Page 90 - Macromolecular Crystallography

IN-HOUSE MACROMOLECULAR DATA COLLECTION 79

generators are very actively being used as they are and, if possible, to obtain its space group and cell
mechanically robust and, if well maintained and dimensions.
parts are still available, can see tens of years of ser-
vice (in the author’s own laboratory we have an old 5.2.1 Rigaku MSC X-ray generators
Elliot GX-18 big wheel generator with a 70-micron
focus, for which we have enhanced the vacuum sys- Rigaku FR-E Superbright and Rigaku FR-E Super-
tem by putting in turbo-molecular pumps, which bright DW are the highest brilliance generators cur-
will out-perform all generators on the market except rently on the market and operate with a 70 µm ×
for those of highest brilliance – FR-E, 007 HF, and 70 µm focal spot size and a power of 2 kW, with
Microstar, discussed below). a maximum operating voltage of 60 kV and a cur-
In this section I shall only cover the X-ray gen- rent varying up to 45 mA dependent on the target
erators that are currently being sold commercially. material. The rotating anode has a diameter of
Many laboratories have moved away from col- 280 mm and revolves at 9000 r.p.m. The large wheel
lecting a large amount of data in-house to using and the fast rotation allows rapid heat dissipation
synchrotrons as their preferred method of acquir- from the anode and hence permits a higher load-
ing native data and phases for structure solution. ing (in terms of voltage and current). This concept,
These groups consequently only use in-house sys- of having a large wheel to dissipate the heat over
tems to screen crystals prior to taking them to a a large area, came in with the Elliot GX-13 and
synchrotron. In the author’s opinion, it really pays GX-18 series of generators (which Enraf-Nonius con-
dividend to have a very bright X-ray source in-house tinued to make for a short time after purchasing
for three reasons. Firstly, if one has grown a very Elliot from GEC). For the GX-13 and 18, the wheel
small crystal of a given macromolecule from initial is a 457 mm (18 inches) in diameter and spins at
crystallization trials, being able to characterize it in 3000 r.p.m. Therefore, a larger wheel allows heat
terms of its space-group, cell dimensions, and cell dissipation over a larger surface area as compared
contents may give a good indication of the direc- with its smaller counterpart, and spinning the wheel
tion in which to proceed with further crystallization faster will allow more heat dissipation but will in
attempts. For example if one is trying to cocrys- turn place a greater mechanical demand on the drive
tallize a protein – DNA complex and there turns motor, bearings, and seals.
out not to be DNA in the lattice as judged by the The development of better bearings and ferro-
cell volume and Vm), then clearly conditions have fluidic seals, as compared to the older lip-seals, has
to be altered in order to steer the crystallization allowed the wheel to be spun faster and cooled more
attempts in a direction towards obtaining crystals efficiently. The downside of having a very large
of the complex. The most optimistic chance of per- wheel is that it is more awkward to remove and
forming this operation reliably on small, weakly clean, since handling jigs are required for this oper-
diffracting crystals is achieved by having an in- ation compared with a standard 99 mm wheel, as
house generator of the highest brilliance. Secondly, found on the RU200 and RU300 generators and on
it may occur that, at a critical time, due to lack of theRigakuMSC007HF,whichcanbeeasilyremoved
beam time at a synchrotron, one has an urgency to by hand. The FR-E and the FR-E DW (which has the
collect and try to phase a structure in-house. Then, capability of collecting at two wavelengths by hav-
with the highest brilliance generator one is going ing a band of copper and chromium on the same
to be able to collect data to the highest possible wheel and compatible optics for in-house SAD phas-
resolution in the fastest time. Thirdly, if only one ing) are flagship generators but their initial high cost
crystal is available, and the cryocooling conditions and high running costs, in terms of ferrofluidic seals,
have not been determined, and if the crystal does has meant that they have only been purchased by
not ‘travel well’ to a synchrotron, it pays to have a more affluent laboratories.
good source of X-rays close to the where the crystal Rigaku MSC has recently introduced a UltraX-18
was grown in order to assess its diffracting power generator which runs at 18 kW with a wide range of