International
Tables for Crystallography Volume C Mathematical, physical and chemical tables Edited by E. Prince © International Union of Crystallography 2006 |
International Tables for Crystallography (2006). Vol. C. ch. 3.4, pp. 162-167
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This section deals with the mounting of two categories of specimens:
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Category 2 is further divided into single crystals of small organic and inorganic molecules, and those of biological macromolecules at both ambient and cryogenic temperatures. Commonly used methods of mounting specimens for both camera and diffractometer, and most other detector systems are described.
The bibliography is necessarily selective and wherever possible has been restricted to journals and textbooks that are readily accessible to a crystallographic laboratory. It should also be noted that there exist, worldwide, various centres specializing in synchrotron-radiation and neutron diffraction techniques. Within these centres lies a wealth of experience in sample handling and preparation. For specialist purposes, communication with local contacts at such centres may provide invaluable assistance.
Informative accounts of the powder method of recording diffraction patterns have been given by Klug & Alexander (1954), D'Eye & Wait (1960) and Dent Glasser (1977). There are three principal methods of preparing polycrystalline specimens for mounting in powder cameras:
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The most common method of preparing samples of polycrystalline materials is to encase them in thin-walled capillary tubes, for Debye–Scherrer camera work, or into sample holders, for Guinier camera and diffractometer measurements. This technique has the advantage that the sample can be readily protected from attack by oxygen, carbon dioxide and water vapour, and, if necessary, the sample preparation can be undertaken in an inert atmosphere (Lange & Haendler, 1972; D'Eye & Wait, 1960). The precise details of sample preparation and mounting will be dependent on the type of camera or diffractometer used, but the particle size should be generally less than 10 µm for stationary samples and diffractometer work. A slightly larger particle size, 45 µm, can be used for Debye–Scherrer camera work if the specimen is rotated. Foit (1982) has described a simple method of filling thin-walled capillaries using an ultrasonic vibrator. A frequent problem affecting intensity measurements from powder specimens is caused by preferred orientation when powder samples are packed or pressed. McMurdie, Morris, Evans, Paretzkin & Wong-Ng (1986) have described a method of sample preparation suitable for a diffractometer that minimizes this problem.
Capillaries made from lithium beryllium borate (Lindemann glass), borosilicate (e.g. Pyrex glass), or fused silica are commercially available in a variety of internal diameters. For very high temperatures, thin-walled ceramic or metal capillaries can be used. The diffraction pattern of the metal can be used as an internal standard. Capillaries that are suitable for materials that react with glass can be made from various organic polymers. Table 3.4.1.1 lists details of capillaries and other containers suitable for encasing powder specimens.
For optimum results, tube diameters should be between 0.3 and 0.5 mm with wall thicknesses of 0.02 to 0.05 mm. The materials listed above, except where stated, give diffuse diffraction patterns. If necessary, control diffraction patterns, recorded only from the capillary or other container, should be taken.
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In the bonded method, the polycrystalline material is mixed with an adhesive such as gum tragacanth or ethyl cellulose, and the mixture is wetted with water or aqueous alcohol to form a viscous paste. The paste is then rolled between two glass slides or extruded through a glass capillary, using a glass or metal piston, to form a cylindrical sample. This can be cut to length and either glued, fixed with plasticine, or cemented (for high-temperature work) to the camera mounting pin. Alternatively, the sample can be compressed and compacted in a die to form a solid rod, or, for diffractometers, into a disc. In the case of very small quantities of material, the powder can be smeared with silicone vacuum grease over the surface of a disc-shaped silica crystal. The silica can then be used as an internal standard.
In the fibre-supported method, a silica, Lindemann, or borosilicate glass fibre moistened with adhesive (Canada balsam diluted with xylene, collodion, gum tragacanth and water, dilute fish glue) is dipped into the powder. Experience has shown that powder adhesion to the fibre is often improved if non-drying glues or viscous oils are employed. Hairs of fine organic filaments have been used in place of glass fibres, and for high temperature above 1270° C metal wires are useful. Once again, the metal diffraction patterns can act as internal standards. For extruded metal wires, the wire itself acts as the specimen, and the diameter can be reduced by etching if it is too large, or a glancing-angle diffraction technique can be employed. Various specialized holders for diffraction studies of polycrystalline samples can be found in annual conference proceedings such as EPDIC (European Powder Diffraction Conference, Switzerland: Trans Tech Publications) and Advances in X-ray Analysis (Proceedings of the Annual Conference on the Applications of X-ray Diffraction, New York/London: Plenum). The journals Reviews of Scientific Instruments (American Institute of Physics) and Nuclear Instruments and Methods (Elsevier, North-Holland) also provide useful sources of information.
A number of devices have recently been described to study polycrystalline specimens under non-ambient conditions. Rink, Mathias & Schlenoff (1994) have designed a portable sample housing for work at room temperature with samples that are air or moisture sensitive. A review of designs and desirable features for high-temperature furnaces suitable for X-ray diffractometers has been given by McKinstry (1970). More recently, Puxley, Squire & Bates (1994) have described an in situ cell fitted to a Siemens D-500 powder diffractometer that allows samples in flowing or static reactive gas environments at atmospheric pressure and at temperatures up to 1273 K. These authors also review other developments in the field of high-temperature furnaces for polycrystalline X-ray diffraction published since the McKinstry article in 1970. Brown, Swapp, Bennett & Navrotsky (1993) have devised methods to minimize the uncertainties in temperature at the sample and in the position of the sample itself. Tarling, Barnes & Mackay (1984) have adapted a Guinier–Lenné high-temperature powder camera to include a gas rinsing system and a specially designed mini-environment cell in which conditions of industrial furnacing can be simulated. In the neutron area, Lorenz, Neder, Marxreiter, Frey & Schneider (1993) have developed a mirror furnace working at up to 2300 K and suitable for polycrystalline or single-crystal samples.
