The Inner Hydration in Surfactant/Cholesterol Vesicles Differs from the Outer One: A Spectroscopic Investigation

Abstract

Vesicles contain two aqueous regions: inner core and outer-tobulk. It has remained an open question whether hydration behaviour in the inner core differs from the outer-to-bulk region, mostly owning to the inability of the conventional spectroscopic techniques to deconvolute the contribution from these two regions. We, using THz-FTIR spectroscopy (1.5-13.5 THz) experimentally probe the inner hydration of three differently charged surfactant/cholesterol vesicles composed of SDS, CTAB and Brij 30. Both dynamic light scattering (DLS) and atomic force microscopy (AFM) measurements affirm the transition from micelles to vesicles as cholesterol is added into surfactant solutions. FTIR measurements show that hydration behaviour changes significantly as micelles are converted into vesicles, the change been exclusively caused due to the formation of an inner core. Our measurements on the hydrogen bond stretch and librational motion of the inner hydration show distinct features compared to the overall hydration, which in turn is found to be surfactant type and cholesterol concentration dependent.

Addition of cholesterol alters the hydration at the surface of model lipids: a spectroscopic investigation

“…In our previous study, we observed that the addition of cholesterol does not perturb the hydration of the surfactant interface. 23 This leads us to approximate that in the lipid interface also, cholesterol would not affect the interfacial hydration noticeably and we take a hyd % a 0 hyd , which finally concludes that f 0 hyd 4 f hyd . This inequality leads to very useful information as it manifests that more water molecules are accommodated in the hydration layer of lipids in the presence of cholesterol compared to the unmodified liposomes.…”

“…THz measurements enables us to explicitly determine the hydration at the interface as the calculation of Δ α ( ν ) subtracts the bulk contribution. 23 Thus, the estimated peak frequencies and lifetimes manifest the interfacial information only.…”

“…22 In a very recent study, using the THz spectroscopy measurement, we have reported that the inner hydration of a cholesterol/surfactant vesicle is distinctly different from outer hydration, and the difference changes with the content of cholesterol as well as the charge type of the surfactant(s). 23 These studies have unambiguously established the altered water dynamics at the lipid interface, the extent of which in turn is lipid specific. While several attempts have been made toward understanding the hydration behavior of lipids, it has still not been extensively explored whether cholesterol plays any role in modifying lipid hydration specially/specifically considering the fact that the addition of cholesterol does modify the lipid structures.…”

Thermo-Resistive Phase Behavior of Trivalent Ion-Induced Microscopic Protein-Rich Phases: Correlating with Ion-Specific Protein Hydration

“…A more explicit insight of protein hydration is obtained from the difference spectra, Δα(ν) = α(ν) protein+salt+water – α(ν) salt+water (Figure ). Interestingly, the Δα(ν) profiles are not featureless, rather they show certain peaks, and the overall Δα(ν) profiles could be fitted using a damped harmonic oscillator model ,,− normalΔ α ( ν ) = ∑ i = 1 N a i ω 0 , i ν 2 4 π 3 true[ ν 2 ω 0 , i 2 π 2 + ( ν d , i 2 + ω 0 , i 2 4 π 2 − ν 2 ) 2 true] where a i , ω 0, i , and ν d , i stand for the amplitude, the damping width, and the center frequency of the i th damped harmonic oscillator mode, respectively (see the Supporting Information section for details). Two representative fitting profiles for pure BSA and La 3+ -containing BSA (both incubated at 70 °C) are shown in Figure .…”

Terahertz Spectroscopy of Aqueous Solutions of Sodium Halides (NaX): Self- and Cross-Correlation Contributions of Ions and Hydration Shell Water for X– = F–, Cl–, Br–, and I–

“…In recent years, extensive studies on structural properties of aqueous solutions have been conducted using IR and Raman spectroscopy, − inelastic neutron diffraction, X-ray diffraction, and terahertz (THz) spectroscopic techniques. − The effects of ions on the dynamics of water have been primarily obtained from various time-resolved spectroscopic techniques, such as femtosecond nonlinear IR spectroscopy, dielectric relaxation spectroscopy, and ultrafast optical Kerr effect (OKE) spectroscopy. ,,, The water molecules in ionic hydration shells influence the interactions and dynamics of hydrogen bond network dynamics and such changes can be captured through terahertz (THz) spectroscopy. ,, Far infrared or THz spectroscopy is a unique technique for studying the intermolecular structure and dynamics of ionic solutions, including specific ion effects. , …”