Analytical Protocols for Quantitative Evaluation of [4Fe-4S]-maquette Spectra

<p>A step-by-step tutorial is presented for the quantitative analysis of UV-vis spectra of <em>&#39;as isolated&#39;</em> [4Fe-4S]-maquettes that contain&nbsp;diamagnetic, [4Fe-4S]²⁺ clusters,&nbsp;as chromophores. The UV-vis model is justified by the schematic molecular orbital diagram of Fe-S(sulfide) and Fe-S(thiolate) bonding. The spectral analysis is based on integrated peak intensities, which is superior to using absorption maxima (<span class="math-tex">\(\lambda _{max}\)</span>), when the chemical composition of the chromophores are not identical, but similar. Three spectra (two model cluster complexes and a metalloprotein active site) provide&nbsp;the&nbsp;reference for converting spectral intensities to concentrations.</p> <p>The UV-vis modeling is demonstrated for a prototypical <span class="math-tex">\([Fe_4S_4(CIACGAC)(\beta ME)]^{2-}\)</span>&nbsp;complex (FdM-7 maquette)&nbsp;and the&nbsp;<span class="math-tex">\([Fe_4S_4(\beta ME)_4]^{2-}\)</span>&nbsp;complex formed under identical conditions, but without the presence of a peptide.</p>