One-dimensional polymers based on [{CpMo(CO)2}2(mu,eta2-P2)]: solid-state conformation analysis by NMR spectroscopy and DFT calculations

Reaction of the complex [{CpMo(CO)2}2(mu,eta2-P2)] (1) with CuI halides leads to the quantitative formation of the novel one-dimensional linear polymers [CuX{Cp2Mo2(CO)4(mu,eta2:eta1:eta1-P2)}](infinity) (X=Cl (4), Br (5), I (6)). The same products 4 and 5 were obtained when 1 was treated with CuCl2 and CuBr2, respectively. The solid-state structures are compared and their remarkable influence on the respective (31)P magic angle spinning (MAS) NMR spectra is interpreted with the help of density functional theory (DFT) calculations on the model compounds [{(CuX)2{Cp2Cr2(CO)4(mu,eta(2):eta1:eta1-P2)}2}3] (X=Cl (4 a), Br (5 a)) in which the molybdenum atoms are replaced by their lighter homologue chromium.     

Studies on werner clathrates. Part 131. Selective criteria in werner clathrates. Six crystal structures with bis(isothiocyanato)tetra(4-vinylpyridine)nickel(II) as host

This paper addresses the general question: what are the significant guest properties selected by this host when interacting with guest molecules in the liquid phase, resulting in cocrystallization of the host and guest? In particular, to what extent do π electrons in a guest molecule effect its potential as a guest? Werner clathrates of the host [Ni(NCS)₂(4-ViPy)₄] with mixtures of tetrahydrofuran (THF) and cyclic hydrocarbons as guests have been synthesised and their structures elucidated. Clathrate (1): [Ni(NCS)₂(4-ViPy)₄](1.78 THF)(0.22 cyclohexane), crystallizes in the orthorhombic space groupP _bcn a=9.976(6),b=20.630(25),c=19.861 (4) Å,V=4087ų,Z=4,R=0.087 for 1461 reflections; (2): [Ni(NCS)₂(4-ViPy)₄](1.76 THF)(0.24 cyclohexene),P _bcn ,a=9.987(7),b=20.614(4),c=19.898(4)Å,V=4096ų,Z=4,R=0.084 for 1304 reflections; (3): [Ni(NCS)₂(4-ViPy)₄](0.48 THF)(0.52 1,3-cyclohexadiene), tetragonalI4₁/a,a=16.898(3),b=16.898(3),c=26.463(6)Å,V=7556ų,Z=8,R=0.120 for 1698 reflections; (4): [Ni(NCS)₂(4-ViPy)₄](0.36 THF)(1.04 1,4-cyclohexadiene),I4₁/a,a=16.986(4),b=16.986(4),c=25.896(15)Å,V=7472ų,Z=8,R=0.103 for 2025 reflections; (5): [Ni(NCS)₂(4-ViPy)₄](0.35 THF)(1.05 benzene),I4₁/a,a=17.102(10),b=17.102(10),c=25.498(8)Å,V=7458ų,Z=8,R=0.118 for 2200 reflections; (6): [Ni(NCS)₂(4-ViPy)₄](3 benzene), triclinicP1,a=10.432(24),b=11.155(9),c=21.581(7)Å, α=78.70(5), β=82.60(7), γ=74.09(13)°,V=2361ų,Z=2,R=0.078 for 3427 reflections. Host-guest ratios and, for mixtures of guests, guest1/guest2 ratios, were elucidated by density and NMR. We show that the conformational freedom of the substituted pyridines is not the primary reason for the clathrating ability of Werner hosts. All six structures show no host-guest interaction at the level of van der Waals interactions. As non-bonding interactions are not observed between the host and guest, this study shows that the above host's selectivity by enclathration of particular guest molecules cannot be accounted for by solid state structural analysis.     

Polypeptide and carbohydrate structure of an intact glycoprotein from Raman optical activity

A vibrational Raman optical activity (ROA) study of bovine alpha1-acid glycoprotein (AGP) is reported. Using the recently introduced ChiralRAMAN instrument from BioTools, Inc., a high-quality ROA spectrum of AGP, measured as a small circularly polarized component in the scattered light, was obtained in the range of 200-1800 cm-1. Comparison with the ROA spectra of beta-lactoglobulin and N,N'-diacetylchitobiose reveals features consistent with previous suggestions that the peptide component of AGP has a structure based on the lipocalin fold, and that the first two glycosidic links after the N-links to asparagine in the pentasaccharide core are of the beta(1-4)-type. A detailed analysis of the band patterns may ultimately provide information on the more conformationally heterogeneous and functionally crucial peripheral oligosaccharide segments. Hence, information about both the polypeptide and carbohydrate components may be obtained from the ROA spectra of intact glycoproteins.     

