Competitive Substitution and Electron Transfer in Reactions between Haloamminegold(III) and Halocyanoaurate(III) Complexes and Thiocyanate

Kinetics for reactions between thiocyanate and trans-Au(CN)(2)Cl(2)(-), trans-Au(CN)(2)Br(2)(-), and trans-Au(NH(3))(2)Cl(2)(+) in an acidic, 1.00 M perchlorate aqueous medium have been studied by use of conventional and diode-array UV/vis spectroscopy and high-pressure and sequential-mixing stopped-flow spectrophotometry. Initial, rapid formation of mixed halide-thiocyanate complexes of gold(III) is followed by slower reduction to Au(CN)(2)(-) and Au(NH(3))(2)(+), respectively. This is an intermolecular process, involving attack on the complex by outer-sphere thiocyanate. Second-order rate constants at 25.0 degrees C for reduction of trans-Au(CN)(2)XSCN(-) are (6.9 +/- 1.1) x 10(4) M(-)(1) s(-)(1) for X = Cl and (3.1 +/- 0.7) x 10(3) M(-)(1) s(-)(1) for X = Br. For reduction of trans-Au(CN)(2)(SCN)(2)(-) the second-order rate constant at 25.0 degrees C is (3.1 +/- 0.1) x 10(2) M(-)(1) s(-)(1) and the activation parameters are DeltaH() = (55 +/- 3) x 10(2) kJ mol(-)(1), DeltaS() = (-17.8 +/- 0.8) J K(-)(1) mol(-)(1), and DeltaV() = (-4.6 +/- 0.5) cm(3) mol(-)(1). The activation volume for substitution of one chloride on trans-Au(NH(3))(2)Cl(2)(+) is (-4.5 +/- 0.5) cm(3) mol(-)(1), and that for reduction of trans-Au(NH(3))(2)(SCN)(2)(+) (4.6 +/- 0.9) cm(3) mol(-)(1). The presence of pi-back-bonding cyanide ligands stabilizes the transition states for both substitution and reductive elimination reactions compared to ammine. In particular, complexes trans-Au(CN)(2)XSCN(-) with an unsymmetric electron distribution along the X-Au-SCN axis are reduced rapidly. The observed entropies and volumes of activation reflect large differences in the transition states for the reductive elimination and substitution processes, respectively, the former being more loosely bound, more sensitive to solvational changes, and probably not involving any large changes in the inner coordination sphere. A transition state with an S-S interaction between attacking and coordinated thiocyanate is suggested for the reduction. The stability constants for formation of the very short-lived complex trans-Au(CN)(2)(SCN)(2)(-) from trans-Au(CN)(2)X(SCN)(-) (X = Cl, Br) by replacement of halide by thiocyanate prior to reduction can be calculated from the redox kinetics data to be K(Cl,2) = (3.8 +/- 0.8) x 10(4) and K(Br,2) = (1.1 +/- 0.4) x 10(2).     

Supramolecular control of valence-tautomeric equilibrium on nanometer-scale gold clusters

This communication describes the preparation and characterization of a valence tautomer complex covalently attached to gold nanoparticles. Variable-temperature IR spectroscopy is used to determine the equilibrium thermodynamic parameters for the valence tautomerization. These results are compared with a nonsurface combined valence tautomer complex. The results show that surface confinement attenuates both DeltaH degrees and DeltaS degrees . We attribute these changes to a reduced accessible molecular surface area.     

