ABSTRACT

Basic Information

Abstract Number: 1230 - 5
Author Name: Lawrence D Ziegler - Boston University
Session Title: Pittsburgh Spectroscopy Award
Event Type: Awards
Event Title: Ultrafast Vibrational Energy Relaxation and Fluctuation Dynamics in Water, Salt Solutions and Model Lipid Systems

Presider Name:Singh Manocha
Affiliation:The Pittsburgh Conference

Date: Tuesday, March 19, 2013
Start Time: 03:20 PM (Slot #5)
Location: 114

Abstract Content

Ultrafast measurements of vibrational energy relaxation (VER) and vibrational photon echo responses provide both structural and dynamical information about molecules in aqueous solutions on the femtosecond to picosecond timescale. We have used both of these techniques to learn about the structure and dynamics of waters near the hydrophobic and aqueous sites in lipid bilayers. For example, distinct rates of ν3 antisymmetric stretching mode VER of N2O can be distinguished for N2O solvated in the acyl tail, interfacial water and bulk water regions of hydrated DOPC (dioleoylphosphatidylcholine) bilayers. The lifetime of the interfacial N2O population is hydration dependent and attributed to changes in the density of ν3 resonant intermolecular states. Thus, the N2O VER rate becomes a novel and experimentally convenient tool for reporting on the structure and dynamics of interfacial water in lipids and, potentially, in other biological systems. The mechanism of bend-libration combination energy relaxation in neat H2O (~ 2130 cm-1) is determined. This feature and an underlying continuum region are resonant with the ν3 mode of N2O. The linear absorption spectra of aqueous salt solutions show large spectral changes in this libration-bend combination region of the water spectrum that are attributed to first solvation shell effects around cations. These effects follow a Hofmeister series dependence and exhibit a similar trend in ultrafast VER anisotropy measurements. Photon echo measurements of N2O in water and octanol, a model for the acyl chain region of lipids, exhibit very different fluctuation dynamics. A dispersed echo technique must be carried out for this region of the spectrum due to the contribution of the overlapping water bands. Ultrafast 2DIR analysis of these features and 2DIR results on N2O in phospholipids will be discussed. The generalization of this N2O approach for studies of biological waters more generally will be considered.