The Analytical and Surface Chemistry (ASC) program of the Division of Chemistry will support the research program of Prof. Heather Allen of The Ohio state University. Prof. Allen's research program focuses on studying the interactions between water molecules and lipid membranes. Prof. Allen and her students will utilize state of the art surface sensitive non linear spectroscopic techniques to elucidate the organization of water molecules on and about the surface between the lipids in different surface phases. Improving the state of understanding of water at air-lipid-water interfaces will impact scientific thought across many disciplines including biology, environmental science and nanotechnology. For example, it will increase our understanding of aerosol chemistry since water content and the organization of water molecules on the surface of aerosol droplets greatly impact their reactivity and potential toxicity when inhaled in urban and rural areas. The study will provide an excellent educational opportunity for graduate students, undergraduate students, high school students and postdoctoral trainees to carry out a fundamental research project at the interface of chemistry and atmospheric sciences.
Surface water, ion, and organic molecule organization plays a relatively unrecognized role at the ocean surface, which then impacts marine aerosol activity and chemistry, and in some cases, electrification of thunderclouds. Atmospheric aerosol reactivity has a longer standing accepted relevance, particularly for the coastal urban atmosphere. Additionally, chemical systems that incorporate phospholipid molecules such as dipalmitoyl phosphotidylcholine has specific relevance to lung surfactant organization and studies of such can shed light on macroscopic phenomena such as oxygen diffusion. We have studied a series of atmospherically and biologically relevant chemical systems to reveal molecular-level organization. We have revealed that an ion’s preference for the surface region of water is regulated by a combination of factors: size, shape, surface charge, polarizability, counter cation identity, and surface active organic molecule identity and concentration. Implementing state of the art surface spectroscopy and microscopy methods has enabled us to deconvolve the complexities of molecular organization at the air-water interface. Advances in our laboratory with interface-selective vibrational sum frequency generation (VSFG) spectroscopy and more recently Brewster angle microscopy (BAM) have provided insight into the intricate details of lipid head group interactions with ions such as calcium, magnesium, potassium, and sodium. The phosphate group of the head groups of phospholipids was shown to exhibit extraordinary dehydration and hydration character depending on environment. The lipid chains help to counter balance organization of lipid films. Salts such as CaCl2, MgCl2, KCl, and NaCl impact lipid layer organization in ways not currently predicted. Without surface lipids such as fatty acids, ions still form distinct interfacial distributions, but the driving forces are the ions themselves as opposed to the ordered charges of lipid surface layers.
