to tighter government regulations and further development of spectroscopic tools for chirality evaluation [5]
To explain the observation discussed above, we examine if the amino acid dimers are mainly formed in solution or in the gas phase during the electrospray processes and the influence of the relative stabilities of the monomeric subunits
HSerAsn+ and HValAsn+ dimers investigated using infrared multiple-photon dissociation (IRMPD) spectroscopy, aided by a three-tiered computational approach which explores the conformational spaces of the four dimers systematically

Summary

Introduction

The potential lethal consequence associated with chirality in pharmaceuticals has led to tighter government regulations and further development of spectroscopic tools for chirality evaluation [5]. Regulatory demands and the need for better chiral spectroscopic tools have inspired considerable research efforts in characterizing chirality recognition events at the molecular level to gain a fundamental understanding of their driving forces. Chirality recognition is defined as the ability of a chiral probe, e.g., a chiral light or a chiral molecule, to differentiate between the two enantiomers of a chiral molecule [6]. While chirality recognition is well known to play an important role in biology and (supramolecular) organic syntheses, it is difficult to characterize in detail the noncovalent intermolecular interactions responsible in the condensed phase

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Results

Conclusion