Shadow indices

C2Descriptor+ Accelrys Inc. www.accelrys.com/cerius2/descriptor.html Topological indices, information content indices, fingerprint descriptors, physicochemical properties, charged partial surface area descriptors, shadow indices... 

Figure 5 Ranges of isomer shifts observed in various oxidation and spin states of iron (given relative to a-iron at 300 K). Shadowing indicates the most frequently observed configurations. (From Greenwood and Gibb. With kind permission from Springer Science Business Media)...

Theses are calculated from the 3D molecular structure, which is defined with coordinates of all atoms in the molecule. The step from 2D to 3D description of molecules is the crucial one [40-42]. The 3D structure is an ambiguously defined quantity, which depends on molecular environment, i.e., it is different in crystal structure, in solutions, or in vacuo. If it is theoretically determined it depends on the computational method. However, the 3D structures form a basis for a broad range of descriptors. Examples are mass distribution descriptors such as moment of inertia or gravitation index, and shape indices such as shadow indices, surface area indices, and van der Waals indices [29,40,41]. 

A number of - shape descriptors are defined in terms of principal moments of inertia. Moreover, principal moments of inertia are used to provide a unique reference framework for the calculation of the - shadow indices, and in general are used as - alignment rules of the molecules. They are encountered among - WHIM descriptors and used by the CoMMA method. 

Several shape descriptors are defined within more general approaches to - molecular descriptors. This is the case of - Kier shape descriptors, -> shape profiles, -> shadow indices, -> WHIM shape descriptors, - Sterimol shape parameters L/Bj and B1/B5, molecular - periphery codes, and -> centric indices. Other approaches to the study of molecular surface and shape are Mezey 3D shape analysis and Hopfinger - molecular shape analysis. -> Triangular descriptors have also been used to characterize molecular shape to search for similarities among molecules. 

Among the several CODESSA descriptors, implemented in the homonymous software CODESSA (Comprehensive DEscriptors for Structural and Statistical Analysis) [Katritzky and Gordeeva, 1993 CODESSA- Katritzky, Lobanov et al., 1996 Katritzky, Lobanov et al, 1996], are molecular weight, molecular volume, —> count descriptors, —> topological indices, charge descriptors, shadow indices, charged partial surface area descriptors, quantum-chemical descriptors, and —> electric polarization descriptors. 

Fig. 5. The optical absorption spectrum and the electronic structure of Vs" ", (a) Experimental data, where a photodissociation action spectrum of a rare-gas complex, Vs+Ar, was measured by observing a photofragment, Vs+. (b) Density-functional calculation of the spectrum for the most stable isomer illustrated in the inset. The bars show oscillator strengths the solid line a spectral profile, (c) Density-of-states profiles of the majority or and the minority-spin electrons obtained by the density-functional calculation. The shadows indicate occupied electronic levels. The vanadium pentamer ion. Vs" ", was shown to be in the spin triplet state with a trigonal bipyramid structure, where the average bond length was 2.4...

Shadow indicates redundancy of the system or multiple systems... 

Figure 6. SERS spectra at (A) cyt. c adsorbed silver electrode in 5 mM 4-PYS, (B) 4-PYS adsorbed silver electrode in 0.01 mM cyt. c, and (C) silver electrode in 5 mM 4-PYS. Shadow indicates the peaks for cyt. c.

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