EVA descriptors

EVA descriptors were proposed by Ferguson et al. [Ah, 47]. The EVA descriptor (EigenVAlue) extracts structural information from infrared spectra. The eigenva-... 

Examples of such descriptors are - WHIM descriptors and -> G-WHIM descriptors of size and shape, -> EA indices, - quasi-Wiener index, - Mohar indices, several - shape descriptors, - EVA descriptors and EEVA descriptors. 

EigenVAIue descriptors EVA descriptors eigenvalues -> algebraic operators (O characteristic polynomial) eigenvalues of the adjacency matrix eigenvalue-based descriptors eigenvectors -> algebraic operators (O characteristic polynomial)... 

Electronic EigenVAIue descriptors EEVA descriptors -> EVA descriptors electronic polarizability electric polarization descriptors electronic polarization - electric polarization descriptors... 

EVA descriptors were recently proposed by Ferguson et al. [Ferguson et al, 1997 Turner et al., 1997] as a new approach to extract chemical structural information from mid- and near-infrared spectra. The approach is to use, as a multivariate descriptor, the vibrational frequencies of a molecule, a fundamental molecular property characterized reliably and easily from the potential energy function. The EigenVAIue (EVA) descriptor is a function of the eigenvalues obtained from the normal coordinate matrix they correspond to the fundamental vibrational frequencies of the molecule, which can be calculated using standard quantum or molecular mechanical methods from -> computational chemistry. 

As the final step, the EVA function is sampled at fixed increments of L cm along the BPS axis, this samping results in the 4000/L values that define the EVA descriptor uniform length. 

The frequency range being fixed, the sampling parameter L determines the total number of EVA descriptor elements L should be maximized so as to reduce computational overhead and minimized to catch all the useful information. The optimal L value depends on the selected o value. 

The EVA descriptors are among - 3D-descriptors, independent of any molecular alignment, giving information about molecular size, shape and electronic properties. Moreover, the EVA descriptors show only a moderate dependence on conformations. 

Figure E-3. Bounded Frequency Scale with superimposed EVA descriptors for two compounds.

EVA function -> EVA descriptors evaiuation set external evaluation set -> data set... 

Examples of geometrical descriptors are the - quantum-chemical descriptors, -> moment of inertia, - length-to-breadth ratio, -> surface areas, - volume descriptors, - CPSA descriptors, -> EVA descriptors, -> WHIM descriptors, 3D-MoRSE descriptors, -> interaction energy values, spectrum-like descriptors. 

Attention to the combination of the molecular geometry with chemical atomic information has led to the development of spectral molecular representations given, for example, by -> 3D-MoRSE descriptors [Schuur and Gasteiger, 1996], - RDF descriptors [Hemmer et al, 1999], - spectrum-like descriptors [Novic and Zupan, 1996], -+ EVA descriptors [Ferguson et al, 1997], -> SWM signals [Todeschini et al, 1999], and - Blurock spectral descriptors [Blurock, 1998]. 

Examples of applications of the rules to obtain uniform length descriptors are - EVA descriptors, - topological charge indices, atomic walk count sequence, -+ SE-vectors, - molecular profiles, -> 3D-MoRSE descriptors, - autocorrelation descriptors. 

Description SYBYL module for the calculation of EVA descriptors, CoMFA and CoMSIA fields, also including several QSAR tools. Last release 6.1... 

Ginn, CM., Turner, D.B., Willett, P, Ferguson, A.M. and Heritage, T.W. (1997). Similarity Searching in Files of Three-Dimensional Chemical Structures Evaluation of the EVA Descriptor and Combination of Rankings Using Data Fusion. J.Chem.lnfComputScL, 37, Till. 

Electronic Eigenvalue descriptors = EEVA descriptors —> EVA descriptors... 

Gravitational indices 3D-MoRSE descriptors EVA descriptors EEVA desCTiptors WHIM desaiptors GETAWAY desCTiptors... 

The molecular matrix M and the matrix Z are the natural starting point for the calculation of several 3D atomic and molecular descriptors, such as quantum-chemical descriptors, —> molecular interaction fields, EVA descriptors, WHIM descriptors, GETAWAYdescriptors,... 

Examples of spectral indices are WHIM descriptors and G-WHIM descriptors of size and shape, EA indices, —> quasi-Wiener index, Mohar indices, several —> shape descriptors, —> EVA descriptors, —> EEVA descriptors, and —> 4D-MS descriptors. 

This implies at least one rule to define a fixed number L of elements in each vector and one rule to fill in the vector elements when the values are missing (for example, filling in with zero values). Examples of uniform-length descriptors are EVA descriptors, topolcgical charge indices, atomic walk count sequence, —> SE-vectors, molecular profiles, spectra descriptors, 3D-MoRSE descriptors, autocorrelation descriptors, affinity fingerprints, and most of the string... 

Any set of molecular descriptors used to represent molecules in a fixed and ordered sequence was called basis of descriptors [Randic, 1992c Randic and Trinaj Stic, 1993a Baskin, Skvortsova et al., 1995]. Abasis of descriptors can be defined (a) selecting a class of homogeneous naturally ordered descriptors ( path counts, connectivity indices, 3D-MoRSE descriptors, EVA descriptors, Burden eigenvalues, etc.) (b) by using a few ad hoc selected descriptors such as one —> lipophilicity descriptor, one steric descriptor and one —> electronic descriptor, as used in classical QSAR. 

Optimising the EVA descriptor for prediction of biological activity. Org. Biomol. Chem., 2,3301-3311. 

Turner, D.B. and Willett, P. (2000a) Evaluation of the EVA descriptor for QSAR studies. 3. The use of a genetic algorithm to search for models with enhanced predictive properties (EVA GA). 

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