Efficient approach to high barrier packaging using microfibrillar cellulose and shellac

This paper presents an investigation on the enhancement of the barrier properties of paperboard and paper. Microfibrillar cellulose (MFC) and shellac were deposited on the fibre based substrates using a bar coater or a spray coating technique. The air, oxygen and water vapour permeability properties were measured to quantify the barrier effect of the applied coatings. In addition, the mechanical properties were determined and image analysis of the structure was performed to examine the coating adhesion. The air permeance of the paperboard and papers was substantially decreased with a multilayer coating of MFC and shellac. Furthermore, for the MFC and shellac coated papers, the oxygen transmission rate decreased several logarithmic units and the water vapour transmission rate reached values considered as high barrier in food packaging (6.5 g/m² 24 h). The analysis of mechanical and morphological properties indicated good adhesion between the coating and the base substrate.     

Als ein neues Reagens auf Phlorogluzin, Katechin und ihre Derivate

Ohne Zusammenfassung     

Zur regioselektiven nucleophilen Addition an 2,3-Dihydrobilatriene-abc

Donors are added regioselectively to position 10 of 2,3-dihydrobilatrienes-abc in a reversible reaction, which is complicated in case of strongly basic donors due to the easy deprotonation of the partially saturated ring. Compared to the bilatrienes-abc the addition equilibrium is retarded by about two orders of magnitude.

     

Photocatalytic deoxygenation of N–O bonds with rhenium complexes: from the reduction of nitrous oxide to pyridine N-oxides

The accumulation of nitrogen oxides in the environment calls for new pathways to interconvert the various oxidation states of nitrogen, and especially their reduction. However, the large spectrum of reduction potentials covered by nitrogen oxides makes it difficult to find general systems capable of efficiently reducing various N-oxides. Here, photocatalysis unlocks high energy species able both to circumvent the inherent low reactivity of the greenhouse gas and oxidant N₂O (E⁰(N₂O/N₂) = +1.77 V vs. SHE), and to reduce pyridine N-oxides (E_1/2(pyridine N-oxide/pyridine) = −1.04 V vs. SHE). The rhenium complex [Re(4,4′-tBu-bpy)(CO)₃Cl] proved to be efficient in performing both reactions under ambient conditions, enabling the deoxygenation of N₂O as well as synthetically relevant and functionalized pyridine N-oxides.

A rhenium-based photocatalyst enables the deoxygenation of several compounds containing N–O bonds, such as N₂O and pyridine N-oxides.     

Free-energy calculations of protein-ligand cation-pi and amino-pi interactions: from vacuum to proteinlike environments

To probe the role of cation-pi and amino-pi interactions in the context of protein-ligand interactions, the stability of 55 X-ray cation/amino-pi motifs involving the Ade moieties of cofactor molecules and Arg, Lys, Asn, or Gln side chains of their host protein was evaluated using quantum chemistry calculations. The conjunction of vacuum interaction energies, vibrational entropy, and solvation contributions led to identify Arg-Ade as the most favorable cation/amino-pi complex in the solvents considered, followed by Asn/Gln-Ade and Lys-Ade: their minimum interaction free energies are approximately equal to -7, -4, and -2 kcal/mol, respectively, in the solvents of dielectric constant similar to that estimated for proteins (i.e., acetone, THF, and CCl(4)). Remarkably, these free-energy values of cation/amino-pi interactions correlate well with their frequency of occurrences in protein-ligand structures, which corroborates our approach in the absence of experimental data.     

Proton uptake of rhodobacter capsulatus reaction center mutants modified in the primary quinone environment

