Determination of the thermal modification degree of beech wood using thermogravimetry

Thermal modification is one of the environmental friendly wood preservation technologies. During this process, changes of the main woody cell wall components occur, which lead to improved dimensional stability, lower hygroscopicity and improvement in biological durability. Several chemical reactions which occur during thermal treatment of wood caused changes in wood properties. During TG measurements, thermal decomposition reactions, which was not completed during previous thermal modification process, continued in wood samples, meaning that more thermally treated samples exhibited lower mass losses in a certain or whole temperature range up to 600 °C. Therefore, mass loss, obtained within selected temperature range, could be used as a marker of previous thermal treatment. The aim of the present work is to evaluate suitability of a thermogravimetric method (TG) for determination of a degree of thermal treatment of beech wood. On the basis of thermally untreated sample and those which were thermally modified at 180, 190, 200, 210, 215 and 220 °C in the absence of oxygen, respectively, and with known values of mass loss during the modification processes, several calibration curves were constructed. They represent mass loss in a certain temperature range during TG measurement versus mass loss during previous thermal modification. In a temperature range from 130 to 300 °C and from 130 to 320 °C under nitrogen atmosphere, a linear dependence was observed; correlation coefficients R ² were 0.87 and 0.91, respectively. In wider temperature range and under air atmosphere, lower correlation coefficients were obtained. High correlation coefficient, higher than 0.95, was observed in a temperature range from 25 to 130 °C under both atmospheres. In this region, dehydration due to rehydration of thermally modified samples occurs. The results of this work were compared with those obtained for Norway spruce.     

Phase behavior of mixtures of oppositely charged nanoparticles: heterogeneous Poisson-Boltzmann cell model applied to lysozyme and succinylated lysozyme

We study the phase behavior of mixtures of oppositely charged nanoparticles, both theoretically and experimentally. As an experimental model system we consider mixtures of lysozyme and lysozyme that has been chemically modified in such a way that its charge is nearly equal in magnitude but opposite in sign to that of unmodified lysozyme. We observe reversible macroscopic phase separation that is sensitive not only to protein concentration and ionic strength, but also to temperature. We introduce a heterogeneous Poisson-Boltzmann cell model that generally applies to mixtures of oppositely charged nanoparticles. To account for the phase behavior of our experimental model system, in addition to steric and electrostatic interactions, we need to include a temperature-dependent short-ranged interaction between the lysozyme molecules, the exact origin of which is unknown. The strength and temperature dependence of the short-ranged attraction is found to be of the same order of magnitude as that between unmodified lysozyme molecules. The presence of a rather strong short-ranged attraction in our model system precludes the formation of colloidal liquid phases (or complex coacervates) such as those typically found in mixtures of globular protein molecules and oppositely charged polyelectrolytes.     

Template-Free Self-Assembly of Artificial De Novo Viral Coat Proteins into Nanorods: Effects of Sequence,Concentration, and Temperature

The self-assembly of protein polymers is a promising route to prepare sophisticated functional nanostructures. However, the interplay between protein self-assembly by itself and its co-assembly with a template is not well understood. Silk-based protein polymers that co-assemble with DNA to form rod-like artificial viruses are herein developed and the effects of silk block length, concentration, and temperature in the self-assembly of the proteins alone are characterized by using a combination of bulk dynamic light scattering (DLS) and single-molecule atomic force microscopy (AFM). Protein nanorods were slowly formed (up to hours) through the interaction of the silk-like blocks. The proteins present a silk-length dependent critical elongation concentration, and above it the amount and size of nanorods rapidly increase. Temperature-dependent light scattering data was adequately fitted into a cooperative model of nucleation–elongation. These results are also important to understand the self-assembly of designed viral coat proteins with DNA templates to form artificial virus-like particles and help us to define general guidelines to design proteins with the ability to precisely organize matter at the nanoscale.     

Time-resolved small-angle neutron scattering during heat-induced fibril formation from bovine beta-lactoglobulin

We study in situ the kinetics of heat-induced fibrilar aggregation of bovine beta-lactoglobulin at pH 2.0 and 80 degrees C for the first time by time-resolved small-angle neutron scattering. A simple model for the scattering from a mixture of monodisperse charged spheres (monomeric beta-lactoglobulin) interacting via a screened electrostatic repulsion and noninteracting long cylinders (protein fibrils) is used to describe the data. The experimental data are fitted to the model and the concentration of the monomeric protein and the protein incorporated in fibrils are obtained as adjustable parameters. Thus, a simple physical model allows the determination of realistic kinetic parameters during fibrilar protein aggregation. This result constitutes an important step in understanding the process of irreversible fibrilar aggregation of proteins.     

Synthese de la meso-α,β bis(diamino-2,6 phenyl) octamethyl porphyrine

α,γ-Meso bis-(2,6-diaminophenyl) octamethyl porphyrin and derivatives have been prepared by an easy synthesis avoiding the separation of stereoisomers and represent a new kind of tetrafunctionalised porphyrin.     

