Geology topics

Dean C. Luehrs

Publications and source records attributed to Dean C. Luehrs.

3 recordsLinked to original sources

USGS1998

Estimation of octanol/water partition coefficients using LSER parameters

The logarithms of octanol/water partition coefficients, log Kow , were regressed against the linear solvation energy relationship (LSER) parameters for a training set of 981 diverse organic chemicals. The standard deviation for log Kow was 0.49. The regression equation was then used to estimate log Kow for a test of 146 chemicals which included pesticides and other diverse polyfunctional compounds. Thus the octanol/water partition coefficient may be estimated by LSER parameters without elaborate software but only moderate accuracy should be expected.

Advances in Environmental Research↗

USGS1997

Evaluation of estimation methods for organic carbon normalized sorption coefficients

A critically evaluated set of 94 soil water partition coefficients normalized to soil organic carbon content ( K oc ) is presented for 11 classes of organic chemicals. This data set is used to develop and evaluate K oc estimation methods using three different descriptors. The three types of descriptors used in predicting K oc were octanol/water partition coefficient ( K ow ), molecular connectivity ( m X t ) and linear solvation energy relationships (LSERs). The best results were obtained estimating K oc from K ow , though a slight improvement in the correlation coefficient was obtained by using a two-parameter regression with K ow and the third order difference term from m X t . Molecular connectivity correlations seemed to be best suited for use with specific chemical classes. The LSER provided a better fit than m X t but not as good as the correlation with K oc . The correlation to predict K oc from K ow was developed for 72 chemicals; log K oc = 0.903* log K ow + 0.094. This correlation accounts for 91% of the variability in the data for chemicals with log K ow ranging from 1.7 to 7.0. The expression to determine the 95% confidence interval on the estimated K oc is provided along with an example for two chemicals of different hydrophobicity showing the confidence interval of the retardation factor determined from the estimated K oc . The data showed that K oc is not likely to be applicable for chemicals with log K ow < 1.7. Finally, the K oc correlation developed using K ow as a descriptor was compared with three nonclass-specific correlations and two 'commonly used' class-specific correlations to determine which method(s) are most suitable.

Water Environment Research↗

USGS1995

Linear solvation energy relationship of the limiting partition coefficient of organic solutes between water and activated carbon

A linear solvation energy relationship has been found for 353 values of the limiting adsorption coefficients of diverse chemicals: log K = −0.37 + 0.0341 V i − 1.07β + D + 0.65 P with R = 0.951, s = 0.51, n = 353, and F = 818.0, where V i is the intrinsic molar volume; β is a measure of the hydrogen bond acceptor strength of the solute; D is an index parameter for the research group which includes the effects of the different types of carbon used, the temperature, and the length of time allowed for the adsorption equilibrium to be established; and P is an index parameter for the flatness of the molecule. P is defined to be unity if there is an aromatic system in the molecule or if there is a double bond or series of conjugated double bonds with no more that one non-hydrogen atom beyond the double bond and zero otherwise. A slightly better fit is obtained if the two-thirds power of V i is used as a measure of the surface area in place of the volume term: log K = −1.75 + 0.227 V 2/3 − 1.10β + D + 0.60 P with R = 0.954, s = 0.49, n = 353, and F = 895.39. This is the first quantitative measure of the effect of the shape of the molecule on its tendency to be adsorbed on activated carbon.

Environmental Science & Technology↗