Similar structural motifs

This reviews contends that, throughout the known examples of facial selections, from classical to recently discovered ones, a key role is played by the unsymmetri-zation of the orbital phase environments of n reaction centers arising from first-order perturbation, that is, the unsymmetrization of the orbital phase environment of the relevant n orbitals. This asymmetry of the n orbitals, if it occurs along the trajectory of addition, is proposed to be generally involved in facial selection in sterically unbiased systems. Experimentally, carbonyl and related olefin compounds, which bear a similar structural motif, exhibit the same facial preference in most cases, particularly in the cases of adamantanes. This feature seems to be compatible with the Cieplak model. However, this is not always the case for other types of molecules, or in reactions such as Diels-Alder cycloaddition. In contrast, unsymmetrization of orbital phase environment, including SOI in Diels-Alder reactions, is a general concept as a contributor to facial selectivity. Other interpretations of facial selectivities have also been reviewed [174-180]. 

The limited number of characterized complexes of arsine and arsenide ligands contain some similar structural motifs to those exhibited for equivalent phosphorus ligands. Coordination numbers of two, three, or four are observed with monomeric up to decameric zinc complexes structurally determined by X-ray crystallography. 

In Sect. 4.2 we expand on pseudogap tuning concepts and illustrate these ideas and applications to the isotypic Mg2Cu6Ga5, Mg2Znn, and Na2Au6ln5. Because all the ACs we have obtained have very similar structural motifs, their structural regularities will be discussed together later in Sect. 5. 

General Methods for Searching Similar Structural Motifs... 

To activate carbon dioxide for chemical reactions, it is advantageous to fix and destabilize this rather inert molecule. An important strategy to control and influence the reactivity of CO2 is its coordination to amines, metal-bound imido moieties, or metal centers (144), which leads to a decrease of the CO bond order, while the molecule in most cases becomes considerably bent. In biochemical pathways, the CO2 adduct of the coenzyme biotin (17) is involved in various carboxylation and transcarboxylation reactions (146). Similar structural motifs could become important functional building blocks for bioinspired photoreactions involving carbon dioxide activation steps (Fig. 18). 

What, if anything, can be said about the evolutionary relationship between apoLp-III and exchangeable vertebrate apolipoproteins Both bind to lipoproteins and seem to have similar structural motifs. Whether apoLp-III is the ancestor of the vertebrate proteins can not be stated with... 

All bridged dimers feature a central Ln202 core (type I), which in the presence of strong donor molecules such as THF, DME, OPPh3, or pyridine dissociate into mononuclear species with either octahedral (type II) or trigonal bipyramidal structures (type III). Similar structural motifs are found in cyclic silsesquioxane-based rare earth siloxides. In the presence of donors, distorted octahedral (V) or distorted trigonal bipyramidal complexes (IV) are formed, which in solution through loss of donor solvent may be in equilibrium with their respective dimers (see Lanthanides Coordination Chemistry) ... 

Figure 8.19 Similar structural motifs between (a) a co-crystal hydrate of theophylline and citric acid, (b) citric acid monohydrate and (c) theophylline monohydrate. ...

The pictures here are of small proteins, as proteins go, and the structures of large proteins, which may he ten times or more the size of chymotrypsin, are much more complex and generally contain a number of different, or similar, structural motifs. There is clear evidence that these and other such modules , as we may call them, have heen planted in different proteins by evolutionary descent from some primeval protein ancestors. Moreover, as... 

It has been suggested that the active sites in proteins are better conserved than the overall fold [27]. If so, then one should be able to identify not only distant ancestors with the same global fold and same biochemical activity, but also proteins with similar functions but different global folds. Nussinov and coworkers empirically demonstrated that the active sites of eukaryotic serine proteases, subtilisins, and sulfhydryl proteases exhibit similar structural motifs [216]. Furthermore, in a recent modeling study of S. cerevisiae proteins, active... 

In this research, the authors used molecular overlay to investigate the stereochanical structure-activity relationship among picaridin and AI3-37220 diastereoisomers and deet (Figure 4.4). It is clear from the study that most active compounds, picaridin RS, AI3-37220 SS, and deet, have very similar structural motifs, which leads to a high degree of matching of the relevant parts of a molecule. A sharp contrast to this is the stereochanical similarity/dissimilarity between these three active structures vis- -vis the less active isomers of AI3-37220 and picaridin. 

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