Novel Excited Quintet State in Porphyrin: Bis(quinoline−TEMPO)−yttrium−tetraphenylporphine Complex
作者:Luca Maretti、Saiful S. M. Islam、Yasunori Ohba、Takashi Kajiwara、Seigo Yamauchi
DOI:10.1021/ic0511827
日期:2005.12.1
synthesized, and the properties of the excitedstates generated by photoexcitation of porphyrin were studied by time-resolved (TR) and pulsed two-dimensional electron paramagnetic resonance (EPR) spectroscopy. A TR-EPR spectrum was observed in the quartet (S=3/2) or quintet (S=2) states generated from interactions of one or two radicals with the photoexcited tripletstate of the porphyrin. The zero-field
Spin Coupling in the Supramolecular Structure of a New Tetra(Quinoline−TEMPO)Yttrium(III) Complex
作者:Luca Maretti、Marilena Ferbinteanu、Fanica Cimpoesu、Saiful S. M. Islam、Yasunori Ohba、Takashi Kajiwara、Masahiro Yamashita、Seigo Yamauchi
DOI:10.1021/ic0610841
日期:2007.2.1
The newly synthesized tetra(quinoline-TEMPO)yttrium(III) potassium salt shows interesting structural features at the molecular and supramolecular levels, revealed by the analysis of the X-ray diffraction data. The magnetic susceptibility and EPR data corroborated with structural considerations showed that the exchange and dipolar spin coupling interactions are taking place at the nodes assembling the supramolecular 2D structure. The Y(III) center shows antiprismatic octacoordination, close to the idealized D-2 symmetry. The diamagnetic transition metal plays no role in mediating the radical interactions since the TEMPO-type fragments are remote from the chelating moieties of the ligand. In turn, significant interaction occurs on the nodes consisting in the quasi-rectangular coordination of potassium counterions by the spin-bearing TEMPO groups coming from four distinct complex units. The antiferromagnetic susceptibility was consistently modeled by a spin Hamiltonian based on the rectangle topology of four spins S = (1)/(2). The fitted exchange parameters are J(a) = -5.1 cm(-1) and J(b) = -3.4 cm(-1) for the edges, imposing J(d) = 0 for the diagonal. These values are in excellent agreement with the ab initio results J(a) = -4.83 cm(-1), J(b) = -3.44 cm(-1), J(d) = -0.07 cm(-1) obtained in a CASSCF(12,8) calculation. Based on the reliability of the ab initio results we were able to select the presented J parameters among several versions of multiple solutions with acceptable goodness of the fit. A methodological caveat about the artifacts of the automatic use of best fit parameters, in the absence of supplementary criteria, in the context of relative blindness of magnetic susceptibility modeling, is raised. The details of the EPR spectrum at 10 K are also consistent, in the frame of dipolar approximation, with the model of four interacting spins at the nodes of the supramolecular assembling.
Antioxidant reactivity toward nitroxide probes anchored into human serum albumin. A new model for studying antioxidant repairing capacity of protein radicals
A new strategy to evaluate accessibility of antioxidants to radical proteins has been developed using nitroxide prefluorescent probes anchored into human serum albumin (HSA). Binding association constants for the nitroxide probes C343T and QT with HSA were 5 x 10(4) and 9 x 10(4) M-1, respectively. Rate constants for the nitroxide reduction by antioxidants in HSA were determined finding k(HSA)/k(buffer) ratio of 0.8, 1.9, and 0.075 for ascorbic acid, Trolox, and caffeic acid, respectively, for the nitroxide C343T reduction. (C) 2009 Elsevier Ltd. All rights reserved.