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Water-soluble phthalocyanine (Pc) derivatives have been studied extensively as not only effective photosensitizers for photodynamic therapy (PDT), but also G-quadruplex ligands which have the poten...

Background: Amyloid β (Aβ) peptide deposition is considered as the main cause of Alzheimer’s disease (AD). Previously, we have shown that a Zn containing neutral phthalocyanine (Zn-Pc) inhibits Aβ fibril formation. Objective: The objective of this study is to investigate the effects of a cationic gallium containing Pc (GaCl-Pc) on Aβ fibril formation process. Methods and Results: Aβ fibril formation was induced by incubating synthetic Aβ peptides in a fibril forming buffer, and the amount of fibril was evaluated by ThT fluorescence assay. GaCl-Pc dosedependently inhibited both Aβ1-40 and Aβ1-42 fibril formation. It mainly inhibited the elongation phase of Aβ1-42 fibril formation kinetics, but not the lag phase. Western blotting results showed that it did not inhibit its oligomerization process, rather increased it. Additionally, GaCl-Pc destabilized preformed Aβ1- 42 fibrils dose-dependently in vitro condition, and decreased Aβ levels in the brain slice culture of APP transgenic AD model mice (J20 strain). Near-infrared scanning results showed that GaCl-Pc had the ability to bind to Aβ1-42. MTT assay demonstrated that GaCl-Pc did not have toxicity towards a neuronal cell line (A1) in culture rather, showed protective effects on Aβ-induced toxicity. Moreover, it dosedependently decreased Aβ-induced reactive oxygen species levels in A1 culture. Conclusion: Thus, our result demonstrated that GaCl-Pc decreased Aβ aggregation and destabilized the preformed fibrils. Since cationic molecules show a better ability to cross the blood-brain barrier, cationic GaCl-Pc could be important for the therapy of AD.

5,15-Diazaporphyrins are porphyrin analogues with imine-type sp2-hybridized nitrogen atoms at the meso-positions. Even though these compounds are more electron-deficient than regular porphyrins, the use of iron diazaporphyrins as catalysts has not been reported. Herein, we disclose the synthesis, structure, and electronic properties of iron(III) 5,15-diazaporphyrins. We evaluate their structures and electronic natures by X-ray analysis and electrochemical analyses. We also demonstrate that chloroiron(III) 5,15-diazaporphyrins exhibit high catalytic activity in the direct oxidation of alkanes due to their intrinsic electron-deficient nature. On the basis of stoichiometric reactions of iron(III) diazaporphyrin with iodosylbenzene as an oxidant, it was possible to demonstrate the existence of an iodosylbenzene-iron diazaporphyrin adduct reaction intermediate that serves as a reservoir to generate oxo-iron species.

Subphthalocyanine (SubPc) macrocycles are known as an interesting class of nonplanar aromatic dyes. Despite documented high fluorescence and singlet oxygen quantum yields, the properties of SubPcs in photodynamic therapy (PDT) are underestimated, because their absorption bands do not reach a significant wavelength range. With this in mind, we combined a SubPc ring and a SubPc ring by introducing a common benzene ring and obtained a SubPc dimer (2) and trimer (3) with the Q-band at the near-IR region, owing to the expansion of the [Formula: see text] electron conjugated system. In this study, we reported1O2generation abilities of 2 and 3based on the applied absolute singlet oxygen quantum yields ([Formula: see text]absolute). Subsequent research revealed that 2 and 3 showed the potential to generate1O2to not only in toluene but also in DMSO. Although the photocytotoxicity of 2 and 3 were investigated upon photo-irradiation with a low light dose of approximately 1.5 J/cm2, 2 and 3 showed almost negligible toxic properties toward HEp2 cells.

Oxidation of 5,15-dithiaporphyrin with meta-chloroperbenzoic acid afforded the corresponding S,S-tetraoxide in good yield. The resultant 5,5,15,15-tetraoxo-5,15-dithiaporphyrin exhibited the highly electron-deficient nature as elucidated by the electrochemical analysis and theoretical calculations. Treatment of tetraoxodithiaporphyrin with zinc(II) acetate and nickel(II) acetate provided the corresponding metal complexes efficiently. Owing to its enhanced Lewis acidity of the metal center by the electron-deficient ligand, the nickel complex underwent facile axial ligation to form pentacoordinate and hexacoordinate high-spin (S=1) complexes in solution and solid, respectively. The binding constant of pyridine to the NiII center was significantly higher than those of conventional porphyrin NiII complexes. Temperature-dependent magnetic susceptibility measurements of the high-spin NiII complex revealed the presence of weak ferromagnetic interactions.

A bis(NiII -porphyrinyl)aminyl radical with meso-C6 F5 groups was prepared as a spin-delocalized stable aminyl radical with a doublet spin state. Upon addition of pyridine, both NiII centers became hexacoordinated by accepting two axial pyridines, which triggered a spin-state change of the NiII centers from diamagnetic (S=0) to paramagnetic (S=1). The resulting high-spin NiII centers interact with the aminyl radical ferromagnetically to give rise to an overall sextet state (S=5/2). Importantly, this coordination-induced spin-state switching can be conducted in a reversible manner, in that washing of the high-spin radical with aqueous hydrochloric acid regenerates the original doublet radical in good yield.

