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A J Leo

Publications and source records attributed to A J Leo.

8 recordsLinked to original sources
PubMed2000

Evaluating hydrogen-bond donor strength.

A parameter that measures hydrogen-bond donor (HBD) strength of solutes is useful in modeling many biological interactions. The solvents octanol and chloroform, have about equal HBD strength and thus will accommodate the hydrogen-bond acceptor (HBA) groups in solutes about equally well. Because the solvent octanol has a strong acceptor oxygen, solutes with HBD groups will favor it over chloroform on that basis. With its eight alkane carbons, octanol also favors solutes with a significant amount of alkane character, a property referred to in this paper as 'excess alkane affinity' (XAA). On the other hand, it is easier to form a cavity in the solvent chloroform, so larger solutes tend to favor that solvent. After allowing for XAA and molecular volume, the difference between log P(oct) and log P(clf) is a measure of the effective sum of HBD. This value is given the symbol epsilonalpha and appears to be on the same scale as Abraham's summation operatoralpha(2)(H).

Algorithms↗
PubMed1999

Correlation and estimation of gas-chloroform and water-chloroform partition coefficients by a linear free energy relationship method.

A linear free energy relationship, LFER, has been used to correlate 150 values of gas-chloroform partition coefficients, as log Lchl with a standard deviation, sd, of 0.23 log units, a correlation coefficient r2 of 0.985, and an F-statistic of 1919. The equation reveals that bulk chloroform is dipolar/polarizable, of little hydrogen-bond basicity, but as strong a hydrogen-bond acid as bulk methanol or bulk ethanol. However, the main influence on gaseous solubility in chloroform is due to solute-solvent London dispersion interactions. A slightly modified LFER has been used to correlate 302 values of water-chloroform partition coefficients, as log Pchl. The correlation equation predicts log Pchl for a further 34 compounds not used in the equation with sd = 0.17 log units. When the LFER is applied to all 335 log Pchl values, the resulting equation has sd = 0.25, r2 = 0.971, and F = 2218.

Chloroform↗
PubMed1989

Toward a quantitative comparative toxicology of organic compounds.

Correlation equations between logP (P = octanol water partition coefficient) and the biological activity of alcohols has been derived for 101 examples on all sorts of systems, from simple proteins to whole animals. This provides an overview of the toxic nature of hydrophobic compounds which can be used as a basis for comparison of more complex chemicals. About 100 examples of the hydrophobic effects of chemicals, other than alcohols, to various living systems or their parts are presented for comparison. It is clear that hydrophobic xenobiotics are toxic to almost every form of life, including humans (or parts there of).

Animals↗
PubMed1987

Some advantages of calculating octanol-water partition coefficients.

Reliable values for the octanol-water partition coefficients of small solutes used in enzyme binding/inhibition studies are desirable if a hydrophobic effect is being examined. Many investigators will grant that measuring each solute by shake-flask is the ideal, but reversed-phase HPLC data is becoming more commonplace since it is easier to obtain. This note examines one study where HPLC hydrophobicity, from an apparently valid procedure, obscured an obvious hydrophobic relationship. Another example is cited where probable errors in shake-flask measurement also lead to an erroneous conclusion. In both instances, values obtained from a simple method of calculation of log P(o/w) values could have provided a warning.

Chromatography, High Pressure Liquid↗
PubMed1987

Extension of the fragment method to calculate amino acid zwitterion and side chain partition coefficients.

The fragment method of calculating partition coefficients (P) has been extended to include the common amino acids (AAs). The results indicate that polar and charged side chains influence the hydrophobicity of atoms in the side chain in a predictable manner. Field effects, as evidenced through polar proximity factors and bond factors, need to be considered for accurate estimation of transfer phenomena. The calculated log P and delta G degree ' values of the 20 AAs agree well with the observed values. Pro calculates to be more hydrophilic than the observed log P. Hydrophobicity scales for peptide side chain residues are compared and evaluated in terms of suitability. Calculated pi values for nonpolar side chain residues agree well with the observed values; calculated values for uncharged polar side chain residues deviate by about 0.6 log units except for Gln and Cys; and polar side chain residues with charged side chains calculate as too hydrophilic. Reasons for the differences are explored. We also suggest that tightly bound water to polar moieties in amino acids and peptides may be transferred into the octanol phase during partitioning experiments. A quantitative methodology is presented which characterizes the thermodynamic partitioning of groups and individual atoms in amino acids and proteins.

Amino Acids↗