anzhi Li

DNA binding, DNA cleavage and BSA interaction of a mixed-ligand copper(II) complex with taurine Schiff base and 1,10-phenanthroline

The DNA-binding properties and DNA-cleavage activities of a Cu(II) complex, [Cu(sal-tau(phen)]·1.5H2O (sal-tau=a Schiff base derived from salicylaldehyde and taurine, phen=1,10-phenanthroline), have been investigated by using UV-Vis absorption, fluorescence, circular dichroism (CD) spectra and agarose gel electrophoresis. Results indicated that this Cu(II) complex can bind to calf thymus DNA (CT-DNA) via an intercalative mode and shows efficient cleavage activity in the absence and presence of reducer. Its intrinsic binding constant Kb (1.66×10(4)M(-1)) was calculated by absorption spectra and its linear Stern-Volmer quenching constant K(sq) (3.05) was obtained from florescence spectroscopy, as well as the cleaving reaction rate constant k1 (2.0×10(-4)s(-1)) was acquired from agarose gel electrophoresis. Meanwhile, the interactions of the complex with BSA have also been studied by spectroscopy. Results showed that the complex could quench the intrinsic fluorescence of bovine serum albumin (BSA) remarkably through a static quenching process, and induce a conformational change with the loss of helical stability of protein.

Synthesis, crystal structure and interaction of L-valine Schiff base divanadium(V) complex containing a V2O3 core with DNA and BSA.

A divanadium(V) complex, [V2O3(o-van-val)2] (o-van-val=Schiff base derived from o-vanillin and L-valine), has been synthesized and structurally characterized. The crystal structure shows that both of the vanadium centers in the complex have a distorted octahedral coordination environment composed of tridentate Schiff base ligand. A V2O3 core in molecular structure adopts intermediate between cis and trans configuration with the O1V1⋯V1AO1A torsion angle 115.22 (28)° and the V1⋯V1A distance 3.455Å. The binding properties of the complex with calf thymus DNA (CT-DNA) have been investigated by UV-vis absorption, fluorescence, CD spectra and viscosity measurement. The results indicate that the complex binds to CT-DNA in non-classical intercalative mode. Meanwhile, the interaction of the complex with bovine serum albumin (BSA) has been studied by UV-vis absorption, fluorescence and CD spectra. Results indicated that the complex can markedly quench the intrinsic fluorescence of BSA via a static quenching process, and cause its conformational change. The calculated apparent binding constant Kb was 1.05×10(6)M(-1) and the binding site number n was 1.18.

DNA binding, BSA interaction and SOD activity of two new nickel(II) complexes with glutamine Schiff base ligands.

Two hexacoordinated octahedral nickel(II) complexes, [Ni(o-van-gln)(phen)(H2O)](1) and [Ni(sal-gln)(phen)(H2O)](2) [o-van-gln=a Schiff base derived from o-vanillin and glutamine, sal-gln=a Schiff base derived from salicylaldehyde and glutamine, phen=1,10-phenanthroline], have been synthesized and characterized by elemental analysis, IR spectra and single crystal X-ray diffraction. X-ray studies showed that nickel atoms of both 1 and 2 exhibit distorted NiN3O3 octahedral geometry. In each crystal, intermolecular hydrogen bonds form a two-dimensional network structure. DNA-binding properties of these two nickel(II) complexes were investigated by using UV-Vis absorption, fluorescence, circular dichroism (CD) spectroscopies and viscosity measurements. Results indicated that the two complexes can bind to calf thymus DNA (CT-DNA) via an intercalative mode, and complex 1 exhibits higher interaction with CT-DNA than complex 2. Furthermore, the interactions between the nickel(II) complexes with bovine serum albumin (BSA) have been studied by spectroscopies. The results indicated that both complexes could quench the intrinsic fluorescence of BSA in a static quenching process. The binding constants (Kb) and the numbers of binding sites (n) obtained are 1.10×10(5)M(-1) and 1.05 for complex 1 and 5.05×10(4)M(-1) and 0.997 for complex 2, respectively. Site-selective competitive binding investigation indicated that the binding sites of both the complexes are located in site I of sub-domains IIA of BSA. Assay of superoxide dismutase (SOD) activity of the nickel(II) complexes revealed that they exhibit significant superoxide scavenging activity with IC50=3.4×10(-5)M for complex 1 and 4.3×10(-5)M for complex 2, respectively.

