Molecular Dynamics Study of Cured ED-20 Epoxy Resin for Predicting the Glass Transition Temperature and Relationship with Structure Features.

A structural model of ED-20 epoxy resin cured by triethylenetetramine was constructed using a molecular dynamics (MD) simulation method. In order to model the epoxy resin hardening, we modified a typical stepwise protocol introducing cross-links between the amino groups and epoxide carbon atoms that allowed us to reproduce experimentally observed glass transition temperature at the value of 360-364 K. The set of MD trajectories of the final molecular-mechanical model can be useful for analysis of alterations in structural and physical properties of the epoxy resin depending on scaleable parameters. The relationships among qualitative alterations in macromolecular structure, the glass transition temperature, and the number of imposed cross-links were elucidated. Analysis of intermolecular interactions between the largest macromolecules and other molecules of a system made it possible to observe the features of the transition from glassy to the viscoelastic state of the studied polymer during the temperature rise.

Effective and simple approach for colchicine determination in saffron parts.

Crocus sativus (Iridaceae) or saffron is important for its flavoring properties in the food industry and its medicinal properties in the pharmaceutical industry. Real saffron must meet the quality requirements set to FDA or ISO specifications, and in addition, must be safe and non-toxic. An "autumn crocus" or scientific name Colchicum spp. (Colchicaceae) is a plant that contains a highly toxic alkaloid colchicine. The problem is that Colchicum autumnale is often mistaken for C. sativus. This study aim is to develop the high-performance liquid chromatography method for determining the presence of colchicine in C. sativus stigma, flowers and corms, and then for solving the issue of saffron possible falsification and toxicity. The chromatographic separation was performed on ACE C18 column (5.0 µm, 250 mm × 4.6 mm), by using 0.1% acetic acid in water and acetonitrile as the mobile phase and UV detector (350 nm). Current analysis showed that all Crocus raw materials didn't contain colchicine. This confirms the safety of saffron and its parts for using in the development of substances based on them. The proposed method was successfully applied on C. autumnale corms and showed good separation and colchicine identification. The presence of tricyclic proto-alkaloid colchicine in plant products is not a new phenomenon, however, the need for new sensitive analytical methods that can detect it in food and medicine still exists. The identification and confirmation of colchicine absence in saffron raw materials are important for further herbal drug development and for the food industry.

Pseudocyclic Form of 4-Hydroxypyrrolidine-2-carboxanilide Podands with Trioxyethylene Chain: Modeling, Conformational Search, and NMR Analysis.

The 4-hydroxypyrrolidine-2-carboxanilide podand salt demonstrates catalytic activity in asymmetric Biginelli reaction. The systematic search for prevalent conformational state of the cation was carried out by computer simulations in combination with one- and two-dimensional NMR experiments. For that purpose, we proposed a novel algorithm for the generation and selection of conformers based on molecular dynamics and clustering in the space of principal components. The search had found an important trend of the podand to form a pseudocyclic structure with a horseshoe-shaped conformation of the oligooxyethylene fragment. This conformation is stabilized by different types of intramolecular hydrogen bonds between the acidic and basic centers of the two 4-hydroxypyrrolidine-2-carboxanilide residuals (branches). The proposed approach had made it possible to identify the major structural factors, providing a correlation between the calculated and experimental chemical shifts of hydrogen atoms in the 1H NMR spectra of the protonated podand.