Comparison of Adsorption Probabilities of O(2) and CO on Copper Cluster Cations and Anions

Reactions of size-selected copper cluster cations and anions, Cu(n)(±), with O(2) and CO have been systematically investigated under single collision conditions by using a tandem-mass spectrometer. In the reactions of Cu(n)(±) (n = 3-25) with O(2), oxidation of the cluster is prominently observed with and without releasing Cu atoms at the collision energy of 0.2 eV. The reactivity of Cu(n)(+) is governed to some extent by the electronic shell structure; the relatively small reaction cross sections observed at n = 9 and 21 correspond to the electronic shell closings, and those at odd sizes in n ≤ 16 match with the clusters having no unpaired electron. On the other hand, the reactivity of Cu(n)(-) exhibits no remarkable decrease by the electronic shell closings and the even-numbered electrons. These behaviors may be due to an influence of the electron detachment of the reaction intermediate, Cu(n)O(2)(-). Both the cations and anions show the dominant formation of Cu(n-1)O(2)(±) in n ≤ 16 and Cu(n)O(2)(±) in n ≥ 17 in the experimental time window. By contrast, Cu(n)(-) (n = 3-11) do not react with CO at the collision energy of 0.2 eV, while Cu(n)(+) (n = 3-19) adsorb CO though the cross sections are relatively small. The difference in the reactivity between the charge states can be understood in terms of the frontier orbitals of the Cu cluster and O(2) or CO.     

Silver complexes with unsaturated thiacrown ethers: inclusion behavior of conformationally restricted macrocycles

The reactions of 18- and 21-membered unsaturated thiacrown ethers, 18-UT-6 and 21-UT-7, with CF(3)COOAg in acetone afforded novel silver(I) complexes Ag(I)(18-UT-6)(CF(3)COO) and Ag(I)(2)(21-UT-7)(CF(3)COO)(2), respectively. The crystal structure of Ag(I)(18-UT-6)(CF(3)COO) shows that the silver atom occupies the cavity of the 18-UT-6 and the geometry around the silver atom has a distorted five-coordinate square pyramidal arrangement. The crystal structure of Ag(I)(2)(21-UT-7)(CF(3)COO)(2) shows that the two silver atoms and all sulfur atoms are nearly coplanar and the two trifluoroacetate groups are located at the opposite sides of the plane. The stoichiometry for the complexation of 15-UT-5, 18-UT-6, and 21-UT-7 with CF(3)COOAg in solution was examined by (1)H NMR measurement. The titration plots of 15-UT-5 and 21-UT-7 show a distinct inflection point at 1:1 and 2:1 metal/macrocycle ratios, respectively, whereas the plot of 18-UT-6 gradually changes at the range of 1:1 to 2:1. From these results, 15-UT-5 and 21-UT-7 were found to show inclusion selectivity for number of silver ions, respectively, whereas 18-UT-6 showed low selectivity for the inclusion number of metals. Comparison of the oxidation and reduction potentials of the silver(I) complexes with those of free macrocycles and CF(3)COOAg revealed that unsaturated thiacrown ethers become difficult to be oxidized by complexation with CF(3)COOAg, and CF(3)COOAg becomes difficult to be reduced by complexation with unsaturated thiacrown ethers.     

The role of carotenoids in the photoadaptation of the brown-colored sulfur bacterium Chlorobium phaeobacteroides

The brown-colored sulfur bacterium Chlorobium (Cb.) phaeobacteroides 1549 (new name, Chlorobaculum limnaeum 1549) contains many kinds of carotenoids as well as bacteriochlorophyll (BChl) e. These carotenoids were identified with C18-high-performance liquid chromatography, absorption, mass and proton nuclear magnetic resonance spectroscopies and were divided into two groups: the first is carotenoid with one or two phi-end groups such as isorenieratene and beta-isorenieratene and the second is carotenoid with one or two beta-end groups such as p-zeacarotene, beta-carotene and 7,8-dihydro-beta-carotene. The latter 7,8-dihydro-beta-carotene was found to be a novel carotenoid in nature. OH-gamma-Carotene glucoside laurate and OH-chlorobactene glucoside laurate were also found as minor components. The distribution of BChl e homologs in Cb. phaeobacteroides cultivated under various light intensities did not change, but the carotenoid to BChl e ratio changed markedly: carotenoid with the phi-end group maintained the same ratio to BChl e, whereas that with the beta-end group increased with increasing light intensity. The cells cultured under low-light intensity contained more phi-end carotenoids than beta-end. In Cb. phaeobacteroides the wavelength of the Qy band of BChl e aggregates did not change. We suggested that Cb. phaeobacteroides photoadapts to light intensity by changing the carotenoid composition.     

Increasing fluorous partition coefficients by solvent tuning

Low partition coefficients of fluorous components have been a persistent problem in liquid-liquid separations using perfluoroalkanes as the fluorous phase. Solvent tuning of both the nonfluorous and the fluorous phase dramatically enhances the partitioning of light or polar fluorous molecules into the fluorous liquid phase, while minimally effecting partition coefficients of nonfluorous molecules. These findings suggest an expanded scope for liquid-based separations in fluorous biphasic catalysis, fluorous-tagged reagents, fluorous-supported oligomer synthesis, and related areas. [reaction: see text]     

Dislocations in silicon observed by high-voltage,high-resolution electron microscopy

Dislocations in deformed silicon crystals have been studied by high-resolution electron microscopy with the axial illumination along the [110] direction using a 1 MV electron microscope. Extended 60 dislocations, Z-shape faulted dipoles and stacking fault tetrahedra were observed in atomic level. The results demonstrated the potentiality of highvoltage, high-resolution electron microscopy for the study of atomic configurations of structural defects.     

Chemical modification of hydroxyl groups of poly(vinyl alcohol) by a glycosidation reaction

A new procedure for chemical modification of poly(vinyl alcohol) (PVA) was established by a glycosidation reaction of hydroxyl groups in PVA with triacetylated sugar oxazoline 1 . ¹H and ¹³C NMR analyses indicated that triacetylated N‐acetyl‐D‐glucosamine (GlcNAc) was introduced onto a PVA backbone selectively via a β‐O‐glycoside linkage. Deacetylation of triacetylated GlcNAc‐substituted PVA 2 resulted in GlcNAc‐substituted PVA 3 in good yield. These modified PVAs 2 and 3 exhibited solubilities and thermal properties different from the original PVA.