Metal–organic framework in an l-arginine copper(ii) ion polymer: structure, properties, theoretical studies and microbiological activity

Abstract

A novel 1D polymeric copper(II) complex with L-arginine and a linear bridged 4,4′-bipyridine with a formula of {[Cu(L-Arg)₂(μ-4,4′-bpy)]Cl₂·3H₂O}_∞ (1) (where L-Arg = L-arginine, 4,4′-bpy = 4,4′-bipyridine) was synthesized. The crystal structure and properties of the product were characterized using X-ray diffraction, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), spectroscopic techniques (FT-IR, Raman, NIR-vis-UV electronic and EPR), magnetic methods, and microbiological examinations. The crystals of 1 crystallized in a trigonal system and a space group of P3₂21 was characterized with a = b = 12.31 Å, c = 18.45 Å, V = 2420 ų, Z = 3, α = β = 90° and γ = 120°. The N and O donor atoms of trans-chelated L-Arg zwitterions and two N atoms of the 4,4′-bpy molecule form a tetragonal distorted octahedral geometry around the copper(II) ions with static character (T = 0.748). The diffuse-reflectance electronic spectrum of 1 is characteristic of the [CuN₂N^′₂O₂] chromophore. The EPR spectrum of frozen 1 (at 77 K) dissolved in water is related to the N₂O₂ set (g_⊥ = 2.057, g_‖ = 2.258 and A_‖ = 169 G). The structure of the [Cu(L-Arg)₂(μ-4,4′-bpy)]²⁺ model complex was optimized at the B3LYP and B3LYP-D3 levels. The calculations of the atomic spin densities on the atoms in the doublet state of the model complex revealed that, with regard to the ligands, the spin population is distributed mainly over the oxygen and nitrogen atoms of L-arginine. The antimicrobial activities were examined against the Gram-positive and Gram-negative bacteria strains: Streptococcus mutans, Enterococcus hirae, Bacillus subtilis, Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli, Salmonella enterica, Shigella flexneri; and fungi: Saccharomyces cerevisiae, Candida albicans. Complex 1 exhibited strong antimicrobial activity against bacteria and fungi, both in their growth inhibition as well as in microbial killing.