Rika Tanaka

In Vitro Heavy-Atom Effect of Palladium(II) and Platinum(II) Complexes of Pyrrolidine-Fused Chlorin in Photodynamic Therapy

Introduction of a heavy atom into photosensitizers generally facilitates intersystem crossing and improves the quantum yield (Phi(Delta)) of singlet oxygen ((1)O(2)), which is a key species in photodynamic therapy (PDT). However, little information is available about the physiological importance of this heavy-atom effect. The aim of this study is to examine the heavy-atom effect in simple metallochlorins in vitro at the cellular level. 1,3-Dipolar cycloaddition of azomethine ylide to 5,10,15,20-tetrakis(pentafluorophenyl)porphyrinato palladium(II) and platinum(II) afforded metallochlorins 4b and 4c in yields of 17.1 and 12.9%, respectively. The Phi(Delta) values increased in the order of 4a (0.28) < 4b (0.89) < 4c (0.92) in C(6)D(6). The photocytotoxicity of 4a, 4b, and 4c was evaluated in HeLa cells at a light dose of 16 J x cm(-2) with lambda > 500 nm and increased in the order of 4a < 4b < 4c at the concentration of 0.5 microM. The photocytotoxicity of 4b and 4c was significantly inhibited by addition of sodium azide, but not D-mannitol, suggesting that (1)O(2) is the major species causing cell death. Our results clearly indicate that 4b and 4c act as efficient (1)O(2) generators due to the heavy-atom effect in a cellular microenvironment as well as in nonphysiological media.

Using Stable Radicals To Protect Pentacene Derivatives from Photodegradation

Organic transistors and organic devices have a variety of applications in molecular electronics and in the up-andcoming area of organic molecular spintronics. The use of inexpensive and facile ink-jet methods is possible for the fabrication of organic semiconductors. Pentacene and its derivatives 7] have attracted increasing interest as promising electronic materials owing to their high hole mobility. Pentacene is the most promising candidate for organic fieldeffect transistor (OFET) applications. However, its chemical instability in the presence of light and air prevents practical applications. Efforts have been made to improve the stability by the addition of substituents. 7] The most notable example is 6,13-bis(triisopropylsilylethynyl)pentacene, 10] in which the 6and 13-positions of pentacene are protected by triisopropylsilylethynyl groups. For this pentacene derivative, extremely high hole mobility of 1.8 cm V 1 s 1 was reported for the thin film. However, the addition of substituents to photoactive carbon sites prevents further functional modifications because both the 6and 13-positions are blocked by the substituents and also the characteristic nature of the pentacene moiety is changed. Herein, we report a new method that utilizes a stable radical to protect pentacene derivatives from photodegradation. During the course of our systematic studies of pconjugated spin systems with high-spin photo-excited states for functional materials, we have discovered that a combination of two unstable species (photoreactive pentacene and a radical) leads to remarkable protection from photodegradation and an enhancement in solubility in common organic solvents. These effects are advantageous for practical applications of acene derivatives in molecular electronic devices. Radicals are well-known energy scavengers of the photoexcited state. We have utilized this characteristic of radicals to scavenge the energy of the photoexcited state of pentacene. Two novel radical pentacene hybrids, Pen–Ph–OV (1a) and Pen–Ph–NN (2a) and their precursors (1 b and 2b) were synthesized (Scheme 1; Pen, Ph, OV, and NN denote pentacene, phenyl, oxo-verdazyl radical, and nitronyl nitroxide radical moieties, respectively). We demonstrate the remarkable photochemical stability induced by the attachment of

Anion-Controlled Assembly of Four Manganese Ions: Structural, Magnetic, and Electrochemical Properties of Tetramanganese Complexes Stabilized by Xanthene-Bridged Schiff Base Ligands

The reaction of manganese(II) acetate with a xanthene-bridged bis[3-(salicylideneamino)-1-propanol] ligand, H(4)L, afforded the tetramanganese(II,II,III,III) complex [Mn(4)(L)(2)(μ-OAc)(2)], which has an incomplete double-cubane structure. The corresponding reaction using manganese(II) chloride in the presence of a base gave the tetramanganese(III,III,III,III) complex [Mn(4)(L)(2)Cl(3)(μ(4)-Cl)(OH(2))], in which four Mn ions are bridged by a Cl(-) ion. A pair of L ligands has a propensity to incorporate four Mn ions, the arrangement and oxidation states of which are dependent on the coexistent anions.

Syntheses, Characterization, and Antitumor Activities of Platinum(II) and Palladium(II) Complexes with Sugar-Conjugated Triazole Ligands

Four platinum(II) and palladium(II) complexes with sugar‐conjugated bipyridine‐type triazole ligands, [PtIICl2(AcGlc‐pyta)] (3), [PdIICl2(AcGlc‐pyta)] (4), [PtIICl2(Glc‐pyta)] (5), and [PdIICl2(Glc‐pyta)] (6), were prepared and characterized by mass spectrometry, elemental analysis, 1H‐ and 13C‐NMR, IR as well as UV/VIS spectroscopy, where AcGlc‐pyta and Glc‐pyta denote 2‐[4‐(pyridin‐2‐yl)‐1H‐1,2,3‐triazol‐1‐yl]ethyl 2,3,4,6‐tetra‐O‐acetyl‐β‐D‐glucopyranoside (1) and 2‐[4‐(pyridin‐2‐yl)‐1H‐1,2,3‐triazol‐1‐yl]ethyl β‐D‐glucopyranoside (2), respectively. The solid‐state structure of complex 6 was determined by single‐crystal X‐ray‐diffraction analysis. These complexes exhibited in vitro cytotoxicity against human cervix tumor cells (HeLa) though weaker than that of cisplatin.

