Kazuo Saito

A critical study of the measurement and calibration of circular dichroism.

Abstract A critical study has been made of circular dichroism (CD) measurements at the wavelengths around 500, 290, and 220 nm. Instruments calibrated at 290 nm with (+)-camphor-10-sulfonic acid gave results for molecular ellipticities [θ] showing deviations up to >30%, at both 220 and 490 nm. Older instruments tended to given higher values of [θ] at 490 nm and lower values at 220 nm, probably due to the age of the Pockel cells. A proposal is made to use d -pantolactone and (+)-tris(ethylenediamine) cobalt (III) iodide monohydrate as calibration standards at 220 and 490 nm, respectively, together with (+)-camphor-10-sulfonic acid at 290 nm.

OPTICAL ISOMERS OF 2,2′-DIAMINOBIPHENYLBIS(ETHYLENEDIAMINE) COBALT(III) CHLORIDE AND ITS RELATED COMPLEXES1

Abstract Several cobalt(III) complexes incorporating 2,2′-diaminobiphenyl(dabp) and other 2(2N)- or 4N-type ligands were prepared and resolved by chemical and chromatographic methods: (1) [Co(en)2(dabp)]Cl22H2O, (2) [Co(l-pn)2(dabp)] (ClO4)34H2O, (3) [Co(l-chxn)2(dabp)](ClO4)33H2O, (4) α-[Co(trien)(dabp)](ClO4)3, (5) α-[Co(2S,9S-dimetrien)(dabp)] (ClO4)3 2H2O, (6) α-[Co(3S,8S-dimetrien)(dabp)] (ClO4)33H2O, (7 [Co(tren)(dabp)]Cl35H2O, (8) [Co(bpy)2(dabp)] Cl33H2O. The complexes (1), (4) and (8) gave one pair of enantiomers, Δ(Λ) and Λ(δ), and the complexes (2) and (3) gave only one Δ-isomer. The absolute configuration of the complexes (5) and (6) was found to be Λ, and that of (7) was not determined because of unsuccessful resolution. The three geometric isomers of the complex (2) were separated and their structures assigned.

Preparation and circular dichroism of rhodium(I) complexes containing optically active trans-cyclooctene

Abstract Three new rhodium(I) compounds containing optically active trans -cyclooctene ( trans -C 8 H 14 ) were prepared: [RhL {(+) D - trans -C 8 H 14 } 2 ] (L = acetylacetonate and 1,3-diphenyl-1,3-propanedionate) and [Rh 2 Cl 2 {(+) D - trans -C 8 H 14 } 4 ]. The absorption and circular dichroism spectra were measured and compared with those of [Pt 2 Cl 4 {(-) D - trans -C 8 H 14 } 2 ]. The absolute configuration of coordinated alkenes is correlated with the CD spectra in the wave number regions, (20–30) x 10 3 cm -1 and 40 x 10 3 cm -1 . In the former range the CD sign is the reverse of that of platinum(II)—alkene complexes, but in the latter region the CD signs are equal.

Doubly-bridged binuclear complexes of oxomolybdenum(V) and oxotungsten(V) containing sexadentate ligands

Binuclear oxomolybdenum(V) and oxotungsten(V) complexes of the type, [M2(O)2(μ-X)(μ-X1)]”, where M=Mo, W;X.X1=O, S; L=edta, pdta (n=2-), tpen, tppn (n=2+) (edta4– =ethylenediaminetetraacetate(4–), pdta=R- orR,S-propylenediaminetetraacetate(4–), tpen=N,N,N1,N1-tetrakis(2-pyridyhnethyl)-ethylenediamine, and tppn=R- orR,S-N,N,N1,N1-tetrakis(2-pyridylmethyl)-propylenediami ne) are reviewed with respect to their preparation, structure, spectroscopic properties, reactivities, and in particular asymmetric distortion around the bicyclo [4.1.1 ] type core and stereoselectivity related to this distortion,

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.

Optical Inversion and Substitution of Coordinated Olefins in Optically Active Trans(N)-Chloro-L-Prolinatoolefinplatinum(II) Complexes in Organic Solvents

Optical isomerism due to asymmetric coordination of some olefins such as propylene and trans-2-butene was first studied by Paiaro and Panunzi.l We have synthesized diastereomers of the type trans(Nolefin)[PtCl(L-prol)(olefin)] crystalline,2 and discussed the absolute configuration of coordinated olefins on the basis of circular dichroism (CD) spectroscopy.3 The complexes with such olefins as trans-2-butene and 2-methyl-2-butene gave no change in u.v. absorption and CD in organic solvents such as ethanol, chloroform and acetone. When the same olefin as the ligand was added, the CD changed, the u.v. absorption remaining unchanged. (Figure 1) This fact suggests that only the inversion of the coordinated olefin takes place.

Production of Radioisotopes of Niobium by Irradiation of Zirconium with Protons

For the purpose of obtaining neutron-deficient radioisotopes of niobium to be used for the study of decay scheme and for carrier-free tracer, separation of niobium from irradiated zirconium was examined by solvent extraction and radio- colloid formation. Extraction of niobium fluoride with methyl-iso-butyl ketone was successful, but the extraction was retarded in the absence of carrier. Extraction with chloroform in the presence of tribenzylamine in concentrated hydrochloric acid solution appeared to be most useful for a practical production. Back-extraction was substantiated with various solutions including mineral acid, caustic alkali, and hydrogen peroxide. To remove the last trace of ingredients in the aqueous solution, radiocolloid formation in concentrated caustic alkali or ammonia solution and re-dissolution in hydrochloric acid were very useful. The product consisted only of isotopes of niobium and was used for the carrier-free source. Hafnium, always present in natural zirconium, gave radioisotopes of tantalum, but they did not vitiate the measurement of radioactivity of niobium isotopes. (auth)