Hot recombination of photogenerated ion pairs

The recombination dynamics of ion pairs generated upon electron transfer quenching of perylene in the first singlet excited state by tetracyanoethylene in acetonitrile is quantitatively described by the extended unified theory of photoionization/recombination. The extension incorporates the hot recombination of the ion pair passing through the level-crossing point during its diffusive motion along the reaction coordinate down to the equilibrium state. The ultrafast hot recombination vastly reduces the yield of equilibrated ion pairs subjected to subsequent thermal charge recombination and separation into free ions. The relatively successful fit of the theory to the experimentally measured kinetics of ion accumulation/recombination and free ion yield represents a firm justification of hot recombination of about 90% of primary generated ion pairs.     

Iodide fluorescence quenching of sol-gel immobilized BSA

Several potential applications of sol-gel immobilized proteins may require drying the gel before use. The attendant shrinkage may sterically restrict the penetration of solutes to the entrapped protein. In this study, collisional quenching of intrinsic bovine serum albumin (BSA) fluorescence by dissolved iodide was used to quantitatively compare the accessibility of protein molecules entrapped in hydrated and dried sol-gel monoliths. The results show that iodide penetration to immobilized BSA is sterically restricted by approximately 25% in hydrated gels and 50% in dried gels, relative to the quenching behavior of dissolved BSA. The further decrease upon drying is consistent with the overall degree of monolith shrinkage.     

Diazeniumdiolate ions as leaving groups in anomeric displacement reactions: a protection-deprotection strategy for ionic diazeniumdiolates

Diazeniumdiolate ions [R2N-N(O)=N-O-] are of growing interest pharmacologically for their ability to generate up to two molar equivalents of bioactive nitric oxide (NO) spontaneously on protonating the amino nitrogen. Accordingly, their stability increases as the pH is raised. Here we show that the corresponding beta-glucosides [R2N-N(O)=N-O-Glc] decreased in stability with pH; when R2N was diethylamino, the rate equation was kobs = ko + kOH- [OH-], where ko = 7.8 x 10-7 s-1 and kOH- = 5.3 x 10-3 M-1 s-1. The primary products were 1,6-anhydroglucose and the regenerated R2N-N(O)=N-O- ion. The results were qualitatively similar to those of beta-glucosyl fluoride and p-nitrophenoxide, whose hydrolyses have been rationalized as proceeding via a glycal oxide intermediate. This chemistry offers a convenient strategy for protecting heat- and acid-sensitive diazeniumdiolate ions during manipulations that would otherwise destroy them. As an example, a poly(urethane) film that generated NO in physiological buffer at a surface flux comparable to that of the mammalian vascular endothelium was prepared by glucosylating the ionic diazeniumdiolate group attached to the diol monomer before reacting it with the bis-isocyanate, then removing the saccharide with base when the protecting group was no longer needed.     

The synthesis of mesogenic polymers provoked by molecular mobility. polysiloxanarylenes

An approach to the synthesis of potentially thermotropic liquid crystalline polymers based on parallel investigation of their molecular mobility was realized. The initial idea was provoked by the observation that there exists some correspondence of molecular mobility data and the ability of a polymer to form a liquid crystalline phase. Previously this phenomenon was demonstrated on the example of a series of thermotropic main chain polymers with flexible dimethylsiloxane spacers of variable length. The relation between the structure of the main chain and local molecular mobility of different fragments was investigated in a series of regular polysiloxane-silarylenes containing rigid aromatic sequences. Molecular mobility was studied by dielectric spectroscopy in solution and in solid state. The structure of the main chain has been changed by variation of the repeated fragments' length, substituents and joint groups. The data of molecular mobility and their conformity with the chain structure were used for directed synthetic search of desired mesogenic polymers.     

Korn's Inequalities for Junctions of Spatial Bodies and Thin Rods

The dependence on the small parameter ε of constants in Korn's inequalities is investigated for domains which are obtained by joining thin rods to an elastic spatial body. The external ends of the rods are clamped. The asymptotic accuracy of the derived inequalities is achieved by certain distribution of weight multipliers and powers of ε in L₂-norms of displacements and their derivatives while the introduced weights differ for longitudinal and transversal components of displacement fields in the rods. © 1997 by B.G. Teubner Stuttgart-John Wiley & Sons, Ltd.     

Synthesis and optical characterization of photoactive poly(2‐phenoxyethyl acrylate) copolymers containing azobenzene units,prepared by frontal polymerization using novel ionic liquids as initiators

2‐Phenoxyethyl acrylate (2‐PEA) was polymerized alone and in the presence of an azobenzene comonomer derived from Disperse Red‐1, N‐ethyl‐N‐(2‐hydroxyethyl)‐4‐(4‐nitrophenylazo)aniline (MDR‐1), by using the frontal polymerization technique. Two novel ionic liquids, recently synthesized by us, were used as initiators: tetrabutylphosphonium persulfate (TBPPS) and trihexyltetradecylphosphonium persulfate (TETDPPS). Even if their concentrations were smaller than those found when benzoyl peroxide and terbutylperoxy neodecanoate were used, these compounds gave rise to stable propagating polymerization fronts characterized by relatively low maximum temperatures and good velocities. Moreover, at variance to these latter, TBPPS and TETDPPS prevent bubble formation, thus allowing the use of the obtained materials in optical applications. The obtained polymers were characterized by infrared spectroscopy (FTIR), their thermal properties were determined by differential scanning calorimetry, and their optical properties were studied by absorption spectroscopy in the UV–vis region. Finally, the nonlinear optical (NLO) properties of the 2‐PEA/MDR‐1 copolymers obtained with TBPPS and TETDPPS were performed according to the Z‐Scan technique with prepared film samples. It has been proven that samples with higher MDR‐1 content (0.05 mol %) exhibited outstanding cubic NLO activity with negative NLO refractive coefficients around n₂ = ?1.7 × 10^?3 esu. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

The critical temperature for the BCS equation at weak coupling

For the BCS equation with local two-body interaction λV(x), we give a rigorous analysis of the asymptotic behavior of the critical temperature as γ»0. We derive necessary and sufficient conditions onV(x) for the existence of a nontrivial solution for all values of γ>0.     

Search for strange-quark matter in galactic cosmic rays

Summary A method for detecting strange-quark matter is discussed. In order to confirm the existence of strange-quark matter in the cosmic radiation, a new instrument under construction for a balloon experiment is presented. Due to the relevance of its scientific content, this paper has been given priority by the Journal Direction.     

Bare and effective fluid description in brane world cosmology

We extend the classical Damour–Ruffini method and discuss Hawking radiation spectrum of high-dimensional rotating black hole using Tortoise coordinate transformation defined by taking the reaction of the radiation to the spacetime into consideration. Under the condition that the energy and angular momentum are conservative, taking self-gravitation action into account, we derive Hawking radiation spectrums which satisfy unitary principle in quantum mechanics. It is shown that the process that the black hole radiates particles with energy ω is a continuous tunneling process. We provide a theoretical basis for further studying the physical mechanism of black-hole radiation.