The cationic Ga(III) and Zn(II) phthalocyanines carrying N-methyl-pyridinium groups at eight peripheral β-positionshave been synthesized. These complexes are highly soluble in dimethyl sulfoxide (DMSO) and moderately soluble in water and phosphate buffered saline (PBS); both Ga(III)Cl and Zn(II) complexes have shown no aggregation in water up to 1.2 × 10−4 and 1.5 × 10−5 M, respectively. A higher water-solubility of Ga(III)Cl complex as compared to Zn(II) complex is ascribed to the presence of an axially coordinated chloride. The spectroscopic properties, photogeneration of singlet oxygen (1O2), and cytotoxicity of these complexes have been investigated. The absolute quantum yields (ΦΔabsolute) for the photogeneration of singlet oxygen using Ga(III)Cl and Zn(II) complexes have been determined to be 4.4 and 5.3%, respectively, in DMSO solution. The cytotoxicity and intracellular sites of localization of Ga(III)Cl and Zn(II) complexes have been evaluated in human HEp2 cells. Both complexes, localized intracellularly in multiple organelles, have shown no cytotoxicity in the dark. Upon exposure to a low light dose (1.5 J/cm2), however, Zn(II) complex has exhibited a high photocytotoxicity. The result suggests that Zn(II) complex can be considered as a potential photosensitizer for Photodynamic therapy (PDT).

5,15-Diazaporphyrins are porphyrin analogues with imine-type sp

Interaction between an Ga(III) phthalocyanine (Pc) derivative bearing eight N-methylpyridinium groups at peripheral β-positions (2,3,6,7,10,11,14,15-octakis-[N-methyl-(4-methylpyridinium-3-yloxy)phthalocyaninato] chloro gallium(III) iodide (GaPc)) and an all parallel-stranded tetrameric G-quadruplex formed from a heptanucleotide d(TTAGGGT) ([d(TTAGGGT)]4) has been investigated to elucidate the molecular recognition of G-quadruplex DNA by the Pc derivative, which provides a useful insight as to the design of G-quadruplex ligands suitable for various in vitro and in vivo applications. We found that GaPc binds to the A3G4 and G6T7 steps of [d(TTAGGGT)]4, with binding constants of (21 ± 2) × 106 and (0.09 ± 0.06) × 106 M−1, respectively, to form a 2:1 complex. Obviously, upon the binding of GaPc to each of the sites, the π-π stacking and electrostatic interactions of the Pc moiety and positively-charged side chains of GaPc with a G-quartet and the negatively-charged phosphate groups in nearby phosphodiester bonds of the DNA, respectively, are major driving forces for the complexation. Considering the similarity in the local structural environment between the A3G4 and G6T7 steps of [d(TTAGGGT)]4, the remarkably large difference in the GaPc-binding affinity between them is most likely accounted for by the effect of the polarity of the GaPc-binding site on the intermolecular electrostatic interaction. This finding provides valuable insights as to the design of Pc derivatives as G-quadruplex ligands.

Fused benzene rings to antiaromatic compounds generally improve their stability but attenuate their antiaromaticity. The opposite case is now reported. NiII benzonorcorroles were synthesized and the effect of benzo-fusion on the antiaromaticity was elucidated. The benzo-fusion resulted in significant decrease of the HOMO-LUMO gaps and enhancement of the paratropic ring current effect. Furthermore, the introduction of the benzo groups induced singlet diradical character in the antiaromatic porphyrinoid.

Pyrrocorphin is an air-sensitive porphyrinoid with a highly reduced hexahydroporphyrin core. In contrast, pyrrolidine-fused pyrrocorphin (Pyr) obtained by successive 1,3-dipolar cycloaddition reactions of azomethine ylide to 5,10,15,20-tetrakis(pentafluorophenyl)porphyrin is less air-sensitive. In order to reveal the effect of highly reduced porphyrin rings on the physicochemical properties of their metal complexes, we have prepared diamagnetic (S=0) Ni(II) complex Ni(II)(Pyr). The addition of excess pyridine (Py) to the toluene solution of Ni(II)(Pyr) yielded five-coordinate Ni(II)(Pyr)(Py), which was then completely converted to six-coordinate paramagnetic (S=1) Ni(II)(Pyr)(Py)2. The latter was characterized by UV-Vis, 1H NMR, CV, SQUID, and X-ray crystallography as well as DFT calculations. As compared with analogous complexes of porphyrin (Por), chlorin (Chl), and isobacteriochlorin (Iso) reported by Herges and co-workers (R. Herges et al., Inorg. Chem. 2015), Ni(II)(Pyr)(Py)2 has longer equatorial NiN and shorter axial NiN bonds. The CV study has shown a large decrease in HOMO-LUMO gap as the reduction of porphyrin ring proceeds, which has further been confirmed by UV-Vis and DFT calculation. Titration studies using 1H NMR and UV-Vis have shown that the first binding constant of pyridine toward Ni(II)(Pyr) is ca. 4 times as large as that of Ni(II)(Iso) and ca 230 times as large as that of Ni(II)(Por). Thus, we have concluded that the binding constant of pyridine to Ni(II) porphyrinoid increases by the following order: Por

In contrast to the general tendency that six coordinate iron(iii) porphyrin complexes with neutral oxygen ligands adopt a high-spin state in a wide range of temperature, some complexes with substituted pyridine N-oxides have exhibited spin-crossover from high-spin to low-spin states with decreasing temperature both in solution and in the solid state.

Dinuclear rhodium(I) complexes, [Rh(4-Me-pf) (cod)]2 (1), [Rh(3,5-Me2-pf) (cod)]2 (2), [Rh(4-Me-pf) (nbd)]2 (3), [Rh(3,5-Me2-pf) (nbd)]2 (4), and [Rh(2,6-F2-pf) (nbd)]2 (5), have been synthesized and characterized by X-ray structure analysis, 1H, 13C, and 19F NMR, UV–vis, ESI-TOF-MS, and elemental analysis. In these complexes, two rhodium atoms are bridged by two formamidinato ligands and each rhodium atom is coordinated by one chelating cod or nbd ligand to form an approximately square planar coordination structure with two nitrogen atoms and two double bonds. The Rh··Rh distances are in the range of 3.2668 to 2.9726 A, suggesting a direct bonding interaction between two rhodium atoms. Variable temperature NMR studies in CD2Cl2 solution have revealed that 1–5 exhibit a novel dynamic behavior, that is, an interconversion between two enantiomers. The activation parameters for racemization have been determined by the line shape analyses of the 1H and 19F NMR spectra taken at various temperatures. Variable temperature NMR studies have also revealed that the rotation rates of the four aryl groups around N–C(aryl) bonds are extremely different in each complex. The cyclic voltammetry study has shown that the oxidation potentials corresponding to Rh23+/Rh2+ are 0.41 V in the cod complexes (1 and 2) while those in the nbd complexes (3–5) have shown negative shift by ca. 0.2 V. The reasons for the difference in dynamic behaviors and redox properties among these complexes have been discussed.

