Keto - Enol Tautomerism as a Polarity Indicator in Ionic Liquids

2004 ◽  
Vol 57 (2) ◽  
pp. 149 ◽  
Author(s):  
Martyn J. Earle ◽  
Brian S. Engel ◽  
Kenneth R. Seddon
Keyword(s):  
Ionic Liquids ◽  
Ground State ◽  
Tautomeric Equilibrium

The keto–enol tautomeric equilibrium for pentane-2,4-dione has been explored in several ionic liquids and these data have been used to give an indication of their polarities in the ground state. The results suggest higher apparent polarities than have been previously indicated by the use of solvatochromatic dyes.

The keto–enol tautomerization of ethyl acetoacetate in choline ionic liquids: the role of cation and anion in switching the tautomeric equilibrium

2021 ◽  
Vol 23 (12) ◽  
pp. 7386-7397
Author(s):  
Madhu Deepan Kumar ◽  
Madhavan Jaccob
Keyword(s):  
Ionic Liquids ◽  
Ethyl Acetoacetate ◽  
Tautomeric Equilibrium ◽  
Specific Role ◽  
The Individual

In the present study, the specific role of the individual cations and anions of ionic liquids in shifting the tautomeric equilibrium of EAA was investigated.

Fluorescence Emission Properties of the Cation of 4-Aminopyrazole(3,4-d) pyrimidine, an Adenine Analogue: Evidence for Phototautomerism

1980 ◽  
Vol 35 (11-12) ◽  
pp. 878-889 ◽  
Author(s):  
Jacek Wierzchowski ◽  
Marian Szczęśniak ◽  
David Shugar
Keyword(s):  
Ground State ◽  
Emission Band ◽  
Aqueous Media ◽  
Fluorescence Emission ◽  
Emission Spectra ◽  
Wavelength Dependence ◽  
Tautomeric Equilibrium ◽  
Excitation Spectra ◽  
Tautomeric Forms ◽  
Wavelength Emission

A study has been made of the emission spectra at room temperature, in aqueous and alcoholic media, of 4-aminopyrazolo(3,4-d)pyrimidine (APP) and some of its methylated derivatives. The cationic forms APPH+, N2-methyl-APPH+ and N7-methyl-APPH+ exhibit intense fluorescence un­der these conditions, the first two exhibiting excitation spectra which differ from the absorption spectra, pointing to the existence of a tautomeric equilibrium in the ground state. From the shape of the excitation spectra, and comparisons with methylated analogues in fixed tautomeric forms, it follows that the emission of APPH+ originates exclusively from the species N(2)-H,N(7)-H+, the other forms being non-fluorescent. The proportion of the emitting species, calculated from the ex­citation wavelength dependence of the quantum yield, is in good agreement with data for the ground state. The emission spectrum of APPH+ in aqueous medium consists of two bands with λmax 360 nm and 430 nm, which exhibit identical excitation spectra, but are quenched to different extents by H3O+. The 430 nm emission band is absent in alcoholic media. A similar behaviour is exhibited by N7-methyl-APPH+, whereas the neutral form of this analogue exhibits only the 430 nm band. These results indicate that the long wavelength emission band of APPH+ originates from the rare tautomeric species N(7)-H formed in the excited state by photodissociation of the N(2)-H proton from the species N(2)-H,N(7)-H+. This is further confirmed by results obtained with the aid of the basicity method, as well as by salt efects in non-aqueous media. Consideration is given to the possibility of such processes occurring in other analogues of nucleic acid derivatives.

The Effect of Pre-solvation in the Ground State on Photoinduced Electron Transfer in Ionic Liquids

2014 ◽  
Vol 43 (9-10) ◽  
pp. 1550-1560 ◽  
Author(s):  
Masayasu Muramatsu ◽  
Satoe Morishima ◽  
Tetsuro Katayama ◽  
Syoji Ito ◽  
Yutaka Nagasawa ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Ionic Liquids ◽  
Ground State ◽  
Photoinduced Electron Transfer

Studies of the effect of hydrogen bonding on the absorption and fluorescence spectra of all-trans-retinal at room temperature

1992 ◽  
Vol 70 (3) ◽  
pp. 880-887 ◽  
Author(s):  
S. Alex ◽  
H. Le Thanh ◽  
D. Vocelle
Keyword(s):  
Raman Spectroscopy ◽  
Hydrogen Bonding ◽  
Ground State ◽  
Fluorescence Spectra ◽  
Room Temperature ◽  
Tautomeric Equilibrium ◽  
Absorption And Fluorescence Spectra ◽  
Large Excess ◽  
Vis Spectroscopy ◽  
Uv Visible

Ultraviolet (UV)–visible and fluorescence spectra were obtained for complexes of ATR and TFA at different ratios and in four different solvents: hexane, chloroform, dichloromethane, and methanol. In the first three solvents, a large excess of TFA generates retinylic cations that absorb from 459 to 600 nm. Also, in CHCl3, Raman spectroscopy and fluorescence indicate that some aggregated species like ATR:(TFA)n, with λmax of ca. 470 nm, are present. In methanol, TFA protonates the solvent and it is CH3O+H2 which interacts with ATR so that only blue-shifted H-bonded ATR is present. From these results, it is shown that in the tautomeric equilibrium [Formula: see text], form (1) is always favored in the ground state whatever the solvent. In the excited state in hexane and in methanol, (1) is rapidly transformed into (2). In CH2Cl2 and CHCl3, this transformation is absent so that there is no energy dissipation, with the result that the retinal complexes become more unstable. Keywords: all-trans-retinal, fluorescence, H-bonds, trifluoroacetic acid, UV–vis spectroscopy.

Renilla Bioluminescence: A Morphologic Approach to the Location of Photocytes

1974 ◽  
Vol 32 ◽  
pp. 208-209
Author(s):  
Ben O. Spurlock ◽  
Milton J. Cormier
Keyword(s):  
Excited State ◽  
Ground State ◽  
Molecular Basis ◽  
Light Emission ◽  
Chemical Basis ◽  
Electronic Excited State ◽  
Colonial Form ◽  
The Common ◽  
Eighteenth And Nineteenth Centuries ◽  
Catalyzed Oxidation

The phenomenon of bioluminescence has fascinated layman and scientist alike for many centuries. During the eighteenth and nineteenth centuries a number of observations were reported on the physiology of bioluminescence in Renilla, the common sea pansy. More recently biochemists have directed their attention to the molecular basis of luminosity in this colonial form. These studies have centered primarily on defining the chemical basis for bioluminescence and its control. It is now established that bioluminescence in Renilla arises due to the luciferase-catalyzed oxidation of luciferin. This results in the creation of a product (oxyluciferin) in an electronic excited state. The transition of oxyluciferin from its excited state to the ground state leads to light emission.

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