Descriptors general

The dose descriptor may also implicate uncertainties which require the application of an assessment factor. For example, the use of a LOAEL as the dose descriptor generally entails more uncertainties to the derivation process than the use of a NOAEL and thus entails a greater assessment factor. Even when a NOAEL is used as dose descriptor the application of an assessment factor may be necessary. For example, if teratogenic effects were observed at dose levels only slightly higher than the NOAEL, an assessment factor is applied in order to account for the steep dose-response curve. 

In Section 2.1 the main chromatographic descriptors generally used in routine HPLC work were briefly discussed. Retention factor and selectivity are the parameters related to the analyte interaction with the stationary phase and reflect the thermodynamic properties of chromatographic system. Retention factor is calculated using expression (2-1) from the analyte retention time or retention volume and the total volume of the Uquid in the column. Retention... 

GAP HOMO-LUMO energy gap -> quantum-chemical descriptors Geary coefficient -> autocorrelation descriptors general aN-index -> determinant-based descriptors... 

Basicity. The only basicity descriptor generally available for a large number of amines is pK, (measured in water). 

Analogous relationships between BCF and other descriptors, generally collinear with log have been derived such as water solubility (Metcalf et ai, 1973, 1975 Chiou et aL, 1977 Kenaga and Goring, 1980). The bioconcentration factors for Daphnia, molluscs, mussels, algae and microorganisms have also been related to log P or water solubility (Table 4.14). 

Linear scaling relationships correlate the heat of adsorption of molecules with the heat of adsorption of a descriptor, generally of the heteroatom of the molecule. Abild-Pedersen et al. [41] observed that the heat of adsorption of AH fragments correlates... 

As far as foam quality is concerned, rich and creamy are probably the most frequently used words dense and tight are also often associated. These four descriptors generally refer to a foam consisting of many small bubbles, whereas the foam comprised of mainly large bubbles is said to be a loose, lacy foam its texture is lacking in richness or tightness. 

The next and very important step is to make a decision about the descriptors we shall use to represent the molecular structures. In general, modeling means assignment of an abstract mathematical object to a real-world physical system and subsequent revelation of some relationship between the characteristics of the object on the one side, and the properties of the system on the other. 

Steinhauer and Gasteiger [30] developed a new 3D descriptor based on the idea of radial distribution functions (RDFs), which is well known in physics and physico-chemistry in general and in X-ray diffraction in particular [31], The radial distribution function code (RDF code) is closely related to the 3D-MoRSE code. The RDF code is calculated by Eq. (25), where/is a scaling factor, N is the number of atoms in the molecule, p/ and pj are properties of the atoms i and/ B is a smoothing parameter, and Tij is the distance between the atoms i and j g(r) is usually calculated at a number of discrete points within defined intervals [32, 33]. 

The data analysis module of ELECTRAS is twofold. One part was designed for general statistical data analysis of numerical data. The second part offers a module For analyzing chemical data. The difference between the two modules is that the module for mere statistics applies the stati.stical methods or rieural networks directly to the input data while the module for chemical data analysis also contains methods for the calculation ol descriptors for chemical structures (cl. Chapter 8) Descriptors, and thus structure codes, are calculated for the input structures and then the statistical methods and neural networks can be applied to the codes. 

The general procedure in a QSPR approach consists of three steps structure representation descriptor analysis and model building (see also Chapter X, Section 1.2 of the Handbook). 

Odor perception and description are highly subjective in nature. Nevertheless, there is a generally agreed-upon odor vocabulary that is used to characterize individual ingredients and finished fragrances. Table 1 shows some commonly used odor descriptors grouped into five general classifications. 

JM Sutter, SL Dixon, PC Jurs. Automated descriptor selection for quantitative structure-activity relationships using generalized simulated annealing. I Chem Inf Comput Sci 35(I) 77-84, 1995. 

In general, receptor theory uses indirect mathematical models to estimate descriptors of drug effect. These descriptors still must be used with the proviso that biological systems may still modify drug effect in a system-dependent manner and thus predictions of therapeutic effect must be made with caution across different systems. 

In general, the described techniques provide an effective, flexible, and relatively fast solution for library design based on analysis of bioscreening data. The quantitative relationships, based on the assessment of contribution values of various molecular descriptors, not only permit the estimation of potential biological activity of candidate compounds before synthesis but also provide information concerning the modification of the structural features necessary for this activity. Usually these techniques are applied in the form of computational filters for constraining the size of virtual combinatorial libraries and... 

---