Hydrolysis Of 4-nitrophenyl Phosphate Research Articles

Determination of Cancer Cell-Based pH-Sensitive Fluorescent Carbon Nanoparticles of Cross-Linked Polydopamine by Fluorescence Sensing of Alkaline Phosphatase Activity on Coated Surfaces and Aqueous Solution.

The tumor-specific sensitive fluorescence sensing of cellular alkaline phosphatase (ALP) activity on the basis of host-guest specific and pH sensitivity was conducted on coated surfaces and aqueous states. Cross-linked fluorescent nanoparticles (C-FNP) consisting of β-cyclodextrin (β-CD)/boronic acid (BA) and fluorescent hyaluronic acid [FNP(HA)] were conjugated to fluorescent polydopamine [FNP(pDA)]. To determine the quenching effect of this system, hydrolysis of 4-nitrophenyl phosphate (NPP) to 4-nitrophenol (NP) was performed in the cavity of β-CD in the presence of ALP activated photoinduced electron transfer (PET) between NP and C-FNP. At an ALP level of 30-1000 U/L, NP caused off-emission of C-FNP because of their specific host-guest recognition. Fluorescence can be recovered under pH shock due to cleavage of the diol bond between β-CD and BA, resulting in release of NP from the fluorescent system. Sensitivity of the assays was assessed by confocal imaging not only in aqueous states, but also for the first time on coated surfaces in MDAMB-231 and MDCK cells. This novel system demonstrated high sensitivity to ALP through generation of good electron donor/acceptor pair during the PET process. Therefore, this fluorescence sensor system can be used to enhance ALP monitoring and cancer diagnosis on both coated surfaces and in aqueous states in clinical settings.

Organoruthenium(II) compounds with pyridyl benzoxazole/benzthiazole moiety: studies on DNA/protein binding and enzyme mimetic activities

We report herein synthesis and characterization of four new organoruthenium(II) complexes of the type [RuH(CO)(PPh3)2(L1,2)]Cl (1, 3) and [Ru(CO)(Cl)2(AsPh3)(L1,2)] (2, 4) derived from the reaction of [RuHCl(CO)(EPh3)3] (E = P or As) with 2-(pyridine-2yl)benzoxazole (L1) and 2-(pyridine-2yl)benzthiazole (L2). Single-crystal X-ray diffraction data of 2 proved octahedral geometry of the complexes with a 1 : 1 ratio between the metal and the coordinated ligands. The binding affinities of 1–4 toward calf-thymus DNA (CT-DNA) and BSA were thoroughly studied by various spectroscopic techniques. Furthermore, the coordination compounds exhibit catecholase-like activities in the aerial oxidation of 3,5-di-tert-butylcatechol to the corresponding o-quinone and phosphatase-like activities in the hydrolysis of 4-nitrophenyl phosphate to 4-nitrophenolate ion. The kinetic parameters have been determined using Michaelis–Menten approach. The highest kcat values suggested that coordination compounds exhibit higher rates of catalytic efficacy.

Investigating the kinetics of paramagnetic-beads linked alkaline phosphatase enzyme through microchannel resistance measurement in dielectric microchip

Real time monitoring of electrolyte resistance changes during hydrolysis of 4-nitrophenylphosphate (pNPP) by alkaline phosphatase (ALP) bound on paramagnetic-beads was performed into a small dielectric channel. The reaction kinetic fit with a non-competitive substrate-inhibition equation. Michaelis–Menten apparent constant, KMapp, was determined as 0.33±0.06mM and the maximum apparent rate, Vmaxapp as 98±5pMs−1. The detection limits were 15fM for ALP and 0.75mM for pNPP. This miniaturized device constitutes a powerful tool for analysis of interaction between ligands.

