Molecular Recognition of Imidazole-Based Drug Molecules by Cobalt(III)- and Zinc(II)-Coproporphyrins in Aqueous Media

The methods of ¹H NMR, spectrophotometric titration, mass spectrometry and elemental analysis are applied to determine the selective binding ability of Co(III)- and Zn(II)-coproporphyrins I towards a series of imidazole-based drug molecules with a wide spectrum of pharmacological activity (metronidazole, histamine, histidine, tinidazole, mercazolil, and pilocarpine) in phosphate buffer (pH 7.4) simulating the blood plasma environment. It is shown that in aqueous buffer media, Co(III)-coproporphyrin I, unlike Zn(II)-coproporphyrin I, binds two imidazole derivatives, and the stability of mono-axial Co-coproporphyrin imidazole complexes is two to three orders of magnitude higher than that of similar complexes of Zn-coproporphyrin I. The studied porphyrinates are found to have the highest binding ability to histamine and histidine due to the formation of two additional hydrogen bonds between the carboxyl groups of the porphyrinate side chains and the binding sites of the ligands in the case of histidine and a hydrogen bond between the amino group of the ligand and the carbonyl oxygen atom of the carboxyl group of the porphyrinate in the case of histamine. The structures of the resulting complexes are optimized by DFT quantum chemical calculations. The results of these studies may be of use in the design of biosensors, including those for the detection, control and verification of various veterinary drug residues in human food samples.

Molecular Recognition of Imidazole Derivatives by Co(III)-Porphyrinsin Phosphate Buffer (pH = 7.4) and Cetylpyridinium Chloride Containing Solutions

Bymeans of spectrophotometric titration and NMR spectroscopy, the selective binding ability ofthe Co(III)-5,15-bis-(3-hydroxyphenyl)-10,20-bis-(4-sulfophenyl)porphyrin (Со(III)Р1) andCo(III)-5,15-bis-(2-hydroxyphenyl)-10,20-bis-(4-sulfophenyl)porphyrin (Со(III)Р2) towards imidazole derivatives of various nature (imidazole (L1), metronidazole (L2), and histamine (L3)) in phosphate buffer (pH 7.4) has been studied. It was found that in the case of L2, L3 the binding of the "first" ligand molecule by porphyrinatesCo(III)P1 and Co(III)P2 occurs with the formation of complexes with two binding sites (donor-acceptor bond at the center and hydrogen bond at the periphery of the macrocycle), while the "second" ligand molecule is added to the metalloporphyrin only due to the formation of the donor-acceptor bond at the macrocycle coordination center. The formation of stable complexes with two binding sites has been confirmed by density functional theory method (DFT) quantum chemical calculations and two-dimensional NMR experiments. It was shown that among the studied porphyrinates, Co(III)P2 is more selective towards to L1-L3 ligands, and localization of cobalt porphyrinates in cetylpyridinium chloride (CPC) micelles does not prevent the studied imidazole derivatives reversible binding. The obtained materials can be used to develop effective receptors for recognition, delivery, and prolonged release of drug compounds to the sites of their functioning. Considering that cetylpyridinium chloride is a widely used cationic biocide as a disinfectant, the designed materials may also prove to be effective antimicrobial agents.