Effect of H2O on Na+ diffusivity in beta alumina

The effect of H₂O on Na⁺ diffusivity in polycrystalline, and single crystal, beta-alumina was investigated. We found no evidence that water affects the diffusion kinetics and conclude that H₂O is not as easily introduced as a blocking impurity into either the grain boundaries or fast conducting planes, nor is Na⁺ easily removed from the structure by leaching.     

Enhanced Single‐Chain Magnet Behavior via Anisotropic Exchange in a Cyano‐Bridged MoIII–MnII Chain

Anisotropic magnetic exchange is of great value for the design of high performance molecular nanomagnets. In the present work, enhanced single‐chain magnet (SCM) behavior is observed for a Mo^III–Mn^II chain that exhibits anisotropic magnetic exchange. Self‐assembly of the pentagonal bipyramidal [Mo(CN)₇]^4? anion and the Mn^II unit with a tridentate ligand results in a neutral double zigzag 2,4‐ribbon structure which exhibits SCM behavior with a high relaxation barrier of 178(4) K. Open magnetic hysteresis loops are observed below 5.2 K, with a coercive field of 1.5 T at 2 K. Interestingly, this SCM can be considered to be a result of a step‐wise process based on our previously reported Mn₂Mo single‐molecule magnets (SMMs).     

Enhanced Single-Chain Magnet Behavior via Anisotropic Exchange in a Cyano-Bridged MoIII–MnII Chain

Anisotropic magnetic exchange is of great value for the design of high performance molecular nanomagnets. In the present work, enhanced single-chain magnet (SCM) behavior is observed for a Mo^III–Mn^II chain that exhibits anisotropic magnetic exchange. Self-assembly of the pentagonal bipyramidal [Mo(CN)₇]⁴⁻ anion and the Mn^II unit with a tridentate ligand results in a neutral double zigzag 2,4-ribbon structure which exhibits SCM behavior with a high relaxation barrier of 178(4) K. Open magnetic hysteresis loops are observed below 5.2 K, with a coercive field of 1.5 T at 2 K. Interestingly, this SCM can be considered to be a result of a step-wise process based on our previously reported Mn₂Mo single-molecule magnets (SMMs).     

Unprecedented head-to-head right-handed cross-links between the antitumor bis(mu-N,N'-di-p-tolylformamidinate) dirhodium(II,II) core and the dinucleotide d(ApA) with the adenine bases in the rare imino form

Reactions of the anticancer active compound cis-[Rh2(DTolF)2(CH3CN)6](BF4)2 with 9-ethyladenine (9-EtAdeH) or the dinucleotide d(ApA) proceed with bridging adenine bases in the rare imino form (A*), spanning the Rh-Rh bond at equatorial positions via N7/N6. The inflection points for the pH-dependent H2 and H8 NMR resonance curves of cis-[Rh2(DTolF)2(9-EtAdeH)2](BF4)2 correspond to N1H deprotonation of the metal-stabilized rare imino tautomer, which takes place at pKa approximately 7.5 in CD3CN-d3, a considerably reduced value as compared to that of the imino form of 9-EtAdeH. Similarly, coordination of the metal atoms to the N7/N6 adenine sites in Rh2(DTolF)2{d(ApA)} induces formation of the rare imino tautomer of the bases with a concomitant substantial decrease in the basicity of the N1H sites (pKa approximately 7.0 in CD3CN-d3), as compared to the imino form of the free dinucleotide. The presence of the adenine bases in the rare imino form, due to bidentate metalation of the N6/N7 sites, is further corroborated by DQF-COSY H2/N1H and ROE N1H/N6H cross-peaks in the 2D NMR spectra of Rh2(DTolF)2{d(ApA)} in CD3CN-d3 at -38 degrees C. Due to the N7/N6 bridging mode of the adenine bases in Rh2(DTolF)2{d(ApA)}, only the anti orientation of the imino tautomer is possible. The imino form A* of adenine in DNA may result in AT-->CG transversions or AT-->GC transitions, which can eventually lead to lethal mutations. The HH arrangement of the bases in Rh2(DTolF)2{d(ApA)} is indicated by the H8/H8 NOE cross-peaks in the 2D ROESY NMR spectrum, whereas the formamidinate bridging groups dictate the presence of one right-handed conformer HH1R in solution. Complete characterization of Rh2(DTolF)2{d(ApA)} by 2D NMR spectroscopy and molecular modeling supports the presence of the HH1R conformer, anti orientation of both sugar residues about the glycosyl bonds, and N-type conformation for the 5'-A base.     

