00000caa a22000003i 4500 UP-1685594773862388630 Buklod 20210322194338.0 m | | ta 210322s2019 xx r |||| u|eng d (iLib)UPBAG-00039569058 STII-DOST BAG rda eng ARTICLE-2815 Pineda, Ernest Guiller S. author. Effect of solvent on Gd (DOTA)- complex formation a preliminary investigation [Research note] by Ernest Guiller S. Pineda and Aaron Joseph L. Villaraza. 2019. pages 151-153 illustrations 26 cm text rdacontent unmediated rdamedia volume rdacarrier Includes bibliographical references (page 153) The thermodynamic stability and kinetic inertness of gadolinium-based MRI contrast agents remains an important research topic in the field of radiological contrast agent development. In this study, the kinetics and thermodynamics of Gd3+-complex formation with the macrocyclic ligand DOTA (i.e., 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid) was investigated under aqueous (acetate buffer pH 5.8) and non-aqueous (MeOH) conditions. Using Job?s method of continuous variation, solutions were prepared of increasing mole fraction of Gd3+ relative to xylenol orange (XO, i.e., 3,3′-bis[N,N-bis(carboxymethyl)aminomethyl]-o-cresolsulfonephthalein) in MeOH, and their absorbances were measured at 582nm.The kinetics of complex formation via ligand substitution of DOTA and DO3A (i.e., 1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid) with Gd-XO under aqueous and non-aqueous conditions were determined using UV-Vis spectrophotometry. Furthermore, the thermodynamic parameters of DOTA complexation with Gd3+ for both solvent conditions were compared by measuring the heats of injection using isothermal titration calorimetry. Results of this study demonstrate that XO forms a well-defined 1:1 stoichiometry with Gd3+ regardless of solvent polarity. Meanwhile, the rate of ligand substitution between Gd-XO and the macrocyclic ligand is effectively minimized under non-aqueous conditions (kobs, buffer= 33.9±1.0x10?3 s?1; kobs,MeOH = 5.62±2.22x10?3 s?1). The binding reaction of Gd3+ with DOTA has comparable negative ΔG values in the two solvents (ΔGbuffer= â??9.28±0.57kcal/mol; ΔGMeOH = â??8.19±0.14kcal/mol), suggesting that the reaction is equally spontaneous under both conditions. However, computation of global thermodynamic properties demonstrate that the reaction is entropically-driven in acetate buffer in comparison with MeOH where the reaction is enthalpy-driven. Finally, the nature of solvent has an effect on the metal-to-ligand stoichiometry (N) of the resulting complex, which in acetate buffer (N = 1:1) is lower than that in MeOH (N = 1:2). These results are important in the context of optimizing reaction conditions in the preparation of related MRI contrast agents. (Author's abstract) Chemistry. Binding kinetics. Calorimetry. Gadolinium-based mri contrast agents. Isothermal titration ligand exchange reaction. Solvent effects. Thermodynamics. Villaraza, Aaron Joseph L. author. The Philippine Journal of Science Vol. 148, no. 1, March 2019. Request full-text access via UPB University Library through https://forms.gle/KZjBv7aRtY6jiL5E9 (viewed 22 March 2021) FI UPBAG UPBAG-MAIN ARTICLE-2815 Analytics