Published papers

A novel benzotriazinyl radical with a 2,1,3-thiadiazolo fused ring (1,3-diphenyl-1,2-dihydro-[1,2,5]thiadiazolo[3′,4′:3,4]benzo[1,2-e]-1,2,4-triazine-2-yl; NSNBT) was prepared and characterized by ESR measurement, cyclic voltammetry, and X-ray crystallographic analysis. By a detailed study of bond lengths and angles, it was found that the molecular structure of NSNBT borrows characteristics both from 2,1,3-benzothiadiazole and from the unsubstituted benzotriazinyl radical, and the central phenyl ring presents a phenanthrene-type bond alternation. Molecules were shown to be arranged in a π-stacked columnar structure, with columns connected to each other through sulfur-sulfur interactions in the crystal. It exhibited strong antiferromagnetic interactions (J/kB = -434 K) derived from its dimer structure.

A novel benzotriazinyl radical, 3-tert-butyl-7-trifluoromethyl-1,4-dihydro-1-phenyl-1,2,4-benzotriazin-4-yl (2), was prepared and its magneto-structural correlation was investigated. An X-ray crystallographic analysis revealed that 2 forms a 1D column assembly, however, pi-pi interaction was not the driving force of the column structure. The magnetic susceptibility obeyed the Curie-Weiss law with C = 0.369 emu K mol(-1) and theta = +0.7 K. The thermal behavior of wmT was described using the 1D ferromagnetic chain model with J/k(B) = +0.91 K.

Electron-donating dihydrobenzindolocarbazoles (BICs) 1 a-c, which adopt planar disk-shaped geometries, were prepared by gold(I)-catalyzed cyclization as a key step. Due to the presence of a 1,4-phenylenediamine (PD) moiety in the framework, they undergo reversible one-electron oxidation to the corresponding Wurster's Blue (WB)-type species that exhibits NIR absorptions up to λ=1200 nm. In the case of the N,N'-dimethyl derivative, cation radical 1 c(+.) is stable enough to be isolated as a salt and X-ray analysis indicated paraquinoid-type bond alternation in the WB core unit, whereas the bond lengths in the peripheral benzene rings are identical to those in the neutral donor. Upon electrochemical interconversion, the redox pairs of 1 a-c and 1 a-c(+.) exhibited an electrochromic response in the UV/Vis/NIR region, which was accompanied by a drastic change in the fluorescence spectrum because only neutral donors 1 a-c are highly emissive (Φ(F) : 0.7-0.8).

A new radical, 7-phenyl-1,3-bis(4-biphenylyl)-1,4-dihydro-1,2,4-benzotriazin-4-yl (2), was prepared from the iodo group-substituted benzotriazinyl radical 1 with phenyltriolborate salt by the Suzuki–Miyaura cross-coupling reaction at room temperature. An X-ray crystal structural analysis clarified its crystal structure. ESR measurements and DFT calculations revealed that its unpaired electron was more delocalized over the molecule than that of Blatter’s radical due to the substituent effect.

Cu(I)-mediated annulation reaction of a 1,1′-(1,3-butadiyne)-8,8′-(2,5-thiophene)-bridged carbazole dimer 10 with amines provided the N-substituted carbazole-based isophlorines 11a–11c. A similar annulation reaction with selenium in the presence of hydrazine monohydrate afforded hetero-core-modified isophlorine 12. The oxidation of 12 generated the corresponding 21-selena-23-thiaporphyrin 13, which exhibited NIR absorption. The intramolecular charge transfer from Se to S was confirmed by the 1H NMR results along with DFT calculations.

Several tetrakis(phenylethynyl)- and (phenylethynylphenylethynyl)-substituted carbazole-based thiaporphyrins were synthesized. These π-extended porphyrins display remarkably intensified and red-shifted absorption bands in the NIR region up to 1126 nm due to perturbation by the phenylethynyl substituents.

Cu(I)-mediated alkoxylation of doubly 1,3-butadiyne-bridged carbazole dimer 1, followed by acid-catalyzed cyclization, provided furan-bridged carbazole dimer 3, while annulation reaction of 1 with selenium in the presence of hydrazine monohydrate provided selenophene-bridged carbazole dimer 5a. Oxidation of isophlorin 5a afforded carbazole-based selenaporphyrin 5b, which possessed distinct aromaticity and produced intensified and red-shifted absorption bands in the near-IR region.

Peripherally ethynylated carbazole-based core-modified porphyrins were synthesized by sequential metal-catalyzed coupling and annulation reactions. Experimental results and DFT calculations both confirm that the π-conjugated networks of the resulting porphyrins effectively delocalize over the entire macrocycle, including the ethynyl substituent groups.

The carbazole- and indolone-based porphyrinoids 3 and 4 were synthesized by stepwise transition-metal-catalyzed coupling reactions. Palladium metalation of 4 produced 4Pd, which exhibits near-infrared absorption.

