Modulation of Ground- and Excited-State Dynamics of [2,2′-Bipyridyl]-3,3′-diol by Micelles

Abstract

The binding of [2,2'-bipyridyl]-3,3'-diol (BP(OH)(2)) with ionic and neutral surfactants like cetyltrimethylammonium bromide (CTAB), sodium dodecyl sulfate (SDS), and Triton X-100 (TX-100) has been studied by steady-state and time-resolved fluorescence spectroscopy. The absorption as well as emission spectra of BP(OH)(2) are highly sensitive toward the variation of surfactant concentration and hydrophobicity of the environment. The fluorescent state of the diketo form gains stability in surfactant assemblies, leading to a red-shifted emission spectra. A sharp increase in the fluorescence quantum yield near critical micellar concentration (CMC) is encountered followed by saturation. This indicates a complete encapsulation of BP(OH)(2) in the micelles. The maximum fluorescence quantum yield in anionic SDS is rationalized by the formation of cationic fluorophore at the Stern layer. The increase in quantum yield in neutral TX-100 is attributed to higher microviscosity experienced by the fluorophore in the palisade layer. A direct support in favor of this argument in TX-100 is provided by the viscosity dependence exhibited by the probe in different concentrations of sucrose solutions. CTAB exhibiting only hydrophobic effect shows least increase in qunatum yield of BP(OH)(2) among all the surfactants. Time-resolved fluorescence study of BP(OH)(2) in micelles is used as a tool to monitor the extent of micellization in the lipophilic cavity. An increase in fluorescence quantum yield as well as lifetime of BP(OH)(2) upon micellization indicates an enhanced extent of ESIDPT in hydrophobic medium.

Role of intramolecular hydrogen bonding in the excited-state intramolecular double proton transfer (ESIDPT) of calix[4]arene: A TDDFT study

“…A large number of organic molecules which undergo ESIPT have been identified, such as 4'-N,Ndiethylamino-3-hydroxyflavone (DEAHF) [18], 2,5-bis(2-benzoxazolyl)-4-methoxyphenol (BBMP) [19], and 2-(2'-hydroxyphenyl)benzazole (HBO) [20]. Specifically, [2,2'-bipyridyl]-3,3'-diol (BP(OH) 2 ) [21,22], a diaminobipyridine based C 3 -symmetrical disk molecule (TAB) [23], and a subgroup molecule (DAC) [23] show interesting excited-state intramolecular double proton transfers (ES-IDPT).…”

Unusual Binding of a Potential Biomarker with Human Serum Albumin

“…[26] The tautomerization process of BP(OH) 2 in neat solvents primarily involves two forms (Scheme 1 b). [31] The DE tautomer, which is associated with two intramolecular hydrogen bonds, exists in the ground state in all solvents and absorbs at 350 nm. [32] However, the DK that is generated during ESIDPT, is solely responsible for the strong green emission in BP(OH) 2 , with a quantum yield that varies from 0.2 to 0.4.…”

“…[32] The ground state of the DK tautomer is only observed to an appreciable extent in water, owing to the formation of intermolecular-hydrogen-bonded water complexes. [31] This result is manifested by the presence of a second absorption band in water between 400-430 nm. Both the DE and DK tautomers have negligible dipole moments, as established by various theoretical [33,34] and electrooptical measurements.…”

“…Both the DE and DK tautomers have negligible dipole moments, as established by various theoretical [33,34] and electrooptical measurements. [35] Owing to the nonpolar nature of the ground and excited states, this fluorophore has a propensity to bind to hydrophobic nanocavities in systems like cyclodextrins, [23,36] micelles, [31] zeolites, [37] binary mixtures of 1,4-dioxane/water, [38] and HSA. [23] The encapsulation of BP(OH) 2 in albuminÀSDS (sodium dodecyl sulfate) aggregates, as observed in our very recent study, can be used as a marker for determining the nature of protein-surfactant interactions.…”

“…One may recall that the absorption spectra of BP(OH) 2 in aqueous buffer at pH 7 has two bands: one at 350 nm (which is ascribed to the DE form) and another between 400-430 nm (the DK tautomer), as discussed previously. [31] In aqueous solution, free BP(OH) 2 emits in the green-light region at 465 nm, with a fluorescence lifetime of 600 ps. Upon binding to HSA, an increase in the emission intensity is accompanied by a red shift of 25 nm and an increase in the contribution of the lifetime of the HSA-bound probe (to about 3.7 ns) as a function of HSA concentration, thus demonstrating the incorporation of the probe into the hydrophobic pockets of the protein.…”