Biophysical Journal 64: 1110-1112 (1993)
© 1993 the Biophysical Society

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Evidence of partial rotational order in gel phase DPPC.

Department of Biological Sciences, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213.

ABSTRACT

It is shown how the dichroic ratio of the symmetric methylene stretching modes depends upon both the rotational order of hydrocarbon chains about their long axis and the tilting of the long chains with respect to the bilayer normal. Use of a recent determination of the tilt angle from x-ray measurements together with recent dichroic infrared data yields a rotational order parameter g = -0.30 compared to g = 0 for complete disorder and g = +/- 1 for complete order. The negative value of g corresponds to a preference for the plane defined by the chain carbons to be more perpendicular than parallel to the plane defined by the tilt direction and the bilayer normal.