Effect of Silica Particle Size on Polymer Adsorption. Morphological,Energetic and Conformational Relationships

A series of six chemically treated and untreated fumed silicas with increasing particle size (ranging from the nano- to the micrometer size) was prepared. Surface areas (and morphologies) and surface energies were determined by nitrogen adsorption and inverse gas chromatography, respectively. The adsorption of a series of PDMS with different and well-defined molecular weights was studied at different polymer concentrations. Amounts of adsorbed polymer were determined by gravimetry and the energies of adsorption were assessed by flow-microcalorimetry. Results are discussed in terms of particle surface energy and morphology effects on the conformation and the inter-connectivity of adsorbed polymer molecules.     

Stereochemical basis for the anti-chlamydial activity of the phosphonate protease inhibitor JO146

JO146, a mixture of two diastereomers of a peptidic phosphonate inhibitor for Chlamydial HtrA (CtHtrA), has reported activity against Chlamydia species in both human and koala. In this study we isolated the individual diastereomers JO146-D1 and JO146-D2 (in ≥90% purity) and assessed their individual inhibitory activity against the serine protease human neutrophil elastase (HNE) which is structurally and functionally related to CtHtrA, as well as in Chlamydia trachomatis cell culture. JO146-D2 [S,S,R-Boc-Val-Pro-Val^P(OPh)₂], the isomer with the physiologically relevant valine at P1, had an approximate 2.5 – fold increase in in vitro HNE inhibition potency over JO146-D1 [S,S,S-Boc-Val-Pro-Val^P(OPh)₂] and greater than 100 – fold increase in cellular anti-chlamydial activity compared to JO146-D1 which possesses the unnatural valine at P1. JO146 and the individual diastereomers had excellent selectivity for the serine protease HNE over the potential off-target serine proteases trypsin and chymotrypsin. Docking studies supported the biological data with a geometrically unfavoured interaction observed between the P1 valine residue of JO146-D1 and the enzyme S1 sub-pocket.     

Kinetics of thiophene hydrodesulfurization over a supported Mo–Co–Ni catalyst

In this study, the kinetics of thiophene (TH) hydrodesulfurization (HDS) over the Mo–Co–Ni-supported catalyst was investigated. Trimetallic catalyst was synthesized by pore volume impregnation and the metal loadings were 11.5 wt % Mo, 2 wt % Co, and 2 wt % Ni. A large surface area of 243 m²/g and a relatively large pore volume of 0.34 cm³/g for the fresh Mo–Co–Ni-supported catalyst indicate a good accessibility to the catalytic centers for the HDS reaction. The acid strength distribution of the fresh and spent catalysts, as well as for the support, was determined by thermal desorption of diethylamine (DEA) with increase in temperature from 20 to 600 °C. The weak acid centers are obtained within a temperature range between 160 and 300 °C, followed by medium acid sites up to 440 °C. The strong acid centers are revealed above 440 °C. We found a higher content of weak acid centers for fresh and spent catalysts as well as alumina as compared to medium and strong acid sites. The catalyst stability in terms of conversion as a function of time on stream in a fixed bed flow reactor was examined and almost no loss in the catalyst activity was observed. Consequently, this fact demonstrated superior activity of the Mo–Co–Ni-based catalyst for TH HDS. The activity tests by varying the temperature from 200 to 275 °C and pressure from 30 to 60 bar with various space velocities of 1–4 h^?1 were investigated. A Langmuir–Hinshelwood model was used to analyze the kinetic data and to derive activation energy and adsorption parameters for TH HDS. The effect of temperature, pressure, and liquid hourly space velocity on the TH HDS activity was studied.     

Synthesis of one‐, two‐ and three‐ring macrocyclic,bifunctional compounds for use in radiolabelling monoclonal antibodies

The synthesis of new linked bis‐ and tris‐ring tetraazamacrocyclic (bifunctional) reagents for use in an alternative strategy for radiolabelling antibodies is described. For comparison with the above systems, a new single ring bifunctional system incorporating a dioxocyclam ring is also reported.     