A comprehensive account of cryogenic studies pertinent to both polycrystalline and single-crystal samples is given by Rudman (1976). Nieman, Evans, Heal & Powell (1984) have described a device for the preparation of low-temperature samples of noxious materials. The device is enclosed in a vanadium can and is therefore only suitable for neutron diffraction studies. Ihringer & Küster (1993) have described a cryostat for powder diffraction, temperature range 8–300 K, for use on a synchrotron-radiation beam line at HASYLAB, Germany (Arnold et al., 1989).)
Small single crystals of inorganic and organic materials, suitable for intensity data collection, are normally glued to the end of a glass or vitreous silica fibre, or capillary (Denne, 1971b; Stout & Jensen, 1968). A simple device that fits onto a conventional microscope stage to facilitate the procedure of cementing a single crystal to a glass fibre has been constructed by Bretherton & Kennard (1976). The support is in turn fixed to a metal pin that fits onto a goniometer head. For preliminary studies, plasticine or wax are useful fixatives, since it is then relatively easy to alter the orientation of the support, and hence the crystal, as required. For data-collection purposes, the support should be firmly fixed or glued to the goniometer head pin. The fibre should be sufficiently thin to minimize absorption effects but thick enough to form a rigid support. The length of the fibre is usually about 10 mm. Kennard (1994) has described a macroscope that allows specimens to be observed remotely during data collection and can also be used for measurement of crystal faces for absorption correction. Large specimens can be directly mounted onto a camera or onto a specially designed goniometer (Denne, 1971a; Shaham, 1982). A method using high-temperature diffusion to bond ductile single crystals to a metal backing, for strain-free mounting, has been described by Black, Burdette & Early (1986).
Prior to crystal mounting, it is always prudent to determine the nature of any spatial constraints that are applicable for the proposed experiment. Some diffractometers have relatively little translational flexibility, and the length of the fibre mount or capillary is critical. For some low-temperature devices where the cooling gas stream is coaxial with the specimen mount, the orientation of the fibre (and crystal) on the goniometer head may also need careful alignment.
Many proprietary adhesives can be used (see Table 3.4.1.2), but it should be remembered that adhesives such as epoxy resins are often permanent, and attempts to dismount specimens lead to crystal damage. Some adhesives contain organic solvents that may react with the sample, and others may be X-ray sensitive and deteriorate with exposure. In low-temperature work, some adhesives shrink or become brittle. Ideally, the adhesive should have the same thermal characteristics as the crystal and its mount. An account of how strong stresses on adhesives, typically used to mount single crystals, induced by low and high temperatures is given by Argoud & Muller (1989a). The stresses appear to cause anisotropic modifications to secondary extinction, leading to discrepancies in the intensities of symmetry-related reflections. Beeswax and paraffin wax were found to be free from such stresses. Crystals that are sensitive to air can be mounted inside capillary tubes or other containers, as listed in Table 3.4.1.1. A useful summary of the methods available has been provided by Rao (1989). All adhesives and containers will give diffraction patterns, typically comprising diffuse bands, that contribute to the general background, and that may change with ageing. Minimal amounts of adhesive and thin-walled capillaries should be used. If the background diffraction is critical, it is highly recommended that diffraction patterns of the container and/or adhesive are recorded separately as controls.
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The morphology of a given crystal will normally dictate the way that it is mounted, particularly for data-collection purposes. Thus, prismatic crystals and needle-shaped crystals are usually mounted with the longest dimension parallel to the fibre, in order to minimize systematic errors due to absorption. Jeffery (1971) and Wood, Tode & Welberry (1985) have described devices for shaping crystals into spheres and cylinders, respectively. A solvent lathe whereby a string moistened with solvent is used to shape the crystal is described by Stout & Jensen (1968).
As in the case of polycrystalline samples, a number of devices have been described to study single crystals at elevated pressures and at a range of temperatures. The mounting of the sample is very dependent on the device and radiation used. In recent years, the field of high-pressure crystallography has expanded significantly, and several sample holders based on the diamond-anvil cell have been reported for pressures up to 10 GPa. Recent papers include those by Alkire, Larson, Vergamini, Schirber & Morosin (1985) for neutron diffraction, and Malinowski (1987) and Leszczynski, Podlasin & Suski (1993) for X-ray diffraction.