To determine the optimal conditions for the stabilization of cationic zinc phthalocyanine (ZnPc4+) monomers within an aqueous medium, the adsorption behavior of ZnPc4+ on the surface of an anionic clay nanosheet was investigated. It was determined that ZnPc4+ could be adsorbed as a monomer on the surface of an anionic clay nanosheet dispersed in an aqueous medium, containing up to 0.9 ZnPc4+ per cationic exchange site on the clay nanosheet. It was observed that the concentration of ZnPc4+ monomers in the aqueous solution was negligible when the concentration of ZnPc4+ was low. When ZnPc4+ monomers – after having been adsorbed on the surface of the anionic clay nanosheet – were photoexcited by visible light (690 nm) in the presence of 9,10-antracenediyl-bis(methylene) dimolonoic acid (ADMA), the typical absorbance of ADMA at 398 nm decreased with an increase in irradiation time. This is indicative of the photogeneration of a singlet oxygen in aqueous ZnPc4+, due to a highly stabilized ZnPc4+ monomer on anionic clay nanosheet surface. The external quantum yield of decomposed ADMA in the presence of the anionic clay nanosheet colloid in aqueous medium was measured to be 2.62 × 10−5.

Copper complexes of corroles have recently been a subject of keen interest due to their ligand non-innocent character and unique redox properties. Here we investigated bis-copper complex of a triply-linked corrole dimer that serves as a pair of divalent metal ligands but can be reduced to a pair of trivalent metal ligands. Reaction of triply-linked corrole dimer 2 with Cu(acac)2 (acac=acetylacetonate) gave bis-copper(II) complex 2Cu as a highly planar molecule with a mean-plane deviation value of 0.020 A, where the two copper ions were revealed to be divalent by ESR, SQUID, and XPS methods. Oxidation of 2Cu with two equivalents of AgBF4 gave complex 3Cu, which was characterized as a bis-copper(II) complex of a dicationic triply-linked corrole dimer not as the corresponding bis-copper(III) complex. In accord with this assignment, the structural parameters around the copper ions were revealed to be quite similar for 2Cu and 3Cu. Importantly, the magnetic spin-spin interaction differs depending on the redox-state of the ligand, being weak ferromagnetic in 2Cu and antiferromagnetic in 3Cu.

Lantern-type dinuclear complexes, cis-[Ru2{3,5-(CF3)2-pf}2(O2CMe)2Cl] and [Ru2{3,5-(CF3)2-pf}3(O2CMe)Cl] (3,5-(CF3)2-pf− = N,N′-bis[3,5-bis(trifluoromethyl)phenyl]formamidinate anion), were prepared and characterized. The cis-(2:2) and (3:1) arrangements of the formamidinate and acetate bridging ligands around the Ru25+ core were confirmed by the X-ray crystal analysis as well as 1H and 19F NMR spectra (measured at 25 °C in CD2Cl2), where paramagnetic shifts were observed for the signals due to the unpaired electrons in the dinuclear core. Variable-temperature magnetic moments (2–300 K) showed the existence of three unpaired electrons in the dinuclear units with the large D values (60 cm−1 for the cis-(2:2) Ru25+ complex and 50 cm−1 for the (3:1) Ru25+ complex). The electronic state with S = 3/2 was also ascertained by the EPR spectra measured in solid at 4 K and in frozen toluene/dichloromethane solution at 15 K, absorption spectra in dichloromethane and cyclic voltammograms (CVs) in THF using tetra-n-butyl ammonium perchlorate (TBAP) as electrolyte.

Fused benzene rings to antiaromatic compounds generally improve their stability but attenuate their antiaromaticity. The opposite case is now reported. Ni

Low-spin iron(III) tetrapropylchlorins [ Fe ( TnPrC ) L2]±(L = HIm, 1-MeIm, DMAP, CN-, 4-CNPy,tBuNC) adopt the dxy-type ground state regardless of the nature of axial ligands. Among the complexes examined, [ Fe ( TnPrC )(tBuNC )2]+has shown quite unique spectroscopic properties as described below. (1)1H NMR signals were extremely broad as compared with those of other complexes. In particular, 5,20- CH2(α) signal was too broad to detect. (2) No signals except Cγwere observed in13C NMR spectra. (3) Tetragonal splitting parameter (|Δ|) estimated by the EPR g values at 4.2 K reached as much as 12.4 λ, which is the largest |Δ| value among all the low-spin iron(III) porphyrins and porphyrinoids reported previously. On the basis of these results, we have concluded that [ Fe ( TnPrC )(tBuNC )2]+adopts the low-spin iron(III) with (dxz, dyz)4(dxy)1electronic ground state at 4.2–30 K where the EPR spectra are taken, while it should be expressed as the low-spin Fe ( II ) chlorin π-radical cation [ FeII( TnPrC.)(tBuNC )2]+at ambient temperature where the NMR spectra are taken.

A dinuclear copper(II) phthalocyanine complex with 12 2,6-dimethylphenoxyl groups at the peripheral positions of the [ CuPc ]2 framework, where [ CuPc ] units are linked by a common annulated benzene ring to give the planar dinuclear structure, was prepared and characterized. The introduced bulky 2,6-dimethylphenoxyl groups were revealed to effectively suppress the aggregation of the dinuclear complex in the toluene solution, showing a considerably red-shifted Q-band at 838 nm. The EPR spectrum (measured in the frozen toluene solution at 15 K) and temperature-dependent magnetic moment indicated the existence of antiferromagnetic interaction between the copper(II) ions. The exchange integral J was estimated to be -1.8 cm-1 using Bleaney Bowers equation for the S1 = S2 = 1/2 system. The long-range interaction ( Cu – Cu distance = 10.7 Å) through the common annulated benzene ring between two [ CuPc ] units was confirmed by the DFT calculation result.

