R. Prabu

Synthesis, characterization, and antimicrobial activities of nickel(II) and copper(II) Schiff-base complexes

Ni(II) and Cu(II) metal complexes of simple unsymmetrical Schiff-base ligands derived from salicylaldehyde/5-methylsalicylaldehyde and ethylenediamine or diaminomaleonitrile (DMN) were synthesized. The ligands and their complexes were characterized by elemental analysis, 1H NMR, FT IR, and mass spectroscopy. The electronic spectra of the complexes show d–d transitions in the region at 450–600 nm. Electrochemical studies of the complexes reveal that all mononuclear complexes show a one-electron quasi-reversible reduction wave in the cathodic region. ESR spectra of the mononuclear copper(II) complexes show four lines, characteristic of square-planar geometry, with nuclear hyperfine spin 3/2. The copper(II) complexes show a normal room temperature magnetic moment value μ eff = 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 were also carried out. The in vitro antimicrobial activity of the investigated compounds was tested against human pathogenic bacterias such as Staphylococcus aureus, Bacillus subtilis, Klebsiella pneumonia, Pseudomonas aeruginosa and Escherichia coli. The antifungal activity was tested against Candida albicans. Generally, the metal complexes have higher antimicrobial activity than the free ligands.

New acyclic Schiff-base copper(II) complexes and their electrochemical, catalytic, and antimicrobial studies

A new series of acyclic mononuclear copper(II) complexes have been prepared by Schiff-base condensation derived from 5-methylsalicylaldehyde, diethylenetriamine, tris(2-aminoethyl) amine, triethylenetetramine, N,N-bis(3-aminopropyl)ethylene diamine, N,N-bis(aminopropyl) piperazine, and copper perchlorate. All the complexes were characterized by elemental and spectral analyses. Electronic spectra of the complexes show a d–d transition in the range 500–800 nm, electrochemical studies of the complexes show irreversible one-electron-reduction process around −1.10 to −1.60 V. The reduction potential of the mononuclear copper(II) complexes shifts toward anodic direction upon increasing the chain length of the imine compartment. ESR spectra of the mononuclear copper(II) complexes show four lines, characteristic of square-planar geometry, with nuclear hyperfine spin 3/2. The copper(II) complexes show a normal room temperature magnetic moment value μ eff = 1.72–1.76 BM, close to the spin-only value of 1.73 BM. Electrochemical and catalytic studies of the complexes were compared on the basis of increasing the chain length of the imine compartment. All the complexes were screened for antifungal and antibacterial activities.

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.

Fabrication of α-Fe2O3 Nanoparticles for the Electrochemical Detection of Uric Acid

α-Fe2O3 nanoparticles were synthesized using the hydrolysis method. The prepared sample was characterized by various techniques. The synthesized nanoparticles were used to modify glassy carbon (GC) electrode and the modified electrode was used to detect uric acid (UA) by cyclic voltammetry (CV) and chronoamperometry (CA). At the modified GC electrode, UA is oxidized with less positive potential than the bare GC electrode. The effect of scan rate and the substrate concentration on the modified electrode have also been discussed. The electrochemical studies revealed that the product will exhibit potential applications in the development of sensors.

Electrochemical, catalytic and antimicrobial activity of N-functionalized tetraazamacrocyclic binuclear nickel(II) complexes

The five binuclear nickel(II) complexes have been synthesized by the Schiff base condensation of 1,8-[bis(3-formyl-2-hydroxy-5-methyl)benzyl]-l,4,8,11-tetraazacyclo-tetradecane (PC) with appropriate aliphatic diamines and nickel(II) perchlorate. All the five complexes were characterized by elemental and spectral analysis. The electronic spectra of the complexes show three d-d transition in the range of 550-1055 nm due to 3A2g→3T2g(F), 3A2g→3T1g(F) and 3A2g→3T1g(P). These spin allowed electronic transitions are characteristic of an octahedral Ni2+ center. Electrochemical studies of the complexes show two irreversible one electron reduction waves at cathodic region. The reduction potential of the complexes shifts towards anodically upon increasing the chain length of the macrocyclic ring. All the nickel(II) complexes show two irreversible one electron oxidation waves at anodic region. The oxidation potential of the complexes shift towards anodically upon increasing the chain length of the macrocyclic ring. The catalytic activities of the complexes were observed to be increase with increase the macrocyclic ring size. The observed rate constant values for the catalytic hydrolysis of 4-nitrophenyl phosphate are in the range of 5.85×10(-3) to 9.14×10(-3) min(-1). All the complexes were screened for antimicrobial activity.

