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 R_f of 5.9%. The experimental r_e-parameters of tetramezine diastereomers agreed with our B3LYP/cc-pVTZ and MP2/cc-pVTZ calculations, which predicted the total energy of the meso form (C_i 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.

Gelatin, a water-soluble protein, shows unique gellification properties, which determine the active commercial availability of gelatin hydrogels in modern alimentary, cosmetic, and pharmaceutical applications. The traditional sources of gelatin for industrial technologies are pork and bovine skin and bones, which sometimes produce religious and some other restrictions. In recent years, there has been a significant increase in the production of gelatin from alternative sources, such as raw fish materials. Unfortunately, fish gelatin is characterized by weak gelling ability and a decrease in gelation and melting temperature, which are a consequence of the amino acid composition and structural features of fish gelatin. One of the ways to strengthen the natural gelling properties of fish gelatin is the structural modification of gelatin hydrogels by the introduction of polysaccharides of various natural origins. We have studied the association of our laboratory-made fish gelatin with three polysaccharides, namely, κ-carrageenan, alginate, and chitosan, which have distinct chemical structures and gelling capabilities. Structural features of the studied systems were analyzed by small-angle X-ray scattering (SAXS), powder X-ray diffraction (PXRD), and scanning electron microscopy (SEM). We applied computer modeling of molecular interactions between fish gelatin and polysaccharides by means of molecular docking and molecular dynamics approaches. The existence of a correlation between the structure of gelatin-polysaccharide systems and their physicochemical properties was demonstrated by wetting angles (flow angles) and dynamic light scattering (DLS) studies of hydrodynamic sizes and surface ζ-potential.

The equilibrium geometry of the boat conformation (C_s 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 r_e-parameters for the boat conformation of the MDABH molecule were determined to be (bond lengths in Å; angles in degrees, C_s 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.