Hydrogen-bonded glycine–HCN complexes in gas phase: structure, energetics, electric properties and cooperativity

Abstract

Twelve hydrogen-bonded complexes of glycine and hydrogen cyanide have been studied using high-level quantum-chemical calculations in gas phase. In particular, six 1:1 glycine-HCN dimers and six 1:2 glycine-HCN trimers have been considered. Besides the characteristics of the hydrogen bonds and their effect on molecular structure and energetics, several molecular electric properties have been calculated utilising two different models: MP2/6-31 ++ G(d,p) and DFT-B3LYP/6-31 ++ G(d,p). Although the structural parameters calculated by the two models are similar, equilibrium electronic energies of the clusters show model dependence. The lowest energy dimer is same in both the models which is ca. 3.0 kcal/mol more stable than the highest energy dimer. However, the lowest energy trimer is different in two methods. The energetic difference of stability between the highest and lowest trimer is 4.2 kcal/mol (4.4 kcal/mol) at an MP2 (B3LYP) level of calculation. The bond angles of glycine, in particular, are quite sensitive to the hydrogen-bond formation. Four out of six trimers are found to be strongly cooperative in both the models. Significant changes of dipole moments and polarisabilities of isolated glycine and hydrogen cyanide are observed due to the formation of hydrogen bonding. The Rayleigh scattering intensities of all clusters are much larger than those of their constituent monomers.

NMR properties of hydrogen-bonded glycine cluster in gas phase

“…Our optimized structure of the glycine molecule (shown in Fig. 1) is supposed to be the most stable and abundant of all the C s glycine conformations [46] It matches closely with the geometry obtained in earlier works [52,57,58]. Moreover, this conformer has already been identified by electron diffraction [37], microwave spectroscopy [40,42] and Jet-cooled Raman spectroscopy [53].…”

Effect of hydrogen‐bonded interactions on the energetics and spectral properties of the astromolecule aminoacetonitrile

“…Both HCN and GLY have featured in innumerous theoretical and experimental quantum‐chemical investigations. Moreover, different models of quantum chemical calculations have been used, in last few years, to investigate on the hydrogen‐bonded interaction of HCN and GLY with same or other molecules . In this respect, it is important to know how AAN molecules interact with other molecules in space.…”

“…The process of hydrogen bond (H‐bond) formation in biomolecular systems and, in particular, the effect of intramolecular and intermolecular H‐bonded interaction on chemical and structural properties of molecules are topics of continuing interest in science. H‐bond formation has investigated with a great variety of techniques and different aspects of H‐bonds in molecular systems are being reported regularly . Because of the sensitivity of the vibrational spectrum to the hydrogen bond formation, IR spectroscopy provides a definitive criterion for the detection of hydrogen bonds.…”

“…Glycine, conversely, is popular among quantum‐chemists because of its structural simplicity, high flexibility and relative abundance within protein structures activity. It is also studied, extensively and intensively, both experimentally and theoretically, from a wide variety of angles including astrochemistry . Since a carboxyl, COOH group is present at one end of GLY and an amino, NH 2 group at the other end, GLY can form multiple H‐bonds with other molecules acting simultaneously as a proton acceptor and a proton donor.…”

“…In previous works, we have performed detailed quantum‐chemical analysis of the effect of H‐bond formation on different aspects of HCN···HCN, HCN···GLY, and GLY···GLY molecular clusters . In the present work, we are interested to observe the effect of H‐bond formation on the electronic structure, electric and spectroscopic properties of isolated aminoacetonitrile (AAN) and its H‐bonded clusters, AAN···HCN and AAN···GLY.…”