Pseudokinetics for the copolymerization of butadiene and styrene produced using n-butyl lithium and N,N,N′,N′-tetramethylethylenediamine,considering different reactivities of the structural units

The anionic solution copolymerization of butadiene and styrene prepared by anionic living polymerization using an initiator composed of n-butyl lithium, and N,N,N′,N′-tetramethylethylenediamine as active center modifier was modeled as a tetrapolymerization. The kinetic model proposed considering that the reactivity of the active sites is different because of varying configurations cis, trans, vinyl, and styryl. From the reaction scheme expressions to rate of monomers consumption, microstructure and dyad formation were obtained. With the first-order Markov model, the expressions for the fraction of active sites and dyad distribution as a function of the conditional probabilities were obtained. Therefore, the model proposed is different to kinetic models previously reported, because it allows obtaining the parameters kinetic in order to know the distribution of the isomeric species presents in the copolymerization of butadiene and styrene, and the intrinsic reactivity of configurational active sites. The rate constants were determined by fitting to the conversion and dyad experimental data using the nonlinear least square method. The experimental data reported in the literature, monomer conversion and microstructure, in addition to dyad sequence distribution were correctly predicted.     

Stability of diphenylalanine peptide nanotubes in solution

Over the last couple of years, self-organizing nanotubes based on the dipeptide diphenylalanine have received much attention, mainly as possible building blocks for the next generation of biosensors and as drug delivery systems. One of the main reasons for this large interest is that these peptide nanotubes are believed to be very stable both thermally and chemically. Previously, the chemical and thermal stability of self-organizing structures has been investigated after the evaporation of the solvent. However, it was recently discovered that the stability of the structures differed significantly when the tubes were in solution. It has been shown that, in solution, the peptide nanotubes can easily be dissolved in several solvents including water. It is therefore of critical importance that the stability of the nanotubes in solution and not after solvent evaporation be investigated prior to applications in which the nanotube will be submerged in liquid. The present article reports results demonstrating the instability and suggests a possible approach to a stabilization procedure, which drastically improves the stability of the formed structures. The results presented herein provide new information regarding the stability of self-organizing diphenylalanine nanotubes in solution.     

Physicochemical properties of novel pectin/<Emphasis Type="Italic">Aloe</Emphasis> gel membranes

Nowadays, an increased interest on the development of novel biomaterials for different applications has been observed. The biopolymers such as proteins, lipids, polysaccharides or their combinations have been used for the manufacturing of novel membranes. The pectin is a polysaccharide that previously has been used only or combined with polymeric matrices, but the formulation of PEC/AG has not been evaluated yet. The aim of this work was to evaluate the physicochemical properties of a novel PEC/AG membrane. A mixture of pectin citric (PEC)/Aloe gel (AG) was prepared to manufacture membranes at 100/0 (control), 90/10, 80/20, 70/30, 60/40 and 50/50 proportions (% v/v) by casting method. Water vapor permeability (WVP), solubility, ATR-FTIR spectroscopy, microstructure, mechanical and optical properties were assessed for the produced membranes. The PEC/AG membranes showed a yellowish color, low UV light transmission at 200 nm and no significant changes in the opacity values. In addition, the microstructure by scanning electron microscopy (SEM) showed changes on the surface appeared as differently sized structures. An analysis of the total area of the 3284 cm^?1 showed rearrangement of hydrogen bonds of the polysaccharide macromolecules, suggesting an enhanced interaction between the PEC and AG chains. In addition, all the membranes of PEC/AG showed high solubility (100%), low WVP and better toughness, extensibility and plasticity as compared with the control. The assessed physicochemical properties of the produced membranes suggested that they may be used as biomaterial for multiple applications in the medical, pharmaceutical, cosmetic or food industries.     

Light-Activated Metal Complexes that Covalently Modify DNA

Many drugs in current clinical use rely on mechanisms of action that involve damage to nucleic acids. While this has been a successful therapeutic approach for many years, the major limitation of these agents is systemic cytotoxicity, resulting from damage caused to healthy cells. Photoactive metal complexes offer the possibility of combining two successful treatment modalities for cancer and other diseases by providing DNA damage similar to that obtained with cisplatin, but in a spatially and temporally controlled manner, as with phototherapy. Recent progress in the field has provided metal complexes that can be triggered to create covalent adducts with nucleic acids both in vitro and in cells. Furthermore, several of these agents have been shown to induce cytotoxicity in cancer cell lines, in vitro tumor models, and in vivo animal models. In the last year, new compounds have been reported that can be activated with low energy light within the “therapeutic window,” where light penetration through tissue is sufficient to access larger volume tumors. This review highlights the advances that demonstrate the potential of light-activated metal complexes as therapeutics and research tools for biomedical applications.     

