Solvation Descriptors for Zwitterionic α-Aminoacids; Estimation of Water–Solvent Partition Coefficients, Solubilities, and Hydrogen-Bond Acidity and Hydrogen-Bond Basicity

Abstract

The literature data on solubilities and water–solvent partition coefficients have been used to obtain properties or “Absolv descriptors” for zwitterionic α-aminoacids: glycine, α-alanine (α-aminopropanoic acid), α-aminobutanoic acid, norvaline (α-aminopentanoic acid), norleucine (α-aminohexanoic acid), valine (α-amino-3-methylbutanoic acid), leucine (α-amino-4-methylpentanoic acid), and α-phenylalanine. Together with equations that we have previously constructed, these descriptors can be used to estimate further solubilities and partition coefficients in a variety of organic solvents and in water–methanol and water–ethanol mixtures. It is shown that equations for neutral solutes are inadequate for the description of solubilities and partition coefficients for these α-aminoacids, and our equations developed for use with both neutral and ionic solutes must be used. The Absolv descriptors include those for hydrogen-bond acidity, A , and hydrogen-bond basicity, B . We find that both of these descriptors are far smaller in value than those for compounds that contain the corresponding ionic groups. Thus, A for α-alanine is 0.28, but A for the ethylammonium cation is 1.31; B for α-alanine is 0.83, and yet B for the acetate anion is no less than 2.93. The additional descriptors that we developed for equations that involve ions, J + and J – , are very significant for the α-aminoacids, although numerically smaller than for ionic species such as EtNH 3 + and CH 3 CO 2 – .

Substituent Effects on the Basicity of Patriscabrin A and Lettucenin A: Evolution Favors the Aromatic?

“…To assess the aromatic character of the 6- and 7-membered rings in patriscabrin A and lettucenin A, we computed NICS zz values (Figure ). For patriscabrin A, the neutral form does not show significant aromatic character, even in water, where the zwitterionic character is favored. , For completeness, we include the gas-phase results in the Supporting Information…”

Descriptors for High‐Energy Nitro Compounds; Estimation of Thermodynamic, Physicochemical and Environmental Properties

“…(1) and Eq. (2) are shown in Table 1 for partition from water and from the gas phase to the relevant solvents that we shall encounter [12–15, 18].…”

“…[7] adopted a different approach altogether. They used Abraham solute descriptors [8–10], calculated through the ABSOLV program [11], together with previously‐determined equations [12, 13] to estimate water‐solvent partitions, P , for a number of high‐energy nitro compounds. However, the ABSOLV descriptors did not yield very good predictions.…”

Limiting Diffusion Coefficients for Ions and Nonelectrolytes in Solvents Water, Methanol, Ethanol, Propan-1-ol, Butan-1-ol, Octan-1-ol, Propanone and Acetonitrile at 298 K, Analyzed Using Abraham Descriptors

“…Note that for positively charged solutes J − = 0, for negatively charges solutes J + = 0, and for nonelectrolytes J + =J − = 0. For the specific case of zwitterionic aminoacid solutes both J + and J − are necessary to characterize the solutes [29].…”