Self‐association, tautomerism and E–Zisomerization of isatin–phenylsemicarbazones – spectral study and theoretical calculations

Abstract

The self-association and tautomerism of (E)-isatin-3-4-phenyl(semicarbazone) Ia and (E)-N-methylisatin-3-4-phenyl (semicarbazone) IIa were investigated in solvents of various polarity. In weakly interacting non-polar solvents, such as CHCl 3 and benzene, phenylsemicarbazone concentrations above 1×10 À5 mol dm À3 result in the formation of dimers or higher aggregates of E-isomers Ia and IIa. This aggregate formation prevents room temperature E-Z isomerization of la and IIa to more stable Z-isomers. In contrast to the situation in non-polar solvents, E-Z isomerization from the monomeric form of phenylsemicarbazone Ia and IIa E-isomers occurs in highly interactive polar solvents including MeOH and DMF only at temperatures above 70°C. Moreover, decrease in phenylsemicarbazone concentration below 1×10 À4 mol dm À3 in these highly solute-solvent interacting systems leads to aggregate dissociation, and a new hydrazonol tautomeric form with a high degree of conjugation predominates in these solutions. Theoretical calculations confirm obtained experimental results.

Fluorescence of isatin N‐phenylsemicarbazones: aggregation and hydrazide–hydrazonol tautomerism

“…Ia and IIa UV–Vis spectra clearly indicate the absence of hydrazonol C form in CHCl 3 . The fluorescent intensity dependence on Ia and IIa concentration at 330 nm excitation can be explained by concurrent monomer B and associated form A excitation because of the associated form A concentration increase with increasing overall semicarbazone concentration.…”

“…There are several types of tautomeric equilibria: keto–enol, imine–enamine, nitroso–oxime, azo‐hydrazone, ammonium–azonium, lactim–lactam and so on . In our few previous works, we investigated the interesting solution behavior of substituted isatin N ‐phenylsemicarbazones subjected to unusual hydrazide–hydrazonol tautomeric equilibrium . Depending on concentration and solvent polarity, isatin N ‐phenylsemicarbazones occur in solution as the associated hydrazide form A, monomeric hydrazide form B and a hydrazonol form C .…”

“…Depending on concentration and solvent polarity, isatin N ‐phenylsemicarbazones occur in solution as the associated hydrazide form A, monomeric hydrazide form B and a hydrazonol form C . These forms are in equilibrium (Scheme ) …”

Interações de ligantes imínicos com peptídeos amiloides e metais essenciais implicados em processos neurodegenerativos

“…Diversas espécies são prováveis para hidrazonas derivadas do grupamento oxindólico, visto que podem apresentar além da isomeria geométrica, tautomeria [70,101] . [101] .…”

“…As energias destas interações podem afetar significativamente as propriedades eletrônicas da molécula no que tange a formação de tautômeros ou isômeros. Estas características podem ser encontradas tanto em solução quanto no sólido [96,101] . Propriedades similares aos nossos compostos foram observadas em outros estudos.…”