Identification of mixed di-cation forms of G-quadruplex in solution

Multinuclear NMR study has demonstrated that G-quadruplex adopted by d(G(3)T(4)G(4)) exhibits two cation binding sites between three of its G-quartets. Titration of tighter binding K(+) ions into the solution of d(G(3)T(4)G(4))(2) folded in the presence of [Formula: see text] ions uncovered a mixed mono-K(+)-mono- [Formula: see text] form that represents intermediate in the conversion of [Formula: see text] into di-K(+) form. Analogously, [Formula: see text] ions were found to replace Na(+) ions inside d(G(3)T(4)G(4))(2) quadruplex. The preference of [Formula: see text] over Na(+) ions for the two binding sites is considerably smaller than the preference of K(+) over [Formula: see text] ions. The two cation binding sites within the G-quadruplex core differ to such a degree that [Formula: see text] ions bound to the site, which is closer to the edge-type loop, are always replaced first during titration by K(+) ions. The second binding site is not taken up by K(+) ion until K(+) ion already resides at the first binding site. Quantitative analysis of concentrations of the three di-cation forms, which are in slow exchange on the NMR time scale, at 12 K(+) ion concentrations afforded equilibrium binding constants. K(+) ion binding to sites U and L within d(G(3)T(4)G(4))(2) is more favorable with respect to [Formula: see text] ions by Gibbs free energies of approximately −24 and −18 kJ mol(−1) which includes differences in cation dehydration energies, respectively

Development of Quebracho (Schinopsis balansae) Tannin-Based Thermoset Resins

One of the major challenges currently in the field of material science is finding natural alternatives to the high-performing plastics developed in the last century. Consumers trust synthetic products for their excellent properties, but they are becoming aware of their impact on the planet. One of the most attractive precursors for natural polymers is tannin extracts and in particular condensed tannins. Quebracho (Schinopsis balansae) extract is one of the few industrially available flavonoids and can be exploited as a building block for thermoset resins due to its phenol-like reactivity. The aim of this study was to systematically investigate different hardeners and evaluate the water resistance, thermal behavior, and chemical structure of the quebracho tannin-based polymers in order to understand their suitability as adhesives. It was observed that around 80% of the extract is resistant to leaching when 5% of formaldehyde or hexamine or 10% of glyoxal or furfural are added. Additionally, furfuryl alcohol guarantees high leaching resistance, but only at higher proportions (20%). The quebracho-based formulations showed specific thermal behavior during hardening and higher degradation resistance than the extract. Finally, these polymers undergo similar chemistry to those of mimosa, with exclusive reactivity of the A-ring of the flavonoid

Solubilization of ibuprofen for freeze dried parenteral dosage forms

Ibuprofen, a weakly acidic non-steroidal anti-inflammatory drug having poor aqueous solubility, is a challenging drug for the development of pharmaceutical formulations, resulting in numerous research attempts focusing on improvement of its solubility and consequently bioavailability. Most studies have been done for solid dosage forms, with very little attention paid to parenterals. Hence, the main purpose of the present study was to enhance ibuprofen solubility as a result of formulation composition and the freeze drying process. Moreover, the purpose was to prepare a freeze dried dosage form with improved ibuprofen solubility that could, after simple reconstitution with water for injection, result in an isotonic parenteral solution. Solubility of ibuprofen was modified by various excipients suitable for parenteral application. Drug interactions with selected excipients in the final product/lyophilisate were studied by a combined use of XRPD, DSC, Raman and ssNMR. Analyses of lyophilized samples showed solubility enhancement of ibuprofen and in situ formation of an ibuprofen salt with the alkaline excipients used

Modulation of non-bilayer lipid phases and the structure and functions of thylakoid membranes: effects on the water-soluble enzyme violaxanthin de-epoxidase

The role of non-bilayer lipids and non-lamellar lipid phases in biological membranes is an enigmatic problem of membrane biology. Non-bilayer lipids are present in large amounts in all membranes; in energy-converting membranes they constitute about half of their total lipid content-yet their functional state is a bilayer. In vitro experiments revealed that the functioning of the water-soluble violaxanthin de-epoxidase (VDE) enzyme of plant thylakoids requires the presence of a non-bilayer lipid phase. P-31-NMR spectroscopy has provided evidence on lipid polymorphism in functional thylakoid membranes. Here we reveal reversible pH- and temperature-dependent changes of the lipid-phase behaviour, particularly the flexibility of isotropic non-lamellar phases, of isolated spinach thylakoids. These reorganizations are accompanied by changes in the permeability and thermodynamic parameters of the membranes and appear to control the activity of VDE and the photoprotective mechanism of non-photochemical quenching of chlorophyll-a fluorescence. The data demonstrate, for the first time in native membranes, the modulation of the activity of a water-soluble enzyme by a non-bilayer lipid phase

Comparing condensed and hydrolysable tannins for mechanical foaming of furanic foams

This study examined the potential of hydrolysable tannin in comparison to condensed tannins for the production of furanic foams. The results indicate that chestnut tannin presents lower reactivity and requires a stronger acid for the polymerization. Additionally, foamability and density were found to be dependent on both surfactant concentration and tannin type, allowing lower densities for mimosa tannin and lower thermal conductivities for chestnut-based foams. Mimosa tannin was found to have the highest compression strength, followed by quebracho and chestnut, promising thermal conductivity of around 50 mW/m center dot K for 300 kg/m(3) foams, which suggests that chestnut foams have the potential to performing highly when the density is reduced. Chemical analysis revealed that the methylene moieties of the furanics are non-specific and produces new covalent bonds with nucleophilic substrates: -OH groups and free-positions in the flavonoids. Overall, this study opens new perspectives for the application of hydrolysable tannins in polymer and material science