The complex rheological behavior of an aqueous cationic surfactant solution investigated in a Couette-type viscometer

In this paper the behavior of an aqueous surfactant solution in a rotational Couette viscometer is investigated. It is shown that this behavior depends strongly upon time, upon the way in which the flow curve is obtained (with increasing or decreasing shear rate), upon the temperature, and upon the concentration of the solution. Furthermore, the results also reveal a pronounced dependence upon the size of the actual measuring system used. It is shown that the slip-velocity concept is not applicable to explain this dependence.     

A comparative study of the pyrolytic and electron impact-induced fragmentations of 4-phenylbutanoic acid and some analogues

By use of deuterium labelling it is shown that the mechanisms of fragmentation of the title compounds upon Curie-point pyrolysis and electron impact are essentially different. For example, the pyrolytic expulsion of water from 4-phenylbutanoic acid is a 1,2 eliminations, whereas upon electron impact water is expelled via a 1,4 elimination; the generation of styrene from this acid proceeds via a concerted mechanism upon pyrolysis, but via a stepwise mechanism upon electron impact.     

On the role of nuclear motions in electron and excitation transfer rates: Importance of transfer-integral dependence upon nuclear coordinate

The role of nuclear degrees of freedom in modifying the electron or exciton transfer rates between molecules is investigated. In addition to the usual Franck-Condon overlap factors which arise from the overlaps of initial and final vibrational states, we discuss a dependence of the transfer integral upon nuclear motions, a dependence which has been often cited, but nearly always ignored, in the usual dynamical theories of transfer processes. We show, within a Bom-Oppenheimer treatment, that the transfer integral dependence upon librational, rotational and vibrational modes can profoundly change both the rate itself and its functional dependences (upon temperature, upon orientation, etc.). Using a simple cosine form for the dependence of the transfer integral upon the modifying nuclear mode and a simple displaced-oscillator transformation, we obtain a closed-form solution for the transfer rate, which includes a new overlap factor arising from the dependence of the transfer integral upon nuclear coordinates. Some general remarks about the role of this dependence are made, and applications to particular transfer systems are briefly discussed.     

Pyrolysis mass spectrometry of methionine

The mechanisms of some fragmentation of methionine upon Curie-point pyrolysis have been studied by the use of deuterium labelling. They lead to products having the same nominal mass but essentially different elemental compositions compared with ions generated by electron impact on methionine. For exaple, upon pyrolysis the product with mass 116 is due to a 1,2 elimination of hydroxylamine from the title compound, whereas upon electron impact the ion with m/e 116 is generated by successive loss of a molecule of water and of a methyl radical from the molecular ion; the generated of product m/e 101 proceeds via successive loss of a molecule of water, carbon monoxide and of hydrogen upon pyrolysis, but via a one-step elimination of methanethiol upon electron impact. No evidence has been found for a diketopiperazine formation by a bimolecular process upon pyrolysis, although this type of reaction is well known for α-amino acids.     

Changes in the isotropic shielding of the 17O nucleus upon torsion in terminal oxygen systems: a computational study on their origin

We are presenting a computational study on the isotropic shielding, charge, and orbital contributions to the shielding of oxygen in benzaldehydes (Ar-CHO), nitrobenzenes (Ar-NO2), phenyl isocyanates (Ar-NCO), anilides (Ar-NHCOCH3), and N-sulfinylamines (Ar-NSO). In particular, changes upon ortho substitution of the aromatic ring and upon torsion of the unsubstituted parent molecules are examined. The experimentally observed changes in (17)O chemical shift, be they upfield or downfield, upon substitution by ortho-alkyl groups are reproduced well by the calculations. Relaxed torsional scans of the parent systems reveal that (a) charges change as expected from resonance arguments and (b) changes in isotropic shielding are monotonic and in line with changes upon substitution, with N-sulfinylaniline as an exception. In general, the changes in isotropic shieldings are explained in terms of changes in molecular orbitals, their energies, and relative alignments, whose mixing is magnetically active. Thus, for example, the observed deshielding of (17)O upon methyl substitution and upon torsion of benzaldehyde is mainly caused by a contribution from the pi-type oxygen lone pair, yet how these contributions change is fundamentally different. As a consequence, the experimentally observed downfield shift upon methyl substitution cannot be interpreted to imply a change in torsion angle between the phenyl ring and the aldehyde group. For N-sulfinylaniline, the consecutive downfield shifts upon methyl and tert-butyl substitution and the associated changes in torsion angle are in contrast to the 45 degrees maximum in isotropic shielding that is determined from a relaxed torsional scan.     

