Oligomeric carbocation-like species from protonation of chloroalkanes

The protonation of chloroethane by the strongest known solid superacid, the carborane acid H(CHB(11)Cl(11)), has been studied by quantitative IR spectroscopic methods to track mass balance and uncover previously unobserved chemistry. In the first step, an intermediate EtCl·H(CHB(11)Cl(11)) species without full proton transfer to EtCl can be observed when d(5)-deuterated chloroethane is used. It rapidly eliminates HCl (but not DCl) to form ethyl carborane, Et(CHB(11)Cl(11)), which binds a second molecule of chloroethane to form the Et(2)Cl(+) chloronium ion. This undergoes a slower, previously unrecognized HCl elimination reaction to form a butyl carborane, Bu(CHB(11)Cl(11)), beginning an oligomerization process whereby unsymmetrical dialkylchloronium ions decompose to alkyl carboranes of formula Bu(C(2)H(4))(n)(CHB(11)Cl(11)) up to n = 4. Over time, a parallel competing process of de-oligomerization take place in the presence of free carborane acid that finishes with the formation of hexyl or butyl carboranes. Upon heating to 150 C, the final products are all converted to the remarkably stable tert-butyl cation carborane salt.     

Turbid media optical properties derived from the characteristics of propagating laser radiation beams

The possibility is studied to develop a straightforward analytical approach to the determination of the optical properties of liquid turbid media having forward-peaked scattering indicatrices. The approach is based on investigating the in-depth behavior of the radius and the axial intensity of a laser radiation beam propagating through the turbid medium. Based on the small-angle approximation, the detected forward-propagating light power spatial distribution, at relatively small or large optical depths along the beam axis, is obtained asymptotically in analytical form allowing one to derive relatively simple expressions of the extinction, reduced-scattering and absorption coefficients and the anisotropy factor of the medium through the characteristics of the propagating light beam. Preliminary experiments have also been performed, using Intralipid dilutions of different relatively low concentrations and measuring the cross-sectional radial distribution of the detected light power at different depths along the beam axis. The corresponding on-axis detected light power profiles have been measured independently as well. The experimental results are consistent with the analytical expressions obtained that allow one to estimate the optical coefficients and the anisotropy factor of the investigated media on the basis of the measured beam characteristics. The values obtained are near those predicted by other researchers.     

The nature of the hydrated proton H(aq)+ in organic solvents

The nature of H(H2O)n(+) cations for n = 3-8 with weakly basic carborane counterions has been studied by IR spectroscopy in benzene and dichloroethane solution. Contrary to general expectation, neither Eigen-type H3O x 3 H2O(+) nor Zundel-type H5O2(+) x 4 H2O ions are present. Rather, the core species is the H7O3(+) ion.     

Spectral properties and supramolecular inclusion complex formation between 2-styrylbenzothiazolium dye and cyclodextrins

The effect of native and randomly methylated β-CDs on the absorption and steady-state fluorescence spectra of 2-(4-dimethylaminostyryl)-3-(2-hydroxyethyl)-benzothiazolium chloride (DHB) in aqueous buffer solutions with various pH values was studied. The inclusion with both CDs at pH 7.2 barely changed the UV spectra, whereas significant variations were produced in the emission spectra in all buffer solutions. In all cases the CDs increase guest fluorescence. The 1:1 stoichiometry of the inclusion complexes of the dye with both CDs was established according to the modified Benesi-Hildebrand method. Binding constant values were calculated using the iterative nonlinear least-squares regression approach. The pH of the solution and the type of the CD affected complex stability. The results indicate that native β-CD possesses better complexing ability towards DHB than randomly substituted β-CD and that the most stable inclusion complexes are formed in basic medium because of the structural changes in the guest molecule. In basic medium an attempt is made to interpret the proposed mechanism in terms of molecular rearrangement which take place as the dye penetrates the CD cavity.     