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.

Synthesis of New Acyclic Schiff Base Oxovanadium(IV) Complexes and Their Electrochemical, Catecholase, and Antimicrobial Studies of Minimum Inhibitory Concentration

Catalytically active complexes containing [VO(IV)L] were synthesized by using Schiff base ligands L1–5 and vanadyl sulfate. Ligands L1–5 were obtained by the condensation of 5-methylsalicylaldehyde with diethylene triamine (L1), tris(2-aminoethyl)amine (L2), triethylene tetramine (L3), N,N-bis(3-aminopropyl)ethylenediamine (L4) and N,N- bis(aminopropyl) piperazine (L5). All the complexes were characterized by elemental and spectral analysis. ESR spectra for the mononuclear [VO(IV)L] complexes show eight lines, square pyramidal geometry. Room temperature magnetic moment for the complexes was around 1.73 B.M. Electrochemical and catalytic studies of the complexes were compared on the basis of chain length of the imine compartment. All the [VO(IV)L1–5] complexes were screened antibacterial activity of MIC.

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.

Spectral, electrochemical, luminescence, and dye-sensitized solar cell studies of mono and d-f hetero binuclear cryptates

Mono and hetero binuclear cryptates, [Gd(III)ML]+ [M = VO(IV), Co(II), Ni(II), Cu(II)], were synthesized by a 2-step method. The ligand L represents the deprotonated anionic cryptate obtained by the 2+3 condensation of tris-(2-aminoethyl)amine with 2,6-diformyl-4-nitrophenol. The complexes were characterized by elemental analysis, spectral, magnetic, and electrochemical studies. Fluorescence of Gd(III) ion in the cavity was quenched by the encapsulated Cu(II) and Ni(II) ions. [GdCoL(NO3)]+ cryptate had a high lifetime value compared to other cryptates. The cyclic voltammogram showed that the reduction potential values of [Gd(M)L] M = VO(IV), Co(II), Ni(II), and Cu(II) complexes were in the following order: Cu(II) > Ni(II) > Co(II) > VO(IV). The efficiency (h) of the cryptate based dye-sensitized solar cell (DSSC) increases in the following order: [GdVOL(NO3)]+ < [GdCoL(NO3)]+ < [GdCuL(NO3)]+ < [GdHL] < [GdNiL(NO3)]+.

Synthesis, Spectral, Electrochemical, Magnetic and Biological Studies of Tet-A Based Binuclear Mn(III) Complexes

A new phenoxo-bridged Tet-a based binuclear manganese(III) complexes were synthesized by the Schiff base condensation reaction of the compound 1,8–[bis(3-formyl-2-hydroxy-5-methyl)benzyl] -5,5,7,12,12,14- hexamethyl -l,4,8,11-tetraazacyclotetradecane (PC–a) and 1,8– [bis(3-formyl-2-hydroxy-5-bromo)benzyl]- 5,5,7,12,12,14-hexamethyl-l,4,8,11-tetraazacyclotetradecane (PC–b) with triethylenetetramine and manganese(II) perchlorate hexahydrate. Their synthesized complexes were confirmed by analytical and spectral analysis. The phenolate oxygen atom is acting as bridge between two unsymmetrically coordinated Mn atoms. Electrochemical studies of the complexes reveal that all the redox processes are irreversible in nature. Low temperature magnetic study shows that the complexes exhibit antiferromagnetic exchange interaction between the two metal ions. The spectral and magnetic behavior of the complexes is discussed.