Computer simulations of the solvation dynamics of Coumarin 153 in dimethylsulfoxide

We report molecular dynamics (MD) simulations of the solvation dynamics of Coumarin 153 in liquid dimethylsulfoxide using two distinct sets of partial charges for the coumarin probe. The excited state dipole moment of the coumarin and the dynamic Stokes shift in solution depend significantly on the type of charge distributions used. Nevertheless, the overall characteristics of the solvation responses obtained from both sets of charges are very similar and show good agreement with time-dependent Stokes shift experiments. Microscopic details of the solvent reorganization around the probe are discussed in light of the charge transfer upon photoexcitation.     

Photooxidized products of recombinant alpha A-crystallin and W9F mutant

Human lenses contain many photosensitizers that absorb light at wavelengths above 300 nm, most notably UVA light (320-400 nm). Kynurenine (Kyn) and 3-hydroxykynurenine (HK), two of the best-known photosensitizers in the human lens, may play a significant role in photooxidation-related changes in lens proteins, such as conformational change and aggregation. In vitro irradiation experiments with proteins indicate that the Trp residue (with maximal absorption at 295 nm) is more susceptible to photooxidation by UVB light (280-320 nm) than by UVA light, but most UVB light below 300 nm is screened by the cornea and little reaches the lens, especially the nuclear region where nuclear color develops. Therefore, if photooxidation is an important contributor to nuclear color or nuclear cataract, it must arise from a photosensitized reaction. In the present study, we use recombinant alpha A- and its Trp-deficient mutant W9F as models to study the effects of UVA irradiation in the presence of HK or Kyn and of UVB (300 nm) irradiation on alpha-crystallins. alpha A-crystallin showed a large decrease in Trp fluorescence and a large increase in non-Trp (blue) fluorescence after the HK-sensitized or 300 nm photooxidation. For the W9F mutant, a smaller decrease in protein fluorescence (lambda ex at 280 nm) and a smaller increase in blue fluorescence than for the wild-type alpha A-crystallin were observed. A decrease in the near-UV CD was also observed for both photooxidized alpha A and the W9F mutant. The effect of Kyn sensitization is smaller than that of HK sensitization. A study of chaperone-like activity indicated that only 300 nm photooxidized alpha A and the W9F mutant increased the ability to protect insulin from dithiothreitol-induced aggregation. Thus, sensitized photooxidation can occur in amino acids other than Trp by UVA in the presence of HK or Kyn with effects similar to, albeit smaller than, those of direct UVB (300 nm) photooxidation.     

Synergic effect of triphenylphosphine oxide (TPPO) on the extraction of Hg(II), Se(IV), Co(II) and Mn(II) with fluorinated pyrazolone (HPMTFP)

Extraction of Hg(II), Se(IV), Mn(II) and Co(II) has been carried out with 1-phenyl-3-methyl-4-trifluoroacetyl-2-pyrazolin-5-one (HPMTFP) and triphenylphosphine oxide (TPPO) into chloroform from pH 1–10. Quantitative extraction of Hg(II), Mn(II) and Co(II) at pH 4 with equimolar 0.05M (PMTFP+TPPO) in chloroform was observed. Se(IV) remains unextracted at this pH range. The stoichiometric composition of the extracted complexes M(PMTFP)₂·nH₂O (M=Mn, Hg), M(PMTFP)₂·2TPPO (M=Mn and Co) and Co(PMTFP)₂·TPPO·H₂O at less than 0.1M TPPO has been established. The formation constantsK _m,0 andK _m,n and stability constants _m,n have been computed. The analytical method developed was applied to the IAEA standard reference material (SRM) potato fluor V-4 for the determination of these elements using NAA technique.     

Preparation,properties and x-ray crystal structure of a complex of bis(triphenylphosphoranylidene)ammonium iodide with 7,7,8,8-tetracyano-P-quinodimethane: (PPN)2(TCNQ)3(CH3CN)2

Bis(triphenylphosphoranylidene)ammonium iodide (PPN⁺I^?) forms a 2:3 complex with TCNQ [(PPN)₂(TCNQ)₃(CH₃CN)₂] that provides an example of a TCNQ complex containing acetonitrile in the crystal lattice; the material is a semi-conductor with trimerised TCNQ stacks.     

Hyperfine structure studies of Tantalum

A narrow bandwidth ring dye laser pumped by an argon ion laser has been used to investigate the hyperfine structure of the even and odd parity levels of tantalum by optogalvanic spectroscopy in the wavelength range 5640 to 6050 Å. Seventeen transitions have been observed and eight of these have not been reported in the literature so far. These transitions involve 27 levels with 15 odd and 12 even parity configurations. The magnetic dipole hyperfine interaction constants A and the electric quadrupole interaction constants B for these levels have been computed and compared with the data available in literature. The results for the levels at 34799.71 cm^?1, 26960.46 cm^?1 and 19657.78 cm^?1 are reported for the first time.     

