Synthesis and characterization of some oxovanadium(V) complexes with internally functionallized oximes. Crystal and molecular structure of heptacoordinated [VOCl{ON=C(CH3) (C4H3S-2)}2] · CH3OH

New heteroleptic oxovanadium(V) chloro oximato complexes of the type [VO{Cl}_3-n {ON=C(CH₃)(Ar)} _n ] (where Ar = C₄H₃O-2, C₄H₃S-2, C₅H₄N-2 and n = 1 or 2) have been synthesized in excellent yields by the reaction of VOCl₃ with the sodium salts of corresponding internally functionallized oximes in refluxing anhydrous benzene. The complexes are characterized by elemental analyses and spectroscopic techniques (FT-IR, ¹H-, ¹3C{¹H}- and ⁵¹V-NMR). FAB mass spectral analysis of one of the derivatives, [VOCl{ON=C(CH₃)C₄H₃S}₂] indicates the monomeric nature of the complex. ⁵¹V-NMR spectral studies of these complexes suggest tetra-coordination around the vanadium atom in solution. However, the single crystal X-ray diffraction study of a redistribution product [VOCl{ON=C(CH₃)(C₄H₃S-2)}₂] · CH₃OH obtained on recrystallization of [VOCl₂{ON=C(CH₃)(C₄H₃S-2)}] from a methanol-hexane mixture shows the vanadium(V) atom is hepta-coordinated with distorted pentagonal bipyramidal geometry. The oxo-atom occupies the axial position while the weakly coordinated CH₃OH group is trans to the V=O atom. The two oximato ligands in the approximate pentagonal plane are bonded to the central vanadium atom in dihapto (η²-N, O) manner with the formation of three-membered rings. The V–Cl bond occupies the fifth position in the approximate plane.     

Preparation and polymerization of a diisocyanate from the Diels-Alder adduct of levopimaric acid and acrylic acid

Starting from tetrahydroabietic acid the model compounds tetrahydroabietoyl chloride, 2-aminoethyltetrahydroabietate hydrochloride, and 2-isocyanatoethyltetrahydroabietate have been prepared. Carbamate and urea derivatives of the isocyanate have been prepared. A Diels-Alder adduct of levopimaric acid and acrylic acid has been prepared and converted to its diacid chloride. The β-aminoethyl ester hydrochloride has been synthesized and converted to a diisocyanate which has been polymerized with poly(tetramethylene glycol) and also with p-phenylenediamine. Dimerex resin, a technical polymerized rosin, has been similarly converted to a diisocyanate. This isocyanate has not proven to be useful as a polymer-forming intermediate.     

Determining sequences and post-translational modifications of novel conotoxins in Conus victoriae using cDNA sequencing and mass spectrometry

A combination of cDNA cloning and detailed mass spectrometric analyses was employed to identify novel conotoxins from Conus victoriae. Eleven conotoxin sequences were determined using molecular methods: one belonging to the A superfamily (Vc1.1), six belonging to the O superfamily (Vc6.1-Vc6.6) and four members of the T superfamily (Vc5.1-Vc5.4). In order to verify the sequences and identify the post-translational modifications (excluding the disulfide connectivity) of three Conus victoriae conotoxins, vc1a, vc5a and vc6a, deduced from sequences Vc1.1, Vc5.1, and Vc6.1, respectively, liquid chromatography/electrospray ionization ion trap mass spectrometry, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and nanospray ionization ion trap mass spectrometry with collisionally induced dissociation were performed on reduced and alkylated venom fractions. We report that vc1a, the native form of alpha-conotoxin Vc1.1 (an unmodified 16 amino acid residue peptide that has notable pain-relieving capabilities), includes a hydroxyproline and a gamma-carboxyglutamate residue. Conotoxin vc5a is a 10-residue peptide with two disulfide bonds and a hydroxyproline and vc6a is a 25 amino acid peptide with three disulfide bonds.     

pH-DEPENDENCE OF RHODAMINE B SEMIQUINONE DISMUTATION RATE IN AQUEOUS ALCOHOLIC SOLUTION

Abstract— A single transient species is observed in absorption following the flash irradiation of dilute deoxygenated aqueous alcoholic solutions of rhodamine B in hte pH range 5.5–7.0 The second-order decay constant for this semiquinone radical is an approximate linear function of the prevailing hydrogen ion concentration, the transient persisting for a period of from several seconds in neutral solution to several hours at pH = 12.
The slow rate of decay and its pH-dependence are explained in terms of an electron or H-atom transfer between the (unobserved) protonated and (observed) unprotonated semiquinone radical with simultaneous regeneration of hte D^+> and production of the leuco-dye DH:—
D·+ DH·⁺→ D⁺+ DH
Insofar as the reactant concentrations are controlled by the acid dissociation constant K^a of DH^.+ the data are consistent with a value of 5.5±1.0 for pK_a and a pH-independent rate constant K_o of 1.3±0.5×10⁶ 1. Mole^-1 sec^-1 at 20C.     

