CW EPR as a tool to study paramagnetic centers: from simple inorganic systems to complex macromolecules

CARLOS D. BRONDINO

Rosario

Workshop; Workshop Frontiers in Magnetic Resonance, from Materials to Biological Systems; 2013

IBR-UNR

CW EPR as a tool to study paramagnetic centers: from simple inorganic systems to complex macromolecules       Carlos D. Brondino Departamento de Física, Facultad de Bioquímica y Ciencias Biológicas, Universidad Nacional del Litoral, Campus Universitario, S3000ZAA Santa Fe, Argentina e-mail brondino@fbcb.unl.edu.ar Continuous wave Electron Paramagnetic Resonance (CW EPR) is a spectroscopic technique extensively employed in the physicochemical characterization of simple inorganic systems and redox enzymes that contain paramagnetic centers in their structures. Since its beginnings by ~1944, CW EPR was mainly used to evaluate the tensorial magnitudes associated with the anisotropic and isotropic interactions that govern the magnetic resonance phenomenon in simple inorganic/organic systems and to understand how the magnetic interactions between the paramagnetic centers modulate the spectral properties of the isolated ions [1]. In this line, we will analyze some examples of mononuclear and dinuclear inorganic systems studied by single crystal CW EPR to show the potential capability of the technique in the characterization of simple paramagnetic systems. The use of CW EPR in the characterization of more complex systems, as is the case of redox enzymes that present paramagnetic centers in their structure, is relatively more recent and can be considered as an extension of the experience gained with the above mentioned simpler systems. The redox enzymes we will analyze may include distinct type of redox centers (usually situated ~ 10-20 Å away) connected by long chemical pathways which are involved in electron transfer processes [2]. In addition, despite the long both distances and chemical paths, they can present weak magnetic couplings produced by spin-spin interactions such as dipolar and isotropic exchange [2,3]. We will discuss how CW EPR can be advantageously used to determine intercenter distances, to assign the EPR active centers with those of the structure, to evaluate the integrity of the electron transfer pathways in distinct protein conditions, and how the technique can be used to obtain structural information that cannot be obtained with conventional structural techniques. [1] a) N. I. Neuman, M. Perec, P. J. González, M. C. G. Passeggi, A. C. Rizzi, and C. D. Brondino Journal of Physical Chemistry A 2010, 114, 13069-13075. b) N. I. Neuman, V. G. Franco, F. M. Ferroni, R. Baggio, M. C. G. Passeggi, A. C. Rizzi, and C. D. Brondino Journal of Physical Chemistry A 2012, 116, 12314-12320. [2] C. D. Brondino, M. G. Rivas, M. J. Romão, J. J. G. Moura, I. Moura, Accounts of Chemical Research, 2006, 39, 788-796. [3] P. J. González, G. I. Barrera, A. C. Rizzi, J. J. G. Moura, M. C. G. Passeggi, C. D. Brondino Journal of Inorganic Biochemistry 2009, 103, 1342-1346.