We report the pKa values for 15 mono- and disubstituted hydroxycoumarins determined using UV-vis absorbance spectroscopy and computational methods. Six of these values, including the pKa of 5-hydroxycoumarin, are reported for the first time. While the primary focus is on the effects of hydroxyl substitution on the benzene ring, we also examine how a 4-methyl substituent may influence acidity in a subset of four coumarin pairs. The experimental results are supported by two kinds of density functional theory calculations. Time-dependent DFT (TD-DFT) models of the UV-vis spectra show strong agreement with experimental observations of 30 species and facilitate spectral interpretation. In addition, pKa values are predicted through a thermodynamic-cycle calculation that combines gas-phase Gibbs free energies with solvation free energies. This computational method accurately reproduces pKa values for a training set (mean absolute error, MAE = 0.37) and yields predictions for the full experimental data set (MAE = 0.65). Together, the experimental and computational results provide a comprehensive view of the structure-acidity relationships in a diverse series of simple hydroxycoumarins.
In this paper we validate Group Contribution (GC) parameters for substituted phenols and dihydroxybenzenes including catechol, resorcinol and hydroquinone with respect to a recently developed Group Contribution method for estimating the heat of formation of organic compounds with chemical accuracy (1 kcal/mol). For the...
Robert J. Meier, P. Rablen· Applied Sciences· 0 citations
Gibbs free energy values obtained from quantum-chemical calculations were used to determine the formation constants of homo- and heteroligand copper(II) complexes with various ligands (amino acids, diimines, and phosphorylated dithiocarbamates) in an aqueous medium. A computationally robust, yet moderately expensive, l...
N. S. Aksenin, Mikhail S. Bukharov, V. Shtyrlin et al.· Inorganics· 0 citations
The thermodynamics of protonation equilibria and equilibria between enol and keto tautomers occurring in naturally found hydroxy derivatives of trans-resveratrol analogues were investigated. Reaction Gibbs free energies at room temperature were obtained using the B3LYP functional together with a continuum solvation mod...
A. Kováčová, M. Michalík, Vladimír Lukeš· ACS Omega· 0 citations
Cocrystallization has emerged as an important strategy in supramolecular chemistry for tuning the physicochemical properties of active pharmaceutical ingredients (APIs). In this study, a cocrystal composed of nitrofurantoin (NF) and 4-hydroxybenzamide (4HBAM) is systematically investigated using combined experimental a...
A. Shukla, Eram Khan, Sarita Yadav et al.· Spectrochimica Acta Part A -...· 0 citations
This study investigates structure-property and structure-limitation relationships in a series of newly synthesised low-molecular-weight acylhydrazone derivatives obtained via ultrasonic-assisted condensation of heterocyclic aldehydes (pyrimidine, morpholine, and imidazole derivatives) with 4-methyl-1,2,3-thiadiazole-5-...
S. Kotowicz, M. Korzec, Jan Grzegorz Małecki et al.· Chemistry· 0 citations