Synthesis, crystal structure, and DNA interaction of an oxovanadium(IV) complex containing L-valine Schiff base and 1,10-phenanthroline

A new oxovanadium(IV) complex, [VO(sal-val)(phen)] CH3OH H2O (sal-val = Schiff base derived from salicylaldehyde and L-valine, phen = 1,10-phenanthroline), has been synthesized and characterized by elemental analysis, IR spectra, and single-crystal X-ray diffraction. This crystal belongs to monoclinic crystal system, C2/c space group with crystallographic data: a = 28.031(4) Å, b = 9.342(3) Å, c = 19.198(4) Å, β = 99.425(2)°, and Z = 8. The VIV was six-coordinate to form an octahedral geometry. In the crystal, intermolecular hydrogen bonding and π–π stacking formed the 1-D network. DNA-binding properties of this oxovanadium(IV) complex with calf-thymus DNA (CT-DNA) were investigated using UV, fluorescence, and circular dichroism spectra. The complex can bind to CT-DNA via intercalation.

Spectroscopic study on acid-induced unfolding and refolding of apo-neuroglobin

pH-induced unfolding and refolding of apo-neuroglobin (apo-Ngb) were investigated by UV, fluorescence, circular dichroism (CD) spectra and light scattering measurements. Results revealed that apo-Ngb became partially unfolded at around pH 5.0, with evidences from a red shift in the fluorescence spectra, a decrease in the far-UV CD and a sharp peak in the light scattering intensity. Further lowering of the pH reversed these effects, suggesting that apo-Ngb folds back to a compact state. At pH 2.0, the apo-Ngb forms a folding intermediate known as molten globule (MG), which is possessed of native-like secondary structure and almost complete loss of tertiary structure. Based on these results, the acid-induced denaturation pathway of apo-Ngb can be illustrated from the native state (N), via a partially unfolded state (U(A)) to the molten globule state (MG).

Tetra­kis(μ3-2-{[1,1-bis­(hydroxy­meth­yl)-2-oxidoeth­yl]imino­meth­yl}-6-methoxy­phenol­ato)tetra­nickel(II) tetra­hydrate

The title complex, [Ni4(C12H15NO4)4]·4H2O, has crystallographic fourfold inversion symmetry, with each NiII ion coordinated in a slightly distorted square-pyramidal coordination environment and forming an Ni4O4 cubane-like core. In the crystal structure, intermolecular O—H⋯O hydrogen bonds connect complex and water molecules to form a three-dimensional network. The O atom of one of the unique hydroxymethyl groups is disordered over two sites, with the ratio of occupancies being approximately 0.79:0.21.

Synthesis, structure and spectroscopic studies on DNA binding, BSA interaction of a nickel(II) complex containing l–methionine Schiff base and 1,10-phenanthroline

Abstract A new nickel(II) complex, [Ni(o-van-L-met)(phen)(CH3OH)] (o-van-L-met = Schiff base derived from o-vanillin and l-methionine, phen = 1,10–phenanthroline), has been synthesized and characterized by elemental analyses, IR spectra, and single-crystal X-ray diffraction. The crystal structure shows nickel is six-coordinate in a distorted octahedral geometry. In this crystal, molecules form a 2-D plane structure via hydrogen bonds and π–π interactions. The interaction of the complex with calf thymus DNA (CT-DNA) was investigated by absorption, fluorescence, circular dichroism (CD), spectroscopies, and viscosity measurement. The complex binds to CT-DNA in an intercalative mode with a binding constant of (4.7 ± 0.5) × 104 M−1. The interaction of the complex with bovine serum albumin (BSA) was also studied by the multispectroscopic methods. Results illustrated that the nickel(II) complex can effectively quench the intrinsic fluorescence of BSA via a static quenching mechanism and cause conformational changes. The binding constant Kb was (6.3 ± 1.6) × 104 M−1 and the binding site number n was 0.96 ± 0.04; its bind site was located within subunit IIA of BSA.

