Copper complexes as chemical nucleases

Redox active mononuclear and binuclear copper(II) complexes have been prepared and structurally characterized. The complexes have planar N-donor heterocyclic bases like 1,10-phenanthroline (phen), dipyridoquinoxaline (dpq) and dipyridophenazine (dppz) ligands that are suitable for intercalation to B-DNA. Complexes studied for nuclease activity have the formulations [Cu(dpq)2(H2O)] (ClO4)2.H2O (1), [CuL(H2O)2(μ-ox)](ClO4)2 (L = bpy,2; phen,3; dpq,4; and dppz,5) and [Cu(L)(salgly)] (L = bpy,6; phen,7; dpq,8; and dppz,9), where salgly is a tridentate Schiff base obtained from the condensation of glycine and salicylaldehyde. The dpq complexes are efficient DNA binding and cleavage active species. The dppz complexes show good binding ability but poor nuclease activity. The cleavage activity of thebis-dpq complex is significantly higher than thebis-phen complex of copper(II). The nuclease activity is found to be dependent on the intercalating nature of the complex and on the redox potential of the copper(II)/copper(I) couple. The ancillary ligand plays a significant role in binding and cleavage activity

Structural model for the Cu-B site of dopamine beta-hydroxylase: Crystal structure of a copper(II) complex showing N3OS coordination with an axial sulfur ligation

A copper(II) complex containing a NSO-donor Schiff base and NN-donor 2,2'-bipyridine has been prepared and structurally characterized. The square pyramidal complex with an axial sulfur ligation is a structural model for the CUB site of dopamine-hydroxylase in its oxidized form. The copper(II) complex is catalytically active in the oxidation of ascorbic acid by dioxygen mediated by a copper(I) species which is proposed to have a four-coordinate structure with a N3S coordination geometry

%Structural model for the Cu<SUB>B</SUB> site of dopamine &#946;-hydroxylase: crystal structure of a copper(II) complex showing N<SUB>3</SUB>OS coordination with an axial sulfur ligation

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Synthesis, crystal structure and nuclease activity of bis(dipyridoquinoxaline)copper(I) perchlorate

2185-2190A copper(I) complex [Cu(dpq)2](ClO4) (1), where dpq is dipyrido-[3,2-d:2',3'-f]-quinoxaline, is prepared and structurally characterized. The complex crystallizes in the orthorhombic space group Pnna with the unit cell parameters a =7.7797(9)Å, b = 20.185(2)Å, c = 16.593(2) Å, V = 2605.6(5) Å3, Z = 4. The structure was refined to R = 0.0713 for 2525 reflections with 1127 having I &gt; 2σ(I) and 192 parameters. The cationic complex has the copper(I) center bonded to two N,N-donor dpq ligands giving a distorted tetrahedral coordination geometry with a Cu-N distance of 2.05Å. The crystal structure displays extensive π-π stacking interactions involving the planar aromatic rings of dpq. Such an interaction gives rise to the formation of chains and the perchlorate anions are located in-between the chains. The complex is diamagnetic and exhibits a metal to ligand charge transfer band at 442 nm (ε, 6000 M-1 cm-1) in MeCN and a perchlorate stretch at 1088 cm-1 in the IR spectrum in KBr phase. It shows a quasi-reversible cyclic voltammetric response at 0.17 V (ΔEp = 120 mV) at 50 mV s-1 in DMF for the Cu(II)/Cu(I) couple. Complex 1 is a chemical nuclease. It shows efficient nuclease activity on treatment with supercoiled DNA in presence of hydrogen peroxide. The nuclease activity of 1 is found to be better than [Cu(phen)2]+ under similar reaction conditions. Mechanistic studies have shown minor groove binding of the complex and the involvement of hydroxyl radicals in the DNA cleavage reactions

Synthesis, crystal structure and nuclease activity of bis(dipyridoquinoxaline)copper(I)perchlorate