Synthesis, characterization, catalytic, antimicrobial, DNA binding and cleavage studies of N-functionalized tetraazamacrocyclic binuclear copper(II) complexes

A series of binuclear copper(II) complexes of N-functionalized cyclam derivatives has been prepared by the Schiff base condensation of 1,8-[bis(3-formyl-2-hydroxy-5-methyl)benzyl]-l,4,8,11-tetraazacyclo-tetradecane (PC-a), 1,8-[bis(3-formyl-2-hydroxy-5-bromo)benzyl]-l,4,8,11-tetraazacyclo-tetradecane (PC-b) with appropriate aliphatic diamines, and copper(II) perchlorate. All the complexes were characterized by elemental, FT-IR, UV–Vis, ESI and ESR spectral analysis. The room temperature magnetic moment studies depicts the presence of an antiferromagnetic interaction in the binuclear complexes, which is also observed from the broad ESR spectra with a g value of 2.10–2.11. Variable-temperature magnetic susceptibility study of the complex [Cu2L2a](ClO4)2 shows that the calculated −2J value is 219 cm−1, which conveys a spin–spin interaction between the two copper(II) ions. The catechol oxidation and hydrolysis of 4-nitrophenylphosphate were carried out by using the complexes as a catalyst. All the above metal complexes were screened for antimicrobial and human pathogenic fungal activity. The binding of the complexes to calf thymus DNA (CT-DNA) has been investigated with UV–Vis and fluorescence spectroscopy. All complexes display significant cleavage property of circular plasmid pBR322 DNA into linear form. Spectral, electrochemical, magnetic and catalytic studies support the distortion of the copper ion geometry that arises as the macrocyclic ring size increases.

Synthesis, characterization, catalytic, and biological studies of macrobicyclic binuclear nickel(II) complexes of 1,8-difunctionalized cyclam derivatives

New Schiff base binuclear nickel(II) complexes of N-substituted cyclam derivatives have been prepared by template condensation of 1,8-[bis(3-formyl-2-hydroxy-5-bromo)benzyl]-l,4,8,11-tetraazacyclo-tetradecane (PC) with appropriate aliphatic diamines and nickel(II) perchlorate. The ligand possesses two coordination sites, an N4O2 amine compartment and N3O2/N4O2 imine compartment. The structural features of the complexes have been confirmed by elemental analysis, IR, UV–Vis, and mass spectra. From the data, octahedral geometry around the two nickels has been suggested. The electrochemical behavior of the complexes show two irreversible one-electron reduction process in the cathodic region and show two irreversible one-electron oxidation process at the anode. Hydrolysis of 4-nitrophenylphosphate using the complexes as catalysts have been carried out. Antimicrobial screening data show good results. The binding of the complexes to calf thymus DNA (CT DNA) has been investigated with absorption and emission spectroscopy. Ni2L1 displays significant cleavage of circular plasmid pBR322 DNA to linear form. Spectral, electrochemical, and catalytic studies support distortion of the nickel geometry that arises as the macrocyclic ring size increases.

Spectral, Electrochemical, Fluorescence, Kinetic and Anti-microbial Studies of Acyclic Schiff-base Gadolinium(III) Complexes

Centre for Advanced Studies in Botany, University of Madras, Guindy Maraimalai Campus, Chennai 600 025, IndiaReceived June 5, 2012, Accepted August 1, 2012A new series of acyclic mononuclear gadolinium(III) complexes have been prepared by Schiff-base con-densation derived from 5-methylsalicylaldehyde, diethylenetriamine, tris(2-aminoethyl) amine, triethylene-tetramine, N,N-bis(3-aminopropyl)ethylene diamine, N,N-bis(aminopropyl) piperazine, and gadolinium nitrate.All the complexes were characterized by elemental and spectral analyses. Electronic spectra of the complexesshow azomethine (CH=N) within the range of 410-420 nm. The fluorescence efficiency of Gd(III) ion in thecavity was completely quenched by the higher chain length ligands. Electrochemical studies of the complexesshow irreversible one electron reduction process around −2.15 to −1.60 V The reduction potential ofgadolinium(III) complexes shifts towards anodic directions respectively upon increasing the chain length. Thecatalytic activity of the gadolinium(III) complexes on the hydrolysis of 4-nitrophenylphosphate was determin-ed. All gadolinium(III) complexes were screened for antibacterial activity. Key Words : Schiff-base ligands, Gadolinium(III) complexes, Fluorescence, Kinetic, Anti-microbialIntroductionIn the past decade, a great attention has been devoted tothe design and the synthesis of macrocyclic ligands and theirlanthanide complexes are a fascinating area of research,owing to their importance in basic and applied chemistry. Inparticular, acyclic Schiff bases have successfully been pro-posed as excellent systems in the formation of mono, homo,hetero nuclear lanthanide complexes.

