Fluorescence Study of the Solvation of Fluorescent Probes Prodan and Laurdan in Poly(ε-caprolactone)-block-poly(ethylene oxide) Vesicles in Aqueous Solutions with Tetrahydrofurane

Abstract

Steady-state and time-resolved fluorescence measurements were used to study the relaxation of the microenvironment of hydrophobic probes 6-propionyl-2-(dimethylamino)naphthalene (prodan) and 6-dodecanoyl-2-(dimethylamino)naphthalene (laurdan) in systems containing vesicles formed by the amphiphilic diblock copolymer poly(epsilon-caprolactone)-block-poly(ethylene oxide) (PCL-PEO) and water/tetrahydrofurane (THF) solvent mixtures. It was found that in case of prodan, both steady-state and time-resolved emission spectra were composed of two subspectra corresponding to the emission of prodan molecules located (i) in fairly rigid (effectively viscous) and hydrophobic domains of the vesicles close to the PCL/PEO interface and (ii) in a more polar and less viscous medium (in the bulk solution). The fraction of the emission from the more polar microenvironment increases with increasing content of THF in the system. Laurdan, in contrast to prodan, appeared to be solubilized preferentially in the hydrophobic domains up to 30 vol % of THF content, and its emission spectra changed only due to swelling of hydrophobic PCL domains by added THF. The study shows that the analysis of the time-resolved emission from a probe distributed in two media is, in principle, possible, but it is quite complex and appreciably less accurate, and the relaxation times are ill-defined averages of several processes. The bimodal or shoulder-containing time-resolved spectra have to be decomposed in pertinent time-resolved subspectra and treated separately. Another important result of the study is a piece of knowledge concerning the motion of the probe with respect to the vesicle. In the studied complex system, not only the relaxation of the solvent and reorganization of polymer segments around the fluorescent headgroup of the probe affect the emission but also a lateral motion of the probe with respect to the nanoparticle within the lifetime of the excited state contributes significantly to the relaxation and to the relatively slow time-resolved Stokes shift.

Profiling of dynamics in protein–lipid–water systems: a time-resolved fluorescence study of a model membrane protein with the label BADAN at specific membrane depths

“…It was found to consist of two subspectra with different lognormal line shapes. An asymmetric line shape was ascribed to PRODAN in a hydrophobic environment and a symmetric line shape to PRODAN in a nonviscous polar environment (Sachl et al 2008). Further support for the chosen spectral line shapes comes from fluorescence of tryptophan, an intrinsic polarity probe of proteins.…”

Laurdan and Di-4-ANEPPDHQ probe different properties of the membrane

“…Laurdan is one of the most commonly used probes to discern lipid packing in biomembranes [ 14 – 16 ]. Thus, its photo-physical properties have been widely studied [ 17 – 20 ].…”

Selective estimation of C-reactive protein in serum using polymeric formulations without antibody

“…The interaction of these chains seems to curtail the fluorescence since the fluorophore buried to an altogether different environment. Fluorescence emission is known to be very sensitive to the interplay of the excited fluorophore with its microenvironment [23]. We assumed that fluorescence of P2 is strongly affected by interaction with P1.…”