Phase behaviour of tri-n-butylmethylammonium chloride hydrates in the presence of carbon dioxide

The phase behaviour of the system water?Ctri-n-butylmethylammonium chloride (TBMAC)?CCO₂ was investigated by pressure-controlled differential scanning calorimetry in the range 0?C10?mol% TBMAC in water and at CO₂ pressures ranging from 0 to 1.5?MPa. In the absence of CO₂, an incongruent melting hydrate, which estimated composition corresponds to TBMAC·30H₂O, crystallizes at temperatures below ?13.6?°C and forms with ice a peritectic phase at approximately 3.9?mol% TBMAC. In the presence of CO₂ at pressures as low as 0.5?MPa, curves evidenced the presence of an additional phase exhibiting congruent melting at temperatures that are strongly pressure dependent and significantly higher than those of hydrates obtained without CO₂. This new phase, whose enthalpy of dissociation and CO₂ content increase slightly with CO₂ pressure, was identified as a mixed semi-clathrate hydrate of TBMAC and CO₂ of general formula: (TBMAC?+?xCO₂)·30H₂O.     

Blends of polycarbonate and acrylic polymers: Crystallization of polycarbonate

The microstructure of amorphous polymer blends has been extensively studied in the past, but now there is a growing interest for polymer blends where one or more of the components can crystallize. In this study we investigate such blends, namely miscible polycarbonate (PC)/acrylic blends. Using small angle X-ray scattering (SAXS) measurements, combined with atomic force microscopy (AFM), electron microscopy (SEM), and optical microscopy, we demonstrate that the amorphous acrylic component mostly segregates inside the spherulites between the lamellar bundles (interfibrillar segregation). Varying the PC molecular weight or the mobility of the amorphous component (by changing its molecular weight and T_g) does not change the mode of segregation. So far qualitative predictions of the mode of segregation in semicrystalline polymer blends have been proposed using the δ parameter (the ratio between the diffusion coefficient D of the amorphous component in the blend and the linear crystallization rate G), introduced by Keith and Padden. Our results suggest that other parameters have to be considered to fully understand the segregation process. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. B Polym. Phys. 36: 2197–2210, 1998     

Rheological Behavior and Non-enzymatic Degradation of a Sulfated Galactan from Halymenia durvillei (Halymeniales, Rhodophyta)

The rheological behavior of a sulfated galactan extracted from Halymenia durvillei, a red seaweed collected in the coastal waters of a small island of Madagascar (Nosy-be in Indian Ocean), was investigated in dilute and semi-dilute solutions. In dilute solution with NaCl at 0.3?M, the polysaccharide adopted a coil conformation whereas, at higher concentrations, the polymer had the behavior of shear-thinning fluid, typical of polymer with high molar mass or semi-rigid conformation. Degradations of this lambda carrageenan-like, using radical depolymerization, and high-pressure homogenization led to several samples of various and controlled molar masses. The measure of their intrinsic viscosities permitted the determination of the relationship of Mark?CHouwink?CSakurada.     

Total Synthesis of (−)‐Zampanolide and Structure–Activity Relationship Studies on (−)‐Dactylolide Derivatives

