Appraisal of through-bond and through-space substituent effects via molecular electrostatic potential topography

Through-bond (TB) and through-space (TS) substituent effects in substituted alkyl, alkenyl, and alkynyl arenes are quantified separately using molecular electrostatic potential (MESP) topographical analysis. The deepest MESP point over the aromatic ring (V(min)) is considered as a probe for monitoring these effects for a variety of substituents. In the case of substituted alkyl chains, the TS effect (79.6%) clearly dominates the TB effect, whereas in the unsaturated analogues the TB effect (～55%) overrides the TS effect.     

Sustained release drug delivery using supramolecular hydrogels of the triblock copolymer PCL–PEG–PCL and α-cyclodextrin

Supramolecular hydrogels (SMGel) have attracted much attention as a drug and gene delivery system in recent years. In this study, SMGels based on the tri-block copolymer of poly-ε-caprolactone–polyethylene glycol–poly-ε-caprolactone (PCL–PEG–PCL) and α-cyclodextrin (α-CD) were prepared and evaluated for the delivery of two model drugs, naltrexone hydrochloride and vitamin B₁₂. Tri-block copolymers were synthesized easily in 15 min by ring-opening polymerization using the microwave irradiation technique, and their structures were determined by gel permeation chromatography and nuclear magnetic resonance methods. SMGels composed of various concentrations of the copolymer and α-CD were prepared and characterized for their rheological behaviour, their gel formation time and in vitro drug release profile. The results indicated that copolymers with a PCL to PEG ratio of 1:4 are suitable for SMGel preparation. The most viscose system with good syringeability was prepared by mixing 12 % wt α-CD and 10 % wt of copolymer. The gelation was found to occur within a minute after mixing. The viscosity of the hydrogel systems was determined as a function of shear rate. Finally, in vitro B₁₂ release through the hydrogel systems was studied. Up to 80 % of Vitamin B₁₂ was released through this system during a period of 20 days. Rheological evaluation revealed that the hydrogel has shear thinning properties, and the system regained its ground rheological state in a time dependent manner. Polymer concentration did not affect the drug release profiles. Finally, it was concluded that such systems are appropriate drug delivery systems due to their ability to provide a controlled drug release profile and their shear thinning thixotropic behaviour, which makes them syringeable and injectable.     

Vibrational assignment of aluminum(III) tris-acetylacetone

The geometry, frequency and intensity of the vibrational bands of aluminum(III) Tris-acetylacetone Al(AA)3 and its 1,3,5-(13)C derivative were obtained by the Hartree-Fock (HF) and Density Functional Theory (DFT) with the B3LYP, B1LYP, and G96LYP functionals and using the 6-31G* basis set. The calculated frequencies are compared with the solid IR and Raman spectra. All of the measured IR and Raman bands were interpreted in terms of the calculated vibrational modes. Most computed bands are predicted to be at higher wavenumbers than the experimental bands. The calculated bond lengths and bond angles are in good agreement with the experimental results. Analysis of the vibrational spectra indicates a strong coupling between the chelated ring modes. Four bands in the 500-390 cm(-1) frequency range are assigned to the vibrations of metal-ligand bonds.     

γ‐Spiroiminolactone Synthesis by Reaction of Acetylenic Esters and α‐Dicarbonyl Compounds in the Presence of Aryl Isocyanide

The highly reactive 1∶1 intermediate produced in the reaction of aryl isocyanides and acetylenic esters was trapped by the α‐dicarbonyl compounds to yield γ‐spiroiminolactone derivatives in good yields.     

A population biological model with a singular nonlinearity

We consider the existence of positive solutions of the singular nonlinear semipositone problem of the form $\left\{ \begin{gathered} - div(|x|^{ - \alpha p} |\nabla u|^{p - 2} \nabla u) = |x|^{ - (\alpha + 1)p + \beta } \left( {au^{p - 1} - f(u) - \frac{c} {{u^\gamma }}} \right),x \in \Omega , \hfill \\ u = 0,x \in \partial \Omega , \hfill \\ \end{gathered} \right. $ where Ω is a bounded smooth domain of ? ^N with 0 ∈ Ω, 1 < p < N, 0 ? α < (N ? p)/p, γ ∈ (0, 1), and a, β, c and λ are positive parameters. Here f: [0,∞) → ? is a continuous function. This model arises in the studies of population biology of one species with u representing the concentration of the species. We discuss the existence of a positive solution when f satisfies certain additional conditions. We use the method of sub-supersolutions to establish our results.     

Highly stereoselective construction of functionalized cyclopropanes from the reaction between acetylenic esters and C-H acids in the presence of triphenylarsine

A one-pot triphenylarsine-catalyzed synthesis of trans-cyclopropane derivatives is achieved by means of the reaction between acetylenic esters and C-H acids in the presence of triphenylarsine. This procedure is simple and proceeds under mild reaction conditions. Its success depends on the choice of solvent, temperature and C-H acid used.     

Kinetics of the water-gas shift reaction in Fischer-Tropsch synthesis over a nano-structured iron catalyst

Based on formate and direct oxidation mechanisms, three Langmuir-Hinshelwood-Hougen-Watson (LHHW) kinetic models of the water-gasshift (WGS) reaction over a nano-structured iron catalyst under Fischer-Tropsch synthesis (FTS) reaction conditions were derived and compared with those over the conventional catalyst. The conventional and nanostructured Fe/Cu/La/Si catalysts were prepared by co-precipitation of Fe and Cu nitrates in aqueous media and water-oil micro-emulsion, respectively. The WGS kinetic data were measured by experiments over a wide range of reaction conditions and comparisons were also made for various rate equations. WGS rate expressions based on the formate mechanism with the assumption that the formation of formate is rate determining step were found to be the best.     

Diastereoselective synthesis of chloro‐ and fluoro‐aniline containing phosphonate esters in a three‐component condensation

New phosphonate ester derivatives were obtained by in situ stereo‐specific reaction between triphenyl phosphite and dialkyl acetylenedicarboxylates in the presence of a series of halogenated anilines. Spectroscopic data and X‐ray crystallography analysis are in agreement with the gauche arrangement for the two vicinal protons in the structures. © 2010 Wiley Periodicals, Inc. Heteroatom Chem 21:222–227, 2010; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20600     

An Efficient Synthesis of N-Alkyl-1,4-Dihydro-4-Oxo-3-Quinolinecarboxylic Acid via 2-(2',2',2'-Tri-Chloro)Ethylidene-3-Oxo-3-(2'-Chlorophenyl)Propionate

A clay catalyzed synthesis of 2-(2',2',2'-trichloro)ethylidene-3-oxo-3-(2''-chlorophenyl)propionate (2) and its application for the preparation of various N-alkyl-1,4-dihydro-4-oxo-3-quinolinecarboxylic acids (5a-e) has been described.