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.     

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.     

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.     

Highly effective DNA photocleavage by novel "rigid" Ru(bpy)(3)-4-nitro- and -4-amino-1,8-naphthalimide conjugates

The synthesis of the two novel 1,8-naphthalimideruthenium conjugates Ru-Nap-NO(2) and Ru-Nap-NH(2) and their photophysical evaluation upon interaction with DNA is reported. Significant changes were seen in both the absorption and emission spectra upon interaction of both conjugates with DNA, from which large binding constants were determined. Moreover, highly efficient DNA cleavage was observed upon irradiation for 5 min, during which supercoiled DNA was converted to nicked and linear DNA by Ru-Nap-NH(2).     

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     

Light-driven OR and XOR programmable chemical logic gates

Photoelectrodes made of nanocrystalline titanium dioxide modified with various pentacyanoferrates exhibit unique photoelectrochemical properties; photocurrent direction can be switched from anodic to cathodic and vice versa upon changes in photoelectrode potential and incident light wavelength (PhotoElectrochemical Photocurrent Switching, PEPS effect). At certain potentials, anodic photocurrent generated upon UV irradiation has the same intensity as the cathodic photocurrent generated upon visible irradiation. Under these conditions, simultaneous irradiation with UV and visible light results in compensation of anodic and cathodic photocurrents, and zero net photocurrent is observed. This process can be used for construction of unique light-driven chemical logic gates.     

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.     

Scattering of light from assemblies of oriented rods

The scattering patterns are calculated from anisotropic rods having an arbitrary angle of the polarizability axis with respect to the rod axis. The effect of a distribution of orientation of the rods is explored. This leads to a change in scattering patterns produced by orienting the rods upon stretching the sample. The scattering patterns are affected by the relationship between the refractive indexes of the rods and that of the surroundings. The influence of the optic axis orientation angle changing upon orienting the rods is explored. Theoretical patterns are compared with experimental ones obtained upon stretching polytetrafluoroethylene (PTFE) films.     

Deuterium kinetic isotope effects in microsolvated gas-phase E2 reactions: Methanol and ethanol as solvents

The gas-phase reactions of F(-)(CH(3)OH) and F(-)(C(2)H(5)OH) with t-butyl bromide have been investigated to explore the effect of the solvent on the E2 transition state. Kinetic isotope effects (KIEs) were measured using a flowing afterglow-selected ion flow tube (FA-SIFT) mass spectrometer upon deuteration of both the alkyl halide and the alcohol. Kinetic isotope effects are significantly more pronounced than those previously observed for similar reactions of F(-)(H(2)O) with t-butyl halides. KIEs for the reaction of F(-)(CH(3)OH) with t-butyl bromide are 2.10 upon deuteration of the neutral reagent and 0.74 upon deuteration of the solvent. KIEs for the reaction of F(-)(C(2)H(5)OH) with t-butyl bromide are 3.84 upon deuteration of the neutral reagent and 0.66 upon deuteration of the solvent. The magnitude of these effects is discussed in terms of transition-state looseness. Additionally, deuteration of the neutral regent and deuteration of the solvent do not produce completely separable isotope effects, which is likely due to a crowded transition state. These results are compared to our previous work on S(N)2 and E2 solvated systems.     

The photoionization detector : Theory, performance and application as a low-level monitor of oil vapour

The photoionization detector (PID) is being developed for the detection of low centrations of oil in the carbon dioxide coolant of gas-cooled reactors. In this paper the theoretical response of the PID is derived and compared with its practical response and with that of the flame ionization detector (FID). The PID response is shown to depend primarily upon ionization potential and molar concentration unlike FID response which depends upon carbon number. The dependence of PID response upon the carrier gas used is discussed and the citerion of detection using the PID to measure oil vapour in carbon dioxide was found to be 2ppb.     

