Infrared Spectroscopy of Aqueous Carboxylic Acids:  Malic Acid

Abstract

Quantitative infrared (IR) titration of 1.80 M malic acid is presented where factor analysis (FA) was used to obtain the principal species' spectra and their abundances. Three malic species and three water species were obtained. The distribution of the species as a function of pH was made from which their pK a values were determined. The experimental points of the distribution curves correspond to the values calculated from the thermodynamic equilibrium equations. A precise determination of aqueous malic IR bands was obtained from the real spectra of the malic species. The hydrates' hydration numbers were determined to be 2.0 ± 1.0, 3.0 ± 2.0, and 4.0 ± 0.5 for malic acid, mono-, and disodium malate, respectively. The hydrates are stable throughout the pH range where the species are present. The double and single CO stretch bands of malic acid are situated at 1719 and 1272 cm-1, respectively. The antisymmetric and symmetric CO stretch bands of mono- and disodium malate are situated at 1580, 1400 cm-1 and 1563, 1395 cm-1, respectively. Malic acid shows four very broad bands in the 3800−1800 cm-1 region as a continuous absorption assigned to the OH stretch of hydrogen bonded water and alcoholic groups to carboxylic groups. The 2930 and 2580 cm-1 bands, which are far from the 3500 cm-1 band, indicate strong hydrogen bonds. Disodium malate shows one large band at 3320 cm-1 assigned to the OH stretch of solvated water and alcoholic groups. Monosodium malate has the bands of both malic and disodium malate slightly displaced, but with half their intensities.

3D-boxlike polyaniline microstructures with super-hydrophobic and high-crystalline properties

“…In addition, a strong and broad band at 3234 cm À1 assigned as the hydrogen bonded N-H vibration is observed [24] that is a evidence of hydrogen bond existing in 3D-boxlike microstructures and can be regarded as a driving force for 1D-nanofibers forming 3D-boxlike microstructures via a self-assembly process. In addition, there is a carbonyl absorption of the carboxylic acid end groups in PFSEA at 1679 cm À1 that is assigned to a hydrogen bonded C]O stretch [25], indicating that PFSEA acts as the dopant. Moreover, the vibration bands at 1155 and 1248 cm À1 , which are ascribed to the symmetric and asymmetric CF 2 stretches, are also observed [26], further indicating that the 3D-boxlike microstructures are doped with PFSEA as the dopant.…”

Probing water dynamics with OH−

“…Several studies have also been performed on electrolyte solutions [13][14][15][16], but the hydroxide solutions have received less attention than others and are only rarely quoted in the literature [17][18][19]. Based on the present knowledge about the microscopic structure of hydroxide aqueous solutions [20][21][22][23][24], these look instead very interesting.…”

1‐D Open‐Channeled 3‐D Supramolecular Self‐Assembled Frameworks Encapsulating Unprecedented Cyclic (H2O)8 Clusters or Solvent Molecules

“…are present in fruits and living cells, and they also play an important role in biological processes. [28][29][30] Currently we are exploring the self-assembly of metal ions with ligands that are capable of forming hydrogen bonds and bringing about π-π interactions, and that behave as directional motifs capable of extending the dimensionality of the channel-containing product materials. In the present work, by using H 3 …”