Electronic structure contributions to electron-transfer reactivity in iron-sulfur active sites: 2. Reduction potentials

This study utilizes photoelectron spectroscopy (PES) combined with theoretical methods to determine the electronic structure contributions to the large reduction potential difference between [FeCl(4)](2)(-)(,1)(-) and [Fe(SR)(4)](2)(-)(,1)(-) (DeltaE(0) approximately 1 V). Valence PES data confirm that this effect results from electronic structure differences because there is a similarly large shift in the onset of valence ionization between the two reduced species (DeltaI(vert) = 1.4 +/- 0.3 eV). Specific electronic contributions to DeltaI(vert) have been investigated and defined. Ligand field effects, which are often considered to be of great importance, contribute very little to DeltaI(vert) (DeltaE(LF) < -0.05 eV). By contrast, electronic relaxation, a factor that is often neglected in the analysis of chemical reactivity, strongly affects the valence ionization energies of both species. The larger electronic relaxation in the tetrathiolate allows it to more effectively stabilize the oxidized state and lowers its I(vert) relative to that of the chloride (DeltaE(rlx) = 0.2 eV). The largest contribution to the difference in redox potentials is the much lower effective charge () of the tetrathiolate in the reduced state, which results in a large difference in the energy of the Fe 3d manifold between the two redox couples (DeltaE(Fe)( )(3d) = 1.2 eV). This difference derives from the significantly higher covalency of the iron-thiolate bond, which decreases and significantly lowers its redox potential.     

Syntheses and spectroscopic studies on zinc(II) and mercury(II) complexes of isatin-3-thiosemicarbazone

Zinc(II) and mercury(II) complexes were prepared by reacting isatin-3-thiosemicarbazone (ISTSCH) with zinc(II) acetate or mercury(II) bromide. The complexes were characterized by IR, Raman, diffuse reflectance, ¹H and ¹³C NMR spectra and elemental analysis. Tetrahedral structures for Zn(ISTSC)₂ and Hg(ISTSCH)Br₂ are suggested.     

The Effects of UVA-I (340-400 nm), UVA-II (320-340 nm) and UVA-I+II on the Photoisomerization of Urocanic Acid in vivo

Abstract— Ultraviolet B radiation (280-320 nm) can systemically suppress contact hypersensitivity (CHS), delayed type hypersensitivity (DTH) and tumor rejection responses in mice. Several models have been postulated for the initiation of this UVB-induced immune suppression and, although the complete mechanism is unclear, our early studies suggested that initiation is via the activation of a photoreceptor in the skin, identified as urocanic acid (UCA). Recent preliminary data from our laboratory and others indicated that UVA (320-400 nm)-emitting broadband sunlamps can also isomerize UCA but may not lead to immune suppression, in contrast to UVB-emitting sunlamps, which cause both effects. Although the reason for this inconsistency is unknown, the emission spectra of UVA lamps contain differing amounts of UVB, UVA-I (340-400 nm) and UVA-II (320-340 nm) from those of UVB sources. In this study we determined a detailed dose-response for the isomerization of UCA in mouse skin using the UVA-I, UVA-II and UVA-I+II wavelength ranges. The dose-response curves obtained were put on an equal energy basis by quantum correction and the possibility of wavelength interaction for this effect investigated. A simple additive wavelength interaction between UVA-I, UVA-II, and UVA-I+II was observed for trans-UCA photoisomerization. This result indicates that the failure of UVA-I, UVA-II or UVA-I+II radiation to induce immune suppression of the CHS response in an animal model is not due to complex wavelength interactions and/or the presence of an in vivo endogenous photosensitizer of UCA isomerization. Other factors, such as downstream blocking by UVA of the cis -UCA generated signal, may be involved.     

Depression in the cloud point of Tween in the presence of glycol additives and triblock polymers

Cloud point (C_P) measurements of Tween 20 and Tween 80 were carried out in the presence of various glycol oligomers and triblock polymers (TBP). The cloud points of both Tween 20 and 80 decrease in the presence of both types of additives. Among the glycol oligomeric additives, ethylene glycol monobutyl ether was found to reduce the C_P maximum. An increase in the repeating units of polymeric glycol additives leads to a decrease in C_P. Reduction in the C_P in the presence of TBP depends upon the increase in hydrophobic/hydrophilic ratio among the polypropylene to polyethylene units.     

