The molecular structure of anionic species of 2,4,5,7‐tetranitrofluorescein as studied by electrospray ionisation, nuclear magnetic resonance and X‐ray techniques

Abstract

Among the fluorescein dyes, the behaviour of their nitro derivatives in solution is most unusual, and yet at the same time rarely studied. In this study, their 13 C nuclear magnetic resonance and electrospray spectra are reported, which confirm, in concert with their ultraviolet-visible spectra, the molecular structures of the neutral and ionic species of 2,4,5,7-tetranitrofluorescein observed in different solvents and at various pH values. A peculiar property of this dye consists in its lactonisation of the double-charged anion, contrary to the wellknown coloured and fluorescent dianions of fluorescein, eosin, etc. Also, this dianion-lactone exhibits high ability for opening the pyran ring. This cleavage takes place at much lower pH values as compared with those for fluorescein and its halogen derivatives. The ruptured species can be formed as either lactone or carbinol; the latter appears as a result of the nucleophilic attack of a HO À on the central carbon atom. The corresponding molecular structures are identified via the electrospray method and X-ray analysis. The behaviour of some other nitrofluoresceins in alkaline media is also considered. Coloration TechnologySociety of Dyers and Colourists † Just now, an article "Syntheses of novel acid-base indicators by nitration of phenolphthalein and fluorescein" by Y. Negishi,

Protolytic Equilibria in Organized Solutions: Ionization and Tautomerism of Fluorescein Dyes and Related Indicators in Cetyltrimethylammonium Chloride Micellar Solutions at High Ionic Strength of the Bulk Phase

“…The samples of 4,5-dinitrofluorescein, 4,5-dinitro-2,7-dibromofluorescein, 4,5-dibromo-2,7-dinitrofluorescein, 4,5-dibromo-2-nitrofluorescein, 2,4,5,7-tetranitrofluorescein thiofluorescein, 2,4,5,7-tetrabromothiofluorescein, 4-nitrothiofluorescein, 4,5-dinitrothiofluorescein, 4,5-dibromo fluorescein, 3 ,4 ,5 ,6 -tetrabromofluorescein, and 4,5-dinitro-N-ethylazafluorescein were used in previous studies [15,37,38,47,48]. They were synthesized in the laboratory of Prof. A.V.…”

“…Involving of nitro derivatives in research led to interesting results. In this case, both R 2− and HR − anions may form lactonic anions L 2− and HL − [15,29,37,38,47,48]. The lactonic structure of 2,4,5,7-tetranitrofluorescein dianion R 2− in solution was proved using IR-and NMR-spectroscopy [37,38].…”

“…Much more complicated is the equilibrium in the case of the main group of fluorescein dyes with the free COOH group. Basing on a series of our previous studies [7,15,31,[37][38][39][40][41][42]47,48,57], we propose the following generalized scheme of a detailed protolytic equilibrium (Scheme 4). The symbols H3R + , H2R, HR − , and R 2− designate the stoichiometric composition irrespective of the molecular (ionic) structure.…”

“…Accordingly, new works appear on the protolytic and spectral properties of both previously known [28][29][30][31][32] and new [25,[33][34][35] or previously little studied [36][37][38][39][40][41][42] fluorescein compounds, including data analysis in the gas phase [43][44][45].…”

“…The most widely studied and applied are fluorescein and its halogen derivatives [14,[16][17][18][19][20][21][22][23][26][27][28][30][31][32]39]. Some new properties of nitro derivatives [15,29,37,38,46,47] and thio analogues of fluorescein [48] have been also described. Besides, these representatives of fluorescein group have been left poorly studied up to now, the more so, that recently a new kind of tautomerism has been revealed for nitro derivatives: the chain-ring tautomerism of anions [47].…”