Descriptor Technology

we introduce frequently used descriptors classified by the structure of the descriptor itself linear, treelike, and field descriptors. 

The problem can be addressed by taking a more flexible set of fragments resulting in the hashed fingerprints approach [176, 177]. Instead of checking the occurrence of individual fragments, all atom paths up to a certain length (five or seven in practice) are enumerated. Since there are too many different paths to reserve a bit for each, a 

Linear representations are by far the most frequently used descriptor type. Apart from the already mentioned structural keys and hashed fingerprints, other types of information are stored. For example, the topological distance between pharmacophoric points can be stored [179, 180], auto- and cross-correlation vectors over 2-D or 3-D information can be created [185, 186], or so-called BCUT [187] values can be extracted from an eigenvalue analysis of the molecular adjacency matrix. 

Note that no three-dimensional information is used for generating the feature tree the descriptor is therefore conformation independent. 

A linear descriptor naturally contains an ordering of its elements, which makes it very easy to compare them. In a tree structure however, it is not clear which parts should be mapped onto each other. Different mappings will result in different similarity values  

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Model Development Data sets, Descriptors, Technologies, and Applicability... 

The Hopfen descriptors have been developed at Novartis as a novel combination of a number of molecular descriptor technologies that have been published previously, but merged in an approach that is intended to better describe the molecules under consideration (49). In addition, efforts have been made to fully parameterize the descriptor generation program to permit the user, complete control over the generation process and allow the descriptors to be adapted for the particular problem domain of... 

Several other descriptors based on the topology of molecules were developed and have been successfully applied. Reviews on descriptor technology can be found in [19, 20, 22, 30]. The following discussion focuses on three recently developed descriptors used in the application study in section 3. The selection of descriptors was based on availability and speed of the software. 

Wavelet coefficient descriptors (WCDs) ° exemplify how the WT enhances the quality of current descriptor technology and enables the development of improved models. WCDs are an adaptation of the transferable atom equivalent (TAE) descriptors developed by Breneman and Rhem. TAE descriptors are derived by quantifying the distributions of multiple electronic properties computed on electronic van der Waals surfaces, which are defined as the 0.002-e-au isosurfaces (Figure 15). TAE descriptors encode the... 

Statistical methods can also be utilized to form probability models or to estimate the likelihood of particular descriptors forming the known classes. Chemical Computing Group Inc. has recently developed a new technology. 

This review will highlight the interrelationships between basic photopolymer science and practical applications of this technology. Each application of photopolymer technology can be described in terms of three primary descriptors the mode of exposure, the mechanism of the photopolymer reaction employed and the visualization method used. Using this foundation, the widely diverse applications of photopolymer technology to electronic materials, printing materials, optical and electro-optical materials, the fabrication of devices and polymeric materials, adhesives and coating materials will be discussed. 

Caron, G., Reymond, F., Carrupt, P.A., Girault, H.H. and Testa, B. (1999) Combined molecular lipophilicity descriptors and their role in understanding intramolecular effects. Pharmaceutical Science el Technology Today, 2, 327-335. 

The QSAR models can be used to estimate the treatability of organic pollutants by SCWO. For two chemical classes such as aliphatic and aromatic compounds, the best correlation exists between the kinetic rate constants and EHOMO descriptor. The QSAR models are compiled in Table 10.13. By analyzing the behavior of the kinetic parameters on molecular descriptors, it is possible to establish a QSAR model for predicting degradation rate constants by the SCWO for organic compounds with similar molecular structure. This analysis may provide an insight into the kinetic mechanism that occurs with this technology. 

HT technology for catalysts-automated synthesis and testing appears to be reasonably adapted to date, but further improvements are expected for HT catalysts characterization, which is still restricted to costly and in general ex-situ spectroscopic techniques. These tools would provide the new catalyst descriptors needed to improve the ability to predict catalytic performances without testing. 

Perminova, I. V., N. Grechischcheva, and V. S. Petrosyan. 1999. Relationships between structure and binding affinity of humic substances for PAHs Relevance of molecular descriptors. Environmental Science and Technology 33 3781. 

As an alternative to describing molecules by their structural features (substruc-tural elements, functional groups) and similarly to CoMFA, this approach uses field points to describe the van der Waals and electrostatic minima and maxima that surround molecules and compares these field points. The field points that are used are derived from molecular electrostatic potential descriptors. The XED model is marketed by Cresset Biomolecular and forms the basis for the proprietary virtual screening technology FieldPrint [95]. 

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