For X-ray powder diffraction spectra collected by an area detector of MarCCD on macromolecular crystallography beamline of SSRF,an energy calibration method was developed using LaB_6(660a) powder diffraction for in-situ rapid energy calibration of the X-rays without changing the experimental conditions.The intensity of each diffraction ring was integrated,and the accurate peak positions were fitted by Pseudo-Voigt function model.The sample's interplanar spacing for XRD analysis and the calibrated energy were obtained by the PCPDFWIN code and by fitting all the energies with the least-square method.The exposure time and the sample-to-detector distance were found no effect on accuracy of the energy calibration,and the in-situ energy calibration could be done with an accuracy of better than 0.4‰in 7-18 keV.This method is applicable to other X-ray beamlines.
It was reported that the a-helix of protein molecules could be destroyed when they were exposed to the electromagnetic field(EMF) and finally the signal transduction could be affected.To study this effect,one signal molecule,insulin,was exposed to electromagnetic fields at different combinations of the field strength,repetition rate and exposure time.For the first time,structural biology approach was used to detect the EMF effect.The results of a series of measurements on the interaction of electromagnetic fields with insulin in vitro are described.Under our experimental conditions,no effects of electromagnetic field exposure were observed on the molecular conformation.
