A new oxovanadium(IV) complex, [VO(o-Van-Asn)(Phen)]·1.5CH₃OH (o-Van-Asn is the Schiff base derived from o-vanillin and L-asparagine, Phen＝1,10-phenanthroline) has been synthesized. In the synthetic procedure of title complex, a methanol solution of o-vanillin (0.1522 g, 1 mmol) was added to a stirred mixture of L-asparagine (0.1321 g, 1.0 mmol) and potassium hydroxide (0.0561 g, 1 mmol) in hot methanol. The resultant yellow solution was then stirred at 333 K for 1 h. Subsequently, an aqueous solution (2 mL) of vanadyl sulfate hydrate (0.2540 g, 1 mmol) was added dropwise and stirred for 2 h continuously. Finally, a methanol solution (5 mL) of 1,10-phenanthroline (0.1980 g, 1 mmol) was then added dropwise, and the mixture was stirred continuously for 3 h. The resultant solution was filtered and kept at room temperature, and reddish brown blocky crystals suitable for X-ray diffraction were obtained after several days. It was characterized by IR and single crystal X-ray diffraction. It crystallized in triclinic crystal system, P-1 space group with the cell parameters: a＝0.98990(10) nm, b＝1.21591(11) nm, c＝1.28349(12) nm, α＝66.8180(10)o, β＝83.816(2)o, γ＝66.4150(10)o, V＝1.2992(2) nm³, D_c＝1.430 g·cm^-3, Z＝1, F(000)＝580, R₁＝0.0626, wR₂＝0.1631. The interactions of the complex with calf thymus DNA (CT-DNA) and bovine serum albumin (BSA) were carried out in 10 mmol·L^-1 Tris-HCl/10 mmol·L^-1 NaCl (pH 7.1) buffer solutions. In the experiment of interactions with CT-DNA, absorption titrations were carried out by using a fixed complex concentration to which increments of DNA stock solutions were added. The complex-DNA solutions were incubated for 2 h before the absorption spectra in the 150～250 nm wavelength range were recorded. For fluorescence experiments, the complex solution was added to the fixed concentration CT-DNA solutions treated with ethidium bromide. The emission spectra was recorded range from 535 to 675 nm at the excitation wavelength of 258 nm. Circular dichroism (CD) spectra were measured with a quartz cell of 1 cm path length after the increasing concentration of complex was added to the fixed concentration CT-DNA solutions for 2 h. Each sample solution was scanned in the range of 220～320 nm with a scan speed of 100 nm·min^-1 and 1 s response time. Viscosities of the DNA-complex system were measured at (30.0±0.1) ℃ using an Ubbelodhe viscometer. The results indicate that the complex binds to CT-DNA with a weak intercalative mode. The binding constant K_b obtained from absorption spectra was 2.17×10³ L·mol^-1, and the linear Stern-Volmer quenching constant K_sq obtained from fluorescence spectra was 1.44. Meanwhile, the interactions of the complex with BSA have also been studied by spectroscopy. The results indicate 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 K_b was 8.9×10⁴ and the binding site number n was 1.04.

Key words: oxovanadium complex, L-asparagine schiff base, crystal structure, DNA, bovine serum albumin (BSA)