title: Studying Water Hydrogen-Bonding Network near the Lipid Multibilayer with Multiple IR Probes.
abstract: A critical difference between living and nonliving is the existence of cell membranes, and hydration of membrane surface is a prerequisite for structural stability and various functions such as absorption/desorption of drugs, proteins, and ions. Therefore, a molecular level understanding of water structure and dynamics near the membrane is important to perceive the role of water in such a biologically relevant environment. In our recent paper [ J. Phys. Chem. Lett. 2016 , 7 , 741 ] on the IR pump-probe study of the OD stretch mode of HDO near lipid multibilayers, we have observed two different vibrational lifetime components of OD stretch mode in the phospholipid multibilayer systems. The faster component (0.6 ps) is associated with OD groups interacting with the phosphate moiety of the lipid, while the slower component (1.9 ps) is due to choline-associated water molecules that are close to bulklike water. Here, we additionally use hydrazoic acid (HN3) as another IR probe of which frequency is highly sensitive to its local H-bonding water density. Interestingly, we found that the vibrational lifetime of the asymmetric azido stretch mode of HN3in the lipid multibilayer system is similar to that in neat water, whereas its orientational relaxation is a bit slower than that in bulk water. This indicates that due to the tight packing of lipid molecules, particularly the head parts, in the gel phase, HN3molecules mostly stay near the choline group of lipid and interact with water molecules in the vicinity of choline groups. This suggests that membrane surface-adsorbed molecules such as hydrophilic drug molecules may interact with choline-associated water molecules, when the membrane is in the gel phase, instead of phosphate-associated water molecules.
authors.affiliation: Center for Molecular Spectroscopy and Dynamics, Institute for Basic Science (IBS) , Seoul 02841, Republic of Korea.|Department of Chemistry, Korea University , Seoul 02841, Republic of Korea.
authors.forename: Achintya
authors.identifier: http://orcid.org/0000-0002-6252-1763
authors.initials: A
authors.lastname: Kundu
authors.affiliation: Center for Molecular Spectroscopy and Dynamics, Institute for Basic Science (IBS) , Seoul 02841, Republic of Korea.|Department of Chemistry, Korea University , Seoul 02841, Republic of Korea.
authors.forename: Pramod Kumar
authors.identifier: http://orcid.org/0000-0001-8837-3167
authors.initials: PK
authors.lastname: Verma
authors.affiliation: Space-Time Resolved Molecular Imaging Research Team, Korea Basic Science Institute (KBSI) , Seoul 136-075, Republic of Korea.
authors.forename: Jeong-Hyon
authors.initials: JH
authors.lastname: Ha
authors.affiliation: Center for Molecular Spectroscopy and Dynamics, Institute for Basic Science (IBS) , Seoul 02841, Republic of Korea.|Department of Chemistry, Korea University , Seoul 02841, Republic of Korea.
authors.forename: Minhaeng
authors.identifier: http://orcid.org/0000-0003-1618-1056
authors.initials: M
authors.lastname: Cho
mesh_terms: D001386:Azides / Q000737:chemistry*; D005456:Fluorescent Dyes / Q000737:chemistry*; D006860:Hydrogen Bonding; D008055:Lipids / Q000737:chemistry*; D015394:Molecular Structure; D013055:Spectrophotometry, Infrared; D014867:Water / Q000737:chemistry*
chemical_list: D001386:Azides; D005456:Fluorescent Dyes; D008055:Lipids; D014867:Water; C007972:hydrazoic acid