Spectroscopic and DFT Study on the Interaction System of Vanadium with l-Proline in Aqueous Solution

Betaine mediated enhancement of thermal stability and acidity tolerance of vanadium(V) solutions

A panel of novel vanadium(IV)-betaine complexes has been synthesized according to new and efficient methodologies and characterized through both spectroscopic techniques and thermal analyses. Vanadium(IV)-betaine solutions have been electrochemically oxidized and the effect of betaine ligands on the thermal and pH stability of vanadium(V) solutions has been evaluated under different temperature and acidity conditions. The obtained results displayed a remarkable effect for both of the examined parameters, achieving the preparation of aqueous vanadium(V) solutions displaying long term stability at more than 55 °C under mild acidic conditions. The species formed in the betaine rich vanadium(V) solutions have been sprectroscopically identified in relationship with the acidity of the solution, and the obtained results were confirmed through computational techniques. Vanadium-betaine based solutions have been finally tested in a lab-scale redox flow battery setup, providing preliminary insight into the possible use of this type of electrolyte in VRFBs.

DFT and MP2 investigations of L-proline and its hydrated complexes

A theoretical study of L-proline-nH(2)O (n = 1-3) has been performed using the hybrid DFT-B3LYP and MP2 methods together with the 6-311++G(d,p) basis set. The results show that the P2 conformer is energetically favorable when forming a hydrated structure, and the hydration of the carboxyl group leads to the greatest stability. For hydrated complexes, the adiabatic and vertical singlet-triplet excitation energies tend to decrease with the addition of water molecules. The hydration energy indicates that in the hydrated complexes the order of stability is: binding site 2 > binding site 1 > binding site 3, and binding site 12 > binding site 23 > binding site 13. As water molecules are added, the stabilities of these hydrated structures gradually increase. In addition, an infrared frequency analysis indicated that there are some differences in the low-frequency range, which are mainly dominated by the O-H stretching or bending vibrations of different water molecules. All of these results should aid our understanding of molecular behavior and provide reference data for further studies of biological systems.