Liquid-crystalline polymer composites with CdS nanorods: structure and optical properties

We report on the structure, uniaxial orientation, and photoluminescent properties of CdS nanorods that form stable nanocomposites with smectic C hydrogen-bonded polymers from the family of poly(4-(n-acryloyloxyalkoxy)benzoic acids. TEM analysis of microtomed films of nanocomposites reveals that CdS nanorods form small domains that are homogeneously distributed in the LC polymer matrix. They undergo long-range orientation with the formation of one-dimensional aggregates of rods when the composite films are uniaxially deformed. The Stokes photoluminescence was observed from CdS NRs/LC polymer composites with emission peak located almost at the same wavelength as that of NRs solution in heptane. An anti-Stokes photoluminescence (ASPL) in polymer nanocomposites was found under the excitation below the nanoparticles ground state. The mechanism of ASPL was interpreted in terms of thermally populated states that are involved in the excitation process. These nanocomposites represent an unusual material in which the optical properties of anisotropic semiconductor nanostructures can be controlled by mechanical deformation of liquid-crystalline matrix.     

Focused Microwave-Assisted Extraction and LC Determination of Ketoprofen in the Presence of Preservatives in a Pharmaceutical Cream Formulation

A simple and rapid open-vessel focused microwave-assisted extraction (FMAE) method followed by LC analysis was developed for the determination of ketoprofen lysine salt in the presence of methyl p-hydroxybenzoate and propyl p-hydroxybenzoate preservatives in topical cream. Extraction were performed in acetone/potassium dihydrogenphosphate (25 mM, pH 3.0) (70:30 v/v) by reaching a target temperature of 65 °C in a 10 min linear ramp. The chromatographic separation was performed on a Discovery RP-Amide C16 column (250 × 4.6 mm I.D., 5 μm particle size). The optimal mobile phase consisted of acetonitrile/potassium dihydrogen phosphate 25 mM adjusted to pH 3.0 with phosphoric acid (50:50 v/v). The complete analytical procedure was validated with regard to limit of quantification, linearity, precision and accuracy. The method was linear over the concentration range of 0.08–0.12 mg mL⁻¹; the relative standard deviations of intra- and inter-day assays were 1.9–2.3 and 1.8% respectively. The limit of quantification was 0.54 μg mL⁻¹. The proposed method shows many advantages as short extraction time, little solvent consumption without requiring further sample clean-up steps before liquid chromatographic analysis and is proposed for vast scale screening of cream dosage forms aimed to the detection of counterfeit and substandard drugs.

     

Kinetics and mechanism of the oxidation of glycolaldehyde by tetrachloroaurate(III)

The kinetics of the reaction between glycolaldehyde (GA) and tetrachloroaurate(III) in acetic acid-sodium acetate buffer has been studied. The reaction is first-order with respect to [Au^III] as well as [GA]. Both H⁺ and Cl⁻ ions retard the rate of reaction. AuCl₄⁻, AuCl₃(OH₂), and AuCl₃(OH)⁻ are the reactive species of gold(III) with gradually increasing reactivity. A reaction mechanism involving two-electron transfer rate determining steps has been proposed. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 613–619, 1998     

Negatively charged micelles directed synthesis of snow-ball flower like superparamagnetic Ni nanoparticles and investigation of their properties

Snow-ball flower like Ni nanoparticles have been synthesized using negatively charged micelles. Negatively charged micelles incorporate the Ni⁺² onto its head group by electrostatic attraction and again a surfactant layer is arranged on positively charged Ni and thus in a repetitive way layer-by-layer a snow-ball flower like structure is formed. After reduction of Ni⁺² to Ni atom by sodium borohydride and hydrated hydrazine the Ni clusters (3 nm) are formed and confined in micelles in snow-ball flower like pattern. The sizes of these nanoflowers are of 30 nm order. The particles are superparamagnetic in nature with blocking temperature about 117 K.     

Palladium-catalyzed Suzuki-Miyaura cross-coupling reaction of organoboronic acids with N-protected 4-iodophenyl alanine linked isoxazoles

Suzuki-Miyaura coupling reaction of N-protected 4-iodopheyl alanine isoxazoles with arylboronic acids, catalyzed by palladium, efficiently produce benzyl-N-(4-bipheyl)-2-(3-methyl-5(E)-2-aryl-1-ethenyl-4- isoxazolyl)-amino-2-oxoethyl) carba-mates in good yields. This process is first of its kind to construct carbon-carbon bond formation having biaryl motif on amino acid linked isoxazole moiety.     

