Synthesis, characterization, crystal structure and BSA binding studies of two novel copper(II) complexes: [trans-Cu(en)2(H2O)2](p-methoxycinnamate)2 and [trans-Cu(en)2(H2O)2](p-nitrocinnamate)2·2H2O

Two mononuclear copper(II) complexes of composition [trans-Cu(en)2(H2O)2](p-methoxy cinnamate)2,1 and [trans-Cu(en)2(H2O)2](p-nitrocinnamate)2·2H2O,2 (where en = ethylenediamine) were synthesized by the addition of strong chelating base ethylenediamine to hydrated Cu(II) cinnamates, Cu(p-methoxy/p-nitrocinnamate)2·xH2O in methanol–water mixture. The newly synthesized complexes have been characterized by physicochemical, spectroscopic techniques and X-ray crystallography. The complex 1 crystallizes in the monoclinic crystal system with space group, P21/c and complex 2 crystallizes in the monoclinic crystal system with space group, C2/c. X-ray structure determination revealed ionic structures consisting of one complex cation [trans-Cu(en)2(H2O)2]2+, two p-methoxycinnamate anions in complex 1 while complex 2 consists of one complex cation [trans-Cu(en)2(H2O)2]2+, two p-nitrocinnamate anions and two water molecules of crystallization. The interactions of these complexes with bovine serum albumin (BSA) were investigated using fluorescence spectroscopy. The result of fluorescence titration revealed that the complexes can quench the intrinsic fluorescence of BSA through both static and collisional (dynamic) quenching mechanism. Quenching constant, association binding constant and number of binding sites were calculated by using modified Stern–Volmer and Scatchard equation. Both complexes display good binding propensity to bovine serum albumin protein with 4.07 × 105 and 1.88 × 105 M−1 binding constant value for complexes 1 and 2 respectively, indicating strongest protein-binding ability in complex 1 as compared to 2.

Figure optionsDownload as PowerPoint slideTwo new Cu(II) cinnamate complexes, [trans-Cu(en)2(H2O)2](p-methoxycinnamate)2, 1 and [trans-Cu(en)2(H2O)2](p-nitrocinnamate)2·2H2O, 2 have been synthesized and characterized by thermogravimetric analysis, spectroscopic techniques and X-ray crystallography. Packing analysis has revealed the presence of intricate network of supramolecular hydrogen bonding interactions (N–H⋯O and O–H⋯O) along with π–π interactions which provides robustness to the crystal lattice in both complexes. The analysis of interactions of these complexes with BSA indicated the presence of both static as well as dynamic quenching.Figure optionsDownload as PowerPoint slide