Synthesis and characterization of new unsymmetrical ‘side-off’ tetra and hexa coordinate homobinuclear Cu(II) and heterobinuclear Cu(II)–Zn(II) complexes: Magnetic, electrochemical and kinetic studies

A new class of phenol based unsymmetrical side-off tetra and hexa coordinate homobinuclear Cu(II) and heterobinuclear Cu(II)–Zn(II) complexes have been synthesized and characterized by elemental and spectral analysis. The electronic spectra of all the complexes show “Red shift” in LMCT band, for the ligand H2L2 compared to that of the ligand H2L1 due to the relatively higher electron donating nature of their substitutents. The homobinuclear Cu(II) complexes (1 and 2) illustrate an antiferromagnetic interaction (μeff: 1.58 and 1.60BM) at 298K with a broad EPR signal. Variable temperature magnetic moment study of the binuclear copper (II) complexes shows that the extent of antiferromagnetic coupling is greater in the case of H2L2 complexes than H2L1 complexes (−2J values: 192cm−1 and 184cm−1 respectively). The heterobinuclear Cu(II)–Zn(II) complexes (3 and 4) have a magnetic moment value close to the spin only value with four hyperfine EPR signals. Electrochemical studies of the complexes reveal that all the binuclear complexes show two irreversible one-electron transfer reduction waves in the cathodic region. There is an “anodic shift” in the first reduction potential of the complexes, of the ligand H2L1 when compared to that of the ligand H2L2 due to the presence of relatively higher electron donating N-substituents in the later case than in the former case. The catecholase activity of the complexes reveals that the homobinuclear Cu(II) complexes show higher catalytic activity than the corresponding heterobinuclear Cu(II)–Zn(II) complexes. In the hydrolysis of 4-nitrophenylphosphate, the heterobinuclear Cu(II)–Zn(II) complexes show better catalytic activity than the corresponding homobinuclear Cu(II) complexes.

New Acyclic Schiff-Base Nickel(II) Complexes and their Electrochemical, Kinetic, and Antimicrobial Studies

Five new nickel(II) complexes were synthesized. All the complexes were characterized by elemental and spectral analysis. Electronic spectra of the complexes show d–d transition in the range of 500–800 nm. Electrochemical studies of the complexes show an irreversible one-electron reduction process around –0.65 to –0.91 V and an irreversible one-electron oxidation process around 0.87 to 1.00 V. The reduction and oxidation potential of nickel(II) complexes shifts toward cathodic and anodic directions, respectively, upon increasing the chain length. The catalytic activity of the nickel(II) complexes on the hydrolysis of 4-nitrophenylphosphate was determined. All the nickel(II) complexes were screened for antibacterial activity.

New Unsymmetric Dinuclear Copper(II) Complexes of Trans-disubstituted Cyclam Derivatives: Spectral, Electrochemical, Magnetic, Catalytic, Antimicrobial, DNA Binding and Cleavage Studies

Six new binuclear copper(II) complexes have been prepared by template condensation of the dialdehydes 1,8-[bis(3-formyl-2-hydroxy-5-methyl)benzyl]-l,4,8,11-tetraazacyclotetradecane (PC-a) and 1,8-[bis(3-formyl-2-hydroxy-5-bromo)benzyl]-l,4,8,11-tetraazacyclotetradecane (PC-b) with appropriate aliphatic diamines, and copper(II) perchlorate. The structural features of the complexes have been confirmed by elemental analysis, IR, UV-vis and mass spectra etc. The electrochemical behavior of all the copper(II) complexes show two irreversible one electron reduction process. The room temperature magnetic moment studies depict the presence of an antiferromagnetic interaction in the binuclear complexes. The catechol oxidation and hydrolysis of 4-nitrophenylphosphate were carried out by using the complexes as catalyst. The antimicrobial screening data show good results. The binding of the complexes to calf thymus DNA (CT DNA) has been investigated with absorption and emission spectroscopy. The complex [<TEX>$Cu_2L^{1a}$</TEX>] displays significant cleavage property of circular plasmid pBR322 DNA in to linear form. Spectral, electrochemical, magnetic and catalytic studies support the distortion of the copper ion geometry that arises as the macrocyclic ring size increases.