Flash-induced absorbance spectroscopy was used to analyze the proton uptake and electron transfer properties of photosynthetic reaction centers (RC) of Rhodobacter capsulatus that have been genetically modified near the primary quinone electron acceptor (Q(A)). M246Ala and M247Ala, which are symmetry-related to the positions of two acidic groups, L212Glu and L213Asp, in the secondary quinone electron acceptor (QB) protein environment, have been mutated to Glu and Asp, respectively. The pH dependence of the stoichiometry of proton uptake upon formation of the P+Q(A)- (H+/P+Q(A)-) and PQ(A) (H+/Q(A)-) (P is the primary electron donor, a noncovalently linked bacteriochlorophyll dimer) states have been measured in the M246Ala --> Glu and the M247Ala --> Asp mutant RC, in the M246Ala-M247Ala --> Glu-Asp double mutant and in the wild type (WT). Our results show that the introduction of an acidic group (Glu or Asp) in the QA protein region induces notable additional proton uptake over a large pH region (approximately 6-9), which reflects a delocalized response of the protein to the formation of Q(A)-. This may indicate the existence of a widely spread proton reservoir in the cytoplasmic region of the protein. Interestingly, the pH titration curves of the proton release caused by the formation of P+ (H+/P+: difference between H+/P+Q(A)- and H+/PQ(A)- curves) are nearly superimposable in the WT and the M246Ala --> Glu mutant RC, but substantial additional proton release is detected between pH 7 and 9 in the M247Ala --> Asp mutant RC. This effect can be accounted for by an increased proton release by the P+ environment in the M247Ala --> Asp mutant. The M247Ala --> Asp mutation reveals the existence of an energetic and conformational coupling between donor and acceptor sides of the RC at a distance of nearly 30A.     

Structural Properties Governing Retention Mechanisms on Immobilized Artificial Membrane (IAM) HPLC Columns

The aims of this study were to investigate whether three commercially available immobilized artificial membrane (IAM) HPLC columns yield collinear data for neutral compounds, and whether IAM scales are distinct from the log P_oct (partition coefficient in the octanol/H₂O system) scale. With these objectives, the retention mechanisms on the IAM HPLC columns were analysed by linear solvation free‐energy relationships (LSERs). A set of 68 neutral model compounds with known solvatochromic parameters and log P_oct values was investigated, allowing a regular and broad exploration of property space. The resulting solvatochromic equations clearly indicate that the three IAM stationary phases retain small neutral solutes by a balance of intermolecular forces closely resembling those underlying partitioning in octanol/H₂O and retention on a reversed‐phase LC‐ABZ HPLC column. For all systems, the solute's size and hydrogen‐bond‐acceptor basicity are the two predominant factors, whereas dipolarity/polarisability and hydrogen‐bond‐donor acidity play only minor roles.     

Enhancement of selectivity and resolution in the enantioseparation of uncharged compounds using mixtures of oppositely charged cyclodextrins in capillary electrophoresis

The enantiomeric separation of some nonsteroidal anti-inflammatory drugs (NSAIDs) was investigated in capillary electrophoresis (CE) using dual systems with mixtures of charged cyclodextrin (CD) derivatives. A significant enhancement of selectivity and resolution could be achieved in the enantioseparation of these analytes in their uncharged form by the simultaneous addition of two oppositely charged CD derivatives to the background electrolyte. The combination of the single-isomer cationic CD, permethyl-6-monoamino-6-monodeoxy-beta-CD (PMMAbetaCD) and the single-isomer polyanionic CD, heptakis-6-sulfato-beta-cyclodextrin (HSbetaCD) in a pH 2.5 phosphoric acid-triethanolamine buffer, was designed and employed for the enantioseparation of profens. The improvement in selectivity and resolution can be attributed to the fact that the two CDs, which lead to independent and enantioselective complexation with the analyte enantiomers, have not only opposite effects on the electrophoretic mobility of these compounds but also opposite affinity patterns towards the enantiomers of these compounds. Binding constants for these enantiomers with each CD were determined using linear regression approach, in order to be able to predict the effect of the concentrations of the two CDs on enantiomeric selectivity and resolution in such dual systems.     

Insight into Three‐Coordinate Aluminum Species on Ethanol‐to‐Olefin Conversion over ZSM‐5 Zeolites

Commercial bioethanol can be readily converted into ethylene by a dehydration process using solid acids, such as Brønsted acidic H‐ZSM‐5 zeolites, and thus, it is an ideal candidate to replace petroleum and coal for the sustainable production of ethylene. Now, strong Lewis acidic extra‐framework three‐coordinate Al³⁺ species were introduced into H‐ZSM‐5 zeolites to improve their catalytic activity. Remarkably, Al³⁺ species working with Brønsted acid sites can accelerate ethanol dehydration at a much lower reaction temperature and shorten the unsteady‐state period within 1–2 h, compared to >9 h for those without Al³⁺ species, which can significantly enhance the ethanol dehydration efficiency and reduce the cost. The reaction mechanism, studied by solid‐state NMR, shows that strong Lewis acidic EFAl‐Al³⁺ species can collaborate with Brønsted acid sites and promote ethanol dehydration either directly or indirectly via an aromatics‐based cycle to produce ethylene.