Homo- and hetero-dinuclear nickel(II), copper(II), and oxidovanadium(IV) complexes of a Schiff-base-fused phthalocyanine (pc) with bulky substituents, 2,6-dimethylphenoxy and t -butyl groups, were prepared and characterized. The introduced salen-like Schiff-base unit was shown to affect the spectral feature based on the pc unit in the near infrared region, the Q band being widely split over 600–800 nm. A fairly large ferromagnetic interaction ( J = 6.0 cm −1 ) was observed for the Cu II (pc)–Cu II (salen) homo-dinuclear complex, while an antiferromagnetic interaction ( J = −3.2 cm −1 ) was observed for the Cu II (pc)–V IV O(salen) hetero-dinuclear complex.

Lantern-type dinuclear complexes, cis-[Ru2(4-Me-pf)2(O2CMe)2Cl] and trans-[Ru2(2,6-Et2-pf)2(O2CMe)2Cl] (4-Me-pf− = N,N′-bis(4-methylphenyl)formamidinate ion and 2,6-Et2-pf− = N,N′-bis(2,6-diethylphenyl)formamidinate ion), were prepared and characterized. The dinuclear structures with cis- and trans-arrangements of the bridging ligands were confirmed by the X-ray crystal structures as well as 1H NMR spectra (298 K) in CD2Cl2, where the proton signals were observed at widely spread positions δ = − 80 to 25 ppm. Variable-temperature magnetic moments (2–300 K) showed the existence of three unpaired electrons in dinuclear units with large D values (65 cm− 1 for cis-Ru2II,III and 90 cm− 1 for trans-Ru2II,III).

Liquid chromatography/linear ion trap mass spectrometry (LC/LIT-MS(n)) was used to construct a database of disperse dyes. Fifty-three standard dyes were subjected to LC/LIT-MS(n) and characterized based on their mass spectra (MS, MS(2), and MS(3)), values of λmax (maximum absorption wavelength in the UV-visible spectrum), and retention times. The results demonstrate that it is possible to reliably identify coexisting dyes that cannot be separated by LC or detected by diode array detection due to their low molecular absorption coefficients. In addition, the by-products included in the standard dyes were found to provide important information for the identification and discrimination of dyestuffs synthesized using different processes. The confirmation of the effectiveness of LC/LIT-MS(n) analysis in detecting small amounts of disperse dyes in this study shows its potential for use in the discrimination of dyed fibers obtained at crime scenes.

Electronic structures of five- and six-coordinate iron(III) corrolazine complexes are determined by means of1H NMR,13C NMR, EPR, and Mössbauer spectroscopy as well as SQUID magnetometry. A series of five-coordinate complexes, [FeIII(TBP8Cz)(L)]* where the axial ligands(L) are cyanide(CN-), imidazole(HIm), 1-methylimidazole(1-MeIm), 4-(N,N-dimethylamino)pyridine(DMAP), pyridine(Py), 4-cyanopyridine(4-CNPy), and tert-butylisocyanide(tBuNC), are obtained by the addition of 1 to 2 equiv. of the ligands to the dichloromethane solutions of FeIII(TBP8Cz) at 298 K: TBP8Cz is a trianion of 2,3,7,8,12,13,17,18-octakis(4-tert-butylphenyl)corrolazine. These complexes commonly show the S = 3/2 at 298 K. By contrast, formation of the six-coordinate complexes depends on the nature of the axial ligands. While the addition of 3 equiv. of CN-has completely converted FeIII(TBP8Cz) to (Bu4N)2[FeIII(TBP8Cz)(CN)2] at 298 K, the conversion to the bis-adduct is only attained below ca. 200 K in the case of HIm, 1-MeIm, and DMAP even in the presence of 50 equiv. of the ligands. If the axial ligand is Py, 4-CNPy, ortBuNC, the formation of [FeIII(TBP8Cz)(L)2] is confirmed only at an extremely low temperature (15 K). Close inspection of the1H NMR and EPR spectra has revealed that all the bis-adducts adopt the (dxy)2(dxz, dyz)3ground state. While FeIII(TBP8Cz) forms paramagnetic bis- and mono-adduct in toluene solution at 298 K in the presence of excess amount of CN-andtBuNC, respectively, the corresponding porphyrazine complex, [FeIII(TBP8Pz)]Cl , forms diamagnetic bis-CN and bis-tBuNC under the same conditions: TBP8Pz is a dianion of 2,3,7,8,12,13,17,18-octakis(4-tert-butylphenyl)-porphyrazine. Thus, the iron(III) ion of porphyrazine complex is more easily reduced than that of the corresponding corrolazine complex.

Cationic 2,9,16,23-tetra(3-N,N,N-trimethylaminoethyloxy)phthalocyaninatozinc(II) (complex 1) and 22,23-di(4-N,N,N-trimethylaminophenyl)benzo[b]-7,8,12,13,17,18-hexa(4-t-butylphenyl) porphyrazinatozinc(II) (complex 2) were loaded on the surface of silica gel by use of an electrostatic interaction with deprotonated silanol groups of silica gel. While complex 1 formed its dimer with increase in the amount of the complex in the composite, complex 2 hardly formed the dimer in the composite due to the steric hindrance of its peripheral substituents. 1,3-diphenylisobenzofuran was photo-oxidized using the composites as the sensitizer in aerated methanol. The reaction proceeded with singlet dioxygen generated by the visible-light irradiation upon the sensitizer. While the initial reaction rate with the composite of complex 2 steadily increased in accordance with increase in the amount of the complex, that with the composite of complex 1 at first increased, but subsequently decreased due to the formation of the photo-inactive dimer. Bilirubinditaurate was also photo-oxidized using the composites as the sensitizer in an aerated aqueous solution. The reaction proceeded with superoxide instead of singlet dioxygen. The relationship between the initial reaction rate and the amount of the complex was similar to that in methanol.

