Ligand K-edge X-ray absorption spectroscopy of [Fe4S4]1+,2+,3+ clusters: changes in bonding and electronic relaxation upon redox

Sulfur K-edge X-ray absorption spectroscopy (XAS) is reported for [Fe(4)S(4)](1+,2+,3+) clusters. The results are quantitatively and qualitatively compared with DFT calculations. The change in covalency upon redox in both the [Fe(4)S(4)](1+/2+) (ferredoxin) and the [Fe(4)S(4)](2+/3+) (HiPIP) couple are much larger than that expected from just the change in number of 3d holes. Moreover, the change in the HiPIP couple is higher than that of the ferredoxin couple. These changes in electronic structure are analyzed using DFT calculations in terms of contributions from the nature of the redox active molecular orbital (RAMO) and electronic relaxation. The results indicate that the RAMO of HiPIP has 50% ligand character, and hence, the HiPIP redox couple involves limited electronic relaxation. Alternatively, the RAMO of the ferredoxin couple is metal-based, and the ferredoxin redox couple involves extensive electronic relaxation. The contributions of these RAMO differences to ET processes in the different proteins are discussed.     

Methane generated during photocatalytic redox reaction of alcohols on TiO2 suspension in aqueous solutions

Studies on the photo-catalytic redox reaction of C1–C3 alcohols such as methanol, ethanol and 2-propanol were carried out in aqueous solution containing TiO₂ photocatalyst (0.1% w/v) as suspension using 350 nm light. Other hydrocarbons such as ethane and ethene in the case of ethanol, and propene in the case of 2-propanol with low yields were produced along with the major photolytic products methane and carbon dioxide. The yields of methane and CO₂ were found to be dependent on the light exposure time and ambient conditions. Methane yields were higher in 2-propanol and ethanol systems than in methanol system, showing their better hole-scavenging properties. In the aerated condition, methane was produced during photolysis of all alcohols in the presence of TiO₂ and the yield was comparable to those observed in the corresponding CO₂-saturated systems. The overall results reveal that the surface adsorbed, as well as in-situ-generated CO₂ from photo-oxidation of alcohols are equally responsible for methane formation through photo-reduction in presence of TiO₂. In the O₂-saturated system, the methane yield was lower as compared to that in aerated system, in contrast to the CO₂ yield. In N₂O-and N₂-purged systems, the yield of methane was observed to be low, inferring that the methane generation has not taken place through photodecomposition/photodissociation of alcohols. Again, photolysis of alcohols without TiO₂ did not generate any methane.     

Dispersion-free solvent extraction of U(VI) in macro amount from nitric acid solutions using hollow fiber contactor

The applicability of dispersion-free solvent extraction (DFSX), through microporous hydrophobic membrane has been studied. The hollow fiber membrane contactor, with surface area of 381 cm² was employed to extract U(VI) in macro concentration (35 g dm⁻³) from aqueous acidic solutions. Prior to deployment of this technique for recovery of U(VI) from oxalate supernatant waste, chemical parameters such as extractant concentration, feed acidity, concentration of U(VI) in feed were studied. The study revealed that 30% tri-n-butyl phosphate (TBP) in n-dodecane as an extractant and feed in 3 M HNO₃ gave an optimum extraction of U(VI) and it was possible to strip back utilizing 0.05 M HNO₃. It was established to recover more than 90% of U(VI) from oxalate supernatant waste, which was often generated from nuclear chemical facilities.     

Quantification of aromaticity in oxocarbons: the problem of the fictitious "nonaromatic" reference system

Despite the extensive research reported in the literature, the concept of aromaticity has eluded rigorous quantification. The main reason for this undesirable reality is the fact that aromaticity is a differential property. While bond orders, atomic charges and electronegativity differences are properties of the molecule under analysis, the aromaticity concept often refers to the difference between some property of the molecule and that of an artificial "nonaromatic" reference system. A rigorous definition of such a reference system is non-existing and therefore constituting the main barrier to obtain a satisfactory quantification of the aromatic concept. Oxocarbon acids and their anions are examples where the criteria of aromaticity that use reference systems are unsuccessful, only NICS criterion gives satisfactory results. Wiberg bond indexes and 17O NMR chemical shifts are also useful to study such compounds.     