Peptides Derived from Vascular Endothelial Growth Factor B Show Potent Binding to Neuropilin-1

Vascular endothelial growth factors (VEGFs) regulate significant pathways in angiogenesis, myocardial and neuronal protection, metabolism, and cancer progression. The VEGF-B growth factor is involved in cell survival, anti-apoptotic and antioxidant mechanisms, through binding to VEGF receptor 1 and neuropilin-1 (NRP1). We employed surface plasmon resonance technology and X-ray crystallography to analyse the molecular basis of the interaction between VEGF-B and the b1 domain of NRP1, and developed VEGF-B C-terminus derived peptides to be used as chemical tools for studying VEGF-B - NRP1 related pathways. Peptide lipidation was used as a means to stabilise the peptides. VEGF-B-derived peptides containing a C-terminal arginine show potent binding to NRP1-b1. Peptide lipidation increased binding residence time and improved plasma stability. A crystal structure of a peptide with NRP1 demonstrated that VEGF-B peptides bind at the canonical C-terminal arginine binding site. VEGF-B C-terminus imparts higher affinity for NRP1 than the corresponding VEGF-A₁₆₅ region. This tight binding may impact on the activity and selectivity of the full-length protein. The VEGF-B₁₆₇ derived peptides were more effective than VEGF-A₁₆₅ peptides in blocking functional phosphorylation events. Blockers of VEGF-B function have potential applications in diabetes and non-alcoholic fatty liver disease.     

Discovery of a New Class of Non‐imidazole Oxazoline‐Based Histamine H3 Receptor (H3R) Inverse Agonists

H ₃ R inverse agonists based on an aminopropoxy‐phenyloxazoline framework constitute highly valuable druglike lead compounds that display efficacy in a mouse model of recognition memory.

     

The role of gluten in a pound cake system: A model approach based on gluten–starch blends

In order to evaluate the role of gluten in cake-making, gluten–starch (GS) blends with different ratios of gluten to starch were tested in a research pound cake formula. The viscosities of batters made from commercial GS blends in the otherwise standardised formula increased with their gluten content. High viscosities during heating provide the batters with the capacity to retain expanding air nuclei, and thereby led to desired product volumes. In line with the above, increasing gluten levels in the cake recipes led to a more extended oven spring period. Cakes with a starch content exceeding 92.5% in the GS blend suffered from substantial collapse during cooling. They had a coarse crumb with a solid gummy layer at the bottom. Image analysis showed statistical differences in numbers of cells per cm², cell to total area ratio and mean cell area (p < 0.05). Both density and mean cell area were related to gluten level. Moreover, mean cell area and cell to total area ratio were the highest for cakes with the lowest density and highest gluten levels. Relative sodium dodecyl sulfate (SDS, 2.0%) buffer (pH 6.8) extractabilities of protein from cakes baked with the different GS blends decreased with gluten content and were strongly correlated with the intensity of collapse. Taken together, the results teach that protein gives the cakes resistance to collapse, resulting in desirable volumes and an optimal grain structure with uniform cell distribution.     

New insights in dispersion mechanisms of carbon black in a polymer matrix under shear by rheo‐optics

The dispersion behavior of different carbon black grades was investigated in a common elastomer matrix under shear using a transparent plate‐and‐plate counter‐rotating shear cell coupled with an optical microscope. The objective was to investigate the effect of carbon black intrinsic characteristics (specific area and structure) on dispersion mechanisms. Shear conditions were selected to study independently erosion and rupture mechanisms. The independent study of rupture and erosion mechanisms brings new findings on the respective effect of the filler intrinsic characteristics on each mechanism: (a) Rupture is a sudden mechanism occurring above a critical shear stress, which depends on the pellet size. The rupture criterion appears not to depend on the carbon black specific area or the structure. (b) Erosion proceeds via the detachment of a fixed eroded volume per strain unit and is driven by the applied shear stress and strain. Erosion is a local mechanism. The erosion rate depends on the carbon black characteristics. Faster erosion was measured for a carbon black with a higher structure at equivalent specific area or with a lower specific area at equivalent structure. This in situ characterization of dispersion mechanisms highlights that the effect of the carbon black characteristics on the two main dispersion mechanisms (rupture and erosion) is completely different. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Perspectives to breed for improved baking quality wheat varieties adapted to organic growing conditions

Northwestern European consumers like their bread to be voluminous and easy to chew. These attributes require a raw material that is rich in protein with, among other characteristics, a suitable ratio between gliadins and glutenins. Achieving this is a challenge for organic growers, because they lack cultivars that can realise high protein concentrations under the relatively low and variable availability of nitrogen during the grain-filling phase common in organic farming. Relatively low protein content in wheat grains thus needs to be compensated by a high proportion of high-quality protein. Organic farming therefore needs cultivars with genes encoding for optimal levels of glutenins and gliadins, a maximum ability for nitrogen uptake, a large storage capacity of nitrogen in the biomass, an adequate balance between vegetative and reproductive growth, a high nitrogen translocation efficiency for the vegetative parts into the grains during grain filling and an efficient conversion of nitrogen into high-quality proteins. In this perspective paper the options to breed and grow such varieties are discussed.