Microwave-assisted solvent-free synthesis and luminescence properties of 2-substituted-4,5-di(2-furyl)-1<Emphasis Type="Italic">H</Emphasis>-imidazoles

A solvent-free microwave-assisted method for the synthesis of 2-substituted-4,5-di(2-furyl)-1H-imidazoles was developed. Imidazoles with moderate to good yields were produced by condensation of furil with aldehydes over acidic alumina impregnated with ammonium acetate, and they were characterized by FT-IR, HRMS, ¹H NMR and ¹³C NMR spectroscopy. Crystal structure of 2,4,5-tri-2-furyl-1H-imidazole (I) in the orthorhombic space group Pbca was reported, which showed more coplanarity than the reported crystal structure of I in the monoclinic space group Cc. Moreover, their luminescent properties were investigated. It was found that the organic small molecule compounds synthesized possess higher fluorescence quantum efficiency (up to 0.508) in a 0.1 M H₂SO₄ aqueous solution dissolved in 0.5 mL of CH₃OH; along with higher stability; also the emission of some compounds synthesized in the solution was sensitive to the polarity of the solvents.     

Synthesis of potential inhibitors of glycosyltransferases representing UDP-GlcNAc

Based on rational design of the transition state analog inhibitors of glycosyltransferases, four model glycomimetics of this type, viz. benzyl 2-thio-α-dfructofuranoside 1-diethylphosphate (XIa), its β-anomer (XIb), and their ethyl 2-thio analogs — α-anomer (XIIa) and β-anomer (XIIb), were synthesized. In addition, fourteen precursors arising during the synthesis of the desired final model compounds (XI and XII), partially or fully acetylated benzyl and/or ethyl 2-thiofructofuranoside 1-diethyl phosphates, were isolated and characterized with the aim to prepare complete series of glycomimetics, representing donor UDP-GlcNAc designated for biological assays on human GnT’s, viz. GnT-I, Core2GnT, and GnT-V.     

Characterisation and coagulation performance of polysilicate-ferric-zinc

A new type of coagulant, polysilicate-ferric-zinc (PSFZn) with different Fe/Zn molar ratios, was synthesised using water glass (industrial grade, w(SiO₂) = 21 mass %, ρ = 1.34 × 10³ kg m^?3, modulus = 3.2), FeSO₄ · 7H₂O, ZnSO₄, and NaClO₃ by way of co-polymerisation in the same (Fe + Zn)/Si molar ratio based on polysilicate-ferric (PSF). The effect of the Fe/Zn molar ratios on the morphology and structure was systematically investigated using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD) analysis. Three samples, namely PSFZn4, PSFZn1, and PSFZn0.25, represented Fe/Zn molar ratios of 4, 1, and 0.25, respectively, and were selected for a comparative study while a constant (Fe + Zn)/Si molar ratio equal to 1 was maintained. Accordingly, PSFZn was found to be a complex compound rather than a simple mixture of raw materials. With the decrease in Fe/Zn, a great change occurred in the surface morphology, from a tetrahedral cluster structure to a lamellar structure. The Fe—O and Fe—O—Si bonds were gradually replaced by Zn—O and Zn—O—Si. However, the crystalline peaks were more obvious with the increase in the number of zinc ions; hence the new polymer would be formed from iron, zinc, and polysilicate. In addition, the coagulation performance of PSFZn was investigated using a surface water sample. PSFZn4 exhibited a better coagulation performance than the other PSFZn coagulants. Additionally, the trends in changes in pH with different coagulation times after adding PSFZn were studied relative to PSF and FS. The replacement of zinc ions with iron ions could effectively counter the rapid decrease in pH. The effect of settling time on the coagulation efficiency was also investigated. PSFZn4 exhibited a better settlement performance than PSF and poly aluminium chloride (PAC). Hence, the partial substitution of zinc salt with iron salt not only addresses the inadequacies of iron salt but also improves the coagulation efficiency of zinc salt in water treatment.     

Antioxidant activity of rosemary extracts in solution and embedded in polymeric systems

The rosemary extract was encapsulated in polyethylene or in covalently-based network gels. The covalent gels were obtained by the reaction of isocyanate end-capped polyethylene glycol (PEG) with β-cyclodextrin or glycerol. The 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay was used to evaluate the antioxidant activity (AA) of rosemary extract entrapped in polymeric structures and in ethanol or water solutions. The AA of the rosemary extract was determined using a DPPH radical for samples prepared in ethanol, and a water-soluble derivative, the sulphonated DPPH radical (DPPH-SO₃Na), for the rosemary extract in water. Formulation of the rosemary extract in polymeric gels ensures a rapid release which determines the AA values similar to those in solution.     

Preparation of quaternary pyridinium salts as possible proton conductors

On basis of earlier experimental experience, the transfer of protons in salts of the organic cation-inorganic anion type occurs primarily through directional arrangement of the anion-anion type short hydrogen bonds. The submitted work presents the preparation of quaternary pyridinium salts of inorganic hydrogen anions in the absence of solvent molecules in their crystal structure. These substances can form only the above-described anion-anion type hydrogen bonds; in addition, the absence of solvate anions increases the stability of the prepared compounds. A total of six substituted pyridinium salts were prepared, four of which have not been described yet: 1,2,4,6-tetraphenylpyridinium perchlorate, 1-benzyl-2,4,6-trimethylpyridinium perchlorate, 1,4-dimethylpyridinium hydrogen sulphate, 1,4-dimethylpyridinium dihydrogen phosphate, 1,4-dimethylpyridinium hydrogen sulphate, and 1,2-dimethyl-5-ethylpyridinium dihydrogen phosphate. Three of these substances were characterised by X-ray structural analysis: 1,2,4,6-tetraphenylpyridinium perchlorate crystallises in the orthorhombic system, space group Pbca; 1-benzyl-2,4,6-trimethylpyridinium perchlorate crystallises in the monoclinic system, space group P2₁/c; and 1,4-dimethylpyridinium dihydrogen phosphate crystallises in the monoclinic system, space group C2/c. This structure contains an oriented anion network bond by short anion-anion type hydrogen bonds with the donor acceptor lengths of 2.567(3) Å and 2.557(3) Å and thus fulfils the requirements of a good proton conductor.     

