A PHYTOCHROME PHOTOTRANSFORMATION STUDY USING TWO-LASER/TWO-COLOR FLASH PHOTOLYSIS: ANALYSIS OF THE DECAY MECHANISM OF I700*

The mechanism of I₇₀₀ decay, representing an early event in the phytochrome P_r→ P_fr phototransformation, was reanalyzed in the microsecond range by conventional laser flash photolysis as well as by two-laser/two-color flash photolysis. Three kinetic models that might describe the I₇₀₀ decay mechanism following P_r excitation were considered: a parallel, a sequential, and an equilibrium model. These models were used to mathematically simulate both the one- and two-laser flash experiments in an effort to select the model best describing the I₇₀₀ decay. The sequential model could be excluded already on the basis of the one-laser flash photolysis results alone. Discussion of the two-laser/two-color flash rcsults in the context of the equilibrium and the parallel models is presented.     

THE PHOTOPHYSICS OF 5-METHOXYINDOLE. A NON-EXCIPLEX FORMING INDOLE: ADDITIONAL EVIDENCE FOR TWO CLASSES OF EXCIPLEXES*

Abstract— 5-Methoxyindole is a non-exciplex forming indole, and its excited state behavior is qualitatively different from that of indole and its methyl substituted derivatives. This fact supports the idea that there are two limiting classes of exciplexes, charge-transfer and dipole-dipole stabilized. The fluorescence quantum yield in water is 0.29 with a lifetime of 4.0 ns at 25d?C. The activation energy for fluorescence quenching in water is 15.9 pM 0.5 kJ/mol, which is smaller than for indole and the methyl substituted indoles which have been measured. In cyclohexane at 25d?C, the fluorescence quantum yield is 0.63 with a lifetime of 6.7 ns. The fluorescence is efficiently quenched by electron scavengers, as is the case for other indoles. Some electron ejection to solvent probably occurs in both solvents.     

Coupling versus surface-etching reactions of alkyl halides on GaAs(100): I. CF3CH2I reactions

We report the rich surface chemistry exhibited by the reactions of 1,1,1-trifluoroethyl iodide (CF3CH2I) adsorbed onto gallium-rich GaAs(100)-(4 x 1), studied by temperature-programmed desorption (TPD) and low-energy electron diffraction (LEED) studies and X-ray photoelectron spectroscopy (XPS). CF3CH2I adsorbs molecularly at 150 K but dissociates, below room temperature, to form a chemisorbed monolayer of CF3CH2 and I species. Recombinative desorption of molecular CF3CH2I competes with the further reactions of the CF3CH2 and I chemisorbed species. The CF3CH2 species can either undergo beta-fluoride elimination to yield gaseous CF2=CH2 or it can undergo self-coupling to form the corresponding higher alkane, CF3CH2CH2CF3. A second coupling product, CF3CH2CH=CF2, is also evolved, and it is postulated that migratory insertion of the liberated CF2=CH2 into the surface-carbon bond of the chemisorbed CF3CH2 is responsible for its formation. The iodines, formed by C-I scission in the chemisorbed CF3CH2I, and the fluorines, derived from beta-fluoride elimination in CF3CH2, react with the surface gallium dimers, and Ga-As back-bonds to generate five etch products (GaF, AsF, GaI, AsI, and As2) that desorb in the temperature range of 420 to >600 K. XPS data reveal that the surface stoichiometry remains constant throughout the entire annealing temperature range because of the desorption of both gallium- and arsenic-containing etch products, which occur sequentially. In this article, plausible mechanisms by which all products form and the binding sites of these reactions in the (4 x 1) reconstruction are discussed. Factors that control the rate constants of etch product versus hydrocarbon product formation and in particular how they impact on the respective desorption temperatures will be discussed.     

Review: Kedrinskii,I.A. and Yakovlev,V.G., Li-ionnye akkumulyatory (Li-Ion Batteries)

Russian Journal of Applied Chemistry -     

Review: Tarasov,A.V., Besser,A.D., Mal'tsev,V.I., and Sorokina,V.S., Metallurgicheskaya pererabotka vtorichnogo svintsovogo syr'ya (Metallurgical Processing of Secondary Lead)

Russian Journal of Applied Chemistry -     

Kinetic performance limits of constant pressure versus constant flow rate gradient elution separations. Part I: theory

We report on a general theoretical assessment of the potential kinetic advantages of running LC gradient elution separations in the constant-pressure mode instead of in the customarily used constant-flow rate mode. Analytical calculations as well as numerical simulation results are presented. It is shown that, provided both modes are run with the same volume-based gradient program, the constant-pressure mode can potentially offer an identical separation selectivity (except from some small differences induced by the difference in pressure and viscous heating trajectory), but in a significantly shorter time. For a gradient running between 5 and 95% of organic modifier, the decrease in analysis time can be expected to be of the order of some 20% for both water–methanol and water–acetonitrile gradients, and only weakly depending on the value of V_G/V₀ (or equivalently t_G/t₀). Obviously, the gain will be smaller when the start and end composition lie closer to the viscosity maximum of the considered water-organic modifier system. The assumptions underlying the obtained results (no effects of pressure and temperature on the viscosity or retention coefficient) are critically reviewed, and can be inferred to only have a small effect on the general conclusions. It is also shown that, under the adopted assumptions, the kinetic plot theory also holds for operations where the flow rate varies with the time, as is the case for constant-pressure operation. Comparing both operation modes in a kinetic plot representing the maximal peak capacity versus time, it is theoretically predicted here that both modes can be expected to perform equally well in the fully C-term dominated regime (where H varies linearly with the flow rate), while the constant pressure mode is advantageous for all lower flow rates. Near the optimal flow rate, and for linear gradients running from 5 to 95% organic modifier, time gains of the order of some 20% can be expected (or 25–30% when accounting for the fact that the constant pressure mode can be run without having to leave a pressure safety margin of 5–10% as is needed in the constant flow rate mode).     

