Hydrogen-bond directed palladium-catalyzed allylic substitution of cyclic substrates

The regioselectivity of the Pd-catalyzed allylic substitution of cyclic substrates possessing an adjacent amide functional group was investigated. With imide-like nucleophiles, six-membered ring substrates were found to proceed with a high level of regiodirection whereas hydrogen-bond directed addition was not a significant factor in the five-membered ring substrates.     

Sensitive, Selective, Precise and Accurate LC–MS Method for Determination of Clonidine in Human Plasma

A selective and sensitive liquid chromatography–mass spectrometric method in ESI (+ve) mode was developed and validated completely in human plasma. Clonidine and IS, carbamazapine, were extracted from human plasma via liquid–liquid extraction with ethyl acetate. Following evaporation under nitrogen, the residue was reconstituted with mobile phase and analyzed using API 4000 LC–MS–MS system. An isocratic program with binary mobile phases (0.1% formic acid in water and acetonitrile) was used to separate interference peaks by a C18 analytical column. Linearity range was 0.49–73.98 ng mL^?1. The intra- and inter-day accuracy and precision were within acceptable limits (≤15%). This method was successfully applied to a single dose 25 μg tablets BE study of clonidine in healthy male volunteers.     

Halobenzene activation by heterofullerenes: computational investigation of oxidative addition activity

Potential of Pd‐ and Ni‐substituted fullerenes for oxidative addition of halobenzenes was investigated using density functional theory. The metal centers in the catalysts were found to be the potential reaction sites. Adsorption of halobenzenes was mildly exergonic over both the compounds. Activation of all halobenzenes was observed over both the compounds. Oxidative addition of C₆H₅I was found to be the least energy intensive process with a free energy requirement that was 3 times smaller than that for C₆H₅F over C₅₉Pd. Activities of both the catalysts were found to be comparable with the end products differing in the coordination of phenyl ring with the heterofullerenes.     

Influence of experimental parameters on dominant energy transfer mechanisms

Three pairs of dyes which operate as efficient energy transfer dye lasers in ethanol have been investigated to understand the dominant energy transfer mechanisms taking place in them. Special attention is given to the experimental configuration which is expected to influence the energy transfer rate constants over an order of magnitude or two. Fluorescence lifetimes have also been studied using time correlated single photon counting technique. It is found that apart from the excitation source and the concentration of dyes, the experimental configuration has a crucial role to play in determining the dominant energy transfer mechanism.     

Ground-state recovery of coumarin dyes by pump-probe technique with picosecond pulses

Rotation-free transmission measurements governed by ground-state recovery of coumarin 102, coumarin 138 and coumarin 339 dyes in ethanol solutions were performed for the first time by pump-probe technique using 35 ps pulses of Nd:YAG laser at 355 nm. Recovery of absorption is characterized by simple exponential behaviour with relaxation times of 4.0, 3.7 and 3.0 ns respectively for C 102, C 138 and C 339. These values are comparable to the lifetimes of the first excited singlet states.     

Microdetermination of nitro groups in organic compounds

Summary A simple procedure for microdetermination of nitro groups in organic compounds is described. It is based on reduction with palladium-on-carbon catalyst in acetic acid in a modified Roth apparatus.

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Zusammenfassung Ein einfaches Verfahren zur Mikrobestimmung von Nitrogruppen in organischen Verbindungen wurde beschrieben. Es beruht auf der Reduktion in Essigsäure mit Palladium-Kohle als Katalysator in einem modifizierten Apparat nachRoth.

     

A model for diffusion of mulucomponent information

The epidemic model of diffusion of news (or disease) is generalized to describe the diffusion of a multi‐component information. The multivaluedness of information in our model arises due to the large number (k) of constituent components or items of the information in question. When the different components of information are assumed to bear no hierarchy, the master equation of the model contains an intractably large number of variables (2 ^k ). The dynamics of the model, however, displays some simplifying features, one of which is the conservation of homogeneity of distribution of population over the different information vectors (in the sense defined in the text). The homogenized version of the model is found to be numerically tractable. The growth curves for large k continue to display sigmoid shapes, but with large ‘saturation times’. The dependence of ‘saturation time’ (i.e. the time required for spread of all the information in almost the entire population) on various parameters of the model, for uniform initial distributions, is numerically investigated. The ‘saturation time’ is found to vary inversely with the intensity of interaction (ß) and the size of population (N), as expected. An important numerical feature that emerges is that the ‘saturation time’ seems to be in linear proportion to the number of information items (k).     