Oxidation of essentially pure intermediate-spin iron(III) porphyrinates such as ruffled Fe(T i PrP)ClO 4 and saddled Fe(OETPP)ClO 4 produces the corresponding six-coordinate iron(III) porphyrin(por) radical cations [Fe(Por )(ClO 4 ) 2 ], where T i PrP and OETPP are dianions of 5,10,15,20-tetraisopropylporphyrin and 2,3,7,8,12,13,17,18-octaethyl-5,10,15,20-tetraphenylporphyrin, respectively. Spin–spin interactions in these complexes are very much different; while ruffled [Fe(T i PrP )(ClO 4 ) 2 ] exhibits no antiferromagnetic coupling, saddled [Fe(OETPP )(ClO 4 ) 2 ] does exhibit it. The difference in magnetic behaviors has been explained in terms of the deformation mode and electron configuration of these complexes.

A series of low-spin, six-coordinate complexes [Fe(TBzTArP)L(2)]X (1) and [Fe(TBuTArP)L(2)]X (2) (X = Cl(-), BF(4)(-), or Bu(4)N(+)), where the axial ligands (L) are HIm, 1-MeIm, DMAP, 4-MeOPy, 4-MePy, Py, and CN(-), were prepared. The electronic structures of these complexes were examined by (1)H NMR and electron paramagnetic resonance (EPR) spectroscopy as well as density functional theory (DFT) calculations. In spite of the fact that almost all of the bis(HIm), bis(1-MeIm), and bis(DMAP) complexes reported previously (including 2) adopt the (d(xy))(2)(d(xz), d(yz))(3) ground state, the corresponding complexes of 1 show the (d(xz), d(yz))(4)(d(xy))(1) ground state at ambient temperature. At lower temperature, the electronic ground state of the HIm, 1-MeIm, and DMAP complexes of 1 changes to the common (d(xy))(2)(d(xz), d(yz))(3) ground state. All of the other complexes of 1 and 2 carrying 4-MeOPy, 4-MePy, Py, and CN(-) maintain the (d(xz), d(yz))(4)(d(xy))(1) ground state in the NMR temperature range, i.e., 298-173 K. The EPR spectra taken at 4.2 K are fully consistent with the NMR results because the HIm and 1-MeIm complexes of 1 and 2 adopt the (d(xy))(2)(d(xz), d(yz))(3) ground state, as revealed by the rhombic-type spectra. The DMAP complex of 1 exists as a mixture of two electron-configurational isomers. All of the other complexes adopt the (d(xz), d(yz))(4)(d(xy))(1) ground state, as revealed by the axial-type spectra. Among the complexes adopting the (d(xz), d(yz))(4)(d(xy))(1) ground state, the energy gap between the d(xy) and d(π) orbitals in 1 is always larger than that of the corresponding complex of 2. Thus, it is clear that the benzoannelation of the porphyrin ring stabilizes the (d(xz), d(yz))(4)(d(xy))(1) ground state. The DFT calculation of the bis(Py) complex of analogous iron(III) porphyrinate, [Fe(TPTBzP)(Py)(2)](+), suggests that the (d(xz), d(yz))(4)(d(xy))(1) state is more stable than the (d(xy))(2)(d(xz), d(yz))(3) state in both ruffled and saddled conformations. The lowest-energy states in the two conformers are so close in energy that their ordering is reversed depending on the calculation methods applied. On the basis of the spectroscopic and theoretical results, we concluded that 1, having 4-MeOPy, 4-MePy, and Py as axial ligands, exists as an equilibrium mixture of saddled and ruffled isomers both of which adopt the (d(xz), d(yz))(4)(d(xy))(1) ground state. The stability of the (d(xz), d(yz))(4)(d(xy))(1) ground state is ascribed to the strong bonding interaction between the iron d(xy) and porphyrin a(1u) orbitals in the saddled conformer caused by the high energy of the a(1u) highest occupied molecular orbital in TBzTArP. Similarly, a bonding interaction occurs between the d(xy) and a(2u) orbitals in the ruffled conformer. In addition, the bonding interaction of the d(π) orbitals with the low-lying lowest unoccupied molecular orbital, which is an inherent characteristic of TBzTArP, can also contribute to stabilization of the (d(xz), d(yz))(4)(d(xy))(1) ground state.

Photoluminescence (PL) properties of meso-tetraphenylporphine-4, 4′, 4″, 4‴-tetracarboxylic acid (H2TPP(COOH)4) bound to ZnO nanoparticle were studied. With 1.2 H2TPP(COOH)4 molecules per ZnO particle, the PL intensity of H2TPP(COOH)4 with a 325 nm excitation was increased to a 3.2-times larger value by the conjugate formation with ZnO. The excitation spectrum of PL gave an evidence of an emission of H2TPP(COOH)4 by an energy transfer from ZnO. An analysis based on the Forster theory gave a reasonable value of 1.8 nm for the average distance between H2TPP(COOH)4 and emissive surface defects on the ZnO particle.

The optical absorption and photoluminescence measurements were carried out for ZnO nanoparticle–tetraphenylporphyrin (TPP) systems made of four kinds of TPP’s with and without p -aminophenyl groups. The ZnO particles were treated with l -cysteine in order to make a ZnO–( l -cysteine)–TPP binding. However, this binding was not formed because of an absence of the ZnO–( l -cysteine) binding. In the case of metal-free TPP’s, the central hydrogen atoms of the TPP ring were replaced by a Zn atom during an aging of 2–4 weeks. An energy transfer from photoexcited ZnO to TPP occurs by a collision between ZnO and TPP in the dispersed medium.

