A fast and portable microspectrophotometer for protein crystallography

Spectroscopic measurements on crystals during X-ray data collection provide additional information on the composition of the crystal and can be used in the interpretation of structural data. This paper describes a portable microspectrophotometer to obtain UV-visible-near-IR spectra from single crystals during X-ray measurements. The instrument consists of a deuterium lamp, optical fibres, a pair of mirror lenses and a monochromator equipped with a photodiode array detector. Spectra can be recorded in short periods of time (a few milliseconds) from a measurement area of 0.10 mm diameter or smaller. The device can be used to monitor spectral changes in crystals during time-resolved X-ray experiments so that the X-ray camera can be triggered at the right moment as determined by the spectrum, thereby eliminating much of the present guesswork from such studies.