Israfil I. Guseinov: A pioneer of the quantum theory of atomic,molecular, and nuclear systems*

This article, written on behalf of Guseinov's friends and colleagues in honor of his 80th birthday, presents a brief biography and an overview of the major themes of his scientific researches. This is an opportunity to summarize Guseinov's main contributions to the quantum theory of atoms, molecules, and nuclei. Some aspects of Guseinov's career and research are highlighted here. © 2013 Wiley Periodicals, Inc.     

Book Review: Bulanova,M.V., Buyanov,Yu.I., and Sidorko,V.R., Vzaimodeistvie redkozemel'nykh metallov so svintsom (Interaction of Rare-Earth Metals with Lead)

Russian Journal of Applied Chemistry -     

Expert system for pharmaceutical analysis. I. Selection of the detection system in high-performance liquid chromatographic analysis: UV versus amperometric detection

The usefulness of amperometric detection in pharmaceutical analyses was investigated for different groups of drugs. The UV response at 254 nm and that at the absorption maximum of the solute were compared with the electrochemical signal obtained. The minimum detectable concentration (nanograms on-column) of each substance is reported for the three different detection systems. This comparison was performed for 72 drugs (local anaesthetics, antipyretics, tricyclic antidepressants, sulphonamides, sex hormones, beta-adrenoceptor blocking agents, phenothiazines, alkaloids, diuretics and penicillins). The median limit of detection of the amperometric detector (see definition in the text) is 1.0 ng on-column and the median gain in sensitivity, compared with UV detection is 22.5.     

Ab Initio Calculations of Hydroxoplatinum Compounds: I. Hexahydroxoplatinum(IV), (V), and (VI) Complexes

The structural and spectral data on Pt(OH) ₆ ⁿ clusters (n = ?2, ?1, 0) obtained by ab initio methods have been considered. The data for n = ?2 are in good agreement with the published data on hexahydroxoplatinates(IV).     

Bioactive saponins and glycosides. XVI. Nortriterpene oligoglycosides with gastroprotective activity from the fresh leaves of Euptelea polyandra Sieb. et Zucc. (1): structures of Eupteleasaponins I, II, III, IV, V, and V acetate

The saponin fraction from the fresh leaves of Euiptelea polyandra Sieb. et Zucc. was found to exhibit potent gastroprotective activity. Fourteen new nortriterpene saponins called eupteleasaponins were isolated from the saponin fraction with gastroprotective activity. The structures of eupteleasaponins I, I1, III, IV, V, and V acetate were determined on the basis of chemical and physicochemical evidence as 3-O-alpha-L-rhamnopyranosyl(1-->2)-beta-D-glucopyranosyl(1 -->3)-beta-D-xylopyranosylakebonoic acid 28-O-beta-D-glucopyranosyl ester, 3-O-alpha-L-rhamnopyranosyl(1-->2)-[alpha-L-rhamnopyranosyl(1 -->4)-beta-D-glucopyranosyl(1-->3)-beta-D-xylopyranosylakebonoic acid 28-O-beta-D- D-glucopyranosyl(1-->3)-beta-D-xylopyranosylakebonoic acid 28-O-beta-D-glucopyranosyl ester, 3-O-alpha-L-rhamnopyranosyl(1-->2)-alpha-L-rhamnopyranosyl(1 -->4)-beta-D-glucopyranosyl(1-->3)-beta-D-xylopyranosylakebonoic acid 28-O-beta-D-glucopyranosyl ester, 3-O-alpha-L-rhamnopyranosyl(1 -->2)-[alpha-L-arabinopyranosyl(1-->4)-alpha-L-rhamnopyranosyl(1-- >4)]-beta-D- glucopyranosyl(1-->3)-beta-D-xylopyranosylakebonoic acid 28-O-beta-D-glucopyranosyl ester, 3-O-alpha-L-rhamnopyranosvl(1-->2)-[alpha-L-arabinopyranosyl (1 -->4)-beta-L-rhamnopyranosyl(1 -->4)]-beta-D-glucopyranosyl(1 -->3)-beta-D-xylopyranosylakebonoic acid, 3-O-alpha-L-rhamnopyranosyl(1 -->2)-beta-D-glucopyranosvl(1-->3)-beta-D-xylopyranosyleupteleo genin, and 3-O-alpha-L-rhamnopyranosyl(1-->2)-6"-O-acetyl-gamma-D-glucopyranosyl(1 -->3)-beta-D-xylopyranosyleupteleogenin.