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Time-resolved EPR spectra were observed by means of the transient EPR technique for two kinds of fullerene dimers C120 and C120O in the lowest excited triplet (T1) states and compared with those of mono-adducts of fullerene (C60). It was found that zero-field splitting (zfs) parameters of both dimers are nearly the same as those of the monomers, indicating that the excitation is almost completely localized at one of the two fullerene units in the T1 state. © 2002 Elsevier Science B.V. All rights reserved.

Time-resolved EPR spectra of the lowest excited triplet state of boron subphthalocyanine chloride were measured in toluene at various temperatures. Based on the observed and simulated spectra electronic structure and molecular motion of the triplet state (super 1)T was analyzed, in solid and fluid solution.

It has been possible to use cw-electron paramagnetic resonance to investigate a fulleropyrrolidine with two covalently linked nitroxides in its ground state. Time-resolved electron paramagnetic resonance and spin-echo detected electron paramagnetic resonance were used to study the fulleropyrrolidine in the photoexcited state following pulsed laser excitation.

W-band time-resolved electron paramagnetic resonance (TREPR) spectroscopy was used in observing the lowest excited doublet (D1) in solution. Also observed were the doublet (D0) and quartet (Q1) ground states in an axial-ligating p-pyridylnitronylnitroxide radical and a MgTPPn complex. Two electron spin polarization mechanisms were established in a radical-triplet pair, namely, radical-triplet pair and ESP transfer mechanisms. The capacity of TREPR spectroscopy to allow the separate observation of D1 from D0 and Q1 affirms its effectiveness in the observation of the D1 state of a radical-triplet pair in solution.

The dissociation of the benzyl radical is the first step of the photochemical reaction of bis(S-benzyl-1,2-diphenyl-1,2-ethylenedithiolato)metal (Ni, Pd, Pt) complexes. The excited triplet states of these complexes cause the photoreactions in the order of 100 ns. Time-resolved electron paramagnetic resonance studies and ultraviolet absorption studies characterize the stable intermediate metal complexes. The conversion of the dithiolato ligand to a dithiolato-dithilene resonance type is the reason for their stability.

The time-resolved and optical EPR spectroscopic analysis of fluorine-substituted magnesium tetraphenylporphines (TPP) indicates that the 3(a(sub 2u)3(sub g)) and 3(a(sub 1u)e(sub g)) configuration are mixed through vibronic coupling in the excited triplet state. The measurement of absorption coefficients and intensities of vibronic bands reveals that the zero-field splitting parameter is proportional to the number of substituents. The magnitude of CI mixing is different for singlet and excited states and is maximum for magnesium difluoro TPP.

Angle-selected 14N-ENDOR was used to investigate the electronic state of the copper unpaired electron orbitals and their relative orientation in a distorted coordination environment. Tetrahedral distortion decreases the 14N HFC remarkably in the Cu/Ni(ipsal)2, Cu/Zn(ipsal)2 and Cu/Zn(msal)2 and effects a corresponding decrease in the n(super 2) values obtained from the EHMO method. The orientation of the g tensor is connected to the orientation of the unpaired electron orbital. The unpaired electron orbital in d9 complexes are oriented in the direction of the strongest ligand field.

The ground electronic states of cobalt tetraphenylporphyrin ((Co(III)TPP)1+) and octaethylporphyrin ((Co(III)OEP)1+) cation radicals, with a concentration on the A1u and A2u mixing under temperature and axial-ligand dependence were discussed by EPR spectroscopy. The (Co(III)OEP)1+ complexes displayed significant changes due to axial ligand and spectral broadening at high temperature upon ligation with Br, Cl and CN anions. On (Co(III)TPP)1+ complexes, changes with axial ligands and temperature differences were observed upon ligation with ClO4 and Br anions.

The synthesis and characteristics of mono-and bis[4-(3-hydroxy-2-methyl-4quinolinoyloxy)-2,2,6,6-tetramethylpiperidin-1oxil](meso-tetraphenylphorphyrinato) yttrium-III complexes is presented. A porphyry metal complex, which enable to the design of more efficient photoreaction centers and longer- lived radical ion pairs using a spin-forbidden transistors are obtained.

The electron spin resonance (ESR) method is used for examining the electronic structures of tridentate imino nitroxyl diradical complex with copper(II) (Cu-bisimpy) and its related compounds. Multifrequency electron spin resonance spectroscopy has clarified the unique electronic structure of a square planar copper(II) complex with an imino nitroxyl diradical, which has undergone a strong ferromagnetic interaction caused by a covalent bonding effect.

