Studies on Schiff Base Complexes with Aza-Crown Ether Pendants as Synthetic Hydrolases for p-Nitrophenyl Picolinate in Brij35 Surfactant Micellar Solution

Schiff base complexes with aza-crown ether pendants have been synthesized and employed as models for hydrolase enzymes by studying the kinetics of their hydrolysis reactions with p-nitrophenyl picolinate (PNPP) in Brij35 surfactant micellar solution. A kinetic model of PNPP cleavage catalyzed by these complexes is proposed. The effects of complex structures and reaction temperature on the rate of catalytic PNPP hydrolysis have also been examined. The rate increases with pH of the buffered Brij35 micellar solution under 25°C; all four complexes exhibited high activity in the catalytic PNPP hydrolysis. The catalytic activity of the phenyl-bridged Schiff base complex is larger than that of ethyl-bridged Schiff base complex for the same substituent and metal. The catalytic activity of manganese(III) complex is superior over cobalt(II) complex in catalyzing hydrolysis of PNPP under the same ligand. The pseudo-first-order rate for PNPP hydrolysis catalyzed by CoL¹ containing aza-crown ether is 2.96 × 10⁴ times that of spontaneous hydrolysis of PNPP in Brij35 surfactant micellar solution at pH = 7.60, [S] = 2.0 × 10^?4 mol dm^?3.     

Synthesis,Spectral, Thermal Studies of Co(II), Ni(II), Cu(II) and Zn(II)‐arginato Complexes. Crystal Structure of Monoaquabis(arginato‐κO,κN)copper(II). [Cu(arg)2(H2O)].NaNO3

Transition metal complexes of arginine (using Co(II), Ni(II), Cu(II) and Zn(II) cations separately) were synthesized and characterized by FTIR, TG/DTA‐DrTG, UV‐Vis spectroscopy and elemental analysis methods. Cu(II)‐Arg complex crystals was found suitable for x‐ray diffraction studies. It was contained, one mole Cu^II and Na⁺ ions, two arginate ligands, one coordinated aqua ligand and one solvent NO₃^? group in the asymmetric unit. The principle coordination sites of metal atom have been occupied by two N atoms of arginate ligands, two carboxylate O atoms, while the apical site was occupied by one O atom for Cu^II cation and two O atoms for Co^II, Ni^II, Zn^II atoms of aqua ligands. Although Cu^II ion adopts a square pyramidal geometry of the structure. Co^II, Ni^II, Zn^II cations have octahedral due to coordination number of these metals. Neighbouring chains were linked together to form a three‐dimensional network via hydrogen‐bonding between coordinated water molecule, amino atoms and O atoms of the bridging carboxylate groups. Cu^II complex was crystallized in the monoclinic space group P2₁, a = 8.4407(5) Å, b = 12.0976(5) Å, c = 10.2448(6) Å, V = 1041.03(10) ų, Z = 2. Structures of the other metal complexes were similar to CuII complex, because of their spectroscopic studies have in agreement with each other. Copper complex has shown DNA like helix chain structure. Lastly, anti‐bacterial, anti‐microbial and anti‐fungal biological activities of complexes were investigated.     

Comparative Reactivity of Phosphate Ester Hydrolysis Catalyzed by Mononuclear and Hetero-Dinuclear Complexes Containing the Lanthanum Ion (III)

The hydrolysis of bis(p-nitrophenyl phosphate)(BNPP) and p-nitrophenyl phosphate (NPP) were strongly promoted by the mononuclear La^III[(N,N-bis(3-carboxyl)-2-hydroxysalicylidene)ethylenediamine] and the hetero-dinuclear Cu^IILa^III[(N,N-bis(3-carboxyl)-2-hydroxysalicylidene)ethylenediamine] complexes at 35 °C in 50% aqueous DMSO. The results indicated that the hetero-dinuclear Cu^IILa^III complex exhibited a relatively higher catalytic function on NPP hydrolysis, while the hydrolysis of BNPP was slightly more efficient in the presence of the mononuclear La^III complex than that in the presence of the Cu^IILa^III complex, and this case was discussed by the different spacer requirements for NPP and BNPP hydrolysis. In addition, widely differing pH-rate profiles were obtained: saturated curves for NPP hydrolysis and bell-shaped curves for BNPP hydrolysis, and thus different kinetic treatments were employed to obtain the relative parameters.     

