Quantifying the electronic effect of substituted phosphine ligands via molecular electrostatic potential

Values of the molecular electrostatic potential minimum (V(min)) corresponding to the lone pair region of several substituted phosphine ligands (PR(3)) have been determined at the DFT level. The V(min) value is proposed as a quantitative measure of the electronic effect of the PR(3) ligands. Good linear correlation between V(min) and Tolman electronic parameter of PR(3) has been obtained. V(min) is also proportional to the pK(a) values of the conjugate acids of PR(3), viz., [PR(3)H](+). Further, the DeltaE values of the reaction Ni(CO)(3) + PR(3) --> Ni(CO)(3)PR(3) and ScH(3) + PR(3) --> ScH(3)PR(3) are also linearly proportional to the V(min) values. However, if there is a strong metal to phosphorus pi-back-bonding, the DeltaE and V(min) do not fit to a line. It is also found that the standard reduction potential as well as the enthalpy change corresponding to the electrochemical couple eta-Cp(CO)(PR(3))(COMe)Fe(+)/eta-Cp(CO)(PR(3))(COMe)Fe(0) is linearly proportional to the V(min) values of PR(3). These correlations suggest that V(min) is a quantitative measure of the sigma-donating ability of the phosphine. It is hoped that, in phosphine-metal coordination chemistry, the V(min) based electronic parameter could be more advantageous than nu-CO and pK(a) based electronic parameters as it solely represents the inherent electronic property of the ligand.     

Accurate calculation of aromaticity of benzene and antiaromaticity of cyclobutadiene: new homodesmotic reactions

Newly designed homodesmotic reactions based on radical systems predict an absolute aromaticity of 29.13 kcal/mol for benzene and an absolute antiaromaticity of 40.28 kcal/mol for cyclobutadiene at the MP4(SDQ)/6-31G(d,p) level.     

Density-fluctuation-induced swelling of polymer thin films in carbon dioxide

We report an anomalous swelling of polymer thin films in carbon dioxide (CO(2)) which is associated (in both locus and form) with the density fluctuation ridge that forms along the extension of the coexistence curve of gas and liquid in the P-T phase diagram. Neutron reflectivity results showed that CO(2) could be sorbed to a large extent ( approximately 60%) in thin polymer films even when the bulk miscibility of the polymer with CO(2) is very poor. The anomalous swelling is found to scale with the polymer radius of gyration (R(g)) and extends to a distance approximately 10 R(g).     

Rashba spin-orbit coupling probed by the weak antilocalization analysis in InAlAs/InGaAs/InAlAs quantum wells as a function of quantum well asymmetry

We have investigated the values of the Rashba spin-orbit coupling constant alpha in In(0.52)Al(0.48)As/In(0.53)Ga(0.47)As/In(0.52)Al(0.48)As quantum wells using the weak antilocalization (WAL) analysis as a function of the structural inversion asymmetry (SIA) of the quantum wells. We have found that the deduced alpha values have a strong correlation with the degree of SIA of the quantum wells as predicted theoretically. The good agreement between the theoretical and experimental values of alpha suggests that our WAL approach for deducing alpha values provides a useful tool in designing future spintronics devices that utilize the Rashba spin-orbit coupling.     

Spin-filter device based on the Rashba effect using a nonmagnetic resonant tunneling diode

We propose an electronic spin-filter device that uses a nonmagnetic triple barrier resonant tunneling diode (TB-RTD). This device combines the spin-split resonant tunneling levels induced by the Rashba spin-orbit interaction and the spin blockade phenomena between two regions separated by the middle barrier in the TB-RTD. Detailed calculations using the InAlAs/InGaAs material system reveal that a splitting of a peak should be observed in the I-V curve of this device as a result of the spin-filtering effect. The filtering efficiency exceeds 99.9% at the peak positions in the I-V curve.     