Fast antimicrobial screen test (FAST): improved screen test for detecting antimicrobial residues in meat tissue

The Fast Antimicrobial Screen Test (FAST) is a simple and quick screening test developed to detect antibiotic and sulfonamide residues in food animal carcasses in slaughter establishments. This microbial inhibition test detects antimicrobials that are allowed to be used in food animals. It has the ability to detect these antimicrobials at or above the allowable limit in carcass kidney fluids in 6 h. Laboratory evaluations show that the lower limit of detection (LLD) of FAST and the Calf Antibiotic and Sulfa Test (CAST) for antibiotics tested was the same, but the LLD for sulfonamides of FAST was lower than the LLD of CAST. Compared with the Swab Test on Premises (STOP) developed in 1977, the LLD's of FAST for both antibiotics and sulfonamides were significantly better. Under field conditions, the sensitivity of FAST and CAST to antibiotic and sulfonamide residues in animal kidneys was not significantly different, but the time required by FAST was significantly lower than CAST (6 versus 18 h). Compared with the STOP, the sensitivity and the range of detection by FAST for all antimicrobials were significantly higher and the testing time was lower (18 versus 6 h).     

Spontaneous formation of vesicles and chiral self-assemblies of sodium N-(4-dodecyloxybenzoyl)-L-valinate in water

A novel N-acylamino acid surfactant, sodium N-(4-dodecyloxybenzoyl)-L-valinate (SDLV), has been synthesized. The aggregation behavior of the surfactant in aqueous solution has been studied by surface tension, fluorescence probe, microscopy, and dynamic light scattering (DLS) techniques. The amphiphile has a very low critical aggregation concentration (cac). These studies have suggested formation of large bilayer structures in water. The mean apparent hydrodynamic radius, RH, of the self-assemblies in dilute aqueous solution obtained from DLS measurements confirmed formation of large aggregates. The FT-IR spectra of the amphiphile have indicated strong intermolecular amide hydrogen bonding in the self-assemblies in aqueous solution. The microenvironment of the fluorescence probes is highly nonpolar and viscous in nature. The circular dichroism (CD) spectra of SDLV were recorded in water and in a 1:1 water-methanol mixture. The CD spectra have indicated the presence of chiral aggregates in aqueous solution above the cac. The microstructure of the aggregates has been studied by use of optical and transmission electron microscopy. Both types of micrographs have shown the presence of a variety of morphologies including giant spherical vesicles, tubules, twisted ribbons, and helical strands in aqueous solutions.     

Quark masses in a BCS-like approach usingQ\bar Q potentials

Using a BCS like equation we have computed constituent quark masses as a function of a parameterC. This parameter is a measure of the effective strength of the interaction for off-the-mass-shell, localised \(q\bar q\) pairs and is given byC=R/E, whereE is the energy required to separate the pair to a distanceR. Several phenomenological flavour independent \(q\bar q\) potentials and correlation functions yield results similar in nature. Predictions for distribution functions of intrinsic sea quarks have been made.     

Oxidation of selected sugars with Mn(III)

Glucose, fructose, xylose, arabinose, and sucrose have been determined titrimetrically using manganese(III) sulfate as an oxidant. On reaction in the dark, glucose consumes 5, fructose 7, xylose and arabinose 6 each, and sucrose after hydrolysis 12 equivalents of Mn(III) per mole, respectively. Sucrose has also been estimated following other methods and the results have been compared. Two leaf sample extracts are analyzed for the determination of reducing sugar and total reducing matter and the results are compared with those obtained by the other method.     

Characterization of polymeric vesicles of poly(sodium 11-acrylamidoundecanoate) in water

A polysoap poly(sodium 11-acrylamidoundecanoate) was synthesized from sodium 11-acrylamidoundecanoate in water. The molecular weight of the polymer was determined by gel permeation chromatography and static light scattering techniques. Fluorescence probe studies in water have suggested the formation of hydrophobic domains within the same polymer chain. The microenvironment of the hydrophobic domains is highly ordered. The packing of the hydrocarbon chains in the hydrophobic domains formed by intra-chain association increases upon decrease of pH. The transmission electron micrograph revealed large vesicular aggregates in dilute aqueous solution. Temperature-dependent fluorescence anisotropy of the 1,6-diphenyl-1,3,5-hexatriene probe demonstrated stability of the vesicles.     

Viscosity of Potassium Trioxalato Complexes of Al(III), Fe(III), Co(III), and Cr(III) in Aqueous Solution Between 15° and 35°C

The viscosity of dilute aqueous solutions of K₃[AI(ox)₃]·3H₂O, K₃[Fe(ox)₃]·3H₂O, K₃[Co(ox)₃]·3H₂O, and K₃[Cr(ox)₃]·3H₂O complexes, as well as K₂(ox)·H₂O, were measured between 15 and 35°C. Those of CoCl₂, 6H₂O, FeCl₃, A1₂(SO₄)₃·18H₂O, and CrCl₃·6H₂O were measured at 25°C. These data were analyzed by the Jones–Dole equation. The ionic B coefficients of the above complex anions were discussed in terms of ion–solvent interactions and the overall change in B associated with complex formation.