Solvatochromism and prototropism in methyl 6-aminonicotinate: failure to observe amine-imine phototautomerism in solvents

Excited state proton transfer based fluorescent molecular probes and their application in studying lipid bilayer membranes

The distribution and prototropic equilibria of 1-naphthol (NpOH) in lipid bilayer membrane.

Application of Fluorescence Emission for Characterization of Albendazole and Ricobendazole Micellar Systems: Elucidation of the Molecular Mechanism of Drug Solubilization Process

Albendazole (ABZ) and ricobendazole (RBZ) are referred to as class II compounds in the Biopharmaceutical Classification System. These drugs exhibit poor solubility, which profoundly affects their oral bioavailability. Micellar systems are excellent pharmaceutical tools to enhance solubilization and absorption of poorly soluble compounds. Polysorbate 80 (P80), poloxamer 407 (P407), sodium cholate (Na-C), and sodium deoxycholate (Na-DC) have been selected as surfactants to study the solubilization process of these drugs. Fluorescence emission was applied in order to obtain surfactant/fluorophore (S/F) ratio, critical micellar concentration, protection efficiency of micelles, and thermodynamic parameters. Systems were characterized by their size and zeta potential. A blue shift from 350 to 345 nm was observed when ABZ was included in P80, Na-DC, and Na-C micelles, while RBZ showed a slight change in the fluorescence band. P80 showed a significant solubilization capacity: S/F values were 688 for ABZ at pH 4 and 656 for RBZ at pH 6. Additionally, P80 micellar systems presented the smallest size (10 nm) and their size was not affected by pH change. S/F ratio for bile salts was tenfold higher than for the other surfactants. Quenching plots were linear and their constant values (2.17/M for ABZ and 2.29/M for RBZ) decreased with the addition of the surfactants, indicating a protective effect of the micelles. Na-DC showed better protective efficacy for ABZ and RBZ than the other surfactants (constant values 0.54 and 1.57/M, respectively), showing the drug inclusion into the micelles. Entropic parameters were negative in agreement with micelle formation.

Electro-catalytic degradation pathway and mechanism of acetamiprid using an Er doped Ti/SnO2–Sb electrode

Schematic of the degradation pathway of acetamiprid, which shows the molecular structures of the intermediate species.

Solvatochromic, spectroscopic and DFT studies of a novel synthesized dye: l-(4-Dimethylaminophenyl)-2-(5H-phenanthridine-6-ylidene)-ethanone (6-KMPT)

A novel solvatochromic l-(4-dimethylaminophenyl)-2-(5H-phenanthridine-6-ylidene)-ethanone (6-KMPT) dye was synthesized and characterized by means of NMR, IR, mass spectroscopies. Also, it was studied using UV-vis and fluorescence spectroscopic methods in a broad range of solvents. UV-vis results showed that increasing 6-KMPT concentration dose not cause molecular aggregation in chloroform. Varying the temperature in the range from 25 to 55 degrees C dose not have a significant effect on the characteristics bands of the molecule. However, in the presence of surfactant SDS the UV-vis spectrum undergoes drastic alteration. This phenomenon is related to the removal of hydrogen atom from nitrogen atom of phenanthridine moiety. Fluorescence spectroscopic results showed that 6-KMPT has an appreciable fluorescence quantum yield. The effect of excitation wavelength, concentration of 6-KMPT, concentration of oxygen and surfactants (SDS, C(16)TAB, CPC, Brij-35) were studied. Further results showed that the fluorescent behavior of 6-KMPT can be attributed to planarity induced by intramolecular hydrogen bonding which can in turn be destroyed by anionic surfactant SDS. Results showed that oxygen and SDS can be operate as fluorescence quencher compounds for 6-KMPT and Stern-Volmer plot showed a straight line. Fluorescence polarization and anisotropy of 6-KMPT in chloroform strongly depend on concentration. The 6-KMPT exhibits solvent-induced spectral band shifts. By using Lippert equation, the change of dipole moment of 6-KMPT molecule upon excitation was estimated as 6.39 D. Furthermore, absorption, fluorescence emission, Stokes shift values and fluorescence quantum yield (Phi(F)) of 6-KMPT in different solvents of polarity were determined. Maximum Phi(F) value of 0.372 for 6-KMPT molecule was found in ethanol solvent with a Stokes shift of 2446.8 cm(-1). The results of DFT calculations showed that tautomer 2c (enol) energetically is more stable than tautomer 2b (keto) in gas phase whereas it was vice versa in CHCl(3).