Acceleration of nucleophilic attack on an organophosphorothioate neurotoxin, fenitrothion, by reactive counterion cationic micelles. Regioselectivity as a probe of substrate orientation within the micelle

31P NMR and UV-vis spectrometric evidence has revealed an unexpected regioselectivity in the reaction of fenitrothion, 1, an organophosphorus pesticide, with the cetyltrimethylammonium (CTA) surfactants CTAOH and CTAMINA, that incorporate the reactive counterions OH- and MINA- (the anti-pyruvaldehyde 1-oximate anion). While both micellar solutions accelerate decomposition of 1 compared to aqueous OH- alone, CTAMINA produced the largest rate enhancement (ca. 10(5)) at a pH (8.39) appropriate for environmental applications. In the absence of surfactant, reaction proceeds solely via the SN2(P) pathway. In the presence of surfactant but below the critical micelle concentration (cmc), a competitive SN2(C) pathway was observed in addition to SN2(P). Above the cmc, however, the CTAOH reaction again proceeded solely via the SN2(P) pathway while both pathways were operative with CTAMINA. The changes in reactivity and mechanistic pathway are discussed in terms of premicellar and micellar influences on rates and regioselectivity. A proposal that would account for the observed regioselectivity in the micellar system is that the aromatic ring and aliphatic side-chains of 1 are oriented toward the micellar interior, while the P=S moiety faces the aqueous pseudophase.     

Development and implementation of an angle detector using nanoporous silicon-based photovoltaic sensor

The present work deals with the design, development, and implementation of an angle detector using n-ATO/p-PSi photovoltaic sensor. Nanoporous structures have been developed over p-type porous silicon wafers by anodization technique under optimized conditions. Photoluminescence studies of porous silicon show emission between 700 and 702 nm for the constant excitation at 350 nm, which illustrates that the band gap can be tuned according to the HF:H₂O:C₂H₅OH ratio. n-ATO/p-PSi O heterojunction photovoltaic sensor has been developed by cost-effective Spray pyrolysis method. I–V characteristics under dark and different illumination intensities have been investigated, and the results are discussed. The fabricated sensor is employed for sensitive angle detection of a light source. The sensor is attached to a DC motor, which rotates at 30 rpm. When the light is from the source incident on the light sensor, a dc voltage has been produced, which in turn is amplified, and the signal has been used to stop the motor. The motor is coupled to a rotary transducer, which is calibrated to read or display 0–3.60 V for 0–360°. Paper presented at the Third International Conference on Ionic Devices (ICID 2006), Chennai, Tamilnadu, India, Dec. 7–9, 2006.     

Polymeric microspheres: a delivery system for osteogenic differentiation

Advanced drug delivery systems employing controlled release technology are being developed to address many of the difficulties associated with traditional methods of drug administration. Controlled release technology involves the use of devices such as polymer‐based disks, rods, pellets, or microspheres (MSs) that encapsulate drugs, genes, cytokines, and growth factors and release them in specific location within the body in a controlled fashion, for relatively long periods of time. Among these, microencapsulation is one of the core technologies used in polymer‐based drug delivery systems. In this regard, MS serves as microcarriers for sustain drug release facilitating their use for invasive or minimally invasive treatment. MS has significant potential for the application in bone repair, intra‐articular treatment of osteoarthritis, and biological bone growth. The present review compiles the recent advances in polymeric MS for application in bone and cartilage regeneration. Copyright © 2017 John Wiley & Sons, Ltd.     

Pyridinium dichlorophosphinomethylides

Seven new pyridinium dichlorophosphinomethylides 2 have been obtained from dichlorophosphinylation of the pyridinium methylides generated in situ. 2 give 1,3‐bis(alkoxycarbonyl)‐2‐phosphaindolizines 4 through 1,5‐electrocyclization of the intermediate, bis(pyridinium ylidyl)phosphenium chloride 3 which is generated either from disproportionation of 2 or from the reaction of 2 with pyridinium methylide. Formation of 3 has been confirmed by carrying out a crossed reaction. 3‐Substituted 2 forms 4 regiospecifically. Intramolecular 1,5‐cyclocondensation of 2‐methylpyridinium dichlorophosphinomethylide is preferred over its disproportionation. © 2001 John Wiley & Sons, Inc. Heteroatom Chem 12:602–609, 2001     

Extreme events on complex networks

A wide spectrum of extreme events ranging from traffic jams to floods take place on networks. Motivated by these, we employ a random walk model for transport and obtain analytical and numerical results for the extreme events on networks. They reveal an unforeseen, and yet a robust, feature: small degree nodes of a network are more likely to encounter extreme events than the hubs. Further, we also study the recurrence time distribution and scaling of the probabilities for extreme events. These results suggest a revision of design principles and can be used as an input for designing the nodes of a network so as to smoothly handle extreme events.     

Synthesis and structural characterization of Ni(II) complexes containing a heterocyclic NO donor ligand

Five novel nickel(II) complexes have been successfully synthesized with a heterocyclic ligand, Opdac, [Ni(Opdac)₂]Cl₂ (1), [Ni(Opdac)₂(CH₃OH)₂]Br₂(CH₃OH)₂ (2), [Ni(Opdac)₂]I₂ (3), [Ni(Opdac)₂NO₃]NO₃ (4) and [Ni(Opdac)₂ClO₄]ClO₄ (5) where Opdac = 4-(1-H-1,3-benzimidazole-2-yl)-1,5-dimethyl-2-phenyl-1-2-dihydro-3-H-pyrazol-3-one. All the complexes were characterized by elemental analysis, molar conductivity, CHN analysis, magnetic susceptibility measurements, spectroscopic studies and TG/DTA methods. In all the complexes, Opdac acts as a bidentate ligand coordinating to Ni(II) ion via the benzimidazole imine nitrogen and the pyrazolone oxygen atoms. The complexes 1 and 3 have a tetrahedral geometry while 2, 4 and 5 have an octahedral geometry around the Ni(II) center.     

Some remarks on global asymptotic stability of neural networks with constant time delay

An elegant proof of a previously reported criterion for the uniqueness and global asymptotic stability of the equilibrium point of a class of neural networks with constant time delay is presented. The present proof yields some interesting observations.     

Chemistry of N,N-Dimethylaminoalkylchalcogenolate Complexes of Palladium(II) and Platinum(II)

Abstract

Four different series of N,N-dimethylaminoalkylchalcogenolates, viz. Me₂NCH₂ CH₂E^?, Me₂NCH(Me)CH₂E^?, Me₂NCH₂CH(Me)E^?, and Me₂NCH₂CH₂CH₂E^? (E = S, Se, Te), (referred as E^∩N) have been synthesized and characterized. Their reactions with palladium(II) and platinum(II) precursors have been explored. Complexes of the general formula, [MCl(E^∩N)]_n, [MCl(E^∩N)₂]_n, [MCl(E^∩N)(PR₃)], [M₂Cl₂(μ-E^∩N)₂(PR₃)₂], [M₂(μ-E^∩N)₂(P^∩P)₂]²⁺, etc. have been isolated. All the complexes have been characterized by elemental analysis, IR, NMR (¹H, ¹³C, ³¹P, ⁷⁷Se, ¹²⁵Te, ¹⁹⁵Pt), UV-vis, and FAB mass spectral data. A weak absorption in the electronic spectra of [MCl(E^∩N)(PR₃)] has been attributed to metal mediated ligand-to-ligand charge transfer and showed pronounced chalcogen dependence being red shifted on moving from S → Se → Te. Structures of several complexes have been established by X-ray diffraction analyses. Thermal behavior of some of these complexes has been investigated by TGA.