Structural variations in a family of orthodialkoxyarenes organogelators

A series of low mass organic gelators (LMOGS) 1 to 6 whose chemical structures have in common an orthodialkoxyarene feature was prepared in order to compare the shape of their fibrillar network as investigated by small-angle neutron scattering (SANS) experiments. All members of the family exhibit a pronounced tendency to bundle formation by merging isolated fibers in extended packets of average diameter >500 A. Variations of the 2D packing symmetry are observed from hexagonal to square orderings with close derivatives of the reference member 2,3-didecyloxyanthracene (DDOA). Networks in which the fraction of isolated fibers is significant enough to allow for their SANS identification are those for 6,7-dichloro-2,3-didecyloxyanthracene (Cl(2)DDOA) and 2,3-dodecyloxy-9,10-anthraquinone (5). For this latter, the monodispersity of the cross-sections (thickness=74 A) is remarkable and the rectangular shape (b/a approximately 0.12) accounts for a merging mechanism into anisotropic bundles (ribbons).     

Effect of temperature on the acid-base properties of the alumina surface: microcalorimetry and acid-base titration experiments

Sorption reactions on natural or synthetic materials that can attenuate the migration of pollutants in the geosphere could be affected by temperature variations. Nevertheless, most of the theoretical models describing sorption reactions are at 25 degrees C. To check these models at different temperatures, experimental data such as the enthalpies of sorption are thus required. Highly sensitive microcalorimeters can now be used to determine the heat effects accompanying the sorption of radionuclides on oxide-water interfaces, but enthalpies of sorption cannot be extracted from microcalorimetric data without a clear knowledge of the thermodynamics of protonation and deprotonation of the oxide surface. However, the values reported in the literature show large discrepancies and one must conclude that, amazingly, this fundamental problem of proton binding is not yet resolved. We have thus undertaken to measure by titration microcalorimetry the heat effects accompanying proton exchange at the alumina-water interface at 25 degrees C. Based on (i) the surface sites speciation provided by a surface complexation model (built from acid-base titrations at 25 degrees C) and (ii) results of the microcalorimetric experiments, calculations have been made to extract the enthalpic variations associated respectively to first and second deprotonation of the alumina surface. Values obtained are deltaH1 = 80+/-10 kJ mol(-1) and deltaH2 = 5+/-3 kJ mol(-1). In a second step, these enthalpy values were used to calculate the alumina surface acidity constants at 50 degrees C via the van't Hoff equation. Then a theoretical titration curve at 50 degrees C was calculated and compared to the experimental alumina surface titration curve. Good agreement between the predicted acid-base titration curve and the experimental one was observed.     

Inclusion complexes of EMPO derivatives with 2,6-di-O-methyl-beta-cyclodextrin: synthesis, NMR and EPR investigations for enhanced superoxide detection

The free radical trapping properties of eight 5-alkoxycarbonyl-5-methyl-1-pyrroline N-oxide (EMPO) type nitrones and those of 5,5-dimethyl-1-pyrroline N-oxide (DMPO) were evaluated for trapping of superoxide anion radicals in the presence of 2,6-di-O-methyl-beta-cyclodextrin (DM-beta-CD). (1)H-NMR titrations were performed to determine both stoichiometries and binding constants for the diamagnetic nitrone-DM-beta-CD equilibria. EPR titrations were then performed and analyzed using a two-dimensional EPR simulation program affording 1 : 1 and 1 : 2 stoichiometries for the nitroxide spin adducts with DM-beta-CD and the associated binding constants after spin trapping. The nitroxide spin adducts associate more strongly with DM-beta-CD than the nitrones. The ability of the nitrones to trap superoxide, the enhancement of the EPR signal intensity and the supramolecular protection by DM-beta-CD against sodium L-ascorbate reduction were evaluated.     

Chiral spiro Cu(I) complexes. Supramolecular stereocontrol and isomerisation dynamics by the use of TRISPHAT anions

Association of enantiopure TRISPHAT anion (1) with chiral spiro [Cu(LL')2] complexes (LL' = 2-R-phen, 2, 6-R-bpy, 3, and 2-iminopyridine, 4) leads to an efficient NMR enantiodifferentiation. Variable temperature 1H NMR spectroscopy has been used to determine the isomerisation kinetics of these pseudo-tetrahedral complexes and to evaluate their configurational stability; the latter depending on the structure of the diimine ligands. In the case of the 2-anthracenyl-phen derivative, a decent level of supramolecular stereocontrol was noted (d.e. up to 45%); the configuration of the complex being determined by electronic circular dichroism (ECD).     

Liquid-column sustainment driven by acoustic wave guiding

We report on the formation and sustainment of liquid columns with aspect ratios much larger than the value at the onset of the Rayleigh-Plateau instability. This is achieved by using the passive feedback of the radiation pressure applied on the column surface by an acoustic beam injected at the upper end of the column and guided along it. We develop an analytical model that describes the coupling between the acoustic wave guiding and the balance between acoustic and capillary surface forces exerted on the column surface and find a satisfactory agreement with the experiment.     

