Quantum diffusion in solid H2?Ne solutions

Quantum diffusion in solid hydrogen containing 0.02–0.25 mol.% neon has been investigated by the calorimetric method in temperature range 1–3 K. The concentrations of orthohydrogen were 0.23; 0.5 and 1 mol. %. The parameter studied was characteristic configurational relaxation time τ. Heat capacity is very sensitive to space distribution of orthohydrogen molecules. Therefore, the determination of configuration relaxation rate has been performed by observing the time dependence of heat capacity. A neon impurity in the indicated concentration is observed to accelerate quantum diffusion in hydrogen. The magnitude of the effect diminishes as the temperature increases.     

Using the fundamental equation of constrained motion with inequality constraints

In this paper we investigate a computational approach to keeping a moving particle within a predefined annulus or a predefined bounded space, formed by two concentric spheres with radii L_min and L_max, respectively, assuming that said particle cannot maintain a perfectly circular trajectory. The study develops an algorithm for dealing with a system in which constraints are expressed as inequalities. The proposed approach expresses the trajectory in terms of winding/unwinding logarithmic spirals with transitions, expressed as damped vibrations, between them. These transitions are necessary to resolve incompatibility between initial conditions for winding/unwinding spirals. Equations of motion for the particle are obtained by using the Fundamental Equation of Constrained Motion. The obtained simulation results show that such an approach produces the desired pseudo-periodic type of motion, and the particle stays within the predefined region of space for a long duration, although no cycle of its trajectory is repeated.     

Delayed fluorescence of porphyrins in different media

Lifetimes of TPPS₄ (meso-tetraphenylporphine tetrasulfonate) triplet states were measured for liquid solutions of different acidity and viscosity and as a function of acceptor concentration for different acceptors (bovine serum albumin, tryptophan and furfuryl alcohol). Triplet lifetimes were estimated by monitoring the decay of TPPS₄ delayed fluorescence of E-type. The lifetime of delayed fluorencence depends on the concentration of O₂, since the latter is an effective quencher of the triplet state. The lifetime is shown to be influenced mainly by degree of aggregation state of TPPS₄ and, therefore, by the pH of the solution, decreasing with pH and for each pH remaining constant over a wide range of acceptor concentrations. The monomeric species is found to have the longest triplet lifetime in aqueous phosphate-buffered saline solution at neutral pH, especially when bound to albumin, despite of the low viscosity and protonated nature of the medium.     

Phosphoryl Containing Podands as Carriers in Plasticized Membrane Electrodes Selective to Quaternary Ammonium Surfactants

Open chain polyethers with phosphoryl-containing terminal groups have been studied as carriers in plasticized membrane electrodes that are selective towards cationic surfactants. Host–guest complexation has also been studied by means of batch extraction and bulk membrane transport experiments. For the various guests, the bulk membrane (chloroform) transport rate decreases in the series tetraalkyl ammonium > alkyl pyridinium > alkyl ammonium, while the series of solvent extraction efficiency is exactly opposite; an explanation for this behaviour is proposed. The performance of electrode membranes follows the series for bulk membrane transport. Among the ISE membranes of various composition, one containing the longest (seven oxygen atoms) podand, o-nitrophenyl octyl ether (plasticizer), and sodium tetraphenyl borate (anionic additive) performs the best. The slope of the electrode function equals 58.5 mV/decade, the detection limit for dodecyltrimethylammonium is 3.2 × 10^-6 M. ISE response time is 5–10 s, the working pH range is 2–11 and lifetime is at least 6 months. The electrode selectivity is significantly better than that of conventional ion-association and crown ether based electrodes.     

