Cross polarization/magic angle spinning (CP/MAS)(13)C (solid state high resolution) NMR spectra were observed for chlorosomes and BChlc aggregates. Similarity of both kinds of spectra (except for some signals assignable to proteins and lipids in chlorosomes) indicates that BChlc's in chlorosomes are present just as in synthetic BChlc aggregates. Chemical shifts for C13(1) carbonyl and C3(1) hydroxylethyl carbons indicate hydrogen bonding between them. Comparison of solution and solid state(13)C NMR chemical shifts shows the five coordinated nature of BChlc aggregates. Some chemical shift differences were attributable to ring currents shifts. Their comparisons with calculated ring current shift values predicted structures for the aggregates. Cross polarization dynamics of the CP/MAS(13)C NMR signals explored dynamic and structural nature of the BChlc aggregates.
Magnetic circular dichroism (MCD) and absorption spectra have been measured on three intact photosynthetic pigments with the chlorin ring as macrocycle: chlorophyll a, bacteriochlorophyll c and d, in various hydrophilic organic solvents. The MCD intensity of a Qy(0-0) transition for the Mg chlorin derivative was sensitive to the coordination state of the central Mg atom by the solvent molecules. The coordination number has been characterized in terms of the relationship between the ratio of Qy(0-0) MCD intensity to its dipole strength (B/D) and the difference in energies of Qx(0-0) and Qy(0-0) transitions. This relationship depends not only on the coordination number of the magnesium (Mg) atom but also on the coordination interaction of the solvent molecules to the Mg atom, and can clarify the spectroscopic change of chlorosomes by alcohol treatment. We propose that the correlation between the MCD intensity of Qy(0-0) transition and the energy difference can be used as a new measure for determining the coordination number of the Mg atom and for estimating the interaction strength of the Mg atom with solvent molecules.
A self-assembled monolayer of l-cysteine was prepared on Au(111) under potential control. Cyclic
voltammetry and in situ electrochemical scanning tunneling microscopy were employed to investigate the
molecular adsorption and adlayer structure in perchloric acid solution. The molecules chemically adsorb
on Au(111) and form a well-defined adlayer. A new structure of (4 × √7)R19° was observed in the double-layer region. A phase transition at the positive potential region resulted in the appearance of a disordered
layer. A structural model is proposed to interpret the molecular registry with Au(111) substrate.
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