Yoshinobu Nagawa

Synthesis and photophysical properties of ruthenium(II) charge transfer sensitizers containing 4,4′-dicarboxy-2,2′-biquinoline and 5,8-dicarboxy-6,7-dihydro-dibenzo[1,10]-phenanthroline

Abstract Ruthenium (II) complexes of the type cis -Ru(H 2 dcbiq) 2 X 2 and cis -Ru(H 2 dcdhph) 2 X 2 , where H 2 dcbiq=4,4′-dicarboxy-2,2′-biquinoline, H 2 dcdhph=5,8-dicarboxy-6,7-dihydro-dibenzo[1,10]-phenanthroline, and X=Cl − , NCS − or CN − , have been synthesized and spectroscopically characterized. The resulting complexes show a broad and intense metal-to-ligand charge transfer (MLCT) band in the visible region with a peak between 580 and 700 nm and are emissive at room temperature. The ground-state first p K a value of cis -Ru(H 2 dcbiq) 2 (NCS) 2 ( 2 ) was determined to be 2.9 by the spectrophotometric method. Photoelectrochemical measurements show that all dyes, when anchored to a nanocrystalline TiO 2 film electrode, present low light-harvesting efficiencies due to inefficient driving force for electron injection into the conduction band of TiO 2 from their lower energy MLCT band. The photoelectrochemical performance of 2 was also investigated on a number of oxide semiconductor thin films such as Nb 2 O 5 , ZnO, SnO 2 and In 2 O 3 . The results show that a high value of short-circuit photocurrent ( J sc ) is observed for the semiconductors having a low-energy conduction band potential (SnO 2 and In 2 O 3 ). In the dye 2 -sensitized TiO 2 film, the absorbed photon-to-current conversion efficiency (APCE) spectrum shows an absorption band selective electron injection yield, while a wavelength independent electron injection yield is observed when dye 2 is anchored to SnO 2 . These results indicate that the lowest excited MLCT state is energetically favorable for electron injection into the conduction band of SnO 2 but not for TiO 2 .

A new synthetic method for rotaxanes via tandem claisen rearrangement, diesterification, and aminolysis

A novel methodology to make rotaxanes via covalent bond formation has been developed. Rotaxanes composed of crownophanes having two phenolic hydroxy groups as a molecular rotor and an axle having diamide moieties were synthesized in moderate yields via three step processes: tandem Claisen rearrangement, intramolecular diesterification, and aminolysis.

Structural characterization of lipid A component of Erwinia carotovora lipopolysaccharide

The chemical structure of the lipid A component of lipopolysaccharide excreted into the liquid medium by the plant pathogenic enterobacterium Erwinia carotovora FERM P-7576 was characterized. It consists of a β-1′, 6-linked glucosamine disaccharide which carries ester-and amide-bound fatty acids and phosphate similar to the lipid A from other gram-negative bacteria. The lipid A preparation was not uniform in the number and composition of the fatty acids linked to the disaccharide. Four prominent lipids A were involved, they were composed of five to seven residues of fatty acid. Among them the major component was hexa-acyl lipid A, in which the hydroxyl group at position 3′ and the amino group of the non-reducing glucosamine unit carry 3-dodecanoyl-oxytetradecanoyl residues. Positions 2 and 3 of the reducing glucosamine unit were substituted by 3-hydroxytetradecanoic acid. In the hepta-acyl lipid A, an additional hexadecanoic acid was linked to the hydroxyl group of the 3-hydroxytetradecanoyl residue at position 2 of the hexa-acyl lipid A. Two penta-acyl lipids A were the homologs of the hexa-acyl lipid A with decreasing acylation. Dodecanoic acid was missing from one, and 3-hydroxytetradecanoic acid from another. 3-Dodecanoyloxytetradecanoyl residue at position 3′ differentiates E. carotovora lipid A from that of other gram-negative bacteria.

Synthesis and characterization of dinuclear lanthanide(III) and yttrium(III) cryptates of a hexavalent anionic polydentate ligand

Abstract Reaction of tris(2-aminomethyl)amine with bis(hydroxybenzaldehyde) (1) in presence of M(CF3SO3)3 (M=Y, Gd, Tb, Dy, Ho, Er, Tm) in methanol yielded the dinuclear lanthanide(III) and yttrium(III) cryptates [M2L] (2). The structure of [Y2L] was established by X-ray crystallography. Each yttrium ion is in a seven-coordinate environment composed of three imine nitrogen atoms, one apical nitrogen atom, and three oxygen atoms. The dinuclear complexes were found to be a host for Rb+ and Cs+.

Spontaneous macrocyclization via recombination of a Schiff-base linkage

Abstract A macrocyclic compound that has two salenH 2 moieties was synthesized via recombination of an acyclic Schiff base in quite high yield, and was characterized by X-ray crystallography. The recombination occurred in a slow diffusion system of chloroform–methanol, where the starting material may spontaneously form a molecular assembly suitable for the subsequent reaction. This assumption was supported by the crystal structure of an analogue of the acyclic Schiff base.

Synthesis of chiral crownophanes via tandem Claisen rearrangement

Abstract A synthetic route for crownophanes containing a chiral binaphthyl unit using tandem Claisen rearrangement is described to demonstr te the versatility of this approach. Molecular recognition by the resulting crownophane for butylurea is also investigated.

Calculations of internal rotational pathways of peri substituted naphthalenes by molecular mechanics

Abstract Internal rotational pathways of 1-phenylnaphthalene, 1,8-diphenylnaphthalene, 1,8-di- o -tolylnaphthalene and 1,1′-binaphthyl have been studied by the MM2′ molecular mechanics method. The conformations of substituents and the deformations of naphthalene rings in equilibrium and saddle point conformers are discussed.

[3]Rotaxane synthesized via covalent bond formation can recognize cations forming a sandwich structure

A novel [3]rotaxane composed of two 25-membered crownophanes and one axle molecule having two anthryl end groups was successfully synthesized via covalent bond formation followed by aminolysis, and can incorporate caesium ion into the space between the two macrocycles as a 1 : 1 sandwich-type complex, whereas it makes a 1 : 2 complex with lithium ion.

Stepwise synthesis of crownophanes having either one or two hydroxy groups via Claisen rearrangement

Abstract Bis(naphthyl)crownophanes having an isobutenyl group and different ring size were synthesized. By control of the reaction temperature and time, both the first-step product having one hydroxyl group and the second-step product having two hydroxy groups can be isolated in high yields.

Calculations of structures of biphenyl and alkylbiphenyls by molecular mechanics

Abstract MM2′ parameters for “mechanical” calculation of biphenyl are revised on the basis of Bastiansens gas phase electron diffraction data. These parameters well reproduce the structures of energy minimum conformer of biphenyl and of alkylbiphenyls.