Kinetic study of the hydroxide ion attack on and DNA interaction with high spin iron(II) Schiff base amino acid chelates baering ONO donors

Kinetic study of some novel high spin Fe(II) complexes of Schiff base ligands derived from 5-bromsalicyaldehyde and amino acids with the OH^? ion and DNA has been carried out. Based on the kinetic data, the rate law and a plausible mechanism were proposed. Kinetic data of the base catalyzed hydrolysis imply pseudo first-order double stage process due to the presence of mer- and fac-isomers. The observed rate constants k _obs were correlated with the effect of a substituent R in the structure of ligands. The rate constants and activation parameters are in good agreement with stability constants of the studied complexes. Reactivity of the complexes towards DNA correlated well with the reported binding constants.     

Kinetics and mechanism of the reaction of novel low spin Fe(II)-azo amino acid complexes with hydrogen peroxide in aqueous solutions and in aqua-methanol binary mixtures

Kinetics of Fe(II)-azo complexes derived from amino acids (DL-phenylalanine, DL-tryptophane, histidine and alanine) and p-nitroso aromatic substituted amines (N,N-dimethylamino-4-nitrosoaniline and N,N-dimethylamino-4-nitrosoaniline) with hydrogen peroxide in the aqueous solutions and under pseudo-first order conditions have been studied. The reaction exhibits two-stage kinetics. The reaction mechanism was proposed and discussed in terms of complex structure, pH and nature of the medium. The activation parameters and pK _a values were evaluated and correlated with the structural effects of the complexes.     

Enthalpy and entropy changes associated with mixed ligand chelates of Cu(II) and Ni(II) with 4-methoxy picolinic acid N-oxide and some amino acids in aqueous medium

The stability constants of mixed complexes of Cu(II) and Ni(II) with 4-methoxy picolinic acid N-oxide, and glycine, α-alanine, proline and hydroxy-proline have been determined at various temperatures by the potentiometric method in 0·1 M ionic strength. The formation constants of the mixed complexes have been evaluated and are in good agreement with statistically expected values. The enthalpy and entropy values have been calculated from 1∶1∶1 stability constants temperature coefficient data. From the enthalpy values of the mixed complexes it may be concluded that the bond strengths are not equal to the average of the bond strengths inMA ₂ andMB ₂ type parent complexes. The entropy values have been found to be favourable for ternary complex formation.     

Kinetic studies on the formation of ternary complexes in the reaction of diaquonitrilotriacetatonickelate(II) with amino acids in aqueous solution

Summary Kinetics of formation of ternary complexes in the reaction of Ni(NTA)(H₂O) ₂ ^– with several amino acids, LH^± (glycine, -alanine, -alanine, L-valine and L-phenylalanine) have been studied by a pH indicator method using stopped-flow spectrophotometry. The results conform to 1/k_obs = 1/k + [H⁺]/ kKT_L where K is the equilibrium constant for formation of Ni(NTA)(–L)(H₂O)^2–, and k is the specific rate constant for the subsequent rate-determining ring-closure step leading to Ni(NTA)(=L)^2–. For the different amino acids studied, the k values decrease in the sequence: glycine > -alanine > L-phenylalanine > L-valine > -alanine. These k values areca. 1000 times lower than the values for complexation of Ni(NTA)(H₂O) ₂ ^– with NH₃ and imidazole and the spread in k values is much less than the pK_a values of the amino acids. The relative rates are enthalpy controlled and the S values are highly negative in conformity with ring closure as the rate determining step.     

Formation of unusual molecular rectangles and squares containing low spin and high spin Co(II) and Fe(II) centers