Various types of furnace have been designed for high-temperature studies of single crystals. These are based either on radiative heat transfer mechanisms [e.g. Swanson & Prewitt (1986); temperatures up to 1400 K], electrically heated gas streams [e.g. Tsukimura, Sato-Sorensen & Ghose (1989); temperatures up to 1600 K], or flame heaters [e.g. Miyata, Ishizawa, Minato & Iwai (1979); temperatures up to 2600 K]. Furnaces specific to Weissenberg geometry (Adlhart, Tzafaras, Sueno, Jagodzinski & Huber, 1982) and Laue diffraction (Bhat, Clark, El Korashy & Roberts, 1990) have also been reported. There are many techniques available for mounting single crystals for high-temperature diffraction (Hazen & Finger, 1982), and a detailed account using an MgO-based ceramic cement is given by Swanson & Prewitt (1986). A recent paper by Peterson (1992) summarizes previous work in the design of high-temperature furnaces and describes a flame-heated gas-flow furnace operating in the range 373 to 1573 K. For this system, the crystals can be mounted either directly onto the thermocouple bead with a paste of fine platinum particles and oil, particularly useful if the crystal is to be exposed to a gas mixture that controls oxygen fugacity, or sealed under high vacuum in an ampoule made from 0.2 or 0.3 mm diameter silica capillary. In the latter case, the main support for the crystal is a 0.2 mm Pt wire threaded through a 0.3 mm diameter silica glass capillary. A 0.05 mm Pt/13Rh lead is welded to the end of this support to form the thermocouple bead. The wire is then wound around the outside of the capillary. A 0.05 mm Pt lead is welded to the other end of the 0.2 mm Pt wire and is threaded through a hole in the capillary near the base. The whole assembly can be mounted on a goniometer head that has only translational adjustments. For neutron diffraction, Lorenz, Neder, Marxreiter, Frey & Schneider (1993) have described a mirror furnace operating upto 2300 K. The sample support is normally a thin ceramic tube or rod of Al2O3 or ZrO2 to which the sample may be glued with a ceramic cement. Neder, Frey & Schulz (1990) have described a versatile holder for high-temperature neutron studies. One part of the crystal is ground away to leave a stem, which is then fixed to an alumina rod with a ceramic glue based on zirconia. The ceramic glue is surrounded by a cylinder of BN to minimize spurious scattering.
A comprehensive account of low-temperature diffraction is given by Rudman (1976). Procedures for the selection and transfer of crystals to diffractometers have been described by Boese & Bläser (1989) and Kottke & Stalke (1993). These procedures are applicable down to temperatures of 213 and 193 K, respectively. The latter authors do not recommend the use of capillaries, but describe a device employing the oil-drop mounting technique pioneered by Hope (1987, 1988). Lippman & Rudman (1976) have used a mechanically refrigerated gas stream to achieve temperatures down to approximately 150 K, and the use of liquid nitrogen extends the range to 77 K. Devices such as the Oxford Cryostream can be readily fitted to diffractometers and other types of camera. Closed-cycle refrigerators, liquid-helium-based devices (e.g. Henriksen, Larsen & Rasmussen, 1986; Argoud & Muller, 1989b; Zobel & Luger, 1990; Graafsma, Sagerman & Coppens, 1991; Toyoshima, Hoya & Ohshima, 1991) further extend the low-temperature limit to 5 K, but often involve substantial blind regions and collision zones. For sample mounting in these devices, it is essential to have good heat conduction to the crystal. Zobel & Luger (1990) describe a taper-formed sample holder made of special copper screwed to the cold head. A steel injection needle with a Be wire inside (0.3 mm diameter and exactly 2 mm in length) is fitted into a 0.5 mm bore hole. The crystal is glued with Araldite to the Be needle, which has little X-ray absorption but good heat conduction. In addition to diffractometer-based devices, Moret & Dallé (1994) have described an adaptation of the closed-cycle refrigerator for a precession goniometer, and various authors have reported systems utilizing Weissenberg geometry for both X-rays and neutrons (e.g. Hohlwein & Wright, 1981; Adlhart & Huber, 1982; Allen et al., 1982). Reference should be made to the individual papers for methods of mounting, including spatial and any other constraints.
Crystals of biological macromolecules are normally grown from an aqueous solution (see Subsection 3.1.1.2 ), and when growth is complete are in equilibrium with the mother liquor. Changes in this equilibrium may often result in crystal damage, so the most important aspect of crystal mounting in this case is to preserve the crystal in its state of hydration. This is most readily accomplished by sealing the crystal in a thin-walled quartz or glass capillary tube (King, 1954; Holmes & Blow, 1966). The crystal adheres to the inside of the tube by surface-tension effects through a small droplet of liquid, and a further pool of liquid at one end maintains the required degree of hydration. The general principles involved are well described by Rayment (1985). D'Aprile & Moretto (1975) have described two simple devices, a small electric heater for melting the wax used for sealing the capillary and a refrigerating microcell to prevent heat affecting the wet crystal, which are very useful for mounting wet single crystals in capillary tubes.
Alternatively, crystals can be grown directly within capillary tubes (Phillips, 1985) or microdialysis cells such as those described by Zeppezauer, Eklund & Zeppezauer (1968). A further mounting device particularly useful for enzymatic studies is the flow cell (Wyckoff et al., 1967), in which the specimen is immobilized while mother liquor, or buffer with substrates or inhibitors, is allowed to flow over the crystal. A useful account of this device is given by Petsko (1985). More recently, Edwards (1993) has described a yokeless flow cell, which uses a plastic cone fixed to a brass mounting pin with a wire harness to support the quartz capillary. Although the device was originally designed for Laue studies, its simplicity and practicality should make it useful for a wide range of diffraction experiments. Pickford, Garman, Jones & Stuart (1993) have designed a mounting cell that allows the humidity around a protein crystal to be varied in a controlled manner. This may be particularly useful for crystals where the solvent content is high and the molecular packing, and hence the diffraction intensities, highly dependent on the precise amount of solvent present.
The relatively short crystal lifetimes and large volumes of intensity data often dictate that crystals of biological macromolecules be mounted so that data collection can be accomplished in the most efficient manner, for example, with a symmetry axis parallel to the rotation axis of the collection device. Samples crystallizing in the form of thin plates that have to be aligned perpendicular to the capillary axis can be wedged using cotton lint fibres (Narayana, Weininger, Heuss & Argos, 1982), or mounted on a fibre plug (Przybylska, 1988).
