Crystal structures of two substituted biphenyl derivatives: 5,5′-di t-butyl-2-2′-biphenyldiol and 5,5′-dimethyl-2,2′-biphenyldiol

5,5-Di t-butyl-2,2-biphenyldiol (I), C₂₀H₂₆O₂, crystallizes in the orthorhombic space group P2₁2₁2₁ with a = 18.243(2), b = 9.947(2), c = 9.685(3) Å, and Z = 4; 5,5-dimethyl-2,2-biphenyldiol (II), C₁₄H₁₄O₂, crystallizes in the monoclinic space group P2₁/c with a = 9.959(2), b = 7.932(3), c = 15.392(2) Å, = 105.43(2)°, and Z = 4. The aromatic rings are tilted by 52.7(1) and 43.8(1)° to each other in compounds (I) and (II), respectively. Strong intra- and inter-molecular H-bonds connect the molecules in the crystals.     

Inhomogeneous nature of UV absorption bands of bulk and surface oxygen-deficient centers in silica glasses

Photochemical and photoluminescence studies of oxygen-deficient centers stabilized in the bulk and on the surface of silica glasses clearly demonstrate the inhomogeneous nature of the absorption and luminescence spectra of oxygen-deficient centers. The conclusion is drawn that the inhomogeneity of the absorption spectra is due to the dispersion of the energy of the S₀-S₁ transition, while the inhomogeneity of the luminescence spectra is due to the dispersion of the energy barrier of intersystem crossing. The inhomogeneous nature of the oxygen-deficient centers in silica glasses is assumed to be caused by a small dispersion in the geometrical parameters of different groups of centers with similar chemical properties.     

Antimony(III) fluoride: inclusion complexes with crown ethers

Four crystalline molecular complexes between antimony(III) fluoride and 18-membered crown ethers have been obtained and their structures investigated by single crystal X-ray diffraction techniques: [18-crown-6·SbF₃], C₁₂H₂₄F₃O₆Sb,P2₁2₁2₁,a=8.328(4),b=11.573(4),c=18.094(4),V=1744(1)³,Z=4; [benzo-18-crown-6·SbF₃], C₁₆H₂₄F₃O₆Sb,P2₁/n,a=10.490(2),b=13.714(1),c=13.442(2), =101.94(1)°,V=1892(1)³,Z=4; [cis-syn-cis-dicyclohexano-18-crown-6·SbF₃·CH₃OH], C₂₁H₄₀F₃O₇Sb,P2₁/n,a=8.270(4),b=23.386(3),c=12.772(1), =96.31(2)°,V=2455(1)³,Z=4; [cis-anti-cis-dicyclohexano-18-crown-6·SbF₃], C₂₀H₃₆F₃O₆Sb,Pna2₁,a=21.091(8),b=12.829(5),c=8.437(3),V=2283(2)³,Z=4. All species are the perching-type complexes with the antimony fluoride above the cavity and the metal lone pair pointed toward the center of the crown ring. The antimony atom interacts with all six crown oxygen atoms with Sb–O distances of 2.837(2)–3.344(2) . The antimony atom is displaced from the least square plane of the crown oxygen atoms at the distances of 1.288–1.383 .     

Palladium-catalyzed direct heck arylation of dual pi-deficient/pi-excessive heteroaromatics. Synthesis of C-5 arylated imidazo[1,5-a]pyrazines

A general and efficient synthesis of 5-aryl imidazo[1,5- a]pyrazines by palladium-catalyzed coupling of the corresponding 8-substituted derivatives with aryl halides is described. The scope of this new reaction for the imidazo[1,5- a]pyrazine ring system was explored using three readily available 8-substituted precursors, X = NH2, NMe2, and OMe, as well as 8-aryl derivatives, X = Ar'. On the basis of these results as well as studies using a deuterated derivative, a Heck-like mechanism is proposed for this transformation.     

Direct C-glycosylation by indium-mediated alkynylation on sugar anomeric position

Indium-mediated alkynylation reaction was studied for the direct preparation of C-glycosides. Easily available starting sugar derivatives with an acetyl group at the anomeric position were tested as electrophiles toward alkynylindium reagents under Barbier conditions. Good yields and stereoselectivities were observed during the reaction. The alkynylation was applied to the synthesis of an alpha-(1-->6)-C-disaccharide analogue of isomaltoside.     

Peptide cysteine thiyl radicals abstract hydrogen atoms from surrounding amino acids: the photolysis of a cystine containing model peptide

Peptide cysteine thiyl radicals were generated through UV-photolysis of disulfide precursors, in order to follow intramolecular reactions of those radicals with neighboring amino acids. When reactions were carried out in D(2)O, there was a significant incorporation of deuterium specifically into the C(alpha)-H bonds of glycine residues in positions i+1 and i-1 to the Cys residue, indicating a fast reversible H-atom transfer. This H-atom transfer occurred prior to the formation of final, nonradical products including free thiol, thioaldehyde, and aldehyde. Such fast H-atom transfer is relevant to biologic conditions of oxidative stress and to the stabilization of proteins against oxidation, where the formation of carbon-centered radicals in proteins may lead to fragmentation, intramolecular cross-linking, aggregation and/or epimerization.     

Positional disorder manifested as compositional in a pseudo‐C2‐symmetrical Pd complex

The title compound {2‐[3,5‐bis(trifluoromethyl)‐1H‐pyrazol‐1‐ylmethyl]‐6‐(3,5‐dimethyl‐1H‐pyrazol‐1‐ylmethyl)pyridine}methylpalladium(II) tetrakis[3,5‐bis(trifluoromethyl)phenyl]borate, [Pd(C₁₈H₁₈F₆N₅)][B(C₈H₃F₆)₄], crystallizes as discrete cations and anions. The cation possesses a pseudo‐twofold axis about which positional disorder of the tridentate ligand is exhibited. The four substituents on the two pyrazole rings exhibit CH₃/CF₃ disorder, while all other atoms are ordered. Thus, this disorder can be conveniently described `locally' as compositional, while `globally' for the entire tridentate ligand it is positional. The anion also exhibits typical rotational positional disorder in three of the CF₃ groups. All disordered CF₃ groups were modeled with idealized C_3v geometry.     

Uniqueness of large radial solutions and existence of nonradial solutions for a superlinear Dirichlet problem in annulii

Here we establish the existence of infinitely many nonradial solutions for a superlinear Dirichlet problem in annulii. Our proof relies on estimating the number of radial solutions having a prescribed number of nodal regions. We prove that, for k>0 large, there exist exactly two radial solutions with k nodal regions (connected components of ). The problem need not be homogeneous.     

Sesquitransitive and Localizing Operator Algebras

An algebra of operators on a Banach space X is said to be transitive if X has no nontrivial closed subspaces invariant under every member of the algebra. In this paper we investigate a number of conditions which guarantee that a transitive algebra of operators is “large” in various senses. Among these are the conditions of algebras being localizing or sesquitransitive. An algebra is localizing if there exists a closed ball B ∌ 0 such that for every sequence (x _n ) in B there exists a subsequence and a bounded sequence (A _k ) in the algebra such that converges to a non-zero vector. An algebra is sesquitransitive if for every non-zero z ∈ X there exists C > 0 such that for every x linearly independent of z, for every non-zero y ∈ X, and every there exists A in the algebra such that and ||Az|| ≤ C||z||. We give an algebraic version of this definition as well, and extend Jacobson’s density theorem to algebraically sesquitransitive rings. The second and the third authors were supported by NSERC.