Effect of Structure on Charge Distribution in the Isatin Anions in Aprotic Environment: Spectral Study

Abstract

Five isatin anions were prepared by deprotonation of initial isatins in aprotic solvents using basic fluoride and acetate anions (F− and CH3COO−). The F− basicity is sufficient to deprotonate isatin NH hydrogen from all the studied compounds. This process is reversible. In the presence of proton donor solvents, the anions form the corresponding isatins. The isatin hydrogen acidity depends on the overall structure of the isatin derivatives. The anions were characterized by ultraviolet–visible (UV–Vis), Fourier transform infrared (FTIR) and nuclear magnetic resonance (NMR) spectroscopy. Interestingly, the anions form aggregates at concentrations above 10−3 mol·dm−3. Further, the effect of cations on the UV–Vis spectra of the studied anions was studied. Charge transfer and its distribution in the anion depends on the radius and the cation electron configuration. The alkali metal cations, tetrabutylammonium (TBA+), Mg2+ and Ag+, interact with the C-2 carbonyl oxygen of the isatin anion. The interaction has a coulombic character. On the other hand, Cd2+, Zn2+, Hg2+, Co2+, and Cu+ cations form a coordinate bond with the isatin nitrogen.

Isatin-1,8-Naphthalimide Hydrazones: A Study of Their Sensor and ON/OFF Functionality

“…These are compounds which are substituted on the isatin moiety. This substitution leads to more consistent isatin nitrogen free electron pair involvement into the conjugation with the isatin π-electron system [23]. The isatin aromatic system charge density increasing decreases the tautomeric process probability.…”

Effect of a =X-NH-Fragment, (X = C, N), on Z/E Isomerization and ON/OFF Functionality of Isatin Arylhydrazones, ((Arylamino)Methylene)Indolin-2-Ones and Their Anions

“…Hydrazone 1 upon the addition of TBAF provided a Z anion, in which the negative charge was located on the nitrogen of the hydrazone part of the molecule. The immediate formation of this anion was observed on the 1 H-NMR spectra by the presence of characteristic signals [ 14 ] with chemical shifts from 6.85 to 6.6; 8.1 to 8.2 and NH signals from 13 to 9 ( Supplementary Figure S7 ). This anion has a smaller charge transfer than para nitro derivatives.…”

“…In the presence of TBAF, in CHCl 3 , the Z -isomer of hydrazone 3 weakly absorbs at 525 nm and the band maximum at 424 nm is shifted to 408 nm ( Figure 8 b). Such changes in the UV-Vis spectrum are characteristic for isatin aza anions and isatin hydrazone anions [ 14 , 15 ]. This was probably due to the higher stability of the intramolecular hydrogen bond in CHCl 3 and the different solvation or dissociation of TBAF in DMF and CHCl 3 , respectively.…”

“…The acidic nature of the NH hydrogens of isatin arylhydrazones allows us to generate hydrazone anions using a suitable base. By selecting the base and the hydrazone structure, one can specifically generate either the anion of the hydrazone formed by the cleavage of NH hydrogen from the hydrazone moiety of the molecule, or the cleavage of NH hydrogen from isatin [14]. Tetrabutylammonium fluoride (TBAF) is a base capable of generating an anion by cleaving NH hydrogen from a hydrazone molecule (Scheme 6).…”

Uso da técnica SERS para imageamento de complexos de cobre (II) em células >i<HeLa>/i< e para caracterização do complexo de superfície da 5-nitroisatina em prata

“…Para a obtenção da solução do complexo Ag(nisa) 1 ml da solução estoque de nisa foi adicionado à 1 ml de uma solução estoque 10 mM de acetato de prata preparada em DMSO seco, segundo procedimento adaptado descrito por Tisovský et al 106 . Neste caso o ânion acetato é suficientemente básico para abstrair o próton ácido da nisa, formando a espécie aniônica nisa -, que participa do complexo.…”