Tailored Transition-Metal Coordination Environments in Imidazole-Modified DNA G-Quadruplexes

Two types of imidazole ligands were introduced both at the end of tetramolecular and into the loop region of unimolecular DNA G-quadruplexes. The modified oligonucleotides were shown to complex a range of different transition-metal cations including Ni^II, Cu^II, Zn^II and Co^II, as indicated by UV/Vis absorption spectroscopy and ion mobility mass spectrometry. Molecular dynamics simulations were performed to obtain structural insight into the investigated systems. Variation of ligand number and position in the loop region of unimolecular sequences derived from the human telomer region (htel) allows for a controlled design of distinct coordination environments with fine-tuned metal affinities. It is shown that Cu^II, which is typically square-planar coordinated, has a higher affinity for systems offering four ligands, whereas Ni^II prefers G-quadruplexes with six ligands. Likewise, the positioning of ligands in a square-planar versus tetrahedral fashion affects binding affinities of Cu^II and Zn^II cations, respectively. Gaining control over ligand arrangement patterns will spur the rational development of transition-metal-modified DNAzymes. Furthermore, this method is suited to combine different types of ligands, for example, those typically found in metalloenzymes, inside a single DNA architecture.     

A novel two‐dimensional nickel(II) coordination polymer with 1,4‐bis(1,2,4‐triazol‐1‐ylmethyl)benzene and azide ligands

The coordination geometry of the Ni^II atom in the title complex, poly[diazidobis[μ‐1,4‐bis(1,2,4‐triazol‐1‐ylmethyl)benzene‐κ²N⁴:N^4′]nickel(II)], [Ni(N₃)₂(C₁₂H₁₂N₆)₂]_n, is a distorted octahedron, in which the Ni^II atom lies on an inversion centre and is coordinated by four N atoms from the triazole rings of two symmetry‐related pairs of 1,4‐bis(1,2,4‐triazol‐1‐ylmethyl)benzene (bbtz) ligands and two N atoms from two symmetry‐related monodentate azide ligands. The Ni^II atoms are bridged by four bbtz ligands to form a two‐dimensional (4,4)‐network.     

Redox switchable ligands suitable for transition metal ions: Protonation,complexation and electrochemical properties of a ferrocene-modified tetraamine diketone and its saturated analogue

Abstract

The new ferrocene-containing water-soluble ligands 1 and 2 were synthesized and their protonation and complexation properties toward Ni^II and Cu^II studied as a function of pH, by means of potentiometric titration experiments. Electrochemical measurements were performed in aqueous solution on pure 1 and 2 and in the presence of Ni^II and Cu^II cations, in the pH range 2–12, allowing us to determine the redox potential values relative to the ferrocene oxidation in the free ligands and in their Ni^II and Cu^II complexes. 1 and 2 behave as redox switchable ligands, the former enhancing, the latter decreasing its binding ability upon oxidation of the appended ferrocene function. Besides, the Cu^II complex of ligand 1 and the Ni^II complex of ligand 2 behave as two-centre two-electron redox systems, the complexed metal cation being subject to further oxidation to M^III.     

Synthesis, solid state and solution structures of two isomeric dicopper(II) complexes with functionalized azetidine ligands

Reported are the crystal and solution structures (determined by X-ray crystallography and EPR spectroscopy/simulation of the EPR spectra, respectively) of two dinuclear Cu^II complexes, coordinated to isomeric dinucleating azetidine-based ligands, whose N₃ cavities (pyridine/azetidine/secondary amine) are bridged by para- or meta-substituted phenyl groups. The Cu^II sites in the two dinuclear systems are similar to each other and as expected from the known structure of the corresponding mononuclear complex. The significant differences between the crystal structures of the mono- and the two dinuclear complexes and between the crystal and the solution structures are due to the elasticity of the Cu^II coordination sphere, the flexibility of the dinucleating ligands and subtle changes related to weak interactions (crystal lattice, solvation, anion coordination/ion pairing).     

