DFT study of the molecular and crystal structure and vibrational analysis of cisplatin

DFT and periodic-DFT (PAW-PBE method, code VASP) calculations have been performed to study the structural and vibrational characteristics of cis-diamminedichloroplatinum(II) (cisplatin) at molecular and outside molecular level. To estimate the effect of the intermolecular interactions in crystal on the structural and vibrational properties of cisplatin, three theoretical models are considered in the present study: monomer (isolated molecule), hydrogen bonded dimer and periodic solid state structures. The work focused on the role of the theoretical models for correct modeling and prediction of geometrical and vibrational parameters of cisplatin. It has been found that the elaborate three-dimensional intermolecular hydrogen bonding network in the crystalline cisplatin significantly influences the structural and vibrational pattern of cisplatin and therefore the isolated cisplatin molecule is not the correct computational model regardless of the theoretical level used. To account for the whole intermolecular hydrogen bonding network in direction of both a and c axis and for more reliable calculations of structural and vibrational parameters periodic DFT calculations were carried out in the full crystalline periodic environment with the known lattice parameters for each cisplatin polymorph phase. The model calculations performed both at molecular level and for the periodic structures of alpha and beta cisplatin polymorph forms revealed the decisive role of the extended theoretical model for reliable prediction of the structural and vibrational characteristics of cisplatin. The powder diffraction pattern and the calculated IR and Raman spectra predicted beta polymorph form of our cisplatin sample freshly synthesized for the purposes of the present study using the Dhara's method. The various rotamers realized in the polymorph forms of cisplatin were explained by the low population of the large number of rotamers in solution as well as with the high rotamer interconversion rate due to the low energy barrier.

Mechanisms of removal of three widespread pharmaceuticals by two clay materials

Pharmaceutical residues presence in the environment is among nowadays top emergent environmental issues. For removal of such pollutants, adsorption is a generally efficient process that can be complementary to conventional treatment. Research of cheap, widely available adsorbents may make this process economically attractive. The aim of the present work was to evaluate the capacity of two clay materials (exfoliated vermiculite, LECA) to adsorb gemfibrozil, mefenamic acid and naproxen in lab-scale batch assays. Results show that both adsorbents are able to remove the pharmaceuticals from aqueous medium. Although vermiculite exhibited higher adsorption capacities per unit mass of adsorbent, LECA yielded higher absolute removals of the pharmaceuticals due to the larger mass of adsorbent. Quantum chemistry calculations predicted that the forms of binding of the three molecules to the vermiculite surface are essentially identical, but the adsorption isotherm of naproxen differs substantially from the other two's. The linear forms of the latter impose limits at lower concentrations to the removal efficiencies of these pharmaceuticals by vermiculite, thereby electing LECA as more efficient. Notwithstanding, vermiculite's high specific adsorption capacity and also its much faster adsorption kinetics suggest that there may be some benefits in combining both materials as a composite adsorbent solution.

Substituent effects on the croconate dyes in dye sensitized solar cell applications: a density functional theory study

Using the density functional theory (DFT), we studied two model croconate dyes, one with an electron-donating substituent (CR1) and the other with an electron-withdrawing group (CR2). The geometric, electronic, and optical properties of these dyes were compared. Upon switching from CR1 to CR2, a considerable bathochromic shift was observed in the electronic absorption spectrum. We also investigated the adsorption behavior of the two dyes on a TiO2 (101) anatase surface by employing periodic DFT simulations. The periodic electronic-structure calculations revealed that the diketo group of CR1 bound more strongly to the TiO2 surface than that of CR2, with a binding strength comparable to that of a typical organic D-π-A dye. In this work we evaluate in particular the effect of the electron withdrawing/donating nature of the substituent on the electronic, optical, and adsorption properties of the croconate dyes. Finally, we hope that the present study will help in the design of highly efficient dyes for dye sensitized solar cells by considering substituent effects. Graphical abstract Effect of substituent on binding energy and charge transfer.