Complex formation of Zn-, Ni-, and Pd-derivatives of purpurin-18 with serum albumin

We analyzed the spectral characteristics of the complexes of Zn²⁺, Ni²⁺, and Pd²⁺ derivatives of purpurin-18 with human serum albumin (HSA) in aqueous buffer at pH 7.0. Pd²⁺ in the coordination sphere of purpurin-18 decreased the affinity to HSA compared to the respective complexes of zinc and nickel derivatives. Since the formation of complexes with HSA is an important parameter of photodynamic activity of tetrapyrrolic compounds, the differential affinity of metal derivatives of purpurin-18 to this protein should be considered for the optimization of photosensitizers.     

Five Coordinated Zinc(II) and Tris‐Chelate Cadmium(II) Complexes with 2,2′‐Diamino‐5,5′‐dimethyl‐4,4′‐bithiazole – Syntheses,Spectroscopic Characterization,and Crystal Structure

The new synthesized ligand (DADMBTZ = 2,2′‐diamino‐5,5′‐dimethyl‐4,4′‐bithiazole), which is mentioned in this text, is used for preparing the two new complexes [Zn(DADMBTZ)₃](ClO₄)₂. 0.8MeOH.0.2H₂O ( 1 ) and [Cd(DADMBTZ)₃](ClO₄)₂ ( 2 ). The characterization was done by IR, ¹H, ¹³C NMR spectroscopy, elemental analysis and single crystal X‐ray determination. In reaction with DADMBTZ, zinc(II) and cadmium(II) show different characterization. In 2 , to form a tris‐chelate complex with nearly C₃ symmetry for coordination polyhedron, DADMBTZ acts as a bidentate ligand. In 1 , this difference maybe relevant to small radii of Zn²⁺ which make one of the DADMBTZ ligands act as a monodentate ligand to form the five coordinated Zn²⁺ complex. In both 1 and 2 complexes the anions are symmetrically different. 1 and 2 complexes form 2‐D and 3‐D networks via N‐H···O and N‐H···N hydrogen bonds, respectively.     

Synthesis and structure of enaminoketones of pyrazole containing 2-thione(selenone)benzimidazolyl fragments and their zinc and cadmium complexes

New ligand systems based on 4-formyl-5-hydroxypyrazole and 1-aminobenzimidazole derivatives are synthesized. The obtained enamines and their Zn²⁺ and Cd²⁺ metal complexes of composition ML₂ were investigated using the IR, heteronuclear (¹H, ¹³C, ¹⁵N, ⁷⁷Se, ¹¹³Cd) and two-dimensional NMR spectroscopy (COSY, HSQC, HMBC). The data of physicochemical investigations and quantum-chemical calculations showed that the ligands exist in the ketoamine tautomeric form. Quantum-chemical simulation of Zn(II) and Cd(II) complexes showed that the zinc complexes adopt the pseudo-tetrahedral and the cadmium complexes pseudo-octahedral configuration.     

Interactions of the ethanolamino groups of nanofilms with Co(II), Ni(II), Cu(II), Zn(II), and Cr(III) ammoniates at the surface of PVC plates

Interactions of nanofilms containing ethanolamino groups with cobalt(II), nickel(II), copper(II), and zinc(II) ammoniates at the surface of polyvinylchloride plates and with chromium(III) ammoniate in a solution of ammonium chloride were studied. It was found that the groups of the film, together with chloride ions, displace all ammonia molecules from the inner coordination sphere of the metal. The average number of the ethanolamino N atoms of the film participating in formation of the metal ion coordination sphere is 3.35, 3.47, 3.67, 3.42, and 3.37 for Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, and Cr³⁺ complexes, respectively. The average number of chloride ions is 2 for Co²⁺, Ni²⁺, Cu²⁺, and Zn²⁺ and 3 for Cr³⁺. The coordination number of the central atoms is 6. The Cr³⁺ ion forms a coordination sphere composed of three N atoms and three chloride ions and a coordination sphere (charged 1+) made up of four N atoms and two chloride ions, with the third chloride ion being in the outer sphere. The Co²⁺, Ni²⁺, and Cu²⁺ ions form uncharged coordination spheres of two types: (1) with four N atoms and two chloride ions and (2) with three N atoms, two chloride ions, and the O atom of the ethanol hydroxyl group.     

