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Samuel H. Yalkowsky - One of the best experts on this subject based on the ideXlab platform.
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estimation of Melting Points of organics
Journal of Pharmaceutical Sciences, 2017Co-Authors: Samuel H. Yalkowsky, Doaa AlantaryAbstract:Abstract Unified physicochemical property estimation relationships is a system of empirical and theoretical relationships that relate 20 physicochemical properties of organic molecules to each other and to chemical structure. Melting point is a key parameter in the unified physicochemical property estimation relationships scheme because it is a determinant of several other properties including vapor pressure, and solubility. This review describes the first-principals calculation of the Melting Points of organic compounds from structure. The calculation is based on the fact that the Melting point, T m , is equal to the ratio of the heat of Melting, ΔH m , to the entropy of Melting, ΔS m . The heat of Melting is shown to be an additive constitutive property. However, the entropy of Melting is not entirely group additive. It is primarily dependent on molecular geometry, including parameters which reflect the degree of restriction of molecular motion in the crystal to that of the liquid. Symmetry, eccentricity, chirality, flexibility, and hydrogen bonding, each affect molecular freedom in different ways and thus make different contributions to the total entropy of fusion. The relationships of these entropy determining parameters to chemical structure are used to develop a reasonably accurate means of predicting the Melting Points over 2000 compounds.
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comparison of two methods for estimation of Melting Points of organic compounds
Industrial & Engineering Chemistry Research, 2007Co-Authors: Akash Jain, Samuel H. YalkowskyAbstract:This study compares the Melting point predictions of UPPER to MPBPWIN for over 2200 organic compounds. The average absolute error (AAE) and root-mean-square error (RMSE) in Melting point prediction using UPPER are 30.1 deg and 39.7 deg, while MPBPWIN gives an AAE of 44.5 deg and RMSE of 58.4 deg. UPPER provides more accurate Melting point predictions because it accounts for both the additive enthalpic and nonadditive entropic contributions to Melting.
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Estimation of Melting Points of Organic Compounds
Industrial & Engineering Chemistry Research, 2004Co-Authors: Akash Jain, Gang Yang, Samuel H. YalkowskyAbstract:A combination of additive group contributions and nonadditive molecular parameters is employed to estimate the normal Melting Points of 1215 organic compounds. The Melting Points are calculated from the ratio of the total phase change enthalpy and entropy of Melting. The total phase change enthalpy of Melting is calculated from the enthalpic group contributions, whereas the total phase change entropy of Melting is estimated using a semiempirical equation based on only two nonadditive molecular parameters. The average absolute error in estimating the Melting Points of these organic compounds is 33.2 K. This is a relatively low value considering the wide range of pharmaceutically and environmentally relevant organic compounds included in this data set.
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a combined group contribution and molecular geometry approach for predicting Melting Points of aliphatic compounds
Industrial & Engineering Chemistry Research, 1999Co-Authors: Luwei Zhao, Samuel H. YalkowskyAbstract:A combined approach that utilizes both group contribution and simple molecular geometric parameters is employed to predict normal Melting Points for a variety of aliphatic compounds. The Melting Points are estimated from the ratio of the enthalpy and the entropy of Melting. The former is calculated from the sum of enthalpic group contributions and correction factors, whereas the latter is calculated using a modification of Walden's rule. Approximately 1040 Melting point data were compiled and analyzed by multiple regression. The root-mean-square error of the estimation is 34.4 K. This is relatively low given the complexity of Melting and the diversity of the database used. A comparison of the proposed method with the method of Joback and Reid8 was performed on 50 aliphatic compounds that were not used in the training set. The average absolute error for this method is approximately 20%, whereas that for the Joback and Reid data is 34%. The higher prediction accuracy of the proposed method suggests that the...
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group contribution methods for predicting the Melting Points and boiling Points of aromatic compounds
Industrial & Engineering Chemistry Research, 1994Co-Authors: Pahala Simamora, Samuel H. YalkowskyAbstract:Simple methods are proposed to estimate the boiling Points and the Melting Points of aromatic compounds from chemical structure. The transition temperatures are determined by the estimation of both the enthalpy and the entropy of transition. The enthalpies of boiling and Melting are both estimated as additive constitutive properties. The entropy of boiling is assumed to be constant as described by Trouton's rule, while the entropy of Melting is estimated using a modification of Walden's rule. The latter utilizes the nonadditive nonconstitutive molecular property, rotational symmetry
German L Perlovich - One of the best experts on this subject based on the ideXlab platform.
