Squared substructure

Besides specifications on atoms, bonds, branches, and ring closure, SLN additionally provides information on attributes of atoms and bonds, such as charge or stereochemistry. These are also indicated in square [ ] or angle < > brackets behind the entity e.g., trans-butane CH3CH=[s=t]CHCH3). Furthermore, macro atoms allow the shorthand specification of groups of atoms such as amino adds, e.g., Ala, Protein2, etc. A detailed description of these specifications and also specifications for 2D substructure queries or combinatorial libraries can be found in the literature [26]. 

Structural data are readily available from the database, but it must be assumed that they were not originally collected with the requirements of the particular correlation in mind. It is essential that the substructure investigated be tightly defined, and that this is confirmed by careful checks of structures in the data set retrieved. (This requirement is squarely at odds with that for statistical respectability, for which the largest possible data set is generally desirable.) A last resort, if the question is important enough, is to collect new data. The structures examined can then be designed to answer specific questions. The answers to the questions will not, however, be available for months or even years. 

According to Jensen, the dimensionality of a structure (or of a substructure of the same) is indicated by enclosing its compositional formula in square brackets and prefixing an appropriate symbol. ... 

Absolute measurements of the 2PA cross section of chromophores are experimentally very demanding and difficult to implement for routine studies of new materials. This is mainly due to the fact that the 2PA excitation rate in a sample does not depend simply on the square of the average intensity, (f(r, t)), but on the average of the square of the intensity, (f(r, t) ) (r and t are the special and temporal coordinate) [63,64,78]. These two quantities are not the same if the laser piflse has substructure in space and time [85,86]. Thus, absolute 2PA determinations that rely on the measurements of signals proportional to the excitation rate, such as the 2P-induced fluorescence... 

It is interesting that in the 3-dimensional structures of them, obtained from X-ray diffraction data [24-26], they can be superimposed on one another at the point of the largest common substructure [31]. Figure 7 shows a three dimensional stereoscopic view of the common part of them, which were superimposed by the least squares method. 

Substructure in the halo tends to increase the annihilation signals because of the dependence of the annihilation rate on the square of the dark matter den-... 

Fe(III) is observed and revealed by Mossbauer spectroscopy. This unique behaviour is indicative of a particular substructure in the gel where ferrocene units are mainly located at the surface of the material. A completely different situation is observed for the bi-silylated xerogel obtained from 102 for which a Cottrelian charge transfer is observed and it exhibits a classical reversible voltammogram the peak current scales linearly with the square root of scan rate. Moreover, it is impossible to achieve a complete Fe(II)/Fe(ni) oxidation although the process is still reversible. Such behaviour demonstrates that some of the ferrocenyl units are not accessible and do not participate in the electrochemical process103. 

Figure 5. Example of a relative pharmacophore, with the privileged biphenyltetrazole substructure as the special point (shown as a square), and the connections to the other centres (dotted lines).

The vernier model also turned out to be an approximation. It is now clear that although the metal atoms in these stmctures are similar to that found in the fluorite parent structure, the anion array is continuously modulated, and expands or contracts throughout the structure to fill the space optimally with respect to the chemical and crystallographic constraints that apply. Although for some modulation wavelengths the anion array is well described in terms of a square net or a hexagonal net, this is not universally correct, and the modulated description is a more accurate representation of the anion substructure. 

When the central metal atom is free of auxiliary ligands there are more possibilities for coordination of AnEryt. Keeping to the square-planar coordination Cu(II) builds complexes with two AnEryt, as shown in Fig. 16. Three structures of the type A2[Cu(AnErytH 2)2] 4 H2O (A2 6 4 H2O) with A = Li, Na and K [85,86] have been determined. The structures of Na and K on the one hand and Li on the other hand differ in the coordination of the alkali ions to the deprotonated diol functions of the Cu(AnErytH 2) substructure. The Cu-0 bond length averages 1.93 A and the O-C-C-0 angle of AnErytH 2 grows in dependence on the cation from 33.7 (Li) to 35.4° (K). 

Quantitative structure-activity relationship Root mean square error Receiver-operating characteristic Recursive partitioning Support vector machine TOPological Substructural Molecular Design Topological polar surface area... 

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