New 14-membered trans-di-substituted ‘tet-a’ macrocycles and their copper(II) and nickel(II) complexes: Spectral, magnetic, electrochemical, crystal structure, catalytic and antimicrobial studies

Copper(II) and nickel(II) complexes of new trans-di-substituted macrocyclic ligands incorporating three different benzoyl groups, 1,8-bis-(benzoyl)-5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane (L 1), 1,8-bis-(2-nitrobenzoyl)-5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane (L 2), and 1,8-bis-(4-nitrobenzoyl)-5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane (L 3) have been synthesized. The ligands and complexes were characterized by elemental and spectral analysis. Further, the X-ray crystal structure of one of the ligand, L 1, has been determined. N-benzoylation causes red shift in the λ max values of the complexes. The cyclic voltammogram of the complexes of ligand L 1 shows one-electron, quasi-reversible reduction wave in the region −0.94 to −1.00 V, whereas that of L 2 and L 3 show two quasi-reversible reduction peaks corresponding to ligand and metal. Nickel complexes show one electron quasi-reversible oxidation wave at a positive potential in the range +0.92 to +1.21 V. The Cu(II) complexes have a magnetic moment value close to the spin-only value with four hyperfine EPR signals. Kinetic studies on the oxidation of pyrocatechol to o-quinone using the copper(II) complexes as catalysts and on the hydrolysis of 4-nitrophenylphosphate using the copper(II) and nickel(II) complexes as catalysts were carried out. The complexes containing electron-withdrawing group shows higher rate-constant values than that with no electron-withdrawing group. All the complexes were screened for antifungal and antibacterial activity.

Synthesis, characterization, crystal structure and antimicrobial activities of new transN, N-substituted macrocyclic dioxocyclam and their copper(II) and nickel(II) complexes

New trans-disubstituted macrocyclic ligands, 1,8-[ N,N-bis(3-formyl-12-hydroxy-5-methyl)benzyl]-5,12-dioxo-1,4,8,11-tetraazacyclotetradecane (L 1), 1,8-[ N,N-bis(3-formyl-12-hydroxy-5-bromo)benzyl]-5,12-dioxo-1,4,8,11-tetraazacyclotetradecane (L 2), N, N-bis[1,8-dibenzoyl]-5,12-dioxo-1,4,8,11-tetraazacyclotetradecane (L 3), N, N-bis[1,8-(2-nitrobenzoyl)]-5,12-dioxo-1,4,8,11-tetraazacyclotetradecane (L 4), and N, N-bis[1,8-(4-nitrobenzoyl)]-5,12-dioxo-1,4,8,11-tetraazacyclotetradecane (L 5) were synthesized. The ligands were characterized by elemental analysis, FT IR, 1H NMR and mass spectrometry studies. The crystal structure of L 1 is also reported. The copper(II) and nickel(II) complexes of these ligands were prepared and characterized by elemental analysis, FT IR, UV–Vis and mass spectral studies. The cyclic voltammogram of the complexes of ligand L 1–3 show one-electron quasi-reversible reduction wave in the region −0.65 to −1.13 V, whereas that of L 4 and L 5 show two quasi-reversible reduction peaks. Nickel(II) complexes show one electron quasi-reversible oxidation wave at a positive potential in the range +0.95 to +1.06 V. The ESR spectra of the mononuclear copper(II) complexes show four lines, characteristic of square-planar geometry with nuclear hyperfine spin 3/2. All copper(II) complexes show a normal room temperature magnetic moment value μ eff 1.70–1.73 BM which is close to the spin only value of 1.73 BM. Kinetic studies on the oxidation of pyrocatechol to o-quinone using the copper(II) complexes as catalysts and hydrolysis of 4-nitrophenylphosphate using the copper(II) and nickel(II) complexes as catalysts were carried out. The ligands and their complexes were also screened for antimicrobial activity against Gram-positive, Gram-negative bacteria and human pathogenic fungi.

