Quantitative assessment of the stereoelectronic profile of phosphine ligands

The stereoelectronic profile of a variety of phosphine ligands (PR3) have been estimated using a combined approach of quantum mechanics (QM) and molecular mechanics (MM). The quantum mechanically derived molecular electrostatic potential minimum (Vmin) of a PR3 ligand at the phosphorus lone pair region provides a direct measure of the total electronic (Eeff) and steric effects (Seff) of the ligand. The difference between the Vmin of unsubstituted PH3 (Vmin(PH3)) and the Vmin of PR3 is considered as Eeff + Seff. It is found that a two-layer QM-MM ONIOM method comprising PH3 in the inner QM layer and the R groups in the outer MM layer is useful to locate the structure of a PR3 ligand in an electronic effect free environment of the substituents. The Vmin of the ONIOM-optimized PR3 at the phosphorus lone-pair region thus provides the quantification of the steric effect as Seff = Vmin(PH3)-Vmin(ONIOM_PR3). Because Vmin(PR3) contains both Eeff and Seff, the Eeff can be easily defined as Eeff = Vmin(ONIOM_PR3)-Vmin(PR3). A modified form of the symmetric deformation coordinate (S4) is calculated for all of the fully optimized and ONIOM-optimized free phosphines to obtain their S4-based steric effect values. Good linear correlation between S4 of ONIOM-optimized phosphines and the MESP-based Seff values was obtained. Further, the determination of the stereoelectronic profile of PR3 ligands has been achieved, leading to a general classification of the ligands into four categories, namely, ligands with (i) (+Eeff, +Seff), (ii) (+Eeff, -Seff), (iii) (-Eeff, +Seff), and (iv) (-Eeff, -Seff), where plus and minus signs indicate electron donation and electron withdrawal properties, respectively.     

Medium effects on zwitterionic-biradicaloid intermediates from two phenyl-alpha-oxoamides. Irradiations in fluid and solid protic media, neat solid phases, and the solid, smectic and isotropic phases of a completely saturated phosphonium salt at different temperatures

The photochemical processes of two N,N-dialkyl phenyl-alpha-oxoamides, N,N-diisopropyl phenyl-alpha-oxoamide (1) and N,N-dibenzyl phenyl-alpha-oxoamide (2), are investigated at different temperatures in methanol and ethylene glycol (to probe the influences of H-bonding and viscosity), in the solid phase of D-sorbitol at room temperature (to compare with the results in the liquid alcohols and to assess the influence of a poorly organized "stiff" environment), in the neat solid phase (to probe the influence of well-ordered, "stiff" matrices), and in the solid, smectic A2 and isotropic phases of methyl-tris-tetradecylphosphonium tetrafluoroborate (1P14BF4) (to assess the ability of the intermediates to respond to subtle changes in the order and polarity of their local environments). From differences between the activation parameters for product pathways from irradiations in methanol and in 1P14BF4, we conclude that the zwitterionic pre-product intermediate from 1 is much more sensitive to the polarity, viscosity and order of its local environment than is the isomeric pre-product biradicaloid intermediate or either of the pre-product intermediates from 2. A very sensitive balance among the medium parameters, as well as internal steric and electronic factors of 1 and 2, controls the reactive pathways of the photochemically generated intermediates.     

Size-dependent electronic and optical properties of an exciton in CdSe/CdS/CdSe/CdS multilayer spherical quantum dot

The electronic and optical properties of a single exciton in a CdSe/CdS/CdSe/CdS quantum dot is studied by using effective mass approximation with parabolic confinement. The Coloumbic interaction between electron and hole is included by Hartree potential. A self-consistent technique is used to calculate the energy eigenvalue and wavefunction of exciton. Based on this approximation we investigate the effect of core size, shell thickness, well width on exciton binding energy, absorption spectra, and oscillator strength. The results provide the tuning possibility of electronic and optical properties of multilayer quantum dot with layer thickness.     

