The EPR pattern of Cr V complexes of D-ribose derivatives Sandra Signorella a, * , Silvia Garcı ´a a , Marcela Rizzotto a , Aviva Levina b , Peter A. Lay b , Luis F. Sala a, * a Departamento de Quı ´mica, Facultad de Ciencias Bioquı ´micas y Farmace ´uticas, UNR, Suipacha 531, 2000 Rosario, Argentina b Centre of Heavy Metals Research, School of Chemistry, University of Sydney, NSW 2006, Australia Received 20 December 2004; accepted 25 February 2005 Available online 4 May 2005 Abstract Adenosine 5 0 -monophosphate, cytidine 5 0 -monophosphate, adenosine and methyl b-D-ribofuranoside form stable Cr V bischelates with the metal bound to the 2,3-cis-diolato moiety of the ribose ring. The EPR spectra of Cr V complexes of these ligands – with the substituent at C1 anti to the 2,3-diolato donor site – possess a common pattern: one quintet at g iso = 1.9803 and one quartet at g iso = 1.9798/7, corresponding to the two geometric isomers of [Cr V (O)(O 2 ,O 3 -ligand]  . The EPR spectra of Cr V bischelates of methyl a-D-ribofuranoside, with the methoxy group at C1 syn to the 2,3-diolato donor site, show a distinct pattern: two quintets at g iso = 1.9793 and 1.9791. This different EPR pattern can be used as an easy way to distinguish between Cr V complexes formed with a- and b-1-substituted D-ribose derivatives. Ó 2005 Elsevier Ltd. All rights reserved. Keywords: Cr(V); Nucleotide; Nucleoside; Riboside; Coordination modes; EPR Pattern 1. Introduction Chromate can cause several DNA lesions, which are responsible for its mutagenic and carcinogenic effects [1,2]. Although the mechanism by which Cr VI causes cancer remains uncertain, oxo-Cr V/IV spe- cies have been proposed as playing important roles in Cr VI -induced toxicity [3–7]. Oxygen-rich molecules, such as carbohydrates and their derivatives, have been found to stabilize oxo-Cr V in neutral aqueous solution [8–12]. Therefore, in vitro studies on the chemistry of these oxo-Cr V complexes can provide information on the nature of the species that are likely to be stabilized in vivo [13]. In this context, EPR spectroscopy has been used to detect stable Cr V species formed with nucleotides [14,15]. However, the structure of the resulting complexes was not established. These EPR studies did not provide information on the superhy- perfine (shf) pattern of the signals (because either the X-band EPR signal was too broad [14] or the EPR signals were not deconvoluted [15]), and the g iso values of the individual Cr V species were not deter- mined. These two EPR parameters are essential to characterize the resulting Cr V complexes [8,16]. In this work, we assign the EPR spectral parameters – g iso , A iso and 1 H a iso – of the Cr V species formed with adenosine 5 0 -monophosphate (AMP), cytidine 5 0 -monophosphate (CMP), adenosine, methyl-a-D- ribofuranoside (a-Rib1Me) and methyl b-D-ribofur- anoside (b-Rib1Me), and we show that the EPR pattern can be used as a ‘‘finger print’’ to identify the Cr V bischelates formed with a- and b-1-substituted D-ribose derivatives. 0277-5387/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.poly.2005.02.025 * Corresponding authors. Tel./fax: +54 341 4350214 (S. Signorella). E-mail addresses: signorel@infovia.com.ar (S. Signorella), inqui- bir@satlink.com (L.F. Sala). www.elsevier.com/locate/poly Polyhedron 24 (2005) 1079–1085