Structural and vibrational investigations of a neurotransmitter molecule: Serotonin (5-hydroxy tryptamine)

The First Noncovalent-Bonded Supramolecular Frameworks of (Benzylthio)Acetic Acid with Proline Compounds, Isonicotinamide and Tryptamine

The co-crystallization of (benzylthio)acetic acid (HBTA) with L-proline (L-PRO), D-proline (D-PRO), DL-proline (DL-PRO), isonicotinamide (INA) and tryptamine (TPA) led to the formation of five novel crystalline compounds: L-PRO^±·HBTA (1), D-PRO^±·HBTA (2), DL-PRO^±·HBTA (3), INA·HBTA (4) and TPA⁺·BTA^- (5). The prepared supramolecular assemblies were characterized by single crystal X-ray diffraction, an elemental analysis, FT-IR spectroscopy and a thermal analysis based on thermogravimetry (TG) combined with differential scanning calorimetry (DSC). Additionally, their melting points through TG/DSC measurements were established. All fabricated adducts demonstrated the same stoichiometry, displayed as 1:1. The integration of HBTA with selected N-containing co-formers yielded different forms of multi-component crystalline phases: zwitterionic co-crystals (1-3), true co-crystal (4) or true salt (5). In the asymmetric units of 1-4, the acidic ingredient is protonated, whereas the corresponding N-containing entities take either the zwitterionic form (1-3) or remain in the original neutral figure (4). The molecular structure of complex 5 is occupied by the real ionic forms of both components, namely the (benzylthio)acetate anion (BTA^-) and the tryptaminium cation (TPA⁺). In crystals 1-5, the respective molecular residues are permanently bound to each other via strong H-bonds provided by the following pairs of donor···acceptor: O_carboxylic···O_carboxylate and N_{pyrrolidinium}···O_carboxylate in 1-3, O_carboxylic···N_pyridine and N_amine···O_carboxylic in 4 as well as N_indole···O_carboxylate and N_aminium···O_carboxylate in 5. The crystal structures of conglomerates 1-5 are also stabilized by numerous weaker intermolecular contacts, including C-H···O (1-3, 5), C-H···S (1, 2, 5), C-H···N (5), C-H···C (5), C-H···π (1-5) as well as π···π (4) interactions. The different courses of registered FT-IR spectral traces and thermal profiles for materials 1-5 in relation to their counterparts, gained for the pure molecular ingredients, also clearly confirm the formation of new crystalline phases.

Structural and vibrational study of a neurotransmitter molecule: Dopamine [4-(2-aminoethyl) benzene-1,2-diol]

Structural and vibrational studies for the most stable conformer of dopamine {4-(2-Aminoethyl) benzene-1, 2-diol} have been carried out at the DFT/B3LYP/6-311++G** level using the Gaussian 09 software. The IR and Raman spectra have been recorded and analyzed in light of the computed vibrational parameters using the DFT and the PEDs computed with the help of the GAR2PED software. Some of the fundamentals have considerably changed frequencies in going from benzene to dopamine. Except the rocking and wagging modes of the NH₂ group the other four modes are pure group modes. The rocking and wagging modes of the NH₂ group show mixing with the other modes. The two OH stretching vibrations are highly localized modes. The Kekule phenyl ring stretching mode is found to remain almost unchanged. The HOMO-LUMO study suggests the existence of charge transfer within the molecule and the energy gap supports the pharmacological active property of the dopamine molecule. The NBO analysis has been carried out to understand the proper and improper hydrogen bonding.

Comparative structural and vibrational study of the four lowest energy conformers of serotonin

A computational investigation of all possible lowest energy conformers of serotonin was carried out at the B3LYP/6-311++G** level. Out of the 14 possible lowest energy conformers, the first 4 conformers were investigated thoroughly for the optimized geometries, fundamental frequencies, the potential energy distributions, APT and natural charges, natural bond orbital (NBO) analysis, MEP, Contour map, total density array, HOMO, LUMO energies. The second third and fourth conformers are energetically at higher temperatures of 78, 94 and 312K respectively with respect to the first one. Bond angles and bond lengths do not show significant variations while the dihedral angles vary significantly in going from one conformer to the other. Some of the vibrational modes of the indole moiety are conformation dependent to some extent whereas most of the normal modes of vibration of amino-ethyl side chain vary significantly in going from one conformer to conformer. The MEP for the four conformers suggested that the sites of the maximum positive and negative ESP change on changing the conformation. The charges at some atomic sites also change significantly from conformer to conformer.