Direct Observation of Coupling between Structural Fluctuation and Ultrafast Hydration Dynamics of Fluorescent Probes in Anionic Micelles

Abstract

The coupling of structural fluctuation and the dynamics of associated water molecules of biological macromolecules is vital for various biological activities. Although a number of molecular dynamics (MD) studies on proteins/DNA predicted the importance of such coupling, experimental evidence of variation of hydration dynamics with controlled structural fluctuation even in model macromolecule is sparse and raised controversies in the contemporary literature. Here, we have investigated dynamics of hydration at the surfaces of two similar anionic micelles sodium dodecyl sulfate (SDS) and sodium dodecylbenzenesulfonate (SDBS) as model macromolecules using coumarin 500 (C500) as spectroscopic probe with femtosecond to picosecond time resolution up to 20 ns time window. The constituting surfactants SDS and SDBS are structurally similar except one benzene moiety in the SDBS may offer additional rigidity to the SDBS micelles through π-stacking and added bulkiness. The structural integrity of the micelles in the aqueous medium is confirmed in dynamic light scattering (DLS) studies. A variety of studies including polarization gated fluorescence spectroscopy and quasielastic neutron scattering (QENS) have been used to confirm differential structural fluctuation of SDS and SDBS micelles. We have also employed femtosecond-resolved Förster resonance energy transfer (FRET) in order to study binding of a cationic organic ligand ethidium bromide (EtBr) salt at the micellar surfaces. The distance distribution of the donor (C500)-acceptor (EtBr) in the micellar media reveals the manifestation of the structural flexibility of the micelles. Our studies on dynamical coupling of the structural flexibility with surface hydration in the nanoscopic micellar media may find the relevance in the "master-slave" type water dynamics in biologically relevant macromolecules.

Probing relaxation dynamics of a cationic lipid based non-viral carrier: a time-resolved fluorescence study

“…Whereas C500 is localized in the polar side (head group region) of the micellar surface, DCM prefers to reside in the more hydrophobic region of the surface of the micelles. 18 The timescale of water relaxation dynamics in the micelle-water interface has been found to be in 10-100 ps range, [19][20][21][22] which was nicely consistent with the relaxation time ($50 ps) reported by ACYMAN. 14 Furthermore, compared to ACYMAN, both C500 and DCM fail to probe the interfacial solvation dynamics of a model protein-surfactant interface.…”

Modulation of Kinetic Pathways of Enzyme–Substrate Interaction in a Microfluidic Channel: Nanoscopic Water Dynamics as a Switch

“…The relative abundance of BW decreases for AOT, whereas that for BHDC increases with increasing mole fraction of Brij‐30. The relative abundance of the bound water molecules and its variation in the presence of a nonionic surfactant probably affects the dynamics of water molecules within the reverse micelle core owing to the coupled nature of the water and surfactant molecules …”

“…In comparison to BHDC, a high abundance of BW is observedi nt he case of the AOT reverse micelles.T he relative abundance of BW decreases for AOT,w hereas that for BHDC increases with increasing mole fraction of Brij-30.T he relative abundance of the boundw ater molecules and its variation in the presence of an onionic surfactantp robably affects the dynamics of water molecules within the reverse micelle core owing to the coupled nature of the water and surfactant molecules. [37] The time-resolved fluorescence of the AC1 dye was monitored to probe the dynamics of water molecules entrapped within the core of the reverse micelles. Figure 4a and be xhibit the steady-state emission spectra of AC1 in the reverse micelles of BHDC and AOT,r espectively.T he fluorescencep eak maximum of AC1 in pure water ( % 515 nm, data not shown) is significantly blueshifted to 424 and 427 nm, respectively,i nt he reversem icelles (W 0 = 8) of BHDC/benzenea nd AOT/benzene, respectively.T he observedb lueshift in the cationic (BHDC/benzene) reversem icellesr elative to the anionic (AOT/benzene) probablyo riginates from the reduced polarity of its interface compared with the latter.H owever,u pon the addition of Brij-30 to both BHDC and AOT reverse micelles, an insignificant shift in the emission peak maximum is observed.…”

Modulation of Ultrafast Conformational Dynamics in Allosteric Interaction of Gal Repressor Protein with Different Operator DNA Sequences

“…FRET distance distribution calculation : Distance distribution function P(r) was evaluated using the procedure described in the previous literature . The decay transient of donor in absence of acceptor were fitted using nonlinear least‐squares fitting procedure (software SCIENTIST from Micromath (Saint Louis, MO, USA) to the following function …”