Differential pulse polarographic determination of trace amounts of vanadium and molybdenum in various standard alloys and environmental samples after preconcentration of their morpholine-4-carbodithioates on microcrystalline naphthalene or morpholine-4-dithiocarbamate cetyltrimethyl-ammonium bromide-naphthalene adsorbent

A highly selective, sensitive, and fairly rapid and economical differential pulse polarographic (DPP) method has been reported for the determination of trace amounts of vanadium and molybdenum in standard alloys and various environmental samples. The morpholine-4-carbodithioates of these metals were retained (>99% recovery) quantitatively on microcrystalline naphthalene in the pH range 4.5-6.9 for vanadium and 1.5-4.5 for molybdenum. These metals were determined by DPP after desorption with 10 ml of 1 M HCl. Vanadium and molybdenum may also be preconcentrated by passing their aqueous solutions under similar conditions on morpholine-4-dithiocarbamate CTMAB-naphthalene adsorbent packed in a column at a flow rate of 1-5 ml min(-1) and determined similarly. The detection limits are 0.20 ppm for vanadium and 0.04 ppm for molybdenum at minimum instrumental settings (signal to noise ratio=2). The linearity is maintained in the following concentration ranges, vanadium 0.50-10.0 and molybdenum 0.10-9.0 ppm, with a correlation factor of 0.9996 (confidence interval of 95%, slopes 0.0196 and 0.01497 muA mug(-1), intercepts 3.65x10(-3) and -1.92x10(-3) respectively) and relative standard deviation of 1.1% in the microcrystalline method, while in the column method, the linearity is maintained in the concentration ranges, 0.50-6.5 for vanadium and 0.10-5.5 ppm for molybdenum with correlation factor of 0.9994 (with confidence interval of 95%, slopes 0.0194, 0.015 muA mug(-1), intercepts 3.60x10(-3) and -1.90x10(-3) respectively) and relative standard deviation of 1.4%. Various parameters such as the effect of pH, reagent, naphthalene and CTMAB concentrations, volume of aqueous phase and interference of a large number of metal ions on the estimation of vanadium and molybdenum have been studied in detail to optimize the conditions for their voltammetric determination at trace level in various standard alloys and environmental samples.     

Complex formation of isocytosine tautomers with PdII and PtII

Isocytosine (ICH) exists in solution as two major tautomers, the keto form with N1 carrying a proton (1a) and the keto form with N3 being protonated (1b). In water, 1a and 1b exist in equilibrium with almost equal amounts of both forms present. Reactions with a series of Pd(II) and Pt(II) am(m)ine species such as (dien)Pd(II), (dien)Pt(II), and trans-(NH(3))(2)Pt(II) reveal, however, a distinct preference of these metals for the N3 site, as determined by (1)H NMR spectroscopy. Individual species have been identified by the pD dependence of the ICH resonances. pK(a) values (calculated for H(2)O) for deprotonation of the individual tautomers complexes are 6.5 and 6.4 for the N3 linkage isomers of dienPd(II) and dienPt(II), respectively, as well as 6.2 and 6.0 for the N1 linkage isomers. The dimetalated species [(dienM)(2)(IC-N1,N3)](3+) (M = Pd(II) or Pt(II)) are insensitive over a wide range of pD. The crystal structure analysis of [(dien)Pd(ICH-N3)](NO(3))(2) is reported. Ab initio calculations have been performed for tautomer compounds of composition [(NH(3))(3)Pt(ICH)](2+), cis- and trans-[(NH(3))(2)PtCl(ICH)](+), as well as trans-[(NH(3))(2)Pt(ICH)(2)](2+). Without exception, N3 linkage isomers are more stable, in agreement with experimental findings. As to the reasons for this binding preference, an NBO (natural bond orbital) analysis for [(NH(3))(3)Pt(ICH-N3)](2+)strongly suggests that intramolecular hydrogen bonding between trans-positioned NH(3) ligands and the two exocyclic groups of the ICH is of prime importance. The calculations furthermore show a marked pyramidalization of the NH(2) group of ICH in the complex once the heterocyclic ligand forms a dihedral angle <90 degrees with the Pt coordination plane.     

High-level expression of soluble human β-defensin-2 fused with green fluorescent protein in Escherichia coli cell-free system

Human β-defensin-2 (hBD2), a small cationic peptide, exhibits a broad range of antimicrobial activity and does not acquire any microbial resistance. To produce this uneasily detectable, degradable, and toxic polypeptide efficiently, an alternative approach based on the Escherichia coli cell-free biosynthesis system was proposed. The approach implies that a polypeptide of interest is synthesized as a fusion protein linked to a green fluorescent protein (GFP) through a cleavable spacer. With batch-mode operation, a significant amount of hBD2 fused with GFP (0.25 mg/mL) can be expressed in this cell-free system. The productivity of the fusion protein can be improved up to 1.2 mg/mL by employing a continuous-exchange cell-free system. Furthermore, the GFP moiety provides directly visible and quantitative monitoring of the polypeptide synthesis, and the product is soluble and stable. This work will be helpful in allowing the rapid and visible expression of other similar defensins using an in vitro cell-free system.     

