Energy levels of the weakly interacting radicals

Energy levels of the weakly interacting radicals are estimated on the basis of planar methyl radical interaction as a model. These levels depend on the given separation r between the centers of mass. The appropriate Schrödinger equation is solved by using the Brillouin-Wigner series method. Analytical forms for the integrals used to estimate matrix elements are derived. The principle of total momentum conservation is strictly obeyed. Some energy levels cannot be estimated as a result of divergence.     

Kopfgruppeneinfluß homologer 1,2-Dihexadecylglycerophospholipide auf die Phasenumwandlungen ihrer Phospholipid/Wasser-Mischungen im heterogenen Zweiphasengebiet

Zusammenfassung Mittels Differential-Scanning-Kalorimetrie wurde der Einfluß des chemischen Aufbaus der Kopfgruppe von 14 Derivaten der 1,2-Di-O-hexadecylglycero-3-phosphorsäure im wasserreichen heterogenen Zweiphasengebiet untersucht. Es wurden die Phasenumwandlungstemperaturen und -enthalpien bestimmt und verglichen. Zusammenhänge zwischen der Variation der Kopfgruppenstruktur und den Trends in den Umwandlungsparametern werden diskutiert.

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A series of hexadecylglycerophospholipids was studied by differential scanning calorimetry in the heterogeneous two-phase region (50 wt. % water). The phase transition temperatures and enthalpies of the hydrated phospholipids were determined and compared. Correlations between the chemical structure of the polar headgroups and the thermodynamical parameters of the phase transitions were discussed.

     

Studies on the Extension of Sequence‐independence and the Enhancement of DNA Triplex Formation

A more elaborate sequence‐independent triple‐helix formation viability study was carried out and extended from a recombination‐like triple‐helical DNA motif of a previous study (J. Mol. Recognition 14, 122–139 (2001)). The intended triple‐helix was formed by mixing one part of a DNA hairpin duplex and one part of a single (or third) strand identical to one of the duplex strands and complementary to the other strand. In contrast to the common purine and pyrimidine motifs in triple‐stranded DNA, the strands of the recombination‐like motif are not monotonously built from pyrimidine only, or purine only, in the sequence. The stability of the recombination‐like motif triplexes with varying sequences was monitored by UV thermal melting curves. The results showed that the order of the stability of the R‐form DNA base triads (J. Mol. Biol., 239, 181–200 (1994)) is G*(G ○ C) > C*(C ○ G) > A*(A ○ T) >T*(T ○ A) (the Watson‐Crick base pair is denoted in the parentheses) in 200 mM NaCl, at pH 7. In an attempt to increase the stability of the triplex in the recombination‐like motif, we replaced cytidine by 5‐methylcytidine (^mC) of the third strand. There is a general trend that ^mC modification stabilizes the complex (<2 °C per ^mC). The complex is furthermore stabilized by Mg²⁺ ion. The Tm increases from 7 to 2 °C from less stable to highly stable triplex by 20 mM Mg²⁺ ion in solution.     

HeI photoelectron spectroscopic (PES) studies of the electronic structure in ω-heterocycle α-cyano polyenic ethyl ester Compounds

Hel photoelectron spectra of ω-heterocycle α-cyano polyenic ethyl ester compounds (1–6) have been given in this paper. Assignment of the spectra is also done with the aid of HeI photoelectron spectroscopic (PES) results of smaller molecules which have similar atomic group to the molecules studied, and the aid of MNDO molecules orbital calculations. The lowest PES experimental ionization potentials (IPs in eV) of different molecules reduce gradually with the increasing number of ethylenic group. The -CO₂C₂H₅ group can be only considered as a substituent.     

