Ruthenium(II) pyridylamine complexes with diimine ligands showing reversible photochemical and thermal structural change.

Ruthenium(II)-TPA-diimine complexes, [Ru(TPA)(diimine)]2+ (TPA=tris(2-pyridylmethyl)amine; diimine=2,2'-bipyridine (bpy), 2,2'-bipyrimidine (bpm), 1,10-phenanthroline (phen)) were synthesized and characterized by spectroscopic and crystallographic methods. Their crystal structures demonstrate severe steric hindrance between the TPA and diimine ligands. They exhibit drastic structural changes on heating and photoirradiation at their MLCT bands, which involve partial dissociation of the tetradentate TPA ligand to exhibit a facially tridentate mode accompanied by structural change and solvent coordination to give [Ru(TPA)(diimine)(solvent)]2+ (solvent=acetonitrile, pyridine). The incoming solvent molecules are required to have pi-acceptor character, since sigma-donating solvent molecules do not coordinate. The thermal process is irreversible dissociation to give the solvent-bound complexes, which takes place by an interchange associative mechanism with large negative activation entropies. The photochemical process is a reversible reaction reaching a photostationary state, probably by a dissociative mechanism involving a five-coordinate intermediate to afford the same product as obtained in the thermal reaction. Quantum yields of the forward reactions to give dissociated products were lower than those of the backward reactions to recover the starting complexes. In the photochemical process, the conversions of the forward and backward reactions depend on the absorption coefficients of the starting materials and those of the products at certain wavelength, as well as the quantum yields of those reactions. The reversibility of the motions can be regulated by heating and by photoirradiation at certain wavelength for the recovery process. In the bpm system, we could achieve about 90 % recovery in thermal/photochemical structural interconversion.

Proton-coupled electron transfer in ruthenium(II)-pterin complexes: formation of ruthenium-coordinated pterin radicals and their electronic structures.

Ruthenium(II)-pterin complexes were prepared using tetradentate and tripodal tris(2-pyridylmethyl)amine (TPA) and tris(5-methyl-2-pyridylmethyl)amine (5-Me3-TPA) as auxiliary ligands together with 2-(N,N-dimethyl)-6,7-dimethylpterin (Hdmdmp) and 6,7-dimethylpterin (Hdmp) as pterin derivatives for ligands. Characterization was made by spectroscopic methods, X-ray crystallography, and electrochemical measurements. The pterin ligands coordinated to the ruthenium centers as monoanionic bidentate ligands via the 4-oxygen of the pyrimidinone moiety and the 5-nitrogen of the pyrazine parts. The striking feature is that the coordinated dmp- ligand exhibits a quinonoid structure rather than a deprotonated biopterin structure, showing a short C-N bond length for the 2-amino group. Those complexes exhibit reversible two-step protonation for both pterin derivatives coordinated to the ruthenium centers to give a drastic spectral change in the UV-vis spectroscopy. Doubly protonated Ru(II)-pterin complexes were stabilized by pi-back-bonding interaction and exhibited clear and reversible proton-coupled electron transfer (PCET) to give ruthenium-coordinated neutral monohydropterin radicals as intermediates of PCET processes. Those ESR spectra indicate that the unpaired electron delocalizes onto the PCET region (N5-C6-C7-N8) of the pyrazine moiety.

Sentinel node biopsy versus elective lymph node dissection in patients with cutaneous melanoma in a Japanese population.

BACKGROUND: In Japan, elective lymph node dissection (ELND) has been the standard treatment for patients with possible nodal melanoma. Sentinel node biopsy (SNB) has now replaced ELND, not only in Japan but also worldwide. The objective of this study was to compare the interim outcomes of SNB and ELND. METHODS: A retrospective study was conducted among patients with clinically node-negative disease treated at our institute with either SNB (n = 30) or ELND (n = 72). RESULTS: The background was similar in the two groups. Nodal metastases were found in 40.0% of patients in the SNB group, but in only 26.4% in the ELND group (P = 0.173). The median follow-up was 31.5 months for the SNB group and 82 months for the ELND group. The incidence of locoregional recurrence and distant metastasis in the SNB group was 10.0% and 16.7%, respectively, and for the ELND group the incidence was 5.6% and 31.9%, respectively. The 3-year disease-free survival rate was similar in the two groups (P = 0.280), and the 3-year disease-free survival rates for node-positive patients were also similar in the two groups (P = 0.90), as were the 3-year disease-free survival rates for node-negative patients (P = 0.193). CONCLUSION: This interim result in a Japanese melanoma population with clinically node-negative disease demonstrated that SNB identified more nodal micrometastases than ELND. This increase in accurate staging likely resulted from the reliable identification of the lymph node field by lymphoscintigraphy, as well as the more detailed pathologic examination of the nodes removed in SNB. It is quite reasonable to perform SNB instead of ELND in this population.

Toward a photochemical and thermal molecular machine: reversible ligand dissociation and binding in a ruthenium(II)-2,2'-bipyridine complex with tris(2-pyridylmethyl)amine.

A Ru(II) complex having tris(2-pyridylmethl)amine (TPA) and 2,2'-bipyridine (bpy), [Ru(TPA)(bpy)]X(2) (X = ClO(4), PF(6)), exhibited a severe distortion of the coordination of the axial pyridine moiety of TPA due to steric hindrance. The complex showed interesting dissociation-binding behavior of the axial pyridine arm to form a solvent adduct with TPA ligation in a unique meridional tridentate fashion. The complex undergoes thermal dissociation to form solvent-coordinated species via an S(N)2-like mechanism with activation energy of 117 kJ/mol. In contrast, the complex showed reversible photochemical dissociation and rebinding via an S(N)1-like mechanism by MLCT irradiation. The photochemical dissociation was accelerated approximately 200-fold faster than the thermal process. The dissociation process involves selective binding behavior toward external ligands (solvents) with pi-acceptor character, which is indispensable, and no sigma-donating molecules could bind to the Ru(II) center. The guest molecule can be released upon photoirradiation after its thermal binding.