Simulation of the Adhesion of Particles to Surfaces

The removal of micrometer and submicrometer particles from dielectric and metal films represents a challenge in postchemical mechanical polishing cleaning. Proper modeling of the adhesive force between contaminant particles and these films is needed to develop optimal solutions to postchemical mechanical polishing cleaning. We have previously developed and experimentally validated a model to describe the adhesion between spherical particles and thin films. This simulation expands previous models to characterize the adhesive interaction between asymmetrical particles, characteristic of a polishing slurry, and various films. Our simulation accounts for the contact area between particles and substrates, as well as the morphology of the surfaces. Previous models fail to accurately describe the contact of asymmetrical particles interacting with surfaces. By properly accounting for nonideal and geometry and morphology, the simulation predicts a more accurate adhesive force than predictions based upon an ideal van der Waals model. The simulation is compared to experimental data taken for both semi-ideal particle-substrate systems (polystyrene latex spheres in contact with silicon films) and asymmetrical systems (alumina particles in contact with various films). Copyright 2001 Academic Press.     

Spectroscopic and biological studies on newly synthesized nickel(II) complexes of semicarbazones and thiosemicarbazones

Nickel(II) complexes, having the general composition Ni(L)2X2, have been synthesized [where L: isopropyl methyl ketone semicarbazone (LLA), isopropyl methyl ketone thiosemicarbazone (LLB), 4-aminoacetophenone semicarbazone (LLC) and 4-aminoacetophenone thiosemicarbazone (LLD) and X=Cl-, 1/2SO(4)2-]. All the Ni(II) complexes reported here have been characterized by elemental analyses, magnetic moments, IR, electronic and mass spectral studies. All the complexes were found to have magnetic moments corresponding to two unpaired electrons. The possible geometries of the complexes were assigned on the basis of electronic and infrared spectral studies. Newly synthesized ligand and its nickel(II) complexes have been screened against different bacterial and fungal growth.     

Determination of 1,3-benzodioxanes in Piper mullesua by high-performance thin-layer chromatography

A new, simple, precise, and rapid high-performance thin-layer chromatographic method was developed for the determination of 6 benzodioxanes in Piper mullesua extract: 1',3'-benzodioxole-5'-(2,4,8-triene-isobutyl nonanoate), 1',3'-benzodioxole-5'-(2,4,12-triene-isobutyl tridecanoate), fargesin, sesamin, asarinin, 1',3'-benzodioxole-5'-(2,4,8-triene-methyl nonanoate). The ingredients were separated on a precoated Silica Gel 60 F254 plate with a solvent system of toluene-acetone (92 + 8). The 6 benzodioxanes were well separated and easily identified in this chromatographic system. The separated benzodioxanes were visualized by color development with a spray reagent consisting of 1 g vanillin dissolved in 100 mL H2SO4-ethanol (5 + 95, v/v). Quantitation was performed by scanning the spots and comparing the integrated areas of compounds in samples with those of standards. Recoveries from samples spiked with known amounts of the benzodioxanes were excellent. The results were comparable with those estimated by liquid chromatography.     

Synthesis and spectral characterization of some oxo-centered,trinuclear mixed-valence iron thiocarboxylates

Some mixed-valence Fe(II) Fe(III) complexes of thiocarboxylic acids and straight chain fatty acids with general formula [Fe(II)Fe(III)(2)O(SOCR)(6)(H(2)O)(3)] and [Fe(II)Fe(III)(2)O(SOCR)(3)(OOCR')(3)(CH(3)OH)(3)] (where, R=CH(3) or C(6)H(5) and R'=C(13)H(27), C(15)H(31) or C(17)H(35)) were synthesized and characterized by elemental analyses, spectral (infrared, electronic and M?ssbauer) studies, molar conductance and magnetic susceptibility measurements. The infrared spectra suggested bridging nature of carboxylate and thiocarboxylate anions along with upsilon(asym)(Fe(3)O) vibrations in the complexes. M?ssbauer studies revealed two resolved quadrupole doublets at 120-315 K confirming the presence of Fe(II) and Fe(III) moieties in the complexes. This was supported by the observed electronic spectral bands in the complexes at room temperature. The spectrum showed a band at around 13,800 cm(-1) which indicated an intervalence-transfer. Magnetic susceptibility measurements showed weak antiferromagnetic coupling related to mixed-valence pairs with S(2)=2, em leader S(1)=S(3)=5/2 spin exchange model. Conductance data indicated, the complexes were non-electrolytes in nitrobenzene. A structure has been established on the basis of these studies.