Abstract: Diethylene-triaminopentaacetate his(isoniazid) (Gd(DTPA-BIN)) was synthesised as acontrast agent for magnetic resonance imaging (MRI). The protonation process of DTPABIN was proposed in the order of the central amine, the terminal ammes, the central carboxyl, the terminal carboxyl, the other terminal carboxyl and central amine. Based on ¹HNMR titration analysis, the sum of the protonation constants for DTPA-BIN is obviouslyhigher than that of DTPA-BMA, which might reflect that the stability of Gd(DTPA-BIN)would be higher than Gd(DTPA-BMA). The water relaxation enhancement behavior of Gd(DTPA-BIN) in aqueous and in BSA solution has been studied. The results indicate that Gd(DTPA-BIN) can integrate non-covalently with BSA mainly in forms of (Gd(DTPA-BIN))·BSA and (Gd (DTPA-BIN))₂ BSA for which the apparent equilibrium constants are 0. 0149mmol^-1·L and 0. 00326mmol^-2·L² respectively. This method would be used tostudy the interactivities between protein and contrast agent.

Key words: Gd (DTPA-BIN), Protonation prccers, Bovine serum albumin, Relaxation