NMR Relaxivities of Paramagnetic Lanthanide-Containing Polyoxometalates

The current trend for ultra-high-field magnetic resonance imaging (MRI) technologies opens up new routes in clinical diagnostic imaging as well as in material imaging applications. MRI selectivity is further improved by using contrast agents (CAs), which enhance the image contrast and improve specificity by the paramagnetic relaxation enhancement (PRE) mechanism. Generally, the efficacy of a CA at a given magnetic field is measured by its longitudinal and transverse relaxivities r₁ and r₂, i.e., the longitudinal and transverse relaxation rates T₁⁻¹ and T₂⁻¹ normalized to CA concentration. However, even though basic NMR sensitivity and resolution become better in stronger fields, r₁ of classic CA generally decreases, which often causes a reduction of the image contrast. In this regard, there is a growing interest in the development of new contrast agents that would be suitable to work at higher magnetic fields. One of the strategies to increase imaging contrast at high magnetic field is to inspect other paramagnetic ions than the commonly used Gd(III)-based CAs. For lanthanides, the magnetic moment can be higher than that of the isotropic Gd(III) ion. In addition, the symmetry of electronic ground state influences the PRE properties of a compound apart from diverse correlation times. In this work, PRE of water ¹H has been investigated over a wide range of magnetic fields for aqueous solutions of the lanthanide containing polyoxometalates [Dy^III(H₂O)₄GeW₁₁O₃₉]^5– (Dy-W₁₁), [Er^III(H₂O)₃GeW₁₁O₃₉]^5– (Er-W₁₁) and [{Er^III(H₂O)(CH₃COO)(P₂W₁₇O₆₁)}₂]¹⁶⁻ (Er₂-W₃₄) over a wide range of frequencies from 20 MHz to 1.4 GHz. Their relaxivities r₁ and r₂ increase with increasing applied fields. These results indicate that the three chosen POM systems are potential candidates for contrast agents, especially at high magnetic fields.     

Purification and Characterization of an Antifungal Chitinase from Citrobacter freundii str. nov. haritD11

The purpose of the research was to study the purification and partial characterization of antifungal alkaline chitinase from a newly isolated Citrobacter freundii haritD11. The enzyme was purified in a three-step procedure involving ammonium sulfate precipitation, dialysis, and Sephadex G-100 gel filtration chromatography. The enzyme was shown to have a relative high molecular weight of 64 kDa by sodium dodecyl sulfate polyacrylamide gel electrophoresis and was purified 7.3-fold with a yield of 18.8 %. It was most active at 35 °C, pH 8.0, with colloid chitin as substrate and was very stable at alkaline pH contradicting the characteristic that most of the bacterial chitinases are active at acidic pH. Further, the purified chitinase exhibited remarkable antifungal activity against pathogenic fungi Aspergillus flavus MTCC 2798 and Aspergillus niger MTCC 9652 showing diametric inhibition zones of 27 mm and 21 mm, respectively.     

Spectral time moment analysis of microgel structure and dynamics

The structure and dynamics of crosslinked nanoparticles (microgels) made out of hydroxypropylcellulose (HPC) polymer chains were studied using dynamic light scattering spectroscopy. The microgel light scattering spectra were found to be highly nonexponential requiring a spectral time moment analysis in which the spectra were fit to a sum of stretched exponentials. Each term offers three parameters for analysis and represents a single spectral mode. At room temperature microgel spectra reveal three modes. Two faster modes are almost diffusive and correspond to apparent sizes of 25 and 450–650 nm. The slowest mode is independent of scattering angle and is reminiscent of the slow polymer mode observed in identical non‐crosslinked polymer solutions. When solution temperature is varied from 23 to 45°C and back, the microgel undergoes a reversible volume phase transition between 40 and 45°C. According to the time‐moment analysis, above the transition temperature two faster modes collapse into one with apparent hydrodynamic radius of 100–150 nm, while the slow mode remains largely unchanged. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 771–781, 2008     

Charge transport and discharge mechanism in (PVC+KClO3) polymer electrolyte films

This paper presents results of the studies on ionic conductivity and transference number measurements on potassium chlorate (KClO₃) complexed polyvinyl chloride (PVC) films prepared by solution-cast technique. Temperature dependence of ionic conductivity and transference number data indicated the dominance of ion-type charge transport in these specimens. The magnitude of conductivity increased with increase in the concentration of the salt and temperature. Using this (PVC+KClO₃) electrolyte, solid-state electrochemical cells were fabricated and their discharge profiles were studied under a constant load of 100 kΩ. Several cell profiles associated with these cells were evaluated and are reported.     

Dependence relation in pregeometries

The aim of this paper is to set a foundation to separate geometric model theory from model theory. Our goal is to explore the possibility to extend results from geometric model theory to non first order logic (e.g. ). We introduce a dependence relation between subsets of a pregeometry and show that it satisfies all the formal properties that forking satisfies in simple first order theories. This happens when one is trying to lift forking to nonelementary classes, in contexts where there exist pregeometries but not necessarily a well-behaved dependence relation (see for example [HySh]). We use these to reproduce S. Buechler's characterization of local modularity in general. These results are used by Lessmann to prove an abstract group configuration theorem in [Le2]. Received February 2, 1999; accepted in final form April 30, 2000.