Adsorption of cationic starch on cellulose studied by QCM-D

The adsorption of cationic starch (CS) from aqueous electrolyte solutions onto model cellulose film has been investigated by the quartz crystal microbalance with dissipation monitoring (QCM-D) and X-ray photoelectron spectroscopy (XPS). The influence of the electrolyte composition and charge density of CS was examined. The adsorption of CS onto cellulose followed the general trends expected for polyelectrolyte adsorption on oppositely charged surfaces, with some exceptions. Thus, as result of the very low surface charge density of the cellulose surface, highly charged CS did not adsorb in a flat conformation even at low ionic strength. The porosity of the film, however, enabled the penetration of coiled CS molecules into the film at high electrolyte concentrations. Differences between the adsorption behavior of CS on cellulose and earlier observations of the adsorption of the same starches on silica could be explained by the different morphologies and acidities of the hydroxyl groups on the two surfaces.     

Light-activated functional mesostructured silica

Mesostructured silica thin films and particles provide highly versatile supports or frameworks for functional materials where a desired function (such as energy transfer, electron transfer, or molecular machines) is induced by molecules deliberately placed in specific regions of the structure. The relatively gentle templated sol–gel synthesis methods allow a wide variety of molecules to be used, and the optical transparency of the framework is very suitable for studies of light-induced functionality. In this paper, three types of functionality are used to obtain fundamental understanding of the materials themselves and to develop active materials that can trap and release molecules from the pores upon command. Photo-induced energy transfer is used to verify that molecules can be placed in specific spatially separated regions of the framework; fluorescence resonance energy transfer is used as a molecular ruler to measure quantitatively the distance between pairs of molecules. Secondly, photo-induced electron transfer is used to obtain fundamental information about the electrical insulating properties of the framework. Finally, two types of molecular machines, a light-driven impeller and a light activated nanovalve, are described. Both machines contain moving parts attached to solid supports and do useful work. The valves trap and release molecules from the mesopores, and the impellers expel molecules from the pores. Applications of the materials to drug delivery and the release of drug molecules inside living cells is described.     

Late-Stage Amination of Drug-Like Benzoic Acids: Access to Anilines and Drug Conjugates through Directed Iridium-Catalyzed C−H Activation

The functionalization of C−H bonds, ubiquitous in drugs and drug-like molecules, represents an important synthetic strategy with the potential to streamline the drug-discovery process. Late-stage aromatic C−N bond–forming reactions are highly desirable, but despite their significance, accessing aminated analogues through direct and selective amination of C−H bonds remains a challenging goal. The method presented herein enables the amination of a wide array of benzoic acids with high selectivity. The robustness of the system is manifested by the large number of functional groups tolerated, which allowed the amination of a diverse array of marketed drugs and drug-like molecules. Furthermore, the introduction of a synthetic handle enabled expeditious access to targeted drug-delivery conjugates, PROTACs, and probes for chemical biology. This rapid access to valuable analogues, combined with operational simplicity and applicability to high-throughput experimentation has the potential to aid and considerably accelerate drug discovery.     

A core level and valence band photoemission study of the (1 1 1) and ( ) surfaces of 3C–SiC

A core level and valence band photoemission study of thick 3C–SiC(1 1 1) and 3C–SiC( ) epilayers grown by sublimation epitaxy is reported. The as introduced samples show threefold 1×1 low-energy electron diffraction patterns. For the Si face and reconstructed surfaces develop after in situ heating to 1100°C and 1300°C, respectively. For the C face a 3×3 reconstruction form after heating to 980°C. A semiconducting behavior is observed for the and 3×3 reconstructed surfaces while the reconstruction show a Fermi edge and thus a metallic-like behavior. The surface state on the surface is investigated and found to have Λ₁ symmetry and a total band width of 0.10 eV within the first surface Brillouin zone. For the Si 2p and C 1s core levels binding energies and surface shifted components are extracted and compared to earlier reported results for 6H– and 4H–SiC.     

