MICROSOLVATION OF BUILDING BLOCKS

Abstract

Laser ablation molecular beam Fourier transform microwave spectroscopy LA-MB-FTMW has provided the first observation of the rotational spectra of the glycine-H$_2$O complex. 45, 3471 (2006)} As a continuation of this work we present the study of monohydrated complexes of alanine, uracil and thymine and the first observations of the dihydrated clusters glycine-(H$_2$O)$_2$ and alanine-(H$_2$O)$_2$. For the microsolvated amino acids only the conformer with \emph{cis}-COOH configuration and bifurcated NH$_2$$\cdots$O=C H-bond has been observed. Both alanine-H$_2$O and glycine-H$_2$O have similar shapes: the water molecule being bonded through two O-H$\cdots$O hydrogen bonds to the carboxylic group of the amino acid. The dihydrated clusters have also comparable structures where the two water molecules form a cycle with the COOH group through sequential H-bonds. The rotational spectra of uracyl-H$_2$O and thymine-H$_2$O show the same complexity than those of the bare molecules111, 3443 (2007)}$^{,}$a, M.E. Sanz and J.L. Alonso, \emph{J. Chem. Phys.} 126, 191103 (2007)} due to the hyperfine structure of two quadrupolar $^{14}$N atoms. The detected conformers show comparable structures with the water molecule bonded through two N-H$\cdots$O and O-H$\cdots$O=C hydrogen bonds to the N bases. The structure of hydrogen bond has been investigated by isotopic substitution.