Takeyuki Akita

Structural and photophysical properties of novel dual fluorescent compounds, 1-aryl-substituted 6-methoxy-4-quinolones.

Dual fluorescent compounds are useful platforms for the development of ratiometric probes and sensors. We have developed a new series of dual fluorescent compounds, 1-aryl-substituted 6-methoxy-4-quinolones, and investigated their structural and photophysical properties. The X-ray crystallographic analysis and ab initio quantum chemical calculations revealed that the developed compounds exhibited 60-75 degrees twisted structures. The dual fluorescence of the compounds were observed in polar solvents, and the ratiometric fluorescence responses to alterations in the acidity and temperature were obtained.

Intramolecular spin-interactions between two nitronyl nitroxide or imino nitroxide radical units linked to thieno[2,3-b]thiophene and thieno[2,3-b]thieno[3′,2′-d]thiophene chromophores

Abstract Diradical species 1N, 1I, 2N, and 2I, in which two nitronyl nitroxide (N) or imino nitroxide (I) radical centers are attached to thieno[2,3-b]thiophene (1) and thieno[2,3-b]thieno[3′,2′-d]thiophene (2) chromophores, respectively, were prepared and their intramolecular exchange interactions were investigated in frozen solutions by means of ESR spectroscopy and magnetic susceptibility measurements at cryogenic temperature. Temperature dependence of the ESR signal intensities due to the triplet state revealed that bis(nitronyl nitroxide) radicals, 1N and 2N, are ground-state singlet species with quite small singlet-triplet gaps. In bis(imino nitroxide) radical 1I the spin interaction was antiferromagnetic and the singlet-triplet gap was estimated to be 2J k B =−18 K . On the other hand, bis(imino nitroxide) 2I was revealed to be a singlet-triplet degenerate species. These results are discussed in terms of the intramolecular NO---S contact along with corroboration by the semi-empirical MO calculations.

Ferromagnetic spin interaction in a crystalline molecular complex formed by inter-heteromolecular hydrogen bonding: a 1 : 1 complex of phenyl nitronyl nitroxide radical and phenylboronic acid

A crystalline molecular complex derived from phenyl nitronyl nitroxide and phenylboronic acid exhibits a ferromagnetic spin interaction (J=+0.65 K) below 30 K: X-ray analysis reveals the crystal structure to be constituted of a one-dimensional array of two component molecules linked alternately by the NO ⋯ HOB hydrogen bond.

Magnetic properties after irradiation of poly(m-phenyleneethynylene) having diazo and nitronylnitroxide groups and its model compounds

Abstract In order to achieve a pure organic high-spin molecule, poly( m -phenyleneethynylene) derivative 1 having diazo groups and nitronyl nitroxide moieties alternately were designed. Its three model compounds, diphenylacetylene derivative 2 , bis(phenylethynyl)benzene derivative 3 , and oligomeric compound 4 having partial structure of 1 have been prepared by the coupling reaction of ethynyl derivatives of phenylnitronylnitroxide and iodo derivatives of diphenyldiazomethane. Field dependence of magnetization after irradiation of 2 and 3 in frozen solutions suggested that the photo-generated species have quartet and quintet ground states with J / k B values of +1.75 and +1.09 K, respectively. However, spin interaction between carbene and nitronylnitroxide through 3,3′-diphenylacetylene moiety is not strong enough to form high-spin chain having long correlation length for 4 .

Experimental and Theoretical Spin Density in a Ferromagnetic Molecular Complex

Abstract The association of phenylboronic acid (no unpaired electron) with the free radical phenyl nitronyl nitroxide (S = 1/2) constitutes an inter-heteromolecular hydrogen bonding system presenting ferromagnetic intermolecular interactions. We have investigated its spin density distribution in order to visualize the pathway of these magnetic interactions. The spin density of this complex was measured by polarized neutron diffraction. The data were treated using both direct and indirect methods. As in the isolated PNN, the main part of the spin density is located on the O-N-C-N-O fragment of the PNN radical. But, with the PNNB, the global spin density distribution give evidences that the phenylboronic acid constitutes a spin transmission path between PNN radicals via hydrogen bonds. The experimental results are compared to those obtained by density functional theory calculations.