Amino-substituted gem-diphosphonic acids: structures of complexes with divalent metal cations in aqueous solutions

A comparative study of complexation of acids R₂N(CH₂)_nCR"(PO₃H₂)₂ (R = H or Me; R" = OH or H; n = 1 or 2) with the Ca²⁺, Mg²⁺, Zn²⁺, and Cu²⁺ cations in aqueous solutions was carried out by vibrational (IR and Raman) and electronic spectroscopy using the data of ESR spectroscopy and conformational analysis (molecular mechanics). The MOPCPO chelate ring is formed in all ML and MHL complexes. The involvement of the N atom in coordination was found only in the Cu²⁺ complexes and is determined by the structure of the ligand. The relationship between the stability constants and the structures of the complexes in aqueous solutions is analyzed.     

L-Arginine and zinc ion effect on recognition and hydrolysis rate of adenosine 5′-triphosphate

Zn²⁺ can interact with adenosine 5′-triphosphate (ATP) by electrostatic and coordination interactions, and the interaction sites between Zn²⁺ and ATP vary at different pH in the ATP–Zn²⁺ binary system. Non-covalent interactions exist between the carboxyl of arginine (Arg) and Zn²⁺, which led to competition between ATP and Arg to interact with Zn²⁺ in the ATP–Zn²⁺–Arg ternary system. Kinetics studies show that the hydrolysis rate constant of ATP in the ATP–Zn²⁺ binary system was 2.44?×?10^?2?min^?1, about 11-fold faster than that (2.27?×?10^?3?min^?1) in the ATP–Zn²⁺–Arg ternary system. This may be attributed to coordination interactions between the carboxyl of Arg and Zn²⁺ and the decreased activity of zinc ion toward the phosphate groups via nucleophilic attack. A mechanism that the hydrolysis occurred through an addition–elimination mechanism is proposed.     

Conformationally regulated fluorescent sensors. Study of the selectivity in Zn versus Cd sensing

The Zn²⁺ and Cd²⁺ complexing properties of four ligands containing a 4,4′-substituted biphenyl moiety are described. Ligands 1 and 3, containing only one 1-aza-18-crown-6 cavity, lead to selective complexation of Cd²⁺ versus Zn²⁺. Ligand 4, with two crown cavities linked to a tetramethylbenzidine unit, is able to form 1:1 complexes with Zn²⁺ and Cd²⁺, showing a higher complexing constant with Zn²⁺ than with Cd²⁺, probably due to enthalpic factors. Several complementary experiments suggest that the 1:1 complexes formed by ligand 4 involve both crown cavities acting together to give rise to clamp structures. The formation of this type of zinc complex gives rise to red shifted emission bands and distinct quenching of the fluorescence. A similar situation is observed with cadmium but the change is then less pronounced. When mixtures of both salts are used, ligand 4 selectively responds to zinc. Finally, ligand 2, which also has two crown cavities but contains nitro rather than amino groups in the biphenyl moiety, shows no propensity to form clamp complexes and, for this reason, it complexes cadmium much more strongly than zinc and binds the former selectively when mixtures of both salts are used in complexing experiments.     