One of the key problems in collecting diffraction data from wet crystals is movement of the specimen within the capillary, i.e. crystal slippage. Numerous ways have been suggested to surmount this problem, including flattening of the capillary surface, surrounding the crystal with a thin film of plastic (Rayment, Johnson & Suck, 1977) and supporting the crystal with fibre plugs in contact with the mother liquor.
Pressure cells. Tilton (1988) has described an attachment that can be used on conventional diffractometers for collecting X-ray data from biomolecular crystals under gas pressures up to 300 atm (30 MPa). The crystals are coated with mineral oil to minimize dehydration (see Subsection 3.4.1.5) and mounted in a quartz glass capillary between two layers of cotton fibres. These fibres give mechanical support to the specimen and protect it from shock during gas pressurization. No plugs of mother liquor or oil are used so that the gas flow is unimpeded. Kundrot & Richards (1986) describe an adaptation of the flow cell for hydrostatic pressure studies up to 0.2 GPa. More recently, Kroeger & Kundrot (1994) have described a gas cell that allows data sets at several partial pressures to be collected from the same crystal.
Useful recent reviews on protein crystallography at low temperatures have been written by Hope (1990) and Watenpaugh (1991).
Crystals of biological macromolecules are very susceptible to radiation damage, and this can severely limit the amount and quality of diffraction data that can be collected per crystal. There have been relatively few systematic studies of this phenomenon (Young, Dewan, Nave & Tilton, 1993; Gonzalez & Nave, 1994; Nave, 1995), but one of the first effects of radiation damage is the deterioration of the high-resolution regions of the pattern, followed by increasing loss of crystallinity. Improvement of crystal lifetime in X-ray beams has been obtained by the addition of free-radical scavengers (Zaloga & Sarma, 1974) and the replacement of the mother liquor with solutions containing 10–20% polyethylene glycol 4000 or 20000 (Cascio, Williams & McPherson, 1984). The use of synchrotron radiation has also led to improved data-per-crystal ratios (Lindley, 1988). The high intensity allows fast collection of data, and the high collimation permits different sections of the same crystal to be used for data collection. This is particularly useful for prismatic crystals, which can be mounted along their largest morphological axis. An alternative method of surmounting this problem, however, is to freeze the protein crystal. As the temperature is decreased, the rate of diffusion of free radicals is reduced, with a corresponding reduction in radiation damage. Appreciable reduction in diffusion rate is achieved even at 250 K, and at 100 K diffusion essentially ceases. Cryogenic measurements not only minimize radiation damage but often lead to improved resolution owing to decrease in thermal motion in the crystal. Increasing the crystal lifetime may be particularly important with respect to multiwavelength anomalous-dispersion measurements in order to derive phase information. Since crystals of biological macromolecules contain substantial amounts of solvent, typically between 35 and 80% by volume, the technical problem is to force the solvent to cool in an amorphous glass-like state, rather than as crystalline ice. The latter normally degrades the crystallinity by expansion and gives rise to powder rings, which complicate data measurement.
Cryoprotectants are normally required to avoid ice formation, and the choice of cryoprotectant will depend on the nature of the mother liquor from which the crystals have been grown. Crystals grown from high salt will usually require high salt concentration in the cryobuffer to avoid dissolution, although the addition of organic solvents may be a useful alternative. Table 3.4.1.3 lists commonly used cryoprotectants and their typical concentrations (Gamblin & Rogers, 1993).
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The introduction of the cryoprotectant can be achieved through: (a) crystal growth in the cryoprotectant; (b) direct transfer of crystal from mother liquor into cryoprotectant buffer either in a single step or in steps of increasing cryoprotectant concentration; (c) dialysis, either direct or stepwise; or (d) exchange of liquor using a flow cell and a gradient maker.
Experience indicates that small crystals are better for cryogenic purposes, presumably because the rate of diffusion of small molecules and the rate of heat loss during rapid freezing is significantly faster than for large crystals. In most cases, there is an increase in the mosaicity (typically by a factor of 2–3), and in large specimens the increase may render the crystals useless for data collection. Successful freezing is often indicated by the crystal remaining transparent. Opacity usually indicates considerable breakdown in the crystallinity. Three commonly used methods for mounting crystals of biological macromolecules for cryogenic measurements are detailed below.
Several airstream devices have been described to cool protein crystals to around 250 K [Marsh & Petsko (1973), temperature range 253 to 303 K; Rossi (1989), temperature range 242 to 335 K; Machin, Begg & Isaacs (1984), 258 to 293 K; Fischer, Moras & Thierry (1985), temperature range 263 to 293 K; Fraase Storm & Tuinstra (1986), 250 to 350 K; Arndt & Stubbings (1987), 248 to 353 K]. The devices of Machin, Begg & Isaacs, Fraase Storm & Tuinstra and Arndt & Stubbings involve thermoelectric modules utilizing the Peltier effect. The space available to accommodate the sample is usually very limited and care has to be taken with the length of the capillary and other aspects of crystal mounting. Hovmöller (1981) has designed an extension to the cooling delivery tube that minimizes air turbulence at the sample. Various devices have been described that operate down to near liquid-nitrogen temperature and that can be fitted to a variety of data-collection systems. These include the rotation camera (Bartunik & Schubert, 1982), and a universal cooling device for precession cameras, rotation cameras and diffractometers (Hajdu, McLaughlin, Helliwell, Sheldon & Thompson, 1985). One of the more versatile devices is the cryostream described by Cosier & Glazer (1986), which uses a pump to effectively separate the liquid-nitrogen supply from the gas outflow; this arrangement eliminates instabilities in the cooling-gas stream; the device works in the range 77.4 to 323.0 K and is commercially available (Oxford Cryosystems, England).
