Crystal contacts

Nucleation due to crystal-to-ciystal contact is greater for equal striking energies than ciystal-to-metal contact. However, the viscous drag of the liquid on particle sizes normaUy encountered hmits the velocity of impact to extremely low values. The assumption that only the largest crystal sizes contribute significantly to the nucleation rate by ciystal-to-crystal contact permits a simple computation of the rate ... 

Water use in copper sulfate plants is mainly used as contact water, noncontact cooling water, washdowns, and as wash water, where solid copper sulfate product is required. Noncontact water is generated as steam condensate from the evaporators and is used to cool the crystallizers. Contact wastewater comes mainly from washdowns, spills, and leaks. Both types of wastewater contain relatively small quantities of copper sulfides and other heavy metals. 

Section II,B, this may be an overestimate of the false positive error rate because many of the apparent consecutive errors correspond to regions of disorder that are ordered in the crystal due to ligand binding or crystal contacts. Also, because disordered regions of length >40 residues are often missed due to false negative predictions of order, the data in... 

It is important to stress that ATR absorbance is strongly affected by the sample/crystal contact. Quantitative results are thus difficult to obtain even if the contact is maintained during the sample rotation that is required to record all four polarized spectra. A reference band that does not show significant dichroism is thus most often used to normalize the polarized absorbances in order to obtain quantitative data. For instance, the 1,410 cm-1 band of PET has often been chosen for that purpose, not only for ATR studies but also for specular reflectance (see below) and even transmission studies when the sample thickness is not uniform. It was shown that an appropriate normalization is possible even if no such reference band is available, by using a combination of two bands with orthogonal dichroism [34]. When performing ATR experiments, one should also make certain that the applied pressure does not create artifacts by affecting the structure of the sample. 

Figure J. Preparation of a welJ-defined single-crystal electrode by four steps, (a) Mirror-rinished crystal is annealed under gas flame, and (b) quenched in air and then pure water, (c) The crystal is covered with a droplet of pure water to protect it from pollution by impurities in air and (d) is introduced into the cell, where the crystal contacts the meniscus of the electrolyte solution. (From Ref. 25.)...

Since crystals form through contacts between protein molecules, it can be expected that altering the surface residues on a protein will alter the ability to form crystals. Altering surface residues to allow better crystal surface contacts can work extremely well for improving crystals (D Arcy et al., 1999 Lorber et al., 2002). Two residues in particular, lysine and glutamic acid, seem to be particularly good residues for mutation. Both are found predominantly on the surface of proteins, and both seem to be disfavored in protein-protein interaction surfaces. Since crystals depend on forming contacts between proteins, this approach may improve the crystal contact surfaces of the proteins in the crystal (Mateja et al., 2002). 

Although the soaking method for heavy-atom derivative preparation is by far the simplest and most common, it is not the only method used. One can first derivatize the macromolecule, and then crystallize. This procedure is less frequently used because of drawbacks such as the inabihty to produce isomorphous crystals due to the disruption of intermolecular contacts by the heavy atoms. Other frequent problems are the introduction of additional heavy-atom sites (a potential complicating factor in phasing) by exposing sites hidden by crystal contacts, and changing the solubility of the derivatized macromolecule. 

Beware of crystal contacts In the crystal, it is possible for a ligand to make important contacts with residues from a neighbouring molecule, producing an artificial mode of binding that is not possible in... 

They form an unusual crystal contact. The dark spheres represent carbohydrate and the light spheres represent protein. The carbohydrate at Asn200 starts from one subunit and covers a neighboring subunit on the same tetramer. The... 

Protein Explorer is a knowledge base with introductory information on many topics about protein structure, such as the origins and limitations of 3D protein structure data, specific oligomers vs. crystal contacts, hydrogen bonds, cahon-pl interactions, etc. Protein Explorer is more user-friendly than the comparable software RASMOL, also available on servers such as ExPASy. 

Sander and Schneider performed an empirical determination of homology thresholds by studying thousands of sequence alignments within the PDB database [19]. One has to keep in mind that perfect sequence similarity not always implies perfect structural agreement a protein crystal structure may vary, typically in loop regions or in domain orientation, as a result of different substrate or cofactor interaction, complex formation or crystal contacts. The curve in Figure 4, however, provides a reliable rule of thumb for those who wonder if their enzyme can be modeled with any degree of confidence. 

If primary nucleation dominates the process, i tends to larger values (say greater than 3), j and k approach zero, and Eq. (18) approaches Eq. (17). Should crystal-impeller and/or crystal-crystallizer impacts dominate, j approaches 1 on the other hand, if crystal-crystal contacts dominate, j approaches 2. 

Poulsen, J.-C.N., Harris, P., Jensen, K.F., and Larsen, S. 2001. Selenomethionine substitution of oritidine-S -monophosphate decarboxylase causes a change in crystal contacts and space group. Acta Crystallogr., Sect. D Biol. Crystallogr. D57(9), 1251-1259. 

Solid crystals — If a crystal contacts a foreign substrate (the working electrode) the total free surface energy O of the system crystal-solution-foreign substrate is given by [i]... 

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