Synthesis and study of the structure of new 3d-metal coordination compounds with substituted 2-amino-4(5H)-ketothiophens

A series of new 3d-metal complexes based on 2-amino-3-(1-methylbenzimidazol-2-yl)-4(5H)-ketothiophen (HL¹) and 2-amino-3-(2-benzothiazolyl)-4(5H)-ketothiophen (HL²) were synthesized. Compounds of the general formulas [ML₂] and [M(HL¹)₂Cl₂] (where M = Co²⁺, Ni²⁺, Zn²⁺, Cu²⁺) were prepared by the reaction of the above mentioned ligands with the corresponding acetate (for [ML₂]) or chloride (for [M(HL¹)₂Cl₂]) salts in a methanol or a methanol–chloroform medium. The choice of the anion in the initial metal salt, as well as the selection of the ligand, is crucial for obtaining coordination compounds with a neutral or deprotonated form of the 2-amino-4(5H)-ketothiophens. Thus, in contrast to HL¹, complexes with the neutral form of HL² cannot be obtained under the same conditions. All the complexes were studied by spectroscopic methods and X-ray crystallography (for [CuL¹₂] · H₂O). The coordination polyhedron of the copper atom is formed by four nitrogen atoms from two ligand anions and the geometry of the coordination sphere is intermediate between tetrahedral and square-planar.     

Properties of the Magnesium(II) and Calcium(II) Complexes of 5‐ and 6‐Uracilmethylphosphonate (5 Umpa2– and 6 Umpa2–) in Aqueous Solution

The stability constants of the 1 : 1 complexes formed between Mg²⁺ or Ca²⁺ and 5 Umpa^2– or 6 Umpa^2– were determined by potentiometric pH titrations in aqueous solution (25 °C; I = 0.1 M, NaNO₃). Based on previously established log K^M_M(R‐PO3) versus pK^H_H(R‐PO3) straight‐line plots (M²⁺ = Mg²⁺ or Ca²⁺; R‐PO₃^2– = simple phosphate monoester or phosphonate ligands where R is a non‐interacting residue), it is shown that the Mg(5 Umpa), Ca(5 Umpa), Mg(6 Umpa) and Ca(6 Umpa) complexes have the stability expected on the basis of the basicity of the phosphonate group in 5 Umpa^2– and 6 Umpa^2–. This means, these ligands may be considered as simple analogues of nucleotides, e. g. of uridine 5′‐monophosphate. In the higher pH range deprotonation of the uracil residue in the M(5 Umpa) and M(6 Umpa) complexes occurs and this leads to the negatively charged M(5 Umpa–H)^– and M(6 Umpa–H)^– species. Based on the comparison of various acidity constants it is shown that the M(5 Umpa) complexes are especially acidic; or to say it differently, the M(5 Umpa–H)^– species are especially stable. This increased stability is attributed to the formation of a seven‐membered chelate involving next to the phosphonate group also the carbonyl oxygen atom at C4 (after deprotonation of the (N3)H site). The formation degree of this chelated isomer reaches about 45% for the Mg(5 Umpa–H)^– and Ca(5 Umpa–H)^– species. No indication for chelate formation was observed for the M(6 Umpa–H)^– complexes.     

Synthesis and characterization of Ni(II), Zn(II), and Cd(II) complexes with dithiophosphonate derivatives

Ammonium salts of p-methoxyphenyldithiophosphonic acid O-alkyl esters (H₃CO-C₆H₄-(RO)P(S)S⁻NH ₄ ⁺ ; R = C₂H₅,-CH₂CH₂CH₂CH₂-, and cyclopentyl) and their complexes with Ni²⁺, Cd²⁺, and Zn²⁺ were prepared. 2,4-Bis(4-methoxyphenyl)-1,3,2,4-dithiadiphosphetane-2,4-disulfide, the so-called Lawesson reagent, was treated with the corresponding alcohol to give the O-alkyl ester of the acid. Dry NH₃ was then purged through the solution of this ester to form the ammonium salt of the O-alkyl dithiophosphonic acids. Nickel complexes of these ligands were formed in acetic acid, while zinc and cadmium complexes were formed in water and an ethanol medium, respectively. The geometry of the coordinated atoms was square planar with Ni²⁺ and tetrahedral with Zn²⁺ and Cd²⁺. Using an alkanediol, two dithiophosphonic acids were bridged, thus forming a ligand with four S atoms for coordination. The zinc and cadmium complexes of these tetradentate ligands were also synthesized. The text was submitted by the authors in English.     

