Infrared spectroscopy of proteins.

Structure and reactivity of water at biomaterial surfaces

Aqueous ion-containing interfaces are ubiquitous and play a key role in a plethora of physical, chemical, atmospheric, and biological processes, from which we mention just a few illustrative examples: (i) Ions at the air/water interface are important for atmospheric chemistry involving ocean surfaces and seawater aerosols, 1-5 as well as that of the Arctic snowpack covered by sea spray. 6,7 (ii) Many salts (such as NaCl) tend to inhibit bubble coalescence, 8-12 which is one of the reasons why foam is formed when waves break in the ocean but not in freshwater lakes. (iii) Brine rejection occurring at the seawater/ice interface has profound climatic effects in polar regions. 13 (iv) The aqueous electrolyte/metal interface is involved in electrode and corrosion processes. 14,15

Specific ion effects at the air/water interface.

A powerful approach to the study of interfaces has been developing rapidly in the past decade. It is based on the spectroscopic methods of second-harmonic (SHG) and sum-frequency generation (SFG). These nonlinear optical techniques, being spectroscopic, provide information at the most fundamental level. A microscopic description of equilibrium and dynamic interface processes requires knowledge of the molecules at the interface, their orientational structure, the energetics that drive chemical and physical processes, and the time scale of molecular motions and relaxation processes. The techniques of second-harmonic and sum-frequency generation have made it possible to selectively probe the chemistry, physics, and biology of gas/liquid, liquid/liquid, liquid/solid, gas/solid, and solid/solid interfaces at the molecular level. In this abbreviated article only liquid interfaces will be considered; gas/solid and solid/solid interfaces are not included. This restriction is necessary because of the enormous increase in SH and SF studies in recent years, which makes it extremely difficult to properly discuss the range of work being carried out around the world. Unfortunately not all of the fine work even in the area of liquid interfaces has been included because of both space and time limitations. A number of review articles are referred to which cover some ofmore » the research material not covered in this article. 99 refs.« less

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Liquid interfaces probed by second-harmonic and sum-frequency spectroscopy

Aqueous surfaces and interfaces are important in many physical, chemical, and biological processes in our world. The adsorption, dissolution, and reaction of atmospheric gases at the surfaces of atmospheric aerosols and oceanic waters play a key role in the composition of our atmosphere and the sustainability of plant and animal species in land waters. The transport and exchange of ions and solutes across the interface between an aqueous phase and hydrophobic biomolecular assemblies underlies some of the most important processes in living plants and animals. Membrane formation, protein folding, and micelle formation all involve, and are often controlled by, bonding interactions with water molecules at their surfaces. The unique physical, chemical, and biological properties of aqueous surfaces arise from the strong hydrogen bonding that occurs between water molecules and the asymmetry in this otherwise tetrahedral bonding coordination that results from the termination of the bulk water phase. Although there has been increased experimental and theoretical effort in recent years focused on developing a molecular picture of the structure and bonding of water layers to other solid, liquid, and gaseous media, consensus on the details of interfacial bonding has been slow or nonexistent in many areas. The adsorption of ions, surfactants, and solute molecules at these interfaces adds a level of complexity to the Geraldine Richmond holds the Richard M. and Patricia H. Noyes Professor of Chemistry position at the University of Oregon. She received her Ph.D. degree under the mentorship of George Pimentel at the University of California, Berkeley, in 1980. From 1980 to 1985 she was on the faculty at Bryn Mawr College and moved to the University of Oregon in 1985 as an associate professor. Richmond is recognized for her fundamental studies of the structure, dynamics, and bonding characteristics of surfaces and interfaces. Her research group uses a combination of linear and nonlinear optical methods, thermodynamic measurements, and theory to characterize interactions at aqueous surfaces, metal and semiconductor surfaces in contact with liquids and adsorbates, and liquid/liquid interfaces. Richmond has received several recent honors for these studies including the 2002 ACS Spectrochemical Analysis Award, the 2001 Oregon Scientist of the Year, and the 1996 Olin-Garvan Medal of the ACS and has been a Fellow of the American Physical Society since 1993. 2693 Chem. Rev. 2002, 102, 2693−2724

Molecular bonding and interactions at aqueous surfaces as probed by vibrational sum frequency spectroscopy.

Using infrared-visible sum-frequency generation we have obtained the OH stretch vibrational spectra of water at the vapor/water interface. From the spectra, we deduce that more than 20% of the surface water molecules have one free OH projecting into the vapor. The spectrum is weakly temperature dependent from 10 to 80 \ifmmode^\circ\else\textdegree\fi{}C. A monolayer of fatty alcohol on water surface terminates the free OH groups and induces an icelike structure in the spectrum.

Q. Du

Papers

Vibrational spectroscopy of water at the vapor/water interface.

Sum-frequency vibrational spectroscopic studies of water interfaces