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Melting Points of one and two component molecular crystals as effective characteristics for rational design of pharmaceutical systems
Acta Crystallographica Section B Structural Crystallography and Crystal Chemistry, 2020Co-Authors: German L PerlovichAbstract:Based on the review of the literature results the database of the fusion temperatures of two-component molecular crystals (1947 co-crystals) and individual components thereof was built up. To improve the design of co-crystals with predictable Melting temperatures, the correlation equations connecting co-crystals and individual components Melting Points were deduced. These correlations were discovered for 18 co-crystals of different stoichiometric compositions. The correlation coefficients were analysed, and the conclusions about the main/determinative and slave components of a co-crystal were made. The comparative analysis of the Melting Points of co-crystals composed from the same components but with different stoichiometry showed a co-crystal Melting temperature growth when increasing the content of a high-Melting component. The differences in the Melting temperatures were determined and discussed for the following: (a) monotropic polymorphic forms, (b) two-component crystals with the same composition and different stoichiometry, and (c) two-component crystals based on racemates and enantiomers. The database analysis revealed the active pharmaceutical ingredients (APIs) and co-formers (CFs) more particularly used for co-crystal design. The approach based on an efficacy parameter allowing the prediction of co-crystals with Melting Points lower than those of individual compounds was developed.
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prediction of sublimation functions of molecular crystals based on Melting Points cocrystal formation thermodynamics application
Crystal Growth & Design, 2017Co-Authors: German L PerlovichAbstract:On the basis of the values contained in the literature published in 1900–2016, we have developed an experimental database including sublimation Gibbs energies, enthalpies, and Melting temperatures of 1515 compounds. We have also suggested an algorithm of database fragmentation which includes groups/clusters with structurally similar compounds. For this aim we used Tanimoto similarity coefficients. Clusterization was carried out for each substance of the test set. All the Points within a cluster were smoothed by a linear function in the coordinates of Gibbs energy vs Melting temperature. Using the training and test sets, it has been shown that the algorithm suggested by us describes experimental data well (rms = 3.89 kJ·mol–1). We have developed quantitative structure–property relationship models based on HYBOT physicochemical descriptors and Melting Points in order to predict sublimation Gibbs energies and enthalpies of molecular crystals. The developed approach was applied to determine cocrystal formatio...
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two component molecular crystals evaluation of the formation thermodynamics based on Melting Points and sublimation data
CrystEngComm, 2017Co-Authors: German L PerlovichAbstract:Based on literature analysis, we have built up a database containing the fusion temperatures of two-component molecular co-crystals and individual compounds (1175 co-crystals/salts). In order to estimate the thermodynamics of two-component crystal formation, we have created a database on the basis of values reported in the literature from 1900 till 2016 inclusive. The database includes values of the enthalpies and Gibbs energies of individual molecular crystals obtained by various methods. The distribution functions of two-component crystals have been analysed using their fusion temperatures, both for the full sample and separately for the salts and the co-crystals. A comparative analysis was conducted to determine the differences in the Melting temperatures of monotropic polymorphic forms, as well as a similar analysis of two-component crystals with the same composition and different stoichiometries. Correlation equations have been obtained, connecting the Melting Points of co-crystals/salts and individual components for 74 active pharmaceutical ingredients and coformers, which enabled us to design co-crystals with predictable Melting temperatures. An approach to estimating co-crystal sublimation thermodynamic characteristics has been developed. The thermodynamic functions of the formation process of 281 co-crystals have been obtained and analyzed. The diagram method has been used to analyze the parameters under study. Analysis of experimental data distribution in the diagram sectors has shown that the number of two-component crystals with enthalpy determined processes of co-crystal/salt formation corresponds to 70.9%, whereas the number of those with entropy determined processes corresponds to 29.1%. A general algorithm for estimating the thermodynamics of the formation of two-component crystals is proposed.
Tommy Hawkins - One of the best experts on this subject based on the ideXlab platform.
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quantitative structure property relationships for Melting Points and densities of ionic liquids
Energy & Fuels, 2005Co-Authors: Steven Trohalaki, Ruth Pachter, Greg Drake, Tommy HawkinsAbstract:Although innumerable different ionic liquids are possible, even basic physical-property data, such as the density and Melting point, exist only for relatively few. Derivation of Melting point quantitative structure−property relationships (QSPRs) for energetic ionic liquids would therefore greatly aid in the molecular design of new compounds. A new class of ionic liquids, based on 1-substituted 4-amino-1,2,4-triazolium bromide and nitrate salts, were recently synthesized and their Melting Points and densities measured. We optimized the molecular geometries of the cations of the ionic liquids using ab initio quantum chemical methods. Melting point QSPRs were then derived from molecular orbital, thermodynamic, and electrostatic descriptors. Good correlations with the experimental data were found. The correlation coefficients for three-parameter Melting point QSPRs and for one-parameter density QSPRs exceed 0.9. Although some of the descriptors that appear in our QSPRs were designed to describe chemical react...
Edward J. Maginn - One of the best experts on this subject based on the ideXlab platform.