Intramolecular photocyclization of 1-(trimethylsilyl)-1,5-hexadien-3-ones

An influence upon the regiochemistry of cyclization due to a 1-trimethylsilyl substituent is indicated upon comparison of the photochemistry of 4a,b and their carbon analogs 5a,b.     

Reversible C-C bond formation: solid state structure of the aldol-like addition product of adamantanone to a 1,5-diazapentadienyllithium,and its solution state retro-aldol dissociation

Analysis of crystals of the lithium complex of the tripodal ligand formed upon addition of adamantanone to a 1,5 diazapentadienyllithium complex reveals a long C-C bond which ruptures upon dissolution in non-co-ordinating solvents.     

Peptide-polymer bioconjugates: hybrid block copolymers generated via living radical polymerizations from resin-supported peptides

A novel strategy for the preparation of peptidic-synthetic bioconjugate block copolymers is based upon sequential condensation and living radical addition polymerizations, each performed upon a solid support.     

Elaeocarpus Alkaloids. The Synthesis of dl-Elaeokanine-A and dl-Elaeokanine-C.

The synthesis of dl-elaeokanine-A and dl-elaeokanine-C is described by an approach which utilizes a nitrone cyclo-addition to generate a β-aminoketone, which upon annulation produces one or the other of the title alkaloids depending upon conditions.     

A backflow effect in smectic C liquid crystals

This paper discusses the influence upon a smectic C liquid crystal cell of backflow induced by the relaxation of alignment following the removal of a strong electric or magnetic field. Our study, based upon a recently proposed continuum theory, concentrates upon the homeotropic configuration in which the smectic layers are parallel to the boundary plates, but some consideration is also given to the bookshelf geometry. Although the governing equations prove to be rather complex, some progress is possible analytically by repeating an approximation made in the corresponding problem for a nematic.     

Fluorescence enhancement of coordination polymeric gel

Instant hydrogelation of coumarin-derivatized glycine has been demonstrated in the absence of long-chain hydrophobic groups upon formation of a zinc(ii) coordination polymer, which exhibits fluorescence enhancement upon gelation.     

Multilayered assemblies composed of brilliant yellow and poly(allylamine) for an optical pH sensor.

Multilayered thin films containing poly(allylamine) (PAA) and brilliant yellow (BY) were prepared on a quartz slide by a layer-by-layer (LBL) deposition technique. The UV-visible spectra of the PAA/BY films were sufficiently changed depending upon the pH value of the solution in which the film was immersed. The response of the PAA/BY films was very fast (within a second) upon pH change from 9.0 to 5.0, while the response time was ca. 100 s upon pH change from 5.0 to 9.0.     

Structural effects upon competitive decomposition pathways of Thiosulfoxide intermediates

Mixtures of sulfides and disulfides are obtained upon reaction of boron trisulfide with a series of allyl aryl suit oxides, with the product distributions dependent upon the structures of the intermediate thiosulfoxides.     

Alkanethiolate self-assembled monolayers as functional spacers to resist protein adsorption upon Au-coated nerve microelectrode

Alkanethiolate self-assembled monolayers (SAMs) of varied chain lengths were adsorbed upon Au-coated nerve microelectrodes and employed as protein-resistant spacers. The microelectrode spiraled as a cuff type can be used for restoring motor function via electrical stimulation on the peripheral nerve system; however, an increase of electrode impedance might occur during implantation. In this work, a thin-film SAMs treatment upon Au/polyimide (PI) surface of the microelectrode provided a hydrophobic characteristic, which retarded protein adsorption at the initial stage and subsequent pileup (or thickening) process. The protein-resistant effect exhibited comparable SAMs of different chain lengths adsorbed upon Au/PI surfaces. The increase of electrode impedance as a function of protein deposition time was mainly correlated with the addition of reactance that was associated with the pileup thickness of the deposited protein. Particularly, the SAMs-modified surface was capable to detach a significant portion of the accumulated protein from the protein-deposited SAMs/Au/PI, whereas the protein-deposited layers exhibited firm adhesion upon Au/PI surface. It is therefore very promising to apply thin-film SAMs adsorbed upon Au-coated surface for bioinvasive devices that have the need of functional electrical stimulations or sensing nerve signals during chronic implantation.     

