Coordination sequence

Chelate ring formation may be rate-limiting for polydentate (and especially macrocyclic) ligand complexes. Further, the rates of formation of macrocyclic complexes are sometimes somewhat slower than occur for related open-chain polydentate ligand systems. The additional steric constraints in the cyclic ligand case may restrict the mechanistic pathways available relative to the open-chain case and may even alter the location of the rate-determining step. Indeed, the rate-determining step is not necessarily restricted to the formation of the first or second metal-macrocycle bond but may occur later in the coordination sequence. 

There are only a limited number of chemical manipulations that a single enzyme can perform, so that for a major chemical change, more than one enzyme is required for example, to convert glucose into ethanol or laetie aeid, more than ten enzymes are required and they function as a coordinated sequence. Such a sequence is called a pathway. Since the first pathways to be elucidated were in the field of metabolism, the term metabolic pathway is a familiar term to almost all biochemists. However, the... 

Enzymes are biological catalysts—i. e substances of biological origin that accelerate chemical reactions (see p. 24). The orderly course of metabolic processes is only possible because each cell is equipped with its own genetically determined set of enzymes. It is only this that allows coordinated sequences of reactions (metabolic pathways see p. 112). Enzymes are also involved in many regulatory mechanisms that allow the metabolism to adapt to changing conditions (see p.ll4). Almost all enzymes are proteins. However, there are also catalytically active ribonucleic acids, the ribozymes" (see pp. 246, 252). 

Searches for similar protein and nucleic acid sequences Protein structures on moving 3D coordinates Sequence retrieval system for cross-referencing databases Searches for similar protein sequences Database of gene sequences... 

BLAST Chime Entrez (NCBI) FASTA GenBank (NCBI) Molecules R Us RasMol (Ras Mac) SRS (EMBL) Searches for similar protein and nucleic acid sequences Protein structures on moving 3D coordinates Sequence retrieval system for cross-referencing databases Searches for similar protein sequences Database of gene sequences Provides coordinates for protein 3D structure and manipulation Provides coordinates for protein 3D structure and manipulation Sequence retrieval system for cross referencing databases... 

The submerged process for the manufacture of citric acid (Fig. 1) involves coordinated sequences of biochemical conversions with the aid of A. niger and various unit operations and chemical conversions. 

However the precise sequence of coordinate participation in the reaction path is solvent dependent. For the case just discussed, the water solvent is rapid, largely because of the small moment of inertia involved in the water molecule reorientations underlying the change of the electrical polarization. Dimethyl formamide (DMF) solvent is less rapid, and the resulting coordinate sequence on the way to the TS [3] is again in the order of decreasing slowness, but now the solvent coordinate is the slowest of the three, followed by the bend angle and finally the C - Cl bond stretch. The reaction path depends on the solvent time scale. 

The fitness function is simply the mapping between points in sequence space and their fitnesses. The fitness landscape is the combination of the fitness function and the neighbor relationship. With neighbors defined by point mutation, for an N-site molecule, the landscape is the N-dimensional surface that results from plotting the fitness function over an N-dimensional Cartesian coordinate sequence space (Fig. 13). 

A zeolitic structure can be described in various crystallographic terms. For many systems it is now possible to specify the following structural features the SBUs, the framework density, the coordination sequences, the unit cell dimensions and composition, the direction of the channels and the aperture (window) dimensions (Atlas of Zeolite Structure Types, 1992 Thomas et al., 1997). The framework density, FD, is defined as the number of T atoms per 1000 A1 (i.e. per 1 nm3) of the structure. 

The simulated annealing method can generate large numbers of hypothetical structures in a short time frame. A non-exhaustive series of simulations based on the unit celL sizes and symmetries of 64 known zeolite structures produced over 5000 hypothetical structures [36]. Many of these structures are not 3-dimensional frameworks, instead forming discrete cages, chains or layers. However, for each different set of input data, each derived structure has a unique set of coordination sequences for the inequivalent T-atoms and therefore has a distinct topology. 

The concept of coordination sequences (CSQ) was originally introduced by Bmnner and Laves,[37] and first applied to zeolite frameworks by Meier and Moeck.[381 In a typical zeolite framework, each T-atom is connected to N 4 neighboring T-atoms through oxygen bridges. These neighboring T-atoms are then linked in the same manner to A S T-atoms in the next shell. The latter are connected with N3 T-atoms, and so forth. Each T-atom is counted only once. In this way, a coordination sequence can be determined for each T-atom of the 4-connected net of T-atoms. It follows that ... 

Coordination sequences have been listed in the Atlas[3] from N up to Nm for each topologically distinct T-atom in every framework structure. For example, the coordination sequences in FAU are as follows ... 

The coordination sequences and the vertex symbol are unique for a particular framework topology, i.e. they can be used to distinguish between different zeolite framework types unambiguously. In this way, frameworks with the same topologies can be easily identified. Currently, it is easier to calculate the coordination sequences and vertex symbol using computer program based on crystallographic data. 

W.M. Meier and HJ. Moeck, The Topology of Three-dimensional 4-Connected Nets Classification of Zeolite Framework Types using Coordination Sequences. J. Solid State Chem., 1979, 27, 349-355. 

In this database, there are lots of query tools. Users could search specified frameworks by choosing space group, number of T-atoms, framework density, unit-cell volume, TD10, framework energy, and cell parameters, etc. Furthermore, other topological parameters, such as vertex symbol and coordination sequences, could also be used to search a framework. 

It should be noted that all the structures in this database have been fully refined assuming a SiC>2 composition. Only structures with low energies comparable with known frameworks are stored in this database. To make sure that all the structures in this database are unique, coordination sequences and vertex symbols are used to get rid of duplicated frameworks. 

Another remarkably coordinated sequence of rearrangements ensued when the dioxygen in the above procedure was replaced by an electron-deficient alkene. The radicals formed from... 

Ion (right). The two nets have the same Schlafli and Vertex Symbol VS (top), but different Coordination Sequence (CS). The rings multi-... 

Zeolite frameworks can be classified according to various schemes (e.g. by pore opening, by structural subunit, by channel system, by framework density, by loop configurations, by vertex symbols, and/or by coordination sequences). Most of these features are defined in the introductory pages of the Atlas of Zeolite Framework Types and then given... 

The interaction between machine and human in a cooperative scenario can take place as a coordinated sequence of tasks performed by the machine and the human sharing the same workplace. When tasks can be performed by both, machine and worker at the same time, these systems are defined as workplace and time-sharing systems (Fig. 2). 

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