Current Frontiers on Liquid-Liquid Interfaces Workshop (original) (raw)
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Spiers Memorial Lecture : Recent experimental advances in studies of liquid/liquid interfaces
Faraday Discussions, 2005
Liquid/liquid interfaces play a key role in many important processes. Studying the molecular structure and interactions that occur at these interfaces can aid in our understanding of more complicated processes such as molecular transport across cell membranes. A variety of techniques have been applied to this pursuit. Here we present selected examples of exciting recent studies using different techniques to examine liquid/liquid interfaces.
Adsorption of Bovine Serum Albumin (BSA) at the Oil/Water Interface: A Neutron Reflection Study
Langmuir, 2015
The structure of the adsorbed protein layer at the oil/water interface is essential to the understanding of the role of proteins in emulsion stabilization, and it is important to glean the mechanistic events of protein adsorption at such buried interfaces. This article reports on a novel experimental methodology for probing protein adsorption at the buried oil/ water interface. Neutron reflectivity was used with a carefully selected set of isotopic contrasts to study the adsorption of bovine serum albumin (BSA) at the hexadecane/water interface, and the results were compared to those for the air/water interface. The adsorption isotherm was determined at the isoelectric point, and the results showed that a higher degree of adsorption could be achieved at the more hydrophobic interface. The adsorbed BSA molecules formed a monolayer on the aqueous side of the interface. The molecules in this layer were partially denatured by the presence of oil, and once released from the spatial constraint by the globular framework they were free to establish more favorable interactions with the hydrophobic medium. Thus, a loose layer extending toward the oil phase was clearly observed, resulting in an overall broader interface. By analogy to the air/water interface, as the concentration of BSA increased to 1.0 mg mL −1 a secondary layer extending toward the aqueous phase was observed, possibly resulting from the steric repulsion upon the saturation of the primary monolayer. Results clearly indicate a more compact arrangement of molecules at the oil/water interface: this must be caused by the loss of the globular structure as a consequence of the denaturing action of the hexadecane.
Current Opinion in Solid State and Materials Science, 2005
The interface where liquid meets solid, and particularly that of water in contact with a solid, is of extreme importance to biological, industrial and environmental processes. Surface science techniques are advancing such that we are now able to obtain similarly detailed information about liquid/solid interfaces as that, which we have come to expect from the gas/solid interface. Vibrational spectroscopy plays a leading role in unraveling chemical events at interfaces. The application of sum frequency generation (SFG) to the aqueous/metal interface was pioneered by Peremans, Guyot-Sionnest and Tadjeddine . Wieckowski, Dlott and co-workers [6] have recently reported improvements to the implementation of SFG at the electrochemical interface that should prove to be quite fruitful for future developments. More conventional Fourier transform infrared spectroscopy (FTIR), especially in the attenuated total reflectance geometry (ATR) , is also well suited to studying the liquid/solid interface. In situ investigations, for instance of the aqueous/Si interface, utilizing this technique have been performed in several groups . In situ scanning tunneling (STM) and atomic force microscopy (AFM) have been instrumental in forming a greater understanding of not only etching and micromachining [16] but also metal deposition and nanostructure formation .
Biophysical Chemistry, 1999
The dynamics of protein adsorption at an oilrwater interface are examined over time scales ranging from seconds to several hours. The pendant drop technique is used to determine the dynamic interfacial tension of several proteins at the heptaneraqueous buffer interface. The kinetics of adsorption of these proteins are interpreted from Ž. tensionrlog time plots, which often display three distinct regimes. I Diffusion and protein interfacial affinity determine the duration of an initial induction period of minimal tension reduction. A comparison of surface pressure profiles at the oilrwater and airrwater interface reveals the role of interfacial conformational changes in the early Ž. stages of adsorption. II Continued rearrangement defines the second regime, where the resulting number of Ž. interfacial contacts per protein molecule causes a steep tension decline. III The final regime occurs upon monolayer coverage, and is attributed to continued relaxation of the adsorbed layer and possible build-up of multilayers. Denaturation of proteins by urea in the bulk phase is shown to affect early regimes.
Spectroscopic studies of molecular interaction at the liquid–liquid interface
Analytical and Bioanalytical Chemistry, 2009
The development of techniques to study the liquid-liquid interface is a major challenge. Spectroscopy in all its forms provides a powerful method of investigation, especially when combined with other optical techniques. Over the last 30 years, there have been significant developments in the methods for studying heterogeneous interfaces. As technology progresses, the sensitivity of existing techniques has been improved but there are major challenges still to be met, such as the measurement of interfacial dielectric constant and viscosity. This paper aims to summarise the use of spectroscopy to study molecular interactions at the liquid-liquid interface.
Adsorption of proteins at solid-liquid interfaces
Cell Biol Int, 1995
This paper concisely rev iews the gene ral principles underl ying protein adsorption fro m aqueous so luti on onto a solid surface. The discussion includes the various stages of the adsorption process, i. e., transport o f the protein molecules towards the su rface, the absorbed amount under equilibrium conditi ons, desorpti on andreadsorption. Among the interacti ons that determine the overall protein adsorption process (1) redi stributi on of charged groups in the interfacial layer, (2) changes in the hydrati on of the sorbent and the pro tein surface, and (3) structural rearrange ments in the protein molecul e play maj or roles. Spec ial attention is given to the relati on between the structu ral stabi lity o f th e pro tei n molecul e and its adsorption behaviour.
Experimental studies on the desorption of adsorbed proteins from liquid interfaces
Food Hydrocolloids, 2005
The desorption of proteins from liquid interfaces depends on the conditions under which they have been adsorbed. At low concentrations, the adsorption process takes a comparatively long time and the molecules arriving at the interface have enough space and time to adsorb and unfold. In contrast, adsorption from higher concentrated solutions is faster and adsorbing molecules strongly compete from the beginning of the process. The rate of desorption is studied as a function of the adsorption layer coverage in order to understand to what extend protein adsorption is reversible. The experimental findings cannot give a clear answer on the reversibility, however, the theoretical analysis shows that desorption rates for proteins are many orders of magnitude lower than those for usual surfactants. q
Molecules at Liquid and Solid Surfaces
Langmuir, 1998
The discovery of structural phase transitions in a series of alkanenitriles, acetonitrile (CH3CN), propionitrile (CH3CH2CN), nonadecanitrile [CD3(CH2)19CN], but not butyronitrile (CH3CH2CH2CN), at the air/water is described. Using sum frequency spectroscopy, the phase transition is manifested by an abrupt change in the orientation and an abrupt change in the vibrational frequency of the CN head group of the interface nitrile molecules. The competition between the distance dependent nitrile-nitrile dipolar interactions and the hydrogen bonding and solvation of the CN moieties is used to describe the phase transitions. A new application of second harmonic and sum frequency generation to study the interfaces of centrosymmetric microscopic particles is presented. Examples of this new use to the adsorption of molecules to a polystyrene microsphere/aqueous interface and the polarization of bulk water molecules by a charged microsphere of polystyrene sulfate are discussed.
A molecular perspective of water at metal interfaces
Nature Materials, 2012
Water-solid interfaces are ubiquitous and of the utmost importance to industry, technology and many aspects of daily life. Despite countless studies from different areas of science, detailed molecular-level understanding of water-solid interfaces comes mainly from well-defined studies on flat metal surfaces. These studies have recently shown that a remarkably rich variety of structures form at the interface between water and seemingly simple flat metal surfaces. Here we discuss some of the most exciting examples of recent work in this area and the underlying physical insight and general concepts that emerge about how water binds to surfaces. A perspective on the outstanding problems, challenges, and open questions in the field is also provided.