Diffusion coefficients of small molecules at the gas-solid interface as measured by the nuclear magnetic resonance pulsed field gradient method

The nuclear magnetic resonance pulsed field gradient method has been used to measure the diffusion coefficients for some low molecular weight compounds adsorbed at the gas-solid interface. The systems studied are ammonia adsorbed upon graphite, methane adsorbed upon graphite, neopentane adsorbed upon graphite and neopentane adsorbed upon titanium dioxide. Results are compared with values obtained from quasi-elastic neutron scattering where available.     

Adaptation of Dynamic Covalent Systems of Imine Constituents to Medium Change by Component Redistribution under Reversible Phase Separation

A dynamic covalent library of interconverting imine constituents, dissolved in an acetonitrile/water mixture, undergoes constitutional reorganization upon phase separation induced by a physical stimulus (heat) or a chemical effector (inorganic salt, carbohydrate, organic solvent). The process has been made reversible, regenerating the initial library upon phase reunification. It represents the behavior of a dynamic covalent library upon reversible phase separation and its adaptation to a phase change, with up-regulation in each phase of the fittest constituents by component selection. Finally, the system exemplifies the splitting of a 2D (square) constitutional dynamic network into a 3D (cube) one.     

Hyperbranched‐upon‐dendritic macromolecules as unimolecular hosts for controlled release

Novel amphiphilic hyperbranched‐upon‐dendritic polymers with a dendritic polyester core, a linear poly(ε‐caprolactone) (PCL) inner shell, and a hyperbranched polyglycerol outer shell have been prepared. The structures of the hyperbranched‐upon‐dendritic polymers were characterized by using NMR spectra. The critical aggregating concentrations (CACs) of those amphiphilic hyperbranched‐upon‐dendritic polymers were measured by using pyrene as the polarity probe. To study the encapsulation performances of those hyperbranched‐upon‐dendritic polymers as unimolecular hosts, inter‐molecular encapsulation was carefully prevented by controlling the host concentrations below their CACs and by washing with good organic solvents. The study on encapsulation of two model guest molecules, pyrene and indomethacin, was performed. The amounts of encapsulated molecules were dependent mainly on the size of inner linear shells. About three pyrene molecules or five indomethacin molecules were encapsulated in hyperbranched‐upon‐dendritic polymers with average PCL repeating units of two but different hyperbranched polyglycerol outer shells, whereas about five pyrene molecules or about 12 indomethacin molecules were encapsulated in those with PCL repeating units of nine. The encapsulated molecules could be released in a controlled manner. Thus, the hyperbranched‐upon‐dendritic polymers could be used as unimolecular nanocarriers with controllable molecular encapsulation dosage for controlled release. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 4013–4019, 2010     

Temperature-triggered fusion of vesicles composed of right-handed and left-handed amphiphilic helical peptides

Vesicles prepared from a mixture of (Sar)(25)-b-(L-Leu-Aib)(6) (SLL) and (Sar)(25)-b-(D-Leu-Aib)(6) (SDL) fused with themselves upon heating to 90 °C. The vesicles also fused with (Sar)(28)-b-(L-Leu-Aib)(8) vesicles upon heating to 90 °C. The temperature-triggered fusion was due to the phase transition of the mixed membrane of SLL and SDL at 90 °C and should be driven by the bending energy stored in the stereocomplex membrane upon taking a vesicular structure.     

Stress relaxation upon cessation of steady flow and the overshoot effect of polymer solutions

The basis for obtaining the steady-state compliance from stress relaxation upon cessation of steady flow (SRUCSF) data is derived. Measurements on three polymer solutions of differing molecular weight, polydispersity, and degree of entanglement coupling show good agreement between results from SRUCSF and creep-recovery experiments in both linear and nonlinear viscoelastic regions. The stress overshoot phenomenon is interpreted in terms of a change in entanglement spacing upon imposition of a shearing field. The phenomenon is analyzed in terms of a relaxation time for re-entanglement, which is found to be much longer than the relaxation time of the shear stress upon cessation of steady flow.     

Pd/C catalysts. Deactivation and behavior of supported Pd particles upon heating

Deactivation of Pd/C catalysts upon heating in H₂ has been studied as a function of support surface composition. The behavior of Pd particles on a chosen part of surface upon sample heating in an electron microscope chamber has been investigated.