Amperometric biosensors based on microflow injection system

Novel electrochemical cells based on a microflow system combined with amperometric enzyme electrodes were developed and served for quantitative determination of various compounds, such as organophosphates and lactose. The resulting biosensors are selective and efficient owing to immobilization of the sensing elements on the electrodes. The sensors are easy to operate, and the procedures are rapid, accurate, reproducible, and inexpensive, requiring neither special skills and training nor complicated instrumentation. The use of a microflow cell ensures the continuous flux of a new substrate, thus preventing the accumulation or adsorption of products to the electrode. Miniaturization of the sensor has two main advantages: (1) it is easy to carry and therefore can be used outdoors as well, and (2) it allows working with low volumes of compounds and reagents, which is highly important when dealing with hazardous compounds.     

Capillary condensation as a morphological transition

The process of capillary condensation/evaporation in cylindrical pores is considered within the idea of symmetry breaking. Capillary condensation/evaporation is treated as a morphological transition between the wetting film configurations of different symmetry. We considered two models: (i) the classical Laplace theory of capillarity and (ii) the Derjaguin model which takes into account the surface forces expressed in terms of the disjoining pressure. Following the idea of Everett and Haynes, the problem of condensation/evaporation is considered as a transition from bumps/undulations to lenses. Using the method of phase portraits, we discuss the mathematical mechanisms of this transition hidden in the Laplace and Derjaguin equations. Analyzing the energetic barriers of the bump and lens formation, it is shown that the bump formation is a prerogative of capillary condensation: for the vapor-liquid transition in a pore, the bump plays the same role as the spherical nucleus in a bulk fluid. We show also that the Derjaguin model admits a variety of interfacial configurations responsible for film patterning at specific conditions.     

Synthesis and biodistribution of bowman-birk soybean protease inhibitor conjugate with amphiphilic polyester

The modification of Bowman-Birk soybean protease inhibitor (BBI) with the monoaldehyde derivative of block copolymer of ethylene oxide and propylene oxide (PE),M _r 2000 is described. The conjugate contains five covalently bound polymer chains per protein molecule, and retains the ability to inhibit trypsin and chymotrypsinlike proteinases. The distribution of native BBI and the BBI-PE conjugate was examined in mice. After iv injection of [¹²⁵I]BBI and [¹²⁵I]BBIPE, both inhibitors distributed very rapidly to the liver, kidney, and lungs, and more slowly to the brain. At the same time-points (up to 24 h), radioactivity in the blood and organs of mice injected with modified inhibitor was higher than that of the native inhibitor. The blood concentration time profile following iv administration of two BBI preparations at a dose 3 mg/kg was reasonable well described by a two-compartment open model with first-order elimination kinetics. The total clearance of BBI-PE decreased by a factor of 8, body mean residence time increased by a factor of 5 in comparison with BBI. A physiological pharmacokinetic model was developed to describe the tissue-to-blood distribution of two inhibitors. One-compartment physiological organ model (flow limited) was used to describe of timecourse profiles of BBI concentration in organs. A two-compartment physiological organ model (membrane limited) was used to predict tissue-to-blood distribution of conjugated BBI in some organs of mice (liver, lungs). The predicted concentration curves of BBI and BBI-PE in blood and organs in mice (with the exception of kidney) showed good agreement with the observed values.     

Effect of the non‐linear screening on a modification of the Debye–Hückel plus hole approximation in complex plasma

The authors analyse two‐component electroneutral systems of classical macroions of finite size and point‐like oppositely charged microions. This article deals with the modification of the Debye–Hückel plus hole approximation when a non‐linear screening effect is taken into account in a complex plasma. Parameters of non‐linear screening of the macroions by surrounding microions are calculated within the framework of the Poisson–Boltzmann approximation. Two effects are found as a result of such calculations: (a) subdivision of all microions into two subclasses, free microions and bound microions and (b) a significant reduction of an effective charge Z^* of the macroion in comparison with its true value Z due to the non‐linear screening by a thin high‐density envelope of the bound microions. We show that the value of a non‐ideal portion of an internal energy differs considerably in the case when the non‐linear screening effect is taken into account in the vicinity of the macroion.