A New Protocol for Ash Wood Modification: Synthesis of Hydrophobic and Antibacterial Brushes from the Wood Surface

The article presents the modification of ash wood via surface initiated activators regenerated by electron transfer atom transfer radical polymerization mediated by elemental silver (Ag⁰ SI-ARGET ATRP) at a diminished catalyst concentration. Ash wood is functionalized with poly(methyl methacrylate) (PMMA) and poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) to yield wood grafted with PMMA-b-PDMAEMA-Br copolymers with hydrophobic and antibacterial properties. Fourier transform infrared (FT-IR) spectroscopy confirmed the covalent incorporation of functional ATRP initiation sites and polymer chains into the wood structure. The polymerization kinetics was followed by the analysis of the polymer grown in solution from the sacrificial initiator by proton nuclear magnetic resonance (¹H NMR) and gel permeation chromatography (GPC). The polymer layer covalently attached to the wood surface was observed by scanning electron microscopy (SEM). The hydrophobic properties of hybrid materials were confirmed by water contact angle measurements. Water and sodium chloride salt aqueous solution uptake tests confirmed a significant improvement in resistance to the absorption of wood samples after modification with polymers. Antibacterial tests revealed that wood-QPDMAEMA-Br, as well as wood-PMMA-b-QPDMAEMA-Br, exhibited higher antibacterial activity against Gram-positive bacteria (Staphylococcus aureus) in comparison with Gram-negative bacteria (Escherichia coli). The paper presents an economic concept with ecological aspects of improving wood properties, which gives great opportunities to use the proposed approach in the production of functional hybrid materials for industry and high quality sports equipment, and in furniture production.     

Impact of the Type of Crosslinking Agents on the Properties of Modified Sodium Alginate/Poly(vinyl Alcohol) Hydrogels

Here, we report on studies on the influence of different crosslinking methods (ionic and chemical) on the physicochemical (swelling ability and degradation in simulated body fluids), structural (FT-IR spectra analysis) and morphological (SEM analysis) properties of SA/PVA hydrogels containing active substances of natural origin. First, an aqueous extract of Echinacea purpurea was prepared using a Soxhlet apparatus. Next, a series of modified SA/PVA-based hydrogels were obtained through the chemical crosslinking method using poly(ethylene glycol) diacrylate (PEGDA, M_n = 700 g/mol) as a crosslinking agent and, additionally, the ionic reaction in the presence of a 5% w/v calcium chloride solution. The compositions of SA/PVA/E. purpurea-based hydrogels contained a polymer of natural origin—sodium alginate (SA, 1.5% solution)—and a synthetic polymer—poly(vinyl alcohol) (PVA, M_n = 72,000 g/mol, 10% solution)—in the ratio 2:1, and different amounts of the aqueous extract of E. purpurea—5, 10, 15 or 20% (v/v). Additionally, the release behavior of echinacoside from the polymeric matrix was evaluated in phosphate-buffered saline (PBS) at 37 °C. The results indicate that the type of the crosslinking method has a direct impact on the release profile. Consequently, it is possible to design a system that delivers an active substance in a way that depends on the application.     

Stabilities and coordination modes of histidine in copper(II) mixed-ligand complexes with ethylenediamine,diethylenetriamine or N,N,N′,N″,N″-pentamethyldiethylenetriamine in aqueous solution

Solution equilibrium studies on the Cu(II)–polyamine–histidine ternary systems (polyamine: ethylenediamine (en), diethylenetriamine (dien), N,N,N′,N″,N″-pentamethyldiethylenetriamine (Me₅dien)) have been performed by pH-potentiometry, UV–Vis spectrophotometry and EPR methods. The obtained results suggest the formation of the mixed-ligand complexes with [Cu(A)(His)]⁺ stoichiometry in all studied systems. Additionally, in the systems with dien and Me₅dien protonated [Cu(A)(H–His)]²⁺ species also exists in acid solution. Our spectroscopic results indicate the tetragonal geometry for the [Cu(en)(His)]⁺, the geometry slightly deviated from square pyramidal for the [Cu(dien)(His)]⁺ and strongly deviated from square pyramidal towards trigonal bipyramidal for the [Cu(Me₅dien)(His)]⁺ species. The coordination modes in these mixed-ligand complexes are discussed.     

A 1:1 cocrystal of baicalein with nicotinamide

Cocrystallization of baicalein with nicotinamide yields a 1:1 cocrystal [systematic name: pyridine‐3‐carboxamide–5,6,7‐trihydroxy‐2‐phenyl‐4H‐chromen‐4‐one (1/1)], C₆H₆N₂O·C₁₅H₁₀O₅. The asymmetric unit contains one baicalein and one nicotinamide molecule, both in neutral forms. Molecules in the cocrystal form column motifs stabilized by an array of intermolecular hydrogen bonds.     

Size versus volume extensivity of a new class of density matrix functionals

Despite being size-extensive, the "second-generation" 1-matrix functionals for the electron-electron repulsion energy V(ee) yield vanishing correlation energy for the homogeneous electron gas. This failure is directly related to the idempotency condition imposed upon an auxiliary matrix that enters the expression for V(ee). In particular, the recently proposed Kollmar-Hess functional is not volume-extensive and thus is incapable of properly describing any delocalized system at its thermodynamic limit.