Ligand design for alkali-metal-templated self-assembly of unique high-nuclearity CuII aggregates with diverse coordination cage units: crystal structures and properties

The construction of two unique, high-nuclearity Cu(II) supramolecular aggregates with tetrahedral or octahedral cage units, [(mu(3)-Cl)[Li subset Cu(4)(mu-L(1))(3)](3)](ClO(4))(8)(H(2)O)(4.5) (1) and [[Na(2) subset Cu(12)(mu-L(2))(8)(mu-Cl)(4)](ClO(4))(8)(H(2)O)(10)(H(3)O(+))(2)](infinity) (2) by alkali-metal-templated (Li(+) or Na(+)) self-assembly, was achieved by the use of two newly designed carboxylic-functionalized diazamesocyclic ligands, N,N'-bis(3-propionyloxy)-1,4-diazacycloheptane (H(2)L(1)) or 1,5-diazacyclooctane-N,N'-diacetate acid (H(2)L(2)). Complex 1 crystallizes in the trigonal R3c space group (a = b = 20.866(3), c = 126.26(4) A and Z = 12), and 2 in the triclinic P1 space group (a = 13.632(4), b = 14.754(4), c = 19.517(6) A, alpha = 99.836(6), beta = 95.793(5), gamma = 116.124(5) degrees and Z = 1). By subtle variation of the ligand structures and the alkali-metal templates, different polymeric motifs were obtained: a dodecanuclear architecture 1 consisting of three Cu(4) tetrahedral cage units with a Li(+) template, and a supramolecular chain 2 consisting of two crystallographically nonequivalent octahedral Cu(6) polyhedra with a Na(+) template. The effects of ligand functionality and alkali metal template ions on the self-assembly processes of both coordination supramolecular aggregates, and their magnetic behaviors are discussed in detail.     

Spectrometrie de Masse D'ozonides Aliphatiques

A primary cleavage of aliphatic ozonides by electron-impact, implying O? O and C? C bond breaking, is described. This mode of degradation, which is not observed for aromatic ozonides, is fav oured by electron releasing substituents. For the cis and trans 4-methyl-2pentene ozonides, the ionization potentials are 8.81 and 8.86 (±0.5) eV, respectively. Two formation thresholds are observed for the [RCHO₂]⁺ion which are interpreted in terms of different modes of ozonide cleavage.     

Two New Antiferromagnetic Nickel(II) Complexes Bridged by Azido Ligands in the Cis Position. Effect of the Counteranion on the Crystal Structure and Magnetic Properties

Two new nickel(II) end-to-end azido-bridged compounds, cis-catena-[NiL(2)(&mgr;-N(3))](n)()(ClO(4))(n)().nH(2)O (1) and [Ni(2)L(4)(&mgr;-N(3))(2)](PF(6))(2) (2), were synthesized and characterized; L is 2-(aminoethyl)pyridine. The crystal structures of 1 and 2 were solved. Complex 1: monoclinic system, space group P2(1)/a, a = 8.637(2) ?, b = 18.9995(7) ?, c = 12.3093(7) ?, beta = 105.92(2) degrees, Z = 4. Complex 2: triclinic system, space group P&onemacr;, a = 9.139(7) ?, b = 10.124(3) ?, c = 12.024(2) ?, alpha = 70.407(14) degrees, beta = 84.19(2) degrees, gamma = 67.67(4) degrees, Z = 1. In the two complexes the nickel atom is situated in a similarly distorted octahedral environment. The two complexes are different; 1 is a one-dimensional helicoidal complex with the two L ligands and the two end-to-end azido bridges in a cis arrangement while complex 2 is a dinuclear system with two end-to-end azido bridges, indicating the extreme importance of the counteranion present (ClO(4)(-) for 1 and PF(6)(-) for 2). The magnetic properties of the two compounds were studied by susceptibility measurements vs temperature. The chi(M) vs T plot for 1 shows the shape for a weakly antiferromagnetically coupled nickel(II) one-dimensional complex without a maximum until 4 K. In contrast, for complex 2 the shape of the chi(M) vs T curve shows a maximum near 40 K, indicating medium antiferromagnetic coupling. From the spin Hamiltonian -J(ij)()S(i)()S(j)(), J values for 1 and 2 were less than -1 and -29.1 cm(-)(1), respectively. The magnetic behavior for 1 and 2 may be explained in terms of the overlap between magnetic orbitals, taking into account the torsion of the Ni(II) atoms and azido-bridging ligands in the two structures.     

Characterisation and cryomagnetic study of a hydrothermally synthesised hydrogen bonded L–M–L type co-ordination polymer

A ligand–metal–ligand type co-ordination polymer [Ni (C₆H₁₂N₄)(NCS)₂(H₂O)₂] _n has been synthesised under controlled hydrothermal conditions. Here 1,3,5,7-tetraazatricyclo[3.3.1]decane [or hexamethylenetetramine (hmt)] has been used as a μ-(N,N′) bidentate spacer molecule. The prepared polymeric complex has been characterised by elemental and spectral analyses. The structure has been confirmed by a single crystal X-ray diffraction study. Magneto-structural correlation has been drawn from cryomagnetic susceptibility measurements (2–300 K) which unequivocally reflects very weak magnetic spin interactions among the long distant octahedral Ni(II) metal centres mediated by hmt and weak hydrogen bonding interactions between the adjacent zigzag one-dimensional polymeric chains carrying into a two-dimensional infinite polymeric framework.     

