New nucleoside analogs from 2-amino-9-(beta-D-ribofuranosyl)purine

Four novel derivatives of 2-amino-9-(beta-D-ribofuranosyl)purine (1) were synthesised and fully characterised. When 1 was reacted with chloroacetaldehyde (a), 2-chloropropanal (b), bromomalonaldehyde (c) and a mixture of chloroacetaldehyde + malonaldehyde (d), 3-(beta-D-ribofuranosyl)-imidazo-[1,2a]purine (2), 3-(beta-D-ribofuranosyl)-5-methylimidazo-[1,2a]purine (3), 3-(beta-D-ribofuranosyl)-5-formylimidazo-[1,2a]purine (4) and 9-(beta-D-ribofuranosyl)-2-(3,5-diformyl-4-methyl-1,4-dihydro-1-pyridyl)purine (5) were formed, respectively. The products were isolated, purified by chromatography and characterised by MS, complete NMR assignment as well as fluorescence and UV spectroscopy. The yields of these reactions were moderate (14-20%). The fluorescence properties differed from those of the starting compound and the quantum yields were considerably lower.     

Development of SnO2/Sb-based ceramic pigments

The color efficiency of ceramic glaze blue pigments obtained by the Pechini method was presented in this work. The fired pigments and enameled samples were characterized by thermogravimetry (TG) and differential thermal analysis (DTA), XRD, UV-VIS-NIR spectroscopy and CIE-L*a*b* color-measurements. The pigments obtained by the Pechini method present a better solubility in the molten glazes than the pigments obtained by the mechanical mixture of the precursor oxides. This revised version was published online in August 2006 with corrections to the Cover Date.     

Folded 2,5-diazapent-3-ene metallacycle in ene-diamido group 4 metal compounds: DFT and AIM analyses

Mononuclear complexes, which contain a dianionic ene-diamido ligand bound to a group 4 metal atom in the formal d⁰ configuration, are analyzed by the DFT method to interpret the electronic origin of the folding at the five-membered 2,5-diazapent-3-ene metallacycle moiety. Geometry optimizations were carried out for the following models, TiCl₂[o-(Me₃SiN)₂C₆H₄], Ti(OPh)₂(DAD), CpTiCl(DAD), CpTiMe(DAD) and Cp₂Zr(DAD) (DAD = HNCHCHNH). They show some common electronic features, the nature of the HOMO, in particular. In all cases, the latter results from the donation of a filled ene-diamido level into an empty σ metal orbital, this being maximized upon the folding of the metallacycle. Such a geometric rearrangement involves the filled nitrogen p_π lobes, while the CC π bond remains essentially uninvolved. The feature is confirmed by the application of the atom in molecules (AIM) theory, that provides no evidence of critical points between the metal center and the pair of two carbon atoms.     

Dynamics of image-potential states on stepped Cu(001) surfaces

The dynamical properties of image-potential states on stepped Cu(117) and Cu(118) surfaces were studied by time- and angle-resolved two-photon photoelectron spectroscopy. The interaction with the step-induced potential leads to quasielastic anisotropic scattering between image-potential-state bands. In particular, resonant interband scattering from image-potential states with quantum numbers n2 to the n=1 band and quasielastic intraband scattering within the n=1 band show high efficiency. In spite of the higher step density of Cu(117), resonant scattering is about four times larger on Cu(118). This distinction is attributed to the different step distributions of the two surfaces and to the concomitant correlation of the step arrangement on short- and long-range scales, which has been studied by scanning tunneling microscopy. Details of the surface band structure lead to different boundary conditions and may weakly affect scattering probabilities. PACS 73.20.At; 79.60.Bm; 79.60.Dp; 79.60.Ht     

EPR spectroscopy of protein microcrystals oriented in a liquid crystalline polymer medium

Correlation of the g-tensor of a paramagnetic active center of a protein with its structure provides a unique experimental information on the electronic structure of the metal site. To address this problem, we made solid films containing metalloprotein (Desulfovibrio gigas cytochrome c(3)) microcrystals. The microcrystals in a liquid crystalline polymer medium (water/hydroxypropylcellulose) were partially aligned by a shear flow. A strong orientation effect of the metalloprotein was observed by EPR spectroscopy and polarizing optical microscopy. The EPR spectra of partially oriented samples were simulated, allowing for molecular orientation distribution function determination. The observed effect results in enhanced sensitivity and resolution of the EPR spectra and provides a new approach towards the correlation of spectroscopic data, obtained by EPR or some other technique, with the three-dimensional structure of a protein or a model compound.     

Measurements of motionally averaged heteronuclear dipolar couplings in MAS NMR using R-type recoupling

A novel MAS NMR approach is presented for the determination of heteronuclear dipolar couplings in unoriented materials. The technique is based on the proton-detected local field (PDLF) protocol, and achieves dipolar recoupling by R-type radio-frequency irradiation. The experiment, which is called R-PDLF spectroscopy, is demonstrated on solid and liquid-crystalline systems. For mobile systems, it is shown that the R-PDLF scheme provides better dipolar resolution as compared to techniques combining conventional separated local field (SLF) spectroscopy with R-type recoupling.     

Finite Josephson junction arrays with open boundaries in magnetic field: Ground state energy and first critical field

We have investigated the size dependence of the ground state energy as a function of the magnetic field in Josephson junction arrays with open boundaries. We present a simple rings model that reproduces with great confidence the size and field dependence of the energy of the system obtained by numerical simulation of the Hamiltonian. From these results we obtained the size dependence of the first penetration field, where the one-vortex state becomes favorable compared to the zero-vortex state.Received: 15 December 2003, Published online: 13 July 2004PACS: 74.81.Fa Josephson junction arrays and wire networks     

An extension to the Wheeler phase-field model to allow decoupling of the capillary and kinetic anisotropies

The formulation of the phase-field problem due to Wheeler et al. [Physica D 66, 243 (1993)] has been adopted and extended as a tool for solidification research by many groups around the World. However, an intrinsic problem of this model is that it couples two physically distinct anisotropies, those associated with the surface energy of the solid-liquid interface and attachment kinetics, into a single anisotropy parameter. In this paper we present a simple extension to the Wheeler model in which we show that introducing a complex form of the anisotropy function allows these two physical parameters to be decoupled.Received: 16 June 2004, Published online: 21 October 2004PACS: 81.10.-h Methods of crystal growth; physics of crystal growth - 81.30.Fb Solidification - 64.70.Dv Solid-liquid transitions