Dissociation of small metal particles induced by surface plasmon excitation with laser light

This paper reports the dissociation of supported metal clusters after illumination with low intensity visible laser light. The process is non-thermal and exhibits a resonant dependence on the laser frequency. This indicates that a surface plasmon excitation preceeds the dissociation.     

Manifold structures on abstract regular polytopes

Summary Abstract regular polytopes are complexes which generalize the classical regular polytopes. This paper discusses the topology of abstract regular polytopes whose vertex-figures are spherical and whose facets are topologically distinct from balls. The case of toroidal facets is particularly interesting and was studied earlier by Coxeter, Shephard and Grünbaum. Ann-dimensional manifold is associated with many abstract (n + 1)-polytopes. This is decomposed inton-dimensional manifolds-with-boundary (such as solid tori). For some polytopes with few faces the topological type or certain topological invariants of these manifolds are determined. For 4-polytopes with toroidal facets the manifolds include the 3-sphereS ³, connected sums of handlesS ¹ × S ² , euclidean and spherical space forms, and other examples with non-trivial fundamental group.     

Anomalous small‐angle X‐ray scattering characterization of composites based on sulfonated poly(ether ether ketone), zirconium phosphates,and zirconium oxide

The morphology and distribution of zirconium oxide and zirconium phosphates in a matrix of sulfonated poly(ether ether ketone) (SPEEK) were investigated with anomalous small‐angle X‐ray scattering (ASAXS) and electron microscopy. ASAXS revealed that ZrO₂ was distributed in the SPEEK matrix in the form of nanoparticles smaller than 13 Å. A decrease in the conductivity suggested that the sulfonic groups were bound to the zirconium oxo species at the particle surface. Furthermore, two kinds of membranes containing zirconium phosphate were investigated. In one case, the phosphate was directly dispersed in the polymer solution for the casting of the membrane. In the other case, the phosphate was previously treated with n‐propyl ammonium and polybenzimidazole. From ASAXS data, the fractal dimension could be estimated. Mass‐fractal behavior was confirmed for the SPEEK membrane containing previously exfoliated zirconium phosphate, with aggregates of 6.3–165 Å. Surface‐fractal behavior was detected for membranes with untreated phosphates, with aggregates of 6.4–185 Å. The untreated phosphates caused an increase in the permeability, without changing the proton conductivity much. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 567–575, 2004     

cyclo-CH2[Sn(CI2)CH2Si(Me2)]2O]: synthesis and complexation behaviour of a novel, cyclic, bidentate Lewis acid and its conversion into a tin-containing fluorosilane with intermolecular Si-F...Sn bridges

Acid-catalysed hydrolysis of [CH2[(Sn(Ph2)CH2Si(OiPr)Me2]2] followed by subsequent reaction with mercuric chloride in acetone afforded the novel silicon- and tin-containing eight-membered ring [cyclo-CH2[Sn(Cl2)CH2Si(Me2)]2O] in good yield, the crystal structure of which is reported. 119Sn NMR and X-ray studies indicate that [cyclo-CH2[Sn(Cl2)CH2Si(Me2)]2O] acts as a bidentate Lewis acid towards chloride ions exclusively forming the 1:1 complex [(Ph3P)2N]+[cyclo-CH2[Sn(Cl2)CH2Si(Me2)]2OCl]- upon addition of [(Ph3P)2N]+Cl- . Also reported are the synthesis and structure of [K(dibenzo[18]crown-6)]+[cyclo-CH2(Sn(Cl2)CH2Si(Me2)]2OF]-, the first completely characterised organostannate with a C2SnCl2F- substituent pattern. No ring-opening polymerisation could be achieved for [cyclo-CH2[Sn(Cl2)CH2Si(Me2)]2O] or for its perphenylated derivative [cyclo-CH2[Sn(Ph2)CH2Si(Me2)]2O]. The reaction of [cyclo-CH2[Sn(Cl2)CH2Si(Me2)]2O] with Me3O+BF4- gave the tin-containing fluorosilane [CH2[Sn(Cl2)CH2Si(F)Me2]2], in which the Si-F bond is activated by intermolecular Si-F...Sn interactions in the solid state.     

SCF MO CI perturbation calculations of inner shell and valence shell vertical ionization potentials

A CI method for calculating inner and valence shell vertical ionization potentials is presented. It is based on ab initio SCF MO calculations for the neutral closedshell ground state followed by CI perturbation calculations for the ground and ion states including all spin and symmetry adapted singly and doubly excited configurations with respect to the main configurations of the state of interest. The state energy is computed by performing a CI calculation for a set of selected configurations, and then adding the contributions of the remaining configurations as estimated by second order Brillouin-Wigner perturbation theory. The use of the same set of MO's for all states together with the CI perturbation method makes the method rather rapid. The numerical results are, in spite of the limited Gaussian basis sets used, in good agreement with experiment.     