Cryocrystallography not only minimizes the effects of radiation damage but also often allows the collection of high-quality, high-resolution data from a single specimen. In the case of very labile systems such as ribosomal particles, it is sometimes the only means of obtaining useful diffraction data. Further, cryocrystallography permits the study of temperature effects on the structure and dynamics of biological macromolecules. In this latter regard, examples include multiple-temperature crystallographic studies on sperm whale myoglobin (Frauenfelder, Petsko & Tsernoglou, 1979; Hartmann et al., 1982; Frauenfelder et al., 1987) and, more recently, ribonuclease-A (Tilton, Dewan & Petsko, 1992; Rasmussen, Stock, Ringe & Petsko, 1992). The future will no doubt see the routine emergence of cryogenic techniques for data collection, using both conventional and synchrotron X-ray sources, from biological macromolecules, with consequent improvement in structure quality and detail.
References
Adlhart, W. & Huber, H. (1982). A low-temperature X-ray Weissenberg goniometer with closed-cycle cooling to about 28 K. J. Appl. Cryst. 15, 241–244.Google ScholarAdlhart, W., Tzafaras, N., Sueno, S., Jagodzinski, H. & Huber, H. (1982). An X-ray camera for single-crystal studies at high temperatures under controlled atmosphere. J. Appl. Cryst. 15, 236–240.Google Scholar
Alkire, R. W., Larson, A. C., Vergamini, P. J., Schirber, J. E. & Morosin, B. (1985). High-pressure single-crystal neutron diffraction (to 20 kbar) using a pulsed source: preliminary investigation of Tl3PSe4. J. Appl. Cryst. 18, 145–149.Google Scholar
Allen, S., Cosier, J., Glazer, A. M., Hastings, T. J., Smith, D. T. & Wood, I. G. (1982). A microprocessor-controlled continuous-flow cryostat for single-crystal X-ray diffraction in the range 10–300 K. J. Appl. Cryst. 15, 382–387.Google Scholar
Archer, J. M. & Lehmann, M. S. (1986). A simple adjustable mount for a two-stage cryorefrigerator on an Eulerian cradle. J. Appl. Cryst. 19, 456–458.Google Scholar
Argoud, R. & Muller, J. (1989a). Effect of stress from the glue on single-crystal X-ray intensities at high or low temperatures. J. Appl. Cryst. 22, 378–380. Google Scholar
Argoud, R. & Muller, J. (1989b). Magnetically coupled crystal holder and liquid-helium cryostat for X-ray four-circle diffractometer studies between 5 and 300 K. J. Appl. Cryst. 22, 584–591.Google Scholar
Arndt, U. W. & Stubbings, S. J. (1987). A miniature Peltier-effect goniometer-head attachment. J. Appl. Cryst. 20, 445.Google Scholar
Arnold, H., Bartl, H., Fuess, H., Ihringer, J., Kosten, K., Löchner, U., Pennartz, P. U., Prandl, W. & Wroblewski, T. (1989). New powder diffractometer at HASYLAB/DESY. Rev. Sci. Instrum. 60, 2380–2381.Google Scholar
Bartunik, H. D. & Schubert, P. (1982). Crystal cooling for protein crystallography with synchrotron radiation. J. Appl. Cryst. 15, 227–231.Google Scholar
Bhat, H. L., Clark, S. M., El Korashy, A. & Roberts, K. J. (1990). A furnace for in situ synchrotron Laue diffraction and its application to studies of solid-state phase transformations. J. Appl. Cryst. 23, 545–549.Google Scholar
Black, D. R., Burdette, H. E. & Early, J. G. (1986). Diffusion bonding of ductile single crystals for strain-free mounting. J. Appl. Cryst. 19, 279–280.Google Scholar
Boese, R. & Bläser, D. (1989). A procedure for the selection and transferring of crystals at low temperatures to diffractometers. J. Appl. Cryst. 22, 394–395.Google Scholar
Bouquiere, J. P., Finney, J. L., Lehmann, M. S., Lindley, P. F. & Savage, H. F. J. (1993). High-resolution neutron study of vitamin B12 coenzyme at 15 K: structure analysis and comparison with the structure at 279 K. Acta Cryst. B49, 79–89.Google Scholar
Bretherton, L. & Kennard, C. H. L. (1976). Crystal mounter. J. Appl. Cryst. 9, 416.Google Scholar
Brown, N. E., Swapp, S. M., Bennett, C. L. & Navrotsky, A. (1993). High-temperature X-ray diffraction: solutions to uncertainties in temperature and sample position. J. Appl. Cryst. 26, 77–81.Google Scholar
Cascio, D., Williams, R. & McPherson, A. (1984). The reduction of radiation damage in protein crystals by polyethylene glycol. J. Appl. Cryst. 17, 209–210.Google Scholar
Cosier, J. & Glazer, A. M. (1986). A nitrogen-gas-stream cryostat for general X-ray diffraction studies. J. Appl. Cryst. 19, 105–107.Google Scholar
D'Aprile, F. & Moretto, R. (1975). Two simple devices for sealing wet single crystals in capillary tubes. J. Appl. Cryst. 8, 696.Google Scholar
Denne, W. A. (1971a). A new concept in goniometer head design. J. Appl. Cryst. 4, 60–66.Google Scholar
Denne, W. A. (1971b). A technique for the rigid mounting of crystals in X-ray diffractometry. J. Appl. Cryst. 4, 400.Google Scholar
Dent Glasser, L. S. (1977). Crystallography and its applications, Chap. 6, pp. 125–155. New York/Cincinnati/Toronto/London/Melbourne: Van Nostrand Reinhold. Google Scholar
Dewan, J. C. & Tilton, R. F. (1987). Greatly reduced radiation damage in ribonuclease crystals mounted on glass fibres. J. Appl. Cryst. 20, 130–132.Google Scholar
D'Eye, R. W. M. & Wait, E. (1960). X-ray powder photography. London: Butterworth. Google Scholar
Edwards, S. L. (1993). Yokeless flow cell for Laue crystallography. J. Appl. Cryst. 26, 305–306.Google Scholar
Fischer, J., Moras, D. & Thierry, J. C. (1985). Single crystal diffractometry: strategy for rapidly decaying poorly diffracting crystals. J. Appl. Cryst. 18, 20–26.Google Scholar
Foit, F. F. Jr (1982). A technique for loading glass capillaries used in X-ray powder diffraction. J. Appl. Cryst. 15, 357.Google Scholar
Fraase Storm, G. M. & Tuinstra, F. (1986). A thermoelectric device for temperature-controlled single-crystal diffractometry. J. Appl. Cryst. 19, 372–373.Google Scholar
Frauenfelder, H., Hartmann, H., Karplus, M., Kuntz, I. D. Jr, Kuriyan, J., Parak, F., Petsko, G. A., Ringe, D., Tilton, R. F. Jr, Conolly, M. L. & Max, N. (1987). Thermal expansion of a protein. Biochemistry, 26, 254–261.Google Scholar
Frauenfelder, H., Petsko, G. A. & Tsernoglou, D. (1979). Temperature-dependent X-ray diffraction as a probe of protein structure dynamics. Nature (London), 280, 558.Google Scholar
Gamblin, S. J. & Rogers, D. W. (1993). Some practical details of data collection at 100 K. In Data collection and processing. Proceedings of the CCP4 Study Weekend, edited by L. Sawyer, N. Isaacs & S. Bailey. Report DL/SCI/R34. SERC Daresbury Laboratory, Cheshire WA4 4AD, England. Google Scholar
Gonzalez, A. & Nave, C. (1994). Radiation damage in protein crystals at low temperature. Acta Cryst. D50, 874–877.Google Scholar
Graafsma, H., Sagerman, G. & Coppens, P. (1991). Closed-cycle helium cryostat for the Huber 511.1 diffractometer circle. J. Appl. Cryst. 24, 961–962.Google Scholar
Hajdu, J., McLaughlin, P. J., Helliwell, J. R., Sheldon, J. & Thompson, A. W. (1985). Universal cooling device for precession cameras, rotation cameras and diffractometers. J. Appl. Cryst. 18, 528–532.Google Scholar
Hartmann, H., Parak, F., Steigemann, W., Petsko, G. A., Ringe-Ponzi, D. & Frauenfelder, H. (1982). Conformational substrates in a protein: structure and dynamics of metmyoglobin at 80 K. Proc. Natl Acad. Sci. USA, 79, 4967–4971. Google Scholar
Hazen, R. M. & Finger, L. W. (1982). Comparative crystal chemistry, pp. 5–16. New York: Wiley. Google Scholar
Henriksen, K., Larsen, F. K. & Rasmussen, S. E. (1986). Mounting a 10 K cooling device without rotating seals on a four-circle diffractometer. J. Appl. Cryst. 19, 390–394.Google Scholar
Hohlwein, D. & Wright, A. F. (1981). A low-temperature Weissenberg camera for neutrons. J. Appl. Cryst. 14, 82–84. Google Scholar
Holmes, K. C. & Blow, D. M. (1966). The use of diffraction in the study of protein and nucleic acid structure. New York: John Wiley. Google Scholar
Hope, H. (1987). Experimental organometallic chemistry. Am. Chem. Soc. Symp. Ser., No. 357. Washington, DC: American Chemical Society.Google Scholar
Hope, H. (1988). Cryocrystallography of biological macromolecules: a generally applicable method. Acta Cryst. B44, 22–26.Google Scholar
Hope, H. (1990). Crystallography of biological macromolecules at ultra-low temperatures. Ann. Rev. Biophys. Biophys. Chem. 19, 107–126.Google Scholar
Hope, H., Frolow, F., van Böhlen, K., Makowski, I., Kratky, C., Halfon, Y., Danz, H., Bartels, K. S., Wittmann, H. G. & Yonath, A. (1989). Crystallography of ribosomal particles. Acta Cryst. B45, 190–199.Google Scholar
Hovmöller, S. (1981). A device which improves the cooling of protein crystals during X-ray data collection. J. Appl. Cryst. 14, 75.Google Scholar
Ihringer, J. & Küster, A. (1993). Cryostat for synchrotron powder diffraction with sample rotation and controlled gas atmosphere in the sample chamber. J. Appl. Cryst. 26, 135–137.Google Scholar
Jeffery, J. W. (1971). Methods in X-ray crystallography, pp. 149–169, 441–444. London/New York: Academic Press. Google Scholar
Kennard, C. H. L. (1994). Direct observation of a crystal during X-ray data collection using a macroscope. J. Appl. Cryst. 27, 668–669.Google Scholar
