A Bisamide Derivative of [Mn(1, 4‐DO2A)] – Solution Thermodynamic, Kinetic, and NMR Relaxometric Studies. Issue 8 (15th February 2016)

• Record Type: Journal Article
• Authors: Forgács, Attila; Tei, Lorenzo; Baranyai, Zsolt; Tóth, Imre; Zékány, László; Botta, Mauro
• Is Part Of: European journal of inorganic chemistry. Issue 8(2016)
• Page Start: 1165
• Page End: 1174
• Publication Date: 2016-02-15
• Subjects: Macrocyclic ligands -- Manganese -- Magnetic resonance imaging -- Imaging agents -- Kinetics; Chemistry, Inorganic -- Periodicals; Organometallic chemistry -- Periodicals; Bioinorganic chemistry -- Periodicals; Solid state chemistry -- Periodicals; 546
• DOI: 10.1002/ejic.201501415
• Languages: English
• ISSNs: 1434-1948

Abstract

Abstract: A new 1, 4‐DO2A‐bisamide [1, 4‐DO2AM; 1, 4‐DO2A = 2, 2′‐(1, 4, 7, 10‐tetraazacyclododecane‐1, 4‐diyl)diacetic acid] ligand was synthesized, and its Mn II complex was prepared and investigated in detail by solution thermodynamic, kinetic, and 1 H and 17 O NMR relaxometric measurements. Although the stability constant of [Mn(1, 4‐DO2AM)] 2+ (log K MnL = 12.64) is 2.5 log K units lower than that of [Mn(1, 4‐DO2A)], its kinetic inertness, investigated through its transmetallation reactions with Zn 2+ ions, is much higher. In particular, the dissociation half‐life ( t 1/2 ) of [Mn(1, 4‐DO2AM)] 2+ is ten times higher than that of [Mn(1, 4‐DO2A)] ( t 1/2 = 556 vs. 49 h, pH 7.4). The longer rotational correlation time ( τ R = 53 ps) for [Mn(1, 4‐DO2AM)] 2+ is mainly responsible for the slightly higher (+20 %) relaxivity ( r 1 = 2.5 mM –1 s –1, 20 MHz, 25 °C) with respect to that of [Mn(1, 4‐DO2A)]. Notably, the water exchange rate of the coordinated water molecule is one order of magnitude slower than that of [Mn(1, 4‐DO2A)] ( 298 k ex = 115 ± 6 × 10 6 s –1 ). Finally, the dynamic properties of [Zn(1, 4‐DO2AM)] were investigated by NMR spectroscopy, and the decoordination and arm‐rotation processes of the acetamide pendant arms were followed. Abstract : The solution thermodynamics, kinetics, and 1 H and 17 O NMR relaxometric properties of the Mn II complex of a 1, 4‐DO2A‐bisamide [1, 4‐DO2A = 2, 2′‐(1, 4, 7, 10‐tetraazacyclododecane‐1, 4‐diyl)diacetic acid] ligand are investigated. The introduction of acetamide arms instead of acetic acid groups results in greater kinetic inertness and higher relaxivity, which compensate for a lower thermodynamic stability.