The effects of solvation upon the acidities of nitroaromatics

Specific solvation of nitrated phenoxide, anilide and benzyl anions is shown to decrease in that order, with concomitant increases in substituent salvation assisted resonance effects — the nitrobenzyl anions are suggested to be essentially charge-delocalized.     

A reservoir-type controlled release device using aqueous-organic partitioning and a porous membrane

A reservoir-type controlled release device based on aqueous-organic partitioning is described. The reservoir is bounded by a microporous or porous membrane, either a hollow fiber or a flat film. The agent partitions between phases at the aqueous-organic interface of the reservoir and the pore mouth, and then diffuses through the membrane pore into a surrounding aqueous solution. The partition coefficient significantly influences the rate of release of the agent. The performance of the system is evaluated using model agents. Controlled release from a reservoir containing a pure organic liquid agent is demonstrated using toluene. Zero-order release is achieved for benzoic acid partitioning from an organic reservoir into water-filled pores, and for nicotine partitioning from an aqueous reservoir into organic-filled pores. Studies using benzoic acid demonstrate the effectiveness of a thin, nonporous coating on slowing the rate of release. A fast-dissolving suspension of benzoic acid in decanol extends the duration of zero-order release. Two agents, nicotine and caffeine, are released simultaneously and independently from a divided reservoir. A simplified mathematical model is presented, and experimental results compared well with those predicted by the model.     

Foliated control theory, II

The main result is a control theorem for the structure space of E with control near the leaves F in M, where : E M is a fiber bundle over the Riemannian manifold M having a compact closed manifold for fiber and F is a smooth foliation of M, each leaf of which inherits a flat Riemannian geometry from M. A similar result has been proved by the authors under the assumption that each leaf of F is one-dimensional and the fiber of : E M is homotopy stable.Both authors were supported in part by the National Science Foundations.     

Critical dynamics of dimers: implications for the glass transition

The Adam-Gibbs view of the glass transition relates the relaxation time to the configurational entropy, which goes continuously to zero at the so-called Kauzmann temperature. We examine this scenario in the context of a dimer model with an entropy-vanishing phase transition and stochastic loop dynamics. We propose a coarse-grained master equation for the order parameter dynamics which is used to compute the time-dependent autocorrelation function and the associated relaxation time. Using a combination of exact results, scaling arguments, and numerical diagonalizations of the master equation, we find nonexponential relaxation and a Vogel-Fulcher divergence of the relaxation time in the vicinity of the phase transition. Since in the dimer model the entropy stays finite all the way to the phase transition point and then jumps discontinuously to zero, we demonstrate a clear departure from the Adam-Gibbs scenario. Dimer coverings are the "inherent structures" of the canonical frustrated system, the triangular Ising antiferromagnet. Therefore, our results provide a new scenario for the glass transition in supercooled liquids in terms of inherent structure dynamics.     

Binding affinity studies of 1,2,3-triazole copper(II) complexes to human serum albumin

Abstract

Two copper(II) complexes with tetradentate 1,4-disubstituted-1,2,3-triazole ligands, [CuL(MeCN)](ClO₄)₂ (1) and [CuL′](ClO₄)₂ (2), have been prepared and characterized by different techniques, including X-ray structure determination, spectroscopic, and electrochemical measurements, as reported elsewhere. Herein, we report the interactions of these complexes, and corresponding free ligands, with human serum albumin (HSA) verifying their relative thermodynamic stability and differences in binding to this protein. Interactions with HSA were verified by CD measurements monitored at 564?nm, up to stoichiometric ratio 2:1 [Complex]:[protein], according to competitive equilibria involving the insertion of copper at the selective N-terminal metal binding site in HSA, and additionally at a secondary nonselective site. Further interactions of these complexes with L-tryptophan residues, and probable supplementary site(s) for the binding, were followed by fluorescence measurements. Analogous experiments with the free L and L′ indicated much weaker interactions. Protein oxidation damage was observed for both complexes, monitored by carbonyl groups formation in the presence of H₂O₂, probably with the participation of reactive oxygen species. Density functional theory calculations exhibit metal-ligand binding interaction energies similar to [Cu(HSA-N_terminal)]⁺, and reinforced the experimental results, showing clearly that such triazole ligands are competitive toward copper(II) in biological medium.     

Limiting Empirical Singular Value Distribution of?Restrictions of?Discrete Fourier Transform Matrices

We determine the limiting empirical singular value distribution for discrete Fourier transform (DFT) matrices when a random set of columns and rows is removed.     

Effective index method for planar lightwave circuits containing directional couplers

A simple and intuitive effective index method for planar lightwave circuits containing directional couplers is proposed. The optimal cladding refractive index of the effective two-dimensional planar waveguide is found according to the coupling length of the directional coupler involved. Numerical examples indicate that this proposed effective index method gives accurate results while saving significant computation time in simulation and design of planar lightwave circuits containing directional couplers.     

The morphology and structure of PS‐b‐P4VP block copolymer films by solvent annealing: effect of the solvent parameter

Lamellae (symmetric) forming polystyrene‐b‐poly(4‐vinylpyridine) (PS‐b‐P4VP) block copolymers (BCPs) were used to produce nanostructured thin films by solvent (toluene) casting (spin‐coating) onto silicon substrates. As expected, strong micellization of PS‐P4VP in toluene results in poorly ordered hexagonally structures films. Following deposition the films were solvent annealed in various solvents and mixtures thereof. A range of both morphologies including micelle and microphase separated structures were observed. It was found that nanostructures typical of films of regular thickness (across the substrate) and demonstrating microphase separation occurred only for relatively few solvents and mixtures. The data demonstrate that simple models of solvent annealing based on swelling of the polymer promoting higher polymer chain mobility are not appropriate and more careful rationalization is required to understand these data. Analysis suggests that regular phase separated films can only be achieved when the copolymer Hildebrand solubility parameter is very similar to the value of the solvent. It is suggested that the solvent anneal method used is best considered as a liquid phase technique rather than a vapor phase method. The results show that solvent annealing methods can be a very powerful means to control structure and in some circumstances dominate other factors such as surface chemistry and surface energies. Copyright © 2009 John Wiley & Sons, Ltd.     

Targeting retroviral Zn finger-DNA interactions: a small-molecule approach using the electrophilic nature of trans-platinum-nucleobase compounds

Noncovalent interactions are ubiquitous in ternary systems involving metal ions, DNA/RNA, and proteins and represent a structural motif for design of selective inhibitors of biological function. This contribution shows that small molecules containing platinated purine nucleobases mimic the natural DNA(RNA)-tryptophan recognition interaction of zinc finger peptides, specifically the C-terminal finger of HIV NCp7 protein. Interaction with platinum results in Zn ejection from the peptide accompanied by loss of tertiary structure. Targeting the NCp7-DNA interaction for drug design represents a conceptual advance over electrophiles designed for chemical attack on the zinc finger alone. These results demonstrate examples of a new platinum structural class targeting specific biological processes, distinct from the bifunctional DNA-DNA binding of cytotoxic agents like cisplatin. The results confirm the validity of a chemical biological approach for metallodrug design for selective ternary DNA(RNA)-protein interactions.