Preparation,Structure, and Properties of All Possible Cyclic Dimers (Diolides) of 3-Hydroxybutanoic Acid

In connection with the proposed structure of a trans-membrane cellular ion channel consisting of a complex between poly[(R)-3-hydroxy butanoate] (P(3-HB)) and calcium polyphosphate, CaPP_i (ca. 150 units each), which is supposed to contain s-cis-bonds or even more highly strained ester conformations, we have prepared and studied the properties of the cyclic dimer of 3-HB, the diolide 1 . All possible forms of 1 , the rac-, the meso-, and the enantiomerically pure (R,R)- and (S,S)-compounds were prepared, purified, and characterized. The synthesis (Scheme 1) started from dimethyl succinate with the key step being the Baeyer-Villiger oxidation of the rac- and meso-2,5-dimethylcyclohexane-1,4-diones 5 . The rac-diolide 1 was resolved by preparative chromatography on a Chiralcel OD column (Fig.1). The crystal structures of rac- 1 (Fig.3) and of meso- 1 (Fig.5) were determined by X-ray diffraction: the diolides 1 contain s-cis-ester bonds and an ester group with a conformation half way to the transition state of rotation (Fig.2). Strain energies for the diolides 1 of up to 17.8 kcal/mol are suggested. Accordingly, these compounds show reactivities similar to those of carboxylic-acid anhydrides or even acid chlorides. They cannot be chromatographed on silica gel, and they react with primary, secondary, and tertiary alcohols, and with amines to form derivatives of open chain 3-HB ‘dimers’, hydroxy acids 6 , esters 7 , and amides 8 (Scheme 2). The rate of acid-catalyzed ring opening of the diolides 1 with alcohols has been measured (Fig.6 and 7). From the results described, we conclude that it is unlikely for strained and reactive ester conformations to occur as part of ion channels through phospholipid bilayers of cells.     

Spin delocalization in 1-heteroallyl monoradicals as a measure of radical stabilization by heterovinyl substituents assessed through the EPR-spectral zero-field D parameter of 1,3-cyclopentanediyl triplet diradicals

The EPR-spectral zero-field splitting parameter D of the localized heterovinyl-substituted 1,3-cyclopentanediyl triplet diradicals T, generated in a 2-methyltetrahydrofuran (MTHF) glass matrix at 77 K through the photochemical deazetation of the corresponding azoalkanes 1-13, is a quantitative measure of the spin-density (rho) variation by the substituents at the radical site in the 1-heteroallylic radicals. From these data, the radical-stabilizing ability of a variety of nitrogen-containing groups has been assessed, which includes imino and hydrazonyl functionalities. The radical stabilization in the heteroallylic radical fragment follows the order X = O < NMe < CH2 < CHMe < NOH approximately NOMe < NNHCHO approximately NNHC(O)NH2 < NPh approximately NNMe2 < NNH2 < CHPh < NNHPh. The lowest D values have been found for the hydrazonyl-substituted derivatives, which implies the lowest spin density at the carbon center and, thus, the most efficacious radical stabilization through spin delocalization. This superdelocalization may be rationalized in terms of nitrogen-centered radical-cationic structures. Localization of the spin at the terminal atom is resisted through the electronegativity effect (O < N < C).     

Ex vivo Application of δ-Aminolevulinic Acid Induces High and Specific Porphyrin Levels in Human Skin Tumors: Possible Basis for Selective Photodynamic Therapy

Abstract— In photodynamic therapy with topically applied δ-aminolevulinic acid porphyrins are acting as photosensitiz-ers. The profile of porphyrin metabolites in normal or in neoplastic skin after administration of δ-aminolevulinic acid has not been determined in detail yet. Thus, to study porphyrin biosynthesis in human skin an organ culture model was developed. Explant pieces of normal skin, ker-atoacanthoma, and basal cell carcinoma were incubated with 1 niM δ-aminolevulinic acid for 36 h. Levels of δ-aminolevulinic acid, porphyrins and porphyrin metabolites were measured in tissues and supernatants. After incubation with δ-aminolevulinic acid, higher porphyrin levels were demonstrated in tumors as compared to normal skin. In supernatants, most of formed porphyrins, preferentially highly carboxylated porphyrin metabolites, were measured. The pattern of synthesized porphyrins differed between normal and neoplastic skin explants. In tissues of basal cell carcinomas protoporphyrin was preferentially shown and tissues of keratoacanthomas were characterized by a predominance of coproporphyrin as compared to normal skin. The results show that explant cultures offer an easy approach to examine the porphyrin biosynthesis of various tissues. The tumor-specific δ-aminolevulinic acid metabolism indicates additional porphyrin metabolites such as coproporphyrin apart from protoporphyrin as effective photosensitizers and may offer a novel approach to tumor-selective photodynamic damage.