Raman and SERS study on ibuprofen metal complexes with biomedical interest

Ibuprofen is one of the most widely used non-steroidal anti-inflammatory drugs (NSAIDs), in which the carboxylate group is available for metal–ligand interactions. The most stable geometries for ibuprofen (in both its protonated and deprotonated forms) were identified by optimizations obtained by the unrestricted Density Functional Theory (DFT). Theoretical study of ibuprofen interacting with Ag colloid in solution, led to two (for the protonated form) and three (for the deprotonated form) different optimized geometries, corresponding to different interaction sites of the Ag₂ cluster. Frequency calculations were performed in the limit of the harmonic approximation, using the aug-cc-pVDZ basis set. Interpretation of the theoretical Raman spectra was performed by the Potential Energy Distribution (PED) analysis of the fundamental vibrations modes. Raman study on the solid Ibuprofen-metal complexes confirmed that Co²⁺ gives monodentate complexes, while Zn²⁺ adopts a bidentate coordination. SERS spectra of metal complexes, suggested that at ppm concentration, the formation of stable 2:1 metal complexes is excluded, while is more probable the formation of 1:1 adduct with bidentate binding on the carboxylic group. The metal reaches its total coordination shell by complexation of water molecules.     

Involvement of histidines 11, 15 and 19 in the binding of zinc to the fusogenic H5WYG peptide

The histidine‐rich GLFHAIAHFIHGGWHGLIHGWYG peptide (H5WYG) coordinates a Zn²⁺ ion and forms a stable peptide–metal complex promoting membrane fusion at physiologic pH. In our previous article titled ‘Histidine‐rich peptide: evidence for a single zinc‐binding site on H5WYG peptide that promotes membrane fusion at neutral pH’ in Journal of Mass Spectrometry (2009, 44, 81–89), tandem mass spectrometry experiments have provided evidence for the binding of a single Zn²⁺ ion to H5WYG and suggested that this binding is shared between H¹¹, H¹⁹ and probably H¹⁵ residues. To clarify the involvement of these histidine residues in the binding to the Zn²⁺ ion and especially to remove the doubt about the implication of the H¹⁵ residue, here we have used three H5WYG mutants termed H5WYGH11A, H5WYGH15A and H5WYGH19A, whose H¹¹, H¹⁵ and H¹⁹ residues were replaced with an alanine residue. The novelty introduced by these new tandem mass spectrometry experiments performed with the mutants is the demonstration that H¹⁵ is involved in the binding of the single Zn²⁺ ion and that it may even favour the setting of another Zn²⁺ ion. Thus, the three histidines H¹¹, H¹⁵ and H¹⁹ could lead to a specific structuring of H5WYG that can promote membrane fusion upon the binding of zinc. Copyright © 2009 John Wiley & Sons, Ltd.     

Stability studies on 1:1 or 1:3 stoichiometry complexes of hexaza tripods with zinc(II), copper(II), nickel(II) and cobalt(II)

The coordination properties of two C₃-symmetry hexaza tripods, 1,3,5-tri(2,5-diazahexyl)benzene (L1) and 1,3,5-tri(2,5-diazaheptyl)benzene (L2), towards Zn²⁺, Cu²⁺, Ni²⁺ and Co²⁺ ions, studied by potentiometric techniques, are reported. Both ligands form quite stable complexes either in a 1:1 or 1:3 M:L stoichiometry, presenting a preferential coordination order: Zn²⁺ < Cu²⁺ > Ni²⁺ > Co²⁺. It is observed that the different configurations of metal complexes are achieved due to the fact that tripodal ligands are flexible and not constrained into a rigid geometry.     