Electron attachment on HI and DI in a uniform supersonic flow: thermalization of the electrons

In order to check the electron thermalization in the CRESU technique (Cinetique de Reaction en Ecoulement Supersonique Uniforme, e.g., "reaction kinetics in a uniform supersonic flow"), electron attachment on HI and DI has been studied in the 48-170 K range. Attachment to HI is exothermic and the reaction is expected to be fast and to proceed at a rate close to the capture limit. On the contrary, attachment to DI is slightly endothermic, and a strong positive temperature dependence of the measured rate coefficient is expected if the electrons are thermal. This dependence is not observed, and we conclude that the electrons are not in thermal equilibrium with the neutrals in the afterglow. A model, based on electron heating by superelastic collisions with the buffer gas, is proposed to explain this fact and implications for previously published results are discussed.     

Biogenetically inspired enantioselective approach to Indolo[2,3-a]- and benzo[a]quinolizidine alkaloids from a synthetic equivalent of secologanin

[reaction: see text] Racemic oxodiester 1 undergoes stereoselective cyclocondensation with (S)-tryptophanol, (S)-(3,4-dimethoxyphenyl)alaninol, or the corresponding amino acids, in a process involving a tandem dynamic kinetic resolution/desymmetrization of diastereotopic groups, to give bicyclic lactams, which are cyclized to substituted indolo[2,3-a]- and benzo[a]quinolizidines.     

Synthesis and characterization of polyurethanes from epoxidized methyl oleate based polyether polyols as renewable resources

Oligomeric polyether polyols were obtained through the acid‐catalyzed ring‐opening polymerization of epoxidized methyl oleate and the subsequent partial reduction of ester groups to give primary alcohols. The oligomers were characterized with titration, spectroscopic techniques (Fourier transform infrared and nuclear magnetic resonance), matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry, size exclusion chromatography, and differential scanning calorimetry. Depending on the degree of reduction, polyols of different hydroxyl content values were obtained and were reacted with 4,4′‐methylenebis(phenyl isocyanate) to yield polyurethanes. These materials, which were characterized by differential scanning calorimetry, thermogravimetric analysis, and dynamic mechanical thermal analysis, could behave as hard rubbers or rigid plastics. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 634–645, 2006     

PHOTOPHYSICAL STUDIES ON THE BINDING OF TETRASULFONATOPHENYLPORPHYRIN TO LENS PROTEINS

Previous studies have shown that mesotetra(p-sulfonatophenyl)porphine (TPPS) binds to lens proteins. This characteristic should increase the residence time of the sensitizer in the lens and therefore enhance the probability of inducing photooxidative damage to that tissue in vivo. Subsequent in vivo studies have verified that contention. The present studies were performed to determine the effect of such binding on the spectroscopy and photophysics of the porphyrins. It was found that the binding of TPPS (1) quenches the fluorescence of lens proteins, (2) causes a shift in the ground state absorption spectra, fluorescence excitation spectra and the triplet excited state spectrum of TPPS to longer wavelengths and (3) results in an increase in the triplet state lifetime of TPPS. In the presence of the isolated crystallins the average triplet lifetime increases in the following order: gamma less than beta less than alpha.     

Recherches sur la structure électronique et les caractéristiques des différentes formes tautomères de la purine

Résumé Les caractéristiques électroniques (énergie, charges , géométrie, moment dipolaire, énergie de transition) des quatre formes tautomères de la purine et des phényl-8 N(1)H et N(3)H purines ont été déterminées par la méthode LCAO améliorée. La forme 9 est trouvée la plus stable à l'état isolé. Une interprétation nouvelle des bandes d'absorption est proposée.

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Researches on the electronic structure and the characteristics of various tautomer forms of Purine

The electronic characteristics (energy, charge , geometry, dipole moment, transition energy) of the four tautomeric forms of the purine and of the phenyl-8 N(1)H and N(3)H purines have been determined by the improved LCAO method. The form 9 is considered as the most stable at the isolated state. A new interpretation of the absorption bands is proposed.

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Zusammenfassung Die elektronischen Charakteristiken (Energie, Ladung , Geometrie, Dipolmoment, Übergangsenergie) der vier Tautomerformen des Purins und der Phenyl-8 N(1)H und N(3)H Purine sind durch die verbesserte LCAO-Methode bestimmt worden. Die Form 9 ist, zum isolierten Stand, als am meisten beständig zu betrachten. Eine neue Erklärung der Absorptionsbänder ist vorgeschlagen.

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Les auteurs remercient le Professeur B. Pullmann (Paris) de l'intérêt qu'il a porté à ce travail, ainsi que Madame H. Feilchenfeld (Jérusalem) pour les résultats inédits qu'elle a bien voulu leur communiquer.     

Geminate rebinding in R-state hemoglobin: kinetic and computational evidence for multiple hydrophobic pockets

Biphasic geminate rebinding of CO to myoglobin upon flash photolysis has been associated to ligand distribution in hydrophobic cavities, structurally detected by time-resolved crystallography, xenon occupancy, and molecular simulations. We show that the time course of CO rebinding to human hemoglobin also exhibits a biphasic geminate rebinding when the protein is entrapped in wet nanoporous silica gel. A simple branched kinetic scheme, involving the bound state A, the primary docking site C, and a secondary binding site B was used to calculate the microscopic rates and the time-dependent population of the intermediate species. The activation enthalpies of the associated transitions were determined in the absence and presence of 80% glycerol. Potential hydrophobic docking cavities within the alpha and beta chains of hemoglobin were identified by computational modeling using xenon as a probe. A hydrophobic pocket on the distal side of the heme, corresponding to Xe4 in Mb, and a nearby site that does not have a correspondence in Mb were detected. Neither potential xenon sites on the proximal side nor a migration channel from the distal to proximal site was located. The small enthalpic barriers between states B and C are in very good agreement with the location of the xenon sites on the distal side. Furthermore, the connection between the two xenon sites is relatively open, explaining why the decreased mobility of the protein with viscosity only slightly perturbs the energetics of ligand migration between the two sites.