Electronic structure of a series of five-coordinate Fe ( OArTAzP ) X ( OAr = octaaryltetraazaporphyrin , X = Cl-, Br-, I-; Ar = 4-tert-butylphenyl) have been examined on the basis of1H NMR,13C NMR, and EPR spectroscopy as well as SQUID magnetometry. These complexes adopt the intermediate-spin state as in the case of analogous complexes reported by Fitzgerald et al. (Inorg. Chem. 1992; 31: 2006-2013) and Stuzhin et al. (Inorg. Chim. Acta 1995; 236: 131-139). The13C NMR studies using13C -enriched complexes at the pyrrole α positions have revealed that the pyrrole- Cαsignals appear at extraordinary upfield positions, i.e. -130 to -250 ppm at 273 K, due to the dz2-a2 uand dπ-3 eginteractions. The Curie plots of the pyrrole- Cαsignals have further revealed that the iodide complex adopts a much purer intermediate-spin state than the bromide and chloride complexes. In contrast to the case of Fe ( OArTAzP ) X , six-coordinate [ Fe ( OArTAzP )( CN )2]-showed the pyrrole- Cαsignal at 47 ppm at 273 K, which indicates that the complex adopts the low-spin state with the ( dxy)2( dxz, dyz)3electron configuration. Thus, the13C NMR chemical shift of the pyrrole- Cαsignal turns out to be quite a good probe to elucidate the spin state and electron configuration of iron(III) tetraazaporphyrins, where the1H NMR spectroscopy is less useful because of the absence of the hydrogen atoms as well as the alkyl or aryl groups directly attached to the meso positions.

International audience; A large up-field shift (−763 ppm) has been observed for the carboxyl carbons of the dichlorido complex TBA[Ru2(O2CCH3)4Cl2] (TBA+ = tetra(n-butyl)ammonium cation) in the 13C NMR spectrum (CD2Cl2 at 25 °C). The DFT calculations showed spin delocalization from the paramagnetic Ru25+ core to the ligands, in agreement with the large up-field shift.

The spin states of microcrystalline samples of [Fe(OMTPP)L2]+ (L = DMAP or Py) have been examined and interpreted using Mossbauer spectroscopy, SQUID magnetometry and X-ray crystallography. The Mossbauer spectra of [Fe(OMTPP)(DMAP)2]+ and [Fe(OMTPP)Py2]+ showed that both of these complexes maintain the low-spin (S = 1/2) state over the 77−300 K temperature range. The spin states of these complexes were further confirmed by SQUID magnetometry. Thus, the magnetic behavior of [Fe(OMTPP)Py2]+ is quite different from that of the structurally related species [Fe(OETPP)Py2]+. The latter complex exhibits a novel spin crossover between the S = 3/2 and S = 1/2 states as revealed by the spectroscopic and magnetic measurements. In order to understand the reasons for the absence of the spin crossover process in [Fe(OMTPP)Py2]+, we have compared the crystal and molecular structures of [Fe(OMTPP)Py2]+ with those of the recently reported species [Fe(OETPP)Py2]+. In the case of [Fe(OMTPP)Py2]+, the Fe−Naxial bond lengths hardly change with temperature and are 2.058(6) and 2.024(4) A at 298 and 80 K, respectively. These results are in sharp contrast to those of the spin crossover complex [Fe(OETPP)Py2]+, in which the Fe−Naxial bonds contract from 2.201(3) A at 298 K to 1.993(3) A at 80 K. We have ascribed the difference in magnetic behavior between [Fe(OMTPP)Py2]+ and [Fe(OETPP)Py2]+ to the difference in molecular packing; the former adopts a densely packed cubic crystal system while the latter shows a less condensed monoclinic system. A cavity calculation has further confirmed the above mentioned assumption. While the cavity sizes around the pyridine ligands in [Fe(OETPP)Py2]+ are 32.08 and 28.88 A3 at 298 K, that in [Fe(OMTPP)Py2]+ is only 19.81 A3. Furthermore, the cavities contract by 17.7% in [Fe(OETPP)Py2]+ when the temperature is lowered from 298 to 80 K whereas the contraction is only 5.3% in the case of [Fe(OMTPP)Py2]+. On the basis of these results, we have concluded that the loosely packed crystal system and the wide cavities around the axial ligands are the important requirements for the occurrence of the spin crossover process in the solid state. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

The electronic states of a series of saddle-shaped porphyrin complexes [Fe(OMTPP)L(2)](+) and [Fe(TBTXP)L(2)](+) have been examined in solution by (1)H NMR, (13)C NMR, and EPR spectroscopy and by magnetic measurements. While [Fe(OMTPP)(DMAP)(2)](+) and [Fe(TBTXP)(DMAP)(2)](+) maintain the low-spin (S = (1)/(2)) state, [Fe(OMTPP)(THF)(2)](+) and [Fe(TBTXP)(THF)(2)](+) exhibit an essentially pure intermediate-spin (S = (3)/(2)) state over a wide range of temperatures. In contrast, the Py and 4-CNPy complexes of OMTPP and TBTXP exhibit a spin transition from S = (3)/(2) to S = (1)/(2) as the temperature was decreased from 300 to 200 K. Thus, the magnetic behavior of these complexes is similar to that of [Fe(OETPP)Py(2)](+) reported in our previous paper (Ikeue, T.; Ohgo, Y.; Yamaguchi, T.; Takahashi, M.; Takeda, M.; Nakamura, M. Angew. Chem., Int. Ed. 2001, 40, 2617-2620) in the context that all these complexes exhibit a novel spin crossover phenomenon in solution. Close examination of the NMR and EPR data of [Fe(OMTPP)L(2)](+) and [Fe(TBTXP)L(2)](+) (L = Py, 4-CNPy) revealed, however, that these complexes adopt the less common (d(xz), d(yz))(4)(d(xy))(1) electron configuration at low temperature in contrast to [Fe(OETPP)Py(2)](+) which shows the common (d(xy))(2)(d(xz), d(yz))(3) electron configuration. These observations have been attributed to the flexible nature of the OMTPP and TBTXP cores as compared with that of OETPP; the relatively flexible OMTPP and TBTXP cores can ruffle the porphyrin ring and adopt the (d(xz), d(yz))(4)(d(xy))(1) electron configuration at low temperature. Therefore, this study reveals that the rigidity of porphyrin cores is an important factor in determining the spin crossover pathways.

