Published papers

A solution ESR spectral investigation on 2-(benzimidazol-2-yl)-4,4,5,5-tetramethyl-1 H -imidazoline-1-oxyl-3-oxide (=BIm-NN) and a magnetic susceptibility measurement of its −(N)H deuterated sample (BIm-NN-d 1 ) were carried out. A moderate amount of spin density was observed in benzimidazole ring bearing a hydrogen-bonding site. There was no appreciable difference in the temperature dependence of magnetic susceptibility between BIm-NN and BIm-NN-d 1 .

Changes in the nature of spin crossover caused by mechanical stressing exerted on the crystalline powders were studied for FeII(phen)2(NCS)2 (phen = 1,10-phenanthroline) and FeII[HB(pz)3]2 (pz = pyrazol-1-yl) by means of a multi-component fitting of the temperature dependence of magnetic susceptibility. The analysis revealed the development and broadening of the ligand field distribution as a consequence of mechanical stressing. This was confirmed by the broadening of Mössbauer and far-infrared spectra.

Self-assembly of [5-(pyrazol-4-yl)-10,20-bis(p-tolyl)-15- (2-ethoxycarbonylphenyl)porphyrinato]-zinc(II) (1), designed to have both a coordination site and a hydrogen bonding site, leads to a stable cyclic trimer array where coordination of the pyrazole nitrogen to the zinc(II) ion as well as hydrogen bonding between carbonyl oxygen and pyrazole NH holds each zinc(II) porphyrin. The recognition event for pyrazole has been confirmed preliminarily in the model studies using [5-(2-ethoxycarbonylphenyl)tris(p-tolyl)porphyrinato]-zinc(II) (3). The zinc(II) porphyrin 3 has large affinity for pyrazole due to the hydrogen bond between pyrazole and the 2-ethoxycarbonyl group in addition to the coordination bonding accompanied by the conformational change of the ethoxycarbonyl group in the coordination process. The 1H NMR, IR, and UV−vis spectra of 1 and its ESI-MS and VPO measurements have revealed the cyclic trimer structure with an overall association constant of 6.0 × 1013 M-2 at 22 °C. The contribution of the hydrogen bond to the total free energy change in trimer formation is estimated to be 7.5 kcal/mol based on a reference trimer system without a hydrogen bonding site. The trimer geometry causes characteristic exitonic interaction between porphyrin units to yield a broad Soret band which is deconvoluted into four components by UV−vis and MCD spectral analyses. Electrochemical measurements have shown that only the first ring-oxidation process proceeds stepwise in the trimer.

The ligand exchange reaction between [M(phen)3]2+ and [M(DIP)3]2+ (where M is the same and M = FeII or NiII, phen = 1,10-phenanthroline, DIP = 4,7-diphenyl-1,10-phenanthroline) has been investigated by reversed phase ion-paired chromatography (RP-IPC). The effect of pH and solvent on the ligand-exchange reaction is studied by monitoring the variation in chromatograms with time after mixing. The results have shown that the ligand exchange reaction between [M(phen)3]2+ and [M(DIP)3]2+ takes place in the pH range of 3–8 and the rate of reaction for nickel(II) complexes is about two times slower than that for iron(II) complexes. Experiments on the effect of various solvents on the ligand-exchange reaction have revealed that the rate of reaction is enhanced by the solvent in the following order: (CH3)2CO > CHCl3 ≥ CH2Cl2 > CH3CN > CH3OH. Elemental analysis and UV-visible spectroscopy confirmed that the products obtained from the ligand-exchange reaction are mixed-ligand complexes containing phen and DIP ligands, i.e., [M(phen)2(DIP)]2+ and [M(phen)(DIP)2]2+.

The interaction of transition metal complexes of cationic porphyrins bearing five membered rings, meso-tetrakis(1,2-dimethylpyrazolium-4-yl)porphyrin (MPzP, M=MnIII, NiII, CuII or ZnII), with calf thymus DNA (ctDNA) has been studied. Metalloporphyrins NiPzP and CuPzP are intercalated into the 5′GC3′ step of ctDNA. MnPzP is bound edge-on at the 5′TA3′ step of the minor groove of ctDNA, while ZnPzP is bound face-on at the 5′TA3′ step of the major groove of ctDNA. The binding constants of the metalloporphyrins to ctDNA range from 1.05×105 to 2.66×106 M−1 and are comparable to those of other reported cationic porphyrins. The binding process of the metallopyrazoliumylporphyrins to ctDNA is endothermic and entropically driven. These results have revealed that the kind of central metal ions of metalloporphyrins influences the binding characteristics of the porphyrin to DNA.