Surface properties of liquid reactive oligomers

Spreading coefficients and the work of adhesion of oligomers to different substrates are calculated based on the results of studying the wettability and surface tension of ED-20 epoxy oligomer and oligooxyethyleneoxypropylene triols. It is shown that the addition of surfactant (ethoxylated alkyl phenols) considerably enhances the wettability of the studied oligomers. It is established that the addition of surfactant imparted to the properties of oligomers and surface energy characteristics of composites based on these oligomers nonlinearly depend on the degree of ethoxylation.     

Structure and properties of epoxy composites cured with new organosilicon amines

The results of the curing of bisphenol A-based epoxy oligomers (ED-20 and NPEL-128) with silicon-containing amines (SCAs) synthesized by the interaction between bifunctional alcohols with different molecular masses and γ-aminopropyltriethoxysilane (AGM-9) are reported. It is shown that, in the case of using SCAs, epoxy oligomer is cured more completely and a higher degree of elasticity in the polymer matrix is achieved without using modifiers, which is impossible in the case when polyethylene polyamines are used.     

Hot-melt adhesive for shrinkable polyethylene collars

A hot-melt adhesive based on poly(ethylene-co-vinyl acetate) is proposed to for use in the anticorrosion insulation of the butt joints of pipelines with shrinkable polyethylene collars.     

Evidence for CH Hydrogen Bonding in Salts of tert-Butyl Cation

Environmentally sensitive: A combination of C?H????anion hydrogen bonding and hyperconjugative charge delocalization explains the sensitivity of the IR spectrum of the tert-butyl cation to its anion (see high-resolution X-ray structure with a CHB(11) Cl(11) (-) counterion). The νCH vibration of the cation scales linearly with the basicity of carborane anions on the νNH scale. The same also holds for the C(6) H(7) (+) benzenium ion.     

Fabrication of Environmentally Biodegradable Lignin Nanoparticles

We developed a method for the fabrication of novel biodegradable nanoparticles (NPs) from lignin which are apparently non‐toxic for microalgae and yeast. We compare two alternative methods for the synthesis of lignin NPs which result in particles of very different stability upon change of pH. The first method is based on precipitation of low‐sulfonated lignin from an ethylene glycol solution by using diluted acidic aqueous solutions, which yields lignin NPs that are stable over a wide range of pH. The second approach is based on the acidic precipitation of lignin from a high‐pH aqueous solution which produces NPs stable only at low pH. Our study reveals that lignin NPs from the ethylene glycol‐based precipitation contain densely packed lignin domains which explain the stability of the NPs even at high pH. We characterised the properties of the produced lignin NPs and determined their loading capacities with hydrophilic actives. The results suggest that these NPs are highly porous and consist of smaller lignin domains. Tests with microalgae like Chlamydomonas reinhardtii and yeast incubated in lignin NP dispersions indicated that these NPs lack measurable effect on the viability of these microorganisms. Such biodegradable and environmentally compatible NPs can find applications as drug delivery vehicles, stabilisers of cosmetic and pharmaceutical formulations, or in other areas where they may replace more expensive and potentially toxic nanomaterials.     

Surface shear rheology of adsorption layers from the protein HFBII hydrophobin: effect of added β-casein

The surface shear rheology of hydrophobin HFBII adsorption layers is studied in angle-ramp/relaxation regime by means of a rotational rheometer. The behavior of the system is investigated at different shear rates and concentrations of added β-casein. In angle-ramp regime, the experimental data comply with the Maxwell model of viscoelastic behavior. From the fits of the rheological curves with this model, the surface shear elasticity and viscosity, E(sh) and η(sh), are determined at various fixed shear rates. The dependence of η(sh) on the rate of strain obeys the Herschel-Bulkley law. The data indicate an increasing fluidization (softening) of the layers with the rise of the shear rate. The addition of β-casein leads to more rigid adsorption layers, which exhibit a tendency of faster fluidization at increasing shear rates. In relaxation regime, the system obeys a modified Andrade's (cubic root) law, with two characteristic relaxation times. The fact that the data comply with the Maxwell model in angle-ramp regime, but follow the modified Andrade's low in relaxation regime, can be explained by the different processes occurring in the viscoelastic protein adsorption layer in these two regimes: breakage and restoration of intermolecular bonds at angle-ramp vs solidification of the layer at relaxation.