Highly selective fluorescence 'turn off' sensing of picric acid and efficient cell labelling by water-soluble luminescent anthracene-bridged poly(N-vinyl pyrrolidone).

A novel, water-soluble, luminescent anthracene-bridged AA-type bi-arm poly(N-vinylpyrrolidone) (ATC-PNVP) was synthesized using a click reaction between alkyne-terminated PNVP and 9,10-bis(azidomethyl)anthracene. The resultant anthracene-bridged PNVP (ATC-PNVP) was characterized using 1H NMR, FTIR, UV-Vis, and fluorescence spectroscopic methods and GPC analysis. ATC-PNVP showed effective fluorescence properties in an aqueous medium. It showed highly selective "turn off" sensing behaviour towards picric acid, a common nitro-aromatic explosive, with a wide linear range of detection of 0.01-0.3 mM and LOD value of 0.006 mM in water. ATC-PNVP-based paper sensors also showed very effective detection of picric acid in the concentration range 0.001-1.0 mM. Its binding with bovine serum albumin (BSA) was studied using steady-state, synchronous and 3D fluorescence spectroscopy and this study showed effective quenching of the intrinsic fluorescence of BSA and occurrence of a FRET-type interaction. Furthermore, this luminescent ATC-PNVP was efficiently used as a fluorescence microscopy labelling agent in NIH-3T3 and HeLa cells, and showed greater uptake and hence better fluorescent labelling in the cytosols of the tested cells than free 9,10-bis(azidomethyl) anthracene. The cell viability study also showed a very good biocompatible and non-toxic nature of ATC-PNVP at lower working concentrations towards each of the types of cells tested.

Kinetics of proton transfer between ortho substituted benzoic acids and the carbinol base of crystal violet in toluene. Ortho effect on the reactivity of benzoic acids in apolar aprotic solvents.

Apolar aprotic solvents are particularly advantageous for investigating the intrinsic ortho effect free from complications of specific solvent effects. A kinetic study for toluene-phase proton transfers between ortho F, Cl, Br, I, OMe, OEt, OPh, OAc, Me, NO(2), COMe, COPh, OH, NH(2), and H benzoic acids and crystal violet carbinol base has shown the forward rate constant (log k(+1)) is the most appropriate reactivity parameter in toluene. log k(+1) (toluene) as compared to other reported reactivity parameters in benzene, toluene, or chlorobenzene has been found more sensitive to the ortho substituent effect. The regression results of the correlation of log k(+1) (toluene) of the acids (except OH and NH(2) substituted ones) according to seven ortho effect models are all very significant, and the best result is given by Fujita-Nishioka's model. The overall analysis reveals that a substituent's ortho effect pattern is a 58:24:18 ratio of its ordinary electrical, proximity electrical, and steric effects and that the proximity electrical effect is the major component to account for the peculiarity of the substituent's ortho effect. The results further favor the transmission of this effect mainly through the molecular cavity. The effect may, however, be outweighed by the steric component for bulky enough substituents, e.g., Me. The enhanced strength exhibited by salicylic acid in toluene has been quantitatively described using Pytela-Liska's σ(HB)(i) parameter. The abnormally high log k(+1) observed for anthranilic acid in toluene has been ascribed to a very extensive homoconjugation in its acid-acid anion complex induced by the acid's three hydrogen bond donors.

Kinetics and mechanism of proton transfer between disubstituted benzoic acids and carbinol base of crystal violet in chlorobenzene.

An investigation on the detailed kinetics of proton transfer between a set of di- and monofluoro- and chloro- (2,3-, 2,5-, 2,6-, 3,5-, 2-, and 3-) benzoic acids (HA) and Crystal Violet carbinol base in chlorobenzene favors a mechanism in terms of fast equilibrium between HA and D to form a H-bonded complex, D...HA, followed by rate-limiting proton transfer along the H-bond to form the colored ion pair DH+A- under the combined influence of monomer HA catalyst, nonreactive cyclic dimer (HA)2 inhibitor, and hyperacidic homoconjugated complex H(HA2) catalyst through a transition state with nearly 60% charge separation.

Chemometric analysis of disubstituent effects on the 13C chemical shifts of the carboxyl carbons (deltaCO) of benzoic acids. A comparative study of the substituent effects on the strength of benzoic acids in apolar aprotic media.

The results of measurements of substituent induced chemical shifts of carboxyl carbons (deltaCO) of dichloro- and difluorobenzoic acids, including the monosubstituted ones with substituents at meta- and/or ortho- positions, in chloroform-d and strengths of these acids (log K) in chlorobenzene show an anomalous reverse trend between deltaCO and log K, while the electron density at carboxyl carbons should influence similarly both deltaCO and log K. A detailed chemometric analysis of comparison of disubstituent effects between deltaCO and log K on the basis of Fujita-Nishioka's multiparameter approach and assumption of additivity of substituent effects shows a dominance of the localized pi-polarization mechanism relative to simple electrostatic effects upon deltaCO. Further, steric factors play a significant role in determining deltaCO whereas with respect to log K they were insignificant. The overall anomaly has been rationalized keeping in mind that, while log K is a gross measure of energy differences between the ionized and unionized forms of the acids, deltaCO is a very sensitive probe for determining changes in electron density at the carboxyl carbon of the unionized acid.