Podophyllotoxin aza-analogue, a novel DNA topoisomerase II inhibitor

The pendant E-ring moiety of the podophyllotoxin aza-analogue 1 that is a potent inhibitor of microtubule assembly was modified in order to acquire inhibitory activity of DNA topoisomerase II. The monophenolic analogue 2 did not exhibit human topoisomerase II inhibition, while the ortho-quinone 3 that was obtained by oxidation of 2 inhibited its catalytic activity (decatenation) in a dose-dependent manner and stimulated double strand DNA breaks in supercoiled circular plasmid DNA, resulting in the production of linear DNA. These results showed that the topoisomerase II inhibition of the ortho-quinone 3 is due to stabilization of the topoisomerase II-DNA covalent binary complex. On the other hand, the ortho-quinone 3 did not inhibit the relaxation process of supercoiled DNA by topoisomerase I at concentrations up to 400 microM, nor was intercalation observed in unwinding measurements of 3. Therefore, the ortho-quinone 3 was shown to be a novel nonintercalative topoisomerase II specific inhibitor that stabilizes the cleavable complex. The present results suggest that the 4'-free hydroxyl group on the E-ring and the sugar moiety on the C-ring are not a prerequisite for topoisomerase II inhibition by podophyllotoxin derivatives.     

Molecular structures and magnetic properties of the mixed-ligand complexes of bis(hexafluoroacetylacetonato)manganese(II), -copper(II), and -zinc(II) with 4,4'-bis(N-tert-butyl-N-oxylamino)-2,2'-bipyridine. Isosceles triangular hetero-three-spin systems consisting of aminoxyls and metal ions

4,4'-Bis(N-tert-butyloxylamino)-2,2'-bipyridine (4) and its 1:1 complexes with bis(hexafluoroacetylacetonato)manganese(II), -copper(II), and -zinc(II) were prepared. An X-ray structure analysis of free ligand 4 reveals that the molecule has a trans conformation with Ci symmetry and the aminoxyl radical center has a short contact of 2.36 A with one of the neighboring molecules. The three 1:1 complexes have mutually similar molecular structures in which the 2,2'-bipyridine moiety has a cis conformation and serves as a bidentate ligand and coordination geometry around the metal atom is a distorted octahedron. The EPR experiments for free ligand 4 and [Zn(hfac)2.4] in frozen solution suggested that the exchange couplings between the two aminoxyls (R) through the 2,2'-bipyridine rings are antiferromagnetic with JR-R/kB = -19.3 +/- 0.5 and -24.3 +/- 0.4 K, respectively. Isosceles triangular three-spin models were applied to the 1:1 magnetic metal complexes to give JR-M/kB = -19.1 +/- 0.2 K and JR-R/kB = -32.9 +/- 0.3 K for [Mn(hfac)2.4] and JR-M/kB = +73 +/- 18 K and JR-R/kB = -24.5 +/- 6.5 K for [Cu(hfac)2.4].     

Interaction between anionic polyelectrolytes and anion exchange membranes and change in membrane properties

Electrodialytic transport properties of anion exchange membranes were measured after formation of anionic polyelectrolyte layers on the membrane surfaces: relative transport number of various anions to chloride ions, current efficiency and apparent diffusion coefficients of neutral molecules. The anionic polyelectrolyte layers were formed by immersing the membrane into an aqueous solution of polycondensation product of sodium naphthalene sulfonate and formaldehyde or polystyrene sulfonic acid.

The change in the relative transport number between anions was remarkable in the anion exchange membrane with high ion exchange capacity by forming the layer. Results were: the relative transport number of sulfate ions to chloride ions decreased and those of nitrate ions to chloride ions, fluoride ions to chloride ions and bromide ions to chloride ions increased compared with the corresponding membrane. Although the apparent diffusion coefficient of neutral molecules suggested clogging of the membrane pores by the polyelectrolyte, anions with higher hydrated ionic diameter were able to permeate through the membrane easily. This means that difference of electrostatic repulsion force against two anions is effective on the change in the relative transport number of anions.     

Tunnel effect in the motion of deformable wavelets

In a previous paper it was shown that the tunnel effect does not occur in the motion of an undeformable wavelet which we obtained by solving the Schrödinger equation and interpreted as representing a single particle. In the present supplementary paper we solve the same Schrödinger equation while modifying one of the restrictive conditions assumed previously, and obtain wavelets which deform in force fields. Tunnel effects are seen in the motion of these deformable wavelets. An apparent inaccuracy pointed out mathematically in these solutions is shown to be insignificant under conditions which are feasible in the physical sense.