Conformations and coherences in structure determination by ultrafast electron diffraction
In this article we consider consequences of spatial coherences and conformations in diffraction of (macro)molecules with different potential energy landscapes. The emphasis is on using this understanding to extract structural and temporal information from diffraction experiments. The theoretical analysis of structural interconversions spans an increased range of complexity, from small hydrocarbons to proteins. For each molecule considered, we construct the potential energy landscape and assess the characteristic conformational states available. For molecules that are quasiharmonic in the vicinity of energy minima, we find that the distinct conformer model is sufficient even at high temperatures. If, however, the energy surface is either locally flat around the minima or the molecule includes many degrees of conformational freedom, a Boltzmann ensemble must be used, in what we define as the pseudoconformer approach, to reproduce the diffraction. For macromolecules with numerous energy minima, the ensemble of hundreds of structures is considered, but we also utilize the concept of the persistence length to provide information on orientational coherence and its use to assess the degree of resonance contribution to diffraction. It is shown that the erosion of the resonant features in diffraction which are characteristic of some quasiperiodic structural motifs can be exploited in experimental studies of conformational interconversions triggered by a laser-induced temperature jump.
Additional Information© 2009 American Chemical Society. Received: November 27, 2008; Revised Manuscript Received: January 15, 2009. Part of the "George C. Schatz Festschrift". We are grateful to the National Science Foundation and National Institutes of Health (NIH grant # RO1-GM081520-01) for funding of this research, and we express our gratitude to Prof. Jack Roberts for inspiring discussions involving conformational change and to Prof. David Wales for a number of helpful comments. M.M.L. acknowledges financial support from the Krell Institute and the US Department of Energy (DoE grant # DE-FG02-97ER25308) for a graduate fellowship at Caltech.
Accepted Version - nihms105951.pdf