Supramolecular triads bearing porphyrin and fullerene via ‘two-point’ binding involving coordination and hydrogen bonding

Supramolecular triads composed of fullerene (C₆₀) as primary electron acceptor, zinc porphyrin (ZnP) as primary electron donor, and either a ferrocene (Fc), or N,N-dimethylaminophenyl (DMA), or N,N-diphenylaminophenyl (DPA) entity as a second electron donor were constructed via a ‘two-point’ binding motif involving axial coordination and hydrogen bonding. The B3LYP/3-21G(*) optimized structures revealed disposition of the three entities of the triads in a triangular fashion. The redox behavior of the different components was studied using cyclic voltammetry in o-dichlorobenzene containing 0.1 M (n-C₄H₉)₄NClO₄. The oxidation potentials of the second electron donor followed the trend: Fc<DMA<DPA, and the free-energy calculations suggested the possibility of the occurrence of sequential hole transfer in these triads. Efficient electron transfer from the excited singlet state of zinc porphyrin to the fullerene entity was observed in all of the studied triads in o-dichlorobenzene. Longer charge-separated states were observed for zinc porphyrin with a carboxylic acid compared with that having an amide group. The ratios of the experimentally determined forward to reverse electron transfer rates, k_CS/k_CR were evaluated to be 10³ for triads formed by zinc porphyrin with a carboxylic acid, suggesting charge stabilization in these triads.     

A stereoselective 3-endo-alkyl-5,6-dehydroisoquinuclidine synthesis.

Cycloaddition of N-carbethoxy-2-alkyl-1,2-dihydropyridines $\text{4}$ with phenylvinylsulfone $\text{5}$ provides adducts $\text{6}$, which upon desulfonylation afford stereoselectively N-carbethoxy-3-$\text{endo}$- alkyl-5,6-dehydroisoquinuclidines $\text{1}$.     

Projective repesentations of the Hilbert Lie group U (H)2 via quasifree statres on the CAR algebra

The group $\text{U}$ (H)₂ of unitary operators (on a Hilbert space H) which differ from the identity by a Hilbert-Schmidt operator may be imbedded in the group of Bogoliubov automorphisms of the CAR algebra over H in such a way as to be weakly inner in any gauge-invariant quasifree representation. Consequently each such quasifree representation determines a projective representation of $\text{U}$ (H)₂. If 0 ? A ? I is the operator on H determining the quasifree representation π_A and ?_A denotes the cyclic projective representation of $\text{U}$ (H)₂ generated from the G.N.S. cyclic vector $\text{Ω}{}_{\mathrm{A}}\text{for}\text{π}{}_{\mathrm{A}}$, then the 2-cocycle in $\text{U}$ (H)₂ determined by ?_A can be given explicitly. We prove that this 2-cocycle is a coboundary if any only if A or 1 ? A is Hilbert-Schmidt. The representations ?_A, on restriction to the group $\text{U}$ (H)₁ consisting of unitaries which differ from the identity by a trace class operator, always determine 2-cocycles which are coboundaries. These representations of $\text{U}$ (H)₁ have already been investigated by 21., 22., 87–110). Thus the Stratila-Voiculescu representations of $\text{U}$ (H)₁ always extend to projective representations of $\text{U}$ (H)₂ and to ordinary representations when A or 1 ? A is Hilbert-Schmidt. This fact enables exploitation of the type analysis of Stratila and Voiculescu to determine the type of the von Neumann algebra ρ_A($\text{U}$(H)₂)″. In the special case where 0 and 1 are not eigenvalues of $\text{A, Ω}{}_{\mathrm{A}}$ is cyclic and separating for ρ_A($\text{U}$(H)₂)″ and hence determines a K.M.S. state on this algebra. It is shown that for special choices of A, type III_λ (0 < λ ? 1) factors ρ_A($\text{U}$(H)₂)″ may be constructed.     

Disodium guanosine 5'-monophosphate self-associates into nanoscale cylinders at pH 8: a combined diffusion NMR spectroscopy and dynamic light scattering study

We report a combined NMR and dynamic light scattering (DLS) study on the size of supramolecular structures formed by disodium guanosine 5'-monophosphate, Na(2)(5'-GMP), at pH 8. In general, two distinct types of aggregate species are present in an aqueous solution of Na(2)(5'-GMP). One type consists of stacking 5'-GMP monomers, and the other contains stacking G-quartets. Both types of aggregates can be modeled as rodlike cylinders. The cylinder diameter is 10 and 26 A for monomer aggregates and quartet aggregates, respectively. For Na(2)(5'-GMP) concentrations between 18 and 34 wt %, the cylinders formed by stacking G-quartets have an average length between 8 and 30 nm, corresponding to a stack of approximately 24-87 G-quartets. These nanoscale aggregates are significantly larger than what had previously been believed for Na(2)(5'-GMP) self-association at pH 8. The length of both types of 5'-GMP aggregates was found to increase with Na(2)(5'-GMP) concentration but was insensitive to the added NaCl in solution. While the aggregate size for monomer aggregates increases with a decrease in temperature, the size of G-quartet aggregates is essentially independent of temperature. We found that the size of G-quartet aggregates is slightly larger in D(2)O than in H(2)O, whereas the size of monomer aggregates remains the same in D(2)O and in H(2)O. We observed a linear relationship between the axial ratio of the 5'-GMP cylinders and the Na(2)(5'-GMP) concentration for both types of 5'-GMP aggregates, which suggests a common stacking mechanism for monomers and G-quartets.     

Unusual aggregates from the oxidation of alkene self-assembled monolayers: a previously unrecognized mechanism for SAM ozonolysis?

Self-assembled monolayers (SAMs) of vinyl-terminated 3- and 8-carbon compounds were generated on Si substrates and reacted at room temperature with approximately 1 ppm gaseous O(3). A combination of atomic force microscopy (AFM), scanning electron microscopy (SEM), Auger electron spectroscopy (AES) and time-of-flight secondary ion mass spectrometry (TOF-SIMS) was used to study the surface composition and morphology after oxidation. A distribution of large ( approximately 0.1-10 microm) organic aggregates was formed, while the surrounding substrate became depleted of carbon compared to the unreacted SAM. This highly unusual result establishes that the mechanism of ozonolysis of alkene SAMs must have a channel that is unique compared to that in the gas phase or in solution, and may involve polymerization induced by the Criegee intermediate (CI). Oxidation at 60% RH led to the formation of a number of smaller aggregates, suggesting water intercepted the CI in competition with aggregate formation. The uptake of water, measured using transmission FTIR, was not increased upon oxidation of these films. In conjunction with literature reports of polymer formation from VOC-NO(x) photooxidations, these results suggest that formation of aggregates and polymers in the atmosphere is much more widespread than previously thought. The implications for the ozonolysis of alkenes on surfaces, for the transformation of organics in the atmosphere, and for the reactions and stability of unsaturated SAMs, are discussed.     

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