Metallomicellar catalysis: effects of bridge-connecting ligands on the hydrolysis of PNPP catalyzed by Cu(II) complexes of ethoxyl-diamine ligands in micellar solution

The syntheses of three ligands are reported: N,N,N′,N′-tetra(2-hydroxyethyl)-1,3-propylene-diamine (1), N,N,N′,N′-tetra(2-hydroxyethyl)-1,10-decadiamine (2), N,N,N′,N′-tetra(2-hydroxyethyl)-1,4-xylyldiamine (3). The catalytic hydrolysis of p-nitrophenyl picolinate (PNPP) by the bivalent metal ion Cu(II) complexes of these ligands was studied kinetically in a buffered CTAB or Brij35 micellar solutions at 25 °C and different pH values. The results indicate that 1:2 and 2:1 complexes of these ligands and metal ion are the active species for the catalytic hydrolysis of PNPP in CATB and Brij35 micellar solutions. The ternary complex kinetic model for metallomicellar catalysis was employed to obtain the relative kinetic and thermodynamic parameters. The effects of the structure of the ligands and the microenvironment of reaction on the hydrolytic reaction of PNPP have been discussed in detail.     

(Croconato‐κ2O,O′)bis­(1,10‐phenanthroline‐κ2N,N′)cobalt(II), and the nickel(II) and copper(II) analogues

The title complexes, [M(C₅O₅)(C₁₂H₈N₂)₂], with M = Co^II, Ni^II and Cu^II, all lie across twofold rotation axes, around which two 1,10‐phenanthroline ligands are arranged in a chiral propeller manner. The Co^II and Ni^II complexes are isostructural, with octa­hedral coordination geometry, while the local geometry of the Cu^II complex is severely distorted from octa­hedral.     

Synthese,Strukturen, NMR‐ und EPR‐spektroskopische Untersuchungen an Übergangsmetallkomplexen monofluorsubstituierter Acylselenoharnstoffliganden

Synthesis, Structures, NMR and EPR Investigations on Transition Metal Complexes of monofluorosubstituted Acylselenourea Ligands The syntheses and the structures of the ligand N, N‐diethyl‐N′‐(2‐fluoro)benzoylselenourea HEt₂mfbsu and the complexes [Ni(Et₂mfbsu)₂] and [Zn(Et₂mfbsu)₂] as well as of the ligand N, N‐diisobutyl‐N′‐(2‐fluoro)benzoylselenourea HBuⁱ₂mfbsu and the complexes [Ni^II(Buⁱ₂mfbsu)₂] and [Pd^II(Buⁱ₂mfbsu)₂] are reported. The ligands coordinate bidendately forming bischelates. The Pd^II and Ni^II complexes are cis coordinated; in [Zn^II(Et₂mfbsu)₂] the ligands are tetrahedrally arranged. The structure of the also obtained bis[diisobutylamino‐(2‐fluorobenzoylimino)methyl]diselenide is reported. The Cu^II complexes of both selenourea ligands could not be isolated. They were obtained as oils. Their EPR spectra, however, confirm the presence of Cu^II bischelates unambiguously. Detailed NMR investigations ‐ ¹H‐, ¹³C‐ and ¹⁹F‐COSY, HMBC and HMQC ‐ on [M^II(Et₂mfbsu)₂] (M = Ni^II, Zn^II) allow an exact assignment of all signals to the magnetically active nuclei of the complexes.     

New complexes of iron(III), cobalt(II), nickel(II) and copper(II) with Schiff bases derived from 2-aminocyclopent-1-ene-1-dithiocarboxylic acid

Summary Fe^III, Co^II, Ni^II and Cu^II, complexes of a new Schiff base ligand, prepared by condensing 2-aminocyclopent-1-ene-1-dithiocarboxylic acid with benzaldehyde (ACB), and also Cu^II and Ni^II complexes of a second Schiff base ligand prepared by condensing 2-aminocyclopent-1-ene-1-dithiocarboxylic acid with salicylaldehyde (ACS), have been prepared and characterized by elemental analyses, conductivity measurements, magnetic and spectral (electronic, i.r. and e.p.r.) studies. The i.r. spectra suggest that both ACB and ACS are acting as bidentate ligands, coordinating through one of the sulphur atoms and through the azomethine nitrogen atom. The magnetic moment of the Fe^III complex indicates spin crossover behaviour. Square planar structures have been assigned to the Cu^II and Ni^II complexes and a tetrahedral structure to the Co^II complex. The e.p.r. spectra of the Cu^II complexes suggest a square planar environment with rhombic distortion around the Cu^II ion.     

