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Internet Electronic Journal of Molecular Design - IEJMD, ISSN 1538-6414, CODEN IEJMAT
| ABSTRACT - Internet Electron. J. Mol. Des. September 2004, Volume 3, Number 9, 544-559 |
Classification of Polar and Nonpolar Aquatic Pollutants Using
Simple Descriptors. Differences between Polarity Prediction and
Narcosis Classification
Guido Sello
Internet Electron. J. Mol. Des. 2004, 3, 544-559
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Abstract:
The problem of toxicity prediction is mainly related to the
necessity of processing many data that most of the time come from
different sources and have different biological meaning. Often, the
real mechanism of action of a toxicant is unclear or difficult to
reproduce; in addition, a chemical compound exercises its toxic
action through many steps that depend both on its structure and on
the specific environment where it is acting. In this perspective, the
classification of compounds can be of great help because decreases
the number of the alternatives to those specific of that class,
allowing a more focused analysis. The classification of narcotic
pollutants into polar and nonpolar sets is certainly an important
aspect of this type of problems. Object classification requires two
principal components: the selection of the molecular descriptors
and the choice of the classification algorithm. The calculation of
the molecular descriptors is performed using our own approach
that is based on empirical equations. We calculated three
descriptors (Helc, HQ+, Elcdif) that are used in pairs (Helc and
Elcdif, or HQ+ and Elcdif). Using two classification algorithms, a
classical neural network and a tree neural network, we analyze two
compound sets; the first contains 190 narcotic pollutants (114
nonpolar and 76 polar), the second contains 30 pollutants (20
nonpolar, 5 polar, 5 acetylcholinesterase inhibitors). In a broad
sense, the first set is used as training set and the second as test set.
The use of simple descriptors allows for a very good classification
of narcotic pollutants demonstrating that it is not necessary to use
high-level theories to make simple operations. On the contrary,
much work is still required to obtain an acceptable theoretical
prediction; part of it is definitely on the modelers' side, but the rest
concerns a better rationalization of the experimental data without
which any model will have problems. Classification of narcotic
pollutants into polar and nonpolar sets is required to ease the
QSAR treatment of their toxic effects. However, there still remain
many questions on the validation of theoretical models using only
experimental data.
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