N-benzoylated 1,4,8,11-tetraazacyclotetradecane and their copper(II) and nickel(II) complexes: Spectral, magnetic, electrochemical, crystal structure, catalytic and antimicrobial studies

A series of N-benzoylated cyclam ligands incorporating three different benzoyl groups 1,4,8,11-tetra-(benzoyl)-1,4,8,11-tetraazacyclotetradecane (L 1), 1,4,8,11-tetra-(2-nitrobenzoyl)-1,4,8,11-tetraazacyclotetradecane (L 2) and 1,4,8,11-tetra-(4-nitrobenzoyl)-1,4,8,11-tetraazacyclotetradecane (L 3) and their nickel(II) and copper(II) complexes are described. Crystal structure of L 1 is also reported. The ligands and complexes were characterized by elemental analysis, electronic, IR, 1H NMR and 13C NMR spectral studies. N-benzoylation causes red shift in the λ max values of the complexes. The cyclic voltammogram of the complexes of ligand L 1 show one-electron, quasi-reversible reduction wave in the region −1.00 to −1.04 V, whereas that of L 2 and L 3 show two quasi-reversible reduction peaks. Nickel complexes show one-electron quasi-reversible oxidation wave at a positive potential in the range +1.05 to +1.15 V. The ESR spectra of the mononuclear copper(II) complexes show four lines, characteristic of square-planar geometry with nuclear hyperfine spin 3/2. All copper(II) complexes show a normal room temperature magnetic moment values μ eff 1.70–1.73 BM which is close to the spin-only value of 1.73 BM. Kinetic studies on the oxidation of pyrocatechol to o-quinone using the copper(II) complexes as catalysts and hydrolysis of 4-nitrophenylphosphate using the copper(II) and nickel(II) complexes as catalysts were carried out. All the ligands and their complexes were also screened for antimicrobial activity against Gram-positive, Gram-negative bacteria and human pathogenic fungi.

Hydrolytic cleavage of DNA-model substrates promoted by polyoxovanadates

Hydrolysis of 4-nitrophenyl phosphate (NPP) and bis-4-nitrophenyl phosphate (BNPP), two commonly used DNA model substrates, was examined in vanadate solutions by means of (1)H, (31)P and (51)V NMR spectroscopy. The hydrolysis of the phosphoester bond in NPP at 50 degrees C and pH 5.0 proceeds with a rate constant of 1.74 x 10(-5) s(-1). The cleavage of the phosphoester bond in BNPP at 70 degrees C and pH 5.0 proceeds with a rate constant of 3.32 x 10(-6) s(-1), representing an acceleration of four orders of magnitude compared to the uncatalyzed cleavage. Inorganic phosphate and nitrophenol (NP) were the only products of hydrolysis. The NMR spectra did not show evidence of any paramagnetic species, excluding the possibility of V(V) reduction to V(IV), indicating that the cleavage of the phosphoester bond is purely hydrolytic. The pH dependence of k(obs) revealed that the hydrolysis proceeds fastest in solutions of pH 5.5. Comparison of the rate profile with the concentration profile of polyoxovanadates shows a striking overlap of the k(obs) profile with the concentration of decavanadate (V(10)). Kinetic experiments at 37 degrees C using a fixed amount of NPP and increasing amounts of V(10) permitted the calculation of catalytic (k(c) = 5.67 x 10(-6) s(-1)) and formation constants for the NPP-V(10) complex (K(f) = 71.53 M(-1)). Variable temperature (31)P NMR spectra of a reaction mixture revealed broadening and shifting of the (31)P resonance upon addition of increasing amounts of decavanadate and upon increasing temperature, implying the dynamic exchange process between free and bound NPP at higher temperatures. The origin of the hydrolytic activity of V(10) is most likely due its high lability and its dissociation into smaller fragments which may allow the attachment of NPP and BNPP into the polyoxovanadate framework.

N-functionalized, cyclam-based unsymmetrical dicompartmental binuclear copper(II) complexes containing 4- and 6-coordination sites: electrochemical, magnetic, catalytic, and antimicrobial studies

A series of unsymmetrical dicompartmental binuclear copper(II) complexes have been prepared by Schiff-base condensation of 1,8-[bis(3-formyl-2-hydroxy-5-bromo)benzyl]-l,4,8,11-tetraazacyclotetradecane (L) with aliphatic and aromatic diamines, copper(II) perchlorate and triethylamine. The complexes were characterized by elemental and spectral analysis. Electronic spectra of the complexes show d–d transitions in the range 663–786 nm. Electrochemical studies of the complexes in DMF show two irreversible one electron reduction processes = −0.62 to −0.77 V and = −0.94 to −1.17 V. Cryomagnetic investigations of the binuclear complexes show −2J values in the range of 154 to 236 cm−1. The rate constants for hydrolysis of 4-nitrophenylphosphate are in the range of 2.27 × 10−2 to 9.21 × 10−2 min−1 and for catecholase activity in the range of 3.06 × 10−2 to 8.35 × 10−2 min−1. All the complexes were screened for antifungal and antibacterial activity.

