The long-range effect induced by untying hydrogen bonds for single cell test using SECM

Elucidating oxidation-based flavour formation mechanism in the aging process of Chinese distilled spirits by electrochemistry and UPLC-Q-Orbitrap-MS/MS

The oxygen-based oxidation process is leading toward the understanding of the flavour formation mechanism of aged Baijiu. However, the oxygen-based oxidation process in Baijiu aging is difficult to explore because of (1) the composition of Baijiu produced in different batches varies a lot and (2) the spontaneous oxidation needs several years or even decades to occur. Hence, the flavour formation mechanism of Baijiu aging was investigated using electrochemistry and UPLC-Q-Orbitrap-MS/MS, which enabled us to solve the two difficulties above. The oxidation reaction on gold surface could accelerate Baijiu aging by catalyzing the transformation from alcohols to acids. Although natural aging contributed more diverse compound changes to Baijiu, the oxygen-based oxidation process during natural aging was similar to that in the electrochemical oxidation as a whole. This study provides new insights to flavour formation mechanism of aged liquors and provides a new way for liquor-related enterprises to optimise the aging process.

Insights into the spontaneity of hydrogen bond formation between formic acid and phthalimide derivatives

We evaluated a group of phthalimide derivatives, which comprise a convenient test set for the study of the multiple factors involved in the energetics of hydrogen bond formation. Accordingly, we carried out quantum chemical calculations on the hydrogen bonded complexes formed between a sample of phthalimide derivatives with formic acid with the intent of identifying the most important electronic and structural factors related to how their strength and spontaneity vary across the series. The geometries of all species considered were fully optimized at DFT B3LYP/6-31++G(d,p), RM1, RM1-DH2, and RM1-D3H4 level, followed by frequency calculations to determine their Gibbs free energies of hydrogen bond formation using Gaussian 2009 and MOPAC 2012. Our results indicate that the phthalimide derivatives that form hydrogen bond complexes most favorably, have in their structures only one C=O group and at least one NH group. On the other hand, the phthalimide derivatives predicted to form hydrogen bonds least favorably, possess in their structures two carbonyl groups, C=O, and no NH group. The ability to donate electrons and simultaneously receive one acidic hydrogen is the most important property related to the spontaneity of hydrogen bond formation. We further chose two cyclic compounds, phthalimide and isoindolin-1-one, in which to study the main changes in molecular, structural and spectroscopic properties as related to the formation of hydrogen bonds. Thus, the greatest ability of the isoindolin-1-one compound in forming hydrogen bonds is evidenced by the larger effect on the structural, vibrational, and chemical shifts properties associated with the O-H group. In summary, the electron-donating ability of the hydrogen bond acceptor emerged as the most important property differentiating the spontaneity of hydrogen bond formation in this group of complexes.