A new total synthesis of the marine macrolide (?)‐zampanolide ( 1 ) and the structurally and stereochemically related non‐natural levorotatory enantiomer of (+)‐dactylolide ( 2 ), that is, ent‐ 2 , has been developed. The synthesis features a high‐yielding, selective intramolecular Horner–Wadsworth–Emmons (HWE) reaction to close the 20‐membered macrolactone ring of 1 and ent‐ 2 . The β‐keto phosphonate/aldehyde precursor for the ring‐closure reaction was obtained by esterification of a ω‐diethylphosphono carboxylic acid fragment and a secondary alcohol fragment incorporating the THP ring that is embedded in the macrocyclic core structure of 1 and ent‐ 2 . THP ring formation was accomplished through a segment coupling Prins‐type cyclization. Employing the same overall strategy, 13‐desmethylene‐ent‐ 2 as well as the monocyclic desTHP derivatives of 1 and ent‐ 2 were prepared. Synthetic 1 inhibited human cancer cell growth in vitro with nM IC₅₀ values, while ent‐ 2 , which lacks the diene‐containing hemiaminal‐linked side chain of 1 , is 25‐ to 260‐fold less active. 13‐Desmethylene‐ent‐ 2 as well as the reduced versions of ent‐ 2 and 13‐desmethylene‐ent‐ 2 all showed similar cellular activity as ent‐ 2 itself. The same activity level was attained by the monocyclic desTHP derivative of 1 . Oxidation of the aldehyde functionality of ent‐ 2 gave a carboxylic acid that was converted into the corresponding N‐hexyl amide. The latter showed only μM antiproliferative activity, thus being several hundred‐fold less potent than 1 .     

A very efficient,copper-free palladium catalyst for the Sonogashira reaction with aryl halides

The new complex [Pd[t-Bu2PCH2N(CH2Ph)CH2P t-Bu2](OAc)2] is a very efficient catalyst for the Sonogashira cross-coupling reaction of aryl halides with acetylenes at room temperature, without co-catalyst.     

FeCp]+-induced hexafunctionalization of hexamethylbenzene with dendrons for the direct synthesis of redox-active iron-centered metallodendrimers

Phenol tri- and nonaallyl dendrons (3 and 7, respectively) were functionalized at the focal position to give the new triallyl dendrons 4 and 6 and the nonaallyl dendrons 11 and 13 that contain a iodoalkyl or a bromobenzyl termini. All these dendrons were used for the [FeCp]+-induced hexafunctionalization of hexamethylbenzene in [FeCp(eta6-C6Me6)][PF6] (1) under mild conditions in the presence of KOH. These reactions directly yielded the 18-allyl and 54-allyl dendrimers 9, 10, and 14 with a [FeCp(eta6-arene)]+ unit located at the dendrimer core. Cyclic voltammetry studies were recorded in THF and DMF with these metallodendrimers and compared with those of analogous dendrimers or complexes of smaller size that contain a [FeCp(eta6-arene)]+ unit at the core. The decreased rate of heterogeneous electron transfer when the dendritic size increases first disclosed by Diederich and Gross is confirmed. The variation of the redox potential of the Fe(II/I) redox system with increasing dendritic size is negligible even in a solvent of high dielectric constant such as DMF. This trend is attributed to fact that the involved "redox" orbital is buried on the metal center, well protected by the shell of alkyl chains (electron-reservoir nature), unlike in ferrocene. The chemical irreversibility increases in THF as the dendrimer size increases, due to more facile ligand substitution with THF at the 19-electron level when the chain bulk increases.     

Tuning the electronic structure of octahedral iron complexes [FeL(X)] (L = 1-alkyl-4,7-bis(4-tert-butyl-2-mercaptobenzyl)-1,4,7-triazacyclononane,X = Cl,CH(3)O,CN, NO). The S = 1/2 <==>3/2 Spin equilibrium of [FeL(Pr)(NO)