A theoretical study of the intermolecular magnetic interaction of [CrN(salpn)] is discussed based on DFT calculations. The close contact between the 2p orbitals on the axial nitrogen and other 3d orbitals besides the 3dxy orbital on the adjacent chromium is effective for ferromagnetic coupling. The magnetic interaction is rationally explained by the significantly large spin polarization of the axial nitrogen.

he theoretical study of the magnetic properties of oxovanadium(IV) complex self-assemblies with tetradentate Schiff base ligands is discussed on the basis of DFT calculations. Large negative spin densities are found on the axial oxygens of the various oxovanadium(IV) complexes. The relationship between the effective exchange parameters Jab and the geometrical parameters for these complexes was studied by changing the position of the neighboring molecules for the purpose of clarifying the mechanism of the ferromagnetic coupling. The intermolecular ferromagnetic interaction of the oxovanadium(IV) complexes with tetradentate Schiff base ligands is significantly affected by the formation of polymeric octahedral structures in the solid state. The overlap between the 2p orbitals of the axial oxygen and the 3d orbitals of the adjacent vanadium is effective for the ferromagnetic coupling. On the other hand, the effect of overlap between the vanadium 3dxy orbitals is too small to lead to magnetic coupling. It was revealed that the intermolecular ferromagnetic interaction of the polynuclear oxovanadium(IV) complexes is significantly affected by the spin polarization on the axial oxygen.

Going around in circles: The copper(I)-mediated annulation of a doubly 1,3-butadiyne-bridged carbazole dimer with amines or Na2S provides isophlorins containing carbazole or thiophene-carbazole moieties, respectively (see scheme). Oxidization of the thiophene-containing isophlorin with MnO 2 gives the corresponding porphyrin, which displays distinct aromaticity and remarkably intensified and red-shifted absorption bands in the near IR region.

The ct-DNA binding properties of methylene blue (MB) including binding constant, thermodynamic parameter and thermal denaturation (T(m)) have been systematically studied by spectrophotometric method. The binding of MB to ct-DNA is quite strong as indicated by remarkable hypochromicity, red shift and equilibrium binding constant (K(b)). Van't Hoff plot of 1/T versus lnK(b) suggests that the MB dye binds exothermically to ct-DNA which is characterized by large negative enthalpy and entropy changes. According to polyelectrolyte theory, the charge release (Z) when ct-DNA interacts with MB is +1.09 which corresponds very well to the one positive charge carried by the MB dye. The K(b) at a low concentration of salt is dominated by electrostatic interaction (90%) while that at a high concentration of salt is mostly controlled by non-electrostatic process (85%). However, the stabilization of the DNA binding event in both cases is governed by non-electrostatic process. A moderate stabilization of double helix ct-DNA occurs when the MB dye binds to ct-DNA as indicated by the increase in T(m) of ct-DNA of about 5.5 degrees C in the presence of MB. This suggests that MB dye possibly binds to ct-DNA via electrostatic and intercalation modes.

The interaction of nickel(II) complex of cationic porphyrins bearing five-membered rings, meso-tetrakis(1,2-dimethylpyrazolium-4-yl) porphyrinatonickel(II) (NiPzP), with synthetic polynucleotides poly(dG-dC) 2 and poly(dA-dT) 2 has been characterized by viscometric, visible absorption, CD and MCD spectroscopic, and melting temperature measurements. The nickel(II) complex NiPzP is intercalated into poly(dG-dC) 2 but outside bound to the major groove of poly(dA-dT) 2. The binding constants of NiPzP to poly(dG-dC) 2 and poly(dA-dT) 2 are in the order of 10 6 M -1 and comparable to those of other reported cationic metalloporphyrins. The binding process of NiPzP to poly(dG-dC) 2 and poly(dA-dT) 2 is endothermic and entropically driven.

A series of mono-, di-, tetra-and hexacationic esters of pyropheophorbide a/b have been designed and synthesized to explore the intercalation of their phorbine ring between the base pairs of double-helical DNA and the influence of their peripheral substituents on the DNA interactions. Mono-(1), di-(2, 3) and tetra-(4, 5) cationic pyropheophorbides are soluble as an oligomeric aggregate in HEPES buffer, but hexa-(6) cationic pyropheophorbide is soluble as a monomer at lower concentrations. The interaction of these cationic pyropheophorbide derivatives with DNA has been investigated by DNA unwinding assay,fluorescence energy transfer, and measurements of the melting temperature of the double-helical DNA and visible absorption spectra. Dicationic 2 and 3 bind outside the double-helical DNA without and/or with self-aggregation and with self-aggregation, respectively, because they cannot intercalate between the base-pairs due to their aggregation. On the other hand, tetracationic 4 and 5 and hexacationic 6 intercalate between the base pairs of the double-helical DNA. The binding mode of the cationic pyropheophorbides a/b is strongly dependent on the number and position of the cationic peripheral substituents of the pyropheophorbides.