Exhaustive analysis of frontal copolymerization of functionalized monovinyl and divinyl monomers

A series of copolymers of 2-hydroxyethyl methacrylate (HEMA)/glycidyl methacrylate (GMA) and ethylene dimethacrylate (EGDM) were synthesized by frontal polymerization (FP). This study was conducted to investigate the effect of crosslink density, type and concentration of initiator, the use of a complex initiator system, porogen, and diluent on the most relevant parameters of FP, such as sustainability of the front, temperature profile, front velocity, and yield. The products were also characterized for intruded pore volume, pore-size distribution, epoxy-functionality number, and surface morphology. Higher crosslink densities (CLDs) and initiator concentration produced higher front velocities, whereas no trend in front temperature was noted. A complex initiation system was effective in stabilizing and increasing the polymerization yield. Relative to suspension polymerization (SP), FP products synthesized without a solvent were microporous, whereas micro-to-macroporous products were obtained in the presence of a solvent (for HEMA-EGDM polymers). We also present, explain, and discuss the exotic patterns observed under a microscope. We observed two basic types of spatial patterns, namely, planar and nonplanar patterns. The type of planar pattern observed under scanning electron microscopy (SEM) has a spatial impulse that appears as a loop followed by regular periodic motion in the radial and axial directions. This behavior gives rise to a repeating pattern that is a few microns thick. Also, nonplanar patterns, namely, layered concentric rings and winding staircase patterns, were observed under SEM.     

Mixed micelle formation with hydrophobic and hydrophilic Pluronic block copolymers: implications for controlled and targeted drug delivery

Pluronic block copolymers offer affluent phase behavioral characteristics and are extensively investigated for drug delivery applications. Hydrophobic Pluronics produce larger aggregates whereas hydrophilic Pluronics often generate small-sized micelles in aqueous milieu. To overcome the limitations and combine the advantages of different kinds of Pluronics the mixing of such two types of Pluronics is studied here, especially for hydrophobic Pluronic L81 and relatively hydrophilic Pluronic P123. Critical micelle concentration (CMC) of the developed binary mixtures was 0.032 mg/ml as evidenced from pyrene fluorescence spectroscopy and is located in between that of the individual Pluronics. Dynamic light scattering (DLS) showed very small particle sizes (～20 nm) and low polydispersity indices for most of the mixed micelles. Transmission electron microscopy (TEM) demonstrated spherical shape of micelles. Based upon the ratio of hydrophobic and hydrophilic Pluronics, dispersions of varied stability were obtained. With 0.1/1.0 wt.% and 0.5/3.0 wt.% of Pluronic L81/P123, stable dispersions were obtained. Stability was assessed from turbidity measurement, size analysis and clarity of dispersion on standing. Micelles were also found to be stable in bovine serum albumin (BSA) solution. Mixed micelles showed fairly high entrapment efficiency, loading capacity and sustained release profile for aceclofenac (Acl), a model hydrophobe. Presence of salt lowered Acl solubilization in micelles. Thermodynamic parameters for Acl solubilization in mixed micelles revealed high partition coefficient values and spontaneity of drug solubilization. Thus, the developed novel mixed micelles hold promise in controlled and targeted drug delivery owing to their very small size, high entrapment efficiency and stability.     

A novel catalyst-free synthesis of vertically aligned silicon nanowire-carbon nanotube heterojunction arrays for high performance electron field emitters

A novel, catalyst-free strategy for the direct synthesis of vertically aligned silicon nanowire-carbon nanotube (SiNW-CNT) heterojunction arrays is presented. Such a heterojunction with the junction area in the nanoscale displays enhanced field emission characteristics at low turn-on field, with a nearly three times increase in the field enhancement factor.