Immobilized Mononuclear and Binuclear Copper(II) Complexes on Chitosan–PVA-Based Composite Films as Dip Catalyst for Dual Enzyme Mimicry

Two
copper(II) complexes, [Cu(2,4-DCBz)2(β-pic)2(H2O)2] 1 and [Cu2(2,4-DCBz)4(γ-pic)4] 2 (where
2,4-DCBz = 2,4-dichlorobenzoate and β/γ-pic = β/γ-picoline),
were synthesized, structurally characterized, and immobilized within
chitosan/poly(vinyl alcohol) (CPVA) films to obtain functional composites
under ambient conditions. Spectroscopic methods, single-crystal X-ray
diffraction, and density functional theory revealed distinct monomeric
and dimeric coordination environments of respective complexes 1 and 2, delineating the role of steric constraints
and non-covalent interactions. Incorporation into the CPVA matrix
yielded stable hybrid films, designated as CPVA1 (complex 1) and CPVA2 (complex 2), which
were comprehensively characterized by SEM, AFM, UV–vis, FT-IR,
and electrochemical (CV) analysis. For both composite films, while
mechanical testing showed good tensile strength and flexibility, the
contact angle measurements indicated favorable surface wettability
for catalytical and antibacterial properties. Functionally, CPVA1, and CPVA2 exhibited strong antibacterial activity
(in silico and in vivo studies)
and oxidase enzyme mimetic activity (phenoxazinone synthetase and
catechol oxidase), showing performance comparable to that of the free
complexes. The catalytic efficiency of CPVA2 was superior,
as evidenced by its improved Kcat values of 3022.2 h–1 for phenoxazinone synthase and 2727.6 h–1 for catechol oxidase. Importantly, when employed as dip catalysts,
the composite films offered a distinct advantage by retaining catalytic
efficiency upon repeated use with minimal leaching. The results demonstrated
that chitosan–PVA–copper(II) hybrid films combine durability,
reusability, and bioactivity, positioning them as sustainable materials
for antibacterial coatings and heterogeneous catalytical applications.