Electronic structures and magnetic properties of Cu(II) complexes with axially coordinated nitronyl nitroxide radicals are discussed on the basis of computational study using density functional theory (DFT) calculation. The tendency of the effective exchange integrals J is examined by changing the position of the nitronyl nitroxide moiety. The spin density distributions for these complexes are also estimated in order to understand the mechanism of the ferromagnetic interaction. The relationship between the geometrical parameters and the magnetic interaction indicates the delocalization of the unpaired electron from the π* orbital of the nitronyl nitroxide group to the 3dz2 atomic orbital of the Cu(II) ion. On the other hand, there is practically no dependence of the overlap between the 3dx2-y2 atomic orbital of the Cu(II) ion and the π* orbital of the nitronyl nitroxide group on the magnitude of the ferromagnetic coupling. It is revealed that the delocalization mechanism is important for the ferromagnetic properties in Cu(II) complexes with axially coordinated nitronyl nitroxide radicals.

The enantioselective binding of [Fe(4,7-dmp)(3)](2+) (dmp: 4,7-dimethyl-1,10-phenantroline) and [Fe(3,4,7,8-tmp)(3)](2+) (tmp: 3,4,7,8-tetramethyl-1,10-phenanthroline) to calf-thymus DNA (ct-DNA) has been systematically studied by monitoring the circular dichroism (CD) spectral profile of the iron(II) complexes in the absence and presence of ct-DNA. The effect of salt concentration and temperature on the degree of enantioselectivity of the ct-DNA binding of the iron(II) complexes, i.e. the molar ratio of Delta- to Lambda-enantiomer in the solution or vice versa has been rigorously evaluated. It is noticeable that Delta-[Fe(4,7-dmp)(3)](2+) and Lambda-[Fe(3,4,7,8-tmp)(3)](2+) are preferentially bound to ct-DNA as reflected in their opposite CD spectral profiles. The preferential binding of the A-enantiomer of [Fe(3,4,7,8-tmp)(3)](2+) to ct-DNA compared to that of the A-enantiomer is associated with the bulkiness of the ancillary ligands due to substitution of four hydrogen atoms in 1,10-phenanthroline for four methyl groups. The determination of enantiomeric inversion constant (K-inv) at various salt concentrations has revealed that the degree of enantioselectivity is salt concentration dependent, indicating that electrostatic interaction is involved in the enantioselective binding of the iron(II) complexes to ct-DNA. Although [Fe(4,7-dmp)(3)](2+) and [Fe(3,4,7,8-tmp)(3)](2+) exhibit an opposite pattern in the CD spectra, the degree of their enantioselectivity (K-inv) is not different from each other significantly. A thermodynamic study on the enantioselective binding of [Fe(4,7-dmp)(3)](2+) to ct-DNA using the van't Hoff plot of lnK(inv) versus 1/T has demonstrated that the enthalpy change (Delta H-o) in the inversion process from the Lambda- to Delta-enantiomer of [Fe(4,7-dmp)(3)](2+) ct-DNA is positive, indicating that the process is endothermic and thus entropically driven. @ 2008 Elsevier Inc. All rights reserved.

The influence of methyl substitution on the thermodynamic parameters for the binding of [Fe(DMP)(3)](2+) and [Fe(TMP)(3)](2+) (DMP = 4,7-dimethyl-1,10-phenanthroline, TMP = 3,4,7,8-tetramethyl-1,10-phenanthroline) to calf thymus DNA (ct-DNA) has been studied by determining their equilibrium binding constants (K-b) at various salt concentrations and temperatures. Kb of the iron(II) complexes to ct-DNA decreases with the salt concentration in the solution, suggesting considerable electrostatic interaction in the ct-DNA binding of the iron(II) complexes. In contrast, Kb of the DNA binding increases with temperature, indicating that the DNA binding reaction of the complex is endothermic and entropically driven. The evaluation of the non-electrostatic binding constant (K-t(0)) based on polyelectrolyte theory has revealed that the K-t(0) portions of the total binding constant (Kb) are relatively large and reach 46.4% for [Fe(DMP)3]2+ at [Na+] = 0.075 m and 43.9% for [Fe(TMP)(3)](2+) at [Na+] = 0.100 M. The contribution of non-electrostatic binding free energy (Delta G(t)(0)) to total binding free energy change (AGO) is extremely large, L e. > 90 % for both iron(II) complexes at [Na+] = 0.05 M, suggesting that the stabilization of the DNA binding is mainly contributed from the non-electrostatic process. The effect of methyl substitution on electrostatic (AGO and non-electrostatic (Delta G(t)(0)) binding free energy changes has been systematically evaluated using the quantity of Delta Delta G(pe)(0) and Delta Delta G(t)(0) relative to that of the parent iron(II) complex, [Fe(phen)(3)](2+). The results indicate that the substitution of hydrogen atoms in the phen ligand by methyl groups decreases slightly the electrostatic binding free energy changes, but tremendously increases the non-electrostatic ones to yield net binding free energy changes which are more favorable for the ct-DNA binding.