In 2022,Franco, Leandro Rezende; Toledo, Kalil Cristhian Figueiredo; Matias, Tiago Araujo; Benavides, Paola Andrea; Cezar, Henrique Musseli; Araujo, C. Moyses; Coutinho, Kaline; Araki, Koiti published an article in Physical Chemistry Chemical Physics. The title of the article was 《Unraveling the acid-base characterization and solvent effects on the structural and electronic properties of a bis-bidentate bridging ligand》.Formula: C6H5NO2 The author mentioned the following in the article:
Understanding the interactions and the solvent effects on the distribution of several species in equilibrium and how it can influence the 1H-NMR properties, spectroscopy (UV-vis absorption), and the acid-base equilibrium can be especially challenging. This is the case of a bis-bidentate bridging ligand bis(2-pyridyl)-benzo-bis(imidazole), where the two pyridyl and four imidazolyl nitrogen atoms can be protonated in different ways, depending on the solvent, generating many isomeric/tautomeric species. Herein, we report a combined theor.-exptl. approach based on a sequential quantum mechanics/mol. mechanics procedure that was successfully applied to describe in detail the acid-base characterization and its effects on the electronic properties of such a mol. in solution The calculated free-energies allowed the identification of the main species present in solution as a function of the solvent polarity, and its effects on the magnetic shielding of protons (1H-NMR chem. shifts), the UV-vis absorption spectra, and the acid-base equilibrium constants (pKas) in aqueous solution Three acid-base equilibrium constants were exptl./theor. determined (pKa1 = 1.3/1.2, pKaa2 = 2.1/2.2 and pKaa5 = 10.1/11.3) involving mono-deprotonated and mono-protonated cis and trans species. Interestingly, other processes with pKaa3 = 3.7 and pKaa4 = 6.0 were also exptl. determined and assigned to the protonation and deprotonation of dimeric species. The dimerization of the most stable neutral species was investigated by Monte Carlo simulations and its electronic effects were considered for the elucidation of the UV-vis absorption bands, revealing transitions mainly with the charge-transfer characteristic and involving both the monomeric species and the dimeric species. The good matching of the theor. and exptl. results provides an atomistic insight into the solvent effects on the electronic properties of this bis-bidentate bridging ligand. In the experimental materials used by the author, we found Picolinic acid(cas: 98-98-6Formula: C6H5NO2)
Picolinic acid(cas: 98-98-6) is used in the preparation of 2-Aminodihydro[1,3]thiazines as BACE 2 inhibitors and their preparation and use in the treatment of diabetes.Formula: C6H5NO2