Two types of conformational dynamics and thermo-sensor properties of praseodymium-DOTA by 1H/13C NMR

• Published in: Inorganica Chimica Acta 2019-02, Vol.486, p.340-344
• Main Authors: Babailov, Sergey P., Zapolotsky, Eugeny N., Kruppa, Alexander I., Stabnikov, Pavel A., Godovikov, Ivan A., Bocharov, Eduard V., Fomin, Eduard S.
• Format: Article
• Language: English
• Subjects: Activation energy; Aqueous solutions; Carbon 13; Conformation dynamics; Dependence; DOTA; Free energy; Free energy of activation; Gadolinium; Lanthanide complexes; Lanthanide-induced shifts in NMR spectra; Molecular dynamics; Molecular magnet; NMR; NMR/MRI temperature sensor; Nuclear magnetic resonance; Praseodymium
• ISSN: 0020-1693; 1873-3255
• DOI: 10.1016/j.ica.2018.10.044

The Praseodymium-DOTA complex has been investigated using the dynamic 1H and 13C NMR methods. Two types of intramolecular dynamics were assigned to: interconversion of SAP and TSAP conformers {with ΔG≠(298 K) 50 ± 3 and 54 ± 4 kJ mol−1 (according to 1H and 13C NMR respectively)} and enantiomerization (with ΔG≠(298K) = 65 ± 2 kJ mol−1). Coordination compound investigated in the paper represents new type of thermometric NMR sensors. [Display omitted] •The Praseodymium-DOTA complex has been investigated using the dynamic 1H and 13C NMR methods.•Two types of intramolecular dynamics were assigned to: interconversion of SAP and TSAP conformers {with ΔG≠(298 K) 50 ± 3 and 54 ± 4 kJ mol−1 (according to 1H and 13C NMR respectively)} and enantiomerization (with ΔG≠(298 K) = 65 ± 2 kJ mol−1). In aqueous medium, [Pr(H2O)(DOTA)]− (I) undergo a intramolecular interconversion between two conformers (here DOTA = 1, 4, 7, 10-tetraaza-1, 4, 7, 10-tetrakis (carboxymethyl)cyclododecan; n = 0, 1, 2). Two types of molecular dynamic processes were found {enantiomerization and interconversion of the square-anti-prismatic (SAP) to twisted-square-anti-prismatic conformers (TSAP)}. The free energies of activation of the SAP to TSAP interconversion (for I complex) are found to be 50 ± 3 and 54 ± 4 kJ mol−1 (according to 1H and 13C NMR respectively). And, the activation free energy of enantiomerization is ΔG≠298 = 65 ± 2 kJ mol−1. It was evaluated that the activation energy of enantiomerization in [Gd(H2O) (DOTA)]− (II) is 64 ± 2 kJ mol−1 (by analysis of the dependence of the free activation energy on the ionic radius of other lanthanide ions). The experimental paramagnetic LIS values of I are well fitted by linear dependence on 1/T. It was found that I may be used as NMR thermometric sensors for controlling the local temperature in aqueous medium.