Effects of salicylate derivate on the competing reaction of chromium(III) complex [Cr(III)(R-SA)(en)2]Cl with apoovotransferrin

Four novel Cr(III) complexes, Bis(ethylenediamine-κ2N,N′)(R-SA-κ2O,O′)chromium(III) chloride (H2SA = salicylic acid, R = 5-F, 5-Cl, 5-Br, 4-CH3 ethylenediamine = en) have been synthesized and three of them are determined by X-ray crystallography. The competition reaction with EDTA and apoovotransferrin (apoOTf) was monitored by UV–Visible (UV–vis) and fluorescence spectra at 37 °C. The reaction with EDTA is only a simple competitive process and no specific selectivity was observed (kEDTA/F410 = 4.07 × 10−3–4.37 × 10−3 M−1 s− 1). While for the reaction with apoOTf, an instable intermediate species (R-SA)–Cr(III)–OTf forms (kOTf/F336 = 1.70 × 10− 1–2.08 × 10−1 M−1 s− 1), where R-SA2− act as the role of synergistic anion. The intermediate is instable and the R-SA2− ligand will then be released with the rate constants of 1.17 × 10− 1 (5-F-SA2−) ≈ 1.01 × 10− 1 (4-CH3-SA2−) > 3.19 × 10− 2 (5-Cl-SA2−) > 3.25 × 10− 3 (5-Br-SA2−) M−1 s− 1. The substitutive groups R on SA have positive influence on charge density of O donor atom, which directly affect the stability of the (R-SA)–Cr(III)–OTf intermediate.