On the level decompositions by the range of an <Emphasis Type="Italic">L</Emphasis>-fuzzy topological space

This paper is on the level decompositions corresponding to the elements in the range of an L-fuzzy topology on a given set and an investigation into the lattice structure of the same. In general, this lattice is not complete and distributive. However, certain necessary and sufficient conditions for it to be modular, distributive, complete and complemented are derived. Atoms and dual atoms of it along with the conditions for their existence are obtained. Certain related properties of it are also discussed here.     

Boxicity of line graphs

The boxicity of a graph H, denoted by , is the minimum integer k such that H is an intersection graph of axis-parallel k-dimensional boxes in R^k. In this paper we show that for a line graph G of a multigraph, , where Δ(G) denotes the maximum degree of G. Since G is a line graph, Δ(G)≤2(χ(G)−1), where χ(G) denotes the chromatic number of G, and therefore, . For the d-dimensional hypercube Q_d, we prove that . The question of finding a nontrivial lower bound for was left open by Chandran and Sivadasan in [L. Sunil Chandran, Naveen Sivadasan, The cubicity of Hypercube Graphs. Discrete Mathematics 308 (23) (2008) 5795–5800].The above results are consequences of bounds that we obtain for the boxicity of a fully subdivided graph (a graph that can be obtained by subdividing every edge of a graph exactly once).     

Poisson process Fock space representation, chaos expansion and covariance inequalities

We consider a Poisson process ?? on an arbitrary measurable space with an arbitrary sigma-finite intensity measure. We establish an explicit Fock space representation of square integrable functions of ??. As a consequence we identify explicitly, in terms of iterated difference operators, the integrands in the Wiener?CIt? chaos expansion. We apply these results to extend well-known variance inequalities for homogeneous Poisson processes on the line to the general Poisson case. The Poincaré inequality is a special case. Further applications are covariance identities for Poisson processes on (strictly) ordered spaces and Harris?CFKG-inequalities for monotone functions of ??.     

Biotin-, fluorescein- and 'clickable' conjugates of phospha-oseltamivir as probes for the influenza virus which utilize selective binding to the neuraminidase

The synthesis of conjugates of phospha-oseltamivir to the well established reporter groups fluorescein and biotin and an approach to multimeric inhibitors is described. We report powerful inhibition of the influenza neuraminidase by these probes and quantify fluorescence quenching during binding of the fluorescein conjugate through titration with the neuraminidase. Thus, we show that they could be useful tools to efficiently inhibit, detect and quantify the virus and the neuraminidase in biological systems.     

Fast and flexible synthesis of pantothenic acid and CJ-15,801

The fast and efficient syntheses of pantothenic acid and the antiparasitic agent CJ-15,801 have been achieved starting from a common imide unit through the selective manipulation of enamide intermediates.     

Spectral studies of copper(II) complexes of tridentate acylhydrazone ligands with heterocyclic compounds as coligands: X-ray crystal structure of one acylhydrazone copper(II) complex

Six copper(II) complexes of 2-hydroxy-4-methoxybenzaldehyde nicotinoylhydrazone (H2hmbn), 2-hydroxy-4-methoxyacetophenone nicotinoylhydrazone (H2hman), 2-hydroxy-4-methoxybenzaldehyde benzoylhydrazone (H2hmbb) and 2-hydroxy-4-methoxyacetophenone benzoylhydrazone (H2hmab) have been synthesized. The complexes viz. [Cu(hmbn)](2)·2H(2)O (1), [Cu(hman)](2) (2), [Cu(hmbb)](2)·2H(2)O (3), [Cu(hmbb)phen]·1(1/2)H2O (4), [Cu(hmbb)(bipy)·H2O] (5) and [Cu(hmab)phen] (6) were characterized by different physicochemical techniques. The crystal structure of [Cu(hman)phen] is obtained and it has a distorted square pyramidal geometry with π-π stacking interactions and significant C-H π interactions.