Studies the structure and electronic state of photoexcited fullerene linked with a nitroxide radical based on an analysis of a two-dimensional electron paramagnetic resonance nutation spectrum. Effective Hamiltonian and resonance field; Dipolar interaction between radical and triplet carbon.

Two-dimensional (2D) Fourier-transform (FT) electron paramagnetic resonance (EPR) nutation experiments were done in order to verify anomalous flip-angle dependence of a FT–EPR spectrum of a photochemically generated spin-correlated radical pair (SCRP). It was demonstrated by both the experiment and theory that the signals of SCRP have additionally higher and lower nutation frequencies than that of a free radical. This spectroscopy provides a direct spectroscopic evidence of spin-correlation within SCRP, and enables one to partially separate SCRP signals from free radical signals in the 2D EPR spectrum. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Troponin (Tn) is a protein that consists of three subunits, troponin C (TnC), troponin I (TnI), and troponin T (TnT), and Tn controls cardiac muscle contraction by calcium ion binding and phosphorylation. The Ca2+-binding site is the E-F hand motif (C helix-loop-D helix) in the N-terminal domain of TnC, and the structural transition induced by Ca2+ is the opening of these helices and the interaction with TnI, probably at the A and B helices. In this paper, we studied structural changes in the TnC-TnI binary complex on Ca2+ binding by double quantum coherence (DQC) distance measurements. We used a binary complex of the cardiac troponin C and I (cTnC and cTnI) complexes, chose four positions of nitroxide spin label at helices A, B, C, and D in the N-terminal domain and chose the E helix in the C-terminal domain as the reference position to study the structural changes on Ca2+ addition. The label positions were (A22C/S98C), (M47C/S98C), (Q58C/S98C), and (C84/S98C) for the A, B, C, and D helices, respectively. The effects of phosphorylation of the cardiac-specific N-terminal region of cTnI were studied using a phosphomimetic cTnI mutant. Analysis of the modulation of the DQC echo signals provided the distribution of the spin-spin distance. The distances averaged over the distribution showed that the labels on the A, B, and C helices decreased, i.e., moved to the E helix, on Ca2+ binding, while the distance of the label on the D helix showed almost no change. Shoulders and/or small separate peaks were observed in the shape of the distribution and were analyzed as the sum of a few Gaussian functions. The Gaussian functions were grouped into two components, components 1 and 2, at the longer and shorter distances, respectively, separated by 0.7-1.5 nm. The fractions of component 2 were ca. 0.1-0.2 in the Ca2+-free state and increased by 0.2-0.3 on Ca2+ addition, suggesting that the increase in component 2 is related to physiological control of cardiac muscle contraction. The phosphomimetic-modification effects on the Ca2+-induced changes of the fraction of components and the distances of the C- and D-helix labels are small. On the other hand, in the A and B helices, there are significant effects on the Ca2+-induced changes in the distances of the components. The different behaviors of A/B and C/D helices support the current model of the phosphorylation effects in which both N-terminal region and regulatory domain of cTnI interact with the A and B helices of cTnC. [ABSTRACT FROM AUTHOR]

Time-resolved electron paramagnetic resonance (TREPR) is a powerful method for the study of excited triple (Tsub1) states, and the TREPR signals of (Tsub1) porphyrins have been observed in fluid solution for the first time. Porphyrins were synthesized and spectral-grade toluene and 2-butanol and special-grade liquid paraffin were used as solvents.

The first time-resolved electron paramagnetic resonance (TREPR) spectrum of a molecule with two paramagnetic centers composed of an excited triplet and a radical in toluene glass is presented. The spectrum is examined as those of the excited doublet (D1) and quartet (Q1) states. The studied molecule is tetraphenylporphinatozinc(II) coordinated by p-pyridyl nitronyl nitroxide. The TREPR spectra was examined by zfs and g values of the radical-triplet pair.

The mechanism involved in the photodissociation of bis(S-benzyl-1,2-diphenyl-1,2-ethylenedithiolato)nickel via EPR and UV-visible absorption spectroscopy is investigated. Specifically, the dissociation of the C-S bonds of the compound resulting in the intermediate formation of the (Ni(S2C2Ph2)(S2(CH2Ph)C2Ph2)) radical is studied to determine whether it occurs in a single step or in a series of steps. Results show that photodissociation occurs by the two-step removal of two benzyl radicals.