Copper(I) complex [Cu(dpq)2](ClO4) (1), where dpq is dipyrido-[3,2-d:2',3'-f]-quinoxaline, is prepared and structurally characterized. The complex crystallizes in the orthorhombic space group Pnna with the unit cell parameters a = 7.7797(9) A, b = 20.185(2) A, c = 16.593(2) Å, V = 2605.6(5) Å3, Z = 4. The structure was refined to R = 0.0713 for 2525 reflections with 1127 having 1 &gt; 2σ(1) and 192 parameters. The cationic complex has the copper(I) center bonded to two N,N-donor dpq ligands giving a distorted tetrahedral coordination geometry with a Cu-N distance of 2.05 Å. The crystal structure displays extensive π-π stacking interactions involving the planar aromatic rings of dpq. Such an interaction gives rise to the formation of chains and the perchlorate anions are located in-between the chains. The complex is diamagnetic and exhibits a metal to ligand charge transfer band at 442 nm (ε, 6000 μ−1 cm−1) in MeCN and a perchlorate stretch at 1088 cm−1 in the IR spectrum in KBr phase. It shows a quasi-reversible cyclic voltammetric response at 0.17 V (ΔEP = 120 mV) at 50 mV s−1 in DMF for the Cu(II)/Cu(I) couple. Complex 1 is a chemical nuclease. It shows efficient nuclease activity on treatment with supercoiled DNA in presence of hydrogen peroxide. The nuclease activity of 1 is found to be better than [Cu(phen)2]+ under similar reaction conditions. Mechanistic studies have shown minor groove binding of the complex and the involvement of hydroxyl radicals in the DNA cleavage reactions

Metal-assisted light-induced DNA cleavage activity of 2-(methylthio)phenylsalicylaldimine Schiff base copper(II) complexes having planar heterocyclic bases

Ternary copper(II) complexes [CuLL']$(ClO_4)$, where HL is NSO-donor Schiff base (2-(methylthio)phenyl)salicylaldimine and L' is NN-donor phenanthroline bases like 1,10-phenanthroline (phen), dipyridoquinoxaline (dpq) and 2,9-dimethyl-1,10-phenanthroline (dmp), are prepared and structurally characterized by X-ray crystallography. The complexes have a distorted square-pyramidal (4+ 1) $CuN_3OS$ coordination geometry. While $[CuL(phen)](ClO_4)$ and $[CuL(dpq)](ClO_4)$ show axial sulfur ligation, $[CuL(dmp)](ClO_4)$ has the sulfur bonded at the equatorial site. The one-electron paramagnetic complexes exhibit axial electron paramagnetic resonance (EPR) spectra in dimethylformamide glass at 77 K. The complexes are redox active and a quasireversible electron transfer process near 0.0 V vs saturated calomel electrode (SCE) in DMF–Tris buffer (1:4 v/v at pH 7.2) involving Cu(II)/ Cu(I) couple is observed for the phen and dpq complexes. The dmp complex exhibits an irreversible reduction proces forming bis(dmp)copper(I) species. A profound effect of the substituents of the phenanthroline bases is observed on the binding of the complexes to the calf thymus (CT) and in the cleavage of supercoiled (SC) pUC19 DNA. The phen and dpq complexes show DNA cleavage activity in presence of mercaptopropionic acid (MPA). The dmp complex is cleavage inactive in presence of MPA. All the complexes show photocleavage activity when irradiated with a monochromatic UV light of 312 nm. The dpq complex also cleaves SC DNA on visible light irradiation at 436, 532 and 632.8 nm but with a longer exposure time and higher complex concentration. The cleavage reactions in presence of MPA are found to involve hydroxyl radical. The photocleavage reactions are found to occur under aerobic conditions showing an enhancement of cleavage in $D_2O$ and inhibition with azide addition suggesting formation of singlet oxygen as a reactive species The roles of sulfur of the Schiff base as photosensitizer and the phenanthroline bases as minor groove binder, and their influence on the photocleavage activity are discussed. The quinoxaline ligand exhibits significant photosensitizing effect assisted by the copper(II) center

Structural model for the Cu<SUB>B</SUB> site of dopamine β-hydroxylase and peptidylglycine α-hydroxylating monooxygenase: crystal structure of a copper(II) complex showing a N<SUB>3</SUB>OS coordination and an axial sulphur ligation

A copper(II) complex [Cu(L)(phen)](ClO<SUB>4</SUB>) (HL, NSO-donor Schiff base ligand) with a Cu<SUP>II</SUP>N<SUB>3</SUB>OS geometry showing axial sulfur ligation is a structural model for the Cu<SUB>B</SUB> site of DβH and PHM, and the complex is catalytically active in the oxidation of ascorbic acid by dioxygen mediated by a copper(I) species