A solid state and solution NMR study of the tautomerism in hydroxyquinoline carboxylic acids

Abstract

Some hydroxyquinoline carboxylic acids and their conjugate acids and bases were characterized by 13C and 15N NMR spectroscopy in solution and in the solid state. Differences in 13C and, in particular, 15N chemical shift patterns allow to distinguish between individual tautomers and confirm the presence of zwitterionic species in the solid state. Solution NMR spectra in dimethyl sulfoxide (DMSO) show effects resulting as a consequence of dynamic exchange and suggest the presence of an equilibrium mixture of hydroxyquinoline carboxylic acid and zwitterionic hydroxyquinolinium carboxylate tautomers.

Synthesis, spectroscopy and computational studies of some biologically important hydroxyhaloquinolines and their novel derivatives

“…Bond lengths (Å) donating and accepting sites between the pyridine and hydroxylic functions, mimicking previously described behaviors of some hydroxyquinoline carboxylic acids [10]. Compound 1a crystallises in space group Pbca (no.…”

“…The development of new and more efficient methodologies to transform hydroxyhaloquinolines to their derivatives which could help to look deeper into reasons of HIV inhibition is a subject of continuous interest in our laboratory [10,[13][14][15][16][17][18]. To understand their reactivity we compared selected geometric parameters such as bond lengths and bond angles presented on Tables 1-5.…”

“…Recently we studied 13 C and 15 N NMR spectra demonstrating proton transfer reactions between the pyridine and carboxylic acid functions of some hydroxyquinoline carboxylic acids [10]. The 1 H and 13 C NMR spectra of 1a-c, 2a,b and 3a-c displayed readily diagnostic signals from methyl protons and carbon atoms.…”

“…They are a family of polar ligands with peculiar properties since they may change either their hydrogen-bond donating or accepting sites through the protonation/deprotonation processes [10].…”

Synthesis, spectroscopy and computational studies of selected hydroxyquinoline carboxylic acids and their selected fluoro-, thio-, and dithioanalogues

“…X-ray crystal structure analysis showed the presence of hydrogen-bond donating and accepting sites between the pyridine and hydroxyl functional groups. We demonstrated by solution and solid state NMR studies [12] the neutral, cationic and anionic species of hydroxyquinoline carboxylic acids obtained by protonation or deprotonation existed a tautomeric equilibrium, which was evaluated by 13 C and 15 N chemical shifts. It has been shown that the analysis of 13 C and 15 N NMR spectra of hydroxyquinoline carboxylic acids gives insight into proton transfer reactions between the pyridine and carboxylic acid functional groups [12,33].…”