Carbon dioxide fixation by zinc(II) complexes with macrocyclic ligand

The copper(II) and zinc(II) coordination mode of HExxH and HxxEH motif in small peptides: The role of carboxylate location and hydrogen bonding network

A comparative investigation of the interaction of three dibenzo-substituted, mixed oxygen–nitrogen donor macrocycles with cobalt(II), nickel(II), copper(II), zinc(II), cadmium(II), silver(I) and lead(II) has been carried out. The thermodynamic stabilities of the respective complexes in 95% methanol (I = 0.1; Et4NClO4, 25 °C) have been determined. All ligands form 1 ∶ 1 (metal ∶ ligand) species with the above metal ions. The results are compared with those obtained previously for related mixed-donor (cyclic) systems. Single crystal structures of six metal complexes of these 20-membered ring ligands have been determined by X-ray diffraction. All of the macrocyclic donor sites participate in binding to the metal ion in the copper(II) and cadmium(II) complexes. The copper complex is six-coordinate, while the cadmium complex is eight-coordinate with the addition of a bidentate nitrato ion. A tri-nuclear complex is formed on complexation with silver(I) in which two silver-containing macrocycles are linked by a bridging two-coordinate silver ion. The metal atoms in each of the cobalt(II), nickel(II) and zinc(II) complexes are six-coordinate, however, they are bound to the macrocycle only at the three secondary amine nitrogen sites. The coordination sphere is completed by two nitrato counterions in the zinc(II) complex, and by a nitrato ion and a methanol molecule in each of the cobalt(II) and nickel(II) complexes.

New insights into the metal ion–peptide hydroxamate interactions: Metal complexes of primary hydroxamic acid derivatives of common dipeptides in aqueous solution

The study of complex formation processes is the scientific basis for the development of electrolytes in electroplating. The data on complexation in the zinc (II)–chromium (III)–cobalt (II)–glycine–water system were obtained. The study of complex formation in the zinc (II)-chromium (III)-cobalt (II)-glycine-water system is relevant due to the possibility of developing electrolytic galvanizing processes and obtaining appropriate coatings with high corrosion resistance. In addition, the alloying of zinc electroplating coatings with chromium, cobalt makes it possible to replace the use of toxic cadmium coatings and use their smaller thicknesses. The solutions were thermostated at 25 °C. The HI 2215 pH/ORPMeter was used to measure pH. The spin-lattice relaxation time T1 was measured on a pulsed NMR spectrometer "Minispecmq20" with a frequency of 19.75 MHz. The constants of the formation of complexes and their accumulation shares were calculated according to the CPESSP program. The paper presents data on previously conducted studies of chromium(III)–water, zinc(II)–glycine–water, chromium(III)–glycine–water and zinc(II)–chromium(III)–glycine–water systems. Data on complexation in the chromium (III)-cobalt (II)-glycine-water system were obtained. The formation of a heteronuclear complex CrCoGly83- has been established. The compositions of heteronuclear compounds, their accumulation fractions and formation constants were established: CrCoZn(HGly)5Gly34+ (lgK= 2.31±0.01); CrCoZn(HGly)3Gly52+ (lgK= -1.36±0.05) and CrCoZn(HGy)2Gly6+ (lgK= -4.23±0.09). The maximum proportion of accumulation of heteronuclear complexes, as studies have shown, is observed in the pH range of 2...6. In this paper, considerations are made about the electrochemical reactivity of heteronuclear compounds. In particular, it is noted that the electrochemical reduction of more electronegative metals, if they are in a heteronuclear complex, should occur with less overvoltage of the reaction. For citation: Berezin N.B., Chevela V.V., Mezhevich Zh.V., Ivanova V.Yu. Complex formation in the system zinc (II)-chromium (III) -cobalt (II)-glycine-water. ChemChemTech [Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol.]. 2023. V. 66. N 6. P. 31-36. DOI: 10.6060/ivkkt.20236606.6789.

