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AB INITIO CHARACTERISATION OF THE STABLE CONFORMERS OF C₄ SUGARS: ERYTHROSE, ERYTHRULOSE AND THREOSE.

J. R. AVILES-MORENO, D. PETITPREZ AND T. R. HUET, Laboratoire PhLAM, UMR 8523 CNRS-Universite de Lille 1, F-59655 Villeneuve d'Ascq Cedex, France.

The importance of sugars (C_nH₂nO_n) in biology and exobiology motivates this study (i. e. the detection of glycolaldehyde (C₂H₄O₂) in Sgr2(N-LMH) cloud by J.M. HOLLIS et al. Astrophys. J. Lett. 540(2000)L107 and the microwave study of glyceraldehyde (C₃H₆O₃) by F.J.LOVAS et al. J.Mol.Spect. 222(2003),263).

To the best of our knowlege, there is no experimental characterisation of C₄ sugars in the gas phase. Therefore we have performed ab initio calculations for the C₄ sugars in order to help further identifications. We have calculated equilibrium rotational constants, electric dipole moments and relative energies of different conformations. The expected accuracy is 0.5% on rotational constants and 1.0% kJ/mol on relative energies.

Concerning erythrose, 14 conformations have been found at the B3LYP/6-311++G(2df,p) level of the theory. The relative energy of all conformations has been optimized at the G3MP2B3 level of the theory. A few conformations are found within a small range of energy, under 5 kJ/mol. These most stable structures are stabilized by intra-molecular hydrogen bonds. Results on rotational constants and electric dipole moments performed at the B3LYP and the MP2 levels of the theory with 6-311++G(2df,p) basis sets suggest that a detection in the microwave region could be possible, using for example FTMW spectroscopy coupled to a molecular beam.

Calculations for erythrulose and threose are in progress.

This work is supported by grants IDRIS number 041715 and 051715.