K. Shanmuga Bharathi

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.

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 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.

Electrochemical, catalytic and antimicrobial activities of N-functionalized cyclam based unsymmetrical dicompartmental binuclear nickel(II) complexes

Five binuclear nickel(II) complexes have been prepared by simple Schiff base condensation of the compound 1,8-[bis(3-formyl-2-hydroxy-5-bromo)benzyl]-l,4,8,11-tetraazacyclotetradecane (L) with appropriate aliphatic or aromatic diamine, nickel(II) perchlorate and triethylamine. All the complexes were characterized by elemental and spectral analysis. Positive ion FAB mass spectra show the presence of dinickel core in the complexes. The electronic spectra of the complexes show red shift in the d-d transition. Electrochemical studies of the complexes show two irreversible one electron reduction processes in the range of 0 to -1.4V. The reduction potential of the complexes shifts towards anodically upon increasing chain length of the macrocyclic ring. All the nickel(II) complexes show two irreversible one electron oxidation waves in the range 0.4-1.6V. The observed rate constant values for catalysis of the hydrolysis of 4-nitrophenyl phosphate are in the range of 1.36x10(-2)-9.14x10(-2)min(-1). The rate constant values for the complexes containing aliphatic diimines are found to be higher than the complexes containing aromatic diimines. Spectral, electrochemical and catalytic studies of the complexes were compared on the basis of increasing chain length of the imine compartment. All the complexes show higher antimicrobial activity than the ligand and metal salt.

Heterogeneous Oxidation of Styrene Using Iron(III) Porphyrin Encapsulated in Mesoporous Molecular Sieves

The catalytic activities of the iron(III) porphyrin encapsulated in mesoporous Al/Ti/V-MCM-41 catalysts were tested in the epoxidation of styrene. The results obtained show that the yield of epoxide formed depends not only on the nature of support materials but also on the combined effects of catalyst and the supports. The yield of epoxide formed were higher for iron(III) porphyrin encapsulated in Ti/V-MCM-41 than that in Al-MCM-41 and MCM-41. The prepared catalytic systems are inexpensive, with the advantages of high activity, selectivity, and reusability. Recycling experiments suggest that no structural changes have occurred to the mesoporous materials during the catalytic reactions.

Synthesis, characterization and bioactive evaluation of copper(II) 5,10,15,20-tetrakis[α,α,α,α-2-(2,6-bis(4-methylpiperazine-1-yl-methyl)-4-iminomethyl phenol)phenyl] porphyrin: A picket-fence porphyrin

We are interested in constructing deeper small cavities by adding more bulky substituents at the ortho-phenyl positions of tetrakis(o-aminophenyl)porphyrin. The synthesis of picket-fence porphyrin is initiated by the preparation of the tetrakis(o-nitrophenyl)porphyrin followed by the nitro to amino reduction and subsequent condensation with Schiff base ligand to form imine linkages of porphyrin complexes. The synthesis and characterization of a new series of picket-fence porphyrins and their copper complexes are described. 5,10,15,20-Tetrakis[alpha,alpha,alpha,alpha-2-(2,6-bis(4-methyl piperazine-1-yl-methyl)-4-iminomethyl phenol)phenyl] porphyrin can be synthesized from 2,6-bis[4-methylpiperazin-1-yl-methyl]-4-formylphenol (L) and 5,10,15,20-tetra[alpha,alpha,alpha,alpha-o-nitropheny1]-porphyrin. 5,10,15,20-Tetra[alpha,alpha,alpha,alpha-o-aminopheny1]-porphyrin was obtained by the reduction of 5,10,15,20-tetra[alpha,alpha,alpha,alpha-o-nitropheny1]-porphyrin. The spectral, electrochemical, antibacterial, antifungal and cytotoxicity properties of all the picket-fence porphyrin complexes were characterized and studied.

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.