Hydrated phosphorus oxyacids alone and adsorbed on nanosilica

Low-temperature (1)Н NMR spectroscopy was used to study states of water bound to phosphoric and phosphonic acids (phosporus oxyacids, POA) alone or adsorbed onto nanosilica OX-50 (specific surface area S(BET)=52 m(2)/g) or A-300 (S(BET)=297 m(2)/g). Concentrated solutions or weakly hydrated solid POA or dried silica/POA powders placed in CCl(4) medium are characterized by different temperature dependences of the chemical shift of the proton resonance (δ(H)) because of partial dissociation of PO-H bonds strongly affected by water amounts and temperature. NMR cryoporometry results show that both small water clusters and nanodomains are present at the interfaces of hydrated solid POA and silica/POA powders. Quantum chemical calculations of the (1)H NMR spectra demonstrate the influence of POA/water cluster structure and dissociation of the PO-H bonds on the δ(H) values.     

Structure and magentic properties of novel chelate complexes of copper(II) and nickel(II) with nitroxide radical ethyl-2-(1-oxyl-2,2,5,5-tetramethylimidazolidin-4-yliden)-3-oxopropanoate

Chelate complexes of copper(II) and nickel(II) with anions of nitroxide radical ethyl-2-(1-oxyl-2,2,5,5-tetramethylimidazolidin-4-yliden)-3-oxopropanoate (HL) are synthesized. The compounds have molecular structure and zero magnetic dimensionality. CuL₂ crystallizes as two polymorphs having mononuclear structure. Ni₂L₄ forms dimeric molecules by virtue of the bridging function of the aldehyde oxygen atoms. Magnetic properties of Ni₂L₄ are determined by antiferromagnetic exchange interactions between the Ni(II) ions (-48(1) K) propagated through the oxygen bridges     

Spectroscopic investigation of thermooxidative destruction of ethers on the surface of modified silica

Thermooxidative processes are investigated by the method of temperature-programmed decomposition with the use of a prism infrared spectrometer. Thermal degradation of —OC₄H₉, —OP(H)(O)OC₄H₉ and —OP(H)(O)OC₂H₅ groups on the surface of modified pyrogenic silicas in air is considered. The resemblance between processes of oxidation of surface PH-groups irrespective of the means of silica modification is shown. Institute of Surface Chemistry, National Academy of Sciences of Ukraine, 31, Nauka Ave., Kiev, 252022, Ukraine. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 3, pp. 326–332, May–June, 1998.     

Special features of calculation for processes of scattering by contrast and strongly absorbing two- and three-dimensional inhomogeneities

A direct problem of scattering for refractive-absorbing scatterers of different shapes and strengths is considered. A rigorous solution for two- and three-dimensional problems and its numerical implementation are obtained on the basis of equations of the Lippmann-Schwinger type in the coordinate space and in the space of special frequencies that is Fourier-conjugate to it. Attention is given to selection of parameters for problem sampling that are fundamentally important for providing adequacy of numerical simulation. Techniques for restricting the Green’s function support and introducing a reserve band are used. The results of numerical calculation for wave fields and secondary sources are given for different scatterers. The major laws connected with the effects of sound wave rescattering are illustrated and discussed.     

Spectra of resonance light scattering of gold nanoshells: Effects of polydispersity and limited electron free path

The effects of the polydispersity of the structure of gold nanoshells and of the limited electron free path in a thin metal layer on the spectra of resonance light scattering of a suspension of two-layer nanoparticles are studied theoretically and experimentally for the first time. It is shown theoretically that both factors lead to a broadening of the plasmon resonance in light scattering and to a change in its magnitude. To experimentally test the calculations, two samples of nanoshells based on gold and silicon dioxide (silica) were synthesized. Nanoshells of sample 1 have a diameter of the core of 90 nm and a broad thickness distribution of shells (with an average value of 30 nm), whereas nanoshells of sample 2 have a diameter of the core of 70 nm and a narrow thickness distribution of shells (with an average value of 12 nm). The core diameter, the shell thickness, and the polydispersity of the structure of nanoparticles are estimated by dynamic light scattering. It is shown that the simulation of the optical properties of nanoparticles with their parameters estimated from the dynamic light scattering data makes it possible to obtain good agreement between experimental and theoretical spectra of light scattering. For nanoshells of sample 1, the inhomogeneous broadening of the scattering spectrum is completely determined by the polydispersity; therefore, the bulk constants of gold can be used in simulation of the spectra of such nanoshells. The main mechanism of the broadening for nanoshells of sample 2 is connected with the limitation of the free path length of electrons, whereas the contribution from the thickness distribution of shells can be neglected.     

Limits for the central production of Theta+ and Xi(--)pentaquarks in 920-GeV pA collisions

We have searched for Theta+(1540) and Xi(--)(1862) pentaquark candidates in proton-induced reactions on C, Ti, and W targets at midrapidity and square root of s = 41.6 GeV. In 2 x 10(8) inelastic events we find no evidence for narrow (sigma approximately 5 MeV) signals in the Theta+ --> pK0(S) and Xi(--) --> Xi- pi- channels; our 95% C.L. upper limits (UL) for the inclusive production cross section times branching fraction B dsigma/dy/(y approximately 0) are (4-16) mub/N for a Theta+ mass between 1521 and 1555 MeV, and 2.5 mub/N for the Xi(--). The UL of the yield ratio of Theta+/Lambda(1520) < (3-12)% is significantly lower than model predictions. Our UL of B Xi(--)/Xi(1530)0 < 4% is at variance with the results that have provided the first evidence for the Xi(--).     

Interaction of unmodified and partially silylated nanosilica with red blood cells

Interaction of red blood cells (RBCs) with unmodified and partially (50%) silylated fumed silica A-300 (nanosilica)was studied by microscopic, XRD and thermally stimulated depolarisation current (TSDC) methods. Nanosilica at a low concentration C _A-300 < 0.01 wt.% in buffered aqueous suspension is characterised by a weak haemolytic effect on RBCs. However, at C _A-300 = 1 wt% all RBCs transform into shadow corpuscles because of 100% haemolysis. Partial (one-half) hydrophobization of nanosilica leads to reduction of the haemolytic effect in comparison with unmodified silica at the same concentrations. A certain portion of the TSDC spectra of the buffered suspensions with RBC/A-300 is independent of the amounts of silica. However, significant portions of the low-and high-temperature TSDC bands have a lower intensity at C _A-300 = 1 wt% than that for RBCs alone or RBC/A-300 at C _A-300 = 0.01 wt.% because of structural changes in RBCs. Results of microscopic and XRD investigations and calculations using the TSDC-and NMR-cryoporometry suggest that the intracellular structures in RBCs (both organic and aqueous components) depend on nanosilica concentration in the suspension.