A New Metalloligand Powerful in Forming Helical Coordination Polymers

A new macrocyclic oxamido carboxylate metalloligand was designed and three heteronuclear coordination polymers of the metalloligand and metal nodes Cu²⁺, Zn²⁺ and Cd²⁺ were prepared. X-ray single crystal analyses (CIF files CCDC nos. 1025722–1025724 for I–III) revealed that multiple favourable features endowed the metalloligand with a strong power to force the metal nodes to generate 1D helical coordination polymers. Thermogravimetric analyses showed that the complexes with Cu²⁺ and Zn²⁺ nodes exhibited moderate thermal stability. The three complexes were also characterized by IR spectra and PXRD.     

Two ZnII coordination complexes assembled by trithiocyanuric acid and two different N‐donor auxiliary ligands

The dipyridyl‐type building blocks 4‐amino‐3,5‐bis(pyridin‐3‐yl)‐1,2,4‐triazole (3‐bpt) and 4,4′‐bipyridine (bpy) have been used to assemble with Zn^II in the presence of trithiocyanuric acid (ttcH₃) to afford two coordination compounds, namely bis[4‐amino‐3,5‐bis(pyridin‐3‐yl)‐1,2,4‐triazole‐κN³]bis(trithiocyanurato‐κ²N,S)zinc(II), [Zn(C₃H₂N₃S₃)₂(C₁₂H₁₀N₆)₂]·2H₂O, (1), and catena‐poly[[[bis(trithiocyanurato‐κ²N,S)zinc(II)]‐μ‐4,4′‐bipyridine‐κ²N:N′] 4,4′‐bipyridine monosolvate], {[Zn₂(C₃H₂N₃S₃)₄(C₁₀H₈N₂)₃]·C₁₀H₈N₂}_n, (2). Single‐crystal X‐ray analysis indicates that complex (1) is a mononuclear structure, while complex (2) presents a one‐dimensional chain coordination motif. In both complexes, the central Zn^II cation adopts an octahedral geometry, coordinated by four N‐ and two S‐donor atoms. Notably, trithiocyanurate (ttcH₂⁻) adopts the same bidentate chelating coordination mode in each complex and exists in the thione tautomeric form. The 3‐bpt co‐ligand in (1) adopts a monodentate coordination mode and serves as a terminal pendant ligand, whereas the 4,4′‐bipyridine (bpy) ligand in (2) adopts a bidentate–bridging coordination mode. The different coordination characters of the different N‐donor auxiliary ligands lead to structural diversity for complexes (1) and (2). Further analysis indicates that the resultant three‐dimensional supramolecular networks for (1) and (2) arise through intermolecular N—H...S and N—H...N hydrogen bonds. Both complexes have been further characterized by FT–IR spectroscopy and elemental analyses.     

Synthesis, crystal structure, and spectroscopic studies of 10-(1-phthalazinylazo)-9-phenanthrol (HL). Complexation of cadmium and zinc chlorides with HL

10-(1-Phthalazinylazo)-9-phenanthrol (HL, I) was synthesized by the reaction between 1-hydrazinophthalazine and 9,10-phenanthrenequinone. The crystal and molecular structures of compound I were determined by X-ray diffraction (XRD). According to XRD, EAS, and ¹H and ¹³C NMR data, a HL molecule in solutions and in crystals exists in the form of quinohydrazone tautomer (b) (s-trans, cis) stabilized by intramolecular N(3)H...O(1) hydrogen bond. The “mobile” H atom is localized at the N(3) atom of the azo group. The phthalazine (A) and phenanthrenequinone (B) moieties of the HL molecule are nearly coplanar. The HL basicity and acidity constants (pK_a = 1.90 and pK_a = 11.65, respectively) and the formation constants of HL complexes with Zn²⁺ and Cd²⁺ and their compositions in solutions were determined. ML₂ · DMFA complexes, where M = Zn²⁺, Cd²⁺, were synthesized. The coordination mode of the L^? ligand with metal atoms was suggested.     