There are two types of electron configuration, (dxy)2(dxz, dyz)3 and (dxz, dyz)4(dxy)1, in low spin iron(III) porphyrin complexes. In order to reveal how the electronic effect of substituents affects the electron configuration of low spin iron(III) porphyrin complexes, we have examined the 13C NMR, 1H NMR, and EPR spectra of a series of tetrabutylammonium (dicyano)[meso-tetrakis(p-substituted phenyl)porphyrinato]ferrate(III), [Fe(p-X–TPP)(CN)2]−Bu4N+, in both CD2Cl2 and CD3OD solutions. The chemical shifts of the meso carbon signals, which sharply reflect the electron configuration of low spin iron(III), have changed to a great extent depending on the electron-donating or electron-withdrawing ability of the para-substituent. The isotropic shifts of the meso-carbon signals of [Fe(p-X–TPP)(CN)2]−Bu4N+ are determined on the basis of the meso-carbon chemical shifts of the corresponding diamagnetic cobalt(III) complexes, [Co(p-X–TPP)(CN)2]−Bu4N+. The plots of the isotropic shifts against Hammett σp values have yielded good linear lines with the slopes, −22 and −69 ppm, in CD2Cl2 and CD3OD, respectively. On the basis of these results, we have concluded that the electron-withdrawing groups at the phenyl para-positions stabilize the (dxy)2(dxz, dyz)3 state while the electron-donating groups at the same positions stabilize the (dxz, dyz)4(dxy)1 state. The conclusion is further supported by the 1H NMR and EPR results.

The field strength of the axial ligands determines the spin state of saddled iron(III) porphyrin complexes. Strong axial ligands (L), such as imidazole and 4-dimethylaminopyridine, lead to the formation of complexes with a pure S=1/2 state, while weak ligands, such as THF, give complexes with a pure S=3/2 state. Intermediate strength ligands, such as pyridine and 4-cyanopyridine, give complexes that show a novel spin crossover between the S=1/2 and S=3/2 states.

An annulated dinuclear palladium(II) phthalocyanine complex ( 1 ) was synthesized and characterized. It was found that 1 worked as a photo-catalyst for the decomposition of 1,3-diphenylisobenzofuran (DPBF) in aerated toluene under the irradiation of the light in the near-infrared (NIR) region (λ > 780 nm).

1H NMR, 13C NMR, and EPR studies of a series of low-spin (meso-tetraalkylporphyrinato)iron(III) complexes, [Fe(TRP)(L)2]X where R = nPr, cPr, and iPr and L represents axial ligands such as imidazoles, pyridines, and cyanide, have revealed that the ground-state electron configuration of [Fe(TnPrP)(L)2]X and [Fe(TcPrP)(L)2]X is presented either as the common (dxy)2(dxz,dyz)3 or as the less common (dxz,dyz)4(dxy)1 depending on the axial ligands. The ground-state electron configuration of the isopropyl complexes [Fe(TiPrP)(L) 2]X is, however, presented as (dxz,dyz)4(dxy)1 regardless of the kind of axial ligands. In every case, the contribution of the (dxz,dyz)4(dxy)1 state to the electronic ground state increases in the following order: HIm < 4-Me2NPy < 2-MeIm < CN- < 3-MePy < Py < 4-CNPy. Combined analysis of the 13C and 1H NMR isotropic shifts together with the EPR g values have yielded the spin densities at the porphyrin carbon and nitrogen atoms. Estimated spin densities in [Fe(TiPrP)(4-CNPy)2]+, which h...

The reaction of copper(II) pentafluorobenzoate ([Cu2(O2CC6F5)4]) with pyrazine (pyz) in methanol gave a polymer complex [Cu(O2CC6F5)2(pyz)]n. The pyz-bridged structure of Cu(O2CC6F5)2 was character...

The electron configuration of a series of low-spin (dicyano){meso-tetrakis(2,4,6-trialkylphenyl)porphyrinato}iron(III) complexes, [Fe(R-TPP)(CN)2]- where R = Me, Et, or iPr, together with the parent [Fe(TPP)(CN)2]-, has been examined in dichloromethane−methanol solution by 1H NMR, 13C NMR, and EPR spectroscopies. While the ferric ion of [Fe(TPP)(CN)2]- has shown a common (dxy)2(dxz,dyz)3 configuration, the ferric ions of the alkyl-substituted complexes [Fe(R-TPP)(CN)2]- have exhibited the preference of a less common (dxz,dyz)4(dxy)1 configuration. Spectroscopic characteristics of the complexes in which ferric ions take the (dxz,dyz)4(dxy)1 configuration are (i) axial type EPR spectra, (ii) downfield shifted pyrrole and meta signals in 1H NMR spectra, and (iii) downfield shifted meso-carbon signals in 13C NMR spectra. Occurrence of the less common (dxz,dyz)4(dxy)1 configuration in [Fe(R-TPP)(CN)2]- has been ascribed to the electronic interaction between iron(dπ) and cyanide(pπ*) orbitals. The interaction s...