The ditopic carbohydrazide and thiocarbohydrazide based ligands H?L1 and H?L2 react with Co(II)(OAc)? to produce the homoleptic Co(II) molecular rectangles 1 and 2, containing either a mixture of high spin and low spin Co(II) sites or exclusively low spin Co(II) centers, respectively, with two mono-deprotonated ligands in a syn-conformation, and the other two doubly-deprotonated ligands in an anti-arrangement. The Co(II) centers are bridged by μ-O/S and μ-N-N groups, respectively. Magnetic susceptibility measurements indicate weak antiferromagnetic coupling between metal centers in 1 and 2, with room temperature magnetic moments of 6.6 and 3.4 μ(B), respectively, in good agreement with two S = 3/2 and two S = 1/2 centers for 1 and four S = 1/2 centers for 2. Reaction of H?L1 and H?L2 with Fe(II)(CF?SO?)? in the presence of a base leads to the formation of μ-O/S bridged homoleptic molecular squares 3 and 4, with the Fe(II) centers in high spin and low spin configurations, respectively at room temperature, as indicated from X-ray structural data and magnetic susceptibility measurements. However, in 3 one Fe(II) site undergoes spin crossover to a low spin state at about 150 K, while 4 stays diamagnetic in the full 2-300 K temperature range. Electrochemistry of 4 showed four distinct reversible red-ox waves associated with step-by-step one electron processes in the molecular square [-0.643 (ΔE(p) = 81 mV), -0.278 (ΔE(p) = 70 mV), +0.565 (ΔE(p) = 65 mV), ~1.1 V], associated with the Fe(II)/Fe(III) red-ox couples.     

Nickel(II) chelates of Schiff bases derived from isatin and chromone with amino acids and substituted hydrazines

Summary Nickel(II) complexes of the Schiff base derivatives of isatin with glycine, -alanine, anthranilic acid, S-methyl hydrazine carbodithioate, the ammonium salt of hydrazine carbodithioate, thiosemicarbazide, and benzoyl hydrazine, and nickel(II) complexes of 6-formyl-7-hydroxy-5-methoxy-2-methyl chromonelideneS-methyl hydrazine carbodithioate and benzoyl hydrazone, were prepared and characterized by elemental analysis, i.r., u.v.-vis spectra and magnetic measurements. All the complexes are octahedral.     

Kinetic and spectroscopic studies of an intermediate in the reaction of the diimine complex trisferrozineiron(II) with hydroxide ion in water and in aqueous methanol

Summary Kinetic and spectroscopic evidence is presented to support the postulate of a ligand-substituted intermediate in the reaction of the trisferrozineiron(II) anion with hydroxide ion in water and in aqueous methanol.     

Ligand exchange and spin state equilibria of Fe(II)(N4Py) and related complexes in aqueous media

We report the characterization and solution chemistry of a series of Fe(II) complexes based on the pentadentate ligands N4Py (1,1-di(pyridin-2-yl)-N,N-bis(pyridin-2-ylmethyl)methanamine), MeN4Py (1,1-di(pyridin-2-yl)-N,N-bis(pyridin-2-ylmethyl)ethanamine), and the tetradentate ligand Bn-N3Py (N-benzyl-1,1-di(pyridin-2-yl)-N-(pyridin-2-ylmethyl)methanamine) ligands, i.e., [Fe(N4Py)(CH(3)CN)](ClO(4))(2) (1), [Fe(MeN4Py)(CH(3)CN)](ClO(4))(2) (2), and [Fe(Bn-N3Py)(CH(3)CN)(2)](ClO(4))(2) (3), respectively. Complexes 2 and 3 are characterized by X-ray crystallography, which indicates that they are low-spin Fe(II) complexes in the solid state. The solution properties of 1-3 are investigated using (1)H NMR, UV/vis absorption, and resonance Raman spectroscopies, cyclic voltammetry, and ESI-MS. These data confirm that in acetonitrile the complexes retain their solid-state structure, but in water immediate ligand exchange of the CH(3)CN ligand(s) for hydroxide or aqua ligands occurs with full dissociation of the polypyridyl ligand at low (<3) and high (>9) pH. pH jumping experiments confirm that over at least several minutes the ligand dissociation observed is fully reversible for complexes 1 and 2. In the pH range between 5 and 8, complexes 1 and 2 show an equilibrium between two different species. Furthermore, the aquated complexes show a spin equilibrium between low- and high-spin states with the equilibrium favoring the high-spin state for 1 but favoring the low-spin state for 2. Complex 3 forms only one species over the pH range 4-8, outside of which ligand dissociation occurs. The speciation analysis and the observation of an equilibrium between spin states in aqueous solution is proposed to be the origin of the effectiveness of complex 1 in cleaving DNA in water with (3)O(2) as terminal oxidant.     

