Starting from 2,9-dimethyl-1,10-phenanthroline, its l-valine derivative, 1,10-phenanthroline-2,9-dimethanoimino- (2,2'- diisopropyl)diacetic acid (L) was synthesized and characterized by eloemental analysis, IR and ^1H NMR. The proptonation constants of L, the stability constants of La(Ⅲ)-L binary complexes have been determined by pH titration method at (25±0.1)℃, I=0.1mol·L^-^1 NaNO~3. The interaction of the lanthanum(Ⅲ) complex with calf- thymus DNA was studied by electronic spectra. Using ethidium bromide as a fluorescence probe, the binding mode of the lanthanum(Ⅲ) complex with calf-thymus DNA was studied spectroscopically. For comparison, the same measurements were carried out with La(Ⅲ)-Phen [La(Ⅲ)-1,10-phenanthroline complex] and La(Ⅲ)-Val [La(Ⅲ)-l-valine complex]. the results indicate that the lanthanum(Ⅲ) complex possibly interacts with calf-thymus DNA by both intercalative and covalent binding.

Key words: PHENANTHROLINE P, VALINE, LANTHANUM COMPLEX, DEOXYRIBONUCLEIC ACID, SPECTROMETRY, ELEMENTAL ANALYSIS, INFRARED SPECTROPHOTOMETRY, PROTON MAGNETIC RESONANCE SPECTROMETRY