Descriptor definition

Positive cooked-beef flavor components as perceived by descriptive sensory panelists are reduced during free radical catalyzed meat flavor deterioration (MFD) while negative flavor notes with descriptor definitions of cardboard and painty intensify, as reviewed recently by Love (13). Although the cardboard and painty off-flavors correlate well with lipid oxidation products and can be measured easily by gas chromatography (1, 14, 18). much less is known about the fate of the positive cooked-beef flavors in this MFD process (13). 

Estrada, E. and Ramirez, A. (1996). Edge Adjacency Relationships and Molecular Topographic Descriptors. Definition and QSAR Applications. J.Chem.Inf Comput.ScL, 36, 837-843. 

The Handbook of Molecular Descriptors collects the definitions, formulas and short comments of molecular descriptors known in chemical literature, our intention being to consider all the known molecular descriptors. The definitions of technical terms, around 1800 in all, are organized in alphabetical order. The importance of a molecular descriptor definition is not related to its length. Only a few old descriptors, abandoned... 

Estrada E, Ramirez A. Edge adjacency relationships and molecular topographic descriptors. Definition and QSAR applications. J Chem Inf Comput Sci 1996 36 837-843. 

We must now mention, that traditionally it is the custom, especially in chemo-metrics, for outliers to have a different definition, and even a different interpretation. Suppose that we have a fc-dimensional characteristic vector, i.e., k different molecular descriptors are used. If we imagine a fe-dimensional hyperspace, then the dataset objects will find different places. Some of them will tend to group together, while others will be allocated to more remote regions. One can by convention define a margin beyond which there starts the realm of strong outliers. "Moderate outliers stay near this margin. 

Two other atomic properties have been used in the definition of atom type, thereby increasing its fuzziness relative to that in the ap and tt descriptors - atomic log P contribution (yielding hydrophobic pairs, hps, and torsions, hts) and partial atomic charges (charge pairs, cps, and charge torsions, cts). 

In this chapter the focus is on structure descriptors. After a definition of this term their properties are described and an oveiwiew is given of some frequently used structure descriptors. 

Nutritional Labeling Descriptors. In order to avoid confusion, descriptive terms must be accompanied by definitions which adequately explain the terms. In the case of nutrition-related claims, analytical sampling offers a means of assuring the accuracy of the stated claims. The USDA s FSIS has proposed a Hst of descriptors relevant for meat and poultry products (Table 3). 

J. B. Casey, W. J. Evans, W. H. PoweU, and T. E. Sloan, "A Stmctural Definitive Descriptor and Numbering System for Cluster Compound Nomenclature," Chemical Abstract Service, presented at the 198th National Meeting of the American Chemical Society, Miami Beach, FI., Sept. 1989. 

These pharmacophore techniques are different in format from the traditional pharmacophore definitions. They can not be easily visualized and mapped to the molecular structures rather, they are encoded as keys or topological/topographical descriptors. Nonetheless, they capture the same idea as the classic pharmacophore concept. Furthermore, this formalism is quite useful in building quantitative predictive models that can be used to classify and predict biological activities. 

Filimonov DA, Poroikov VV, Borodina Y, Gloriozova T. Chemical similarity assessment through multilevel neighborhoods of atoms definition and comparison with the other descriptors. J Chem Inf Comput Sci 1999 39 666-70. 

The E-state indices are atomic descriptors composed of an intrinsic state value I and a perturbation AI that measures the interactions with all other atoms in a molecule. The Kier-Hall electronegativity is the starting point in the definition of the intrinsic state of an atom, which encodes its potential for electronic interactions and its connectivity with adjacent atoms. The intrinsic state of an atom i is [19, 21] ... 

PSA. Hence, we only mention here that the definition of PSA is similar to that of Na and N. Thus, PSA possesses the same disadvantages when compared to thermodynamic H-bond descriptors. In fact, it has been estimated that there is a strong linear relationship between the calculated static PSA and the calculated dynamic polar surface [32, 33]. A further possible simplification using only the number of H-bond forming atoms and PLS statistics was proposed [35]. Excellent correlahons of PSA with the number of H-bond donors and acceptors were published [35, 36]. 

A comparahve analysis of coefficients and descriptors clarifies the relationship between lipophilicity and hydrophobicity (Y in Eq. 4 is the molar volume which assesses the solute s capacity to elicit nonpolar interactions (i.e. hydrophobic forces) which, as also clearly stated in the International Union of Pure and Applied Chemistry definitions [3] are not synonyms but, when only neutral species are concerned, may be considered as interchangeable. In the majority of partitioning systems, the lipophilicity is chiefly due to the hydrophobicity, as is clearly indicated by the finding that the product of numerical values of the descriptors V and of the coefficient v is larger in absolute value than the corresponding product of other couples of descriptors/coefficients [9]. This explains the very common linear rela-... 

The models developed for log D prediction usually aim at being global ones. This, however, does not work on practice. Sheridan et al. [109] noticed that the accuracy of log D prediction of molecules decreased approximately 2-3 times (RMSE = 0.75 versus 1.5-2) as the similarity of the test molecule to the molecules in the training set (using Dice definition with the atom pair descriptors) changed from 1 to 0 (most to least similar). Thus, if a test set molecule had a very similar molecule in the training set, it was possible to accurately predict its log D value. A detailed overview of state of the art methods to access the same problem was published elsewhere [117]. 

While the shape factor, introduced in the previous section, provides a quantitative definition or description of particle shape, there are other descriptors such as flakiness ratio, flakiness index, elongation index and angularity number which are also found to be in vogue. 

Elizabeth Lloyd That you cannot give a full explanation of what s happening in the group without giving an account of the gradient, and, in fact, the difference in socioeconomic gradients - I wouldn t prefer to call them causal myself but that they are descriptors of the situation that you cannot take them away from the explanation and understand it in the same way. I said one explains the phenomena in terms of what types of entities and their properties and so I take that to be a standard definition of a reductionist or anti-reductionist position. 

Each of these columns of this symmetrical matrix may be seen as representing a molecule in the subspace formed by the density functions of the N molecules that constitute the set. Such a vector may also be seen as a molecular descriptor, where the infinite dimensionality of the electron density has been reduced to just N scalars that are real and positive definite. Furthermore, once chosen a certain operator in the MQSM, the descriptor is unbiased. A different way of looking at Z is to consider it as an iV-dimensional representation of the operator within a set of density functions. Every molecule then corresponds to a point in this /V-dimensional space. For the collection of all points, one can construct the so-called point clouds, which allow one to graphically represent the similarity between molecules and to investigate possible relations between molecules and their properties [23-28]. 

This chapter is intended to provide basic understanding and application of the effect of electric field on the reactivity descriptors. Section 25.2 will focus on the definitions of reactivity descriptors used to understand the chemical reactivity, along with the local hard-soft acid-base (HSAB) semiquantitative model for calculating interaction energy. In Section 25.3, we will discuss specifically the theory behind the effects of external electric field on reactivity descriptors. Some numerical results will be presented in Section 25.4. Along with that in Section 25.5, we would like to discuss the work describing the effect of other perturbation parameters. In Section 25.6, we would present our conclusions and prospects. 

Symbols, Definitions and Classification of Calculated Molecular Descriptors... 

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