Effect of preparative conditions on the surface characteristics of mixed zirconium and titanium oxides

The surface characteristics of mixed zirconium and titanium oxides prepared from different starting materials are investigated. One mode of preparation entailed the use of zirconium sulfate and titanium oxysulfate as starting materials and ammonium hydroxide as precipitating agent. The produced oxides were washed to different extents to obtain samples with different sulfate content. A second preparative mode used zirconium oxychloride and titanous chloride as starting materials also with ammonium hydroxide as precipitating agent. The oxidation of the titanous to the titanic form for these oxides was carried out by means of oxygen gas. Resulting samples were heat treated at 400 °C and 600 °C, and textural characteristics determined from the adsorption of N₂ at 77 K, complemented by infrared and thermal studies. The samples precipitated from the oxychloride and chloride salts of zirconium and titanium, as well as those precipitated from the sulfate and oxysulfate salts and washed free of the sulfate ions displayed quite similar textural characteristics. The unheated samples and those heat-treated at 400 °C were mesoporous, with some microporosity, and relatively large surface areas in the order of 200–300 m²/g. Heat treatment to 600 °C led to a relative decrease in surface area, in the order of 100 m²/g, and to the disappearance of microporosity. The mixed zirconium and titanium oxides with a sulfate content of ≈17% displayed significantly lower surface areas, smaller than 10 m²/g, with a prevalence of micro and mesoporosity. Infrared and thermal studies indicated the presence of differently bounded sulfato groups, which seem to have a blocking effect on the pores, resulting in the observed smaller surface areas.     

Risk assessment,development and validation of a GC-ECD-based method for the quantification of cypermethrin from green pea

The present work describes the persistence, dissipation behaviour, half-life, risk assessment and novel gas chromatography method for the residue estimation of cypermethrin in green pea by spraying cypermethrin 10EC at 50 g a.i. ha⁻¹ at fruiting stage followed by another application at a 10 day interval. The sample extraction and cleanup was followed bya modified quick, easy, cheap, effective, rugged, and safe method, and the residues of cypermethrin were determined using a validated gas chromatography method. The initial deposits were found to be 1.21 mg kg⁻¹ following the application of insecticide at 50 g a.i. ha⁻¹. Cypermethrin residues declined to below the detection limit of 0.05 mg kg⁻¹ after 15 days at the recommended dosage. The half-life of cypermethrin was 2.66 days at 50 g a.i. ha⁻¹. For risk assessment studies, the waiting period of 15 days is recommended as safe for consumption for the insecticide. The GC-ECD method was validated according to the SANTE guidelines by various analytical parameters including linearity, accuracy, detection and quantification limits. The developed method is simple, selective and repeatable, and can be used for the standardization of pesticides on fruits and vegetables.     

Synthesis and structural characterisation of novel platinum-based drug candidates with extended functionality by incorporation of bis(diphenylphosphino)ferrocene units as metal chelators

Among the metal-based anticancer drugs, cisplatin (cis-diaminedichloroplatinum(II)) is the most widely used species in therapy. Despite its clinical success, cisplatin still suffers in generating resistance, as well as being highly toxic due to poor selectivity between healthy and sick cells. By molecular design it ought to be possible to generate new cis-platinum compounds with increased selectivity and improved cellular behaviour. In this paper, we report a synthetic pathway for construction of derivatives of 1,1′-bis(diphenylphosphino)-ferrocene, together with their corresponding cis-platinum compounds with the aim testing them for their interaction capacity with respect to various DNA models. We also report a synthetic route for a nucleoside-based cis-platinum compound containing a bidentate ferrocenylphosphine derivative connected through a succinamic-based linker to the 5-position of the heterocyclic moiety of uridine. Our preliminary kinetic investigation of 5-{N-[1-[1′,2-bis(diphenylphosphino)ferrocenyl]ethyl]-N′-[prop-2-yn-3-yl]succinamide} uridinedichloroplatinum(II) showed that this compound reacted faster with the phosphorothioate containing oligonucleotides d(T₆p(S)T₆), with an observed first-order rate constant k_obs=(1.4±0.1)×10⁻⁴ s⁻¹, compared with the G-N7 target in d(T₇GGT₇), for which the observed first-order rate constant is k_obs=(7.2±0.5)×10⁻⁴ s⁻¹.     

Bag like potential and quarkonium

We discuss the properties of charmonium in the frame work of a bag like potential and show that the upsilon and charmonium spectra can be fitted by a common potential.