Pressure effects on lipidic direct phases: the dodecyl trimethyl ammonium chloride-water system

The direct lyotropic polymorphism of dodecyltrimethylammonium chloride (DTAC) was investigated by synchrotron X-ray diffraction at different water concentrations under compression up to 2 kbar, i.e., in the pressure intermediate range where interesting biophysical transformations occur and the functional characteristics of cell membranes are altered. The results show that pressure induces the transition from the hexagonal phase to the micellar Pm3n cubic phase in hydrated samples (c between 0.5 and 0.6, c being the weight concentration of lipid in the mixture) and the transition from the bicontinuous Ia3d cubic phase to the hexagonal phase in drier samples (c = 0.8). By increasing the pressure on very dry samples, a lamellar L(alpha) phase was observed to form transitorily at the Ia3d cubic-hexagonal phase transition. Phase compressibility and then the lipid and water partial molecular compressibilities were derived as a function of pressure and concentration. As a result, we assessed the very low compressibility of the hydration water within the lipid phases, and we demonstrated that the compressibility of DTAC is very dependent on pressure. Moreover, the molecular parameters of DTAC calculated in the different phases during compression confirmed that pressure induces small but continuous conformational changes, definitely different from the large changes observed in lipid molecules forming type II structures.     

Hydroxyphosphoranes tautomers of γ hydroxylated phosphoric esters - structure and acidity

Abstract

The crystal structure of the triethylammonium salts of hydroxyphosphoranes 1a and 2 was resolved by X Ray diffraction. The first one has a TBP geometry slightly deformed with the phosphorus atom at the center, and the second one is a polycylic dimer containing two TBP which present the same deformations. In both cases, the P-O^? bond lengths are short and dioxaphospholane rings planar. These two particular properties can be related to the strong Bronsted acidity of compounds 1a and 2. Effectively, the pKa of hydroxyphosphoranes 1a, 1b and 2, determined by potentiometrical titration in DMF or DMSO solutions are characteristic of strong acids.     

SYNTHESIS OF ALKYL N-CYANO-N-SUBSTITUTED CARBAMATES AND N,N-DISUBSTITUTED CYANAMIDES1

Abstract

The reactions of S,S' methyl cyanodithioimidocarbonate with potassium hydroxide in alkyl or benzyl alcohol furnished the O-alkyl and benzyl O-potassium cyanoimidocarbonates (1–5). The reaction of the potassium salts (1,3, or 4) with a 10% excess of alkyl, allyl or benzyl halides afforded the unknown titled carbamates (6–17). The reaction of 2 with 10% excess benzyl bromide or 5 with 10% excess methyl iodide gave the same product, N-benzyl-N-methyl cyanamide (18). The reactions of 2 with 10% and 55% excess allyl bromide afforded N-allyl-N-methyl cyanamide (19) and N,N-diallyl cyanamide (20), respectively. The reaction of 3 with 28% excess of allyl iodide furnished N-allyl-N-propyl cyanamide (21).

Possible mechanisms and supporting NMR, IR and mass spectra data are discussed.     

Alditols in Organophosphorus Chemistry. Synthesis of New Monomeric,Oligomeric and Bis-Spirophosphoranes

Abstract

New mono, bis and polyspirophosphoranes have been prepared condensing alditols with aminophosphines P(NR₂)₃.     

Novel Tetraspiroorthocarbonates as Successful Anti-shrinking Agents for the Photopolymerization of Epoxy Monomers

A pair of novel tetrafunctional spiroorthocarbonates (TETRASOC) was prepared in three stages. First, glycerol was reacted with tetraethyl orthocarbonate to form a pair of isomeric hemi spiroorthocarbonates (HEMI SOC-OLs) by monocyclization of glycerol. Formation of these two isomers depends on terminal or adjacent hydroxyl groups of glycerol reacting with the tetraethylorthocarbonate to form five and six-membered ring HEMI SOC-OLs. Second, the HEMI SOC-OLs were made to undergo another cyclization reaction by reacting with 1,3-propanediol, to form a pair of spiroorthocarbonates with one hydroxyl group (SOC-OL). In the third stage, the SOC-OL was used as nucleophylic reactant to displace the bromine atom of pentaerythritol bromide to form the final product TETRASOC. A volume change study was carried out to determine the efficiency of TETRASOC as an anti-shrinking additive finding that even at a low concentration of 7 mol%, it caused a 2.18% expansion of the polymeric volume of a bis epoxycyclohexane monomer (3,4-EP). Dynamic Mechanical Analysis (DMA) determined that the flexibilization induced by the TETRASOC in the polyether derived from 3,4-EP did not adversely impact the mechanical properties of the polymer.     

