Photocrystallography

This is a guide for using ThorLabs LED lights for photocrystallography at MX.  Contact Rosie Young if you have any questions. If you want to do photocrystallography, please include it on your EA and email the beamline staff before your experiment.

Considerations

• Crystals should be of good quality and UV-Vis absorption studies should have been done to know the appropriate wavelength of light to use.

• Photosensitive crystals must be mounted with as little exposure to ambient light as possible (depending on the sensitivity, the microscope light can be filtered to allow for mounting), however generally once at 100K they should be stable.

• Collect an initial dataset before starting irradiation studies.

•  Most samples will not react under light irradiation at 100K. The crystals should be warmed (target temperature will be sample dependant), then irradiated. The X-ray diffraction may either be collected at the warm temperature or the crystal may be cooled again before data collection.

Safety

The available LEDs range from Risk Group 0 (eye safe) to Risk Group 3 (hazardous). As such, the system is interlocked through the PSS so that the LEDs cannot be powered on unless the hutch is searched and secured.

Data collection

1. Inform your beamline scientist which LEDs you want to use so they can set up the hardware and perform alignments. Allow at least 30 min.

2. Fill in the “LED Experiment in Progress” sign and attach it to the beamline door so that it is clearly visible.

3. Mount your crystal as normal, considering any exposure to ambient or microscope light and how this may effect the crystal.

4. Collect an initial dataset at 100 K. Check the data quality and processing statistics - if these are poor, it is unlikely that further experiments will be successful.

5. Warm the crystal up to irradiation temperature and collect another dataset.

6. In the LEDs tab of the Controls window, select the correct driver current (consult table of LEDs below) then power (1-100%). To simply turn the light on to 100%, select the LED on button.

7. Collect the number of photocrystallography datasets you wish.

8. After your experiment, select the LED off button to turn off the LED.

Automated data collection (under development)

In the LEDs tab input the wavelength (nm) of the LED, required power level (0-100%), collection interval (eg. 5 min) and total experiment time (eg. 50 min). Press the “collect” button. Monitor progress of the experiment in the terminal window which pops up. Once the experiment is finished, you will see the message “Experiment has ended after ## data collections”. Close the terminal At the end of your experiment, a text file will be written in your collection folder with the experiment parameters to include in your cif and a csv file with be written with the run labels and irradiation times. This will be useful if you want to process your data with CX-ASAP.

Open

Data processing and analysis

CX-ASAP photocrystallography data processing and analysis pipeline under development.

Table of LEDs available