King, M. V. (1954). An efficient method for mounting wet protein crystals for X-ray studies. Acta Cryst. 7, 601–602.Google Scholar
Klug, H. P. & Alexander, L. E. (1954). X-ray diffractometer procedures for polycrystalline and amorphous materials. New York: John Wiley. Google Scholar
Kottke, T. & Stalke, D. (1993). Crystal handling at low temperatures. J. Appl. Cryst. 26, 616–619.Google Scholar
Kroeger, K. S. & Kundrot, C. E. (1994). A gas cell for collecting X-ray diffraction data from proteins. J. Appl. Cryst. 27, 609–612.Google Scholar
Kundrot, C. E. & Richards, F. M. (1986). Collection and processing of X-ray diffraction data from protein crystals at high pressure. J. Appl. Cryst. 19, 208–213.Google Scholar
Lange, B. A. & Haendler, H. M. (1972). A capillary support apparatus for use in glove bags and dry boxes. J. Appl. Cryst. 5, 310. Google Scholar
Lange, G., Lewis, S. J., Murshudov, G. N., Dodson, G. G., Moody, P. C. E., Turkenburg, J. P., Barclay, A. N. & Brady, R. L. (1994). Crystal structure of an extracellular fragment of the rat CD4 receptor containing domains 3 and 4. Structure, 2, 469–481. Google Scholar
Leszczynski, M., Podlasin, S. & Suski, T. (1993). A 109 Pa high-pressure cell for X-ray and optical measurements. J. Appl. Cryst. 26, 1–4.Google Scholar
Lindley, P., Najmudin, S., Bateman, O., Slingsby, S., Myles, D., Kumaraswamy, S. & Glover, I. (1993). Structure of bovine γB-crystallin at 150 K. J. Chem. Soc. Faraday Trans. 89, 2677–2682.Google Scholar
Lindley, P. F. (1988). Crystallographic studies of biological macromolecules using synchrotron radiation. Chemical crystallography with pulsed neutrons and synchrotron X-rays, edited by M. A. Carrondo & G. A. Jeffrey, pp. 509–536. Dordrecht: Reidel. Google Scholar
Lippman, R. & Rudman, R. (1976). A mechanically refrigerated gas stream (to −120°C) and some useful accessories. J. Appl. Cryst. 9, 220–222.Google Scholar
Lorenz, G., Neder, R. B., Marxreiter, J., Frey, F. & Schneider, J. (1993). A mirror furnace for neutron diffraction up to 2300 K. J. Appl. Cryst. 26, 632–635.Google Scholar
Machin, K. J., Begg, G. S. & Isaacs, N. W. (1984). A low-temperature cooler for protein crystallography. J. Appl. Cryst. 17, 358–359.Google Scholar
McKinstry, H. A. (1970). Low thermal gradient high-temperature furnace for X-ray diffraction. J. Appl. Phys. 41, 5074–5079.Google Scholar
McMurdie, H. F., Morris, M. C., Evans, E. H., Paretzkin, B. & Wong-Ng, W. (1986). Methods of producing standard X-ray diffraction powder patterns. Powder Diffr. 1, 40–43.Google Scholar
Malinowski, M. (1987). A diamond high-pressure cell for X-ray diffraction on a single crystal. J. Appl. Cryst. 20, 379–382.Google Scholar
Marsh, D. J. & Petsko, G. A. (1973). A low-temperature device for protein crystallography. J. Appl. Cryst. 6, 76–80. Google Scholar
Miyata, T., Ishizawa, N., Minato, I. & Iwai, S. (1979). Gas-flame heating equipment providing temperatures up to 2600 K for the four-circle diffractometer. J. Appl. Cryst. 12, 303–305.Google Scholar
Moret, R. & Dallé, D. (1994). A novel X-ray precession goniometer for use with stationary single crystals in special environments. Adaptation of a closed-cycle refrigerator. J. Appl. Cryst. 27, 637–646.Google Scholar
Narayana, S. V. L., Weininger, M. S., Heuss, K. L. & Argos, P. (1982). A method to increase protein-crystal lifetime during X-ray exposure. J. Appl. Cryst. 15, 571–573.Google Scholar
Nave, C. (1995). Radiation damage in protein crystallography. In Radiation physics & chemistry, edited by P. Barnes. Oxford: Pergamon.Google Scholar
Neder, R. B., Frey, F. & Schulz, H. (1990). Defect structure of zirconia (Zr0.85Ca0.15O1.85) at 290 and 1550 K. Acta Cryst. A46, 799–809.Google Scholar
Nieman, H. F., Evans, J. C., Heal, K. M. & Powell, B. M. (1984). A technique for the preparation of low-temperature powder samples of noxious materials. J. Appl. Cryst. 17, 372.Google Scholar
Peterson, R. C. (1992). A flame-heated gas-flow furnace for single-crystal X-ray diffraction. J. Appl. Cryst. 25, 545–548.Google Scholar
Petsko, G. A. (1985). Flow cell construction and use. Methods in enzymology, Vol. 114, pp. 141–145. New York: Academic Press.Google Scholar
Phillips, G. N. Jr (1985). Crystallisation in capillary tubes. Methods in enzymology, Vol. 114, pp. 128–131. New York: Academic Press.Google Scholar
Pickford, M. G., Garman, E. F., Jones, E. Y. & Stuart, D. I. (1993). A design of crystal mounting cell that allows the controlled variation of humidity at the protein crystal during X-ray diffraction. J. Appl. Cryst. 26, 465–466.Google Scholar
