Multispectroscopic insight, morphological analysis and molecular docking studies of Cu<sup>II</sup>-based chemotherapeutic drug entity with human serum albumin (HSA) and bovine serum albumin (BSA)
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The interaction studies of Cu<sup>II</sup> nalidixic acid–DACH chemotherapeutic drug entity, [C<sub>36</sub>H<sub>50</sub>N<sub>8</sub>O<sub>6</sub>Cu] with serum albumin proteins, <i>viz</i>., human serum albumin (HSA) and bovine serum albumin (BSA) employing UV–vis, fluorescence, CD, FTIR and molecular docking techniques have been carried out. Complex [C<sub>36</sub>H<sub>50</sub>N<sub>8</sub>O<sub>6</sub>Cu] demonstrated strong binding affinity towards serum albumin proteins <i>via</i> hydrophobic contacts with binding constants, <i>K</i> = 3.18 × 10<sup>5</sup> and 7.44 × 10<sup>4</sup> M<sup>–1</sup> for HSA and BSA, respectively implicating a higher binding affinity for HSA. The thermodynamic parameters ΔG, ΔH and ΔS at different temperatures were also calculated and the interaction of complex [C<sub>36</sub>H<sub>50</sub>N<sub>8</sub>O<sub>6</sub>Cu] with HSA and BSA was found to be enthalpy and entropy favoured, nevertheless, complex [C<sub>36</sub>H<sub>50</sub>N<sub>8</sub>O<sub>6</sub>Cu] demonstrated higher binding affinity towards HSA than BSA evidenced from its higher binding constant values. Time resolved fluorescence spectroscopy (TRFS) was carried out to validate the static quenching mechanism of HSA/BSA fluorescence. The collaborative results of spectroscopic studies indicated that the microenvironment and the conformation of HSA and BSA (α–helix) were significantly perturbed upon interaction with complex [C<sub>36</sub>H<sub>50</sub>N<sub>8</sub>O<sub>6</sub>Cu]. Hirshfeld surfaces analysis and fingerprint plots revealed various intermolecular interactions <i>viz</i>., N–H<b>····</b>O, O–H<b>····</b>O and C–H<b>····</b>O linkages in a 2–dimensional framework that provide crucial information about the supramolecular architectures in the complex. Molecular docking studies were carried out to ascertain the preferential binding mode and affinity of complex [C<sub>36</sub>H<sub>50</sub>N<sub>8</sub>O<sub>6</sub>Cu] at the target site of HSA and BSA. Furthermore, only for Transmission electroscopy microscopy micrographs of HSA and BSA in presence of complex [C<sub>36</sub>H<sub>50</sub>N<sub>8</sub>O<sub>6</sub>Cu] revealed major protein morphological transitions and aggregation which validates efficient delivery of complex by serum proteins to the target site. Communicated by Ramaswamy H. Sarma
