Application of the ab initio Hartree-Fock-Slater method to the calculation of molecular conformations: Ozone and thiozone

The total statistical energy as provided by the ab initio Hartree-Fock-Slater method is tested as a measure of molecular conformation for ozone and thiozone. Comparison is made with single determinant Hartree-Fock calculations for the same molecules.     

Bilirubin as an antioxidant: kinetic studies of the reaction of bilirubin with peroxyl radicals in solution, micelles, and lipid bilayers

Bilirubin (BR) showed very weak antioxidant activity in a nonpolar medium of styrene or cumene in chlorobenzene. In contrast, BR exhibited strong antioxidant activity in polar media such as aqueous lipid bilayers or SDS micelles/methyl linoleate (pH 7.4), where the rate with peroxyl radicals, k(inh) = 5.0 x 10(4) M(-)(1) s(-)(1), was comparable to that with vitamin E analogues, Trolox, or PMHC. An electron-transfer mechanism accounts for the effect of the medium on the antioxidant properties of BR.     

A Versatile Precursor System for Supercritical Fluid Electrodeposition of Main‐Group Materials

For the first time, a versatile electrolyte bath is described that can be used to electrodeposit a wide range of p‐block elements from supercritical difluoromethane (scCH₂F₂). The bath comprises the tetrabutylammonium chlorometallate complex of the element in an electrolyte of 50×10^?3 mol dm^?3 tetrabutylammonium chloride at 17.2 MPa and 358 K. Through the use of anionic ([GaCl₄]^?, [InCl₄]^?, [GeCl₃]^?, [SnCl₃]^?, [SbCl₄]^?, and [BiCl₄]^?) and dianionic ([SeCl₆]^2? and [TeCl₆]^2?) chlorometallate salts, the deposition of elemental Ga, In, Ge, Sn, Sb, Bi, Se, and Te is demonstrated. In all cases, with the exception of gallium, which is a liquid under the deposition conditions, the resulting deposits are characterised by SEM, energy‐dispersive X‐ray analysis, XRD and Raman spectroscopy. An advantage of this electrolyte system is that the reagents are all crystalline solids, reasonably easy to handle and not highly water or oxygen sensitive. The results presented herein significantly broaden the range of materials accessible by electrodeposition from supercritical fluid and open up the future possibility of utilising the full scope of these unique fluids to electrodeposit functional binary or ternary alloys and compounds of these elements.     

Investigation into the voltammetric behaviour and detection of selenium(IV) at metal electrodes in diverse electrolyte media

The voltammetric behaviour of selenium(IV) was studied at platinum and gold electrodes in sulphuric acid, perchloric acid and potassium chloride media as a basis for its voltammetric detection. The best voltammetric behaviour was recorded at gold electrodes with perchloric acid as the supporting electrolyte. The concomitant presence of metals, such as copper or lead, and of model biomolecules, such as bovine serum albumin, in the solution resulted in a deterioration of the electrochemical response for selenium(IV). Quantitative detection of selenium(IV) by square wave anodic stripping voltammetry at both a millimetre-sized gold disc electrode and a microband electrode array revealed linear responses to selenium concentration in the ranges 5–15 μM and 0.1–10 μM, respectively, with 60 s preconcentration. The sensitivities were 6.4 μA μM⁻¹ cm⁻² and 100 μA μM⁻¹ cm⁻² at the disc and the microband array, respectively. The detection limit at the microband electrode array was 25 nM, illustrating the potentiality of such microelectrodes for the development of mercury-free analytical methods for the trace detection of selenium(IV).     

Amphiphilic calixarenes: Probing monolayer stability by selective modification of the hydrophobic-hydrophilic balance

Abstract

The synthesis of calix[4]arenes permuting 1 or 4 C12 acyl chains at the upper rim and 1 or 4 methylene ethyl ester groups at the lower rim is described. The Langmuir compression isotherms of the compounds show that in the case of 1 acyl + 1 ester, there is probably orientation parallel to the air-water interface. For the other systems, orientation is orthogonal to the interface, and for the 4 +4 compound a pseudo collapse with reorientation of the hydrophilic ester groups is observed.     

The effect of inhomogeneities on evaluation of a fractal dimension for objects on a lattice

A comparison of the covering properties of windowsm, m + 1, where the window sidel _m isl _m = 2 ^m , yields an expression for the fractal dimensionD _m which displays directly effects due to periodicity and inhomogeneities. The structure of teD _m versusm curve gives insight into the nature of the representation of the fractal. In some cases bounds forD may be obtained and, if appropriate, the effect of the inhomogeneities due to boundaries, initial conditions, the pixel limit or periodicity can be removed.     

Coordination networks derived from germanium(ii) thioether macrocyclic complexes-the first authenticated chalcogenoether complexes of Ge(ii)

Exocyclic coordination of macrocyclic thioethers to germanium(ii) halides leads to infinite chains (with weak GeX bridges between the chains) or sheet structures containing distorted octahedral Ge(ii) with [S(2)X(2) + X(2)] coordination and bridging thiacrowns.     

Probing the effects of ligand structure on activity and selectivity of Cr(III) complexes for ethylene oligomerisation and polymerisation

A series of distorted octahedral Cr(III) complexes containing tridentate S-, S/O- or N-donor ligands comprised of three distinct architectures: facultative {S(CH(2)CH(2)SC(10)H(21))(2) (L(1)) and O(CH(2)CH(2)SC(10)H(21))(2) (L(2))}, tripodal {MeC(CH(2)S(n)C(4)H(9))(3) (L(3)), MeC(CH(2)SC(10)H(21))(3) (L(4))} and macrocyclic {(C(10)H(21))[9]aneN(3) (L(5)), (C(10)H(21))(3)[9]aneN(3) (L(6)), with [9]aneN(3)=1,4,7-triazacyclononane} are reported and characterised spectroscopically. Activation of [CrCl(3)(L)] with MMAO produces very active ethylene trimerisation, oligomerisation and polymerisation catalysts, with significant dependence of the product distribution upon the ligand type present. The properties of the parent [CrCl(3)(L)] complexes are probed by cyclic voltammetry, UV-visible, EPR, EXAFS and XANES measurements, and the effects upon activation with Me(3)Al investigated similarly. Treatment with excess Me(3)Al leads to substitution of Cl ligands by Me groups, generation of an EPR silent Cr species (consistent with a change in the oxidation state of the Cr to either Cr(II) or Cr(IV)) and substantial dissociation of the neutral S and S/O-donor ligands.     

The first examples of germanium tetrafluoride and tin tetrafluoride complexes with soft thioether coordination--synthesis, properties and crystal structures

The first thioether complexes of the hard Lewis acidic GeF(4) and SnF(4) have been prepared by reaction of [GeF(4)(MeCN)(2)] or [SnF(4)(MeCN)(2)] respectively with the thioether ligand in rigorously anhydrous CH(2)Cl(2) solution. The isolated compounds were characterised spectroscopically (IR, (1)H and (19)F{(1)H} NMR) and by microanalyses. Crystal structures of four representative examples, [GeF(4){MeS(CH(2))(2)SMe}], [GeF(4){EtS(CH(2))(2)SEt}], [SnF(4){EtS(CH(2))(2)SEt}] and [SnF(4){(i)PrS(CH(2))(2)S(i)Pr}], reveal distorted octahedral adducts with chelating thioethers, and weak, secondary Ge-S and Sn-S bonds. These compounds are the first reported examples of thioether complexes with any main group metal/metalloid fluoride acceptor.