Two new pentadentate, pendent arm macrocyclic ligands of the type 1-alkyl-4,7-bis(4-tert-butyl-2-mercaptobenzyl)-1,4,7-triazacyclononane where alkyl represents an isopropyl, (L(Pr))(2-), or an ethyl group, (L(Et))(2-), have been synthesized. It is shown that they bind strongly to ferric ions generating six-coordinate species of the type [Fe(L(alk))X]. The ground state of these complexes is governed by the nature of the sixth ligand, X: [Fe(III)(L(Et))Cl] (2) possesses an S = 5/2 ground state as do [Fe(III)(L(Et))(OCH(3))] (3) and [Fe(III)(L(Pr))(OCH(3))] (4). In contrast, the cyano complexes [Fe(III)(L(Et))(CN)] (5) and [Fe(III)(L(Pr))(CN)] (6) are low spin ferric species (S = 1/2). The octahedral [FeNO](7) nitrosyl complex [Fe(L(Pr))(NO)] (7) displays spin equilibrium behavior S = 1/2<==>S = (3)/(2) in the solid state. Complexes [Zn(L(Pr))] (1), 4.CH(3)OH, 5.0.5toluene.CH(2)Cl(2), and 7.2.5CH(2)Cl(2) have been structurally characterized by low-temperature (100 K) X-ray crystallography. All iron complexes have been carefully studied by zero- and applied-field M?ssbauer spectroscopy. In addition, Sellmann's complexes [Fe(pyS(4))(NO)](0/1+) and [Fe(pyS(4))X] (X = PR(3), CO, SR(2)) have been studied by EPR and M?ssbauer spectroscopies and DFT calculations (pyS(4) = 2,6-bis(2-mercaptophenylthiomethyl)pyridine(2-)). It is concluded that the electronic structure of 7 with an S = 1/2 ground state is low spin ferrous (S(Fe) = 0) with a coordinated neutral NO radical (Fe(II)-NO) whereas the S = 3/2 state corresponds to a high spin ferric (S(Fe) = 5/2) antiferromagnetically coupled to an NO(-) anion (S = 1). The S = 1/2<==>S = 3/2 equilibrium is then that of valence tautomers rather than that of a simple high spin<==>low spin crossover.     

Structure and properties of hydrophobically end-capped poly(ethylene oxide) solutions in the presence of monovalent and divalent cations

Hydrophobically modified poly(ethylene oxide), HMPEO, was studied in concentrated salt solutions. The influence of salts was compared to the effect of temperature on poly(ethylene oxide), PEO. As expected, the addition of monovalent cations (Na(+), K(+)) has the same effect as an increase in temperature in agreement with the thermodynamic properties of PEO: a decrease in solubility, micelle size, and viscosity was observed. Moreover, the intensity of neutron scattering peaks (characteristic of the semi-dilute solutions of these associative polymers) increases due to the collapse of PEO coronae in micelles. Very peculiar behavior was observed in the presence of divalent cations (Ca(2+), Mg(2+)): larger micelle aggregates and higher viscosities, relaxation times, and activation energies were observed by dynamic rheology. This behavior is attributed to interactions between divalent cations and oxygen in PEO backbones close to the micelle core, which may reinforce intermicellar bridges.     

Synthesis of methylenedioxy-bearing 1-aryl-3-carboxylisoquinolines using a modified Ritter reaction procedure

This paper describes original approaches aimed at the preparation of electron-rich 1-aryl-3-carboxylisoquinolines. Our first attempt led to an efficient preparation of 1-hydroxyisoquinoline-3-carboxylic acid methyl ester starting from bromophthalide via a rearrangement of 2-acetylamino-2-(3-oxo-1,3-dihydroisobenzofuran-1-yl)-malonic acid dimethyl ester. However, as its eventual application to the synthesis of methylenedioxy-bearing substrates seemed rather long, a second approach involving an extension of the Ritter reaction to safrole was devised. We thus report that, under proper experimental settings, the use of 54% tetrafluoroboric acid in ether enables a Ritter reaction between safrole and 3,4,5-trimethoxybenzonitrile yielding 17% of 7-methyl-5-(3,4,5-trimethoxyphenyl)-7,8-dihydro-[1,3]dioxolo[4,5-g]isoquinoline. This acidic reagent avoids the extensive decomposition seen when using the classical Ritter reaction conditions (i.e.: concentrated sulfuric acid). Further chemical transformations of this methyl-bearing dihydroisoquinoline led to the methylenedioxy-bearing 1-aryl-3-carboxylisoquinoline. These derivatives are related to the peripheral benzodiazepine receptor ligand PK 11195 as well as falcipain-2 inhibitors and other potential antitumor agents.