Thia-calix[n]pyridines, synthesis and coordination to Cu(i,ii) ions with both N and S donor atomsElectronic supplementary information (ESI) available: emission spectra of compound 1. See http://www.rsc.org/suppdata/cc/b2/b203540e/

The novel thia-calix[n]pyridines (n = 3, 4, 6) coordinated to copper ions through nitrogen and sulfur atoms to give multinuclear complexes whose structures have been determined by X-ray crystallography and NMR spectra.

Syntheses and X-ray crystal structures of tetranuclear [Ag4(μ3-S2O3)(μ-S2O3)(μ-dppm)4] {dppm=bis(diphenylphosphino)methane} and trinuclear [Ag3(μ3-Cl)(μ-S2O3)(μ-dppm)3] clusters

The reaction between AgClO 4 , dppm and Na 2 S 2 O 3 ·5H 2 O affords the tetranuclear [Ag 4 (μ 3 -S 2 O 3 )(μ-S 2 O 3 )(μ-dppm) 4 ] cluster, in which the four Ag atoms form a square bridged by four dppm ligands and the two thiosulfate ligands are bound on both sides of the Ag 4 plane. The S atom of one thiosulfate ion forms bonds with three Ag atoms, while the S atom of the other forms bonds with two Ag atoms. The trinuclear [Ag 3 (μ 3 -Cl)(μ-S 2 O 3 )(μ-dppm) 3 ] cluster is obtained by a reaction of AgCl with dppm and Na 2 S 2 O 3 ·5H 2 O. The structure of the cluster comprises an Ag 3 triangle bridged by three dppm ligands. The S atom of the thiosulfate ion forms a double bridge at the edge of the triangle from one side of the Ag 3 plane and the chloride ion forms a triple bridge from the other side of the Ag 3 plane.

The syntheses, 31P{1H} NMR spectra and cyclic voltammetry of trinuclear [Pd2M(μ3-Se)2(dppe)3]2+ {M=Ni or Pt; dppe=1,2-bis(diphenylphoshino)ethane} and pentanuclear [M′{Pd2(μ3-Se)2(dppe)2}2]2+ (M′=Ni, Pd or Pt) clusters with selenido bridges

Trinuclear [Pd2M(μ3-Se)2(dppe)3]2+ (M=Ni or Pt) and pentanuclear [M′{Pd2(μ3-Se)2(dppe)2}2]2+ (M′=Ni, Pd or Pt) clusters have been prepared using a metalloligand [Pd2(μ-Se)2(dppe)2] and characterized by 31P{1H} NMR spectroscopy and cyclic voltammetry. [Pd2Ni(μ3-Se)2(dppe)3]2+ gives two chemically reversible couples, [Pd2Pt(μ3-Se)2(dppe)3]2+ exhibits one chemically reversible couple and pentanuclear clusters show three couples in each cyclic voltammogram of the reduction process at 255 K. The redox behavior of the clusters is discussed.

Titanium and manganese complexes supported by a xanthene-bridged bis(tripodal N2O2) ligand: isomerization, intramolecular hydrogen bonding and metal-binding ability

A new bis(N2O2) ligand, L(4-), in which two tripodal diamine-bis(phenolate) moieties are bridged by a xanthene backbone, was prepared. The reaction of H4L with 2 equiv. of [Ti(O(i)Pr)4] produced C2 and Cs symmetrical isomers of the dititanium(IV,IV) complex [Ti2(L)(O(i)Pr)4]. The isolated C2 isomer was slowly converted to the Cs isomer via Ti-N bond cleavage to form a 3 : 2 mixture in equilibrium. A similar dimanganese(III,III) complex [Mn2(L)(OMe)2(MeOH)2] was synthesized from a 1 : 2 mixture of H4L and manganese(II) perchlorate in the presence of triethylamine. An X-ray analysis of [Mn2(L)(OMe)2(MeOH)2] revealed that two Mn-N2O4 octahedrons are connected by intramolecular hydrogen bonds as well as a xanthene bridge to form a C2 symmetrical structure. The dimanganese(III,III) complex further reacted with manganese(II) acetate to form the mixed-valence trimanganese(III,II,III) complex [Mn3(L)(μ-OMe)2(μ-OAc)2]. Electrochemical data of the trimanganese(III,II,III) complex indicated that the xanthene-bridged dimanganese(III,III) unit effectively binds a Mn(II) ion in solution.

Photoinduced stepwise bending behavior of photochromic diarylethene crystals

Diarylethene crystals were found to exhibit photoinduced stepwise bending behavior. The bending rate changed significantly during continuous irradiation with ultraviolet (UV) light. This is a new type of photomechanical motion reported previously for various photoresponsive molecular crystals. Furthermore, the delayed bending behavior was observed even after UV light was turned off. The mechanism for the stepwise bending is discussed.

Syntheses and Photochemical Properties of Trimanganese Complexes Containing Naphtyl Moieties

Two trinuclear manganese complexes, [Mn3(μ3–O)(μ–O2CCH2-1-naph)6(py)3] (1) and [Mn3(μ3–O)(μ–O2CCH2 2-naph)6(py)3] (2) (1 or 2-naph-CH2CO2H = 1 or 2-naphtylacetic acid, py = pyridine), were synthesized and characterized by elemental analysis, EXAFS analysis, and X-ray crystallography. Their electrochemical and photochemical behaviors were investigated by cyclic voltammetry (CV), electron absorption spectroscopy, and emission spectroscopy.