Synthesis, electrochemical, magnetic, catalytic and antimicrobial studies of N-functionalized cyclam based trinuclear copper(II) and nickel(II) complexes

Trinuclear copper(II) and nickel(II) complexes have been prepared by using Schiff base ligands derived from 1,8-[bis(3-formyl-2-hydroxy-5-methyl) benzyl]-4,11-dimethyl-l,4,8,11-tetraazacyclotetradecane, and 1,8-[bis(3-formyl-2-hydroxy-5-bromo)benzyl]-4,11-dimethyl-l,4,8,11-tetraazacyclotetradecane with aliphatic and aromatic diamines. All the complexes were characterized by elemental and spectroscopic analysis. Electrochemical studies of the copper(II) complexes in DMF solution show three irreversible one electron reduction process around E pc 1 = −0.59 to −0.80 V, E pc 2 = −0.89 to −1.14 V and E pc 3 = −1.17 to −1.29 V, and for nickel(II) complexes it is around E pc 1 = −0.63 to −0.77 V, E pc 2 = −1.20 to −1.35 V and E pc 3 = −1.60 to −1.74 V. ESR spectra and magnetic moments of the trinuclear Cu(II) complexes show the presence of antiferromagnetic coupling. Cryomagnetic investigation of the trinuclear copper(II) complexes show that the observed −2J values are in the range of 116–178 cm−1. The rate constants for hydrolysis of 4-nitrophenylphosphate by the complexes are in the range of 2.68 × 10−2 to 9.81 × 10−2 min−1. The rate constants values for the catecholase activity of the copper(II) complexes fall in the range of 3.03 × 10−2 to 9.32 × 10−2 min−1. All the complexes.

Synthesis of new unsymmetrical “end-off” phenoxo bridged copper(II), nickel(II) and zinc(II) complexes: spectral, magnetic, electrochemical, catalytic, and antimicrobial studies

A new class of unsymmetrical end-off, aminomethylated N-methylpiperazine and aminomethylated diethanolamine binucleating ligands, 2-[bis(2-hydroxyethyl)aminomethyl]-6-[(4-methylpiperazin-1-yl)methyl]-4-methylphenol (HL1) and 2-[bis(2-hydroxyethyl)aminomethyl]-6-[(4-methylpiperazin-1-yl)methyl]-4-acetylphenol (HL2) were synthesized by following sequential aromatic Mannich reactions. Their mononuclear and binuclear Cu(II), Ni(II) and Zn(II) complexes have been synthesized and their formulation was confirmed by analytical and spectral analysis. The mononuclear Cu(II) complexes have a magnetic moment value close to the spin only value with four hyperfine EPR signals. The binuclear Cu(II) complexes have an antiferromagnetic interaction with a broad EPR signal. Electrochemical studies of the complexes reveal that all the redox processes are irreversible. Catecholase activity of Cu(II) complexes and the hydrolysis of 4-nitrophenylphosphate using Cu(II), Ni(II), and Zn(II) complexes were carried out. Spectral, magnetic, electrochemical, and catalytic behaviors of the complexes are compared on the basis of the p-substituent of the phenolic ring. Some of the complexes show significant growth inhibitory activity against pathogenic bacteria and fungi.

Synthesis, spectral, magnetic, electrochemical and kinetic studies of copper(II), nickel(II) and zinc(II) complexes derived from a phenol-based unsymmetrical “end-off” ligand

