Multiple K-edge XAS for the structural analysis of thiophenolate bridged heterotrinuclear complexes

Abstract

397are ideal to show the possibilities of such multiple edge fits. In a forthcoming publication [Glaser et al. (1998)] we focus on the preparation of these complexes, whereas in this contribution we discuss the structural changes upon oxidation of the complexes determined by X-ray absorption spectroscopy. 51$4 N 55 Figure 1Overall structure of the [LFeCrFeL] "÷ core. Experimental sectionA multiple K-edge X-ray absorption spectroscopic (XAS) approach to determine the structural parameters of an isostructural series of heterotrinuclear thiophenolate-bridged metal-complexes of the general formula [LFeCrFeL]n+ (with n= 1,2,3) is presented. The analysis focuses on the variation of the metal-metal distances and the metal-sulfur distances with the cluster charge n. XAS measurements on the Fe, Cr, and S-Kedges were performed to allow a fit of these distances from these constituent elements. Results show that 3 S atoms and 3 N atoms coordinate each of the terminal Fe atoms, whereas 6 S atoms coordinate the central Cr atom. This symmetry allows extracting structural information with high accuracy especially when the spectra obtained at different edges are refined at the same time.A decrease of the metal-metal distance with increasing cluster charge is also derived from this multiple-edge analysis.

Determination of metal–metal distances: significance and accuracy

“…Exafs measurements on similar compounds with Cr instead of Ni have been reported by Meyer-Klaucke et al (1999). Essentially the same structural model is put in practice here.…”

“…Our approach includes not only multiple K-edge refinements [Zhang et al (1996), Meyer-Klaucke et al (1999)] but also the temperature dependence of the disorder, which we describe by the Debye model. Thus more information is available to extract the metal core structure.…”

Assessing the prospect of XAFS experiments of metalloproteins under in vivo conditions at Indus-2 synchrotron facility, India

“…Raw k 3 (k) for M1dr are presented in the inset of Fig. 5(a), for comparison of the spectral quality with reported data of Zn proteins (Meyer-Klaucke et al, 1999a;Dent et al, 1990;Giachini et al, 2007Giachini et al, , 2010Murphy et al, 1997;Shi et al, 2011;Bobyr et al, 2012;Feiters et al, 2003;Clark-Baldwin et al, 1998;Amiss & Gurman, 1999). Raw k 3 (k) for M1dr are dominated by noise beyond k = 8 A ˚À1 whereas the reported spectra retain good quality up to k ' 11 A ˚À1 .…”

“…M1dr belongs to the M1 Zn metalloprotease family whose sequence homologs are involved in tumor growth, angiogenesis, hormone regulation, immune cell development and Huntington's disease (Kelly et al, 1997). Structural pre-determination for the crystal counterpart of M1dr (with XRD) (Agrawal et al, 2019) Zn-protein serves as a good benchmark for XAFS feasibility tests because of prior extensive XAFS investigations and structural cataloging (Bobyr et al, 2012;Dent et al, 1990;Feiters et al, 2003;Murphy et al, 1997;Tierney & Schenk, 2014;Kleifield et al, 2001;Amiss & Gurman, 1999;Meyer-Klaucke et al, 1999a;Giachini et al, 2007Giachini et al, , 2010Clark-Baldwin et al, 1998;Christianson, 1991;Pace & Weerapana, 2014;Laitaoja et al, 2013); (iv) K-edge XANES is a good marker for XANES calibration due to the fixed and stable (against radiation) Zn 2+ state (Giachini et al, 2010;Penner-Hahn, 2005;Al-Ebraheem et al, 2010;Castorina et al, 2019).…”

“…XANES and first-shell results can be reliably obtained for these MPs that would provide informa-tion on the chemical state of the metal, identity of ligand groups, (N/O):S coordination ratio and geometric distortion (Bobyr et al, 2012;Dent et al, 1990;Feiters et al, 2003;Amiss & Gurman, 1999;Meyer-Klaucke et al, 1999a,b;Giachini et al, 2010;Clark-Baldwin et al, 1998;Christianson, 1991;Pace & Weerapana, 2014;Laitaoja et al, 2013;Smolentsev et al, 2005;Longa et al, 1999;Vlasenko et al, 1999;Sagi et al, 1999;Katsikini et al, 2009;Bertoncini et al, 1999). This information can adequately address diverse biological problems such as disease-marking, binding properties, protein aggregation, multi-site heterogeneity, mutation and cellular catalysis (Smolentsev et al, 2005;Longa et al, 1999;Vlasenko et al, 1999;Sagi et al, 1999;Katsikini et al, 2009;Meyer-Klaucke et al, 1999a;Bertoncini et al, 1999). The prospect of improving the spectral quality of XAFS, to accommodate higher-shellbased novel scientific problems (Giachini et al, 2007;Kleifield et al, 2001;Murphy et al, 1997;Tierney & Schenk, 2014), is addressed.…”