Magnetic properties of substitutional solid solutions of nickel and iron hexacyanoferrate–hexacyanochromate

In order to evaluate the influence of substitution at the central metal ion position in transition hexacyanometallates in some detail, the magnetic studies were carried out on a series of solid solutions of metal hexacyanometallates of the composition M[Fe^II(CN)₆]_{1? x} [Cr^III(CN)₆] _x , where M?=?Ni^II and Fe^III. The temperature and field dependences of magnetization were studied using a superconducting quantum interference device magnetometer. The field dependence of the samples at 5?K shows a hysteresis behaviour. For M?=?Ni^II, the transition temperature increases with increase in the substitution of low-spin Fe(III) by Cr(III) in the hexacyanometallate unit. The saturation magnetization was found to decrease with increase in the iron concentration. The observed variation in the magnetic properties, such as the value of T _C and the nature of magnetic ordering, is attributed to the variation in the composition of the transition-metal ion in the coordination sphere of carbon. On the other hand, for M?=?Fe^III, the transition temperature and saturation magnetization remained almost unchanged, indicating that substitution at the carbon coordination site did not produce any change in the magnetic interaction among the transition-metal ions through the cyanide ions.     

Effects of anionic and cationic micelles on the oxidation of d-dextrose by diperiodatoargentate(III)

The oxidative behavior of d-dextrose toward diperiodatoargentate(III) (DPA) has been studied in the absence and presence of anionic and cationic micelles of sodium dodecyl sulfate (SDS) and cetyltrimethylammonium bromide (CTAB), respectively. The kinetics is based on the reduction of silver(III) to silver(I) by d-dextrose under pseudo-first-order conditions. The monoperiodatoargentate(III) ions act as active oxidants in comparison to that of DPA. The reactions are first- and fractional-order dependence with respect to [DPA] and [d-dextrose], respectively. The reaction rates decrease with [H⁺] and [periodate]. The premicellar environment of SDS and CTAB strongly inhibits the reaction rate. Inhibition is due to favorable thermodynamic/electrostatic binding between the Ag(III) complex and CTAB monomer aggregates. A suitable mechanism involving a one-electron transfer (rate-determining step) from d-dextrose to the silver(III) species has been proposed. Activation parameters have been evaluated and discussed.     

Molecular structure and vibrational spectra of 1,3-bis(4-pyridyl)propane by quantum chemical calculations

The experimental and theoretical study on the structures and vibrations of 1,3-bis(4-pyridyl)propane are presented. The FT-IR and Raman spectra of molecule have been measured. The optimized geometric bond lengths have been obtained by DFT show the best agreements with experimental values. The harmonic vibrational frequencies were calculated and scaled values have been compared with experimental FT-IR and FT-Raman spectra. Majority of the computed wavenumbers were found to be in good agreement with experimental observations. A complete assignment of the fundamentals was proposed based on the total energy distribution (TED) calculation.     

Synthesis of block copolymers by the transformation of cationic polymerization into reversible atom transfer radical polymerization

Azo-containing polytetrahydrofuran (PTHF) obtained by cationic polymerization was used as a macroinitiator in the reverse atom transfer radical polymerization (RATRP) of styrene and methyl acrylate in conjunction with CuCl₂/2,2′-bipyridine as a catalyst. Diblock PTHF–polystyrene and PTHF–poly(methyl acrylate) were obtained after a two-step process. In the first step of the reaction, stable chlorine-end-capped PTHF was formed with the thermolysis of azo-linked PTHF at 65–70 °C in the presence of the catalyst. Heating the system at temperatures of 100–110 °C started the polymerization of the second monomer, which resulted in the formation of block copolymers. The decomposition behavior of the azo-linked PTHF and the structure of the block copolymers were determined by ¹H NMR and gel permeation chromatography (GPC). Kinetic studies and GPC analyses further confirmed the controlled/living nature of the RATRP initiated by the polymeric radicals. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2199–2208, 2002     

Dark–bright optical solitary waves and modulation instability analysis with (2 + 1)-dimensional cubic-quintic nonlinear Schrödinger equation

This paper addresses the (2+1)-dimensional cubic-quintic nonlinear Schrödinger equation (CQNLS) that serves as the model to study the light propagation through nonlinear optical media and non-Kerr crystals. A dark–bright optical solitary wave solution of this equation is retrieved by adopting the complex envelope function ansatz. This type of solitary wave describes the properties of bright and dark optical solitary waves in the same expression. The integration naturally lead to a constraint condition placed on the solitary wave parameters which must hold for the solitary waves to exist. Additionally, the modulation instability (MI) analysis of the model is studied based on the standard linear stability analysis and the MI gain spectrum is got. Numerical simulation and physical interpretations of the obtained results are demonstrated. It is hoped that the results reported in this paper can enrich the nonlinear dynamical behaviors of the CQNLS.     

