Magnetic anisotropy and structural flexibility in the field-induced single ion magnets [Co{(OPPh)(EPPh)N}], E = S, Se, explored by experimental and computational methods.

During the last few years, a large number of mononuclear Co(II) complexes of various coordination geometries have been explored as potential single ion magnets (SIMs). In the work presented herein, the Co(II) S = 3/2 tetrahedral [Co{(OPPh)(EPPh)N}], E = S, Se, complexes (abbreviated as CoO2E2), bearing chalcogenated mixed donor-atom imidodiphosphinato ligands, were studied by both experimental and computational techniques. Specifically, direct current (DC) magnetometry provided estimations of their zero-field splitting (zfs) axial () and rhombic () parameter values, which were more accurately determined by a combination of far-infrared magnetic spectroscopy and high-frequency and -field EPR spectroscopy studies.

Effective coupling of rapid freeze-quench to high-frequency electron paramagnetic resonance.

We report an easy, efficient and reproducible way to prepare Rapid-Freeze-Quench samples in sub-millimeter capillaries and load these into the probe head of a 275 GHz Electron Paramagnetic Resonance spectrometer. Kinetic data obtained for the binding reaction of azide to myoglobin demonstrate the feasibility of the method for high-frequency EPR. Experiments on the same samples at 9.

Temperature-cycle electron paramagnetic resonance.

We report on a novel approach to the study of rates and short-lived intermediates of (bio)chemical reactions that involve paramagnetic species. Temperature-cycle Electron Paramagnetic Resonance (EPR) concerns the repeated heating of a reaction mixture in the cavity of an EPR spectrometer by pulsed irradiation with a near-infrared diode laser combined with intermittent characterization of the sample by 275 GHz EPR at a lower temperature at which the reaction does not proceed. The new technique is demonstrated for the reduction of TEMPOL with sodium dithionite in aqueous solution down to the sub-second time scale.

Analysis of the EPR spectra of transferrin: the importance of a zero-field-splitting distribution and 4-order terms.

Multi-frequency EPR spectroscopy can provide high-level structural information on high-spin Fe sites in proteins and enzymes. Unfortunately, analysis of the EPR spectra of these spin systems is hindered by the presence of broad distributions in the zero-field-splitting (ZFS) parameters, which reflect conformational heterogeneity of the iron sites. We present the analysis of EPR spectra of high-spin Fe bound to human serum transferrin.