Self-assembled polynuclear clusters derived from some flexible polydentate dihydrazide ligands

Polynuclear manganese(II), cobalt(II)/(III), iron(II)/(III) and nickel(II) complexes of a group of flexible polydentate dihydrazone ligands, based on pyridine-2,6-dipicolinic (A), oxalic (B) and malonic (C) subunits are described. Structural details are reported for the linear dinuclear complexes [Ni2(2poap)2(H2O)2](NO3)4 . 2CH3OH . 2.5H2O (1), [Mn2(pttp)(NO3)2(CH3OH)2(H2O)2](NO3)2 . H2O (2) and [Mn2(mapttp)2(NO3)2(H2O)2](NO3)2 . 10H2O (3), a square tetranuclear complex [Co4(pttp)4]Br6 . 9H2O (4), a tetranuclear tetrahedral complex [Ni4(pttp)6](BF4)6F2 . 14H2O (7), and a mixed spin state tetranuclear Ni(II) complex [(2pyoap)2Ni4(CH3OH)4] . 1.5CH3OH (10), with a diamond-like arrangement of metal ions. The paramagnetic metal centers are well separated in each case, leading to weak antiferromagnetic coupling or non-existent spin exchange.     

The formation and reduction of anodic films on electrodeposited ruthenium

The formation and reduction of anodic films on bright ruthenium was investigated using substrates prepared by electrodeposition onto gold-plated platinum from a commercial ruthenium bath operated at 70°C. Anodic films formed on the ruthenium may be reduced by maintaining the electrode at potentials below 0.2 V. The reduction behaviour was markedly affected by the anodization potential and, at short times, by the period of anodization. The bell-shaped cathodic current-time curves observed with films produced at potentials in the region of 1.2 V, suggest that the process in this case involves nucleation of reduction centres on a relatively stable surface layer. The influence of potential, time, and both the concentration and nature of the electrolyte on the extent of anodic film formation was investigated. The results are discussed in terms of the formation of stable phase oxides in the relatively thick anodic film produced on the ruthenium surface.     

Synthesis and chiral HPLC analysis of the dibenzyltetrahydrofuran lignans,larreatricins, 8'-epi-larreatricins, 3,3'-didemethoxyverrucosins and meso-3,3'-didemethoxynectandrin B in the creosote bush (Larrea tridentata): evidence for regiospecific control of coupling

The creosote bush (Larrea tridentata) lignans are linked via 8-8' bonds, with the simplest apparently being E-p-anol derived. Of the latter, four of the six theoretically possible diastereoisomers were isolated, namely (-)-larreatricin, (-)-8'-epi-larreatricin, meso-3,3'-didemethoxynectandrin B and the new compounds, (+)- and (-)-3,3'-didemethoxyverrucosins. Following synthesis of each in either racemic or meso form, and chiral HPLC separation of the antipodes of the racemates, it was established that naturally occurring (-)-larreatricin and (-)-8'-epi-larreatricin were present in 92 and 98% enantiomeric excess, respectively, whereas 3,3'-didemethoxyverrucosin was essentially racemic and 3,3'-didemethoxynectandrin B was in the meso-form. The evidence suggests that formation of these lignans occurs under regiospecific, rather than stereoselective, coupling control. This contrasts with laccase-catalyzed "random" coupling of E-p-anol in vitro which generates the corresponding racemic 8-8', 8-3' and 8-O-4' linked dimeric moieties.     

Cubical sperner lemmas as applications of generalized complementary pivoting

Two cubical versions of Sperner's lemma, due to Kuhn and Fan, are proved constructively without resorting to a simplicial decomposition of the cube, presenting examples of generalized complementary pivoting discussed by Todd (Math. Programming6 (1974)). The first version is essentially equivalent to Sperner's lemma in that it implies Brouwer's fixed point theorem, thereby answering a question raised by Kuhn (IBM J. Res. Develop.4 (1960)). The second has the property that although the structure is that of generalized complementarity, there is a uniquely defined path or algorithm associated with it. The basic structure used is a cubical decomposition of the cube, a special case of a cubical pseudomanifold, presented by Fan (Arch. Math.11 (1960)). Given the existence of a constructive algorithm for Sperner's lemma (see Cohen, J. Combinatorial Theory2 (1967)) and its generalization by Fan J. Combinatorial Theory2 (1967)) allied to the large amount of recent progress in complementary pivot theory, resulting in particular from the works of Lemke (Manage. Sci.11 (1965)) and Scarf (“The Computation of Economic Equilibria”) the computational attractions of a simplicial decomposition have become apparent. However, a cubical decomposition leads to certain advantages when a search for more than one “completely labeled” region is required, and no simplicial construction for the Fan lemma is known.     

Synthesis of Sequence-Selective C8-Linked Pyrrolo[2,1-c][1,4]benzodiazepine DNA Interstrand Cross-Linking Agents

An efficient convergent synthesis of a homologous series of C8-linked pyrrolobenzodiazepine dimers with remarkable DNA interstrand cross-linking activity and potent in vitro cytotoxicity is reported. The "amino thioacetal" cyclization procedure was used to produce the electrophilic DNA-interactive N10-C11 imine moiety during the final synthetic step. In order to construct the key A-ring fragments (9a-d), a versatile convergent approach has been developed to join two units of vanillic acid with alpha,omega-dihaloalkanes of varying length to provide the required bis(4-carboxy-2-methoxyphenoxy)alkanes while avoiding the formation of mixtures of monoalkylated and bisalkylated products.