Air-stable,electron-deficient Fe(II) catalytic porphyrins. Characterization and molecular structures of rare high spin Fe(II) hexacoordinated porphyrins

The synthesis, characterization, and molecular structures of the first air-stable, hexacoordinated high spin Fe(II) porphyrins (1) with axial alcohols are reported (1 = Fe(II) meso-tetrakis(o-dichlorophenyl)-beta-octanitroporphyrin). The structure of 1 with two axial waters is also presented. The very different conformations and metrics observed with the two types of ligands illustrate the acute interplay between ligands, conformations, and spin states in Fe porphyrins.     

Hydrophilicity and acid hydrolysis of water-soluble antibacterial iron(II) Schiff base complexes in binary aqueous solvents

Kinetics of acid hydrolysis of seven antibacterial iron(II) Schiff base complexes has been studied. The Schiff base ligands were derived from sodium 2-hydroxybenzaldehyde-5-sulfonate and a series of amino acids. The hydrolysis rate is studied by spectrophotometric method and compared with complex hydrophilicity. Addition of the organic co-solvent, dimethylsulfoxide or n-propanol, significantly accelerates the hydrolysis.     

Enthalpies of Iron(III) perchlorate and Fe3+ ion transfer from water into aqueous ethanol solvents

Thermal effects of the transfer of iron(III) perchlorate from water into aqueous ethanol solutions at 25.00 ± 0.01°C are determined calorimetrically. The enthalpies of Fe³⁺ ion transfer are calculated. An increase in the enthalpies of iron(III) ion transfer upon a rise in the ethanol content in the system is observed. The Gibbs energies of Fe³⁺ transfer are calculated using the linear correlation of solvation energy on the solvent and ion parameters.     

Kinetic studies on the bromate ion oxidation of 12-tungstocobaltate(II) in aqueous acid

The oxidation of Co^IIW by bromine(V) is a complex process involving an induction period. The reaction was found to be first-order in both [Co^IIW] and [Br^v], and exhibits a complex dependence on [H⁺]. These observations were successfully explained by considering HBrO₂, one of the intermediates formed in the direct but slow reaction between Co^IIW and bromine(V), as the reacting species. The first-order limiting dependence in [H⁺] was due to the involvement of a protic equilibrium of HBrO₂. The induction period appears due to the scavenging effect of Br^– inadvertently present in the medium. It appears to be the first report where HBrO₂ was found to be the reacting intermediate in the oxidation of metal ions and complexes by BrO^– ₃.     

Hydrophobic interaction effects on the kinetics of ligand substitution in binary aqueous mixtures at pentacyano(piperidine)ferrate(II) ion

The kinetics of piperidine replacement by pyridine at the pentacyano(piperidine)-ferrate(II) complex ion was studied under pseudo-first order conditions in binary aqueous mixtures of methanol, t-butanol, p-dioxane, and glycerol, from a mole fraction of co-solvent from 0 to about 0.15. The observed variations can be explained considering the degree of hydrophobic interaction between released ligand and water molecules which changes according to the structure-forming or struucture-breaking effect of added co-solvent on water.     

Novel polydentate phosphonic acids: Protonation and stability constants of complexes with Fe(III) and Cu(II) in aqueous medium

The acido‐basic and the complexation properties of di‐, tri‐, and tetra‐phosphonic acids (H₆L1, H₈L2, and H₁₀L3) toward Fe(III) and Cu(II) were determined by potentiometric titration in aqueous media at 25.0 ± 0.1°C with constant ionic strength (0.1 M, NaClO₄). We have determined six, ten, and eight pK_a values for the di, tri, and tetra‐phosphonic acids, respectively. In acidic conditions, e.g., 0 ≤ pH ≤ 5; iron and copper presented a high affinity toward these ligands to give complex species. With the ligand H₁₀L3, [FeL3H₇], and [CuL3H₆]²⁻ were easily obtained at pH 1.8 and 2.7, respectively. We have determined ten stability constants for the H₁₀L3/Fe system and nine for the H₁₀L3/Cu one; six and four in the cases of H₈L2/Fe and H₈L2/Cu systems, respectively. Finally, five stability constants were calculated for the H₆L1/Fe system and four for the H₆L1/Cu one. We have not observed any insoluble species in these complexes in acidic medium as well as in alkaline solutions. © 2010 Wiley Periodicals, Inc. Heteroatom Chem 21:51–62, 2010; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20575     