2-(Purin-8-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazolyl-1-oxyl-3-oxide (Pu-NN) was designed and synthesized. Two crystalline phases (α- and β-phases) exhibiting different IR spectral patterns at the νNH region were obtained depending on the crystallizing condition. The temperature dependences of the magnetic susceptibility of these two phases followed Curie–Weiss law with θ=−5.7 K (α-phase) and θ=−0.3 K (β-phase) implying intermolecular antiferromagnetic interaction, which were quite different from that of parent benzimidazole derivative, 2-(benzimidazol-2-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1H- imidazolyl-1-oxyl-3-oxide that formed a 1-D ferromagnetic chain induced by an intermolecular hydrogen bonding.

A novel polymeric nitridochromium(V) complex with a Schiff base ligand [CrN(salpn)] [H2(salpn) = N,N′‐disalicylidene‐1,3‐propanediamine] was prepared by photolysis of an azidochromium(III) complex in acetonitrile. X‐ray crystal structure analyses of the starting material {(CH3)2NH2}2[CrCl2(salpn)]Cl (1) and the polymeric complex [CrN(salpn)] (3) were carried out. The orange complex 3 has a linear ···Cr≡N···Cr≡N··· chain structure with the N···Cr distance being 2.508(2) Å. Magnetic data show that 3 has a ferromagnetic intermolecular interaction in the chains (J = +8.4 cm−1).

The self-assembly of zinc(II) porphyrins bearing a pyrazole substituent are reported. 1H NMR, UV/Vis and VPO measurements indicate the formation of a cyclic trimer of zinc(II) pyrazol-4-ylporphyrin and a tetramer of zinc(II) 3,5-dimethypyrazol-4-ylporphyrin by mutual coordination.

Light brown [VO(5-NO2salen)]·2H2O (1; H2(5-NO2 salen)=N,N′-di-5-nitrosalicylidene-1,2-ethanediamine) and orange [VO(5-NO2sal-meso-stien)]·0.5H2O (2; H2(5-NO2sal-meso-stien)=N,N′-di-5-nitrosalicylidene-(R,S)(S,R)-1,2-diphenyl-1,2-ethanediamine) which have linear chain structures in the solid state turn dark brown and yellow-brown, respectively, when ground thoroughly in mortars. The IR spectra of 1 and 2 in Nujol mulls show strong V=O stretching bands at 875 and 905 cm−1, respectively. On the other hand, the spectra of the finely ground complexes in Nujol mulls show very weak V=O stretching bands. X-ray powder diffraction patterns of the ground complexes scarcely show diffraction peaks. The spectroscopic and magnetic data suggest that the linear chain structures in the crystals of 1 and 2 are destroyed on grinding to yield the fragments of the polymeric chains.

The structure and properties of the thermal decomposition products of Fe[Fe(CN)5NO] · x H2O (x = 5 ~ 6) have been studied by Mössbauer and FT-IR spectroscopy, X-ray diffraction, and conductivity measurements. The valence state and coordination environment of the iron ions change dramatically when the nitrosyl ligand is eliminated by heat-treatment under vacuum at 200 °C. The dark blue product obtained by heat-treatment under vacuum at 250 °C is characteristic of the mixed-valence state in Prussian blue analogues. The electrical conductivity of the dark blue product is higher by a factor of 103 than that of the starting material because of the mixed-valence state between Fe(III)[Fe(II)(CN)5] and Fe(II)[Fe(III)(CN)5]. Heat-treatment under vacuum at 350°C yields a new product Fe(II)[Fe(II)(CN)4] the crystal structure of which is different from that of the starting material. The electrical conductivity of the decomposition product obtained at 350 °C is about 105 times higher than that of the starting material.

Optical properties of the monolayers of 5-(1-methyliniidazol-2-yl)- 10,15,20-tris(p-octyloxy-phenyl)porphyrin, 5-(1-methylpyrazol-4-yl)-10,15,20-tris(p-octyloxyphenyl)porphyrin and their zinc(II) complexes have been studied. The π-A isotherms and UV-vis spectra have revealed that the zinc(II) complexes form coordination assemblies between peripheral nitrogen atom and central zinc(II) ion at the air-water interface with very tight molecular packing.

A pair of 5,15-bisdiazoliumylporphyrins with only two meso-substituents, 5,15-bis(1,3-dimethylimidazolium-2-yl)porphyrin 1b and 5,15-bis(1,2-dimethylpyrazolium-4-yl)porphyrin 2b, has been synthesized. The crowded porphyrin 1b intercalates between base pairs of DNA to stabilize the duplex DNA to thermal denaturation due to its high affinity for DNA. The binding of porphyrin 1b to DNA is an exothermic interaction and enthalpically driven. Porphyrin 1b interacts more strongly with poly(dA-dT)2 than with poly(dG-dC)2, and the interaction is more favorable or selective to AT-rich sites than to GC-rich sites.

