Twelfth Annual Sigma Xi Postdoctoral Poster Presentation,

    Feb. 24 ,2005, NIST, Gaithersburg

    Title: Neutron diffraction in membrane research. The Advanced Neutron Diffractometer/Reflectometer.

    Category: Biology

    Authors: M.Mihailescu, F.Castro-Roman, S.White (University of California at Irvine), D.Worcester (University of Missouri, Columbia), C.Majkrzak (NIST Center for Neutron Research)

Presenter: Mihaela Mihailescu

Division: CNBT@NCNR

Tel: 301-975-8327; Fax: 301-921-9847, ella.mihailescu@nist.gov

NCNR, Bldg 235, Stop: 8562, Rm. E120   

Mentors: Stephen White (UC Irvine), Charles Majkrzak (NCNR)

Abstract:

Neutron diffraction is becoming an increasingly important method of investigation for biological matter. In particular, knowledge of the structure of fluid lipid bilayers is needed for understanding complex biological phenomena in cell membranes, as well as for validating molecular dynamics simulation models.

A new instrument, the Advanced Neutron Diffractometer/Reflectometer operating at NCNR, under the "Cold Neutrons for Biology and Technology" project, was employed for high resolution measurements on lipid multilayers.

Neutron diffraction results on lamellar lipid multilayers suffer from the disagreement between dynamical reflectivity and the widely used kinematical approximation, at high values of the reflectivity. It will be shown how the position and distribution of water, and certain carbon atoms along the acyl chains (e.g. at the double bond) can be directly pinpointed using deuterium labeling. A method to correct data for dynamical diffraction effects and a demonstration of how these effects can affect the above mentioned molecular distribution profiles, are presented. Experimental results on the structure of several lipids from the Phosphatidyl-Choline class, are reported. 

Acknowledgments: Research supported through Grants GM68002 and

NIH-RR14812 from the National Center for Research and

Resources, and the University of California at Irvine.