Kinetic and mechanistic study on the thermal reactivity of stabilized phosphorus ylides,part 3: [(Acetyl)(arylcarbamoyl)methylene]triphenylphosphoranes and [(alkoxycarbonyl)(arylcarbamoyl)methylene]triphenylphosphoranes and their thiocarbamoyl analogues

A series of five [(acetyl)(arylcarbabmoyl)methylene]triphenyl‐phosphoranes 1a–e and their thiocarbamoyl analogues 2a–e , [(alkoxycarbonyl)(arylcarbamoyl)methylene]triphenylphosphoranes 3a–e and their thiocarbamoyl analogues 4a–e were prepared and fully characterized. All ylides are found under conditions of flash vacuum pyrolysis to fragment giving arylisocyanate or isothiocyanate and acetyl ylides or alkoxy ylides which undergo thermal extrusion of Ph₃PO. A kinetic study shows that these reactions are unimolecular and are of first‐order nature with no significant substituent effect. The thiocarbamoyl ylides 2 react from 4.6 to 42 times faster than their carbamoyl ylides 1 , while the thiocarbamoyl ylides 4 react from 6.6 to 20.9 times faster than their carbamoyl ylides 3 . © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 39: 6–16, 2007     

Modulational instability of optically induced nematicon propagation

We report the modulational instability （MI） analysis for the modulation equations governing the propagation of coherent polarized light through a nematic liquid crystal （NLC） slab, in the limit of low light intensity and local material response. The linear stability analysis of the nonlinear plane wave solutions is performed by considering both the wave vectors （k,l） of the basic states and wave vectors （K,L） of the perturbations as free parameters. We compute the MI gain, and the MI gain peak is reduced and the stable bandwidth is widened with the increase of the strength of the applied electric field. Further, we invoke the extended homogeneous balance method and Exp-function method aided with symbolic computation and obtain a series of periodic solitonic humps of nematicon profiles admitting the propagation of laser light in the NLC medium.     

Spectrophotometric Determination of Cobalt(II), Nickel(II) and Copper(II) with Acenaphthenequinone Monosemicarbazone (AQSC)

Cobalt(II), nickel(II) and copper(II) complexation with acenaphthenequinone monosemicarbazone (AQSC) has been studied spectrophotometrically. The Co(II), Ni(II) and Cu(II) complexes are soluble in ethanol medium and exhibit maximum absorbance at 410, 420 and 430 nm, respectively. The sensitivity of the reactions are 0.012, 0.02 and 0.01 μg/cm² for cobalt, nickel and copper systems. All the three complexes show maximum and constant absorbance in the pH range 8.4 to 9.8, 6.3 to 8.4 and 5.4 to 8.0 for Co-AQSC, Ni-AQSC and Cu-AQSC, respectively. Nickel and copper in some alloys have also been analysed.     

Computation of collective excitations and elastic constants of expanded trigonal tellurium

The potential function derived from experimental structure factor data gives a repulsive minimum and also an attractive minimum. These two minima correspond to the first and second nearest-neighbour distances. Similar results have been obtained through the use of Percus-Yevick (PY) and hyper-netted chain (HNC) equations. The Hafner molecular dynamics results also show a similar trend. The first, second and third derivatives of the potential function have been obtained from the expression of the potential function. The first and second derivatives have been used to compute the phonon frequencies using Bhatia and Singh's (BS) method. The phonon frequencies obtained from Hubbard and Beeby's (HB) method show similar results. The elastic constants have also been calculated and the values obtained for C₁₁ by different methods are in good agreement. The Grüneisen constant has been calculated by two different methods which are in very good agreement with each other. From the Grüneisen constant the pressure derivative of the diffusion coefficient has been obtained and has been compared with that of Swalin's equation. The results are in excellent agreement with each other.     

Preparation and Evaluation of 125I-Aflatoxin B1

Aflatoxin B₁ (AfB₁), present in fungus infested crops is highly carcinogenic and is measured by immunoassays. ¹²⁵I labeled aflatoxin B₁ is a key reagent for development of radioimmunoassay (RIA) which exhibits less interference and better sensitivity than other immunoassays. Since AfB₁ lacks suitable functional groups for radiolabeling, an oxime derivative of AfB₁ was synthesised and evaluated by UV-spectrophotometry and ¹H NMR spectroscopy. ¹²⁵I-histamine was conjugated to AfB₁ oxime by mixed anhydride method and purified by solvent extraction followed by TLC. The tracer obtained was immunoreactive, stable as ethanolic solution and could be used in RIA.     

Synthesis of a New Class of Arylsulfonylethylsulfonylmethyloxazolines and Thiazolines

A new class of arylsulfonylethylsulfonylmethyl oxazolines and thiazolines were prepared using multistep, one‐pot methodologies exploiting lanthanide alkoxides and under microwave irradiation. The microwave method provides an excellent approach in a single step with high yields.     

Synthesis of 3-[4-(1-Benzofuran-2-yl)-1,3-thiazol-2-yl]-2-(4-aryl)-1,3-thiazolidin-4-one Derivatives as Biological Agents

A protocol for the synthesis of 3-[4-(1-benzofuran-2-yl)-1,3-thiazol-2-yl]-2-(4-aryl)-1,3-thiazolidin-4-one derivatives (5a–e) has been developed from 1-(1-benzofuran-2-yl)-2-bromoethanone (2),which served as a key intermediate for the synthesis of the title compounds. The reaction of compound 2 with thiourea furnished 4-(1-benzofuran-2-yl)-1,3-thiazol-2-amine 3, which upon further reaction with various aromatic aldehydes, gave Schiff bases 4a–e. These Schiff bases, when treated with thioacetic acid in the presence of catalytic amount of anhydrous ZnCl₂, yielded thiazolidinone derivatives 5a–e. All the newly synthesized compounds have been characterized by analytical and spectral data and screened for their antimicrobial and analgesic activity.

Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file.     

Inclusion complexation of 4,4′-dihydroxybenzophenone and 4-hydroxybenzophenone with α- and β-cyclodextrins

The inclusion complexation behaviours of 4,4′-dihydroxybenzophenone (DHBP) and 4-hydroxybenzophenone (HBP) with α-cyclodextrin (α-CD) and β-cyclodextrin (β-CD) were investigated using UV–visible fluorescence, time-resolved fluorescence, molecular modelling, scanning electron microscopy (SEM), FTIR, differential scanning calorimeter, X-ray diffraction, ¹H NMR and molecular modelling techniques. In both molecules, biexponential decay was observed in water, whereas triexponential decay was observed in the CD medium. The DSC thermogram of the DHBP/α-CD and DHBP/β-CD inclusion complex nanomaterials shows the endothermic peak at 60.8, 101.9, 119.6 and 112.8°C. The upfield chemical shift observed for HBP protons reveal that the phenyl ring (without hydroxyl substitution) entered the CD cavity and the hydroxyl group of HBP is exposed outside the CD cavity. The SEM image of DHBP appears as needle-shaped crystals on the micrometre scale, whereas the irregular bar shape was observed for HBP. Transmission electron microscopy images show that both guest molecules formed nano vesicles with α-CD and formed nano rods with β-CD.     

Studies directed toward the synthesis of caylobolide A: convergent synthesis of C21–C40 subunit

Stereoselective synthesis of the C21–C40 core segment of caylobolide A has been achieved following a highly efficient convergent strategy. The key reactions featured in the synthesis are Prins cyclization, reductive radical cyclization, Sharpless asymmetric epoxidation and olefin cross metathesis.