Functional Groups Assisted Tunable Dielectric Permittivity of Guest-Free Zn-Based Coordination Polymers for Gate Dielectrics

The dielectric properties of coordination polymers has been a topic of recent interest, but the role of different functional groups on the dielectric properties of these polymers has not yet been fully addressed. Herein, the effects of electron-donating (R=NH₂) and electron-withdrawing (R=NO₂) groups on the dielectric behavior of such materials were investigated for two thermally stable and guest-free Zn-based coordination polymers, [Zn(L₁)(L₂)]_n ( 1 ) and [Zn(L₁)(L₃)]_n ( 2 ) [L₁=2-(2-pyridyl) benzimidazole (Pbim), L₂=5-aminoisophthalate (Aip), and L₃=5-nitroisophthalate (Nip)]. The results of dielectric studies of 1 revealed that it possesses a high dielectric constant (κ=65.5 at 1 kHz), while compound 2 displayed an even higher dielectric constant (κ=110.3 at 1 kHz). The electron donating and withdrawing effects of the NH₂ and NO₂ substituents induce changes in the polarity of the polymers, which is due to the inductive effect from the aryl ring for both NO₂ and NH₂. Theoretical results from density functional theory (DFT) calculations, which also support the experimental findings, show that both compounds have a distinct electronic behavior with diverse wide bandgaps. The significance of the current work is to provide information about the structure-dielectric property relationships. So, this study promises to pave the way for further research on the effects of different functional groups on coordination polymers on their dielectric properties.     

Simultaneous Determination of Pioglitazone and Glimepiride by High-Performance Liquid Chromatography

A rapid and accurate HPLC method has been developed for simultaneous determination of pioglitazone and glimepiride. Chromatographic separation of the two pharmaceuticals was performed on a Cosmosil C₁₈ column (150 mm × 4.6 mm, 5 m) with a 45:35:20 (v/v) mixture of 0.01 m triammonium citrate (pH adjusted to 6.95 with orthophosphoric acid), acetonitrile, and methanol as mobile phase, at a flow rate of 1.0 mL min^–1, and detection at 228 nm. Separation was complete in less than 10 min. The method was validated for linearity, accuracy, precision, limit of quantitation, and robustness [1, 2]. Linearity, accuracy, and precision were found to be acceptable over the ranges 2.50–30.00 g mL^–1 for pioglitazone and 0.10–10.00 g mL^–1 for glimepiride.     

Determination of Band Structure Parameters and the Quasi‐Particle Gap of CdSe Quantum Dots by Cyclic Voltammetry

Band structure parameters such as the conduction band edge, the valence band edge and the quasi‐particle gap of diffusing CdSe quantum dots (Q‐dots) of various sizes were determined using cyclic voltammetry. These parameters are strongly dependent on the size of the Q‐dots. The results obtained from voltammetric measurements are compared to spectroscopic and theoretical data. The fit obtained to the reported calculations based on the semi‐empirical pseudopotential method (SEPM)—especially in the strong size‐confinement region, is the best reported so far, according to our knowledge. For the smallest CdSe Q‐dots, the difference between the quasi‐particle gap and the optical band gap gives the electron–hole Coulombic interaction energy (J_e1,h1). Interband states seen in the photoluminescence spectra were verified with cyclic voltammetry measurements.     

Chitooligosaccharides: Synthesis,characterization and applications

Chitosans with high degree of polymerization and molecular weight exhibit poor aqueous solubility which is an impediment in their applicability. The low molecular weight chitosans (LMWCs) and chitooligosaccharides (COSs) can be used to avoid this hurdle. The development of an efficient process for reducing the molecular weight of chitosan, without altering its chemical structure, is of great interest to produce tailormade chitosans of varying Degree of Acetylation (DAs) and Degree of Polymerization (DPs). The production of well-defined COS-mixtures, or even pure COS, is of great interest since these oligosaccharides are thought to have several interesting bioactivities and applications. For this proper delineation of their characteristics is needed. Hence it is our attempt to provide an overview of difffernt methods and techniques of their production and characterization. Several methods viz. depolymerization under the action of reagents, enzymes, high energy impact and combinations thereof have been employed to get COS by depolymerization of high molecular weight chitosans. Acid hydrolysis (hydrochloric, nitrous, phosphoric acid, hydrogen fluoride) and oxidative reductive depolymerization (mediated by peroxide, ozone, and persulfate) are important routes for synthesis of COSs. These oligomers can be produced from chitin or chitosan as a starting material by enzymatic conversions. For this, numbers of enzymes have been used. Depolymerization under high energy impact and recombinant approaches are also being tried for production of COSs. LMWC and COS, like parent chitosan, can be used for drug delivery and gene delivery. The efficient and productive processes are needed for separation of COSs into its components or mixture of defined characters. The characterization of COS can be carried out by chromatographic and spectroscopic techniques. Importantly COSs display an array of biological activities as antimicrobial, anticancer/antimetastatic, wound healing acceleration, immunostimulation, apoptosis induction or inhibiton, antioxidant, enzyme inhibiton, antihyperlipidemic, antidiabetic, chemoprevention, and many more. A few of the biological actions are reported only sporadically where as some are persistently taken up by the scientific fraternity to substantiate the claims and propose possible mechanisms of action. However there remains the disagreement of results on COS activities. The disagreements can arise due to poor and variable reporting of the properties of COS such as used in the studies as molecular weight, degree of acetylation, molecular weight distribution, and the pattern of N-acetylation etc. With production of COS of well defined characters it might be possible to understand the modes of actions of COS in better ways.     

Picosecond time-resolved laser emission of coumarin 102: Solvent relaxation

The time-resolved laser emission of coumarin 102 was investigated in various aprotic and protic solvents at picosecond resolution by frequency upconversion technique. The spectral shift of the transient emission spectrum is attributed to solvent reorientation and the results are discussed.     

Analysis of a model scheme incorporating reactant inhibition: Instability of homogeneous solution and formation of spatio–temporal structures

A model scheme incorporating reactant inhibition in the rate process has been analyzed with a view to study the instability of homogeneous solution due to diffusion. Conditions for the occurrence of Turing as well as phase instability are derived and show the existence of multiplicity in the parameter space. The Ginzburg-Landau equation for the system is developed and solved numerically in various regions of the parameter space. The simple model system shows the existence of very rich behavior including normal and inverted bifurcations in the super and subcritical regimes. The various results are analyzed and discussed. © 1993 John Wiley & Sons, Inc.     

Economics of molasses to ethanol in India

Applied Biochemistry and Biotechnology -     

Solvent effect on absorption and fluorescence spectra of coumarin laser dyes: evaluation of ground and excited state dipole moments

The effect of solvents on absorption and fluorescence spectra and dipole moments of coumarin 307 (C307) and coumarin 522B (C522B) have been studied extensively in various solvents, viz., general solvents, alcohols and binary mixtures (acetonitrile-benzene) at 298K. The bathchromic shift observed in absorption and fluorescence spectra of C307 and C522B with increasing solvent polarity indicates that transition involved are pi-->pi*. Solvatochromic correlations were used to obtain the ground and excited state dipole moments. The excited state dipole moments are observed to be greater than their ground state counterparts in all the solvents studied. Further, the experimentally obtained Deltamu were compared with those using normalized polarity terms E(T)(N) from Reichardt equation.