Cross-channel coupling in positron-atom scattering

Coupled-state calculations including positronium channels are reported for positron scattering by atomic hydrogen, lithium and sodium. Integrated cross sections and total cross sections are presented for all three atoms. For lithium differential cross sections are also given. Throughout, comparison is made between results calculated with and without inclusion of the positronium channels. S-wave cross sections for positron scattering by atomic hydrogen in the Ps(1s, 2s, 2p)+H(1s, 2s, 2p) approximation show the high energy resonance first observed by Higgins and Burke in the coupled-static approximation. This resonance has now moved up to 51.05 eV and narrowed in width to 2.92 eV. Other pronounced structure is seen in the S-wave cross sections between 10 and 20 eV; it is tentatively suggested that this structure may be due to the formation of a temporary pseudo-molecular collision complex. Results calculated in the Ps(1s, 2s, , 2p, ,+H(1s, 2s, , 2p, approximation show convergence towards accurate values in the energy region below and in the Ore gap. Contrary to previous work on lithium using only an atomic basis, it is found that coupling to the 3d state of lithium is not so important when positronium channels are included; this is because a mixed basis of atom and positronium states gives a more rapidly convergent approximation than an expansion based on atom states alone. The threshold behaviour of the elastic cross section and the Ps(1s) formation cross section for lithium is investigated. Results in the Ps(1s, 2s, 2p)+Na(3s, 3p) approximation for sodium show good agreement with the total cross section measurements of Kwan et al.     

Continuous chirality measures in transition metal chemistry

The definition of the continuous chirality measure(CCM) is provided and its applications are summarized in this tutorial review, with special emphasis on the field of transition metal complexes. The CCM approach, developed in recent years, provides a quantitative parameter that evaluates the degree of chirality of a given molecule. Many quantitative structural correlations with chirality have been identified for most of the important families of metal complexes. Our recent research has shown that one can associate the chirality measures with, e.g., enantioselectivity in asymmetric catalysis. We also explore a fragment approach to chirality in which we investigate which part of a molecule is responsible for the chirality-associated properties of a given family of compounds.     

Organopolysiloxanes as Chemically Sensitive Coatings for Optical Fibers

Various types of UV-curable organically modified siloxanes have been synthesized by the sol-gel method with the aim of fabricating chemically sensitive coatings for silica optical fibers. The refractive index of the coating material can be tailored in the range from 1.46 to 1.56 and sensitivity towards CO2 is achieved by incorporation of amino groups. The interaction of the cured layers with CO2 or with hydrocarbons has been studied in immersion experiments. Both the reaction of CO2 with incorporated amino groups and the penetration of hydrocarbons into the layer induce changes of the light absorption coefficient and the refractive index of the coating which are detected by measuring the output light intensity from the fiber.     

Ruthenium Cluster Chemistry with Ph2PC6H4-4-C≡CH

The new phosphines Ph₂PC₆H₄-4-CCR [R=SiMe₃ (1), H (2)] have been used to prepare Ru₃(CO)₉(Ph₂PC₆H₄-4-CCSiMe₃)₃ (4) and Ru(CCC₆H₄-4-PPh₂)(PPh₃)₂(-C₅H₅) (3), respectively, the latter with a pendent phosphine. Reaction of 4 with carbonate or fluoride affords Ru₃(CO)₉(Ph₂PC₆H₄-4-CCH)₃ (5) with pendent terminal alkynyl groups, the identity of which was confirmed by a structural study. Reaction of 5 with [Ru(NCMe)(PPh₃)₂(-C₅H₅)]PF₆ or reaction of Ru₃(CO)₁₂ with 3 gives Ru₃(CO)₉{(Ph₂PC₆H₄-4-CC)Ru(PPh₃)₂(-C₅H₅)}₃ (6). Complexes 3–6 have been studied by cyclic voltammetry. Proceeding from Ru₃(CO)₁₂ to 4 or 5 shifts the cluster-centred reduction to more negative potential and affords facile cluster-centred oxidation. Proceeding from 4/5 and 3 to 6 results in similarly-located cluster-centred reduction and peripheral ruthenium-centred oxidation, but results in a lack of observable cluster-centred oxidation. Crystal data for 5·C₆H₁₄: space group P¯1, a=12.760(1) Å, b=17.077(1) Å, c=17.924(2) Å, =108.656(5)°, =96.344(5)°, =93.523(5)°, V=3658.4(6) ų, Z=2, R=0.078, R_w=0.105 for 5008 reflections [I>2.00(I)].     

Palladium-tetraphosphine complex: an efficient catalyst for the coupling of aryl halides with alkynes

The cis,cis,cis-1,2,3,4-tetrakis(diphenylphosphinomethyl)-cyclopentane-[PdCl(eta3-C3H5)]2 system catalyses the coupling of aryl halides with alkynes with very high ratios of substrates-catalyst in good yields; a turnover number of 2600000 can be obtained for the reaction of 4-trifluoromethylbromobenzene with phenylacetylene in the presence of this catalyst.     