Intermolecular Spin-Coupler: Ferromagnetic Spin Interactions Through Hydrogen Bond in the Complexes of Arylboronic Acids with Aryl Nitronyl Nitroxides

Abstract Two crystalline complexes, the complex of p-fluorophenylboronic acid with phenyl nitronyl nitroxide (2) and the complex of p-nitrophenylboronic acid with p-dimethylaminophenyl nitronyl nitroxide (3), were prepared. Both of those complexes as well as the complex of phenylboronic acid with phenyl nitronyl nitroxide (1) exhibit ferromagnetic spin interactions (1: J/kB=+0.65 K, 2: J/kb =+0.58 K, 3: J/kB =+1.35 K). The results are discussed based on the X-ray crystal structure.

Molecular structure and magnetic properties of N,N-bis {4-methoxy-3,5-bis(N-tert-butyl-N-oxyamino)phenyl} aminoxyl. An approach to a stable and high-spin pentaradical

A stable pentaradical, N,N-bis{4-methoxy-3,5-bis(N-tert-butyl-N-oxyamino)phenyl)}aminoxyl, is prepared and its ground state determined to be a sextet (S = 5/2) by SQUID magnetization measurements of the pentaradical diluted in poly(vinyl chloride) matrix.

Ferromagnetic Spin Interaction Through the Inter-Heteromolecular Hydrogen Bond: A 1:1 Crystalline Complex of Phenylboronic Acid and Phenyl Nitronyl Nitroxide

Abstract A crystalline molecular complex derived from phenyl nitronyl nitroxide (1) and phenyl boronic acid (2) exhibits a ferromagnetic spin interaction (J= +0.65 K) below 30 K: An X-ray analysis revealed the crystal structure constituted of one-dimensional array of two component molecules linked alternately by the NO-HOB hydrogen bonds. The NO—HO-B-OH—ON linkage was suggested to act as a path for ferromagnetic spin coupling. An unusual formation of nitrosonium salt (3) was found in the reaction of 1 and BF3. Its molecular and crystal structures were determined.

Theoretical Study on the Exchange Interaction Between Metal Ion and Organic Radical Through Pyridine, Bipyridine and Terpyridine Ligands

Ab initio total energy calculations with the DFT framework based on the geometries obtained by X-ray data were carried out for five complexes composed by copper(II) ion and organic radicals (eg. aminoxyl and carbene) through pyridine, bipyridine and terpyridine rings. It was found that the copper(II) complex having radical substituted at 4-position of aromatic ligand favors ferromagnetic coupling between organic radical and paramagnetic copper(II) ion.

Development of an online two-dimensional high-performance liquid chromatographic system in combination with tandem mass spectrometric detection for enantiomeric analysis of free amino acids in human physiological fluid

An automated two-dimensional HPLC-MS/MS system was designed and developed for the highly selective determination of trace levels of d-amino acids. As the targets, frequently observed ones in mammalian physiological fluids, Ala, Asp, Glu, Leu, Pro and Ser, were selected because these d-amino acids are the potential biomarkers for the early and sensitive diagnoses of various diseases. The target analytes were derivatized with 4-fluoro-7-nitro-2,1,3-benzoxadiazole (NBD-F), then isolated by a reversed-phase column in the first dimension. The NBD-amino acid fractions were automatically collected into the multi-loop device, and introduced into the enantioselective column in the second dimension to separate the d- and l-forms followed by detection by an MS/MS. The obtained resolution values of the enantiomers were 1.87-5.17 and the calibration lines, precision and accuracy were practically sufficient. By using the present 2D HPLC-MS/MS system, trace levels of d-amino acids in complex biological matrices were determined without disturbance by the intrinsic interfering compounds, and successfully applied to the analysis of the human clinical samples (plasma and urine).