Synthesis of Poly(silyne-co-hydridocarbyne) for Silicon Carbide Production

Pre-ceramic polymers have previously been shown to be polymeric precursors to silicon carbide, diamond and diamond-like carbon. Here, we report the synthesis of a pre-ceramic polymer, poly(silyne-co-hydridocarbyne), which was electrochemically synthesized from one monomer containing both silicon and carbon in its structure. The polymer is soluble in common solvents such as CHCl₃, CH₂Cl₂ and THF. Since the polymer contains both silyne and carbyne on its backbone, it can be easily converted to silicon carbide upon heating under an ambient inert atmosphere, or to SiO₂ under ambient air atmosphere. Poly(silyne-co-hydridocarbyne) was characterized with UV/Vis spectroscopy, FTIR, ¹H-NMR, GPC and Raman spectroscopy. Conversion of the polymer to SiC ceramic was accomplished by heating at 1000 and 750°C under an argon atmosphere and characterized with optical microscopy, SEM, X-Ray and Raman spectroscopies.     

Hybrid thermotropic liquid-crystalline block copolymers

A new approach to the preparation of two classes of block copolymers containing liquid-crystalline segments is reported. Copolymers 1 and 2 are constituted by polytetrahydrofuran and side-chain liquid-crystalline polymethacrylate blocks, whereas block copolymers 3 consist of polystyrene and main-chain liquid-crystalline polyester blocks. The synthetic procedures leading to copolymers 1-3 are extremely versatile and can be used to prepare a great variety of block copolymer architectures. In both copolymer classes the chemically different blocks are strongly segregated in the solid and melt phases and undergo individual phase transitions. The mesophase transition temperatures of the liquid-crystalline blocks are very similar to those of the corresponding homopolymers, and their enthalpies are directly proportional to the content of the liquid-crystalline block.     

Light‐Induced Click Reactions

Spatial and temporal control over chemical and biological processes, both in terms of “tuning” products and providing site‐specific control, is one of the most exciting and rapidly developing areas of modern science. For synthetic chemists, the challenge is to discover and develop selective and efficient reactions capable of generating useful molecules in a variety of matrices. In recent studies, light has been recognized as a valuable method for determining where, when, and to what extent a process is started or stopped. Accordingly, this Minireview will present the fundamental aspects of light‐induced click reactions, highlight the applications of these reactions to diverse fields of study, and discuss the potential for this methodology to be applied to the study of biomolecular systems.     

Ultraviolet Radiation‐Induced Downregulation of SERCA2 Mediates Activation of NLRP3 Inflammasome in Basal Cell Carcinoma

Basal cell carcinomas (BCCs) account for majority of skin malignancies in the United States. The incidence of BCCs is strongly associated with exposure of ultraviolet (UV) radiation. Nucleotide‐binding domain, leucine‐rich‐repeat‐containing family, pyrin domain‐containing 3 (NLRP3) inflammasome plays an important role in innate immune responses. Different stimuli such as toxins, microorganisms and particles released from injured cells activate the NLRP3 inflammasome. Activated NLRP3 results in activation of caspase‐1, which cleaves pro‐IL‐1β to active IL‐1β. In this study, we have shown that NLRP3 is expressed in human basal cell carcinomas. The proximal steps in activation of NLRP3 inflammasome are not well understood. Here, we have attempted to elucidate a critical role for Ca²⁺ mobilization in activation of the NLRP3 inflammasome by UVB exposure using HaCaT keratinocytes. We have demonstrated that UVB exposure blocks Ca²⁺ mobilization by downregulating the expression of sarco/endoplasmic reticulum Ca²⁺‐ATPase (SERCA2), a component of store‐operated Ca²⁺ entry that leads to activation of the NLRP3 inflammasome.     

Calculation of linear and nonlinear optical absorption coefficients of a spherical quantum dot with parabolic potential

In the effective mass approximation, we calculated the binding energy and wave function for the 1s-, 1p-, 1d- and 1f-states of a spherical quantum dot (QD) with parabolic potential by using a combination of quantum genetic algorithm (QGA) and Hartree-Fock-Roothaan (HFR) method. In addition, we also investigated the linear and the third-order nonlinear optical absorption coefficients as a function of the incident photon energy for the 1s-1p, 1p-1d and 1d-1f transitions. Our results are shown that the existence of impurity has great influence on optical absorption coefficients. Moreover, the optical absorption coefficients are strongly affected by the incident optical intensity, relaxation time, parabolic potential and dot radius.