Studies of the separation and characterisation of mixtures of starch and cellulose derivatives by use of chromatography and mass spectrometry

In this work a method was developed for characterisation of commercially available polymers consisting of mixtures of substituted cellulose and starch. Selective hydrolysis with specific enzymes was used to achieve separation of the two polymers in the mixture. Enzymes hydrolysing (1→4)-α-D and (1→6)-α-D-glycosidic bonds were used for the starch part and enzymes hydrolysing (1→4)-β-D-glycosidic bonds for the cellulose part. The hydrolysed fraction was separated from the unhydrolysed fraction and characterised by use of size-exclusion chromatography (SEC), to confirm that enzyme hydrolysis of the different polymers had occurred. High-performance anion-exchange chromatography (HPAEC) was performed to determine the amount of unmodified glucose units (UGU) in the fractions. Electrospray ionisation mass spectrometry (ESIMS) was used for determination of the substituents. All products were converted to monomers by acid hydrolysis to simplify mass spectral identification of the substituents. The monomers were further subjected to acetylation with acetic acid anhydride to facilitate identification of the substituents. By combining the results from the different analytical techniques a picture of the samples was obtained.     

Rouse dynamics of colloids bound to polymer networks

We present experimental evidence of a transition in the short-time Brownian motion of colloids from diffusive to subdiffusive, Rouse-like. This transition is seen for particles that are bound, through physical adsorption, to transient polymer networks. The characteristic Rouse scaling of the mean square particle displacement with radical t, found in the experiments, is rationalized using an analytical bead-spring model of a large particle anchored to a set of polymer chains.     

Angular broadening in core‐electron spectroscopy

The role of angular broadening in quantitative core‐electron spectroscopy is investigated using an analytic approach. It is shown why, practically, this effect remains relatively small for a broad range of parameters. A correction factor is derived, suggesting that the replacement of inelastic mean free path by an effective attenuation‐length parameter is not necessarily an optimal choice. The derived expression further proposes useful insight on the contribution of leading experimental parameters and, in particular, on the sharp increase of elastic‐scattering corrections above a (depth dependent) critical angle. Copyright © 2015 John Wiley & Sons, Ltd.     

Hybrid Supramolecular and Colloidal Hydrogels that Bridge Multiple Length Scales

Hybrid nanocomposites were constructed based on colloidal nanofibrillar hydrogels with interpenetrating supramolecular hydrogels, displaying enhanced rheological yield strain and a synergistic improvement in storage modulus. The supramolecular hydrogel consists of naphthyl‐functionalized hydroxyethyl cellulose and a cationic polystyrene derivative decorated with methylviologen moieties, physically cross‐linked with cucurbit[8]uril macrocyclic hosts. Fast exchange kinetics within the supramolecular system are enabled by reversible cross‐linking through the binding of the naphthyl and viologen guests. The colloidal hydrogel consists of nanofibrillated cellulose that combines a mechanically strong nanofiber skeleton with a lateral fibrillar diameter of a few nanometers. The two networks interact through hydroxyethyl cellulose adsorption to the nanofibrillated cellulose surfaces. This work shows methods to bridge the length scales of molecular and colloidal hybrid hydrogels, resulting in synergy between reinforcement and dynamics.     

Counting cubic extensions with given quadratic resolvent

Given a number field k and a quadratic extension $K_2$, we give an explicit asymptotic formula for the number of isomorphism classes of cubic extensions of k whose Galois closure contains $K_2$ as quadratic subextension, ordered by the norm of their relative discriminant ideal. The main tool is Kummer theory. We also study in detail the error term of the asymptotics and show that it is $O(X^{\alpha })$, for an explicit $\alpha <1$.     

Driving oxygen coordinated ligand exchange at nanocrystal surfaces using trialkylsilylated chalcogenides

A general, efficient method is demonstrated for exchanging native oxyanionic ligands on inorganic nanocrystals with functional trimethylsilylated (TMS) chalcogenido ligands. In addition, newly synthesized TMS mixed chalcogenides leverage preferential reactivity of TMS-S bonds over TMS-O bonds, enabling efficient transfer of luminescent nanocrystals into aqueous media with retention of their optical properties.     

Phenylethylidene-3,4-dihydro-1H-quinoxalin-2-ones: promising building blocks for Cu recognition

A series of sulfonamido-substituted phenylethylidene-3,4-dihydro-1H-quinoxalin-2-one derivatives in which both of the fluorophore and ionophore are integrated into one structural unit, have been investigated. They all exhibit high selectivity toward Cu²⁺ in ethanol in the presence of other metallic ions (Zn²⁺, Mg²⁺, Co²⁺, Ni²⁺, Mn²⁺, Ca²⁺, and Ag⁺), as well as fast, stable, and reversible binding, as is evidenced by the observation of a red shift in the UV-vis spectrum, ‘ON-OFF’ fluorescence response. In addition, titration and MALDI-TOF measurements indicated that a 1:1 (and possibly also 2:1 (organic ligand: Cu²⁺) complexes were formed, depending on the relative amount of Cu²⁺ added to the solution of the organic ligand. It was also found that the binding constant could be tuned by modifying the nature and position of the substituents attached to the central benzene ring in the quinoxalone derivative. In acetonitrile, unlike in ethanol, these ligands undergo oxidation-decomposition by Cu²⁺ and therefore, no UV-vVis absorption bands could be observed. However, due to color change (from yellow to transparent) they could be useful as dosimeters in this solvent.     

Multiple double cross-section transmission electron microscope sample preparation of specific sub-10 nm diameter Si nanowire devices

The ability to prepare multiple cross-section transmission electron microscope (XTEM) samples from one XTEM sample of specific sub-10 nm features was demonstrated. Sub-10 nm diameter Si nanowire (NW) devices were initially cross-sectioned using a dual-beam focused ion beam system in a direction running parallel to the device channel. From this XTEM sample, both low- and high-resolution transmission electron microscope (TEM) images were obtained from six separate, specific site Si NW devices. The XTEM sample was then re-sectioned in four separate locations in a direction perpendicular to the device channel: 90° from the original XTEM sample direction. Three of the four XTEM samples were successfully sectioned in the gate region of the device. From these three samples, low- and high-resolution TEM images of the Si NW were taken and measurements of the NW diameters were obtained. This technique demonstrated the ability to obtain high-resolution TEM images in directions 90° from one another of multiple, specific sub-10 nm features that were spaced 1.1 μm apart.