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Publication Date

2008-04-17

Availability

UM campus only

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PHD)

Department

Chemistry (Arts and Sciences)

Date of Defense

2008-03-18

First Committee Member

Konstantinos Kavallieratos - Committee Member

Second Committee Member

Francisco M Raymo - Committee Member

Third Committee Member

Thomas K Harris - Committee Member

Fourth Committee Member

Roger M Leblanc - Mentor

Abstract

It was found that there was a specific interaction between peptidolipid C18H35O (Stearoyl)-Phe-Trp-Ser-His-Glu and paraoxon. The aromatic residue groups were involved in the recognition between paraoxon and the peptidolipid, because the fluorescence of Trp in the peptidolipid at 351 nm was quenched by paraoxon in the subphase. When paraoxon was dissolved in the subphase, the surface potential-area (delta V-A) isotherm for the peptidolipid A displayed an unusual shape. This was interpreted on the basis of Infrared Reflection-Absorption Spectroscopy (IRRAS) results as being due to the reorientation of the benzene ring of paraoxon, which changed from parallel to the air-water interface in the absence of a monolayer to a tilted orientation upon interacting with the peptidolipid Langmuir monolayer. The secondary structure of oganophosphorus acid anhydrolase (OPAA) Langmuir monolayer in the absence and presence of diisopropylfluorophosphate (DFP) in the subphase was also studied by the IRRAS and Polarization Modulated-IRRAS (PM-IRRAS). The shape of OPAA molecules is supposed to be elliptic and the long axis of OPAA was parallel to the air-water interface in the absence of DFP in the subphase, whereas the long axis became perpendicular in the presence of DFP. This result explains the decrease of the limiting molecular area of OPAA Langmuir monolayer when DFP was dissolved in the subphase. Using the Langmuir monolayer technique, the surface properties of aequorin were studied. The results showed that aequorin formed a stable Langmuir monolayer and the surface pressure-area isotherms were dependent on both pH and ionic strength. At a pH higher or lower than 7.6, the limiting molecular area decreased. The addition of calcium chloride to the Tris/HCl buffer subphase (pH 7.6) caused an increase of the limiting molecular area of the aequorin Langmuir monolayer. The fluorescence spectra of a Langmuir-Blodgett (LB) monolayer of aequorin in the presence of calcium chloride indicated that the aequorin transformed to the apoaequorin. The Langmuir monolayer of aequorin and apoaequorin was studied by IRRAS and PM-IRRAS techniques. The different behavior of aequorin and apoaequorin at the air-water interface was explained by the fact that aequorin formed dimers at air-water interface but apoaequorin was monomer. It was more difficult for a dimer to be tilted by the compression of the Langmuir monolayer.

Keywords

Langmuir-Blodgett; Paraoxon; IRRAS; PM-IRRAS; Langmuir

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