Redox potentials of trifluoromethyl-containing compounds

Trifluoromethylation reactions are important transformations in the research and development of drugs, agrochemicals and functional materials. An oxidation/reduction process of trifluoromethyl-containing compounds is thought to be involved in many recently tested catalytic trifluoromethylation reactions. To provide helpful physical chemical data for mechanistic studies on trifluoromethylation reactions, the redox potentials of a variety of trifluoromethyl-containing compounds and trifluoromethylated radicals were studied by quantum-chemical methods. First, wB97X-D was found to be a reliable method in predicting the ionization potentials, electron affinities, bond dissociation enthalpies and redox potentials of trifluoromethyl-containing compounds. One-electron absolute redox potentials of 79 trifluoromethyl substrates and 107 trifluoromethylated radicals in acetonitrile were then calculated with this method. The theoretical results were found to be helpful for interpreting experimental observations such as the relative reaction efficiency of different trifluoromethylation reagents. Finally, the bond dissociation free energies (BDFE) of various compounds were found to have a good linear relationship with the related bond dissociation enthalpies (BDE). Based on this observation, a convenient method was proposed to predict one-electron redox potentials of neutral molecules.     

Nonplanar Shocks and Solitons in a Strongly Coupled Adiabatic Plasma: the Roles of Heavy Ion Dynamics and Nonextensitivity

An investigation has been made on heavy ion‐acoustic (HIA) nonplanar shocks and solitons in an unmagnetized, collisionless, strongly coupled plasma whose constituents are strongly correlated adiabatic inertial heavy ions, weakly correlated nonextensive distributed electrons and Maxwellian light ions. By using appropriate nonlinear equations for our strongly coupled plasma system and the well‐known reductive perturbation technique, a modified Burgers (mB) equation and a modified Korteweg‐de Vries (mK‐dV) equation have been derived. They are also numerically solved in order to investigate the basic features (viz. polarity, amplitude, width, etc.) of cylindrical and spherical shock/solitary waves in such a strongly coupled plasma system. The roles of heavy ion dynamics, nonextensivity of electrons, and other plasma parameters arised in this investigation have significantly modified the basic features of the cylindrical and spherical HIA solitary and shock waves. The findings of our results obtained from this theoretical investigation may be useful in understanding the nonlinear phenomena associated with the cylindrical and spherical HIA waves both in space and laboratory plasmas. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Photoluminescence of exciton and biexciton in GaN nanocolumns

We measured photoluminescence (PL) from excitons and biexcitons in GaN nanocolumns at low temperature and found that the PL spectra of excitons depend on the nanocolumn diameter. Taking into account the polaritonic effect of the excitons, calculation of the PL spectra revealed that the dependence on diameters causes a difference of PL intensity from side surfaces of the nanocolumns. At high excitation intensities, we also observed biexciton emissions and found that the biexciton binding energies are higher than those in bulk samples. Although the mechanism for the increase in the binding energy is not clear at present, we suppose that it arises from a spatial confinement effect due to the nanocolumn morphology.     

Correspondence between GTO and STO molecular basis sets

We present a method for the characterization of the distance between two spaces: one generated by a Gaussian basis set, and another by a Slater basis set. The method is an extension of one previously developed for atoms that has been modified to cover molecular problems. The current version enables us to obtain Slater basis sets capable of reproducing the results (multielectronic wave functions and orbitals) obtained with Gaussian basis sets. The interest of this result arises from the fact that we will be able to profit from the effort invested in the optimization of high‐quality Gaussian basis sets. © 2001 John Wiley & Sons, Inc. J Comput Chem 22: 1655–1665, 2001     

Photochemical and phototoxic properties of ethyl 1,4-dihydro-8-nitro-4-oxoquinoline-3-carboxylate, a new quinoline derivative

The present study demonstrates photoinduced generation of superoxide radical anion and singlet oxygen upon UVA irradiation of ethyl 1,4-dihydro-8-nitro-4-oxoquinoline-3-carboxylate (DNQC), and its cytotoxic/phototoxic effects on murine leukemia L1210 cells. The formation of reactive oxygen species (ROS) was investigated by EPR spectroscopy using in situ spin trapping technique and 4-hydroxy-2,2,6,6-piperidine (TMP) for singlet oxygen ((1)O(2)) detection. The EPR spectra monitored upon photoexcitation of aerated solutions of DNQC in dimethylsulfoxide evidenced the efficient activation of molecular oxygen via Types I and II mechanisms. The cytotoxic/phototoxic effects of DNQC, analysis of cell cycle, induction of apoptosis/necrosis, DNA damage and molecular mechanism of apoptotic death of L1210 cells in dark and in the presence of UVA irradiation were compared. DNQC induced a different cytotoxic/phototoxic effect, which was concentration- and time-dependent. The four highest tested concentrations of non-photoactivated and photoactivated DNQC induced immediate cytotoxic/phototoxic effect after 24h cultivation of L1210 cells. This effect decreased with the time of treatment. The irradiation increased the sensitivity of leukemia cell line on DNQC, but the cell sensitivity decreased with time of processing. Quinolone derivative DNQC significantly induced direct DNA strand breaks in L1210 cells, which were increased with the irradiation of cells. The DNA damage generated by DNQC alone/with combination of UVA irradiation induced cell arrest in G(0)/G(1) and G(2)/M phases, decrease in the number of L1210 cells in Sphase and apoptotic cell death of certain part of cell population after 24 h of influence. DNQC alone/with combination of UVA irradiation induced apoptosis in L1210 cells through ROS-dependent mitochondrial pathway.     

