BackgroundChitosan, a non-toxic, biodegradable and biocompatible polysaccharide has attained great interest in pharmaceutical applications, as versatile drug delivery agent. Chitosan has been already shown to serve as vehicle for sustained drug release by chitosan-vanadium(IV) complex from a chitosan gel matrix. Therefore, chitosan gel proved to retain vanadium and preserve its insulin-mimetic efficacy. Nevertheless, there is a lack of reports concerning complexing equilibria in aqueous solution, in particular when using the more advantageous microcrystalline form of chitosan (MCCh). Microcrystalline chitosan shows a number of valuable features as compared with unmodified chitosan.ResultsExperimental studies on complexing interaction between a special form of biomaterial - microcrystalline chitosan as ligand, L = MCCh, of two exemplary degrees of deacetylation DD (lower 79.8%; higher 97.7%) with M = oxovanadium (IV) ions have been carried out potentiometrically at four ligand-to-metal concentration ratios (2:1, 5:1, 8:1, 10:1). Among the five hydrolysis equilibria of VO2+ reported up to now in the literature, under the conditions of the present work i.e. aqueous solutions of ionic strength I = 0.1 (KNO3) and temperature 25.0 ± 0.1°C, the predominating one was (VO)2(OH)2  2+ formation: log β20–2 = −7.01(2). Analysis of potentiometric results permitted to note that degree of deacetylation does not essentially influence the coordination mode of the complexes formed. In the case of both the two DD values, as well as for all the ligand-to-metal ratios, formation of hydroxyl deprotonated MLH−1 and ML2H−2 moieties has been confirmed potentiometrically (log β11–1 = −0.68(2) for DD = 79.8% and −0.68(2) for DD = 97.7%, log β12–2 = −7.64(6) for DD = 79.8% and −5.38(7) for DD = 97.7%).ConclusionMicrocrystalline chitosan coordinates the vanadyl ions by the hydroxyl groups. Interaction of MCCh with VO2+ ions in aqueous solution occurs within pH 5–7. Amounts of alkali excessive towards -NH2 are needed to deprotonate the OH groups. Deprotonation occurring at the chitosan hydroxyl groups permits a “pendant” or “bridge” model of coordination with VO(IV). Lack of complexation via deprotonation of amine groups, typical for simple cations and the molybdenum anion, has been indicated also by FTIR spectroscopy and EPR.Graphical AbstractCoordination modes of VO(IV) with microcrystalline chitosan (MCCh): (a)- pendant model, (b)- bridge model

Background Thanks to its specific chemical and physical properties, graphene has aroused growing interest in many fields of Science and Technology. The present study focuses on the properties of microcrystalline chitosan (MCCh): a compound known to increase the biocompatibility of various matrices, including those made of graphene layers, enabling the controlled release of molecules of therapeutic compounds. The study exploits the potential of MCCh to complex with metal ions, in this case Mg 2+ , and attempts to describe such interactions when the system is enriched with graphene oxide (GO). These findings would open completely new areas of knowledge about GO as a drug carrier. Results Potentiometric analysis found that in the GO–Mg system, complexes of ML’ type were formed, where M = Mg 2+ ; L’ = GO (log β 11’0 = 9.5 (3)) and ML’ 2 (log β 12’0 = 13.2 (4)), whereas in the GO–Mg 2+ –MCCh system, a mixed-type complex MLL’ was also formed, in which L = MCCh: this complex demonstrated the overall stability constants log β 111’ = 11.2 (3) for degree of deacetylation DD 74.4% and log β 111’ = 12.4 (4) for DD 97.7%. FT-IR analysis showed interactions in the GO–Mg 2+ –MCCh (DD = 97.7%) system. In addition, the amide II—NH band was displaced from 1623 cm −1 to two bands at 1633 cm −1 and 1648 cm −1 , resulting from the interaction of the metal ion, and the absorption band of the corresponding NH in the chitosan acetyl group was shifted from 1304 to 1351 cm −1 . When chitosan with a deacetylation degree lower than 74.4% was applied, the amide bands I and II differed only in their intensity. A greater impact on absorption was observed for the acetyl NH group of chitosan, for which the corresponding band shifted from 1319 to 1361 cm −1 . Conclusions The results confirm the ability of GO–Mg 2+ –MCCh to create complex arrangements. It can form a basic complex of one metal ion and one ligand molecule (GO) in the case of ML’ (where L’ = GO), or two molecules of GO with a metal ion M (Mg 2+ ) in the case of ML’ 2 . A mixed complex of MLL’ type is also formed, with two ligands: L = MCCh with deacetylation degrees DD = 74.4% and 97.7% and graphene oxide L’ = GO. In the latter case, FT-IR spectroscopy was used to confirm the mode of interaction. The GO–Mg 2+ –MCCh system may be used as carrier in modern magnesium containing medicines or as auxiliary substances in pharmacy.

Five new heteroligand cobalt(II) complexes with 2-picolinehydroxamic acid and reduced Schiff base, N-(2-hydroxybenzyl)alanine, were formed in an aqueous solution over a wide pH range. The coordination properties of ligands towards the metal ion were determined using a pH-metric method, and then the speciation model was confirmed by UV–Vis studies. A stacking interaction between the Schiff base phenol ring and the 2-picolinehydroxamic acid pyridine ring was found to improve the stability of the heteroligand species, indicating more effective coordination in mixed-ligand complexes than in their respective binary systems. The antimicrobial properties of heteroligand complexes were determined against Gram-negative and Gram-positive bacteria, as well as fungal strains. The formulation demonstrated the highest bacteriostatic and bactericidal activity (3.65 mM) against two strains of Gram-negative Helicobacter pylori bacteria and towards Candida albicans and Candida glabrata; this is important due to the potential co-existence of these microorganisms in the gastric milieu and their role in the development of gastritis. The binary complexes in the cobalt(II)—2-picolinehydroxamic acid system and 2-picolinehydroxamic acid were not cytotoxic against L929 mouse fibroblasts, neither freshly prepared solutions or after two weeks’ storage. By comparison, the heteroligand complexes within the range 0.91–3.65 mM diminished the metabolic activity of L929 cells, which was correlated with increased damage to cell nuclei. The concentration of the heteroligand species increased over time; therefore, the complexes stored for two weeks exhibited stronger anticellular toxicity than the freshly prepared samples. The complexes formed in an aqueous solution under physiological pH effectively bound to calf thymus DNA in an intercalative manner. This DNA-binding ability may underpin the antimicrobial/antifungal activity of the heteroligand complexes and their ability to downregulate the growth of eukaryotic cells.

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The present work describes the complexation properties of two oxime-containing Schiff bases (used as ligands), viz. 2-hydroxyimino-N′-[1-(2-pyridyl)ethylidene]propanohydrazone (Hpop) and 2-hydroxyimino-N′-[(pyridine-2-yl)methylidene]propanohydrazone (Hpoa), with Co(II) ions in DMSO/water solution. Volumetric (oxygenation) studies were carried out to determine the uptake of molecular oxygen O2 in the formation of the complexes Co(II)-Hpop and Co(II)-Hpoa. The acquired data can be useful in the development of oxygen bioinorganic complexes of metal ions with Schiff base ligands in solution. Their properties allow them to be used as synthetic oxygen transporters. Moreover, the binding of dioxygen could play an important role in the research of catalytic activity by such systems.