Yoichi Sasaki

A facile nmr method for assigning absolute configuration of underivatized α-methyl-α-amino acids using a chiral lanthanoid shift reagent for aqueous solution

Abstract The absolute configuration of α-methyl-α-amino acids can be easily assigned by use of the chiral lanthanoid NMR shift reagent, 1,2-propanediaminetetraacetatoeuropium(III) in aqueous solution.

Solid state dehydration condensation of potassium tetrakis(μ-pyrophosphito-P,P′)diplatinate(II) accompanied by the red shift of the luminescence peak

Yellow crystals of K4[Pt2(pop)4]·2H2O (pop2− = pyrophosphite(2−)) change their color to orange upon dehydration in vacuo or at elevated temperatures with concomitant change in the emission color from green (emission peak at 515 nm) to orange (emission peaks at 520, 570, 670 nm). Thermogravimetric, 31P CP-MAS NMR, electronic and infrared absorption spectral studies indicate that the dehydration is not a simple loss of crystalline waters but involves dehydration condensation between the neighboring complex anions. The original green emission is recovered on dissolving the orange solid in water. Emissions from the dehydrated orange solid are of phosphorescence type (τem ≤ 6 μs). Relative intensity of the three emission peaks depends significantly on dehydration conditions, exciting wavelength and temperature. The orange solid seems to contain various species with different extent and type of condensation. Red shift of the emission peak on dehydration was discussed on the basis of the ligand field theory.

Change in the Color of Luminescence Accompanied by Dehydration of The Solid K4 [Pt2 (P2O5H2)4]·2H2O

Abstract Some crystals of the titled complex undergo the change in the color of luminescence from green to orange in solid state upon dehydration.

Structure and Circular Dichroism of Binuclear Molybdenum (V) Complexes with Optically Active Ligands

Molybdenum ions in various oxidation states are involved in active sites of a variety of enzymes catalyzing redox reactions. 1 Many kinds of model complexes have been prepared and studied with reference to their function as catalysts for the reduction of various simple molecules, including acetylene,azobenzene, and nitrogen. 2–4 Most of them are dimeric molybdenum(V) complexes with one or two oxo or sulfido bridges and L-cysteinate and its derivatives as ligands. Some structures have been revealed by X-ray crystallography, 5 but not discussed with reference to their catalytic activity. Since most of the model complexes have optically active ligands, circular dichroism (CD) should be a useful tool for studying their stereo chemistry. The CD spectra of some molybdenum complexes have been recorded, 6–9 but the relationship to structure was not discussed.