A reversed phase ion-paired chromatographic method that can be used to determine trace amounts of iron (II,III), nickel (II) and copper (II) was developed and applied to the determination of iron (II) and iron (III) levels in natural water. The separation of these metal ions as their 4,7-diphenyl-1,10-phenanthroline (bathophenanthroline) chelates on an Inertsil ODS column was investigated by using acetonitrile-water (80/20, v/v) containing 0.06 M perchloric acid as mobile phase and diode array spectrophotometric detection at 250-650 nm. Chromatographic parameters such as composition of mobile phase and concentration of perchloric acid in mobile phase were optimized. The calibration graphs of iron (II), nickel (II) and copper (II) ions were linear (r > 0.991) in the concentration range 0-0.5, 0-2.0 and 0-4.0 mug ml(-1), respectively. The detection limit of iron (II), nickel (II) and copper (II) were 2.67, 5.42 and 18.2 ng ml(-1) with relative standard deviation (n = 5) of 3.11, 5.81 and 7.16% at a concentration level of 10 ng ml(-1) for iron (II) and nickel (II) and 25 ng ml(-1) for copper (II), respectively. The proposed method was applied to the determination of iron(II) and iron(III) in tap water and sea water samples without any interference from other common metal ions.

Two nitronyl nitroxide derivatives bearing imidazole and benzimidazole ring were prepared and their hydrogen-bonded structures and magnetic properties were characterized.

Structure and magnetic property of 2-(imidazole-2-yl)-4,4,5,5tetramethyl imidazoline-1-oxyl-3-oxide and its metal complexes are studied in order to identify structure-property relationship.

emi-preparative high-performance liquid chromatography has been used for the preparation of copper(II) bacteriochlorophyll a [Cu(II)-BCh]-a] and zinc(II) bacteriochlorophyll a [Zn(II)-BCh]-a]. Both compounds are separated on a reversed-phase Inertsil ODS-2 column using a mobile phase of acetone-methanol (25:75, v/v). The fractionated metallobacteriochlorophylls (M-Bchl-a) are identified by fast atom bombardment mass spectrometry. The spectroscopic parameters such as the wavelength of absorption maxima and the molar extinction coefficients are determined using pure M-Bchl-a obtained by preparative HPLC. The HPLC method proposed here has been demonstrated to be useful for the purification and determination of components of M-Bchl-a.

Iron(II) chelate complexes of 1,10-phenanthroline (Phen), 4,7-dimethyl-1,10-phenanthroline (DMPhen), 3,4,7,8-tetramethyl-1,10-phenanthroline (TMPhen) and 4,7-diphenyl(batho)-1,10-phenanthroline (DPPhen) were prepared and identified by means of absorption and infrared spectroscopy. The characteristic elution of these complexes on an Inertsil ODS column as well as their separation was investigated by ion-paired reversed phase chromatography. Some parameters influencing the separation such as composition of eluent, counter ion species and their concentrations were also studied. It was found that acetonitrile/water (80/20, v/v) containing 0.06 M HC1O4 gave the best separation for each complex.

Changes in the structure and chemical bonding state of coordination complex crystal, iron(II) tris(1,10-phenanthroline) dithiocyanate (FPhN) by mechanical stress were studied by X-ray diffractometry and infrared spectroscopy. FPhN was completely amorphized after milling by a planetary ball-mill for 5 h. Amorphized FPhN recrystallized at 406 K, but no significant change in the thermal decomposition processes was observed. On amorphization, the ligand field strength of phenanthroline in FPhN was reduced and hence the transition from low spin (1A1g) to high spin (5T2g) occurred gradually on heating, as detected by the increase in the effective magnetic moment.

The components of iron(III) chlorophyllin were separated by high-performance liquid chromatography on a reversed-phase Inertsil ODS column. Good retention was achieved with acetonitrile-phosphate buffer (pH 2) (60:40, v/v) containing 0.01 M tetramethylammonium chloride (TMACl) in studies of the chromatographic behaviour with various elution solvents and their mixtures. Three kinds of iron(III) chlorophyll derivatives, i.e., iron(III) pheophorbide a (Fe-Phed a), iron(III) chlorin e6 (Fe-Chl e6) and iron(III) chlorin e4 (Fe-Chl e4), were detected as major components. Standard materials for qualitative and quantitative analysis were derived from chlorophyll a which was extracted from spinach. The required compounds were prepared under strict conditions by the insert reaction of iron(II) chloride with pheophytins to avoid molecular degradation by light or molecular oxygen.