Impact of Crystal Parameters in XRD and DFT Measurements

Abstract

The Zwitterionic property of aminoacids give molecular crystal formation through homodesmotic reaction with smaller organic molecules which can undergo hydrogen bonding interactions. Alpha hydroxyl phenyl acetic acid known as mandelic acid (MA) was added with essential amino acid, L-phenylalanine (LPA) resulted in the formation of molecular crystal with P21 space group otho rhombic crystal containing four units (namely one MA, two LPA and one water) bis-L –phenyl alanine mandelate (BLPAMA) by slow evaporation method. The single crystal obtained was subjected to characterisation studies. Recrystallised BLPAMA using methanol, subjected to slow evaporation method resulted in the formation of non centerosymmetric C2 point group monoclinic single crystal of R-phenylalanine-S-mandelate (RPASMA) confirmed with XRD study. The theoretical DFT study of RPASMA using Gaussian 09 software to study the non-covalent interactions with MO6,6-31++G(d,p) showed encouraging results for the formation of low energy gap, highly reactive RPASMA. The H-bonding in the crystal confirmed by DFT study showed the existence of three units – MA, H and LPA in the crystal. Compared the experimental and theoretical crystal parameters of the reactants (MA, LPA) and product (RPASMA) for the thermo chemical properties, intermolecular hydrogen bonding existing between MA and LPA stabilises the structure of the formed RPASMA crystal resulting in the small difference in energy gap observed from HOMO-LUMO studies indicate the highly reactive character of RPASMA.