(1)H NMR and small-angle neutron scattering investigation of the structure and solubilization behavior of three-layer nanoparticles

Three-layer nanoparticles were prepared by radiation-induced polymerization of 1-10 g/L of methyl methacrylate dissolved in a 0.1 wt % D(2)O solution of polystyrene-poly(methacrylic acid) (PS-PMA) micelles. According to NMR and small-angle neutron scattering (SANS), most of the poly(methyl methacrylate) (PMMA) is adsorbed at the core-shell interface of the particles. A small fraction of shorter PMMA probably sticks to outer parts of the PMA chains. The absorption kinetics and equilibria of benzene and chloroform were studied by NMR and SANS time-resolved experiments. The diffusion front in the PS core is very narrow but quite broad in the PMMA sheet suggesting, thus, a less compact state of PMMA. According to SANS, the diffusion kinetics is almost independent of the PMMA sheet thickness. In contrast to it, the absorption capacity, reflected by both SANS and NMR, increases markedly with the PMMA content in the particle. The maximum amount of solubilized compound depends on its positive interaction with PMMA (expressed by the chi parameter) but is restricted by the growing interface tension between swollen PMMA and D(2)O. In accordance with this conclusion, a particle saturated with benzene can absorb chloroform only at the expense of a part of benzene expelled into the surrounding medium and vice versa. Starting with 10 g PMMA/L (10 times the weight of the original micelles), the particles become unstable when being swollen with a good solvent.     

Structure and phase transitions of DMPC multilamellar vesicles in the presence of Ca<Superscript>2+</Superscript> ions

Results obtained via small-angle neutron scattering studies of the influence of calcium ions on the structure and phase transitions of phospholipid membranes are presented. The main phase transition temperature of 1,2-dimyristoyl-sn-glycero-3-phosphatidylcholine (1 wt %) multilamellar vesicles is demonstrated to increase by more than 1°C even when the calcium-ion content of the solution is low (0.1 mM). Detailed analysis of the multilamellar vesicles transition between “bound” and “unbound” state indicates the continuous character of the investigated process in both liquid and gel phases. The critical Ca²⁺ ion concentrations which initiate the destruction of the multilamellar structures and the formation of unilamellar vesicles are found to be ~0.3 mM in the gel and ~0.4–0.5 mM in the liquid-crystal phases during heating and ~0.5 mM in the phases under study upon cooling.     

Alpha-decay fine structures of U isotopes and systematics for isotopic chains of Po and Rn

A model of the cluster radioactivity of even-even nuclei is presented. In this model, the zero-point vibrations in the charge-asymmetry coordinate determine the cluster formation (spectroscopic factor), while the tunneling in the coordinate of the relative separation of the centers of mass of the cluster and the daughter nucleus determines the penetrability of the barrier of the nucleus-nucleus potential. The quality of the model is demonstrated for describing cluster decay half-lives and the fine structure in alpha decays of even-even U isotopes. The model is applied to describe the alpha decays in the isotopic chains of Po, Rn, and U. The correspondence of the calculated half-lives to the Geiger-Nuttall law is discussed.     

Investigation of latent and short etched heavy ion tracks in solids

In the past five years were carried out SANS (Small-Angle Neutron Scattering measurements in the JINR to investigate latent and short etched tracks in SSNTD. The results demonstrate the suitability of the method to study not etched and short etched tracks to analyse the etching process, e.g. for nuclear track filter production. The results are in good agreement with other methods as conductivity measurements.     

Ruthenium bis(phosphinite) pincer complexes

Resorcinol-based ruthenium bis(phosphinite) complexes were synthesized. Complexes RuCl(CO)[2,6-(Bu^t ₂PO)₂C₆H₃] (9) and RuH(CO)[2,6-(Bu^t ₂PO)₂C₆H₃] (10) were obtained by cyclometallation of 1,3-(Bu^t ₂PO)₂C₆H₃ with RuCl₂(DMSO)₄ in 2-methoxyethanol in the presence of Hünig’s base. The interconversion of complexes 9 and 10 was studied. The addition of carbon monoxide to complexes 9 and 10 yielded 18e adducts, RuCl(CO)₂[2,6-(Bu^t ₂PO)₂C₆H₃] (11) and RuH(CO)₂[2,6-(Bu^t ₂PO)₂C₆H₃] (12), respectively. In the case of complex 9, this reaction is reversible. Reaction of complex 10 with trifluoroacetic acid resulted in complex Ru(CF₃COO)(CO)[2,6-(Bu^t ₂PO)₂C₆H₃] (13), which reacted with carbon monoxide to give complex Ru(CF₃COO)(CO)₂[2,6-(Bu^t ₂PO)₂C₆H₃] (14). Based on the IR spectral data, the TFA ligand in complexes 13 and 14 is bound in a bi- and monodentate fashion, respectively. The structure of compound 9 was determined by X-ray diffraction analysis.     

The extremal function in the Delsarte problem of finding an upper bound for the kissing number in the three-dimensional space

We consider an extremal problem for continuous functions that are nonpositive on a closed interval and can be represented by series in Legendre polynomials with nonnegative coefficients. This problem arises from the Delsarte method of finding an upper bound for the kissing number in the three-dimensional Euclidean space. We prove that the problem has a unique solution, which is a polynomial of degree 27. This polynomial is a linear combination of Legendre polynomials of degrees 0, 1, 2, 3, 4, 5, 8, 9, 10, 20, and 27 with positive coefficients; it has simple root 1/2 and five double roots in (?1, 1/2). We also consider the dual extremal problem for nonnegative measures on [?1, 1/2] and, in particular, prove that an extremal measure is unique.