摘要:

CoMFA (comparative molecular field analysis) has been used to correlate the biodegradability of several classes of compounds. The technique uses an atomic probe to detect the steric and electrostatic fields around a molecule. Good cross-validated correlations were obtained for some series (alcohols, carboxylic acids and linear alkyl benzene sulphonates). Correlations were weaker for esters and benzene sulphonates, and were non-existent for phenols. These results may reflect the unreliability of biodegradation data, but may also be a result of molecular misalignment in the CoMFA procedure. CoMFA appears to be a potentially very useful method for the prediction of biodegradability.

ISSN:1062-936X    

DOI:10.1080/10629369508032979

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

For the majority of commercial chemicals present in the troposphere, the reaction with OH radicals during the day and with NO3radicals at night are the most important abiotic pathways for their degradation and removal from the troposphere. Today, there are only a couple of methods available for estimating the reactivity of commercial chemicals with tropospheric radicals, which are not class specific, he Atkinson fragment contribution method and QSAR models, based on a linear correlation of OH (NO3) radical reactivity with the corresponding ionization energies, allow a rapid estimation of the rate constants of OH or NO3radicals for various classes of organic compounds. Both methods are described and their limitations are discussed. A lot of work has been done to develop QSAR models for tropospheric degradation of commercial chemicals that will be based on calculated quantum chemical descriptors. This fast expanding area of QSAR research is presented and evaluated. Particular emphasis is given to the precision of various methods as well as to the latest results from our laboratory. The recent dramatic development in computing technology enables to precisely calculate energy profiles of tropospheric reactions with OH radicals. The semiempirical andab initiomolecular orbital calculations have been performed for hydrogen abstraction reactions for several classes of tropospheric pollutants. The best results of the high-levelab initiomolecular orbital calculations are presented and discussed.

ISSN:1062-936X    

DOI:10.1080/10629369508032980

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The influence of fulvic acids (FAs) and humic acids (HAs) of different origin on liquid-liquid and solid-phase extraction of hydrophobic organic compounds (HOCs) with broadly varying values of octanol-water partition coefficients Kowhas been investigated. It is shown that the solubilization by dissolved FAs and HAs can lead to a significant decrease in recovery of some HOCs even from very dilute (10–20 mg/l) aqueous solutions of these acids. The results of these investigations and an analysis of the relevant literature data, demonstrate that the extent of solubilization of HOCs by humic substances is determined not only by Kow, but also by the specific structure of the HOCs. The hypothesis of the formation of intramolecular micelles (IMMs) by unaggregated FAs and HAs, and the partition of HOCs between water and the IMMs is put forward to explain the solubilization of HOCs.

ISSN:1062-936X    

DOI:10.1080/10629369508032981

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

In this study a systematic analysis of the predictive capabilities of models built with backpropagation neural networks (BPNN) is made to corroborate the hypothesis that BPNN is capable of modeling the interaction terms in group contribution models, without explicitly adding these as descriptors. The data used for comparison are reactivities of 275 organic compounds towards the atomospheric OH-radical. This dataset was selected because of the internal consistency, reliability and relatively large size of this dataset. While training the network, the minimal Mean Squared Error (MSE) on a test set was used as the stop criterion. This avoids overfitting on the training data, and is most likely to give the best generalizing network. A network trained with a designed training and test set is compared with networks trained on randomly constructed training and test sets. The BPNN model based on designed training and test set not only gives the best model, but also the best predictability on an external validation set, compared both to linear models built with the same training and validation sets, and BPNN models based on randomly constructed training and test sets. The performance of the designed BPNN model is comparable to an existing model which includes interaction terms.

ISSN:1062-936X    

DOI:10.1080/10629369508032982

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Existing models for the reductive dehalogenation reaction under environmentally relevant conditions use Hammett and Taft coefficients as descriptors. Drawbacks of these descriptors are the limited possibilities for interpretation in terms of reaction mechanisms, and the limited availability of these descriptors for more ‘exotic’ substituents. Therefore, in this study new descriptors are tested, using semi-empirical molecular orbital calculations. These descriptors are based on the energetic and electronic properties of the reaction sites and should be able to account for the systematics of the rate constants in a better way than substituent coefficient models. This approach is expected to give reliable estimates of the rate constants even for compounds containing less common structural features. Several relationships for a series of halogenated aromatics are presented here, relating the experimental rate constants to, among others, the calculated activation energy of the rate limiting step in the reductive dehalogenation process. Results show that semi-empirical molecular orbital descriptors are capable of describing the reaction kinetics within a homologous series of compounds. All descriptors can be explained for in terms of reaction mechanisms, thus corroborating the hypothesis about mechanisms taking place in the environment.

ISSN:1062-936X    

DOI:10.1080/10629369508032983

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

This is a scanned image of the original Editorial Board page(s) for this issue.

ISSN:1062-936X    

DOI:10.1080/10629369508032978

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor