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abstracts
The famous Miller experiment to model the primordial soup demonstrated that amino acids can form spontaneously as the essential building blocks of life in solutions. It is, however, still an open question how self-recognition processes influence the transformation of these spontaneously formed amino acids in solvents into higher ordered structures in the solid state, thereby creating chiral materials and catalytically competent structures. The understanding of the first steps of molecular self-assembly processes in such environments will thus give important clues towards the understanding of biological evolution. Most of intermolecular interactions are not very strong and their formation is related to and affected by small changes in the molecular structure and the crystallisation conditions. Continuing our investigations on aggregation of substituted aromatic molecules in the solid state, we studied the influence and boundaries of weak directing substituents like deuterium on the aggregation of small molecules. Hydrogen/deuterium (H/D)-exchange, the smallest possible modification of a molecule, is generally seen as a non dominating parameter in the formation of crystal structures of chemical compounds. On the other hand, it could already be shown that the aggregation of molecules in the solid state of polymorphic N-heterocycle systems like pyridine-N-oxide or acridine can be very sensitive to small changes of the isotopic substitution pattern of the selected molecules. Within our project, the molecular aggregation of amino acids in solution with the formation of molecular aggregates and pre-nucleation clusters in deuterated and non-deuterated systems, and in particular the role of the solvent in these processes, will be studied in both experiment and theory.
abstracts
The families of thiosemicarbazone compounds have been extensively studied due to their wide range potential in medical applications [1]. Some studies with acetophenone derivatives and their coordination complexes [2] reveal that these compounds could be used as a new class of anti-trypanosomal drug candidate. In view of the importance of these compounds, two new thiosemicarbazones (I) and (II) have been synthesized (compound I substituted with Chloro atom and compound II substituted with Bromine atom), and their crystal structure features are presented here. The crystal structures are isostructural and the molecules crystallize in a P21/c space group. In the crystal packing the molecules are connected through N-H···S hydrogen bonds to form a centrosymmetric synthon. The optimized geometry of the compound (I) was calculated from the DFT-B3LYP gradient calculations employing 6-31G (d,p) basis set and calculated vibrational frequencies are evaluated via comparison with experimental values. Molecular stability has been analyzed using Natural Bond Orbital (NBO) and Natural Localized Molecular Orbital (NLMO) analysis and the limits of the molecular electrostatic potential calculated. The HOMO and LUMO energies shows the charge transfer occurs within the molecule. The results showed no significant geometrical differences (distances and angles), when the solid state crystal structure is compared with the optimized structure in the gas phase. Very good agreements have been found between principal vibrational frequencies calculated from the optimized structure and the experimental spectroscopic data [3]. We thank financial support from Spanish Ministerio de Economía y Competitividad (MAT2010-15094, Factoría de Cristalización- Consolider Ingenio 2010, ERDF funds and German Academic Exchange Service (DAAD).
