Spectroscopic Studies of Intramolecular Proton Transfer in 2-(4-Fluorophenylamino)-5-(2,4-Dihydroxybenzeno)-1,3,4-Thiadiazole

Abstract

Spectroscopic studies of the biologically active compound 2-(4-fluorophenylamino)-5-(2,4-dihydroxybenzeno)-1,3,4-thiadiazole (FABT), have been performed. Absorption studies in the UV-Vis region for FABT in polar solvents, like water or ethanol, exhibit the domination of the enol form over its keto counterpart, with a broad absorption band centered around 340 nm. In non-polar solvents such as n-heptane or heavier alkanes the 340 nm absorption band disappears and an increase of the band related to the keto form (approximately 270 nm) is observed. Fluorescence spectra (with 270 nm and 340 nm excitation energies used) show a similar dependence: for FABT in 2-propanol a peak at about 400 nm dominates over that at 330 nm while in n-heptane this relation is reversed. The solvent dependent equilibrium between the keto and enol forms is further confirmed by FTIR and Raman spectroscopies. As can be expected, this equilibrium also shows some temperature dependences. We note that the changes between the two tautomeric forms of FABT are not related to the permanent dipole moment of the solvent but rather to its dipole polarizability.

Spectroscopic Studies of the Quality of Fatty Acid Methyl Esters Derived from Waste Cooking Oil

“…1,742 cm -1 (1,743 cm -1 for the rapeseed oil methyl esters) can be seen for all the analysed esters [37][38]. Noteworthy are the distinct differences in the shape of the bands at 1,770-1,670 cm -1 in the spectrum of the heated and nonheated sunflower oil methyl esters (Fig.…”

“…The potential of the application of the technique for determining FAME content in diesel fuel has been evidenced in the literature. It is associated with the fact that absorption in the C=O [36][37] carbonyl group band (1,700-1,800 cm -1 ) in hydrocarbon fractions is relatively low or absent, whereas absorption of FAME in this region is very intense.…”

Spectroscopic and theoretical studies of fluorescence effects induced by the ESIPT process in a new derivative 2-Hydroxy-N-(2-phenylethyl)benzamide – Study on the effects of pH and medium polarity changes

“…The spectra were normalized at the absorption band maximum. As we can see, the band maximum, corresponding to the π!π � electronic transition [47] (approx. 300 nm), clearly shifts towards the shorter wavelengths, from 301 to 296 nm, depending on the addition of the polar (protic) solvent.…”

The Use of Moldavian Dragonhead Bagasse Waste in Extruded Products

“…Primarily, the main raw material for medicinal purposes is the leaves and flowers of Dracocephalum moldavica used as infusion to treat stomach and liver disorders, headaches and congestion, coronary heart disorders and hypertension (Dastmalchi et al 2007;Yang et al 2014). There are some latest reports showing the application of dragonhead extracts as a therapeutic agent in many dysfunctions: cardioprotective, antiplatelet, neuroprotective, sedatives and anti-aging (Jiang et al 2014;Gagoś et al 2011). Dragonhead seeds are a good source of protein, lipids and fiber (Aprotosoaie et al, 2016;Dziki et al 2013).…”