The equilibrium molecular structure of 3-cyanopyridine according to gas-phase electron diffraction and microwave data and the results of quantum-chemical calculations

Effects of lactic acid and ascorbic acid electrostatic spraying on the physicochemical attributes and microbial diversity of beef aged at mild temperature (10 °C)

This study aimed to clarify the effect of electrostatic spraying of lactic acid (LE) and ascorbic acid (AE) on vacuum-packaged beef aged at 10 °C. The physicochemical attributes, flavor profiles, and microbial diversities were evaluated. Beef steaks were electrostatically sprayed twice with 4% LE, 0.5% AE, or a mixture of them (LAE). Afterward, the beef was vacuum-packaged and aged. All treated beef exhibited a decrease in quality and sensory scores over time. At the end of the study period, the total viable count (TVC) and the total volatile basic nitrogen values in the control group (7.34 log CFU/g and 15.52 mg/100 g, respectively) were higher than those in the acid-treated groups. The LAE group exhibited the best color stability and the lowest TVC and Enterobacteriaceae counts after aging. High-throughput sequencing analysis revealed that acid types and electrostatic spray could change the microbiota structure. Leuconostoc was the dominant bacteria in the AE and LAE groups, while Enterococcus became the predominant bacteria in the NLE and LE groups with aging. This indicates that electrostatic spray combined with acid treatment can ensure beef quality and microbiological safety at mild temperatures.

Equilibrium molecular structure and spectra of 6-methyl-1,5-diazabicyclo[3.1.0]hexane: joint analysis of gas phase electron diffraction, quantum chemistry, and spectroscopic data

The equilibrium geometry of the boat conformation (Cs point group symmetry) of the 6-methyl-1,5-diazabicyclo[3.1.0]hexane (MDABH) molecule, absolutely dominating under normal conditions, was studied by the gas-phase electron diffraction (GED) method at 20 °C with the involvement of NMR, IR, and Raman spectroscopic data and quantum chemical calculations. The potential function of ring-puckering deformation for the MDABH bicyclic system was calculated at the MP2/aug-cc-pVTZ and B3LYP/cc-pVTZ levels. It was found by MP2 calculation that the total energy of the boat conformation is 3.52 kcal mol-1 lower than that of the chair conformation. For the first time, we recorded the IR and Raman spectra for liquid samples of MDABH and assigned their peculiarities only to boat conformation vibrations using the Pulay technique of scaling quantum chemical force fields. In the case of the chair form, transferability of the refined scale factors was used for reliable prediction of the location of its fundamental frequencies. According to the joint structural analysis of the above data, the most important equilibrium geometric re-parameters for the boat conformation of the MDABH molecule were determined to be (bond lengths in Å; angles in degrees, Cs symmetry): C2N1 = 1.466(2), C2C3 = 1.523(2), N1N5 = 1.512(2), C6N1 = 1.440(2), C6C7 = 1.487(2), ∠C2N1N5 = 106.1(2), ∠N1C2C3) = 110.2(4), ∠C2C3C4 = 99.9(4), ∠N1N5C6 = 58.3(1), ∠N1C6N5 = 63.3(1), ∠N1C6C7 = 114.9(6), ∠C6N1C2 = 111.8(1), ∠N5N1C2C3 = 17.3(1), ∠N1C2C3C4 = -26.8(2), θ = C2C3C4/C2N1N5C4 = -26.2(3), φ = N1C6N5/C2N1N5C4 = 74.0(1). Comparison of these and earlier results showed that the NN bond length in the diaziridine ring is very weakly dependent on the cis- or trans-arrangement of substituents at the nitrogen atoms.

Equilibrium structures of the tetramezine diastereomers and their ratio: joint analysis of gas phase electron diffraction, quantum chemistry, and spectroscopic data

For the first time, we applied a gas-phase electron diffraction (GED) method together with vibrational spectroscopy and quantum chemical calculations to investigate the equilibrium geometries of achiral meso and enantiomeric diastereomers of tetramezine [1,2-bis-(3,3-dimethyldiaziridin-1-yl)ethane] and their ratio in the mixture. In the joint structural analysis of these data, a new approach based on PES parameters is used in the framework of a static molecular model (small amplitude motion approximation). The agreement between the theoretical and experimental molecular intensities is characterized by a divergence factor Rf of 5.9%. The experimental re-parameters of tetramezine diastereomers agreed with our B3LYP/cc-pVTZ and MP2/cc-pVTZ calculations, which predicted the total energy of the meso form (Ci point group symmetry) to be lower than that of the enantiomeric form (C2 point group symmetry), by 6.4 and 4.7 kJ mol-1, respectively. The experimentally measured percentages of the meso and both enantiomeric diastereoisomers at 360 K were 70% and 30%, respectively. We characterized the meso form using 2D NMR spectra. Our GED data are in good agreement with the X-ray diffraction analysis of the meso form. This result reflects the weak effect of intermolecular interactions in the crystal. We assigned the IR spectrum bands of the crystalline meso form using the Pulay technique of scaling quantum chemical force fields. In the case of the enantiomeric form calculated at the same level, transferability of the refined scale factors was used for more reliable prediction of the mutual location and interpretation of its fundamental frequencies.