Where's water? The many binding sites of hydantoin.

Sébastien Gruet,Amanda L Steber,Cristóbal Pérez,Melanie Schnell

doi:10.1039/c7cp06518c

Abstract

Prebiotic hydantoin and its complexes with one and two water molecules are investigated using high-resolution broadband rotational spectroscopy in the 2-8 GHz frequency range. The hyperfine structure due to the nuclear quadrupole coupling of the two 14N atoms is analysed for the monomer and the complexes. This characteristic hyperfine structure will support a definitive assignment from low frequency radioastronomy data. Experiments with H218O provide accurate experimental information on the preferred binding sites of water, which are compared with quantum-chemically calculated coordinates. In the 2-water complexes, the water molecules bind to hydantoin as a dimer instead of individually, indicating the strong water-water interactions. This information provides first insight on how hydantoin interacts with water on the molecular level.

Highlights

The search for prebiotic molecules in the interstellar medium (ISM) has been an ongoing effort of astronomy, astrochemistry, and laboratory spectroscopy for several decades
For the complexes with two water molecules, there is evidence to suggest that water forms a dimer which binds to one of the amide groups, forming an hydrogen-bonded eightmembered ring
This illustrates the dominance of water–water interactions

Summary

Introduction

The cyclic amide hydantoin, or glycolylurea, has many interesting qualities, one of them being its tie to prebiotic chemistry. As urea has already been detected in the interstellar medium (ISM),[6] it is likely that hydantoin could be present, as reactions of urea in the gas phase or on ice grain surfaces with glycolic acid would give rise to the formation of hydantoin. Studies providing spectroscopic and structural information on hydantoin are rather limited and mostly dedicated to experiments in the solid phase. We use the low frequency range (2–8 GHz) of our COMPACT spectrometer to analyse and provide accurate molecular parameters of the nuclear quadrupole coupling hyperfine structure, which can be useful for the identification of hydantoin in space.[14,15] Every low-J rotational transition will exhibit this uniquely identifying hyperfine splitting. The knowledge of how water binds to such prebiotic precursors is relevant for modeling chemical processes on interstellar ice grains

Experimental and computational details

Rotational spectroscopy of hydantoin

Hydantoin–water complexes

Summary and conclusions