The decomposition of iron(III) sulfate in air

The decomposition of initially hydrated powders of iron(III) sulfate was carried out in air over the temperature range 823–923 K. The decomposition process, which gave Fe₂O₃ as a solid product, was seen to have zero-order kinetics and an activation energy of 219 kJ·mol^–1. The nature of the product and the kinetics of decomposition were the same for samples decomposed in air and in argon. Sulfate samples with additives of FeS and Fe₂O₃ were also decomposed under similar conditions and the results confirmed the zero-order kinetics (for the case of the Fe₂O₃ additives) and the lack of effect of FeS on the decomposition of iron(III) sulfate.

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Zusammenfassung Anfänglich hydratiertes Eisen(III)-sulfatpulver wurde in Luft im Temperaturbereich 823–923 K zersetzt. Für die Reaktionsordnung des Zersetzungsprozesses, der als Endprodukt festes Fe₂O₃ lieferte, wurde Null und für die Aktivierungsenergie 219 kJ·mol^–1 ermittelt. Die Art des Produktes und der Kinetik der Zersetzung war in Luft und Argon gleich. Unter den gleichen Bedingungen wurden auch Sulfatproben mit Zusätzen von FeS und Fe₂O₃ zersetzt. Die Ergebnisse bekräftigen sowohl die nullte Reaktionsordnung (im Falle von Fe₂O₃ Zusätzen) als auch einen fehlenden Einfluß von FeS auf die Zersetzung von Eisen(III)-sulfat.

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823–923 . , , , 219 · ^–1. . FeS Fe₂O₃ . ( Fe₂O₃) - .

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This work was supported by a grant from the U.S. Department of Energy, Office of Basic Energy Sciences. The authors gratefully acknowledge this support.     

STUDY ON THE PROPERTIES OF BLEND OF NATURAL RUBBER LATEX/METHYL METHACRYLATE GRAFTED RUBBER LATEX BY GAMMA RADIATION

Natural rubber latex(NRL)and methyl methacrylate(MMA)grafted rubber latex were blended in different ratios and irradiated at various absorbed doses by gamma rays from Co-60 source at room temperature.The tensile properties, swelling ratio and permanent set were measured.The maximum tensile strength and modulus at 500% elongation were obtained at an absorbed dose of 8 kGy.Modulus increases from 6.99 MPa to 9.87 MPa for an increase in proportion of MMA grafted rubber from 40% to 60% in the blend at similar absorbed dose.Elongation at break and swelling ratio decrease with increasing absorbed dose as well as the MMA grafted rubber content in the blends.The decreasing trend of permanent set is high up to 5 kGy absorbed dose,and beyond that dose,it becomes almost flat.     

Factors affecting propagating fronts of addition polymerization: Velocity,front curvature,temperatue profile,conversion, and molecular weight distribution

Several properties of propagating fronts of addition polymerization were studied. A power function could be fit to the velocity dependence on initiator concentration, but not with the exponents predicted by current models or in agreement with other published work. Bubbles from the volatile by-products of initiator decomposition were found to affect the front velocity and curvature. The front velocity for triethylene glycol dimethacrylate polymerization was found to depend linearly on temperature over a moderate range. The conversion of methacrylic acid in fronts varied greatly with initiator type and concentration. Benzoyl peroxide produced much lower conversion than t-butyl peroxide, but fronts with tBPO propagated slower. A dual initiator system of BPO and tBPO produced rapidly propagating fronts with good conversion but the contribution of each initiator to the velocity was not additive. The possibility of chain branching was considered. The apparent molecular weight distributions were very broad, often trimodal, and found to depend on initiator type and concentration as well as the tube diameter. The temperature profiles were measured and found to be very sharp for BPO and broader for tBPO but both had front temperatures in excess of 200°C, indicating a high ceiling temperature. © 1995 John Wiley & Sons, Inc.     

Redox behavior of juglone in buffered aq.: Ethanol media

The present work reports the redox mechanism of 5-hydroxynaphthalene-1,4-dione (HND), commonly known as juglone, in buffered aqueous media having 50% of ethanol. HND followed different mechanistic routes depending upon the pH of the media and more than one pK_a were evaluated from the changes in the slope of the E_p vs. pH plot. The change of pH from acidic to neutral conditions was found to switch the mechanism from CEC to EE mechanism. Pulse techniques were utilized to determine the number of electrons involved in the oxidation and/or the reduction step and to ensure the nature of the redox process. Based upon the obtained results, an electrode reaction mechanism was proposed. Computational studies of HND supported the experimental results. UV-Visible spectroscopy was also employed for the detailed characterization of the compound in a wide range of pH and for the determination of its pK_a.