Absolute rate constants for some intermolecular reactions of alpha-aminoalkylperoxyl radicals. Comparison with alkylperoxyls

Seven alpha-aminoalkylperoxyl radicals have been generated by 355 nm laser flash photolysis (LFP) of oxygen-saturated di-tert-butyl peroxide containing mono-, di-, and trialkylamines and a dialkylarylamine. All these peroxyls possess absorptions in the near-UV (strongest for the trialkylamine-derived peroxyls) which permits direct monitoring of the kinetics of their reactions with many substrates. The measured rate constants for hydrogen atom abstraction from some phenols and oxygen atom transfer to triphenylphosphine demonstrated that all seven alpha-aminoalkylperoxyls have similar reactivities toward each specific substrate. More importantly, a comparison with literature data for alkylperoxyls shows that alpha-aminoalkylperoxyls and these alkylperoxyls have essentially the same reactivities. The combination of LFP and alkylamines provides a quick, reliable method for determining absolute rate constants for alkylperoxyl radical reactions, an otherwise laborious task.     

Iron(II) carboxylate complexes based on a tetraimidazole ligand as models of the photosynthetic non-heme ferrous sites: synthesis, crystal structure, and Mössbauer and magnetic studies

The preparations, X-ray structures, and detailed physical characterization are presented for new complexes involving an iron(II) center, a tetraimidazole ligand (TIM), and different carboxylates. [Fe(TIM)(C(6)H(5)CH(2)CO(2))](ClO(4)) (1) crystallizes in the Pbca space group with a = 10.8947(13), b = 20.343(2), and c = 22.833(3) A, Z = 8, and V = 5060.6(11) A(3). [Fe(TIM)(CH(3)CO(2))](ClO(4)) (2) crystallizes in the Ia space group with a = 17.117(2), b = 10.3358(12), and c = 25.658(3) A, beta = 90.301(13) degrees, Z = 8, and V = 4539.5(9) A(3). In both structures, the iron(II) is hexacoordinated to the four N(imidazole) donors of the TIM ligand and the two O donors of a bidentate carboxylate. The flexibility of the carboxylate bidentate coordination, symmetrical or more or less asymmetrical, associated with the steric demand of the TIM ligand results in a remarkable versatility of the Fe(II)N(4)O(2) coordination geometry. The diversity in carboxylate bidentate coordination modes has allowed us to clearly show the importance of the structural and electronic effects, through IR and M?ssbauer spectroscopy, of this apparently tenuous carboxylate shift. Comparison of the structural and M?ssbauer properties of these complexes with the non-heme ferrous site of photosynthetic systems (i) shows that the metric parameters of site 2b, including the symmetrically chelated bidentate carboxylate, are closer to those of the non-heme ferrous site in the bacterial reaction centers of Rhodopseudomonas viridis and R. sphaeroides and (ii) suggests that the ligand environment of the non-heme ferrous center of PS 2 is close to the axially distorted octahedral symmetry resulting from an asymmetrical bidentate coordination of the -CO(2) motif, as in complex 1.     

The Great Myths of Polymer Melt Rheology,Part I: Comparison of Experiment and Current Theory

Abstract

Star polymers consisting of poly(?‐caprolactone), (PCL), grafted onto third generation dendrimer, which had hyperbranched and dendron cores, were studied by polarized light microscopy together with reference linear PCL. The degree of polymerization of the PCL arms in the star polymers ranged between 14 and 81. The star polymers exhibited a greater tendency than the linear polymers to form spherulites. It is suggested that the preference of the star polymers for forming spherulites is due to the presence of amorphous material—dendritic cores and PCL cilia—between crystal lamellae that generates the necessary pressure to force the lamellae to diverge at lamellar branch points. The linear growth rate data followed a single crystallization regime. The fold surface free energy was higher for the star polymers than for their linear analogs. It is proposed that the presence of the large and rigid dendritic cores on the fold surfaces of the star polymer crystals increases the fold surface energy.     

Synthesis and electrochemical behavior of Li2CoSiO4 cathode with pyrrolidinium-based ionic liquid electrolyte for lithium ion batteries

Li₂CoSiO₄, a silicate olivine cathode for lithium rechargeable batteries, is synthesized for the first time by sol–gel method using polyacrylic acid (PAA) as the chelating agent. Coupled thermal and vibrational analysis of the gel and also the X-ray diffraction pattern confirms the formation of the sample at 800 °C. 1-Butyl-1-methyl pyrrolidinium bis(trifluoromethanesulfonyl)imide (BMPyTFSI) solutions of lithium bis(trifuloromethansulfonyl)imide (LiTFSI) having a concentration of 0.2 mol kg^?1 is used as electrolyte. The electrochemical stability window of this electrolyte is found to be >5 V by linear sweep voltammetry technique. The compatibility of Li₂CoSiO₄ with 0.2 mol kg^?1 LiTFSI-BMPyTFSI electrolyte is tested by charge–discharge cycles which show charging and discharging capacities of about 204 and 32 mAh g^?1, respectively, in the first cycle.