Asymmetric induction in an intramolecular [2+2] photocycloaddition within chirally modified zeolite supercages

Photoirradiation of 1-cyano-2-(5-methyl-2-oxa-4-hexenyl)naphthalene, included in NaY zeolites along with chiral inductors, such as diethyl tartrate or phenylalaninol, gives an intramolecular [2+2] photocycloadduct with a maximum 15% ee. The degree of enantioselectivity was found to depend on the Si/Al ratio, the nature of the cations in the zeolites, the structure of the chiral inductors, and the molar ratio of substrate and chiral inductors.     

Synthesis of ruthenium tris(2,2′-bipyridine)-type complexes tethered to peptides at 5,5′-positions

Utilization of 5′-amino-2,2′-bipyridine-5-carboxylic acid allows molecular design of ruthenium tris(bipyridine)-type complexes bearing two different functional groups. In this study, a novel ruthenium tris(bipyridine) derivative bearing viologen and tyrosine as an electron acceptor and donor, respectively, is synthesized. This synthesis exemplifies the effectiveness of the molecular design for functionalizing ruthenium bipyridine-type complexes. The photophysical properties are discussed in comparison with a reference ruthenium complex which has neither the electron acceptor nor donor.     

The Average Degree of Minimally Contraction‐Critically 5‐Connected Graphs

An edge of a 5‐connected graph is said to be 5‐removable (resp. 5‐contractible) if the removal (resp. the contraction) of the edge results in a 5‐connected graph. A 5‐connected graph with neither 5‐removable edges nor 5‐contractible edges is said to be minimally contraction‐critically 5‐connected. We show the average degree of every minimally contraction‐critically 5‐connected graph is less than . This bound is sharp in the sense that for any positive real number ε, there is a minimally contraction‐critically 5‐connected graph whose average degree is greater than .     

Forbidden Triples Containing a Complete Graph and a Complete Bipartite Graph of Small Order

For a graph G and a set \({\mathcal{F}}\) of connected graphs, G is said be \({\mathcal{F}}\) -free if G does not contain any member of \({\mathcal{F}}\) as an induced subgraph. We let \({\mathcal{G} _{3}(\mathcal{F})}\) denote the set of all 3-connected \({\mathcal{F}}\) -free graphs. This paper is concerned with sets \({\mathcal{F}}\) of connected graphs such that \({\mathcal{F}}\) contains no star, \({|\mathcal{F}|=3}\) and \({\mathcal{G}_{3}(\mathcal{F})}\) is finite. Among other results, we show that for a connected graph T( ≠ K ₁) which is not a star, \({\mathcal{G}_{3}(\{K_{4},K_{2,2},T\})}\) is finite if and only if T is a path of order at most 6.     

A necessary and sufficient condition for the existence of a spanning tree with specified vertices having large degrees

Let G be a connected simple graph, let X?V (^G) and let f be a mapping from X to the set of integers. When X is an independent set, Frank and Gyárfás, and independently, Kaneko and Yoshimoto gave a necessary and sufficient condition for the existence of spanning tree T in G such that d _T (x) for all x ∈ X, where d _T (x) is the degree of x and T. In this paper, we extend this result to the case where the subgraph induced by X has no induced path of order four, and prove that there exists a spanning tree T in G such that d _T (x) ≥ f(x) for all x ∈ X if and only if for any nonempty subset S ? X, |N _G (S) ? S| ? f(S) + 2|S| ? ω _G (S) ≥, where ω _G (S) is the number of components of the subgraph induced by S.     

NMR spectroscopic characterization of inclusion complexes of hydroxy-substituted naphthalenes with native and modified β-cyclodextrins

The equilibrium constants (K) for the inclusion complexation of three kinds of β-cyclodextrins (β-CDs: native β-CD, heptakis(2,6-di-O-methyl)-β-CD, and 6-O-α-d-glucosyl-β-CD) with OH-substituted naphthalenes (2-naphthol, 2,3-dihydroxynaphthalene, and 2,6-dihydroxynaphthalene) were determined from the induced chemical shifts of NMR measurements for inclusion complexes: K = 188–1,250 mol^?1 dm³. The modified β-CDs form stable 1:1 inclusion complexes with OH-substituted naphthalenes, and the high stability of inclusion complexes of 2,6-dihydroxynaphthalene having a hydrophobic body and hydrophilic ends is shown. In addition, the structures of inclusion complexes were characterized by 2D ROESY NMR measurements. The differences in the structure of the inclusion complexes were observed for three kinds of naphthol guest molecules. Based on the results, the inclusion abilities enhanced by methylation of the OH groups at the CD rim or the side chain of branched β-CD are discussed.     

Is the 7/2(1)- isomer state of 43S spherical?

We report on the spectroscopic quadrupole moment measurement of the 7/2(1)(-) isomeric state in (16)(43)S(27) [E*=320.5(5) keV, T(1/2)=415(3) ns], using the time dependent perturbed angular distribution technique at the RIKEN RIBF facility. Our value, |Q(s)|=23(3) efm(2), is larger than that expected for a single-particle state. Shell model calculations using the modern SDPF-U interaction for this mass region reproduce remarkably well the measured |Q(s)|, and show that non-negligible correlations drive the isomeric state away from a purely spherical shape.     

Constituents from the bark of Tabebuia impetiginosa

Thirteen new phenolic glycosides were obtained by further study of constituents from the bark of Tabebuia impetiginosa (MART. ex DC) Standley (Bignoniaceae). The structures of these compounds were determined based on NMR, mass spectral and chemical evidence. Most of them have a glycosyl unit esterified by a benzoic acid derivative.