Photochemical Strain‐Release‐Driven Cyclobutylation of C(sp3)‐Centered Radicals

A new photoredox‐catalyzed decarboxylative radical addition approach to functionalized cyclobutanes is described. The reaction involves an unprecedented formal Giese‐type addition of C(sp³)‐centered radicals to highly strained bicyclo[1.1.0]butanes. The mild photoredox conditions, which make use of a readily available and bench stable phenyl sulfonyl bicyclo[1.1.0]butane, proved to be amenable to a diverse range of α‐amino and α‐oxy carboxylic acids, providing a concise route to 1,3‐disubstituted cyclobutanes. Furthermore, kinetic studies and DFT calculations unveiled mechanistic details on bicyclo[1.1.0]butane reactivity relative to the corresponding olefin system.     

Development of a HPTLC method to profile the phytochemicals in Allanblackia parviflora (tallow tree) kernel and seed cakes

HPTLC is a useful and practical analytical tool to characterize plant compositions. This study was focused on exploring the results of high-performance thin-layer chromatography (HPTLC) analysis, particularly as a useful tool for the authentication of Allanblackia parviflora seed and kernel cakes. Bulked samples from sixteen different Ghanaian communities were analysed by HPTLC and their fingerprints were compared. The optimum experimental conditions were established: sample weight of 2.0 g, methanol:water (80:20 v/v) as extraction solvent, 30 min extraction time and twice extraction, ethyl acetate:methanol:water (100:16.5:13.5 v/v) as mobile phase, vanillic acid as derivatisation agent and 7 min of plate heating time after derivatisation. The HPTLC profile generated from extracts across 16 communities and 157 trees was very reproducible and demonstrates the robustness of the technique in characterising the profile.

     

Modified cobalt(II) acetylacetonate complexes as catalysts for Negishi-type coupling reactions: influence of ligand electronic properties on catalyst activity

Four known electronically diverse cobalt(II) acetylacetonate derivatives were synthesized by replacement of the acetylacetonate methyl groups with combinations of tert-butyl, ethoxy, and trifluoromethyl groups in order to study the effect of catalyst electronic properties on the reaction rate and product yield of the cobalt-catalyzed reaction between haloalkenes and butylzinc iodide. Infrared spectroscopy of these compounds showed an increase in the CO stretching frequency as the ligand substituents became more electron withdrawing. These compounds, in addition to cobalt(II) acetylacetonate itself, were evaluated as catalysts for the coupling reaction between (E)-1-iodo-1-octene and butylzinc iodide to form (E)-5-dodecene. Faster reaction rates were observed and higher yields of 5-dodecene were produced when catalysts containing electron-donating ligands were employed. Side reactions, including the homocoupling of 1-iodo-1-octene to produce 7,9-hexadecadiene, were also observed under the reported reaction conditions. The rate of side-product formation was more competitive with the rate of the cross-coupling reaction when slower, electron-deficient catalysts were employed.     

Carbon dioxide reduction by mononuclear ruthenium polypyridyl complexes

New mononuclear ruthenium complexes with general formula [Ru(bid)(B)(Cl)] (bid is (1Z,3Z)-1,3-bis(pyridin-2-ylmethylene)isoindolin-2-ide; B = bidentate ligand 2,2'-bipyridine or R(2)-bpy, where R = COOEt or OMe) were synthesized and tested as precatalysts for the hydrogenative reduction of CO(2) in 2,2,2-trifluoroethanol (TFE) as solvent with added NEt(3). Significant amounts of formic acid were produced by these catalysts and a kinetic analysis based on initial rate constants was carried out. The potential mechanisms including intermediate species for these catalytic systems were investigated by means of quantum chemical calculations to gain deeper insight into the processes. The effect of electron-donating and electron-withdrawing groups on catalyst performance was studied both experimentally and theoretically.