Comprehensive study of the methyl effect on the solvolysis rates of bridgehead derivatives

The effect of a bridgehead methyl group on the hydride ion affinity in the gas phase of bicyclo[1.1.1]pent-1-yl (1+), 1-norbornyl (3+), cubyl (5+), 1-adamantyl (7+), bicyclo[2.2.2]oct-1-yl (9+),and bicyclo[3.1.1]hept-1-yl (11+) cations has been studied using density functional theory and ab initio methods. It is concluded that the methyl group always increases the stability of the substituted cations. The effect of the solvent on the stability of methyl-substituted cations in relation to the unsubstituted cations has been studied using the polarizable continuum model of the self-consistent reaction field theory. In the case of rearranging cations, the nucleophilic assistance of the solvent is determined by means of the interaction energy of the corresponding water complexes. It is concluded that the solvent causes the relative stabilization of the parent cations. As a consequence, most of the methyl-substituted bridgehead derivatives show a lower solvolysis rate than the corresponding unsubstituted compounds. A nonqualitative explanation of the methyl effect on the relative stability of bridgehead cations in both gas phase and solution is given for the first time. The ratios of solvolysis products in the case of rearranging bridgehead cations have also been computed from the relative stability of the intermediate water complexes.     

K-theory for the leaf space of foliations by Reeb components

The K-theory of the C¹-algebra $\text{C}{}^1\text{(V, F)}$ associated to C^∞-foliations (V, F) of a manifold V in the simplest non-trivial case, i.e., dim V = 2, is studied. Since the case of the Kronecker foliation was settled by Pimsner and Voiculescu (J. Operator Theory4 (1980), 93–118), the remaining problem deals with foliations by Reeb components. The K-theory of $\text{C}{}^1\text{(V, F)}$ for the Reeb foliation of S³ is also computed. In these cases the C¹-algebra $\text{C}{}^1\text{(V, F)}$ is obtained from simpler C¹-algebras by means of pullback diagrams and short exact sequences. The K-groups $\text{K}{}_1\text{(C}{}^1\text{(V, F))}$ are computed using the associated Mayer-Vietoris and six-term exact sequences. The results characterize the C¹-algebra of the Reeb foliation of $\text{T}$² uniquely as an extension of C(S¹) by C(S¹). For the foliations of $\text{T}$² it is found that the K-groups count the number of Reeb components separated by stable compact leaves. A C^∞-foliation of $\text{T}$² such that K₁(C¹($\text{T}$², F)) has infinite rank is also constructed. Finally it is proved, by explicit calculation using (M. Penington, “K-Theory and C¹-Algebras of Lie Groups and Foliations,” D. Phil. thesis, Oxford, 1983), that the natural map $\text{μ: K}{}_1\text{,}{}_{\mathrm{\tau }}\text{(BG) → K}{}_1\text{(C}{}^1\text{(V, F))}$ is an isomorphism for foliations by Reeb components of $\text{T}$² and S³. In particular this proves the Baum-Connes conjecture (P. Baum and A. Connes, Geometric K-theory for Lie groups, preprint, 1982; A. Connes, Proc. Symp. Pure Math.38 (1982), 521–628) when V = $\text{T}$².     

E- and Z-isomerism of 2-acetylthiophene oximes

A study on the oximation of a number of 2-acetylthiophenes in order to ascertain the validity of contradictory results previously described is reported. The fact that the steric hindrance is smaller in 2-acetylthiophenes unsubstituted at position-3 than in acetylbenzenes allows in these cases the formation of Z oximes, which even can predominate on the E oximes in the case of a + M substitution at position-5. In the paper is also shown that the E/Z ratio of 2-acetylthiophene oximes can be deduced from the ¹H-nmr spectrum of the crude oxime mixture.     

Accumulation and photocytotoxicity of hypericin and analogs in two- and three-dimensional cultures of transitional cell carcinoma cells

The aim of this study was to investigate the in vitro cellular accumulation, distribution and photocytotoxic effect of hypericin in two-dimensional (2-D) and three-dimensional (3-D) cultured RT-112 transitional cell carcinoma cells of the bladder. In addition, two iodinated derivatives of hypericin were incorporated to investigate whether these analogs, with their increased lipophilicity and heavy-atom effect, display a different biological behavior and optimized photodynamic effect. The results indicate that hypericin and mono-iodohypericin behave similarly in terms of cellular accumulation, spheroidal distribution and photocytotoxic effect. In contrast, di-iodohypericin concentrated to a higher extent in monolayers and spheroids, but the accumulation was restricted to the outermost part of the spheroid. An inverse correlation therefore seems to exist between the extent of cellular uptake under 2-D conditions and the penetration of the compounds in multicellular systems. Moreover, a less pronounced photocytotoxic effect was observed for di-iodohypericin in both 2-D and 3-D cell culture systems. It can be concluded that iodinated derivatives of hypericin do not show an increased cytotoxic effect upon irradiation in either monolayers or spheroids. Moreover, this study shows that when new photosensitizers are preclinically developed, the use of 3-D cell aggregates is critical for a correct evaluation of their efficacy.