Formation constants and assumptions concerning the bonding mode are reported for the complexes present in aqueous solution in the cobalt(II)–, nickel(II)–, copper(II)–, zinc(II)–, and iron(III)–DL-aspartic acid-β-hydroxamic acid (N-hydroxyasparagine, hasn) systems. The amino nitrogen, the hydroxamate nitrogen, and the carboxylate oxygen are the main co-ordinating donor atoms in the cobalt(II)– and nickel(II)–hasn complexes. The hydroxamate oxygens may also take part in co-ordination in the zinc(II)–hasn system. Very stable 1:1 and 1:2 binary complexes are formed in the iron(III)–hasn system, with tridentate co-ordination (hydroxamate and carboxylate oxygens) of the ligand. Mixed hydroxo complexes are proposed at pH > 5. A polymeric species, with composition [Cu4A4H–2]2–, is the most stable complex in the copper(II)–hasn system.

The monohydrazones derived from the condensation of diacetyl and benzil with hydrazine-S-methylcarbodithioate (Dahydth) and (Benhydth) were prepared and their ligation properties with nickel(II), copper(II), palladium(II), zinc(II) and cadmium(II) were studied. A series of bisligand chelates were isolated and characterized. In the zinc(II), cadmium(II) copper(II) and palladium(II) bisligand chelates, both Dahydth and Benhydth act as mononegative bidentate molecules. The Ni(Dahydth-H)2 chelate possesses an octahedral structure where Dahydth acts as a mononegative tridentate ligand. The1H n.m.r. spectra of the two ligands as well as of the diamagnetic metal(II) chelates are discussed. The fragmentation in a mass spectrometer of all these chelates was also studied.

The combination of strong coordination bonds and hydrogen bonding interactions were used to generate a series of supramolecular coordination materials (SCMs), which was achieved by reacting a bis-pyridyl amide ligand, namely N-(4-pyridyl)nicotinamide (4PNA) with copper(II), zinc(II), and cadmium(II) benzoates. The SCMs were structurally characterized using X-ray diffraction and the key intermolecular interactions were identified via Hirshfeld surface analysis. The role of solvent molecules on the supramolecular architecture was analyzed by synthesizing the SCMs in different solvents/solvent mixtures. A solvent-mediated solid-state structural transformation was observed in copper(II) SCMs and we were able to isolate the intermediate form of the crystal-to-crystal transformation process. The luminescence experiments revealed that complexation enhanced the fluorescence properties of 4PNA in the zinc(II) and cadmium(II) SCMs, but a reverse phenomenon was observed in the copper(II) SCMs. This work demonstrated the tuning of supramolecular assembly in coordination compounds as a function of solvents for generating SCMs with diverse properties.

Copper(II) and zinc(II) complexes of two polyimidazole derivatives, 4-(imidazol-4-ylmethyl)-2-(imidazol-2-ylmethyl)imidazole (TRIM) and bis[4-(imidazol-4-ylmethyl)-imidazol-2-yl]methane (TIM), containing three and four methylene-linked imidazole rings as donor groups, have been studied by potentiometry, UV–VIS, EPR and NMR spectroscopic methods. The data revealed that both ligands form extremely stable and varied complexes with zinc(II) and copper(II). In equimolar solutions of the metal ions and TRIM, two and three imidazole co-ordinated MAH and MA species were formed. The complex Zn(TRIM) probably has tetrahedral geometry. The formation of bis-complexes has also been detected with the ligand in excess. The data revealed 6N and 5N co-ordinated central ions in ZnA2 and CuA2, respectively. In MA complexes of TIM, the ligand is co-ordinated to the metal ions via all the four imidazole units. Formation of bis-complexes has only been found in the zinc(II) containing system. Ternary systems of zinc(II)–TRIM and –TIM have also been studied with L-cysteine as a second ligand. The potentiometric and NMR results established the formation of ternary complexes with different protonation states in relatively high amount, in spite of the high stability of the parent complexes.

