DIFFRACTION MEASUREMENTS AT SOURCES

OF SYNCHROTRON RADIATION

J. Hašek

Institute of Macromolecular Chemistry AV CR, Heyrovského nám.2,

162 06 PRAHA 6, hasek@imc.cas.cz

Structure determination of biological macromolecules and their interactions with other molecules important for life play a principal role for understanding their function, i.e. for development of new generation of drugs, for environment, for agriculture, for food industry, for protection of human life, etc. Nowadays, the diffraction experiments performed at sources of synchrotron radiation dominate in successful structure determination of macromolecular systems. The last year, already more than 80 % of ~ 6000 papers publish works based on the use of synchrotron radiation and a percentage of the remaining experiments made using home diffraction equipment is continuously decreasing each year.

There are more than 70 synchrotron sources in 23 countries. Many synchrotrons have more beam lines for macromolecular crystallography, e.g. APS in Argonne USA have 19 beamline specialized for protein crystalography, ESRF in Grenoble 14 beamlines, Spring-8 in Japan 11 beamlines [1], etc.

In spite of the fact that Czech crystallographers use extensive official and unofficial contacts with synchrotrons placed exclusively in west part of European Union, they cope with a critical shortage of measuring time. The average one beamtime a year per one laboratory is hopelessly much low than required for really competitive scientific work in structure biology.

The synchrotron CESLAB (Central European Synchrotron Laboratory) planned if frame of Structural Funds of EU involves in addition to many other unique equipments devoted to medicine, spectroscopy, etc., also a modern macromolecular beamline devoted to protein crystallography solving practically all requirements of protein crystallographers for the next 20-30 years.

The CESLAB is not designed for protein crystallographers only. The synchrotron radiation is required almost in all fields of natural sciences. The construction of CESLAB allows almost any extension or modification of the equipment in future. In spite of the fact that the present design of synchrotron has a maximum 10 beamlines devoted to different scientific areas, the constructions still allows an addition up to several tenth other experiments possibly claimed and designed in future without stopping the operation of the standing beamlines.

All equipment planned for CESLAB has been developed and produced for many years by the best world laboratories. Therefore, it is very reliable and represents a top the world science.

Top of the experimental technique as far as the sources of X-ray radiation represent also newly developed "home sources of radiation". One of them "LYNCEAN compact light source" simulates the standard synchrotron source but instead of the insertion device (e.g. undulator with ~1 cm gap) it uses very intensive IR laser pulse (wavelength ~ 1 mm) synchronized and sent against the intensive electron beam in the storage ring (Fig. 1) http://www.lynceantech.com/sci_tech_cls.html. It allows substantial lowering of energy of the electron beam to get the same wavelength of radiation and thus to reduce the size of the whole equipment (~ 20 m). The small size of the storage ring does not allow to place more beamlines on the ring. However, the only beamline available at LYNCEAN can be split to two or three devices in the experimental hutch.

The principle of LYNCEAN was verified in the factory in California on the functional prototype emitting the radiation. Because the first equipment specialized for protein crystallography is still in stage of verification only, a real brilliance of radiation (dependent strongly on the IR laser parameters) and other characteristics (polarization, divergence, etc.) are still a subject of guesses only. Estimates are at level of a bending magnet of the second generation synchrotrons. The equipments of this type belong undoubtedly to the most perspective radiation sources for future, because it will allow higher diversity and a possibility to purchase their own specialized sources of radiation to the individual research institutions.

Fig.1. Schematic view explaining principles and a function of the LYNCEAN compact light source. Reprinted from http://www.lynceantech.com/sci_tech_cls.html

Another type of "intensive home source of radiation" is MIRRORCLE RAY 20SX designed in Japan. It is based on the same principle as a standard X-ray tube, however the electron beam falling on target is accelerated to very high energy (1 – 20 MeV). It impact of accelerated electron beam produces "bremsstrahlung" (i.e. white radiation) up to very high energies (Fig. 2). The very high energy radiation can pass through thick blocks of concrete or steel. It makes this product especially suitable for industrial testing of quality of buildings or heavy industrial products (the equipment with this determination that can be transported on a large lorry is already in production). The use of MIRROCLE in scientific laboratory (with the required energy of radiation in range 7-13 keV) is very problematic because of immense difficulties with shielding of unwanted very hard and intensive radiation. The efficiency for experiments with monochromatic radiation might be increased by a special design with a "parametric radiation" generated in the monocrystalic target properly oriented against the accelerated electron beam. However, there is no functional prototype and the theoretical data are not enough promising with respect to the price and operational costs (Tab.1).

Table 1. Comparison of radiation from MIRROCLE, X-ray tube and bending magnet. Reprinted from

http://www.photon-production.co.jp/e/PPL-monochroX-ray.html#XAFS

	MIRRORCLE RAY 20 MeV	X-ray tube	Synchrotron bending Magnet
Density @13keV (photons/sec/mrad^2/0.1%λ)	10^10(Present Value: 10^8)	10^8  @8keV	10^11
Brilliance@13keV (photons/sec/mrad^2/mm^2/0.1%λ)	10^14(Present Value: 10^12)	(The case of Micro-focus; 10^12  @8keV)	10^15
Density @13keV (photons/sec/mrad^2/0.1%λ)	10^10(Present Value: 10^8)	10^8  @8keV	10^11
Brilliance@13keV (photons/sec/mrad^2/mm^2/0.1%λ)	10^14(Present Value: 10^12)	(The case of Micro-focus; 10^12  @8keV)	10^15

Fig. 2. Performance of MIRROCLE 6 MeV and 20 MeV. The calculated brilliance [photons/sec/mrad2/mm2/0.1%λ] in the whole spectrum. The 20 MeV model of MIRROCLE is compared to the 6 MeV model for carbon target, to the standard rotating anode, and to the bending magnet of the older generation synchrotrons. The radiation used in protein crystallography should be highly monochromatic and is about 12 keV. Complete removal of radiation over 100 keV represents a serious problem. Reprinted from http://www.photon-production.co.jp/e/PPL-monochroX-ray.html#XAFS

The project is supported by GA AV IAA500500701 and GA ČR 305/07/1073.

[1] J. Hašek, Opportunities for protein Crystallograpny at the Central European Synchrotron Laboratory, Materials Structure, 15 (2008) 19-24.

Keywords:

Synchrotron radiation, protein crystallography, structure determination