1H NMR spectra of a series of high-spin (meso-tetraalkylporphyrinato)iron(III) chlorides, [Fe(TRP)Cl] where R = Me, Et, Pr, or iPr, have been measured at various temperatures in CD2Cl2 solution. In the case of the Et, Pr, and iPr complexes, either the methyl or the methylene signal split into two signals with equal integral intensities at low temperature. In contrast, the Me complex did not show any splitting even at −100 °C. The results have been ascribed to the hindered rotation of the meso-alkyl groups about Cmeso−Cα bonds. The activation free energies for rotation have been determined as 8.0 (−72 °C), 8.5 (−60 °C), and 8.9 (−62 °C) kcal·mol-1 for the Et, Pr, and iPr complexes, respectively, at coalescence temperatures given in parentheses. The small activation free energy for rotation of the isopropyl groups observed in the present system is explained in terms of the nonplanarity of the porphyrin ring, which has been verified both by the X-ray crystallographic analysis and by the EPR spectrum taken in...

There has been much interest directed to lantern-type diuclear metal complexes with direct metal–metal bonds due to their unique properties based on their metal–metal bonds.1,2 Formamidinate ions as well as carboxylate ions are known to work as a dinuclearting ligand to give a lantern-type dinuclear structure.1,2 Dinuclear complexes with the mixing of carboxylato and formamidinato bridges are intriguing, because the chemistry would be newly developed based on the different bridging groups within the dinuclear core. We have reported on the crystal structure rhodium(II) dinuclear complexes with two formamidinatao and two carboxylato bridging ligands in a cis(2:2) arrangement around the dinuclear core, cis-[Rh2(4-Etpf)2(O2CCF3)2(H2O)(MeOH)] (1) and cis-[Rh2(4-Etpf)2(O2CCF3)2(MeOH)2] (2), where 4-Et-pf= N,N¢-bis(4ethylphenyl)formamidinate anion.3,4 They have the same dinuclear structure with similar dimensions other than the difference in the axial ligand between H2O and MeOH (Rh–Rh = 2.4487(7)A, Rh–N(4-Et-pf) = 2.008(4) – 2.012(3)A, Rh–O(O2CCF3) = 2.078(3) – 2.100(3)A, Rh–O(H2O) = 2.453(5) A, and Rh–O(MeOH) = 2.321(3)A for 1; Rh–Rh = 2.4484(6)A, Rh–N(4Et-pf) = 2.005(3) – 2.016(3)A, Rh–O(O2CCF3) = 2.079(2) – 2.115(2)A, and Rh–O(MeOH) = 2.314(2) and Crystal Structure of a Lantern-Type Dirhodium(II) Complex with a cis-(2:2) Arrangement of Two Formamidinato and Two Trifluoroacetato Bridges

To understand the orientation effect of coordinated imidazole ligands, a series of low-spin (tetraalkylporphyrinato)iron(III) complexes, [Fe(TRP)(L)2]+ and [Fe(TRP)(L)(CN)], carrying at least one orientationally fixed imidazole (L) have been prepared. The 1H NMR pyrrole signals of a series of [Fe(TRP)(2-MeIm)2]+ have shown considerable downfield shifts as the meso substituent becomes bulkier, from −30.4 (R = H) to +5.6 ppm (R = iPr) at −71 °C. These complexes have exhibited four pyrrole signals at lower temperature due to the hindered ligand rotation. The spread of the pyrrole signals decreases from 9.4 (Me) to 8.2 (Et) and then to 5.7 (iPr) ppm. The downfield pyrrole signals together with the small spread in [Fe(TiPrP)(2-MeIm)2]+ are in sharp contrast to the other low-spin complexes with orientationally fixed imidazole ligands; the chemical shifts and spreads of the pyrrole signals in [tetrakis(2,4,6-trialkylphenyl)porphyrinato]iron(III) complexes [Fe(R-TPP)(2-MeIm)2]+ (R = Me, Et, iPr) are ca. −20 and c...

It has been reported that diesel exhaust (DE) particulates augment increases in nasal congestion and nasal secretion induced by histamine (His). We also showed that short-term (3-h) exposure to DE induces nasal mucosal hyperresponsiveness to His. Therefore, in the present study we investigated that whether 4-week exposure of guinea pigs to diesel exhaust would likewise induce nasal mucosal hyperresponsiveness to His. Sneezing number, nasal secretion from the nostril, and intranasal airway resistance induced by His were measured as indices of sneezing response, rhinorrhea, and nasal congestion, respectively. Guinea pigs of each group were exposed to filtered air, with or without a low or high concentration of DE for 3, 7, or 28 days. Exposure to a low or high concentration of DE itself did not induce sneezing, nasal secretion, or nasal congestion. However, exposure to a high concentration of DE augmented that the number of sneezes induced by His, whereas exposure to a low concentration of DE had no significant effect. Exposure to DE for 7 and 28 days tended to augment an increase in nasal secretion induced by exposure to His aerosol in a DE concentration-dependent fashion. The augmentation, however, was not statistically significant. Exposure to high or low DE for 3 or 7 days had no significant effect on the increase in intranasal pressure (INP) induced by a 10-min exposure to His aerosol, but exposure to high DE for 28 days augmented the increase in INP induced by His, significantly. Exposure to low DE for 28 days did not augment the increase in INP immediately after inhalation of His aerosol. These results reveal that 4-week exposure to high DE induces nasal mucosal hyperresponsiveness in guinea pigs.

Dynamic NMR study of a series of meso-[Co(TRP)(L)2]Cl, where R is an alkyl group and L is a substituted imidazole, has been carried out. While the complexes with unhindered imidazole show no splitting of the signals, those with bulky imidazoles exhibit change in line shape, indicating the hindered imidazole rotation. The activation free energy increases as R and/or L become bulkier. Based on the red-shifted Soret and Q bands in the UV-Visible and the downfield shifted imidazole protons in the 1H NMR spectra of these complexes as compared with the meso unsubstituted complexes, it is concluded that the deformation of the porphyrin ring slows down the rate of rotation of the coordinated ligand.