Preparation of High Purity Aromatic Hydrocarbons. Part I. Preparation of High Purity Coal-Tar Anthracene

This paper reports a relatively simple and effective method of purification of anthracene produced by “Naftochem” Poland, and describes a procedure for the analysis of its contents by using chromatography methods. The method of purification is based on the following steps:

(1) Selective recrystallization of purified anthracene in dimethylsulfoxide (DMSO).

(2) Removal of traces of DMSO left over after recrystallization.

(3) Zone refining.

The effectiveness of recrystallization and the composition of the purified material were assessed by using thin-layer and gas chromatography, respectively.     

Photoinduced CC‐coupling Reactions of Rigid Diastereomeric Benzophenone‐Methionine Dyads

The reactions of ketone/methionine systems are widely used as efficient and selective sources of biorelevant radical species. In this study, we address intramolecular variants of this couple with respect to its photosynthetic utility and as a mechanistic model of underlying elementary reaction steps of biological importance, especially with respect to the study of photoinitiated electron transport in complex peptides. The outcomes of this study are two‐fold: (1) steady‐state irradiation of sterically constrained benzophenone/methionine dyads afforded stable photocyclization products with high yield and product selectivity. (2) Mechanistic insights into the triplet‐triggered product formation were obtained from an analysis of the flash photolysis results and the molecular structure of the stable product formed upon irradiation. Time‐resolved experiments identified (net) hydrogen‐atom transfer from the methionine as the mechanism of the triplet quenching and the resulting biradicals as the major precursor of the isolated stable product. Both the analyses of triplet quenching and stable‐product formation in the diastereomeric pairs point to effects of chiral center configuration, i.e., significant stereoselectivity is observed for all elementary steps. The underlying stereochemical restraints were quantitatively addressed by means of molecular dynamics simulations.     

The structural, magnetic, hydrogenation and electrode properties of REMg2Cu9?xNix alloys (RE=La, Pr,Tb)

The LaMg₂Cu₉, PrMg₂Cu₉, LaMg₂Cu₄Ni₅, PrMg₂Cu₄Ni₅ and TbMg₂Cu₆Ni₃ alloys were prepared for the investigations of crystal structure, magnetic and hydrogen storage properties. The magnetic properties of several REMg₂Cu_9−xNi_x compounds have been studied up to 9 T and from 2 to 300 K. Tb compounds show a ferrimagnetic (with Ni) or antiferromagnetic (without Ni) behaviour, which can be attributed to the Tb magnetic structure. At high temperature a paramagnetic Curie Weiss behaviour is observed and the effective moment corresponds to that of Tb. A magnetic contribution of Pr moment is observed in both Pr compounds, with larger magnetization for PrMg₂Cu₄Ni₅ and a transition at 3 K. The hydrogen absorption occurs at 95 bar for LaMg₂Cu₉ (3 H f.u.⁻¹) and above 2 bars for LaMg₂Cu₄Ni₅ (1.6 H f.u.⁻¹). The effect of Cu-Ni substitution on the electrochemical properties of LaMg₂M₉ ternary alloys was investigated leading to maximum discharge capacity of 250–310 mAh g⁻¹.      

Conductivity,morphology, interfacial chemistry,and stability of poly(3,4‐ethylene dioxythiophene)–poly(styrene sulfonate): A photoelectron spectroscopy study

X‐ray photoelectron spectroscopy (XPS) has been used to characterize poly(3,4‐ethylene dioxythiophene)–poly(styrene sulfonate) (PEDT/PSS), one of the most common electrically conducting organic polymers. A correlation has been established between the composition, morphology, and polymerization mechanism, on the one hand, and the electric conductivity of PEDT/PSS, on the other hand. XPS has been used to identify interfacial reactions occurring at the polymer‐on‐ITO and polymer‐on‐glass interfaces, as well as chemical changes within the polymer blend induced by electrical stress and exposure to ultraviolet light. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2561–2583, 2003     

On nonlinear Koopman''s construction

We show that there exists a possibility for a nonlinear variant of Koopman's construction. This gives a natural way for introducing nonlinear quantum maps. Applications to quantum chaos are indicated.     