A new unsymmetrical end-off, aminomethylated N-methylpiperazine and aminomethylated diethanolamine armed binucleating ligand, 2-[bis(2-hydroxyethyl)aminomethyl]-6-[(4-methylpiperazin-1-yl)methyl]-4-formylphenol (HL), was synthesized by following sequential aromatic Mannich reactions. Mononuclear and binuclear Cu(II), Ni(II) and Zn(II) complexes were synthesized and characterized by elemental and spectral analysis. The EPR spectrum of the mononuclear copper complex shows four hyperfine splittings and the binuclear complex shows a broad signal due to anti-ferromagnetic interaction. The room temperature magnetic moment of the mono and binuclear copper complexes are 1.72 and 2.68 BM, respectively. Variable temperature magnetic moment study of the binuclear copper(II) complex shows weak antiferromagnetic coupling (−2J value, 21 cm−1). The mononuclear Ni(II) complex is square planar and diamagnetic. The six-coordinate binuclear Ni(II) complex shows a magnetic moment of 3.06 BM. Electrochemical studies of the complexes reveal that all mononuclear complexes show a single irreversible one-electron reduction wave and the binuclear complexes show two irreversible one-electron reduction waves in the cathodic region. Catecholase activity of copper(II) complexes using pyrocatechol as a model substrate and the hydrolysis of 4-nitrophenylphosphate using copper(II), nickel(II) and zinc(II) complexes as catalysts showed that binuclear complexes have higher rate constants than corresponding mononuclear complexes.

Synthesis, spectral, magnetic, electrochemical and catalytic studies of cyclam-based copper(II) and nickel(II) complexes–effect of N-substitution

New N-substituted cyclam ligands 1,8-[bis(3-formyl-2-hydroxy-5-methyl)benzyl]-1,4,8,11-tetraazacyclotetradecane, 1,8-[bis(3-formyl-2-hydroxy-5-methyl)benzyl]-4,11-dimethyl-1,4,8,11-tetraazacyclotetradecane, 1,8-[bis(3-formyl-2-hydroxy-5-bromo)benzyl]-1,4,8,11-tetraazacyclotetradecane, and 1,8-[bis(3-formyl-2-hydroxy-5-bromo)benzyl]-4,11-dimethyl-1,4,8,11-tetraazacyclotetradecane (L1–L4) were synthesized and mononuclear copper(II) and nickel(II) complexes prepared. The ligands and complexes were characterized by elemental analysis, electronic, IR, 1H NMR and 13C NMR spectral studies. N-alkylation causes red shifts in the λmax values of the complexes. Copper(II) complexes show one-electron, quasi-reversible reduction waves in the range −1.04 to −1.00 V. The nickel(II) complexes show one-electron, quasi-reversible reduction waves in the range −1.18 to −1.30 V and one-electron, quasi-reversible oxidation waves in the range +1.20 to +1.40 V. The reduction potential of the copper(II) and nickel(II) complexes of the ligands L1 to L2 and L3 to L4 shift anodically on N-alkylation. The ESR spectra of the mononuclear copper(II) complexes show four lines, characteristic of square-planar geometry with nuclear hyperfine spin 3/2. All copper(II) complexes show a normal room temperature magnetic moment value μeff = 1.70–1.74 BM which is close to the spin only value of 1.73 BM. Kinetic studies on the oxidation of pyrocatechol to o-quinone using the copper(II) complexes as catalysts and on the hydrolysis of 4-nitrophenylphosphate using the copper(II) and nickel(II) complexes as catalyst were carried out. The tetra-N-substituted complexes have higher rate constants than the corresponding disubstituted complexes.

Efficient and selective hydrolysis of 4-nitrophenyl phosphate by a dinuclear copper(II) complex

The aim of this work was to construct chemical models for selective hydrolysis of phosphate monoesters in order to elucidate the role of metal ions in the hydrolytic mechanisms and to develop artificial enzymes for practical applications. A dinuclear copper(II) complex of a cyclohexane-based polyamino polyalcohol provided a selective and by far the highest rate acceleration among the transition metal complexes containing divalent metal ions for the hydrolysis of a phosphate monoester.

Model Chemical Decontamination Studies of Phosphate Esters in Aqueous and Microemulsion Media

The hydrolysis of 4-nitrophenylphosphate (NPP) in the presence of several cobalt(III) amine model systems in oil-in-water microemulsion media was investigated. The reaction was monitored by measuring the absorbance of the nitrophenolate ion produced in the reaction aliquots with time under the experimental condition. The order of effectiveness of the microemulsion system toward the hydrolysis of NPP was found to be cationic > anionic > aqueous. [Cotn 2 (OH)(H 2 O)] 2 + complexes were found to be better promoters of hydrolysis compared to [Coen 2 (OH)(H 2 O)] 2 + in both aqueous and microemulsion systems. Explanation for the above is afforded and the application of the systems for possible environmental decontamination of organophosphates is envisioned.