Proton Transfer Reaction Dynamics of Pyranine in DMSO/Water Mixtures

Abstract

Photoinduced intermolecular excited-state proton transfer (ESPT) reactions are ubiquitous in chemistry and biology. ESPT reactions are extremely sensitive to the nature of water molecules in its microenvironment and thus serve as a sensitive reporter for the water structure and dynamics in a system. Herein, the photoinduced intermolecular ESPT reaction of 8-hydroxypyrene-1,3,5-trisulfonic acid (HPTS, also known as pyranine) has been investigated in various DMSO/water mixtures by using steady-state and time-resolved emission spectroscopy. The DMSO/water binary mixture yields an interesting and anomalous behavior for the proton transfer reaction dynamics of HPTS at a mole fraction of DMSO (X ) of 0.41-0.51, which has also been previously investigated and projected as an anomalous region by molecular dynamics simulation and other experimental techniques. The extreme slowdown of the proton transfer reaction observed at X =0.41-0.51 has been attributed to the slow solvation dynamics, as well as the non-availability of free water molecules at this composition, which are required to solvate the newly generated proton. These observations have been also corroborated by time-resolved area-normalized emission spectra. The dimensionality of the proton diffusion process has been investigated by analyzing the geminate recombination process, and is found to be significantly different in DMSO/water mixtures (X =0.41-0.51) compared with three-dimensional proton diffusion in neat water.

Dynamics of Preferential Solvation of 5-Aminoquinoline in Hexane–Alcohol Solvent Mixtures

“…The last two decades have witnessed intense activity to rationalize this component and devise applications thereof. 19−21 Solvation dynamics in solvent mixtures has been studied extensively, as composition of such mixtures can be easily varied to tune them for applications like metal extraction, 22 enzymatic catalysis, 23 modulation of fluorescence properties of solutes by selective aggregation, 24 stabilization of different forms of the solute, 25,26 etc. Microheterogeneity in these media 27 plays an important role in the process of solvation.…”

Time Evolution of Local pH Around a Photo‐Acid in Water and a Polymer Hydrogel: Time Resolved Fluorescence Spectroscopy of Pyranine

“…Acid‐base reaction is one of the fundamental chemical reactions in nature and has implications in many natural and biological processes . The dissociation equilibrium of an acid HA into proton and its deprotonated species (A − ) is, …”

“…The primary prcocesses of excited state proton transfer (ESPT) of HPTS in a wide variety of media have been monitored by time evolution of the fluorescence from the anion (A − *) and the undissociated acid (HA*). This includes binary solvent mixtures, live biological cell, reverse micelles, micelle, nafione membrane and niosome . ESPT of HPTS has not been studied in polymer hydrogel.…”

“…[8][9][10][11][12] ESPT is implicated in rhodopsin (involved in the vison process) [13] and in green fluorescence protein (GFP). [14][15] The primary prcocesses of excited state proton transfer (ESPT) of HPTS in a wide variety of media [10][11][12][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31] have been monitored by time evolution of the fluorescence from the anion (A À *) and the undissociated acid (HA*). This includes binary solvent mixtures, [10][11]22] live biological cell, [17,18] reverse micelles, [19,30,32] micelle, [21] nafione membrane [30] and niosome.…”

“…[29] ESPT of HPTS has not been studied in polymer hydrogel. In spite of the great deal of work on HPTS, [10][11][12][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31] there has been almost no effort to understand how the local pH around a photo-acid varies with time, following excitation of the photoacd. Huppert and co-workers proposed that rise time of the A À emission scales with pK a * in the case of 2-naphthols and using this they calculated pK a * of pyranine (8-hydroxypyrene-1,3,6trisulphonic acid, HPTS, Scheme 1).…”