Implicit Interval Methods for Solving the Initial Value Problem

Implicit interval methods of Runge–Kutta and Adams–Moulton type for solving the initial value problem are proposed. It can be proved that the exact solution of the problem belongs to interval-solutions obtained by the considered methods. Furthermore, it is possible to estimate the widths of interval-solutions.     

Highly stereo‐efficient synthesis and luminescence properties of novel trans‐regular vinylene– silylene–thiophene polymers

The novel trans‐stereo‐regular silylene–thiophene derivatives ( 4 , 5 ) with perfect consecutive silylene–arylene–silylene–vinylene linkage were synthesized via silylative coupling polycondensation of 2,5‐bis(vinyldimethylsilyl)thiophene ( 2 ) or 5,5′‐bis(vinyldimethylsilyl)‐2,2′‐bithiophene ( 3 ) catalyzed by ruthenium‐hydride complex [RuHCl(CO)(PCy₃)₂] ( 1 ). Their spectroscopic, absorption, and luminescence properties were characterized and compared with those of model compounds containing thiophene or bithiophene chromophores. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 127–137, 2008     

Sulfur radical cation-peptide bond complex in the one-electron oxidation of S-methylglutathione

Neighboring group participation was investigated in the *OH-induced oxidation of S-methylglutathione in aqueous solutions. Nanosecond pulse radiolysis was used to obtain the spectra of the reaction intermediates and their kinetics. Depending on the pH, and the concentration of S-methylglutathione, pulse irradiation leads to different transients. The transients observed were an intramolecularly bonded [>S thereforeNH2]+ intermediate, intermolecularly S thereforeS-bonded radical cation, alpha-(alkylthio)alkyl radicals, alpha-amino-alkyl-type radical, and an intramolecularly (S thereforeO)+-bonded intermediate. The latter radical is of particular note in that it supports recent observations of sulfur radical cations complexed with the oxygen atoms of peptide bonds and thus has biological and medical implications. This (S thereforeO)+-bonded intermediate had an absorption maximum at 390 nm, and we estimated its formation rate to be >or=6x10(7) s(-1). It is in equilibrium with the intermolecularly S thereforeS-bonded radical cation, and they decay together on the time scale of a few hundred microseconds. The S thereforeS-bonded radical cation is formed from the monomeric sulfur radical cation (>S*+) and an unoxidized S-methylglutathione molecule with the rate constant of 1.0x10(9) M(-1) s(-1). The short-lived [>S thereforeNH2]+ intermediate is a precursor of decarboxylation, absorbs at approximately 390 nm, and decays on the time scale of hundreds of nanoseconds. Additional insight into the details of the association of sulfur radical cations with the oxygen atoms of the peptide bonds was gained by comparing the behavior of the S-methylglutathione (S thereforeO+-bonded five-membered ring) with the peptide gamma-Glu-Met-Gly (S thereforeO+-bonded six-membered ring). Conclusions from experimental observations were supported by molecular modeling calculations.     

Factor analysis of transient spectra. Free radicals in cyclic dipeptides containing methionine

Factor analysis is introduced and applied to resolving puzzling behavior in the free-radical chemistry of the cyclic dipeptide cyclo-(D-Met-L-Met). Previously, spectral analysis of the transient absorption spectra, following the hydroxyl radical-induced oxidation of cyclo-(D-Met-L-Met), failed to match expectations seen when transient conductivity was used to monitor the same reaction sequence. In the current work, factor analysis is used to show that a radical cation is formed via the stabilization of the oxidized sulfur through the formation of two-centered three-electron bonds with the lone pairs on oxygen. This previously undetected radical resolves the discrepancy between transient absorption and transient conductivity observations.