<Emphasis Type="Italic">Gluconobacter</Emphasis> sp. cells for manufacturing of effective electrochemical biosensors and biofuel cells

Gluconobacter oxydans bacteria exhibit a unique metabolism for quick and incomplete oxidation of a wide range of different compounds (aldoses, ketoses, mono- and poly-alcohols, etc.). Such biotransformation efficiency with simple biomass production led to the industrial applications of these bacteria in the production of several important commodities. Their respiratory activity can also be successfully studied and used in the field of bioelectrochemistry. The main aim of this review is to present various strategies to improve selectivity of assays using intact/treated cells of G. oxydans, to introduce the application of G. oxydans-based biosensors in selective monitoring of analytes during biotransformation processes and to provide information about utilizable sugars in fermentation media or in biological oxygen demand value determination. The final part of the review describes potential application of G. oxydans cells in the generation of electricity from complex fuels within microbial fuel cells by advanced direct electron transfer route between bacterial cells and electrodes.     

Facile and direct synthesis of symmetrical acid anhydrides using a newly prepared powerful and efficient mixed reagent

An efficient mixed reagent for direct synthesis of symmetrical carboxylic anhydrides from carboxylic acids has been prepared. Carboxylic acids are converted to anhydrides using triphenylphosphine/trichloroisocyanuric acid under mild reaction conditions at room temperature. Short reaction time, excellent yields of products, low cost, availability of reagents, simple experimental procedure, and easy work-up of the products are the main advantages of the presented method.     

Aptamer-based detection of thrombin by acoustic method using DNA tetrahedrons as immobilisation platform

The thickness shear mode acoustic method was used to study the binding of thrombin to DNA aptamers immobilised on the gold surface covered by DNA tetrahedrons. The binding of thrombin to conventional aptamers sensitive to fibrinogen (FBT) and heparin (HPT) exosites as well as to HPT in a loop configuration (HPTloop) made it possible to determine the constant of dissociation (K_D) and the limit of detection (LOD). The sensing system composed of a HPTloop was characterised by K_D = (66.7 ± 22.7) nM, which was almost twice as low as that of FBT and HPT. For this biosensor, a lower LOD of 5.2 nM compared with 17 nM for conventional HPT aptamers was also obtained. Less sensitive sensors based on FBT aptamers revealed an LOD of 30 nM which is in agreement with the lower affinity of these aptamers to thrombin in comparison with that of HPT. The surface concentration of DNA tetrahedrons was determined by the electrochemical method using [Ru(NH₃)₆]³⁺ as a redox probe. These experiments confirmed that the “step by step” method of forming the sensing layer, consisting first in chemisorption of DNA tetrahedrons onto a gold surface and then in hybridisation of the aptamer-supporting part with complementary oligos at the top of the tetrahedron, is preferable. In addition, atomic force microscopy was applied to analyse the topography of the gold layers modified stepwise by DNA tetrahedrons, DNA aptamers and thrombin. The height profiles of the layers were in reasonable agreement with the dimensions of the adsorbed molecules. The results indicate that DNA tetrahedrons represent an efficient platform for immobilisation of aptamers.     

Conversion of phenylacetonitrile in supercritical alcohols within a system containing small volume of water

The reaction of phenylacetonitrile in supercritical methanol and ethanol in a system containing a small volume of water was studied. The effects of various operating conditions, such as reaction temperature, reaction time, the mole ratio of phenylacetonitrile/water/methanol or ethanol on the product yield were systematically investigated. The optimal yield of methyl phenylacetate for phenylacetonitrile in supercritical methanol in a system containing a small volume of water was 70 % at 583 K and 2.5 h. The optimal yield of ethyl phenylacetate for phenylacetonitrile in supercritical ethanol with a small volume of water was 80 % at 583 K and 1.0 h. At the same time, a feasible mechanism was proposed for phenylacetonitrile in supercritical methanol and ethanol in a system containing a small volume of water.     

Zwitterionic structures of selenocysteine-containing dipeptides and their interactions with Cu(II) ions

The molecular structures of a series of selenocysteine-containing dipeptides in their zwitterionic forms were studied using the B3LYP/6-311++G(d,p) level in the aqueous phase. The B3LYP and BH and HLYP functionals in combination with 6-311++G(d,p) and LANL2DZ basis sets were used to investigate the effects of metal coordination on the structural and molecular properties of the dipeptides by complexing them with bivalent copper ions. The results from this DFT study provide valuable insights into the interaction enthalpies (metal ion-binding affinities) and free energies, the influence of the C-terminal moiety on the backbone structural features, the existence of various types of intramolecular H-bond interactions, harmonic vibrational frequencies, along with various other electronic properties pertaining to the zwitterions of the dipeptide molecules as well as their metallic complexes. Metal coordination via the carboxylate groups tends to enhance the planarity of the amide planes. The participations of the N- and C-terminal side-chain moieties in metal-binding markedly enhance the thermodynamic stability of the metalated dipeptides. The theoretical λ_maxvalues, calculated using the TD/DFT level for all the systems, well represent the occurrence of d-d transitions in the Cu-dipeptide complexes.