Thermodynamic study of transthyretin association (wild‐type and senile forms) with heparan sulfate proteoglycan: pH effect and implication of the reactive histidine residue

The tetramer destabilization of transthyretin into monomers and its fibrillation are phenomena leading to amyloid deposition. Heparan sulfate proteoglycan (HSPG) has been found in all amyloid deposits. A chromatographic approach was developed to compare binding parameters between wild‐type transthyretin (wtTTR) and an amyloidogenic transthyretin (sTTR). Results showed a greater affinity of sTTR for HSPG at pH 7.4 compared with wtTTR owing to the monomeric form of sTTR. Analysis of the thermodynamic parameters showed that van der Waals interactions were involved at the complex interface for both transthyretin forms. For sTTR, results from the plot representing the number of protons exchanged vs pH showed that the binding mechanism was pH‐dependent with a critical value at a pH 6.5. This observation was due to the protonation of a histidine residue as an imidazolium cation, which was not accessible when TTR was in its tetrameric structure. At pH >6.5, dehydration at the binding interface and several contacts between nonpolar groups of sTTR and HSPG were also coupled to binding for an optimal hydrogen‐bond network. At pH <6.5, the protonation of the His residue from sTTR monomer when pH decreased broke the hydrogen‐bond network, leading to its destabilization and thus producing slight conformational changes in the sTTR monomer structure. Copyright © 2014 John Wiley & Sons, Ltd.     

The optimal stack spacing for thermoacoustic refrigeration

The characteristic pore dimension in the stack is an important parameter in the design of thermoacoustic refrigerators. A quantitative experimental investigation into the effect of the pore dimensions on the performance of thermoacoustic devices is reported. Parallel-plate stacks with a plate spacing varying between 0.15 and 0.7 mm are manufactured and measured. The performance measurements show that a plate spacing in the stack of 0.25 mm (2.5 deltak) is optimum for the cooling power. A spacing of 0.4 mm (4 deltak) leads to the lowest temperature. The optimum spacing for the performance is about 0.3 mm (3 deltak). It is concluded that a plate spacing in the stack of about three times the penetration depth should be optimal (3 deltak) for thermoacoustic refrigeration.     

Palladium–dppb–borate‐catalyzed regioselective synthesis of cinnamate esters by alkoxycarbonylation of phenylacetylene

The regioselective alkoxycarbonylation of phenylacetylene into various cinnamate esters was achieved with a catalyst system formed from palladium (II), 1,4‐bis(diphenylphosphino) butane (dppb) and salicylborate complex in acetonitrile as a solvent. The influence of various parameters on the overall conversion of phenylacetylene and the selectivity of the reaction were studied systematically by varying the type of palladium complex, acids promoter, CO pressure, temperature and the reaction time. This investigation allowed us to obtain the predominant formation of cinnamate esters with excellent selectivity (90–96%). Copyright © 2008 John Wiley & Sons, Ltd.     

Degradation of 2-Nitrophenol by Dielectric Barrier Discharge System: The Influence of Carbon Doped TiO<Subscript>2</Subscript> Photocatalyst Supported on Stainless Steel Mesh

This study investigated the degradation of 2-nitrophenol (2-NP) in aqueous solution by dielectric barrier discharge (DBD) system alone and its combination with supported TiO₂ photocatalysts. The TiO₂ photocatalyst supported on a stainless steel mesh was synthesised using sol–gel solution of 8% polyacrylonitrile (PAN)/dimethylformamide/TiCl₄ followed by pyrolysis in the furnace under N₂ atmosphere at temperatures of 300, 350, or 400 °C for 3 h holding time. The supported catalysts were characterized for their morphologies, functional groups, crystallinity, surface areas and elemental chemical states by high resolution scanning electron microscope (HRSEM), Fourier transform infrared, X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) surface area, and X-ray photoelectron spectroscopy. The influence of solution pH on the degradation of 2-NP was investigated. The residual concentration of 2-NP and the intermediate compounds were quantified and identified using high-performance liquid chromatography coupled with mass spectrometry (HPLC–MS). The concentration of the dissolved ozone, hydrogen peroxide and hydroxyl radicals generated by the DBD in the presence or absence of a catalyst was monitored using ultraviolet–visible spectroscopy and photoluminescence spectroscopy. The HRSEM, HRTEM, XRD and BET analysis revealed that the optimal thermal conditions to obtain well supported uniformly grown, highly active crystalline TiO₂ catalysts with high specific surface area was 350 °C at a 3 h holding time in N₂ atmosphere with a flow rate of 20 mL/min. The supporting procedure simultaneously carbon doped the photocatalyst. The DBD system alone without catalysts successfully mineralised 58.6% of 2-NP within 60 min while combined DBD/supported TiO₂ nanocrystals achieved 77.5% mineralisation within the same treatment time. The increase in mineralisation rate was attributed to the existence of a synergistic effect between the DBD system and the supported catalysts. 2-NP degradation proceeded via hydroxylation, nitration and denitration using DBD alone and combined DBD/Supported TiO₂ photocatalyst. Catechol, hydroquinone, hydroxyl-1,4-benzoquinone, 2-nitrohydroquinone, and 2,4-dinitrophenol were identified as major intermediate products. The order of production of free reactive species by DBD alone and combined DBD with supported photocatalyst was OH° > H₂O₂ > O₃.The results showed that the combined system was more than effective than DBD alone for the degradation of the 2-NP in aqueous solution.     

