Structural and Electrochemical Analysis of Copper-Creatinine Complexes: Application in Creatinine Detection

The formation of complexes between copper ions and biomolecules plays important roles in biological systems. In this work, the structures and electrochemical properties of copper-creatinine complexes were investigated by both experimental and computational approaches. DFT calculation revealed the possible structures of copper-creatinine complexes and provided the data of formation energies, bond lengths, and charge distribution. The properties of the complexes were further investigated by cyclic voltammetry, UV-visible spectrophotometry, X-ray absorption spectroscopy, and scanning electron microscopy. The combination of experimental and computational findings revealed that Cu II binds with creatinine via the endocyclic nitrogen. In aqueous environment, the [Cu(creatinine) 2 (H 2 O) 2 ] 2+ complex is formed. The reduction of [Cu(creatinine) 2 (H 2 O) 2 ] 2+ formed a stable 1:4 complex between Cu I and creatinine. Importantly, the understanding of the electrochemical behaviors of copper-creatinine complexes leads to the development of a novel sensor for the detection of creatinine, a biomarker for kidney diseases. Although creatinine itself is not electroactive, the complex formation with copper allows the species to be detected electrochemically with the sensitivity of 6.09 ± 0.13 μ A mM −1 and the limit of detection (3s B /m) of 35 μ M.