title: Water in Contact with a Cationic Lipid Exhibits Bulklike Vibrational Dynamics.
abstract: Water in contact with lipids is an important aspect of most biological systems and has been termed "biological water". We used time-resolved infrared spectroscopy to investigate the vibrational dynamics of lipid-bound water molecules, to shed more light on the properties of these important molecules. We studied water in contact with a positively charged lipid monolayer using surface-specific two-dimensional sum frequency generation vibrational spectroscopy with subpicosecond time resolution. The dynamics of the O-D stretch vibration was measured for both pure D2O and isotopically diluted D2O under a monolayer of 1,2-dipalmitoyl-3-trimethylammonium-propane. It was found that the lifetime of the stretch vibration depends on the excitation frequency and that efficient energy transfer occurs between the interfacial water molecules. The spectral diffusion and vibrational relaxation of the stretch vibration were successfully explained with a simple model, taking into account the Förster transfer between stretch vibrations and vibrational relaxation via the bend overtone. These observations are very similar to those made for bulk water and as such lead us to conclude that water at a positively charged lipid interface behaves similarly to bulk water. This contrasts the behavior of water in contact with negative or zwitterionic lipids and can be understood by noting that for cationic lipids the charge-induced alignment of water molecules results in interfacial water molecules with O-D groups pointing toward the bulk.
authors: Max Planck Institute for Polymer Research , Ackermannweg 10, 55128 Mainz, Germany.
authors: Ruth A
authors: RA
authors: Livingstone
authors: FOM Institute AMOLF , Science Park 104, 1098 XG Amsterdam, The Netherlands.|Chinese Academy of Sciences , 1st North Street, ZhongGuanCun, HaiDian District, Beijing 100080, China.
authors: Zhen
authors: Z
authors: Zhang
authors: FOM Institute AMOLF , Science Park 104, 1098 XG Amsterdam, The Netherlands.|The Institute of Photonic Sciences , Mediterranean Technology Park, 08860 Castelldefels, Spain.
authors: Lukasz
authors: L
authors: Piatkowski
authors: FOM Institute AMOLF , Science Park 104, 1098 XG Amsterdam, The Netherlands.
authors: Huib J
authors: HJ
authors: Bakker
authors: Max Planck Institute for Polymer Research , Ackermannweg 10, 55128 Mainz, Germany.
authors: Johannes
authors: J
authors: Hunger
authors: Max Planck Institute for Polymer Research , Ackermannweg 10, 55128 Mainz, Germany.
authors: Mischa
authors: M
authors: Bonn
authors: Max Planck Institute for Polymer Research , Ackermannweg 10, 55128 Mainz, Germany.
authors: Ellen H G
authors: EHG
authors: Backus