Exploring Thermal Stability, Vibrational Properties, and Biological Assessments of Dichloro(<scp>l</scp>-histidine)copper(II): A Combined Theoretical and Experimental Study

Dichloro(l-histidine)copper(II) crystal ([Cu(l-His)Cl₂] complex) was obtained by the slow evaporation method and characterized concerning its thermal stability, phase transformations, and electronic and vibrational properties. X-ray diffraction (XRPD) confirmed that this complex crystallizes with an orthorhombic structure (<i>P</i>2₁2₁2₁ space group). Thermal analyses (TG and DTA) demonstrate stability from ambient temperature up to 460 K, followed by a phase transition from the orthorhombic structure to the amorphous form around 465 K, as confirmed by temperature-dependent XRPD studies. The active modes in Fourier transform infrared (FT-IR) and Raman spectroscopy spectra were suitably assigned via density functional theory (DFT) calculations. Additionally, Hirshfeld surface analysis uncovered the prominence of Cl···H, O···H, and H···H interactions as the primary intermolecular forces within the crystal structure. The antimicrobial activity of the [Cu(l-His)Cl₂] complex was investigated, demonstrating significant efficacy against Gram-positive bacteria (<i>Staphylococcus aureus</i>), Gram-negative bacteria (<i>Pseudomonas aeruginosa</i>), and fungi (<i>Candida albicans</i>). The minimum inhibitory concentration and cell viability tests showed that the complex inhibits the growth of <i>S. aureus</i> bacteria at a concentration of 1.5 μM without causing damage to the human cell line. The pharmacokinetic parameters corroborate the other tested parameters and highlight the [Cu(l-His)Cl₂] complex as a promising alternative for future clinical trials and medicinal applications. The alignment of the pharmacokinetic parameters with other tested criteria highlights the potential of the [Cu(l-His)Cl₂] complex as a promising candidate for future clinical studies.