Gaussian processes on compact symmetric spaces

Paul Lévy studied Gaussian processes (a) with the parameter a running over Euclidean d-space R ^d and he also studied the case when a runs over the d-sphere S ^d . His results were extended by Gangolli in a number of directions, one being the extension to the cases where the parameter a lies in the other two-point homogeneous Riemannian manifolds. In the compact cases Gangolli showed there was a distinction between spheres and projective spaces, in that the process discovered by Lévy which he called Brownian motion parametrized by spheres does not exist for projective spaces. However many interesting Gaussian process exist with parameters running through projective spaces as we show.Sponsored in part by the United States Army under Contract No. DAAG29-75-C-0024 and the National Science Foundation Grant MPS75-06687AO2     

57Fe Mössbauer spectroscopy used to develop understanding of a diamond preservation index model

⁵⁷Fe Mössbauer spectroscopy has provided precise and accurate iron redox ratios Fe²⁺/Fe³⁺ in ilmenite, FeTiO₃, found within kimberlite samples from the Catoca and Camatxia kimberlite pipes from N.E. Angola. Ilmenite is one of the key indicator minerals for diamond survival and it is also one of the iron-bearing minerals with iron naturally occurring in one or both of the oxidation states Fe³⁺ and Fe²⁺. For this reason it is a good indicator for studying oxygen fugacities (fO₂) in mineral samples, which can then be related to iron redox ratios, Fe²⁺/Fe³⁺. In this paper we demonstrate that the oxidation state of the ilmenite mineral inclusion from sampled kimberlite rock is a key indicator of the oxidation state of the host kimberlite assemblage, which in turn determines the genesis of diamond, grade variation and diamond quality. Ilmenite samples from the two different diamondiferous kimberlite localities (Catoca and Camatxia) in the Lucapa graben, N.E. Angola, were studied using Mössbauer spectroscopy and X-Ray Diffractometry, in order to infer the oxidation state of their source regions in the mantle, oxygen partial pressure and diamond preservation conditions. The iron redox ratios, obtained using Mössbauer spectroscopy, show that the Catoca diamond kimberlite is more oxidised than kimberlite found in the Camatxia pipe, which is associated within the same geological tectonic structure. Here we demonstrate that⁵⁷Fe Mössbauer spectroscopy can assist geologists and mining engineers to effectively evaluate and determine whether kimberlite deposits are economically feasible for diamond mining.     

Improved performance in germanium detector gamma-spectrometers based on digital signal processing

In an HPGe spectroscopy system, Digital Signal Processing (DSP) replaces the shaping amplifier, correction circuits, and ADC with a single digital system that processes the sampled waveform from the preamplifier with a variety of mathematical algorithms. DSP techniques have been used in the field of HPGe detector gamma-ray spectrometry for some time for improved stability and performance over their analog counterparts. Recent developments in HPGe detector construction and new liquid nitrogen-free cooling methods have resulted in HPGe detectors which are better adapted to the needs of the application. Some of these improvements in utility have degraded the spectroscopy performance. With DSP, it is possible to reduce the changes, in real time, in several aspects of detector performance on a pulse-by-pulse basis, which is not possible in the old analog environment. In the past, in designing for the analog regime, flexibility was limited by issues of component size, number and cost. In the digital domain, the problem translates to the need for a DSP with enough speed and an efficient algorithm to achieve the desired transformation or correction to the digitally determined pulse shape or height, event-by-event. The use of DSP allows the peak processing to be tuned to the preamplifier peak shape from the detector rather than being set to an average value determined from several detectors of the type in question. The selection of the filter can be automatic or manual. The following corrections are now possible: ballistic deficit correction, peak resolution improvement by reducing the impact of microphonic noise, increase throughput by reducing pulse processing time, and loss-free (zero dead time) counting.     

First nuclear moment measurement with radioactive beams by the recoil-in-vacuum technique: the g factor of the 2+1 state in 132Te

Following Coulomb excitation of the radioactive ion beam (RIB) 132Te at HRIBF we report the first use of the recoil-in-vacuum (RIV) method to determine the g factor of the 2(+)(1) state: g(973.9 keV 2(+) 132Te) = (+)0.35(5). The advantages offered by the RIV method in the context of RIBs and modern detector arrays are discussed.