Synthesis of bischromones by deformylative Mannich type reaction on chromone-3-carbaldehyde using α-aminoacid as the source of amine

Chromone-3-carbaldehyde reacts with N-methylglycine or glycine in the presence of excess formaldehyde to produce N-(chromone-3-ylmethyl)-N-methylglycine or N,N-di(chromone-3-ylmethyl)glycine, respectively, by a deformylative Mannich type reaction. Use of alanine or leucine or methionine in place of glycine produces N-(chromone-3-ylmethyl)alanine/-leucine/-methionine, respectively.     

Early Diagnosis of Diabetes through the Eye

Diabetes mellitus is a metabolic disorder characterized by high blood sugar levels which give rise to complications in the eye, kidneys and the brain. Diabetes triggers the development of ocular diseases like diabetic retinopathy and cataracts which are the leading cause of blindness around the world. The most common method for the diagnosis of diabetes involves measuring the blood sugar levels in the body. One major disadvantage of this method is the fluctuating blood sugar levels which contribute to false negative results. This leads to delay in treatment, eventually causing permanent damage to the organs. Therefore, diagnosis of diabetes at an early stage is very crucial. One biomarker for diabetes related diseases is the formation of Advanced Glycation End‐products (AGEs) that result from the Maillard reaction of proteins with glucose. α‐crystallin in the ocular lens is a small heat shock protein with no protein turnover and hence acts as a record for post‐translational modifications especially glycation which forms AGEs. We have used steady state and time resolved fluorescence measurements to study the spectroscopic changes in α‐crystallin with increase in time of glycation and the intact lenses from diabetic and nondiabetic donors. Overall, this study was focused on developing a noninvasive diagnostic tool for early detection of diabetes mellitus.     

Estimation of Olefin Dimerisation Products by GC/GC–MS and IR Techniques

A GC and IR based protocol was developed for monitoring the isobutene dimerisation process wherein the complete characterisation of the products was carried out by GC coupled with mass spectrometry. In the dimerisation process, LPG from FCC process comprising a mixture of saturated and unsaturated C4 hydrocarbons is subjected to a dimerisation process using a catalyst to produce C8 hydrocarbons. The reaction is carried out keeping in view the demand for high-octane blending components in gasoline. The isooctene generated in the process (mainly from the dimerisation of isobutene) is converted into isooctane having the RON and MON value 100. The monitoring process requires the use of two different column chemistries, viz., a 100 m CPSIL PONA CB non-polar column for C8 and its isomers and an Alumina PLOT column for C4 hydrocarbons. A 100 m non-polar column does not separate the C4 mixture since the column is meant for gasoline range products containing C5 and above hydrocarbons. Therefore, a need was felt for an improvised method which can handle both the analyses simultaneously. A cryogenic oven program starting from 0 °C was developed for separating the isomers of C4 hydrocarbons and C8 hydrocarbons on a single column during the single run by Detailed Hydrocarbon Analyzer. The data obtained using the cryo programme was validated with data obtained using Alumina PLOT column on C4 mixture since the Alumina PLOT column is the widely accepted column chemistry for separating the C4 hydrocarbons. An IR method for the estimation of the total olefin content was developed using 2,2,4-trimethyl pentene-1 as the reference standard. The total olefins generated during the process were identified by GC–MS, quantified by DHA-FID and validated by infrared spectroscopy. A good correlation was found between GC and IR spectral results (correlation coefficient R ²  = 0.99).     

Synthesis of 2([Methyl-5-[(E)-2-aryl-1-ethenyl]-4-isoxazolyl]imino)-1,3-thiazolan-4-ones and Their Mannich Bases

Isoxazolyl chloroacetamides (2) were obtained from 4-amino-3-methyl-5-styrylisoxazoles (1) on reaction with chloroacetyl chloride. Cyclocondensation of 2 with NH₄SCN yielded 2([-methyl-5-(E)-2-aryl-1-ethenyl]-4-isoxazolylimino)-1,3-thiazolan-4-ones(3). Mannich reaction of 3 with formaldehyde and secondary amines gave isoxazolyl thiazolidinone Mannich bases (4 and 5).     

Correlation analysis of structure and reactivity in the oxidation of substituted benzyl alcohols by bis(2,2′-bipyridyl) copper(II) permanganate

The oxidation of substituted benzyl alcohols by bis(2,2′-bipyridyl) copper(II) permanganate (BBCP), leading to the corresponding benzaldehydes is first-order with respect to BBCP. Michaelis-Menten type kinetics were observed with respect to the alcohols. The oxidation of a,a-dideuteriobenzyl alcohol indicated the presence of a substantial kinetic isotope effect. The rates of oxidation of meta- and para-substituted benzyl alcohols were correlated in terms of Charton's triparametric LDR equation whereas ortho- substituted benzyl alcohols were correlated with a four parametric LDRS equation. The results of correlation analyses point to an electron-deficient reaction center in the transition state. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 9–16, 1997.