Crystals mounting

X-ray spectrometer An apparatus used in the X-ray study of crystals in which a fine beam of monochromatic X-rays impinges at a measured angle on the face of a crystal mounted in its path, and in which the intensity of the X-rays diffracted in various directions by the crystal is measured with an ionization chamber mounted on an arm of the spectrometer table, or is recorded photographically. 

The data measurement in an x-ray analysis is typically performed using a computer controlled diffractometer. Except for the crystal mounting and some preliminary procedures, the measurement of intensities is fully automated. It is the next... 

Figure 7.6 shows a schematic set up for TPD. The crystal, mounted on a manipulator in an ultrahigh vacuum chamber, is heated such that the temperature increases linearly in time. The concentration of desorbing species is monitored with a mass spectrometer or with a simple pressure gauge. 

Spectra were obtained using a Digilab FTS-15E Fourier Transform Spectrophotometer. A NaCl crystal mounted in a heated cell (Model 018-5322 Foxboro/Analabs, N. Haven, Ct.) was placed in the infrared beam and the chamber allowed to purge for several minutes while the cell was brought to the desired temperature. The temperature of the cell was controlled using a DuPont 900 Differential Thermal Analyzer interfaced to the spectrometer cell. A chlorobenzene solution (ca. 10 by wt.) of the sample was then applied to the crystal using cotton tipped wood splint. 

The flow of information on the highly reactive alkali organometallics in the 1990s is certainly closely connected to the wider availability of low temperature crystallography and advanced crystal mounting techniques,22 allowing the structural characterization of compounds previously deemed too reactive for investigation. 

In contrast to the allyl system, where the reduction of an isolated double bond is investigated, the reduction of extensively delocalized aromatic systems has been in the focus of interest for some time. Reduction of the systems with alkali metals in aprotic solvents under addition of effective cation-solvation agents affords initially radical anions that have found extensive use as reducing agents in synthetic chemistry. Further reduction is possible under formation of dianions, etc. Like many of the compounds mentioned in this article, the anions are extremely reactive, and their intensive studies were made possible by the advancement of low temperature X-ray crystallographic methods (including crystal mounting techniques) and advanced synthetic capabilities. 

Cryostats have been much used in small-molecule crystallography because they allow rapid cooling to very low temperatures with minimal cold gas consumption and offer great advantages in the area of frost prevention. Unfortunately, most designs employ beryllium shrouds or other nontransparent material, and are of a size which does not lend itself to crystals mounted in capillary tubes and flow cells. A recent advance is the description of a Mylar cryostat specifically designed for... 

Continue with Subheading 3., step 18 in the method. The positive reaction product with this chromogen will be red, with the nuclei a light blue. Rather than dehydrating the specimens in ethanol and xylene, allow them to dry, add 1 drop of Crystal/Mount (Biomeda Corp, Foster City, CA) to the specimen and bake them in a 60°C oven for 30 min. This preparation is permanent and can be cover-slipped with Permount if needed. The Crystal/Mount will form a hard plastic coating on the slide, but it can be damaged by smudging. 

Automated positioning of samples relies on compatibility between the robot and the hardware used for crystal mounting. In 2004, the SPINE (Structural Proteomics in Europe) consortium (www.spineurope.org) established a standard specification for sample holders. This specification is... 

Figure 12.3 SGX-CAT barcode reader station. The 2D barcodes on the base of each crystal mount are read on the...

Muchmore, S. W., Olson, J., Jones, R., Pan, J., Blum, M., Greer, J., Merrick, S. M., Magdalinos, P and Nienaber, V. L. (2000). Automated crystal mounting and data collection for protein crystallography. Structure 8, R243-R246. 

Vemede, X., Lavault, B., Ghana, J., Nurizzo, D., Joly, J., Jacquamet, L., Fehsaz, E, Cipriani, E. and Bourgeois, D. (2006). UV laser-exdted fluorescence as a tool for the visualization of protein crystals mounted in loops. Acta Crystallogr. D 62,253-261. 

In contrast, it is often possible to achieve a modest amount of cooling of crystals mounted in capillaries using an air cooling system, such as the FTS air jet cooler (FTS Systems Inc., P.O. Box 158, Rt 209 Stone Ridge, NY 12484, USA), which allows investigation of the effect of temperatures close to 273 K on a crystal s lifetime and diffraction (Diprose etal., 1999). 

Muchmore, S. W.,etal. (2000). Automated crystal mounting and data collection for protein crystallography. Structure Fold Des. 8, R243-246. 

Protective oil is a good alternative to glue for crystal mounting because of the large residual stress that epoxies can cause. Sensitive species must be handled with special care, because exposure to oxidative atmosphere or anyway to ambient temperature may produce irreversible damage. For this reason, mounting the sample in an inert atmosphere within glove boxes is sometimes necessary. If the sample must be kept at low temperature while under the microscope, special equipment is necessary as proposed by Stalke [34] or by Hope [35]. 

The experiments were performed in stainless steel UHV chambers which were equipped with the instrumentation necessary to perform Auger Electron Spectroscopy (AES), X-ray Photoelectron Spectroscopy (XPS), UV Photoelectron Spectroscopy (UPS), Low Energy Electron Diffraction (LEED), work function measurements (A( )), High Resolution Electron Energy Loss Spectroscopy (HREELS), and Temperature Programmed Desorption (TPD). The Au(lll) crystal was heated resist vely and cooled by direct contact of the crystal mounting block with a liquid nitrogen reservoir. The temperature of the Au(lll) crystal was monitored directly by means of a... 

Until recently, only two reports existed for 1 1 adducts of silver halides with amines, namely AgT piperidine57 and Agl-morpholine.381 The first had a tetrameric cubane structure whilst the second was described as a stair polymer adduct. The range has now been extended to include 2-and 3-methylpyridine, quinoline and triethylamine.382 In each case the adduct was obtained by recrystallization of silver(I) iodide from neat base. The colourless crystals were found to lose base readily on exposure to the atmosphere and structural data were collected from crystals mounted in argon-filled capillaries, containing mother liquor. 

Crystal reaction study mechanistic tools, 296 computer simulation, 297 electronic spectroscopy, 298 electron microscopy, 298 electron paramagnetic resonance (EPR), 299 nuclear magnetic resonance (NMR), 298 Raman spectroscopy, 299 Crystal reaction study techniques crystal mounting, 308 decomposition limiting, 309 polarized IR spectroscopy, 309 temperature control, 308 Cycloreversions, adiabatic photochemical involving anthracenes, 203 excited state properties of lepidopterenes, 206... 

Unfortunately, the working distance for commercial stereo microscopes is rather short, and the microscope also does not accommodate readily the usual large glove box with a vertical or slightly inclined window. A single-chamber evacu-able dry box is available commercially which would appear to be satisfactory for crystal mounting and other operations in which the apparatus is not large.2... 

The precession camera (Fig. 4.23), although the more complicated in its motion, produces the simplest diffraction pattern. X rays enter through the black tube at left to strike the crystal, mounted in a goniometer head. Beyond the crystal are an annular-screen holder (smaller black square) and a film holder (larger black square). The remaining machinery moves crystal, screen, and film in a precessing motion about the X-ray beam. 

Crystallization, experimental methods overview, 1, 207 Crystal mounting, experimental methods overview, 1, 209 Crystal selection, experimental methods overview, 1, 209 CSA, and apparent dynamic NMR, 1, 423 CSD, see Cambridge Structural Database C2-symmetric metallocenes, for polypropylene polymerization, 4, 1058 CT transitions, see Charge-transfer transitions Cubanes... 

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