Structural investigation of liquid formic acid

Biocompatible and Printable Ionotronic Sensing Materials Based on Silk Fibroin and Soluble Plant-Derived Polyphenols

The emergence of ionotronic materials has been recently exploited for interfacing electronics and biological tissues, improving sensing with the surrounding environment. In this paper, we investigated the synergistic effect of regenerated silk fibroin (RS) with a plant-derived polyphenol (i.e., chestnut tannin) on ionic conductivity and how water molecules play critical roles in regulating ion mobility in these materials. In particular, we observed that adding tannin to RS increases the ionic conductivity, and this phenomenon is accentuated by increasing the hydration. We also demonstrated how silk-based hybrids could be used as building materials for scaffolds where human fibroblast and neural progenitor cells can highly proliferate. Finally, after proving their biocompatibility, RS hybrids demonstrate excellent three-dimensional (3D) printability via extrusion-based 3D printing to fabricate a soft sensor that can detect charged objects by sensing the electric fields that originate from them. These findings pave the way for a viable option for cell culture and novel sensors, with the potential base for tissue engineering and health monitoring.

Electron Attachment and Electron Ionization of Formic Acid Clusters Embedded in Helium Nanodroplets

We report the results of an experimental study of electron ionization of large helium nanodroplets doped with formic acid (FA). Several homologous series of cluster anions are observed, including [FA_n-H]^-, undissociated FA_n^-, and these ions complexed with one or more H₂O. Some major features resemble those observed upon sputtering of frozen FA films but they differ significantly from results obtained by electron attachment to bare FA clusters in the gas phase. The FA_n^- and (H₂O)[FA_n-H]^- series show abrupt onsets above n = 2 and 5, respectively. A prominent resonance in the anion yield occurs at 22.5 eV due to the formation of an intermediate He^-*. Also observed are homologous series of [FA-H]^- or [FA₂-H]^- complexed with helium. The cation chemistry is dominated by the production of protonated formic acid clusters, [FA_nH]⁺, but various other homologous cluster ion series are observed as well. Graphical Abstract.

A theory for the surface tensions and contact angles of hydrogen-bonding liquids

The surface tensions of non-hydrogen-bonding, organic liquids can be accurately calculated from their electromagnetic properties, using an approximate form of the Lifshitz theory. A simple extension of this approach to the calculation of the surface tensions of hydrogen-bonding liquids is proposed. It is shown that the higher surface tensions of hydrogen-bonding liquids can be accounted for, with reasonable accuracy, by the increase in dispersion due to the shortened distance of approach between hydrogen-bonded atoms. Similar considerations allow calculations of contact angles on several low-energy solid surfaces in terms of molecular and electromagnetic properties. In accordance with well-known experimental observations, the calculated contact angles of both hydrogen-bonding and non-hydrogen-bonding liquids on the same low-energy surface nearly follow a single, smooth pattern.

Formic and acetic acid aggregation in the liquid state

The microscopic structure of neat formic and acetic acid have been measured by neutron diffraction with H/D substitution on SANDALS at the ISIS neutron spallation source. These data, together with complementary x-ray data, have been modeled via the empirical potential structure refinement (EPSR) method, which integrates information obtained from the diffraction data in a Monte Carlo simulation in order to provide a three-dimensional model of the system under study compatible with the measured structure factors. Two models have been generated for each acid, in order to test their consistency, with positive results. The final structure obtained is that of two liquids that are very similar to each other, with high connectivity although rather disordered. They present a hierarchy of probability for hydrogen bond formation, where weaker bonds involving the carbonyl hydrogen for formic acid or the methyl hydrogen for acetic acid are more abundant than the stronger bonds involving the hydroxyl hydrogen. Cooperative effects are found to be fundamental for the description of aggregation of formic and acetic acid, but the structure in the liquid presents a greater variety of bonds than in the solid state.

Car−Parrinello Molecular Dynamics Simulation of Liquid Formic Acid

First-principles molecular dynamics has been used to investigate the structural, vibrational, and energetic properties of formic acid, formic acid-formate anion dimers, and liquid formic acid in a periodically repeated box with 32 formic acid molecules. We found that in liquid formic acid the hydrogen-bonded clusters mainly consist of linear branching chains. From our simulation, we got good agreement with the available structural and dynamical data. We also studied the proton transfer in the cis-formic acid-formate anion dimer, and we showed that this proton transfer does not have any potential barrier. The hydrogen bonding statistics as well as the mean lifetime of the hydrogen bonds are analyzed.

Aggregation of acetic and propionic acid in argon matrices--a matrix isolation and computational study

Monomeric acetic acid MA and propionic acid MP were isolated in argon matrices at 10K by using a pulse deposition technique. The dimerization of the monomers was induced by warming the matrices from 10 to 40 K. Under these conditions the diffusion of small trapped molecules is rapid and the dimerization could be monitored directly by IR spectroscopy. Both carboxylic acids form the symmetrical dimers B with two strong C=O...HO hydrogen bridges as the thermodynamically most stable dimers. With acetic acid a less stable dimer AA could be obtained if high concentrations of acetic acid in argon were used during the deposition of the matrix. On annealing this dimer rearranges to the more stable BA. In contrast, propionic acid does not form a corresponding less stable dimer under any experimental condition. These observations are rationalized on the basis of DFT and ab initio calculations.

Structure of Liquid Formic Acid Investigated by First Principle and Classical Molecular Dynamics Simulations

The structure of liquid formic acid has been investigated by Car-Parrinello and classical molecular dynamics simulations, focusing on the characterization of the H-bond network and on the mutual arrangement of pairs of bonded molecules. In agreement with previous computational studies, two levels of H-bonded structures have been found. Small clusters, characterized by O-H...O bonds, are held together by weak C-H...O bonds to form large branched structures. From the ab initio simulation we infer the importance of cyclic H-bond dimer configurations, typical of the gas phase. Most of these dimer structures are however found to be embedded into H-bonded chains. When only O-H...O bonds are taken into account, linear H-bond chains are detected as basic structures of the liquid. More branched structures occur when C-H...O bonds are also considered. Regarding the arrangement of molecular pairs, we observed that O-H...O bonds favor the occurrence of configurations with parallel molecular planes, whereas no preferential orientation is observed for molecules forming C-H...O bonds.