Computational Studies on the Thermodynamic and Kinetic Parameters of Oxidation of 2-Methoxyethanol Biofuel via H-Atom Abstraction by Methyl Radical.

In this work, a theoretical investigation of thermochemistry and kinetics of the oxidation of bifunctional 2-Methoxyethanol (2ME) biofuel using methyl radical was introduced. Potential-energy surface for various channels for the oxidation of 2ME was studied at density function theory (M06-2X) and ab initio CBS-QB3 levels of theory. H-atom abstraction reactions, which are essential processes occurring in the initial stages of the combustion or oxidation of organic compounds, from different sites of 2ME were examined. A similar study was conducted for the isoelectronic n-butanol to highlight the consequences of replacing the ϒ CH2 group by an oxygen atom on the thermodynamic and kinetic parameters of the oxidation processes. Rate coefficients were calculated from the transition state theory. Our calculations show that energy barriers for n-butanol oxidation increase in the order of α < O < ϒ < ß < ξ, which are consistent with previous data. However, for 2ME the energy barriers increase in the order α < ß < ξ < O. At elevated temperatures, a slightly high total abstraction rate is observed for the bifunctional 2ME (4 abstraction positions) over n-butanol (5 abstraction positions).

Synthesis, spectral and quantum chemical studies on NO-chelating sulfamonomethoxine-cyclophosph(V)azane and its Er(III) complex.

Computational studies have been carried out at the DFT-B3LYP/6-31G(d) level of theory on the structural and spectroscopic properties of novel ethane-1,2-diol-dichlorocyclophosph(V)azane of sulfamonomethoxine (L), and its binuclear Er(III) complex. Different tautomers of the ligand were optimized at the ab initio DFT level. Keto-form structure is about 15.8 kcal/mol more stable than the enol form (taking zpe correction into account). Simulated IR frequencies were scaled and compared with that experimentally measured. TD-DFT method was used to compute the UV-VIS spectra which show good agreement with measured electronic spectra. The structures of the novel isolated products are proposed based on elemental analyses, IR, UV-VIS, (1)H NMR, (31)P NMR, SEM, XRD spectra, effective magnetic susceptibility measurements and thermogravimetric analysis (TGA).

Spectral and quantum chemical studies on 1,3-bis(N(1)-4-amino-6-methoxypyrimidinebenzenesulfonamide-2,2,4,4-ethane-1,2-dithiol)-2,4-dichlorocyclodiphosph(V)azane and its erbium complex.

Novel 1,3-bis(N(1)-4-amino-6-methoxypyrimidine-benzenesulfonamide-2,2,4,4-ethane-1,2-dithiol)-2,4-dichlorocyclodiphosph(V)azane (L), was prepared and their coordinating behavior towards the lanthanide ion Er(III) was studied. The structures of the isolated products are proposed based on elemental analyses, IR, UV-VIS., (1)H NMR, (13)C NMR, (31)P NMR, SEM, XRD, mass spectra, effective magnetic susceptibility measurements and thermogravimetric analysis (TGA). Computational studies have been carried out at the DFT-B3LYP/6-31G(d) level of theory on the structural and spectroscopic properties of L and its binuclear Er(III) complex. Different tautomers of the ligand were optimized at the ab initio DFT level. Keto-form structure is about 17.7 kcal/mol more stable than the enol form (taking zpe correction into account). Simulated IR frequencies were scaled and compared with that experimentally measured. TD-DFT method was used to compute the UV-VIS spectra which compared by the measured electronic spectra.

Synthesis, characterization and quantum chemical ab initio calculations of new dimeric aminocyclodiphosph(V)azane and its Co(II), Ni(II) and Cu(II) complexes.

The complexes of type [M(2)LCl(2)] in which M=Co(II), Ni(II) and Cu(II) ions and L are 1,3-o-pyridyl-2,4-dioxo-2',4'-bis(3-benzo[d]thiazol-2-yl-2-iminothiophene) cyclodiphosph(V)azane, were prepared and their structures were characterized by different physical techniques (IR, UV-Vis, (1)H NMR, (31)P NMR, mass, TGA, DTA, XRD, SEM, magnetic moment and electrical conductance measurements). Ab initio calculations at the level of DFT B3LYP/6-31G(d) were utilized to find the optimum geometry of the ligand. Spectral characterization of the ligand was simulated using DT-DFT method. Infrared spectra of the complexes indicate deprotonation and coordination of the imine NH. It also confirms that nitrogen atoms of the pyridine group and thiazole group contribute to the complexation. NBO natural charges were computed and discussed in the light of coordination centers. Electronic spectra and magnetic susceptibility measurements as well as quantum chemical calculations reveal square planar geometry for Cu(II) and Ni(II) complexes and tetrahedral geometry for Co(II) complex. The elemental analyses and mass spectral data have justified the M(2)LCl(2) composition of complexes.