CSAR benchmark exercise of 2010: combined evaluation across all submitted scoring functions

As part of the Community Structure-Activity Resource (CSAR) center, a set of 343 high-quality, protein-ligand crystal structures were assembled with experimentally determined K(d) or K(i) information from the literature. We encouraged the community to score the crystallographic poses of the complexes by any method of their choice. The goal of the exercise was to (1) evaluate the current ability of the field to predict activity from structure and (2) investigate the properties of the complexes and methods that appear to hinder scoring. A total of 19 different methods were submitted with numerous parameter variations for a total of 64 sets of scores from 16 participating groups. Linear regression and nonparametric tests were used to correlate scores to the experimental values. Correlation to experiment for the various methods ranged R(2) = 0.58-0.12, Spearman ρ = 0.74-0.37, Kendall τ = 0.55-0.25, and median unsigned error = 1.00-1.68 pK(d) units. All types of scoring functions-force field based, knowledge based, and empirical-had examples with high and low correlation, showing no bias/advantage for any particular approach. The data across all the participants were combined to identify 63 complexes that were poorly scored across the majority of the scoring methods and 123 complexes that were scored well across the majority. The two sets were compared using a Wilcoxon rank-sum test to assess any significant difference in the distributions of >400 physicochemical properties of the ligands and the proteins. Poorly scored complexes were found to have ligands that were the same size as those in well-scored complexes, but hydrogen bonding and torsional strain were significantly different. These comparisons point to a need for CSAR to develop data sets of congeneric series with a range of hydrogen-bonding and hydrophobic characteristics and a range of rotatable bonds.     

Conducting Organic Frameworks Based on a Main‐Group Metal and Organocyanide Radicals

Reactions of the main‐group cation Tl^I with anions of 2,5‐derivatives of TCNQ (TCNQ=7,7,8,8‐tetracyanoquinodimethane) have led to the isolation of a family of unprecedented semiconducting main‐group‐metal–organic frameworks, namely, [Tl(TCNQX₂)], (X=H, Cl, Br, I). A comparison of single‐crystal and powder X‐ray diffraction data revealed the existence of a third polymorph of the previously reported material Tl(TCNQ)] and two distinct polymorphs of [Tl(TCNQCl₂)], whereas only one phase was identified for [Tl(TCNQBr₂)] and [Tl(TCNQI₂)]. These new results are described in the context of the structures of other known binary metal–TCNQ frameworks that display a variety of coordination environments for the central cation, namely, four‐, six‐, and eight‐coordinate, and different arrangements of the adjacent TCNQ radicals—parallel versus perpendicular—in the stacked columns. The halogen substituents affect the structures and the properties of these compounds, owing to both steric and electronic effects as evidenced by the semiconducting properties of crystals of [Tl(TCNQCl₂)] phase I, [Tl(TCNQBr₂)], and [Tl(TCNQI₂)], which correlate well with the distances of adjacent TCNQ radicals in the columns. 1D infinite Hückel model simulations of the band structures of [Tl(TCNQCl₂)] phase I, [Tl(TCNQBr₂)], and [Tl(TCNQI₂)] were conducted with and without consideration of the Tl^I cations, the results of which indicate that the charge mobility does not strictly occur in one dimension. The modulations of the band structures with various assumptions of the energy difference (Δ) between the Tl^I 6s orbital and the TCNQ LUMO orbital were calculated and are discussed in light of the observed properties.