Detecting local heterogeneity and ionization ability in the head group region of different lipidic phases using modified fluorescent probes

Abstract

Local heterogeneity in lipid self-assembly is important for executing the cellular membrane functions. In this work, we chemically modified 2-(2′-hydroxyphenyl)benzoxazole (HBO) and attached a C8 alkyl chain in two different locations to probe the microscopic environment of four lipidic phases of dodecyl β-maltoside. The fluorescence change in HBO and the new probes (HBO-1 and HBO-2) shows that in all phases (micellar, hexagonal, cubic and lamellar) three HBO tautomeric species (solvated syn-enol, anionic, and closed syn-keto) are stable. The formation of multi tautomers reflects the heterogeneity of the lipidic phases. The results indicate that HBO and HBO-1 reside in a similar location within the head group region, whereas HBO-2 is slightly pushed away from the sugar-dominated area. The stability of the solvated syn-enol tautomer is due to the formation of a hydrogen bond between the OH group of the HBO moiety and an adjacent oxygen atom of a sugar unit. The detected HBO anions was proposed to be a consequence of this solvation effect where a hydrogen ion abstraction by the sugar units is enhanced. Our results point to a degree of local heterogeneity and ionization ability in the head group region as a consequence of the sugar amphoterism.

Photophysical properties of hydroxyphenyl benzazoles and their applications as fluorescent probes to study local environment in DNA, protein and lipid

“…Accordingly, less solvation effect is expected as shown in Fig. , and confirmed by fluorescence lifetime measurements .…”

“…In all the lipidic phases, a major peak for the syn ‐keto tautomer around 480 nm is evident. Unlike HBO in buffer, a small contribution from the solvated syn ‐enol tautomer is observed in all lipids in the region 370–380 nm, which was confirmed by fluorescence lifetime measurements . In addition to these tautomers, there is a small contribution from the anion species in the region 400–440 nm, which is more pronounced for HBO‐1, followed by HBO and HBO‐2.…”

“…The same spectra in Fig. were measured for excitation at 380 nm, where only the anion species absorbs . Figure displays the fluorescence spectra, including those of HBO in buffers of pH 7.2 and 12.0 for comparison.…”

“…The blue region represents different layers of water structures. Dark blue: free water, ocean blue: restricted water, light blue: bounded water .…”

A novel non-fluorescent excited state intramolecular proton transfer phenomenon induced by intramolecular hydrogen bonds: an experimental and theoretical investigation

“…Compounds that undergo excited state intramolecular proton transfer (ESIPT) have attracted attention 1 2 3 4 5 6 as, for fluorescent probes 7 8 9 , for use in bioimaging 10 , as light-emitting materials 11 , as photostabilizers 12 , and in photophysical studies 13 14 15 16 17 . The characteristic photophysical feature of a molecule undergoing ESIPT is the sub-picosecond timescale and large Stokes shift, which suggest that the structural geometry of the emissive excited state is significantly displaced from that of the ground state 11 17 18 19 .…”