Effects of Carboxylate Anions on the Molecular Organization of H2O as Probed by 1-Propanol

Substituent effects in aqueous solutions of carboxylate salts studied by x-ray absorption spectroscopy at the oxygen K-edge

The present study aims at probing the influence of different substituents of sodium carboxylate salts R-COO^-:Na⁺ in aqueous solutions, with R = H, CH₃, C₂H₅, CH₂Cl, CF₃, and C₆H₅. X-ray absorption spectroscopy was used in the oxygen K-edge region to highlight the effect of R on the energy position of the O1s-to-π_COO* resonance of the carboxylate ion. Ab initio static exchange and ΔSCF calculations are performed and confirm the experimental observations. We qualitatively discuss the results on the basis of the polar properties of these groups as well as on the basis of the π_COO* orbital energy in the ground states, the oxygen 1s orbital ionization energy, and the O1s-to-π_COO* resonance energy.

Mixing scheme of an aqueous solution of tetrabutylphosphonium trifluoroacetate in the water-rich region

The enthalpic interaction of this particular ionic liquid is extremely high, 16 000 kJ mol⁻¹!

Modeling the antisymmetric and symmetric stretching vibrational modes of aqueous carboxylate anions

The infrared spectra of six aqueous carboxylate anions have been calculated at the M05-2X/cc-pVTZ level of theory with the SMD solvent model, and validated against experimental data from the literature over the region of 1700 cm(-1) to 1250 cm(-1); this region corresponds to the stretching modes of the carboxylate group, and is often interrogated when probing bonding of carboxylates to other species and surfaces. The anions studied here were formate, acetate, oxalate, succinate, glutarate and citrate. For the lowest energy conformer of each anion, the carboxylate moiety antisymmetric stretching peak was predicted with a mean signed error of only 4 cm(-1) using the SMD solvent model, while the symmetric peak was slightly overestimated. Performing calculations in vacuum and scaling was found to generally over-predict the antisymmetric vibrational frequencies and under predict the symmetric peak. Different conformers of the same anion were found to have only slightly different spectra in the studied region and the inclusion of explicit water molecules was not found to significantly change the calculated spectra when the implicit solvent model is used. Overall, the use of density functional theory in conjunction with an implicit solvent model was found to result in infra-red spectra that are the best reproduction of the features found experimentally for the aqueous carboxylate ions in the important 1700 cm(-1) to 1250 cm(-1) region. The development of validated model chemistries for simulating the stretching modes of aqueous carboxylate ions will be valuable for future studies that investigate how carboxylate anions complex with multivalent metal cations and related species in solution.

Effects of constituent ions of a phosphonium-based ionic liquid on molecular organization of H2O as probed by 1-propanol: tetrabutylphosphonium and trifluoroacetate ions

The phosphonium-based cation, [P₄₄₄₄]⁺, is significant amphiphile with strong hydrophobic and equally strong hydrophilic contributions.