Synthesis, crystal structure, and interaction with DNA and BSA of a chromium(III) complex with naph-gly Schiff base and 1,10-phenanthroline

A new chromium(III) complex, [CrCl(naph-gly)phen]⋅H2O (naph-gly = Schiff base derived from 2-hydroxy-1-naphthaldehyde and glycine, phen = 1,10-phenanthroline), has been synthesized and characterized by elemental analysis, electrospray ionization mass spectroscopy, FT-IR, and X-ray single-crystal diffraction. The chromium(III) complex belongs to the trigonal crystal system, P3(1) space group with crystallographic data: a = b = 1.97017(16) nm, c = 1.02991(7) nm, α = β = 90°, γ =120°, V = 3.4621(5) nm3, Dc = 1.476 g⋅cm−3, Z = 6, F(0 0 0) = 1578, R1 = 0.0508, wR2 = 0.0907. There are two independent molecules in the crystallographic asymmetric unit of the chromium(III) complex. Each CrIII is six-coordinate to form an octahedral geometry. In the crystal, a 3-D structure is formed through intermolecular hydrogen bonds. The calf thymus DNA (CT-DNA)- and bovine serum albumin (BSA)-binding properties of the complex have been studied by UV absorption, fluorescence, and circular dichroism (CD) spectroscopy. Results indicate that the chromium(III) complex binds to CT-DNA in an intercalative mode, and it can bind to BSA and cause conformational changes of BSA. A new chromium(III) complex, [CrCl(naph-gly)phen]⋅H2O, with a Schiff base derived from 2-hydroxy-1-naphthaldehyde and glycine and with 1,10-phenanthroline as a co-ligand has been synthesized and characterized by IR and single-crystal X-ray diffraction. The interactions of the complex with DNA and BSA have been investigated by UV absorption, fluorescence, and CD spectra.

(2,2′-Bipyridine-κ2N,N′)[N-(2-oxido-1-naphthyl­idene)threoninato-κ3O1,N,O2]copper(II)

In the title complex, [Cu(C15H13NO4)(C10H8N2)], the Schiff base ligand is derived from the condensation of 2-hydroxy-1-naphthaldehyde and l-threonine. The CuII atom is five-coordinated by one N atom and two O atoms from the Schiff base ligand and by two N atoms from a 2,2′-bipyridine ligand in a distorted square-pyramidal geometry. In the crystal structure, the combination of intermolecular O—H⋯O and C—H⋯O hydrogen bonds leads to a two-dimensional network.

Spectroscopic Studies on Unfolding Processes of Apo-Neuroglobin Induced by Guanidine Hydrochloride and Urea

Neuroglobin (Ngb), a recently discovered globin, is predominantly expressed in the brain, retina, and other nerve tissues of vertebrates. The unfolding processes of apo-neuroglobin (apoNgb) induced by guanidine hydrochloride (GdnHCl) and urea were investigated by spectroscopic methods. In the unfolding processes, apoNgbs tertiary structural transition was monitored by the changes of intrinsic fluorescence emission spectra, and its secondary structural transition was measured by the changes of far-ultraviolet circular dichroism (CD) spectra. In addition, 8-anilino-1-naphthalenesulfonic acid (ANS), a hydrophobic cluster binding dye, was also used to monitor the unfolding process of apoNgb and to explore its intermediates. Results showed that GdnHCl-induced unfolding of apoNgb was via a three-state pathway, that is, Native state (N) → Intermediate state (I) → Unfolded state (U), during which the intermediate was inferred by an increase in fluorescence intensity and the change of CD value. Gibbs free energy changes are 10.2 kJ·mol−1 for the first unfolding transition and 14.0 kJ·mol−1 for the second transition. However, urea-induced unfolding of apoNgb only underwent a two-state transition: Native state (N) → Partially unfolded state (P). The result showed that GdnHCl can efficiently affect the conformational states of apoNgb compared with those of urea. The work will benefit to have an understanding of the unfolding mechanism of apoNgb induced by GdnHCl and urea.