Ab initio molecular orbital study of the complexing behavior of N-ethyl-1-naphthalenecarboxamide as fluorescent chemosensors for alkali and alkaline earth metal ions

A kinetic model of thin-film fluorescent sensors for strategies to enhance chemical selectivity

Thin film chemical sensors are widely used in environmental and industrial applications due to their scalable fabrication and high sensitivity, however they often suffer from low specificity limiting their ability to discriminate between analytes. In this paper we analyse the influence of molecular diffusion and binding interactions on the optical response of thin film fluorescent chemical sensors. We use a computational model to calculate the dynamics of fluorescence quenching due to sorption and desorption of analyte molecules, and compare this with experimental measurements of a conjugated polymer sensor for nitroaromatic vapour. We find that to increase selectivity, such sensors should use thinner films, analyses should concentrate on the recovery dynamics, and sensor materials should be chosen to provide sensor-analyte combinations where diffusion is hindered by strong sensor-analyte binding interactions.

Protonation Equilibria of N-Acetylcysteine

The acid base protonation equilibria of N-acetylcysteine (Nac) and its equilibrium constants in water solutions were determined by the Hyperquad 2008 software assessment from the pH potentiometry data, which provides a diversity of statistics presentations. The effect of a number of organic solvents on the acid base protonation processes was also examined. The solution equilibria of N-acetylcysteine (Nac) were studied at T = 298.15 K in water (w ₁) + organic liquid mixtures [100 w ₂ = 0, 20, 40, 60, and 80%] with an ionic strength of I = 0.16 mol·dm^-3 NaNO₃. Also, the organic solvent's influence was studied based on the Kamlet-Taft linear solvation energy relationship. The experimental results were compared with theoretical ones obtained via the Gaussian 09 calculation computer program. The protonation equilibria of Nac were found to be important in the progress of separation systems in aqueous and non-aqueous ionic solutions. Nac showed a likely good metal dibasic chelating bioligand as the DFT calculations proved two binding sites. Spectrophotometry evaluation was also done for N-acetylcysteine bioligands at various pH values in water solutions then its absorbance ratio was measured.

The "Off-On" Fluorescence Detection of Alkaline Earth Metal Ions by Using 1-Naphthylacetanilide Derivatives: New Cation Sensors Based on Oligo-ethylene Oxides Connecting 1-Naphthylacetanilide at Its Terminals

New fluorescent ionophores containing the 1-naphthylacetanilide moiety based on oligo-ethylene oxide (1(4) and 1(5)) have been synthesized, and their photochemical behaviors have been studied. In the absence of a metal ion, the 1-naphthylacetanilide moiety showed a weak fluorescence emission (fluorescence "off state"). However, complexation with Ca(2+) induced a large enhancement effect on the fluorescence intensity of 1(4) and 1(5) from the naphthalene ring (fluorescence "on" state). This behavior can be explained in terms of a similar twisted intramolecular charge-transfer relaxation mechanism. Such "off-on" fluorescence responses of 1(4) and 1(5) provide the digital detection of alkaline earth metal ions.

Fluorescent photoinduced electron transfer (PET) sensing molecules with p-phenylenediamine as electron donor

Fluorescent photoinduced electron-transfer sensors were made from p-phenylenediamine-substituted azacrown ethers attached with a dansyl group, in which the p-phenylenediamine moiety serves as electron donor and the dansyl group acts as the acceptor. Chelation-enhanced fluorescence was observed upon addition of metal salts. Selective fluorescence response was observed for Mg(2+) and/or Ca(2+) versus Na(+) and K(+) due to size match and charge density sensitivity of the p-phenylenediamine moiety.