Spectroscopic studies of molecular interactions involving 2,6-diethylaniline and N-ethylaniline donors and iodine as an electron acceptor in different solvents.

The charge-transfer complexes of 2,6-diethylaniline (DEA) and N-ethylaniline (NEA) with iodine, as a typical sigma-acceptor were studied spectrophotometrically in chloroform, dichloromethane and carbontetrachloride solutions. Spectral data, formation constants and effect of solvent have been determined. Spectral characteristics and formation constants are discussed in the terms of donor molecular structure and solvent polarity. The stoichiometry of the complexes was established to be 1:1. For this purpose, optical data were subjected to the form of the Rose-Drago equation for 1:1 equilibria. The formation constant (KAD) and molar absorptivities (epsilonlambda) of complexes were determined by least square method. Electronic absorption spectra of the anilines were measured in different solvents. Spectral data were reported and band maxima were assigned to the appropriate molecular orbital transitions. Quantum chemical calculations were performed with the aid of the Gaussian 98 set of programs. The structure were fully optimized at MP2 level using 6-31+G** basis set. The computations show that DEA is not planner with the amino group having a somewhat sp3 hybridization-like character.

Noncovalent attachment of psoralen derivatives with DNA: Hartree-Fock and density functional studies on the probes.

Two psoralen derivatives (probes) were prepared. Their geometries were optimized at the Hartree-Fock (HF) and Density Functional (B3LYP) levels employing 6-31G** and cc-pVDZ basis sets. Their interaction with DNA was investigated using spectrophotometric and computational techniques. Both of them have shown strong binding to calf thymus DNA. The red-shift and hypochromism that detected in the spectrum were taken as an evidence for the strong interaction between these probes and DNA. The spectrophotometric DNA titration data were treated by two different methodologies to calculate the intercalation affinity. Half-reciprocal plots gave binding constants of 5.5065 x 10(4) and 6.4727 x 10(4) for 8-butoxypsoralen (8-BOP) and 8-hexoxypsoralen (8-HOP), respectively. Schatchard plots gave a comparable intercalation binding constants and also the surface binding constants along with the number of intercalated probe molecules per base pair. The interaction between these probes and DNA were studied theoretically. The energy of interaction was computed using molecular mechanics method. Strength of interaction of these probes with different types of DNA was computed and compared. Calculated energies of interaction were compared with the observed intercalation affinities. HOMO and LUMO energies were computed and used to account for the strength of interaction.

Molecular complexes of some anthraquinone anti-cancer drugs: experimental and computational study.

It is known that anti-cancer drugs target DNA in the cell. The mechanism of interaction of anti-cancer drugs with DNA is not fully understood. It is thought that the forces of interaction have some contribution from charge-transfer (CT) binding. The ability of some anthraquinones (AQs) anti-cancer drugs to form CT complexes with well-known electron donor molecules was investigated by NMR. The NMR spectroscopy has indicated the formation of CT complexes between 1,4-bis[[2-(dimethylamino) ethyl]amino]-5,8-dihydroxyanthracene-9,10-dione, (AQ4), and its des-hydroxylated equivalent 1,4-bis[[2-(dimethylamino) ethyl]amino]anthracene-9,10-dione, (AQ4H), as electron acceptors and pyrene (PY) and hexamethylbenzene (HMB) as electron donors. Association constants of the formed CT complexes were determined from the NMR data. AQ4 showed weaker electron accepting power than AQ4H, which could be easily explained on the basis of the electron donating nature of the two-hydroxyl groups. AQ4 and AQ4H have higher stability constant with PY than with HMB. This reflects the weaker interaction of the AQs with the latter, which is a direct effect of the six bulky methyl groups. Electronic absorption spectroscopy of the studied system was performed in chloroform and showed the absence of new absorption bands. The extent of interaction between AQs and donors has been computed using molecular mechanics and quantum mechanics. The computed values were compared with the experimental results of association constants.

Temperature and substituent effects on the dissociation constants of 5-azorhodanine derivatives. Semi-empirical quantum mechanical calculation.

Detailed analysis of the electronic structure and properties of some rhodanine derivatives (RDs) is presented. The aim of the present investigation is to pinpoint the electronic structural similarities and differences, among the series of the studied RDs that govern and determine their acidic, basic and co-ordinative properties. The geometries of the studied rhodanine were fully optimized at the level of AMI semi-empirical method. Relative stabilities of the enol/keto isomers have been calculated. Proton affinities and proton detachment energies were computed for the series of rhodanine studied, at the level of AM1 method and compared with the potentiometrically-determined proton-ligand dissociation constants. Zero-point energy and electron correlations have been taken into consideration. pK(H) have been found to increase with increasing electron-donating nature of the substituents. The resulting linear Hammett plots of pK(H) versus the Hammett constant sigma values indicate the co-planarity of the investigated molecules. The evaluated thermodynamic parameters (deltaG, deltaH and deltaS) indicate that the dissociation processes are non-spontaneous, endothermic and entropically unfavourable.