Rigid searches

The Best database search first identifies all potentially suitable compounds by using loosened constraints, thus including those that would fail a rigid search. Within this preliminary list, the algorithm attempts to modify additionally the conformers so that they can fit the original query while remaining below a certain energy overflow [40]. The use of a Best search is justified when one has to deal with too small hit lists. 

To conclude this computer project, we shall lirst search the potential surface for rotation of u-butane about its 23 C C bond, for which we think we know the answei, then seai ch the potential sutface foi I-butene, foi which we do not. In I -butene, the double bond establishes a rigid plane but the methyl group can take up several d i ffe ren t positions re I at i ve to i t by rotation ab ou t th e 2 - 3 s i n g I e bo n d,... 

The amount of computation necessary to try many conformers can be greatly reduced if a portion of the structure is known. One way to determine a portion of the structure experimentally is to obtain some of the internuclear distances from two-dimensional NMR experiments, as predicted by the nuclear Over-hauser effect (NOE). Once a set of distances are determined, they can be used as constraints within a conformation search. This has been particularly effective for predicting protein structure since it is very difficult to obtain crystallographic structures of proteins. It is also possible to define distance constraints based on the average bond lengths and angles, if we assume these are fairly rigid while all conformations are accessible. 

While melamine is widely used in flexible foams as a fire-retardant, trichlorphenyl phosphate has been the preferred agent for use in rigid foams. However, the introduction of specifications stipulating halogen-free additives has led to a search for alternatives such as halogen-free phosphorus esters, red phosphorus and ammonium polyphosphate. 

Figure 8 plates are friendlier than slip plates (blinds) as their position is apparent at a glance. If slip plates are used, their projecting tags should be readily visible, even when the line is insulated. In addition, spectacle plates are easier to fit than slip plates, if the piping is rigid, and are always available on the job. It is not necessary to search for one, as with slip plates. 

To search for the inverted region, experiments were designed so that the donor-acceptor distances were kept fixed by attaching them to a covalent network of rigid spacers, frozen media, electrostatic com-plexation, and protein frameworks. In all of these cases, the... 

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