The research activities of my group involve the application of lasers to the study of equilibrium and dynamic properties of molecules at liquid and solid interfaces.
To probe the very thin region (~10Å) that constitutes an interface, we use the interface selective techniques of second harmonic and sum frequency generation. Our picosecond and femtosecond lasers provide the high power needed for nonlinear spectroscopy, and the time resolution to study very fast molecular changes and motions. We have developed new methods to (1) measure the absolute orientation of molecules at liquid interfaces, (2) obtain the energetics of adsorption of neutral and charged molecules to the interface, (3) study chemical equilibria and pH at interfaces that we find are markedly different from their bulk values; and a polarity scale for liquid interfaces‹the motions and unexpected orientational phase transitions of long chain amphiphiles at the air/water interface‹using the new method of second harmonic fluctuation spectroscopy, and most recently vibrational spectroscopy, at interfaces, which greatly extends the power to probe chemical and physical phenomena at interfaces.
Using a pump/probe technique, with second harmonic generation as the probe method, has enabled us to observe dynamics at interfaces of excited state cis-trans isomerization, intermolecular energy transfer, solvation dynamics, and rotational molecular motions, which generally differ significantly from their bulk counterparts. We have recently shown that second harmonic spectroscopy can be used to selectively probe the surfaces of centrosymmetric microscopic particles of submicron to micron diameters. Among the surfaces of microscopic particles studied so far are polymer beads in aqueous solution, oil droplet/aqueous emulsions, semiconductor colloids, naturally occurring clay particles, and phospholipid liposomes.
The information obtained includes the absolute population of solutes adsorbed to the particle surface, the free energy of adsorption, the electrostatic potential and charge density of charged microscopic particles, and the observation in real time of the transport of organic molecules across a liposome bilayer. This new application of second harmonic and sum frequency spectroscopy provides a new and promising method to selectively study the interfaces of microscopic structures.
“Ultrafast Intermolecular Energy Transfer in Heavy Water” L. Piatkowski, K.B. Eisenthal, H.J. Bakker, Physical Chemistry Chemical Physics 11, 40, 9033-9038 (2009).
“Water Structure at Air/Acetonitrile Aqueous Solution Interface” Y. Rao, N.J. Turro, K.B. Eisenthal, Journal of Physics Chemistry C 113, 32, 14384-14389 (2009).
“Organic Ions at the Air/Water Interface” Y. Rao, M. Subir, E.A. McArthur, N.J. Turro, K.B. Eisenthal, Chemical Physics Letters 477, 4-6, 241-244 (2009).
“In-Plane Molecular Rotational Dynamics at a Negatively Charged Surfactant/Aqueous Interface” X. Shang, K. Nguyen, Y. Rao, K. B. Eisenthal, Journal of Physical Chemistry C 112, 51, 20375-20381 (2008)
“Orientational Motions of Vibrational Chromophores in Molecules at the Air/Water Interface with Time-Resolved Sum Frequency Generation” Y. Rao, D. Song, N. J. Turro, K. B. Eisenthal, Journal of Physical Chemistry B 112, 43, 13572-13576 (2008)
“Protonation at the Aqueous Interface of Polymer Nanoparticles with Second Harmonic Generation” J. Liu, M. Subir, K. B. Eisenthal, Journal of Physical Chemistry C 112, 40, 15809-15812 (2008)
“Second Harmonic Studies of Ions Crossing Liposome Membranes in Real Time” J. Liu, M. Subir, K. Nguyen, K. B. Eisenthal, Journal of Physical Chemistry B 112, 48, 15263-15266 (2008)
“Second Harmonic Generation in Neurons: Electro-Optic Mechanism of Membrane Potential Sensitivity” J. Jiang, K. B. Eisenthal, R. Yuste, Biophysical Journal 93, 5, L26 (2007)
“Sodium Channels Amplify Spine Potentials” R. Araya, V. Nikolenko, K. B. Eisenthal, R. Yuste, Proceedings of the National Academy of Sciences of the United States of America 104, 30, 12347-12352 (2007)
“Absolute Orientation of Molecules at Interfaces” Y. Rao, M. Comstock, K. B. Eisenthal, Journal of Physical Chemistry B 110, 4, 1727-1732 (2006)
“Imaging Membrane Potential in Dendritic Spines” M. Nuriya, J. Jiang, B. Nemet, K. B. Eisenthal, R. Yuste, Proceedings of the National Academy of Sciences of the United States of America 103, 3, 786-790 (2006)
“Molecular Rotation at Negatively Charged Surfactant/Aqueous Interfaces” K. T. Nguyen, X. M. Shang, K. B. Eisenthal, Journal of Physical Chemistry B 110, 40, 19788-19792 (2006)
“Ultrafast Excited-State Electron Transfer at an Organic Liquid/Aqueous Interface” E. A. McArthur, K. B. Eisenthal, Journal of the American Chemical Society 128, 4, 1068-1069 (2006)