Crystal structure structural principles

Cate J FI, Gooding A R, Podell E, Zhou K, Golden B L, Kundrot C E, Cech T R and Doudna J A 1996 Crystal structure of a group i ribozyme domain principles of RNA packing Science 273 1678-85... 

The program system COBRA [118, 119] can be regarded as a rule- and data-based approach, but also applies the principles of fragment-based (or template-based) methods extensively (for a detailed description sec Chapter 11, Sections 7.1 and 7.2 in the Handbook). COBRA uses a library of predefined, optimized 3D molecular fragments which have been derived from crystal structures and foi ce-field calculations. Each fi agment contains some additional information on... 

Crystallography is a very broad science, stretching from crystal-structure determination to crystal physics (especially the systematic study and mathematical analysis of anisotropy), crystal chemistry and the geometrical study of phase transitions in the solid state, and stretching to the prediction of crystal structures from first principles this last is very active nowadays and is entirely dependent on recent advances in the electron theory of solids. There is also a flourishing field of applied crystallography, encompassing such skills as the determination of preferred orientations, alias textures, in polycrystalline assemblies. It would be fair to say that... 

Together with the structural principles established by the Bragg school concerning the many types of silicates, Goldschmidt s ideas were taken further by Linus Pauling in California to establish the modern science of crystal chemistry. A good early overview of the whole field can be found in a book by Evans (1939, 1964). 

Cate, J. H., et al., 1996. Crystal structure of a group I ribozyme domain Principles of RNA packing. Science 273 1678. 

This by no means exhaustive discussion may serve to indicate the value of the information provided by magnetic data relative to the nature of the chemical bond. The quantum-mechanical rules for electron-pair bonds are essential to the treatment. Much further information is provided when these methods of attack are combined with crystal structure data, a topic which has been almost completely neglected in this paper. It has been found that the rules for electron-pair bonds permit the formulation of a set of structural principles for non-ionic inorganic crystals similar to that for complex ionic crystals the statement of these principles and applications illustrating their use will be the subject of an article to be published in the Zeitschrift fur Kristallographie. 

This physical differentiation of the anions and cations under discussion in regard to size and charge finds expression throughout this paper. Markedly different roles are attributed anions and cations in the construction of a crystal as a result a pronounced distinction between them has been made in the formulation of the structural principles. 

The principles described in the following six sections have been deduced in part from the empirical study of known crystal structures and in part from considerations of stability involving the crystal energy. 

On the other hand, the crystal structures of ionic compounds with small molecular ions depend mainly on how space can be filled most efficiently by the ions, following the principle of cations around anions and anions around cations. Geometric factors such as the relative size of the ions and the shape of molecular ions are of prime importance. More details are given in Chapter 7. 

Important structural principles for ionic crystals, which had already been recognized in part by V. Goldschmidt, were summarized by L. Pauling in the following rules. First rule Coordination polyhedra... 

Precisely, this behavior is found for the host 26 (see Sect. 4.1), another properly tailored carboxylic add (cf. Sect. 4.5). The crystal structure of the 1-butanol associate of 26 (Fig. 18 b) shows the same 12-membered H-bond pattern around a center of symmetry as found for the inclusions of I with MeOH, EtOH, and 2-PrOH and exactly the same building principle (dimeric host and 12-ring formation) as in the 1-PrOH aggregate of 1. Thus, they both belong to the same type lib of building blocks (Fig. 19). 

In principle, structure analysis can be considered as distribution analysis in atomic dimensions. However, from the practical point of view it makes sense to deal separately with structure analysis and to differentiate between molecular structure analysis and crystal structure analysis. Further structure investigations concern near-orders in solids and liquids (e.g. glass). 

---