Photo-induced relaxation and proton transfer in some hydroxy naphthoic acids in polymers

Spectral and time domain fluorescence spectroscopy of gentisic acid molecule in protic and aprotic polymer matrix

In the present work, the effect of polymer microenvironment on the photophysics of gentisic acid molecule [2,5-dihydroxybenzoic acid] (GA), steady-state and time-domain fluorescence measurements at different pH conditions were carried out in protic [polyvinyl alcohol PVA] and aprotic [polymethyl methacrylate (PMMA)] polymer matrices. Change in the proticity of the microenvironment of the polymer traps different ionic species along with the neutral form of rotamer P and R conformers of GA molecule, are found to be responsible for the change in the spectral, multi-exponential decay behaviour. In protic polymer, the appearance of a single emission band indicates, dissociation of the GA molecule is very high, and it present as a monoanion along with hydrogen-bonded P and R rotamers. However, in the basic polymer film, most of the conformers of R converted to the anion. In contrast, protonation slows down the dissociation of both P and R forms in the acidic film. Unlike PVA matrix, in PMMA, dual emission band appears due to slow dissociation of GA molecule and hydrogen-bonded rotamer P, and R form exists with monoanion species. The magnitude of large stokes shifted red emission due to excited-state intramolecular proton transfers (ESIPT) found grater in rotamer P compared to its anionic species (green emission) and a blue emission corresponds to rotamer R.

Excited-State Intramolecular Proton Transfer: A Short Introductory Review

In this short review, we attempt to unfold various aspects of excited-state intramolecular proton transfer (ESIPT) from the studies that are available up to date. Since Weller’s discovery of ESIPT in salicylic acid (SA) and its derivative methyl salicylate (MS), numerous studies have emerged on the topic and it has become an attractive field of research because of its manifold applications. Here, we discuss some critical aspects of ESIPT and tautomerization from the mechanistic viewpoint. We address excitation wavelength dependence, anti-Kasha ESIPT, fast and slow ESIPT, reversibility and irreversibility of ESIPT, hydrogen bonding and geometrical factors, excited-state double proton transfer (ESDPT), concerted and stepwise ESDPT.

Features of partial encapsulation of an ESIPT probe 3-hydroxy-2-naphthoic acid (3HNA) in the nano cavities of β- and γ-cyclodextrin: comparative study with sequestered 3HNA in micelles and reverse micelle

Encapsulation of an excited state intramolecular proton transfer probe within the nanocavity of different confined media.

Impact of micelle ionic electrical double layer structure on the excited state protolytic reaction in the fluorescent probe bound to the colloidal nanoparticles

The fluorescent probe, 2-hydroxynaphthalene(dodecylo)-6-sulfonamide (NSDA) bound selectively to shear plane of various electrostatic charges was synthesized and its photophysical properties have been investigated by means of steady state fluorescence and nanosecond time-resolved spectroscopy. Our experimental data allowed us to determine the excited state proton transfer (ESPT) rate and equilibrium constants of NSDA bound to micelles and to estimate the electric potential value (Ψ) at the particle surface. The spatial dependence of proton movement velocity through electric double layer (EDL) of micelles has been thoroughly analyzed. In this article, a new approach of estimating the values of the micelle potential (Ψ(R)) from the excited state proton transfer rate constant of the fluorescent probe bound at a certain distance (R) to a micellar surface has been proposed. The Ψ(R) values, obtained in this way, are compared with electrophoretic values of the particle potential (ζ). Our results on electrophoretic potentials and the reaction course of the ESPT in colloidal environment may contribute to a deeper understanding of micellar interactions and behavior of the living cells in contact with various diluted substances such as pharmacological drugs, hormones, proteins, and other colloidal particles.

Discovery of 2-naphthoic acid monooxygenases by genome mining and their use as biocatalysts

The large pool of cytochrome P450 (P450) open-reading frames identified in genome sequences has attracted much attention as a resource for new oxidation biocatalysts. P450 genes were cloned from genome-sequenced bacteria and coexpressed with putidaredoxin and its reductase genes to provide the redox partners of P450 in Escherichia coli. Whole-cell assays were performed with 2-naphthoic acid as a substrate. Hydroxylated naphthoic acid products were rapidly detected with two reagents showing different colors in the presence of the products. Two P450s, CYP199A1 and CYP199A2, were found to hydroxylate the substrate to 7- and 8-hydroxy-2-naphthoic acids. The CYP199A1 whole-cell biocatalyst converted 1 mM 2-naphthoic acid to 0.27 mM 7-hydroxy-2-naphthoic acid and 0.53 mM 8-hydroxy-2-naphthoic acid. CYP199A2 exhibited similar regioselectivity to CYP199A1. Furthermore, we found that 8-hydroxy-2-naphthoic acid emits near-white fluorescence when exposed to UV light. These P450s will provide a facile and environmentally friendly synthetic approach to the hydroxynaphthoic acids.