Trace elemental analysis of automotive paints by laser ablation–inductively coupled plasma–mass spectrometry (LA–ICP–MS)

Paints and coatings are frequently encountered as types of materials that are submitted to forensic science laboratories as a result of trace evidence transfers. The aim of this study was to develop a method to complement the commonly used techniques in a forensic laboratory in order to better characterize these samples for forensic purposes. A laser ablation method has been used to simultaneously sample several layers directly prior to introduction into an inductively coupled plasma-mass spectrometer for the detection and quantification of the trace metals present in the layer(s). Time-resolved analysis plots displaying the elemental response and quantification of selected metals are compared to associate/discriminate paint samples. Matrix-matched standards were successfully incorporated into the analysis scheme for quantification of lead in the solid paint samples. Preparation of new matrix-matched standards for quantification of additional elements developed for this study are also presented. A sample set of eighteen (18) survey automotive paint samples have been analyzed with the developed method in order to determine the utility of LA-ICP-MS for trace element analysis of paints.     

Validated HPLC–MS–MS method for determination of azithromycin in human plasma

A validated, highly sensitive, and selective HPLC method with MS–MS detection has been developed for quantitative determination of azithromycin (AZI) in human Na₂EDTA plasma. Roxithromycin (ROX) was used as internal standard. Human plasma containing AZI and internal standard was ultrafiltered through Centrifree Micropartition devices and the concentration of AZI was determined by isocratic HPLC–MS–MS. Multiple reaction monitoring mode (MRM) was used for MS–MS detection. The calibration plot was linear in the concentration range 2.55–551.43 ng mL⁻¹. Inter-day and Intra-day precision and accuracy of the proposed method were characterized by R.S.D and percentage deviation, respectively; both were less than 8%. Limit of quantification was 2.55 ng mL⁻¹. The proposed method was used to determine the pharmacokinetic profile of AZI (250-mg tablets).     

Pharmacokinetic detection of penicillin excreted in urine using a totally internally reflected resonance light scattering technique with cetyltrimethylammonium bromide

A quantitative analysis method for penicillins including ampicillin (AmP), benzyl penicillin (BP), oxacillin (OA) and amoxycillin (AmO) is proposed that makes use of the totally internally reflected resonance light scattering (TIR-RLS) signal from the penicillin at the H₂O/CCl₄ interface in the presence of cetyltrimethylammonium bromide (CTMAB), and enables the pharmacokinetics of penicillin taken orally and excreted through urine to be monitored. Penicillin is coadsorbed with CTMAB at the H₂O/CCl₄ interface in neutral solution, resulting in the formation of ion associates that display greatly enhanced TIR-RLS signals (maximum at 368–372 nm). This enhanced TIR-RLS intensity was found to be proportional to the penicillin concentration over the range 0.2×10^–6 to 2.2×10^–6 mol L^–1, with limits of determination (3) of 5.0×10^–8 to 7.0×10^–8 mol L^–1. Pharmacokinetics studies performed using the present method show that the excretion of orally-taken ampicillin through urine has a half-time of 1.05 h and an excremental quantum over 8 h of 49.3%, respectively.     

Orthogonally Protected, Carboxy-Activated L-Homoisoserine, 2-Methyl-L-homoisoserine, and Homoisocysteine Derivatives. New Building Blocks for Peptide and Depsipeptide Modification

Starting from L-malic, L-citramalic, and rac. thiomalic acids routes to L-homoisoserine, 2-methyl-L-homoisoserine and rac. homoisocysteine have been developed. The new orthogonally protected and carboxy-activated building blocks are GABA as well as -hydroxy and -mercapto acid derivatives, suitable for the construction of peptide and depsipeptide surrogates.     

Determination of total chlorine in waste oil

Summary A simple method has been developed to determine the concentration of organic chlorine in waste oil. The determination is based on the conversion of organic chlorine to inorganic chloride by reaction with sodium biphenyl followed by extraction with nitric acid and a mixture of nitric acid and water. The concentration of chloride is determined by direct potentiometry with an ion-selective electrode. The limit of determination amounts to 3·10^–5 mol·l^–1 chloride ions with a standard deviation of 3.5%. Different samples of waste oil have been analyzed and the results have been compared to those obtained by combustion in a H₂/O₂ flame followed by potentiometric titration with silver nitrate.     

The thermal degradation of poly(diethyl fumarate)

The kinetics and mechanism of the thermal degradation of poly(diethyl fumarate) (PDEF) were studied by thermogravimetry, as well as by analysis of the thermolysis volatiles and polymer residue. The characteristic mass loss temperatures were determined, as were the overall thermal degradation activation energies of three PDEF samples of varying molar mass. Ethylene and ethanol were present in the thermolysis volatiles at degradation temperatures below 300 °C, while diethyl fumarate was also evidenced at higher degradation temperatures. The amount of monomer increased with increasing degradation temperature. The dependence of the molar mass of the residual polymer on the degradation time and temperature was established and the number of main-chain scissions per monomer unit, s/P₀, calculated. A thermal degradation mechanism including de-esterification and random main-chain scission is proposed. The thermal degradation of PDEF was compared to the thermolysis of poly(ethyl methacrylate) (PEMA), poly(diethyl itaconate) (PDEI) and poly(ethyl acrylate) (PEA).