Synthese,Strukturen, NMR‐ und EPR‐Untersuchungen der binuklearen Bis(N,N,N‴,N‴‐tetraisobutyl‐N′,N″‐isophthaloylbis(selenoureato))‐Komplexe des NiII und CuII

Synthesis, Structures, NMR and EPR Investigations of Binuclear Bis(N,N,N‴,N‴‐tetraisobutyl‐N′,N″‐isophthaloylbis(selenoureato)) Complexes of Ni^II and Cu^II The synthesis of binuclear Cu^II and Ni^II complexes of the quadridentate ligand N,N,N‴,N‴‐tetraisobutyl‐N′,N″‐isophthaloylbis(selenourea) and their crystal structures are reported. The complexes crystallize monoclinic, P2₁/c (Z = 2). In the EPR spectra of the binuclear Cu^II complex exchange‐coupled Cu^II‐Cu^II pairs were observed. In addition the signals of a mononuclear Cu^II species are observed what will be explained with the assumption of an equilibrium between the binuclear Cu^II‐complex (Cu^II‐Cu^II pairs) and oligomeric complexes with “isolated” Cu^II ions. Detailed ¹³C and ⁷⁷Se NMR investigations on the ligand and the Ni^II complex allow an exact assignment of all signals of the heteroatoms.     

Synthesis of Two Schiff Base Transition Metal Complexes Bearing Morpholine Side Chains and Kinetics of PNPP Catalytic Hydrolysis in Brij35 Micelle

Two Schiff base transitional metal complexes bearing morpholine side chains were synthesized and characterized, and were used as a simulative hydrolase in the catalytic hydrolysis of p‐nitrophenyl picolinate (PNPP) in this article. A mechanism of PNPP catalytic hydrolysis in the Brij35 micellar solution was proposed and supported by the results of the spectral analysis and the kinetic calculation. The kinetic model of PNPP catalytic hydrolysis was studied. The some kinetic and the thermodynamic constants on the catalytic reaction were calculated. The results of the study show that the metallomicelle made up of the Schiff base transitional metal complexes and Brij35 micelle revealed a good catalytic activity in PNPP catalytic hydrolysis; the rate of the PNPP catalytic hydrolysis is increased following the increase of the pH values in the buffer solution and affected by the polarization action of metal ion of complex.     

Structure,Characterization, and Metal‐Complexation Properties of a New Tetraazamacrocycle Containing Two Phenolic Pendant Arms

The new tetraazamacrocycle 2 (=2,2′‐[[7‐Methyl‐3,7,11,17‐tetraazabicyclo[11.3.1]heptadeca‐1(17),13,15‐triene‐3,11‐diyl]bis(methylene)]bis(4‐bromophenol)) was synthesized and used as a ligand for different metal‐ion complexes. The X‐ray crystal structures of the complexes of the general formula [M(H‐ 2 )]⁺NO ?MeOH (M=Ni²⁺, Zn²⁺), in which only one of the two pendant phenolic OH groups of 2 is deprotonated, were determined. In both complexes, the coordination environment is of the [5+1] type, the four N‐atoms of the macrocyclic framework defining a square‐planar arrangement around the metal center, with similar Ni? N and Zn? N distances of 1.961(9) to 2.157(9) Å and 2.021(9) to 2.284(8) Å, respectively. In contrast, the M? O distances are markedly different, 2.060(6) and 2.449(8) Å in the Ni^II complex, and 2.027(7) and 2.941(9) Å in the Zn^II complex. The UV/VIS spectra of the Ni^II and Cu^II complexes with ligand 2 , and the EPR spectra of the Cu^II system, suggest the same type of structure for the complexes in solution as in the solid state. Theoretical studies by means of density functional theory (DFT) confirmed the experimental structures of the Ni^II and Zn^II complexes, and led to a proposal of a similar structure for the corresponding Cu^II complex. The calculated EPR parameters for the latter and comparison with related data support this interpretation. The singly occupied molecular orbital (SOMO) in these systems is mainly made of a d orbital of Cu, with a strong antibonding (σ*) contribution of the axially bound phenolate residue.     