Hydrogen atom yield in RF and microwave hydrogen discharges

The hydrogen atom yield in pure-H₂ RF and microwave-sustained discharges is investigated both theoretically and experimentally. A particle balance model is developed that provides the concentrations of the H, H₂, H⁺, H ₂ ⁺ , and H ₃ ⁺ species. It is also shown that an approximate solution of this model is adequate for calculating the concentration of H atoms (required, for instance, in diamond film deposition) in the 0.1–10 torr range. Next, the validity of the actinometry technique applied to the determination of the H-atom density in pure-H₂ discharges is examined. Using this diagnostic, it is observed that the H-atom concentration decreases when the vessel wall temperature increases, owing to the increased efficiency of atomic hydrogen recombination on the wall. To overcome this effect, the discharge tube wall is cooled off with dimethyl polysiloxane, a low-loss dielectric liquid. It improves significantly the H-atom concentration at 2450 MHz provided the pressure is typically below a few torr and the power density is not too high.     

Recombination rate constant of free electrons and holes in thin CdSe films

The decay kinetics of electrons generated in thin CdSe films by laser pulse (wavelength 337 nm, pulse duration 8 ns) at 295 K was studied by the microwave photoconductivity method (36 GHz). Based on analysis of the photoresponse decay kinetics and the reactions of free and trapped electrons, holes, and ions, a model for the processes was proposed and the recombination rate constant of free electrons and holes in cadmium selenide was determined, being (4–6)· 10–11 cm³ s⁻¹. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 740–743, May, 2006. The samples were kindly presented by Yu. V. Meteleva.     

Laser flash photolysis study of the decay kinetics of carbocations of 1,2,2,4-tetramethyl-1,2-dihydroquinoline in the porous glass in the presence of methanol

The efficiency of formation and the decay kinetics of carbocations formed under the photolysis of 1,2,2,4-tetramethyl-1,2-dihydroquinoline in methanol and in a porous glass filled with methanol or dried in air or in vacuo were studied by the laser flash photolysis techniques. In MeOH, the carbocations recombine via the second-order law in the reaction with the MeO⁻ anion formed in an equimolar amount and decay via the first-order law in the reaction with the solvent with rate constants of 3·10⁸ L mol⁻¹ s^{− 1} and 1.4·10³ s⁻¹, respectively. When the solution is placed into the porous glass, no recombination of the carbocations with MeO⁻ is observed, and the reaction with the solvent is somewhat inhibited (rate constant 8·10² s⁻¹). More than tenfold inhibition of the reaction of the carbocations with methanol is observed on going to a monolayer of MeOH on the surface. The main route of carbocation decay in the porous glass dried in vacuo is the geminate recombination with the SiO groups. The corresponding kinetics is described in terms of the model of freely diffusing reactants. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2239–2243, October, 2005.     

Effect of cathodic polarization of a steel membrane and the acidity of alcohol solutions of hydrochloric acid on the balance between rates of the reaction of evolution of hydrogen and its solid-phase diffusion

The effect of cathodic polarization of the entrance side of a steel membrane and the concentration of hydrochloric acid (0.99–0.01 M) on the balance between rates of the reaction of evolution of hydrogen and its diffusion through steel (ρ) is studied in hydrochloric-acid solutions of ethanol and ethylene glycol with a constant ionic strength equal to unity. It is demonstrated that ρ lowers down with a shift of the potential of the polarization side of the membrane in the negative direction and increases with diminishing concentration of hydrochloric acid. The results are interpreted with allowance made for the surface coverage by two forms of adsorbed hydrogen, namely, a raised form and a subsurface form.     

Charge Carrier Dynamics in PDPP-F/PCBM Heterojunction Solar Cells

The morphology dependent of migration and recombination kinetics of charge carriers in the polymer solar cell based on poly {2,7'-9,9-dioctylfluorene-alt-5-diethylhexyl-3,6-bis(5-bromothiophen-2-yl)pyrrolo[3,4-c]-pyrrole-1,4-dione}(PDPP-F) was investigated with photo-induced charge carrier extraction by linearly increasing voltage technique. The recombination coefficient of charge carriers decreased and the mobility of charge carriers increased, after the mass ratio of[6,6]-phenyl-C61-butyric acid methyl ester(PCBM) increased from 3:2 to 2:1. Meanwhile, both of them were sensitive to the applied electric field and could be together responsible for the improvement of voltage performance of polymer solar cell.