Albert J. Leo

Bio: Albert J. Leo is an academic researcher from Pomona College. The author has contributed to research in topics: Partition coefficient & Octanol. The author has an hindex of 34, co-authored 64 publications receiving 13290 citations.

Substituent constants for correlation analysis in chemistry and biology

Abstract: Bring home now the book enPDFd substituent constants for correlation analysis in chemistry and biology to be your sources when going to read. It can be your new collection to not only display in your racks but also be the one that can help you fining the best sources. As in common, book is the window to get in the world and you can open the world easily. These wise words are really familiar with you, isn't it?

Hydrogen bonding. Part 34. The factors that influence the solubility of gases and vapours in water at 298 K, and a new method for its determination

Abstract: The solubility of 408 gaseous compounds in water at 298 K has been correlated through eqn. (i), where the solubility is expressed as the Ostwald solubility coefficient, Lw, and the solute explanatory variables are R2 an excess molar refraction, π2H the dipolarity/polarizability, Σα2H and Σβ2H the effective hydrogen-bond acidity and basicity, and Vx the McGowan characteristic volume. A similar equation using the log L16 parameter instead of Vx can also be used; L16 is the Ostwald solubility coefficient on hexadecane at 298 K. log Lw=–0.994 + 0.577R2+ 2.549 π2H+ 3.813Σα2H+ 4.841Σβ2H– 0.869 Vx(i), n= 408 ρ= 0.9976 sd = 0.151 F= 16810 The main factors leading to increased solubility are solute π2H, Σα2H and Σβ2H values; conversely, the corresponding properties of water are dipolarity/polarizability, hydrogen-bond basicity and hydrogen-bond acidity. Solute size plays a minor role, and slightly decreases solubility, contrary to observations on all non-aqueous solvents. It is shown that this peculiar behaviour of water is due to (a) a greater increase in the unfavourable cavity effect with increase in solute size, for solvent water, and (b) a smaller increase in the favourable general dispersion interaction with size, for solvent water.A new method for the determination of log Lw values is put forward, using the relationship Lw=L16/P where L16 is as above, and P is either the water–hexadecane partition coefficient or the water–alkane partition coefficient. For 14 solutes using the former P-value, agreement with values calculated through eqn. (i) is 0.08 log units on average and for 45 solutes using the latter P-value, the corresponding agreement is 0.15 log units, with log Lw values ranging up to 8 log units.

Beware of q2

Abstract: Validation is a crucial aspect of any quantitative structure-activity relationship (QSAR) modeling. This paper examines one of the most popular validation criteria, leave-one-out cross-validated R2 (LOO q2). Often, a high value of this statistical characteristic (q2 > 0.5) is considered as a proof of the high predictive ability of the model. In this paper, we show that this assumption is generally incorrect. In the case of 3D QSAR, the lack of the correlation between the high LOO q2 and the high predictive ability of a QSAR model has been established earlier [Pharm. Acta Helv. 70 (1995) 149; J. Chemomet. 10(1996)95; J. Med. Chem. 41 (1998) 2553]. In this paper, we use two-dimensional (2D) molecular descriptors and k nearest neighbors (kNN) QSAR method for the analysis of several datasets. No correlation between the values of q2 for the training set and predictive ability for the test set was found for any of the datasets. Thus, the high value of LOO q2 appears to be the necessary but not the sufficient condition for the model to have a high predictive power. We argue that this is the general property of QSAR models developed using LOO cross-validation. We emphasize that the external validation is the only way to establish a reliable QSAR model. We formulate a set of criteria for evaluation of predictive ability of QSAR models.

Organic geochemistry of natural waters

Abstract: This book is written as a reference on organic substances in natural waters and as a supplementary text for graduate students in water chemistry. The chapters address five topics: amount, origin, nature, geochemistry, and characterization of organic carbon. Of these topics, the main themes are the amount and nature of dissolved organic carbon in natural waters (mainly fresh water, although seawater is briefly discussed). It is hoped that the reader is familiar with organic chemistry, but it is not necessary. The first part of the book is a general overview of the amount and general nature of dissolved organic carbon. Over the past 10 years there has been an exponential increase in knowledge on organic substances in water, which is the result of money directed toward the research of organic compounds, of new methods of analysis (such as gas chromatography and mass spectrometry), and most importantly, the result of more people working in this field. Because of this exponential increase in knowledge, there is a need to pull together and summarize the data that has accumulated from many disciplines over the last decade.