Synthesis and structures of pyridinecarboxylate-containing zinc(II) complexes in dien and tren system

The complex formation in the zinc(II) - 2-methyldipyrido-[3,2-f:2',3'-h]-quinoxaline (MeDPQ), zinc(II) - L-histidine (HisH) and zinc(II) - 2-methyldipyrido-[3,2-f:2',3'-h]-quinoxaline - L-histidine systems at 37.0 °C on the 0.15 mol dm-3 NaCl background has been investigated by the pH-potentiometry method. A total of 10 complex forms were characterized. Based on the analysis of the complex formation constants and DFT calculations at the B3LYP/TZVPP level, taking into account the solvent effect within the C-PCM model, the structures of Zn(MeDPQ)(HisH)2+, Zn(MeDPQ)(His)+, and Zn(MeDPQ)(His)(OH) complexes were modeled. The higher stability of the homoligand complexes Zn(His)+, Zn(HisH)(His)+, Zn(His)2 and extra-stabilization in the formation constants of the heteroligand complexes Zn(MeDPQ)(HisH)2+ and Zn(MeDPQ)(His)+ were discovered, which was confirmed by the DFT calculations. Higher values of equilibrium constants of the mentioned homoligand forms are explained by coordination to the central nitrogen atom of the imidazole fragment of histidine. Extra-stabilization of heteroligand forms occurs due to d-π-interaction with electron density transfer from π-donor orbitals of oxygen atoms of the carboxy groups of amino acids through the central ion to π-acceptor orbitals of MeDPQ. It is emphasized that the studied zinc(II) complexes, both in binary and ternary systems, can have high biological activity, in particular, due to the nucleophilic attack of the coordinated hydroxide anion on proteins and other biomaterials. This opens up the prospect of using such zinc(II) complexes in medicine. In particular, the studied complexes may exhibit anticancer activity.

Binary and mixed-ligand complexes formed by zinc(II) with imidazole, histamine, and L-histidine ligands (A) have been investigated by potentiometry in aqueous solution at 37 °C and I= 0.15 mol dm–3(Na[ClO4]) and the relevant stability constants are evaluated using advanced computer techniques. The results suggest that in the zinc(II)–imidazole, –histamine, and –L-histidine binary systems, the complex formation process is favoured by the π-electron system of the imidazole group in both the 1 :1 and 1 :2 complexes. It appears that the extra proton in the ZnAH histamine complex and ZnA2H2 and ZnA2H L-histidine complexes resides on the primary amino-group of the respective ligands. The mixed-ligand systems, (i) zinc(II)–imidazole (A)–histamine (B), (ii) zinc(II)–imidazole (A)–L-histidine (B), and (iii) zinc(II)–histamine (A)–L-histidine (B) respectively showed the presence of the mixed species, (i) ZnAB and ZnA2B, (ii) ZnAB, and (iii) ZnAB, ZnABH, and ZnABH2. Formation of ZnA2B in system (i) was found to be less favoured. All other mixed species do have marked stabilities. The probable site of protonation in ZnABH and ZnABH2 species in system (iii) is discussed in terms of their stability constant data.