The influence of a quaternary ammonium salt and MMT on the in situ intercalative polymerization of PMMA

Poly(methylmetacrylate)/montmorillonite (PMMA)/(MMT) nanocomposites were prepared by a one-step in situ intercalative solution polymerization involving the simultaneous modification of the MMT with a quaternary ammonium salt (cetyl-trimethylammonium bromide (CTMAB)), polymerization and polymer intercalation. Using benzoyl peroxide as an initiator, intercalated nanocomposites were formed and characterized by NMR, DSC, TGA, XRD, TEM and SEC. It was observed that it was not the MMT, but rather the CTMAB, that influences the polymerization reaction, especially the reaction yield, the molar mass averages and the molar mass distribution of the PMMA. The thermal stability of the PMMA was improved by the addition of both the MMT and/or the CTMAB.     

Efficiency of the algorithms for the calculation of Slater molecular integrals in polyatomic molecules

The performances of the algorithms employed in a previously reported program for the calculation of integrals with Slater-type orbitals are examined. The integrals are classified in types and the efficiency (in terms of the ratio accuracy/cost) of the algorithm selected for each type is analyzed. These algorithms yield all the one- and two-center integrals (both one- and two-electron) with an accuracy of at least 12 decimal places and an average computational time of very few microseconds per integral. The algorithms for three- and four-center electron repulsion integrals, based on the discrete Gauss transform, have a computational cost that depends on the local symmetry of the molecule and the accuracy of the integrals, standard efficiency being in the range of eight decimal places in hundreds of microseconds.     

One-dimensional excitons in inorganic–organic self-organized quantum-wire crystals [NHC(I)=NH]PbI and [CHSC(=NH)NH]PbI

Optical properties of lead-iodide-based one-dimensional perovskite-type crystals [NH₂C(I)=NH₂]₃PbI₅ and [CH₃SC(=NH₂)NH₂]₃PbI₅ have been investigated theoretically and experimentally. The electronic and excitonic structures are studied based on group theoretical consideration and first-principle band calculation. Strong one-dimensional anisotropy of the optical absorption spectra, large Stokes shifts (1.0 eV) and huge exchange energies (70 meV) indicate that the excitons in these crystals are one-dimensional Frenkel excitons.     

Auxiliary functions for molecular integrals with Slater‐type orbitals. II. Gauss transform methods

The Gauss transform of Slater‐type orbitals is used to express several types of molecular integrals involving these functions in terms of simple auxiliary functions. After reviewing this transform and the way it can be combined with the shift operator technique, a master formula for overlap integrals is derived and used to obtain multipolar moments associated to fragments of two‐center distributions and overlaps of derivatives of Slater functions. Moreover, it is proved that integrals involving two‐center distributions and irregular harmonics placed at arbitrary points (which determine the electrostatic potential, field and field gradient, as well as higher order derivatives of the potential) can be expressed in terms of auxiliary functions of the same type as those appearing in the overlap. The recurrence relations and series expansions of these functions are thoroughly studied, and algorithms for their calculation are presented. The usefulness and efficiency of this procedure are tested by developing two independent codes: one for the derivatives of the overlap integrals with respect to the centers of the functions, and another for derivatives of the potential (electrostatic field, field gradient, and so forth) at arbitrary points. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008     

The Challenge of ab Initio Calculations in Small Neon Clusters

Weakly bound neon dimer, trimer and tetramers are studied at HF and CCSD(T) levels using Dunning, ANO and SIGMA-s basis sets. Their ground-state binding energies are studied along with some structural properties. SIGMA-s basis sets have been developed explicitly for this issue but in a manner that can be readily applied to other atoms for the study of larger weakly bound systems. The difficulties for attaining accurate results on these systems are assessed by the computation of total, atomization and correlation energies, as well as equilibrium distances, with several basis sets of increasing size, ranging from non-augmented to double-augmented versions. Extrapolations are proposed to predict stabilization energies and the results are compared with previously published data.