Alpha-Carbonic Acid Revisited: Carbonic Acid Monomethyl Ester as a Solid and its Conformational Isomerism in the Gas Phase

In this work, earlier studies reporting α‐H₂CO₃ are revised. The cryo‐technique pioneered by Hage, Hallbrucker, and Mayer (HHM) is adapted to supposedly prepare carbonic acid from KHCO₃. In methanolic solution, methylation of the salt is found, which upon acidification transforms to the monomethyl ester of carbonic acid (CAME, HO‐CO‐OCH₃). Infrared spectroscopy data both of the solid at 210 K and of the evaporated molecules trapped and isolated in argon matrix at 10 K are presented. The interpretation of the observed bands on the basis of carbonic acid [as suggested originally by HHM in their publications from 1993–1997 and taken over by Winkel et al., J. Am. Chem. Soc. 2007 and Bernard et al., Angew. Chem. Int. Ed. 2011] is inferior compared with the interpretation on the basis of CAME. The assignment relies on isotope substitution experiments, including deuteration of the OH‐ and CH₃‐ groups as well as ¹²C and ¹³C isotope exchange and on variation of the solvents in both preparation steps. The interpretation of the single molecule spectroscopy experiments is aided by a comprehensive calculation of high‐level ab initio frequencies for gas‐phase molecules and clusters in the harmonic approximation. This analysis provides evidence for the existence of not only single CAME molecules but also CAME dimers and water complexes in the argon matrix. Furthermore, different conformational CAME isomers are identified, where conformational isomerism is triggered in experiments through UV irradiation. In contrast to earlier studies, this analysis allows explanation of almost every single band of the complex spectra in the range between 4000 and 600 cm⁻¹.

Structure and molecular morphology of a novel moisturizing exopolysaccharide produced by Phyllobacterium sp. 921F

Bacterial exopolysaccharides (EPSs) are widely applied in food, cosmetic, and medical industries. The EPS produced by Phyllobacterium sp. 921F was a novel polysaccharide, which exhibits attractive characteristics of high yield, favorable rheological properties, and excellent moisture retention ability. Considering the complexity of polysaccharide structures, specific enzymatic hydrolysis was employed here to resolve the structure of the EPS. End-products including tetra-, hexa- and octa-saccharides were isolated. According to their mass spectroscopy (MS) and nuclear magnetic resonance (NMR) spectra, the backbone of the EPS was found to be mainly comprising a → 4)-β-d-Glcp-(1 → 3)-α-d-Galp(4,6-S-Pyr)-(1 → disaccharide repeating units. Based on atomic force microscopy results, EPS exhibited characteristics that were consistent with a stiff, elongated molecule with no branches. The length and height of the single molecular chain were approximately 600 and 0.7 nm, respectively. Our clarification of structure and molecular morphology of EPS from Phyllobacterium sp. 921F provide a foundation for the industrial application of this potential moisture-retaining material.

Improving thermal control of capillary electrophoresis with mass spectrometry and capacitively coupled contactless conductivity detection by using 3D printed cartridges

A 3D-printed cartridge was developed to improve the interface between a capillary electrophoresis instrument and a mass spectrometer. The thermostated airflow from the CE was guided to the entrance of the electrospray source keeping as much as possible the silica capillary in a proper Joule-heating dissipation environment. Hollow 3D-printed walls made of ABS covered by a 0.2 mm thick copper foil on the inner side were used. The cartridge also allows including up to two capacitively coupled contactless conductivity detectors (C⁴Ds). Experiments about the separation of monoethyl carbonate (a thermally unstable species) shows that the peak area obtained with the original cartridge is only 21% of the value obtained with the 3D-printed cartridge, which demonstrates the improvement in heat dissipation.

A capillary electrophoresis/tandem mass spectrometry approach for the determination of monoalkyl carbonates

Despite monoalkyl carbonates being species prone to hydrolysis, they may be separated by capillary electrophoresis and detected in a mass spectrometer upon ionization by electrospray.