Polyhydroxyl-based surfactants and their physico-chemical properties and applications

This contribution deals with the physical-chemical properties of surfactants carrying hydroxyl groups in the polar part. Topics discussed include surface and colloid properties, micelles (both single and multi-component), general phase behaviour and microemulsions. A general conclusion is that our understanding of polyhydroxy surfactants is increasing, but that further work is needed to unravel certain aspects of this important class of surfactants. Examples of such aspects are the origin of the liquid-liquid phase separation and the adsorption to solid surfaces of polyhydroxy surfactants.     

Orthogonal signal correction, wavelet analysis, and multivariate calibration of complicated process fluorescence data

In this paper, multivariate calibration of complicated process fluorescence data is presented. Two data sets related to the production of white sugar are investigated. The first data set comprises 106 observations and 571 spectral variables, and the second data set 268 observations and 3997 spectral variables. In both applications, a single response, ash content, is modelled and predicted as a function of the spectral variables. Both data sets contain certain features making multivariate calibration efforts non-trivial. The objective is to show how principal component analysis (PCA) and partial least squares (PLS) regression can be used to overview the data sets and to establish predictively sound regression models. It is shown how a recently developed technique for signal filtering, orthogonal signal correction (OSC), can be applied in multivariate calibration to enhance predictive power. In addition, signal compression is tested on the larger data set using wavelet analysis. It is demonstrated that a compression down to 4% of the original matrix size — in the variable direction — is possible without loss of predictive power. It is concluded that the combination of OSC for pre-processing and wavelet analysis for compression of spectral data is promising for future use.     

Flotation de-inking studies using model hydrophobic particles and non-ionic dispersants

A series of non-ionic alcohol ethoxylated surfactants (with HLB within the range of 11.1–12.5) were used as dispersants during flotation of mondisperse hydrophobised silica particles (representing ink particles) in de-inking formulations. Laboratory scale flotation experiments, contact angle, dynamic surface tension and thin film drainage experiments were carried out. The reduction in dynamic surface tension at the air/solution interface (which is dependent on the adsorption kinetics) followed the order C₁₀E₆>C₁₂E₈≈C₁₂E₆>C₁₄E₆ and these values were lower than sodium oleate, which is commonly used in de-inking systems. In addition the non-ionics adsorbed on the hydrophobised silica particles reducing the contact angle. These results indicated that the non-ionic surfactant with the highest CMC (C₁₀E₆) gave (a) the highest rate of adsorption at the air/solution interface (b) the froth with the greatest water content and higher froth volume (c) the lowest reduction in contact angle and (d) the highest flotation efficiency at concentrations above the CMC. It was also observed that flotation occurred, in spite of the fact that thin-film measurements indicated that the adsorption of non-ionic at the air/solution and silica/solution interfaces reduced the hydrophobicity of the particles, as indicated by an increase in stability of the aqueous thin film between the particle and air-bubble. This result suggests that the bubble-ink particle captures mechanism (occurring through rupture of the thin aqueous film separating the interfaces) is not the only mechanism controlling the flotation efficiency and that other parameters (such as the kinetics of surfactant adsorption, foaming characteristics, and bubble size) need to be taken into account. The kinetics is important with respect to the rate of adsorption of surfactant to both interfaces. Under equilibrium conditions, this may give rise to repulsive steric forces between the air-bubble and the particles (stable aqueous thin-films). However, a lower amount of surfactant adsorbed at a freshly formed air bubble or inkparticle (caused by slow adsorption rates) will produce a lower steric repulsive force allowing effective collection of particles by the bubble. Also, it was suggested that the influence of alcohol ethoxylates on bubble-size could effect the particle capture rate and mechanical entrainment of particles in an excessively buoyant froth, which will also play an important role in the flotation recovery.     

Multiple Andreev reflections as a transport problem in energy space

We present an approach for analysing the dc current in voltage biased quantum superconducting junctions. By separating terms from different n -particle processes, we find that the n -particle current can be mapped on the problem of wave transport through a potential structure with n barriers. We discuss the relation between resonances in such structures and the subgap structures in the current–voltage characteristics. At zero temperature we find, exactly, that only processes creating real excitations contribute to the current. Our results are valid for a general SXS junction, where the X region is an arbitrary nonsuperconducting region described by an energy-dependent transfer matrix.