UV-vis spectroscopic study of Co(II)/Co(III) oxidation in poly[M-protoporphyrins] films and their interaction with axial ligands

A bathochromic shift for both Soret and Q bands in the polyCo(III)PP were indicative of Co(III) oxidation state in film. The presence of an isosbestic point indicates a chemical equilibrium between polyCo(III)PP (band I) in polyCo(III)PP with water as axial neutral ligand (band II). Concentration levels of iodide of 10(-1) M showed irreversible broadening of Soret band with a maximum shift from 400 nm to 380 nm attributed to film reduction. The thiocyanate anion shows a remarkable effect on polyCo(III)PP spectra. The degree of configuration interaction for Q and B transitions is nearly constant in air and water for Ni(II)PP, Cu(II)PP and Zn(II)PP films. The poly[Co(III)-protoporphyrin IX] showed strong deviation from the pattern. This result indicates that the Co atom does not present a planar conformation in polyCo(III)PP which is consistent with the less packed structure of this film. The apparent diffusion coefficients (D') were calculated for electroactive species using the polyNi(II)PP chemically modified electrode, with an experiment short enough to avoid preconcentration. D' was compared with D (diffusion coefficient), obtained with the bare working electrode. Apparent diffusion coefficients (D') changed regularly with molecular volume indicating certain molecular sieving effect.     

Inclusion complexes of a bichromophoric diester containing anthracene and naphthalene groups with alpha- and beta-cyclodextrins: thermodynamics and molecular mechanics

Fluorescence and molecular mechanics have been used to study the inclusion complexes of the (9-anthryl)-COO-(CH2)2-OOC-(2-naphthyl) bichromophoric compound with alpha- and beta-cyclodextrins. Emission spectra upon excitation of the naphthalene group denote the presence of non-radiative energy transfer from naphthalene to anthracene, which is influenced by the type of CD. Naphthalene emission also shows two peaks whose ratio of intensities R is sensitive to the medium polarity. The stoichiometry, the formation constants and the changes of enthalpy and entropy upon inclusion of complexes formed were obtained from the change of R with CD concentration and temperature. Both complexes, in agreement with Job's plots, show 1:1 stoichiometry. Quenching, fluorescence depolarization and the analysis of R when all the guests are complexed permit us to explain the possible location of CDs in the complexes formed. Molecular mechanics calculations were also employed to study the formation of 1:1 complexes with both alpha- and betaCDs. The study was mainly performed in the presence of water as a solvent. Results seem to explain the stoichiometries and geometry for both complexes.     

Core ionization energies and multi-peak structure of esca bands in some pentatomic heterocyclic compounds

The core ionization energy and the multi-peak structures of ESCA bands in furan, pyrrole, thiophen and their saturated homologues were obtained. Significant change of ESCA data is observed on going from the saturated to the aromatic compounds. The variations in the core ionization energies seem connected to the mesomeric drift of charge from the heteroatom to the carbon atoms in the aromatic derivatives. Shake-up processes involving charge-transfer transitions are considered to be the major responsible of the observed multi-peak structure in the aromatic compounds.     

Chemoselective syntheses of gamma-butyrolactams using vinyl sulfilimines and dichloroketene

Reactions between vinyl sulfilimines and dichloroketene generated in situ from trichloroacetyl chloride in the presence of zinc-copper couple give mixtures of alpha-dichloro-gamma-butyrolactams and alpha-dichloro-gamma-butyrolactone imines. Fine-tuning of substituents within vinyl sulfilimines results in reactions with good chemoselectivity and yield for lactams.     

Break-up of a Newtonian drop in a viscoelastic matrix under simple shear flow

The effect of matrix elasticity on the break-up of an isolated Newtonian drop under step shear flow is herein presented. Constant-viscosity, elastic polymer solutions (Boger fluids) were used as matrix phase. Newtonian silicon oils were used as drop phase. Three viscosity ratios were explored (drop/matrix), i.e. 2, 0.6 and 0.04. Following the theoretical analysis of Greco [Greco F (2002) J Non-Newtonian Fluid Mech 107:111–131], the role of elasticity on drop fluid dynamics was quantified according to the value of the parameter p=/_em, where is a constitutive relaxation time of the matrix fluid and _em is the emulsion time. Different fluids were prepared in order to have p ranging from 0.1 to 10. At all the viscosity ratios explored, break-up was hindered by matrix elasticity. The start-up transient of drop deformation, at high, but sub-critical capillary numbers, showed an overshoot, during which the drop enhanced its orientation toward the flow direction. Both phenomena increase if the p parameter increases. Finally, the non-dimensional pinch-off length and break-up time were also found to increase with p.This paper was presented at the first Annual European Rheology Conference (AERC) held in Guimarães, Portugal, September 11-13, 2003.     

On the adjunction mapping of very ample vector bundles of corank one

Let be a very ample vector bundle of rank over a smooth complex projective variety of dimension . The structure of being known when , we investigate the structure of the adjunction mapping when .

     

A note about teleparallel supergravity

The supersymmetric extension of teleparallel gravity is discussed. It is found that teleparallel supergravity is equivalent to the usual supergravity when the vierbein, the gravitino field and the connection are not identified with the component of the gauge potential, but are obtained taking the limit in (81), (83) and (84) of P. Salgado, S. del Campo, M. Cataldo, Phys. Rev. D 68, 024021 (2003). It is also shown that the successful formalism of Grignani-Nardelli permits one to obtain teleparallel-supergravity in (2 + 1) dimensions from (3 + 1)-dimensional teleparallel supergravity. Received: 11 May 2005, Published online: 6 October 2005 PACS: 04.65. + e     

Full characterization of the loading of a magneto–optical trap from an alkali metal dispenser

We present an experimental study of the dynamics of a magneto–optical trap (MOT) loaded from an alkali dispenser current controlled source. In our experimental vacuum conditions and for a low trapping force MOT the trap loading process critically depends on the dispensers working regime. This allows to completely characterize the dispensers–MOT system and to determine the best loading conditions.     

Excitable optical waves in semiconductor microcavities

We demonstrate experimentally and theoretically the existence of excitable optical waves in semiconductor microcavities. Although similar to those observed in biological and chemical systems, these excitable optical waves are self-confined. This is due to a new dynamical scenario, where a stationary Turning pattern controls the propagation of waves in an excitable medium, thus bringing together the two paradigms of dynamical behavior (waves and patterns) in active media.