Palladium(II)‐catalyzed catalytic aminocarbonylation and alkoxycarbonylation of terminal alkynes: regioselectivity controlled by the nucleophiles

The aminocarbonylation and alkoxycarbonylation reactions of terminal alkynes took place smoothly and efficiently using a catalyst system Pd(OAc)₂–dppb–p‐TsOH? CH₃CN? CO under relatively mild experimental conditions. The catalytic system was tested and optimized using two different nucleophiles: alcohols and amines. Phenylacetylene (1a) was considered as an alkyne along with diisobutylamine (2b₁) and methanol (2c₁) as nucleophiles. The results showed significant differences in the conversion of 1a and in the selectivity towards the gem or trans unsaturated esters or amides with these nucleophiles. The effects of the type of palladium catalysts, the type of ligands, the amount of dppb and the solvents were carefully studied. With diisobutylamine (2b₁), excellent regioselectivity towards the 2‐acrylamides (gem isomer, 3ab₁) was almost always observed, while trans‐α,β‐unsaturated esters 4ac₁ was the predominant product with methanol (2c₁) as a nucleophile. This remarkable sensitivity in the selectivity of the reaction indicates two different possible mechanistic pathways for these carbonylation reactions. Copyright © 2009 John Wiley & Sons, Ltd.     

Simple method for detection of extremely diluted anti beta-casein antibodies from glass bead based receptors

The current work describes the elaboration of a simple, sensitive and reliable β-casein modified glass beads, for the detection and quantification of its specific antibody anti β-casein. This is an elementary receptor without electronic part, developed by grafting glass bead surface with the antigenic β-casein via 3-aminopropyltriethoxy silane and then glutaraldehyde as cross-linker. The whole is realized by a classical process, called in two steps and in mild conditions where chemical protocol is optimized for β-casein use. The detection and quantification of the specific reaction antibody-receptor is carried out by the technique of the second antibody labeled with horse radish peroxidase (HRP). Our receptor can detect the β-casein antibody present in the serum at dilutions up to a factor 10⁷ in strong ionic strength medium. The same antibody of the same serum and in the same conditions can be detected by ELISA test at dilutions up to a factor 10⁵. The whole test, after our receptor realization, takes about 5 h.     

General decay of solutions in one-dimensional porous-elastic system with memory

In this work we consider a one-dimensional porous-elastic system with memory effects. It is well-known that porous-elastic system with a single dissipation mechanism lacks exponential decay. In contrary, we prove that the unique dissipation given by the memory term is strong enough to exponentially stabilize the system, depending on the kernel of the memory term and the wave speeds of the system. In fact, we prove a general decay result, for which exponential and polynomial decay results are special cases. Our result is new and improves previous results in the literature.     

Exponential stability for laminated beams with a frictional damping

We study a laminated beam which consists of two identical layers of uniform thickness, taking into account that an adhesive of small thickness is bonding the two surfaces thereby producing an interfacial slip. We show that when the frictional damping acts on the effective rotation angle there is no need for any other kind of internal or boundary control to produce exponential stability for the system.     

Best simultaneous approximation in L∞(μ, X)

Let Y be a reflexive subspace of the Banach space X, let (Ω, Σ, μ) be a finite measure space, and let L_∞(μ, X) be the Banach space of all essentially bounded μ ‐Bochner integrable functions on Ω with values in X, endowed with its usual norm. Let us suppose that Σ₀ is a sub‐σ ‐algebra of Σ, and let μ₀ be the restriction of μ to Σ₀. Given a natural number n, let N be a monotonous norm in ?ⁿ . We prove that L_∞(μ, Y) is N ‐simultaneously proximinal in L_∞(μ,X), and that if X is reflexive then L_∞(μ₀, X) is N ‐simultaneously proximinal in L_∞(μ, X) in the sense of Fathi, Hussein, and Khalil [3]. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Testimony of the Correlation Between the Reactive Histidine Residue and the Arginase Catalytic Mechanism Using a Biochromatographic Concept and Mutagenesis Experiments

In a previous paper (Bagnost et al., J Chromatogr B Analyt Technol Biomed Life Sci 853:38–46, 2007), an arginase chromatographic support was developed to study the association mechanism of arginase (an enzyme which can reduce endothelial dysfunction and blood pressure rising in spontaneously hypertensive rats) with nor-NOHA a potential inhibitor of its activity. In this report mutagenesis experiments associated with this biochromatographic approach confirmed that the active-site residue Hist 141 is protonated as imidazolium cation. Hist 141 could function as a general acid to protonate the leaving amino group of l-ornithine during catalysis.