Przybylska, M. (1988). A novel method of mounting a protein crystal on a surface perpendicular to the X-ray capillary. J. Appl. Cryst. 21, 272–273.Google Scholar
Puxley, D. C., Squire, G. D. & Bates, D. R. (1994). A new cell for in situ X-ray diffraction studies of catalysts and other materials under reactive gas atmospheres. J. Appl. Cryst. 27, 585–594.Google Scholar
Rao, Ch. P. (1989). Easy and economic ways of handling air-sensitive crystals for X-ray diffraction studies. J. Appl. Cryst. 22, 182–183.Google Scholar
Rasmussen, B. F., Stock, A. M., Ringe, D. & Petsko, G. A. (1992). Crystalline ribonuclease A loses function below the dynamical transition at 220 K. Nature (London), 357, 423–424.Google Scholar
Rayment, I. (1985). Treatment and manipulation of crystals. Methods in enzymology, Vol. 114, pp. 136–140. New York: Academic Press.Google Scholar
Rayment, I., Johnson, J. E. & Suck, D. (1977). A method of preventing crystal slippage in macromolecular crystallography. J. Appl. Cryst. 10, 365.Google Scholar
Rink, W. J., Mathias, H. G. & Schlenoff, J. B. (1994). Hermetic sample housing for X-ray diffraction studies. J. Appl. Cryst. 27, 666–668. Google Scholar
Rossi, F. A. (1989). Permanent cooling of protein crystals by a collinear air flow. J. Appl. Cryst. 22, 620–622. Google Scholar
Rudman, R. (1976). Low-temperature X-ray diffraction: apparatus and techniques, Chap. 6, pp. 161–179. New York/London: Plenum.Google Scholar
Shaham, H. (1982). A goniometer for large single crystals. J. Appl. Cryst. 15, 469.Google Scholar
Stout, G. H. & Jensen, L. H. (1968). X-ray structure determination: a practical guide, Chap. 4, pp. 71–79. London: Macmillan. Google Scholar
Swanson, D. K. & Prewitt, C. T. (1986). A new radiative single-crystal diffractometer microfurnace incorporating MgO as a high-temperature cement and internal temperature calibrant. J. Appl. Cryst. 19, 1–6.Google Scholar
Tarling, S. E., Barnes, P. & Mackay, A. L. (1984). Simulation of industrial furnacing with powder X-ray diffraction. J. Appl. Cryst. 17, 96–99.Google Scholar
Teeter, M. M., Roe, S. M. & Heo, N. H. (1993). Atomic resolution (0.83 Å) crystal structure of the hydrophobic protein crambin at 130 K. J. Mol. Biol. 230, 292–311.Google Scholar
Teng, T. Y. (1990). Mounting of crystals for macromolecular crystallography in a free-standing thin film. J. Appl. Cryst. 23, 387–391. Google Scholar
Tilton, R. F. Jr (1988). A fixture for X-ray crystallographic studies of biomolecules under high gas pressure. J. Appl. Cryst. 21, 4–9. Google Scholar
Tilton, R. F. Jr, Dewan, J. C. & Petsko, G. A. (1992). Effects of temperature on protein structure and dynamics: X-ray crystallographic studies of the protein ribonuclease-A at nine different temperatures from 98 to 320 K. Biochemistry, 31, 2469–2481. Google Scholar
Toyoshima, N., Hoya, H. & Ohshima, K.-I. (1991). A simple device for mounting a vacuum chamber on a four-circle diffractometer with central χ circle. J. Appl. Cryst. 24, 1074–1075.Google Scholar
Tsukimura, K., Sato-Sorensen, Y. & Ghose, S. (1989). A gas-flow furnace for X-ray crystallography. J. Appl. Cryst. 22, 401–405.Google Scholar
Watenpaugh, K. D. (1991). Macromolecular crystallography at cryogenic temperatures. Curr. Opin. Struct. Biol. 1, 1012–1015.Google Scholar
Wood, R. A., Tode, G. E. & Welberry, T. R. (1985). A lathe-like crystal grinder for grinding pre-aligned crystals into cylindrical cross section. J. Appl. Cryst. 18, 371–372.Google Scholar
Wyckoff, H. W., Doscher, M. S., Tsernoglou, D., Inagami, T., Johnson, L. N., Hardman, K. D., Allewell, N. M., Kelley, D. M. & Richards, F. M. (1967). Design of a diffractometer and flowcell system for X-ray analysis of crystalline proteins with applications to the crystal chemistry of ribonuclease-S. J. Mol. Biol. 27, 563–578.Google Scholar
Young, A. C. M., Dewan, J. C., Nave, C. & Tilton, R. F. (1993). Comparison of radiation-induced decay and structure refinement from X-ray data collected from lysozyme crystals at low and ambient temperatures. J. Appl. Cryst. 26, 309–319.Google Scholar
Zaloga, G. & Sarma, R. (1974). New method for extending the diffraction patterns from protein crystals and preventing their radiation damage. Nature (London), 251, 551–552.Google Scholar
Zeppezauer, M., Eklund, H. & Zeppezauer, E. S. (1968). Micro diffusion cells for the growth of single protein crystals by means of equilibrium dialysis. Arch. Biochem. Biophys. 126, 564–573.Google Scholar
Zobel, D. & Luger, P. (1990). A small 50 K device for a quarter-circle Eulerian cradle diffractometer. J. Appl. Cryst. 23, 175–179.Google Scholar