Kinetic studies on the formation of ternary complexes in the reaction of diaquo-nitrilotriacetato-nickelate(II) and diaquo-anthranilato-N,N′-diacetato-nickelate(II) with amino acids in aqueous solution

Summary Kinetics of formation of ternary complexes from diaquo-nitrilotriacetatonickelate(II), [Ni(nta)(H₂O)₂]^–, and diaquoanthranilato-N, N-diacetatonickelate(II), [Ni(ada)-(H₂O₂] and amino acids have been studied by a pH indicator method using stopped-flow spectrophotontetry. The results conform to 1/k_obs=1/k+[H⁺]/kK·T_L, where K is the equilibrium constant for the formation of [Ni(A)(-L)(H₂O)]^2–(A=nta^3– or ada^3–) and k is the specific rate constant for the subsequent rate-determining ring closure leading to [Ni(A) (=L)]^2–. For the different amino acids, the k values decrease in the sequence: glycine>-alanine>L-phenylalanine>L-Valine>L-methionine>-alanine>sarcosine>N,N-dimethylglycine, and areca. 1000 times smaller than the k values for complexation of [Ni)(nta)(H₂O)₂]^– with monodentate ligands, such as NH₃ and imidazole. The spread of k values is much less than the pK_a values of the amino acids, and can be accounted for on the basis of the proposed mechanism. The relative rates are enthalpy controlled and high negative S values are commensurate with ring closure as the rate-determining step.     

Synthesis and properties of Fe(II), Ni(II), Co(II), and Zn(II) chelates with 4-nitrosemicarbazide

Chelates M(O₂NNCONHNH₂)₂ · 2H₂O (M = Fe, Co, Ni, Zn) were prepared by the reactions of 4-nitrosemicarbazide with appropriate 3d transition metal salts. The structures of the compounds were suggested on the basis of data obtained by physicochemical methods. The compounds obtained were shown to be energetic substances.     

Thermochemical study of the complex formation of copper(II) and nickel(II) iminodiacetates with amino acids in aqueous solutions

The formation of mixed-ligand complexes in the M(II)–Ida–L systems (M = Cu, Ni, L = His, Orn, Lys), where Ida is the iminodiacetic acid residue, was studied by pH-metry, calorimetry, and spectrophotometry. The thermodynamic parameters (logK, Δ_rG⁰, Δ_rH, Δ_rS) of formation of the complexes were determined at 298.15 K and the ionic strength I = 0.5 (KNO₃). The most probable mode of coordination of the chelating agent and the amino acid in the mixed-ligand complexes was elucidated.     

Energetics of lead(II), cadmium(II) and zinc(II) complexes with amino acids

The molar heat capacity and the standard (p ⁰ = 0.1 MPa) molar enthalpies of formation of the crystalline of bis(glycinate)lead(II), Pb(gly)₂; bis(dl-alaninate)lead(II), Pb(dl-ala)₂; bis(dl-valinate)lead(II), Pb(dl-val)₂; bis(dl-valinate)cadmium(II), Cd(dl-val)₂ and bis(dl-valinate)zinc(II), Zn(dl-val)₂, were determined, at T = 298.15 K, by differential scanning calorimetry, and high precision solution-reaction calorimetry, respectively. The standard molar enthalpies of formation of the complexes in the gaseous state, the mean molar metal–ligand dissociation enthalpies, M(II)–amino acid, \( \langle D_{\text{m}} \rangle \)(M–L), were derived and compared with analogous copper(II)–ligand and nickel(II)–ligand.θθ

M(II)–amino acid	\( \Updelta_{\text{f}} H_{\text{m}}^{\text{o}} \)(cr)/kJ mol?1
Bis(glycinate)lead(II), Pb(gly)2	?998.9 ± 1.9
Bis(dl-alaninate)lead(II), Pb(ala)2	?1048.7 ± 1.8
Bis(dl-valinate)lead(II), Pb(val)2	?1166.3 ± 2.5
Bis(dl-valinate)cadmium(II), Cd(val)2	?1243.7 ± 2.7
Bis(dl-valinate)zinc(II), Zn(val)2	?1306.1 ± 2.3