Photochemical reduction of n-tosylsulfilimines with thiolate anion

The reaction between N-tosyldiarylsulfilimines and p-toluenethiolate anion did not take place in the dark even upon heating up to 62° but proceeded smoothly upon irradiation with visible light in DMF at room temperature, affording S-N bond cleavage products.     

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.     

Photochemical transformations—VIII The isomerization of Δ-bicyclo[2.2.1]heptadiene to quadricyclo[2.2.1.0·0]heptane (quadricyclene)

Δ^2,5-Bicyclo[2.2.1]heptadiene (III) upon ultraviolet irradiation was isomerized in 67 per cent yield to the valence tautomeric quadricyclene (IV) which, in turn, upon being heated, reformed III. The reactions of IV with hydrogen, with acetic acid and with bromine were studied.     

Highly selective bioflocculants for extraction of ultradispersed gold particles

It is established that, upon contact with an iron-containing electrolyte, Chlorella vulg. cells are capable of reducing iron and forming nanosized ferromagnetic particles in their biomass. It is revealed that colloidal gold is efficiently extracted from sols upon bioflocculation with such cell culture.     

Regiochemistry of copper(I)-mediated cyclization reactions of halo-dienamides

Reaction of 2-substituted dienamides with catalytic amounts of copper halide/tripyridylamine (TPA) furnishes either 5-exo or 6-endo products with the outcome dependent upon the radical initiating unit. Reaction of 3-substituted dienamides produces beta-lactams via a 4-exo cyclization with termination of the reaction occurring via either halogen atom transfer, trapping with oxygen, elimination, or radical-radical coupling depending upon the diene.     

Conformational changes of high-molecular-weight DNA upon binding to noble metal nanoparticles in solution

Changes in the secondary and tertiary structure of DNA upon binding to silver, gold, and palladium nanoparticles (NPs) in solution were studied using UV spectroscopy, viscometry, dynamic light scattering, flow birefringence, and atomic force microscopy. A method for preparation of NP bioconjugates with DNA was developed. The enhancement of optical anisotropy of the macromolecule upon its contacts with metal NPs was detected. The effect of the formed structures on the persistence length of DNA and on the volume effects in the system was analyzed. A mechanism of NP formation upon the reduction of DNA-bound metal ions was proposed.

     

Fluorescent ratiometry of tetrahomodioxacalix[4]arene pyrenylamides upon cation complexation

[structure: see text] C-1,2-alternate tetrahomodioxacalix[4]arene pyreneamides were synthesized. Pb(2+) coordination gave a quenched monomer and excimer fluorescence emission, while upon Ca(2+) ion binding, the receptor provides an enhanced excimer and declined monomer emission with ratiometric response. The excimer emission spectra changes are rationalized by frontier molecular orbitals that the effective Py-Py interaction induces emission intensity increases upon Ca(2+) ion complexation, whereas there is no such interaction observed upon Pb(2+) binding.     

Interference of elements upon extraction by oxygen-containing extractants: Calculating the distribution coefficients

The extraction of tellurium (IV), tin (IV), and indium (III) by aliphatic alcohols and ketones from hydrochloric acid solutions was studied both upon the individual separation of elements and upon their simultaneous extraction. Electroconductivities of the extracts were measured and, using these data, the dissociation constants of the extracted metal-halogen acids in organic solvents were calculated by Fuoss-Krauss method. A method for calculating the distribution coefficients of elements upon their simultaneous extraction by hydrate-solvate and mixed solvate and hydrate-solvate mechanisms is proposed. It is shown that the calculated distribution coefficients are in good agreement with the experimental data.     

Dissipative structures formed in the layer of magnetic suspension upon the action of rotating elliptically polarized magnetic field

Structural transformations that take place in an ensemble of spherical particles suspended in a liquid layer with finite thickness are studied upon the action of rotating elliptically polarized magnetic field with the polarization plane perpendicular to the plane layer. Results of physical and numerical studies of the transformation of dissipative structure upon variations in the polarization ellipse of magnetic field are reported.