Equilibrium of ion-exchange polymeric membrane with aqueous salt solution and its thermodynamic modeling

A thermodynamic model is proposed to describe distribution of the components between a liquid solution and a swollen membrane undergoing structural transformations. Free energy contributions related to formation of solution-filled micro-cavities in the membrane interior are estimated. Formation of the cavities of different shape is accounted for by using the Helfrich expressions for the bending energy of a curved interface. Three adjustable parameters of the model are related to the hydrophobic polymer matrix of the membrane, while the electrostatic contribution is estimated explicitly. Structural changes in the membrane are described as a transition from spherical to cylindrical cavities. Predominance of cavities having definite shape (spheres, cylinders) results in a specific shift of the Donnan equilibrium, which thus, becomes dependent on the structure of the membrane on the mesoscale. The results of model calculations are compared with the experimental data on the distribution of ions (H⁺, Li⁺, Cs⁺, K⁺, Na⁺, Ca²⁺, Mg²⁺) between the aqueous solution and the membrane. Different types of predicted thermodynamic behavior of the membrane in the liquid solution, including the hysteresis of ion-exchange equilibrium curves, are discussed. The model takes into account the effect of micro-inhomogeneties and helps to establish a link between molecular characteristics of the perfluoropolymer membrane and its macroscopic behavior in the liquid solution.     

Random packings by cubes

Y. Itoh’s problem on random integral packings of the d-dimensional (4 × 4)-cube by (2 × 2)-cubes is formulated as follows: (2 × 2)-cubes come to the cube K ₄ sequentially and randomly until it is possible in the following way: no (2 × 2)-cubes overlap, and all their centers are integer points in K ₄. Further, all admissible positions at every step are equiprobable. This process continues until the packing becomes saturated. Find the mean number M of (2 × 2)-cubes in a random saturated packing of the (4 × 4)-cube. This paper provides the proof of the first nontrivial exponential bound of the mean number of cubes in a saturated packing in Itoh’s problem: M ≥ (3/2)^d. __________ Translated from Fundamentalnaya i Prikladnaya Matematika, Vol. 11, No. 5, pp. 187–196, 2005.     

Floating Electrode Dielectric Barrier Discharge Plasma in Air Promoting Apoptotic Behavior in Melanoma Skin Cancer Cell Lines

Initiation of apoptosis, or programmed cell death, is an important issue in cancer treatment as cancer cells frequently have acquired the ability to block apoptosis and thus are more resistant to chemotherapeutic drugs. Targeted and perhaps selective destruction of cancerous tissue is desirable for many reasons, ranging from the enhancement of or aid to current medical methods to problems currently lacking a solution, i.e., lung cancer. Demonstrated in this publication is the inactivation (killing) of human Melanoma skin cancer cell lines, in vitro, by Floating Electrode Dielectric Barrier Discharge (FE-DBD) plasma. Not only are these cells shown to be killed immediately by high doses of plasma treatment, but low doses are shown to promote apoptotic behavior as detected by TUNEL staining and subsequent flow cytometry. It is shown that plasma acts on the cells directly and not by “poisoning” the solution surrounding the cells, even through a layer of such solution. Potential mechanisms of interaction of plasma with cells are discussed and further steps are proposed to develop an understanding of such systems.     

One-step assembly of carbamoyl substituted annulated 1,4-oxazepines

We present a convenient synthesis of heterocyclic scaffolds using a novel modification of four-component Ugi condensation. Two complementary variants of this useful synthetic strategy provide an efficient one-step assembly of four novel pharmaceutically relevant (hetero)aryl-fused 1,4-oxazepines with different substituents’ profile.     

Entrainment and stimulated emission of ultrasonic piezoelectric auto-oscillators

Theoretical modeling and laboratory tests are conducted for nonlinear auto-oscillating piezoelectric ultrasonic devices coupled to reverberant elastic bodies. The devices are shown to exhibit behavior familiar from the theory of coupled auto-oscillators. In particular, these spontaneously emitting devices adjust their limit-cycle frequency to the spectrum of the body. It is further shown that the auto-oscillations can be entrained by an applied field; an incident wave at a frequency close to the frequency of the natural limit cycle entrains the oscillator. Special attention is paid to the phase of entrainment. Depending on details, the phase is such that the oscillator can be in a state of stimulated emission: the incident field amplifies the ultrasonic power emitted by the oscillator. These behaviors are essential to eventual design of an ultrasonic system that would consist of a number of such devices all synchronized to their mutual field, a system that would be an analog to a laser. A prototype uaser is constructed.     

Novel Mechanism of Bioluminescence: Oxidative Decarboxylation of a Moiety Adjacent to the Light Emitter of Fridericia Luciferin

A novel luciferin from a bioluminescent Siberian earthworm Fridericia heliota was recently described. In this study, the Fridericia oxyluciferin was isolated and its structure elucidated. The results provide insight into a novel bioluminescence mechanism in nature. Oxidative decarboxylation of a lysine fragment of the luciferin supplies energy for light generation, while a fluorescent CompX moiety remains intact and serves as the light emitter.     

Methane as a Selectivity Booster in the Arc‐Discharge Synthesis of Endohedral Fullerenes: Selective Synthesis of the Single‐Molecule Magnet Dy2TiC@C80 and Its Congener Dy2TiC2@C80

The use of methane as a reactive gas dramatically increases the selectivity of the arc‐discharge synthesis of M‐Ti‐carbide clusterfullerenes (M=Y, Nd, Gd, Dy, Er, Lu). Optimization of the process parameters allows the synthesis of Dy₂TiC@C₈₀‐I and its facile isolation in a single chromatographic step. A new type of cluster with an endohedral acetylide unit, M₂TiC₂@C₈₀, is discovered along with the second isomer of M₂TiC@C₈₀. Dy₂TiC@C₈₀‐(I,II) and Dy₂TiC₂@C₈₀‐I are shown to be single‐molecule magnets (SMM), but the presence of the second carbon atom in the cluster Dy₂TiC₂@C₈₀ leads to substantially poorer SMM properties.     

Role of the Polymer Matrix on the Photoluminescence of Embedded CdSe Quantum Dots

The photoluminescence (PL) of CdSe quantum dots (QDs) that form stable nanocomposites with polymer liquid crystals (LCs) as smectic C hydrogen‐bonded homopolymers from a family of poly[4‐(n‐acryloyloxyalkyloxy)benzoic acids] is reported. The matrix that results from the combination of these units with methoxyphenyl benzoate and cholesterol‐containing units has a cholesteric structure. The exciton PL band of QDs in the smectic matrix is redshifted with respect to QDs in solution, whereas a blueshift is observed with the cholesteric matrix. The PL lifetimes and quantum yield in cholesteric nanocomposites are higher than those in smectic ones. This is interpreted in terms of a higher order of the smectic matrix in comparison to the cholesteric one. CdSe QDs in the ordered smectic matrix demonstrate a splitting of the exciton PL band and an enhancement of the photoinduced differential transmission. These results reveal the effects of the structure of polymer LC matrices on the optical properties of embedded QDs, which offer new possibilities for photonic applications of QD–LC polymer nanocomposites.