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.     

An improved max-flow-based lower bound for minimizing maximum lateness on identical parallel machines

In this paper, we introduce a new concept of semi-preemptive scheduling and we show how it can be used to derive a maximum-flow-based lower bound for the P|r_j|L_max which dominates the well-known preemptive lower bound. We show that, in some cases, the proposed bound strictly dominates the preemptive one while having the same complexity.     

Highly oxygenated triterpenes from the roots of Atropa acuminata

Two new oleanane triterpenes; 2alpha,3alpha,24-trihydroxyolean-12-ene-28,30-dioic acid ([structure: see text]) and 2alpha,3alpha,24,28-tetrahydroxyolean-12-ene ([structure: see text]) have been isolated from the roots of Atropa acuminata. Anti-oxidant p-hydroxyphenethyl trans-ferulate ([structure: see text]), beta-sitosterol-3-O-beta-D-glucopyranoside ([structure: see text]) and oleanolic acid ([structure: see text]) have also been reported for the first time from this species. The structures were determined by spectroscopic studies including 2D-NMR.     

Elaboration and characterization of hybrid organic-inorganic gels obtained by reaction of 1,4-butanediol on tetramethoxysilane

New hybrid organic-inorganic gels have been obtained by reaction of 1,4-butanediol, on tetramethoxysilane Si(OMe)₄ dissolved in CCl₄. This reaction does not require water and leads to the formation of polymeric transparent materials.Infrared, ²⁹Si and ¹³C NMR spectroscopy shows that interchange reactions between OMe groups of alkoxide and -O-(CH₂)₄-O of 1,4-butanediol occurred, leading to the monolithic transparent gels in which both organic (Si-O-(CH₂)₄-O-Si) and inorganic (Si-O-Si) bridges are formed.     

Random Poly(Lactic Acid-co-β-Alanine): Synthesis and Characterizations

A series of random polyesteramides (PEAs) within a range of molar composition from 90/10 to 10/90 were synthesized by a direct melt polycondensation of lactic acid and β-alanine. Their structures were fully characterized by NMR spectroscopy. The resulting copolymers are amorphous; they are thermally stable to temperatures up to 254°C, and present increasing glass transition temperatures at increasing amide content. The copolymers were also characterized by FTIR and viscosimetry measurements.     

Polyazomethines Bearing Furan Moieties. Solution Polycondensation of Bis(furanic diamine)s and Aromatic Dialdehydes

A series of new polyazomethines containing furan moieties was synthesized by polycondensation of bifuranic diamine monomers with commercially available aromatic dialdehydes viz., terephthaldehyde (TPA), isophthaldehyde (IPA). Inherent viscosities and number average molecular weights of polyazomethines were in the range 0.90–1.56 dL/g and 10460–17850 (SEC, polystyrene standard), respectively indicating formation of medium to reasonably high molecular weight polymers. The resulting polyazomethines were characterized by solubility tests, viscosity measurements, FTIR, NMR, UV spectroscopy, differential scanning calorimetric (DSC), and thermogravimetric analysis (TGA). These furan-based polyazomethines were essentially amorphous and exhibited glass transition temperatures (Tg) in the 150–190°C range. The temperature at 10% wt loss (T₁₀), determined from TGA of polyazomethines were in the range 300–380°C, indicating their good thermal stability.     

Reaction of unsymmetrical α,β-unsaturated ketones with thiobarbituric acid

Carbocyclization of unsymmetrical 1,5-diarylpenta-1,4-dien-3-ones with thiobarbituric acid afforded previously unknown 7,11-diaryl-3-thioxo-2,4-diazaspiro[5.5]undecane-1,5,9-triones with high regio- and stereoselectivity. The same spiro compounds were also synthesized by three-component condensation of thiobarbituric acid with the corresponding aromatic aldehydes and 4-arylbut-3-en-2-ones.     

A Simplified Wittig Synthesis Using A Solid-Liquid Transfer Process : VII - Direct Transformation of Aromatic and Heteroaromatic Aldehydes into Functionalised Allylic Ethers

Synthesis of allylic ethers from various aldehyde alcohols and β-hydroxylated phosphonium salts was carried out in a single manipulation and with excellent yields.