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Interaction of polypyridyl Cr(III) complexes with bovine serum albumin

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We report a detailed investigation of the interaction of Cr(NN)33+ with bovine serum albumin (BSA), an important protein for the transport of drugs in blood plasma which allows us to understand further the role of Cr(NN)33+ as a sensitizer in photodynamic therapy (PDT). Chromium(III) complexes, Cr(5Cl-phen)33+, Cr(5Me-phen)33+ and Cr(5Ph-phen)33+ (where Cl = chlorine, Me = methyl and Ph = phenyl are substituents in position 5 of the phen = 1,10-phenanthroline bidentate ligand), were used for the present study. The interactions of BSA with Cr(NN)33+ were assessed employing fluorescence spectroscopy and UV–Vis absorption spectroscopy; in addition electrochemical experiments carried out at a liquid/liquid interface gave insight into the relative hydrophobicities of the complexes. We found that chromium complexes bind strongly with bovine serum albumins (BSA) with intrinsic binding constants, Kb, of (3.33 ± 0.08) × 105 M−1, (5.92 ± 0.08) × 105 M−1 and (1.64 ± 0.05) × 105 M−1 at 300.3 K. Analysis of the thermodynamic parameters ΔG, ΔH, and ΔS indicated that hydrophobic interactions played a major role in all the BSA-Cr(NN)33+ association processes. The binding distances and transfer efficiencies for BSA binding reactions were calculated according to the Förster theory of non-radiation energy transfer giving distance (r) of 2.63 nm, 2.94 nm and 3.00 nm for 5Clphen, 5Mephen and 5Ph phenanthroline complexes, respectively. All these experimental results indicate that Cr(NN)33+ binds to serum albumins, by which these proteins could act as carriers of this complex for further applications in PDT.

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Cr(5Cl-phen)33+ :

Tris(5-chloro-1,10-phenanthroline) chromium (III) complex

Cr(5Ph-phen)33+ :

Tris(5-phenyl-1,10-phenanthroline) chromium (III) complex

Cr(5Me-phen)33+ :

Tris(5-methyl-1,10-phenanthroline) chromium (III) complex


Bovine serum albumin


Photodynamic therapy


Fluorescence resonant energy transfer


Interface between two immiscible electrolyte solutions


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The authors thank Consejo Nacional de Investigaciones Científicas y Técnicas de Argentina (CONICET) (Grant number PIP 2015-2017 11220150100628CO), Secretaría de Ciencia y Técnica de la Universidad Nacional de Córdoba (SeCyT-UNC) and Agencia Nacional de Promoción de la Ciencia y la Técnica (ANPCyT) for financial support. P.F.G and C.C.A. are research fellows from CONICET. G.A.A., J.R. and L.M.Y. are researchers from CONICET.

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Correspondence to Gerardo A. Argüello.

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Garcia, P.F., Coronel Arrechea, C., Velo, A. et al. Interaction of polypyridyl Cr(III) complexes with bovine serum albumin. Eur Biophys J 49, 125–132 (2020).

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