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Alkylated urea derivatives have found wide application as starting materials for the production of many drugs, including anticancer drugs, as well as in many other areas. In this work, we studied ethylurea crystalline hydrates using a complex of theoretical and experimental methods. The nature of the intermolecular interactions between ethylurea and water molecules is investigated using topological analyses such as atoms in molecules (AIM), non-covalent interaction (NCI), reduced density gradient (RDG), electron localized functions (ELF), and localized orbital locator (LOL). The hydrogen bond energy is in the range of 1.1295–14.4327 kcal/mol. Also, a highly correlated parabolic relationship between topological parameters (EHB, ρ, and ∇2ρ) and H-bond length was determined. According to RDG data, with an increase in the number of water molecules in ethylurea clusters, the area corresponding to hydrogen bonds increases. The initial ethylurea and its crystalline hydrate were studied by FTIR spectroscopy and X-ray diffraction. The introduction of water molecules into the ethylurea crystal was proved by IR spectroscopy by the appearance of the corresponding absorption bands. X-ray diffraction showed that the initial ethylurea has intense peaks at 11.2, 16.8, 21.4, 22.24, 25.06, 25.78° 2Ɵ, the intensity of which changes when water molecules are introduced into the crystal. [ABSTRACT FROM AUTHOR]

Sulfated polysaccharides are important promising biologically active substances with anticoagulant properties. Biological activity is affected by the method of preparation, as well as the type of the polysaccharide and its molecular structure. In this work, we have considered various methods for the synthesis of promising anticoagulants – polysaccharide sulfates using the example of obtaining agarose sulfate. We compared various sulfating agents: chlorosulfonic acid, sulfamic acid, with various activators, and a deep eutectic solvent mixture of sulfamic acid with urea (in the melt). It has been shown that when urea is used as an activator of the process of sulfation of agarose with sulfamic acid in 1,4-dioxane, agarose sulfate with a high sulfur content (up to 14.5 wt%) is formed, which is close to the use of chlorosulfonic acid as a sulfating agent (with the production of agarose sulfate with 15.0 wt% sulfur). The use of solid catalysts in the process of sulfation of agarose with sulfamic acid leads to the production of agarose sulfate with a sulfur content of up to 14.1 wt% (for a catalyst based on the oxidized carbonaceous material Sibunit-4®). Sulfation of agarose in a deep eutectic solvent – a mixture of sulfamic acid with urea – leads to the production of agarose sulfate with a sulfur content of up to 13.7 wt%. The resulting agarose sulfates were characterized by FTIR spectroscopy, X-ray diffraction, elemental analysis, atomic force microscopy and DFT. [ABSTRACT FROM AUTHOR]

Urea and its derivatives play a significant role in modern organic chemistry and find application in various fields. This study presents the results of investigations of N-methylurea crystalline hydrates. Initial N-methylurea and its crystalline hydrates have been examined by FTIR spectroscopy and X-ray diffraction analysis. It has been found that the incorporation of water molecules into N-methylurea crystals leads to a shift of intensity peaks in both the FTIR spectra and X-ray diffraction patterns. Methylurea crystalline hydrates in the gaseous phase have been additionally explored within the density functional theory at the B3LYP/6-31+G(d,p) level and the theory of atoms in molecules. The nature of water and methylurea molecular interactions via hydrogen bonds have been studied using the electron localization function and noncovalent reduced density gradient. The thermodynamic and nonlinear optical properties of methylurea crystalline hydrate have been determined. The atoms in molecules, electron localization functions, and localized orbital locator topological analyses have been carried out to elucidate the nature of hydrogen bonds in methylurea crystalline hydrates. [ABSTRACT FROM AUTHOR]

Xylan is a polysaccharide found in plant cell walls. It is considered to be a biodegradable polymer, which does not affect negatively the environment. Sulfated xylan derivatives exhibit valuable bioactive properties, in particular, anticoagulant and hypolipidemic. We report on the development of a new method for sulfation of birch wood xylan. Activators of the sulfation reaction with sulfamic acid have been evaluated. Numerical methods have been used to establish the optimum process parameters that ensure the maximum sulfur content in the reaction product. The incorporation of a sulfate group has been confirmed by infrared and nuclear magnetic resonance spectroscopy, and elemental analysis. The initial and sulfated xylans have been comprehensively studied by theoretical methods and the most favorable conformations of the initial xylan and its sulfate have been established. [ABSTRACT FROM AUTHOR]

An electrochemical aptasensor for the detection of tetracycline (TET) is prepared based on a methylene blue (MB)-tagged DNA aptamer, with the sequence 5′-MB-CCC CCG GCA GGC CAC GGC TTG GGTTGG TCC CAC TGC GCG-thiol-3′. The DNA aptamer is chemisorbed on a gold electrode and differential pulse voltammetry (DPV) is utilized for the detection. In particular, upon binding of the TET with the purpose-designed aptamer, there is an increase in the current intensity, as a result of the increased proximity of the MB molecule to the gold surface. The sensor is tested using aqueous samples spiked with TET concentrations between 1 and 1000 nM and a limit of detection (LOD) of 1.2 nM is determined. Furthermore, the dissociation constant is estimated to be 1.4 nM using a Lineweaver–Burk plot. [ABSTRACT FROM AUTHOR]

This paper reviews some of the most common surface modification approaches in biosensing based on self-assembled monolayers with a particular focus on Au film thiolation and SiO2 film silanization. Such approaches are routinely used to alter the materials’ surface properties towards a desired bioresponse. Furthermore, the most appropriate characterization methods towards ensuring successful surface modification are presented including XPS, HREELS, SPFS, Raman and FTIR spectroscopy as well as UPS with specific examples to demonstrate their importance. In addition, the mechanisms of fluorescent and non-fluorescent biotinylation of thiolated Au films and silanized SiO2 are discussed considering its importance in conjugating biomolecules such as enzymes, antibodies or chemokines onto surfaces, which carries high significance for biosensing applications. Finally, within this frame characterization routes towards ensuring effective attachment are discussed. [ABSTRACT FROM AUTHOR]