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The phase problem in neutron crystallography.

Herbert A Hauptman1, David A Langs

  • 1Hauptman-Woodward Medical Research Institute, Inc., 73 High Street, Buffalo, NY 14203-1196, USA. hauptman@hwi.buffalo.edu

Acta Crystallographica. Section A, Foundations of Crystallography
|April 26, 2003
PubMed
Summary

Solving the crystal structure of cyclosporin using neutron diffraction revealed that density positivity is not required and may hinder phase problem solutions.

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Area of Science:

  • Crystallography
  • Structural Biology
  • Neutron Diffraction

Background:

  • The phase problem is a fundamental challenge in crystallography.
  • Positivity of the electron density is often assumed as a constraint for solving the phase problem.
  • Cyclosporin is an important immunosuppressive drug with a complex cyclic peptide structure.

Purpose of the Study:

  • To determine the crystal structure of cyclosporin using only neutron diffraction data.
  • To investigate the role of density positivity in solving the crystallographic phase problem.

Main Methods:

  • Modified Shake-and-Bake procedure.
  • Analysis of experimental neutron diffraction data for cyclosporin monohydrate.

Main Results:

  • The crystal structure of cyclosporin was successfully solved using only neutron diffraction data.
  • The study demonstrated that positivity of the density function is not a necessary prerequisite for solving the phase problem.
  • Initial findings suggest that density positivity might impede phase problem solutions in certain cases.

Conclusions:

  • The assumption of density positivity can be relaxed in crystallographic structure determination.
  • Neutron diffraction data, combined with appropriate algorithms, can overcome the phase problem without relying on density positivity.
  • This research opens new avenues for solving challenging crystal structures where positivity constraints may be problematic.

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