Synthese,Struktur und EPR‐Untersuchungen von binuklearen Bis(N,N,N‴,N‴‐tetraisobutyl‐N′,N″‐isophthaloylbis(thioureato))‐Komplexen des CuII,NiII, ZnII,CdII und PdII

Synthesis, Structure and EPR Investigations of binuclear Bis(N,N,N?,N?‐tetraisobutyl‐N′,N″‐isophthaloylbis(thioureato)) Complexes of Cu^II, Ni^II, Zn^II, Cd^II and Pd^II The synthesis of binuclear Cu^II‐, Ni^II‐, Zn^II‐, Cd^II‐ and Pd^II‐complexes of the quadridentate ligand N,N,N?,N?‐tetraisobutyl‐N′,N″‐isophthaloylbis(thiourea) and the crystal structures of the Cu^II‐ and Ni^II‐complexes are reported. The Cu^II‐complex crystallizes in two polymorphic modifications: triclinic, (Z = 1) and monoclinic, P2₁/c (Z = 2). The Ni^II‐complex was found to be isostructural with the triclinic modification of the copper complex. The also prepared Pd^II‐, Zn^II‐ and Cd^II‐complexes could not be characterized by X‐ray analysis. However, EPR studies of diamagnetically diluted Cu^II/Pd^II‐ and Cu^II/Zn^II‐powders show axially‐symmetric g and A ^Cu tensors suggesting a nearly planar co‐ordination within the binuclear host complexes. Diamagnetically diluted Cu^II/Cd^II powder samples could not be prepared. In the EPR spectra of the pure binuclear Cu^II‐complex exchange‐coupled Cu^II‐Cu^II pairs were observed. According to the large Cu^II‐Cu^II distance of about 7,50Å a small fine structure parameter D = 26·10^?4 cm^?1 is observed; T‐dependent EPR measurements down to 5 K reveal small antiferromagnetic interactions for the Cu^II‐Cu^II dimer. Besides of the dimer in the EPR spectra the signals of a mononuclear Cu^II species are observed whose concentration is T‐dependent. This observation can be explained assuming an equilibrium between the binuclear Cu^II‐complex (Cu^II‐Cu^II pairs) and oligomeric complexes with “isolated” Cu^II ions.     

Hydrolytic reactivities of p-nitrophenyl picolinate accelerated by Schiff base Co(II) complexes in micellar solutions

Two Schiff base Co(II) complexes were synthesized and used to catalyze the hydrolysis of p-nitrophenyl picolinate (PNPP) in Gemini 16-2-16 micellar solution. For comparison, hydrolytic kinetics of PNPP was respectively investigated in the micellar solutions of three kinds of conventional single-chain cationic, anionic, and nonionic surfactants, i.e., hexadecyltrimethylammonium bromide (CTAB), n-lauroylsarcosine sodium (LSS), and polyoxyethylene(23) lauryl ether (Brij35). Experimental results showed that the one complex with small Schiff base ligands exhibited better catalytic activity than the other one with bigger ligands towards the PNPP hydrolysis under comparable conditions, which testified that a relatively open catalytic site is essential for tuning the activities of the two mimic hydrolases. Moreover, compared effects of various micellar solutions demonstrated that Gemini 16-2-16 micellar solution is the best reaction medium relative to its single-chain analogs.     

Synthesis,Crystal Structure,and Properties of Energetic Copper(II) Complex based on 3,5‐Dinitrobenzoic Acid and 1,5‐Diaminotetrazole

Energetic copper(II) complexes based on 3,5‐dinitrobenzoic acid (HDNBA) and 1,5‐diaminotetrazole (DAT), Cu(DNBA)₂(H₂O)₂ ( 1 ) and Cu(DAT)₂(DNBA)₂ ( 2 ) were synthesized and characterized by elemental analysis, IR spectroscopy, single‐crystal and powder X‐ray diffraction. In both complexes, Cu^II was coordinated to a plane tetragon, by four oxygen atoms from two DNBA^– ions and two coordinated H₂O molecules for 1 , and by two oxygen atoms and two nitrogen atoms from different DNBA^– ions and DAT ligands for 2 . Differential scanning calorimetry (DSC) and thermogravimetry (TG) analyses were employed to measure the thermal decomposition processes and non‐isothermal kinetics parameters of the complexes. The thermal decomposition onset temperatures of 1 and 2 are 321 and 177 °C. The apparent activation energies of the first exothermic decomposition peaks of 1 and 2 are 247.2 and 185.2 kJ · mol^–1. Both 1 (35 J, > 360 N) and 2 (12.5 J, > 360 N) are less sensitive than RDX. The catalytic effects on the decomposition of ammonium perchlorate (AP) of 1 and 2 were studied by DSC. All results supported the potential applications of the energetic complexes as additives of solid rocket propellants.     