A series of group 12 metal complexes, [ZnCl2L2]·H2O (1), [ZnBr2L2]·0.75EtOH (2a), [ZnBr2L2]·0.8H2O (2b), [ZnI2L2] (3), [HgCl2L2] (4), [HgBr2L2] (5), and [HgI2L] (6), have been synthesized from a naphthyl-substituted pyridylurea ligand N-(1-naphthyl)-N′-(3-pyridyl)urea (L) and zinc(II) or mercury(II) halides. In the zinc(II) dichloro complex, 1, the chloride ions participate not only in metal coordination but also in N–H⋯Cl hydrogen bonding with the urea NH groups, giving an overall layered structure. In contrast, the coordinated bromide and iodide anions in 2 and 3 are not involved in hydrogen bonding; instead, the urea groups undergo self-association to form nano-tubular structures with various pore sizes stacked by the semi-macrocyclic [ZnX2L2] synthons. Most interestingly, although different solvent molecules [EtOH (2a) and H2O (2b)] can be encapsulated in the nano-tubular zinc dibromo complexes, a competitive experiment conducted in the EtOH/H2O mixed solvents showed that the nanotube can selectively capture the EtOH molecule, as confirmed by X-ray single-crystal diffraction and solid-state fluorescence studies. With the tetrahedral mercury(II) ion, complexes 4 and 5 are isomorphous 2D sheet structures held by N–H⋯O hydrogen bonds and π–π stacking interactions. The 2D sheets are further linked by C–H⋯Cl/Br weak interactions into a hydrogen-bonded 3D framework. Notably, compound 6 contains an uncommon trigonal-planar HgII center and forms a 1D chain structure via the typical urea⋯urea hydrogen bonding and π–π stacking interactions of L, which further aggregates to a 2D parallelogram grid framework through C–H⋯I weak interactions. The solid-state fluorescent properties of L and the complexes 1–6 have also been investigated at room temperature.

Using calorimetric method we determined the thermal effects of reactions of the L-serine complex formation with the doubly charged zinc ion. The heat effects of the reaction of amino acid solution with a solution of zinc(II) were measured at temperatures 288.15, 298.15, and 308.15 K and ionic strengths 0.25, 0.50, and 0.75, against the background of KNO3. The heats of dilution of zinc nitrate in the background electrolyte solution were determined under the same conditions, to introduce respective corrections. The thermochemical data were processed with accounting for all the possible equilibria. The standard thermodynamic characteristics of complex formation processes were calculated. The effects of concentration and temperature on the thermal effects of the complex formation of zinc(II) and L-serine in aqueous solution were estimated.

Copper- and zinc-(II) complexes of various bis(imidazolyl) ligands have been studied by potentiometric, visible and EPR spectroscopic methods. The ligands included bis(imidazol-2-yl)methane (CH2R2), bis-(imidazol-2-yl)methylamine (R2CHNH2) and 3,3-[bis(imidazol-2-yl)]propionic acid (R2CHCH2CO2H) and peptides in which the bis(imidazolyl) groups are coupled at the C-terminus, MeCO-Pro-Leu-Gly-NHCHR2 and ButOCO-Pro-His-Gly-NHCHR2, or the N-terminus, R2CHCH2CO-lle-Ala-Gly-OEt and R2CHCH2CO-lle-His-Gly-OEt (where R = imidazol-2-yl). The data revealed that stable mono- and bis-(ligand) complexes are formed with all ligands and the imidazole nitrogens are the main metal binding sites. Tridentate co-ordination of R2CHNH2 was concluded to exist in the equimolar solutions of copper(II) and R2CHNH2, which results in the formation of a dinuclear mixed-hydroxo complex with imidazole bridging. Deprotonation of the co-ordinated water molecules was also observed around the physiological pH range in the zinc(II)-R2CHNH2complex. The involvement of the side-chain imidazole residues of the peptides ButOCO-Pro-His-Gly-NHCHR2 and especially R2CHCH2CO-lle-His-Gly-OEt in co-ordination has also been demonstrated.

The heats of reaction of zinc(II) with glycylglycine at temperatures 288.15, 298.15, and 308.15 K and ionic strengths 0.25, 0.50, and 0.75 (potassium nitrate as a supporting electrolyte) were determined by calorimetry. The thermochemical results were processed with inclusion of stepwise equilibria. In addition to complexation reactions, “side” protolytic processes were considered. Standard heats of complexation in the system were found by extrapolation to the zero ionic strength by an equation with one individual parameter. The influence of the supporting electrolyte concentration and temperature on the thermodynamic characteristics of the complexation reactions in the glycylglycine-zinc(II) system was considered. The standard enthalpies of formation of ZnGlyGly+, Zn(GlyGly)2, and Zn(GlyGly) 3 − species in aqueous solution were calculated.