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Melting Points of alkali chlorides evaluated for a polarizable and non-polarizable model
The Journal of chemical physics, 2020Co-Authors: Ryan S. Defever, Haimeng Wang, Yong Zhang, Edward J. MaginnAbstract:Accurate molecular models of pure alkali halides are a prerequisite for developing transferable models of molten salts that can predict the properties of complex salt mixtures, such as those including dissolved actinide species and metal ions. Predicting the Melting point of a substance represents a rigorous test of model quality. To this end, we compute the Melting Points of the alkali chlorides for a popular non-polarizable and polarizable model. Neither model yields more accurate predictions of the Melting Points across the entire family of alkali chlorides. Further calculations suggest that this may be because neither model simultaneously represents both the solid and liquid phases with sufficient accuracy across all four alkali chlorides. We find that the deviation from experiment in the model enthalpy of Melting may be a good indicator of the deviation from experiment in the model Melting temperature. Since the enthalpy of Melting is easier to calculate in simulation than Melting temperature, it may be a useful quantity to target when developing new force fields for molten salts.
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molecular dynamics study of the effect of alkyl chain length on Melting Points of cnmim pf6 ionic liquids
Physical Chemistry Chemical Physics, 2014Co-Authors: Yong Zhang, Edward J. MaginnAbstract:Based on molecular dynamics simulations, the Melting Points Tm of a series of 1-alkyl-3-methylimidazolium hexafluorophosphate ionic liquids [CnMIM][PF6] with n = 2, 4, 10, 12, and 14 were studied using the free energy-based pseudosupercritical path (PSCP) method. The experimental trend that the Tm decreases with increasing alkyl chain length for ILs with short alkyl chains and increases for the ones with long alkyl chains was correctly captured. Further analysis revealed that the different trends are the results of the balance between fusion enthalpy and fusion entropy. For the ILs with short alkyl chains (ethyl and butyl groups), fusion entropy plays the dominant role so that [C4MIM][PF6], which has a larger fusion entropy due to its higher liquid phase entropy has the lower Melting temperature. As for the ILs with long alkyl chains, due to the enhanced van der Waals interactions brought about by the long non-polar alkyl chains, enthalpy becomes the deciding factor and the Melting Points increase when the alkyl chain goes from C10 to C14. While the Melting Points for [C2MIM][PF6] and [C4MIM][PF6] were quantitatively predicted and the trends for the long chain ILs were captured correctly, the absolute Melting Points for [C10MIM][PF6], [C12MIM][PF6] and [C14MIM][PF6] were systematically overestimated in the simulations. Three possible reasons for the overestimation were studied but all ruled out. Further simulation or experimental studies are needed to explain the difference.
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predicting Melting Points of quaternary ammonium ionic liquids
Green Chemistry, 2003Co-Authors: David M Eike, Joan F Brennecke, Edward J. MaginnAbstract:A Melting point at or below ambient temperature is an essential property of ionic liquids being considered as non-volatile replacement solvents. Here we use the Quantitative Structure-Property Relationship (QSPR) method to correlate and predict the Melting Points of organic salts based on the quaternary ammonium cation. For a set of 75 tetraalkyl-ammonium bromides, a correlation with R2 = 0.790 is created, and for a set of 34 (n-hydroxyalkyl)-trialkyl-ammonium bromides, two correlations are created with R2 = 0.716 and R2 = 0.766. Descriptors used in the correlations are analyzed to determine structural features that lower Melting point, and Melting Points are predicted for salts that incorporate these features.
Zhen Yang - One of the best experts on this subject based on the ideXlab platform.
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predicting the Melting Points of ionic liquids by the quantitative structure property relationship method using a topological index
The Journal of Chemical Thermodynamics, 2013Co-Authors: Fangyou Yan, Shuqian Xia, Qiang Wang, Zhen YangAbstract:A Quantitative Structure Property Relationship (QSPR) model was developed to predict the Melting Points of ionic liquids (ILs) with diverse classes of cations and anions. The QSPR model was based on the general topological index (TI) proposed in our previous work. The TI was successfully used for the prediction of the decomposition temperature of ILs and the toxicity of ILs in acetylcholine esterase and Leukemia Rat Cell Line. ILs are a class of molten salts which are composed entirely of cations and anions, therefore the descriptors for ILs are generally calculated from cations and anions separately and the interaction between them is neglected. In this study, besides the two sets of TIs generated from cations and anions, a third TI was used to depict the interaction of anions and cations. The QSPR model is on the base of eight kinds of ILs, which are imidazolium, benzimidazolium, pyridinium, pyrrolidinium, ammonium, sulfonium, triazolium and guanidinium. The regression coefficient (R2) and the overall average absolute deviation (AAD) are 0.778 and 7.20%, respectively.