On the Ligand‐to‐Metal Charge‐Transfer Photochemistry of the Copper(II) Complexes of Quercetin and Rutin

In contrast to the UV‐photoinduced ligand photoionization of the flavonoid complexes of Fe^III, redox reactions initiated in ligand‐to‐metal charge‐transfer excited states were observed on irradiation of the quercetin ( 1 ) and rutin ( 2 ) complexes of Cu^II. Solutions of complexes with stoichiometries [Cu^IIL₂] (L=quercetin, rutin) and [Cu^II₂L_n] (n=1, L=quercetin; n=3, L=rutin) were flash‐irradiated at 351 nm. Transient spectra observed in these experiments showed the formation of radical ligands corresponding to the one‐electron oxidation of L and the reduction of Cu^II to Cu^I. The radical ligands remained coordinated to the Cu^I centers, and the substitution reactions replacing them by solvent occurred with lifetimes τ<350 ns. These are lifetimes shorter than the known lifetimes (τ>1 ms) of the quercetin and rutin radical's decay.     

Synthesis and spectral characterization of some investigated thiocarbohydrazone binuclear complexes with an illustrated EPR study for d<Superscript>1</Superscript> complexes

Some new complexes were synthesized using pyrol-2-carbaldhyde thiocarbohydrazone ligand and characterized using physicochemical techniques. The i.r. data reveal that, the ligand acts as a mononegative tetradentate in Ni^II and Cu^II binuclear complexes. Also, they coordinate as mononegative tridentates with Co^II, Cd^II and VO²⁺ ions but in the neutral state with Pt^IV ion in a mononuclear monomer structure for Co^II and Cd^II complexes, but binuclear dimer structure through bridged sulphate for the VO²⁺ complex. The magnetic moment beside the electronic spectral data proposed the complex geometries as a mixed stereochemistry for Ni^II, square-planar for Cu^II, square-pyramidal for VO²⁺ and octahedral for the other complexes. The thermal analysis supports the proposal of the presence or absence of water molecule in or outside the coordination sphere. The EPR spectra of Cu^II and VO²⁺ complexes were illustrated elaborately and some theoretical data were abstracted from EPR curves to support the proposed structures.     

Synthesis,characterization and electrochemical behavior of mononuclear,binuclear nickel(II) and heterobinuclear zinc(II)nickel(II) complexes derived from novel macrobicyclic tricompartmental ligands: kinetics of the catalytic hydrolysis of 4-nitrophenyl phosphate by the complexes

Mononuclear, binuclear Ni^II and heterobinuclear Zn^IINi^II complexes have been derived from lateral macrobicyclic tricompartmental ligands embracing three different donor sets: (i) O₂N₂-donor set, derived from ether oxygens and tertiary amine nitrogens; (ii) N₂O₂-donor set, derived from tertiary amine nitrogens and phenolic oxygens; (iii) O₂N₂-donor set, derived from phenolic oxygens and azomethine nitrogens. Cyclic voltammograms of the mononuclear Ni^II complexes showed irreversible one-electron reduction processes in the –1.2 to –1.3 V region and an irreversible oxidation process in the range +0.8 V potential region. The binuclear complexes showed quasireversible two-step single electron reduction processes around the –1.3 and –1.7 V potential regions. The anodic potential region showed an irreversible oxidation process at +1.0 V. The heterobinuclear Zn^IINi^II complex showed an irreversible reduction of the Ni^II species at –1.55 V. The catalytic hydrolysis towards 4-nitrophenyl phosphate by the mononuclear, binuclear Ni^II complexes and the heterobinuclear complex were found to be appreciable. The pseudo-first order rate constant for the catalytic hydrolysis catalyzed by the binuclear and heterobinuclear complexes were found to be higher (9.8 × 10^–4 s^–1) than that of the corresponding mononuclear complexes (1.3 × 10^–5 s^–1), which ascertain the requirement of two metal ions in close proximity for the binding of the nucleophilic OH and the phosphate group.