The infrared spectra of the long-chain perfluorocarboxylic acid monohydrates differ markedly from those of the anhydrous dimers. Consequently, the structure of the solid perfluorocarboxylic acid monohydrates must differ from any known dimer-containing carboxylic acid crystals. Consideration of the significant features of the infrared spectra of the long-chain perfluorocarboxylic acid monohydrates, supplemented by their Raman spectra, and comparison with the spectra of auxiliary substances have led us to conclude that the rather strong neutral carboxyl-hydroxyl to water bonding can best explain the observations. The infrared spectra indicate the presence of fairly short hydrogen bonds connecting the water molecules to the carbonyl groups. In the construction of the hydrogen bonding pattern of the perfluorocarboxylic acid monohydrates, the oxalic acid dihydrate plays the key role. The striking similarity between the infrared spectra of the oxalic acid dihydrates and the perfluorocarboxylic acid monohydrates in the regions characteristic of water and OH⋯O vibration suggests that the structure of the hydrated carboxyl groups is the same in both crystals. These regions are characterized by the sharp doublet at 3539 cm-1 and 3464 cm-1, which is due to the H2O ν1 and ν3 stretching vibrations, respectively, and the broad absorption between 3000 cm-1 and 1500 cm-1 with the intense band at 1970 cm-1, both associated with the vibration of the OH⋯O group. The later peak consists of two band components at near 1980 cm-1 and 2020 cm-1. These band components show different behaviour when the temperature, polarization or deuteration is changed. In general, the infrared spectra of long-chain perfluorocarboxylic acids represent the system with very short hydrogen bonds connecting the water molecules to the carboxylates. This hydrogen bond pattern should be very similar to that found in the crystals of α-oxalic acid dihydrate.

Small cellular particles (SCPs) are being considered for their role in cell-to-cell communication. We harvested and characterized SCPs from spruce needle homogenate. SCPs were isolated by differential ultracentrifugation. They were imaged by scanning electron microscope (SEM) and cryogenic transmission electron microscope (cryo TEM), assessed for their number density and hydrodynamic diameter by interferometric light microscopy (ILM) and flow cytometry (FCM), total phenolic content (TPC) by UV-vis spectroscopy, and terpene content by gas chromatography-mass spectrometry (GC-MS). The supernatant after ultracentrifugation at 50,000× g contained bilayer-enclosed vesicles whereas in the isolate we observed small particles of other types and only a few vesicles. The number density of cell-sized particles (CSPs) (larger than 2 μm) and meso-sized particles (MSPs) (cca 400 nm–2 µm) was about four orders of magnitude lower than the number density of SCPs (sized below 500 nm). The average hydrodynamic diameter of SCPs measured in 10,029 SCPs was 161 ± 133 nm. TCP decreased considerably due to 5-day aging. Volatile terpenoid content was found in the pellet after 300× g. The above results indicate that spruce needle homogenate is a source of vesicles to be explored for potential delivery use.

Acetylenedicarboxylic acid dihydrate (ADAD) represents a complex with strong hydrogen bonding between the carboxylic OH and the water molecule. An X-ray re-examination of the ADAD crystal structure confirms the O^…O distance of the short hydrogen bonds, and clearly shows different bond lengths between the two oxygen atoms with respect to the carbon atom in the carboxyl group, indicating a neutral structure for the complex. The neutral structure was also confirmed by vibrational spectroscopy, as no proton transfer was observed. The diffraction studies also revealed two polymorph modifications: room temperature (α) and low temperature (β), with a phase transition at approximately 4.9 °C. The calculated vibrational spectra are in satisfactory agreement with the experimental spectra. A comparison of the structure and the vibrational spectra between the ADAD and the oxalic acid dihydrate reveals some interesting details. The crystal structures of both crystal hydrates are almost identical; only the O^…O distances of the strongest hydrogen bonds differ by 0.08 Å. Although it was expected that a larger O^…O spacing in the ADAD crystal may significantly change the infrared and Raman spectra, especially for the frequency and the shape of the acidic OH stretching vibration, both the shape and frequency are almost identical, with all subpeaks topped on the broad OH stretching vibration. The O^…O distance dependent are only in- and out-of-plane OH deformations modes. The presence of polarons due to the ionized defects was not observed in the vibrational spectra of ADAD. Therefore, the origin of the broad OH band shape was explained in a similar way to the acid dimers. The anharmonicity of a potential enhances the coupling of the OH stretching with the low-frequency hydrogen bond stretching, which, in addition to the Fermi resonance, structures the band shape of the OH stretching. The fine structure found as a superposition of a broad OH stretching is attributed to Davydov coupling.