Mati Karelson

Correlation of the Melting Points of Potential Ionic Liquids (Imidazolium Bromides and Benzimidazolium Bromides) Using the CODESSA Program

The melting points of several imidazolium-based ionic liquids or ionic liquid analogues were correlated using the CODESSA program in order to develop predictive tools for determination of suitable ionic liquid salts. The data set consisted of melting point data (degrees C) for 104 substituted imidazolium bromides divided on the basis of the N-substituents into three subsets: A-57 compounds, B-29 compounds, and C-18 compounds. The 45 benzimidazolium bromides form set D. Five-parameter correlations were obtained for (i) set A with R2 = 0.7442, (ii) set B with R2 = 0.7517, and (iii) set D with R2 = 0.6899, while set C was correlated with a three parameter equation with R(2) = 0.9432. These descriptors for predicting the melting points of the imidazolium and benzimidazolium bromides were based on the size and electrostatic interactions in the cations.

QSPR correlation of the melting point for pyridinium bromides, potential ionic liquids.

In an attempt to develop predictive tools for the determination of new ionic liquid solvents, QSPR models for the melting points of 126 structurally diverse pyridinium bromides in the temperature range 30-200 degrees C were developed with the CODESSA program. Six- and two-descriptor equations with squared correlation coefficients (R(2)) of 0.788 and 0.713, respectively, are reported for the melting temperatures. The models illustrate the importance of information content indices, total entropy, and the average nucleophilic reactivity index for an N atom.

QSPR Analysis of Flash Points

A quantitative structure property relationship study of the flash point of a diverse set of 271 compounds provided a general three-parameter QSPR model (R(2) = 0.9020, R(2)(cv) = 0.8985, s = 16.1). Use of the experimental boiling point as a descriptor gives a three-descriptor equation with R(2) = 0.9529. Use of the boiling point predicted by a four-parameter reported relationship gives a three-parameter flash point equation with a R(2) value of 0.9247.

Correlation and Prediction of the Refractive Indices of Polymers by QSPR

A general QSPR model (R2 = 0.940, s = 0.018) was developed for the prediction of the refractive index for a diverse set of amorphous homopolymers with the CODESSA program. The five descriptors, involved in the model, are calculated from the structure of the repeating unit of the polymer. The average prediction error by this model is 0.9%.

QSPR Studies on Vapor Pressure, Aqueous Solubility, and the Prediction of Water−Air Partition Coefficients

The vapor pressures and the aqueous solubilities of 411 compounds with a large structural diversity were investigated using a quantitative structure−property relationship (QSPR) approach. A five-descriptor equation with the squared correlation coefficient (R2) of 0.949 for vapor pressure and a six-descriptor equation with R2 of 0.879 for aqueous solubility were obtained. All descriptors were derived solely from the chemical structure of the compounds. The QSPR correlation equations for vapor pressure and aqueous solubility allow the reliable prediction of water−air partition coefficients.

Reconsideration of solvent effects calculated by semiempirical quantum chemical methods

AM1 and PM3 semiempirical calculations are reported for the solvent effects on the tautomeric equilibria of 2‐pyridone/2‐hydroxypyridine and 4‐pyridone/4‐hydroxypyridine in the gas phase and solution. The solvent effects on the tautomeric equilibria were investigated by self‐consistent reaction field (SCRF) theory implemented in the AMPAC and MOPAC program in two different ways: one in which all the solvent relaxation is included in the quantum mechanics and the total energy must be corrected for the solvent change in energy, method A; and a second in which the quantum mechanics directly includes this term, method B. The calculated (AM1, method A) tautomeric equilibrium constants (log K1) for 2‐pyridone in the gas phase, cyclohexane, chloroform, and acetonitrile are −0.3, 0.3, 0.8, and 1.3, respectively, in good agreement with the experimental data (−0.4, 0.24, 0.78, and 2.17, respectively). For 4‐pyridone/4‐hydroxypyridine differences between calculated log K1 for the gas phase, chloroform and acetonitrile (−6.0, −2.6, and −1.2, respectively) and experimental data (< −1, 0.11, and 0.66, respectively) are larger but the experimental values are also less certain. The experimental acetonitrile data are disturbed by specific interactions. An extension of the SCRF for aqueous solutions is reviewed.

Quantitative Structure−Property Relationship (QSPR) Correlation of Glass Transition Temperatures of High Molecular Weight Polymers

A new quantitative structure−property relationship (QSPR) five-parameter correlation (R2 = 0.946) of molar glass transition temperatures (Tg/M) for a diverse set of 88 polymers is developed with the Comprehensive Descriptors for Structural and Statistical Analysis (CODESSA) program. The descriptors are all calculated directly from the molecular structure, and the approach given is applicable, in principle, to all linear polymers of regular structure.

Normal Boiling Points for Organic Compounds: Correlation and Prediction by a Quantitative Structure−Property Relationship

We recently reported a successful correlation of the normal boiling points of 298 organic compounds containing O, N, Cl, and Br with two molecular descriptors.1 In the present study the applicability of these two descriptors for the prediction of boiling points for various other classes of organic compounds was investigated further by employing a diverse data set of 612 organic compounds containing C, H, N, O, S, F, Cl, Br, and I. The data set was divided into 9 subsets, and additional descriptors were sought for each subset, which, together with the gravitation index and the charged surface area of hydrogen-donor atoms, would model the boiling points. The additional descriptors were then each tested for global relevance and retained only if this was found. A final eight-parameter correlation model was thus deduced which had R2 = 0.965 and a standard error of 15.5 K approaching the estimated average experimental error for the data set. The model appears to be general for a wide variety of organic compounds.

PREDICTION OF POLYMER GLASS TRANSITION TEMPERATURES USING A GENERAL QUANTITATIVE STRUCTURE-PROPERTY RELATIONSHIP TREATMENT

A novel approach to the prediction of the physical properties of polymers is presented. A QSPR study, involving the use of a newly developed statistical package, CODESSA, is described for the Tg of a set of 22 low molecular weight polymers which gave a four-parameter equation with R2 = 0.928. The physical significance of the descriptors selected is discussed.

Quantitative structure-property relationship modeling of beta-cyclodextrin complexation free energies.

CODESSA-PRO was used to model binding energies for 1:1 complexation systems between 218 organic guest molecules and beta-cyclodextrin, using a seven-parameter equation with R2 = 0.796 and Rcv2 = 0.779. Fragment-based TRAIL calculations gave a better fit with R2 = 0.943 and Rcv2 = 0.848 for 195 data points in the database. The advantages and disadvantages of each approach are discussed, and it is concluded that a combination of the two approaches has much promise from a practical viewpoint.