Locating Pb2+ and Zn2+ in Zinc Finger-Like Peptides Using Mass Spectrometry

The binding preferences of Pb²⁺and Zn²⁺ in doubly charged complexes with zinc finger-like 12-residue peptides (Pep), [M_n(Pep-2(n-1)H)]²⁺ have been explored using tandem mass spectrometry. The peptides were synthesized strategically by blocking the N-terminus with an acetyl group and with four cysteine and/or histidine residues in positions 2, 5, 8, and 11, arranged in different motifs: CCHH, CHCH, and CCCC. The MS² spectra of the Pb²⁺ and Zn²⁺ complexes show multiple losses of water and a single methane loss and these provide a sensitive method for locating the metal dication and so elucidating its coordination. The elimination of a methane molecule indicated the position of the metal at the Cys2 residue. Whereas lead was observed to preferentially bind to cysteine residues, zinc was found to primarily bind to histidine residues and secondarily to cysteine residues. Preferential binding of lead to cysteine is preserved in the complexes with more than one Pb²⁺. Key to the mechanism of the loss of water and methane is the metal dication withdrawing electrons from the proximal amidic nitrogen. This acidic nitrogen loses its hydrogen to an amidic oxygen situated four atoms away leading to formation of a five-member ring and the elimination of water.      

Effect of ligand environment on the mechanism of enantiomerization of Be<Superscript>II</Superscript>, Zn<Superscript>II</Superscript>, and Cu<Superscript>II</Superscript> bischelate complexes

The effect of ligand environment on the mechanism of enantiomerization of Be^II, Zn^II, and Cu^II bischelate aminovinylketonate complexes was studied by the B3LYP/6-311++G(d,p) method. Substituents at the nitrogen atom (R = H, Me, Prⁱ) significantly affect the mechanism of enantiomerization. In the beryllium complexes, the diagonal twist mechanism is changed to the dissociation mechanism. In the zinc complexes, only the diagonal twist mechanism is realized. The barrier to reaction monotonically increases with the size of the substituent. In the copper complexes, the effect of substituents manifests itself in the change in the relative stabilities of different forms. At R = H, the square-planar form is more stable, while the tetrahedral configuration is favorable at R = Prⁱ. For the Cu^II complex with R = Me, the energy difference between two forms is less than 1 kcal mol^-1, which leads to stabilization of the squareplanar structure in the solid state, whereas the tetrahedral form is more stable in solution.     

Synthesis and Characterization of [Zn2(4,4′‐bipy)n(AcO)4] – One‐dimensional Chain (n = 1) and One‐dimensional Double‐Chain (n = 2) Coordination Polymers

Two new Zn^II(μ‐4,4′‐bipy) coordination polymers with acetate anions, [Zn(4,4′‐bipy)(AcO)₂] ( 1 ) and [Zn₂(4,4′‐bipy)(AcO)₄] ( 2 ), have been synthesized. The compounds were characterized with elemental analysis, IR‐, ¹H NMR‐, ¹³C NMR spectroscopy and studied by thermal analysis, fluorescence measurements and x‐ray crystallography. The structural studies of compound 1 suggest the structure is a coordination polymer of zinc(II) consisting of linear double chains formed by bridging 4,4′‐bipy ligand and connection of the acetate‐bridged centrosymmetric [Zn₂(OAc)₂]²⁺ nodes.     

Effect of bridging anions on the structure and stability of phenoxide bridged zinc dipicolylamine coordination complexes

A series of four related phenol derivatives, with 2,2′-dipicolylamine substituents at the ortho positions, were prepared and their Zn²⁺ coordination complexes studied by spectroscopic methods. X-ray crystal diffraction analysis of a dinuclear zinc complex with two bridging acetate anions showed a ternary structure with highly charged interior and lipophilic exterior, which helps explain why this class of water-soluble complexes can effectively diffuse through cell membranes. The stability of the dinuclear zinc complexes in aqueous solution was found to be strongly anion dependent; that is, bridging oxyanions, such as acetate and pyrophosphate, lock the two Zn²⁺ cations to the surrounding ligand and greatly enhance ligand/zinc affinity. Overall, the results provide new insight into the structural and mechanistic factors that control the recognition and chemosensing performance of phenoxide bridged dipicolylamine molecular probes.