Effect of pore size on adsorption of a polyelectrolyte to porous glass

The adsorption of quaternized poly(vinylpyridine) (QPVP) on controlled pore glass (CPG) size, over the ionic strength range 0.001-0.5 M was found to display nonmonotonic behavior as a function of pore size. Both adsorption kinetics and ionic strength effects deviated dramatically from behavior typical of adsorption on flat surfaces when the ratio of the pore radius Rp to the polymer hydrodynamic radius Rh became smaller than ca. 2. Ionic strength enhancement of adsorption for small pore sizes was observed at much higher salt concentrations than is typical for polycation adsorption on flat surfaces. The amount of polymer adsorbed per unit surface area of glass GammaA, in 0.5 M NaCl, exhibited a shallow maximum at Rp/Rh approximately 5. Since the value of GammaA for small pore size CPG is strongly depressed by the large surface area, an alternative and more interesting observation is that the amount of polymer adsorbed per gram of CPG, Gammaw, displays a strong maximum when Rp is equal to or slightly smaller than Rh. The efficiency with which QPVP binds anionic micelles to (negatively charged) CPG (grams of surfactant/grams of QPVP) increases strongly with diminishing pore size, indicating that the configuration of polycation bound to small pores favors micelle binding. Since the micelles are larger than small pores, the results indicate that when Rp < Rh, adsorbed polycation molecules reside only partially within the pore. The results of this study are supported by simulations of polyelectrolytes within cylindrical cavities.     

Theoretical modeling of the kinetics of fibrilar aggregation of bovine beta-lactoglobulin at pH 2

The authors propose a kinetic model for the heat-induced fibrilar aggregation of bovine beta-lactoglobulin at pH 2.0. The model involves a nucleation step and a simple addition reaction for the growth of the fibrils, as well as a side reaction leading to the irreversible denaturation and inactivation of a part of the protein molecules. For the early stages of the aggregation reaction, the authors obtain an analytical solution of the model. In agreement with their experimental results, the model predicts a critical protein concentration below where almost no fibrils are formed. The model agrees well with their experimental data from in situ light scattering. By fitting the experimental data with the model, the authors obtain the ionic strength dependent kinetic rate constants for beta-lactoglobulin fibrilar aggregation and the size of the critical nucleus.     

A combined LC-MS/MS and LC-MS3 multi-method for the quantification of iodothyronines in human blood serum

We report here a novel approach for the extraction and analysis of thyroid hormones (TH) and their metabolites (THM) from human serum samples. Our method features a compact, 96-well micro-titre plate-based pre-analytic extraction/clean-up workflow combined with an isotope dilution LC-MS/MS-MS³ analytical method. In particular, these features make possible the detection of iodothyronines at their endogenous concentrations in serum differing by a factor of ca. 10⁴, with potential to semi-automate the pre-analytics. The method was validated by the assessment of linearity, lower limits of quantification and detection (LLOQ and LLOD respectively), intra- and inter-day accuracy, precision, process efficiency (PE), matrix effect (ME) and relative recovery (RE). Calibration curves were linear in the concentration range in sample matrix from 0.1–250 nM for T₃, rT₃, T₄ and 3-T₁AM and from 0.005–1 nM for 3,5-T₂ and 3,3′-T₂. Using a 200-μL sample volume, the analyte dependant LLOQ were in the range 0.005 (3,5-T₂) to 0.25 (T₄) nM and LLOD were between 0.002 (3,5-T₂) and 0.052 nM (T₄). We applied the LC-MS/MS-MS³ method to the analysis of a cross section of patients with disorders of the thyroid hormone axis. T₄, T₃ and rT₃ concentrations (± standard deviation) were 120 ± 18, 1.9 ± 0.4 and 0.45 ± 0.09 nM respectively. 3,3′-T₂ concentrations (± standard deviation) were 0.079 ± 0.022 nM; 3,5-T₂ concentrations were below the LLOQ and/or LLOD in all but a single sample (0.013 nM). This method expands the analytical spectrum to endogenous thyroid hormone metabolites such as 3,5-T₂ which exert biological actions and rT₃ which may act as surrogate markers for disturbed thyroid hormone metabolism.

Graphical abstract

     

Influence of mobile DNA-protein-DNA bridges on DNA configurations: coarse-grained Monte-Carlo simulations

A large literature exists on modeling the influence of sequence-specific DNA-binding proteins on the shape of the DNA double helix in terms of one or a few fixed constraints. This approach is inadequate for the many proteins that bind DNA sequence independently, and that are present in very large quantities rather than as a few copies, such as the nucleoid proteins in bacterial cells. The influence of such proteins on DNA configurations is better modeled in terms of a great number of mobile constraints on the DNA. Types of constraints that mimic the influence of various known non-specifically DNA binding proteins include DNA bending, wrapping, and bridging. Using Monte-Carlo simulations, we here investigate the influence of (non-interacting) mobile DNA-protein-DNA bridges on the configurations of a 1000 bp piece of linear DNA, for both homogeneous DNA and DNA with an intrinsic planar bend. Results are compared to experimental data on the bacterial nucleoid protein H-NS that forms DNA-protein-DNA bridges. In agreement with data on H-NS, we find very strong positioning of DNA-protein-DNA bridges in the vicinity of planar bends. H-NS binds to DNA very cooperatively, but for non-interacting bridges we only find a moderate DNA-induced clustering. Finally, it has been suggested that H-NS is an important contributor to the extreme condensation of bacterial DNA into a nucleoid structure, but we find only a moderate compaction of DNA coils with increasing numbers of non-interacting bridges. Our results illustrate the importance of quantifying the various effects on DNA configurations that have been proposed for proteins that bind DNA sequence independently.     

Condensation d'acides amines sur des meso-amino-2-phenyl porphyrines

The condensation of aminoacids on meso-tetra-(2-aminophenyl) and meso-α,γ-bis-(2,6-diaminophenyl)porphyrins is reported.