Spider Silk-CBD-Cellulose Nanocrystal Composites: Mechanism of Assembly

The fabrication of cellulose-spider silk bio-nanocomposites comprised of cellulose nanocrystals (CNCs) and recombinant spider silk protein fused to a cellulose binding domain (CBD) is described. Silk-CBD successfully binds cellulose, and unlike recombinant silk alone, silk-CBD self-assembles into microfibrils even in the absence of CNCs. Silk-CBD-CNC composite sponges and films show changes in internal structure and CNC alignment related to the addition of silk-CBD. The silk-CBD sponges exhibit improved thermal and structural characteristics in comparison to control recombinant spider silk sponges. The glass transition temperature (Tg) of the silk-CBD sponge was higher than the control silk sponge and similar to native dragline spider silk fibers. Gel filtration analysis, dynamic light scattering (DLS), small angle X-ray scattering (SAXS) and cryo-transmission electron microscopy (TEM) indicated that silk-CBD, but not the recombinant silk control, formed a nematic liquid crystalline phase similar to that observed in native spider silk during the silk spinning process. Silk-CBD microfibrils spontaneously formed in solution upon ultrasonication. We suggest a model for silk-CBD assembly that implicates CBD in the central role of driving the dimerization of spider silk monomers, a process essential to the molecular assembly of spider-silk nanofibers and silk-CNC composites.     

Impact of dietary fiber coatings on behavior of protein-stabilized lipid droplets under simulated gastrointestinal conditions

Multilayer emulsions containing lipid droplets coated by lactoferrin (LF) - anionic polysaccharide layers have improved resistance to environmental stresses (such as pH, salt, and temperature), but their behavior within the gastrointestinal tract (GIT) is currently unknown. The objective of this research was therefore to monitor changes in the physicochemical properties and digestibility of these systems under simulated GIT conditions. Primary emulsions (5% corn oil, 0.5% LF) were prepared using a high-pressure homogenizer. Secondary emulsions (5% corn oil, 0.5% LF, 0.5% polysaccharide) were prepared by incorporating alginate, low methoxyl pectin (LMP) or high methoxyl pectin (HMP) into primary emulsions. Emulsions were then subjected to simulated gastric fluid (SGF) and simulated intestinal fluid (SIF) conditions in sequence. LF, LF-LMP and LF-HMP emulsions were stable to droplet aggregation in the stomach but aggregated in the small intestine, whereas LF-alginate emulsions aggregated in both the stomach and small intestine. The presence of a dietary fiber coating around the initial lipid droplets had little influence on the total extent of lipid digestion in SIF, but LF-alginate emulsions had a slower initial digestion rate than the other emulsions. These results suggest that the dietary fiber coatings may become detached in the small intestine, or that they were permeable to digestive enzymes. Pepsin was found to have little influence on the physical stability or digestibility of the emulsions. The knowledge obtained from this study is important for the design of delivery systems for encapsulation and release of lipophilic bioactive ingredients.     

Model demonstrating the potential for coupled nitrification denitrification in soil aggregates

A model of reactive, multi-species diffusion has been developed to describe N transformations in spherical soil aggregates, emphasizing the effects of irrigation with reclaimed wastewater. Oxygen demand for respiratory activity has been shown to promote the establishment of anaerobic conditions. Aggregate size and soil respiration rate were identified as the most significant parameters governing the existence and extent of the anaerobic volume in aggregates. The inclusion of kinetic models describing mineralization, nitrification, and denitrification facilitated the investigation of coupled nitrification/denitrification (CND), subject to O2 availability. N-transformations are shown to be affected by effluent-borne NH4+-N content, in addition to elevated BOD and pH levels. Their incremental contribution to O2 availability has been found to be secondary to respiratory activity. At the aggregate level, significant differences between apparent and gross rates of N-transformations were predicted (e.g., NH4+ oxidation and N2 formation), resulting from diffusive constraints due to aggregate size. With increasing anaerobic volume, the effective nitrification rate determined at the aggregates level decreases until its contribution to nitrification is negligible. It was found that the nitrification process was predominantly limited to aggregates <0.25 cm. Assuming that nitrification is the main source for NO3- formation, denitrification efficiency is predicted to peak in medium-sized aggregates, where aerobic and anaerobic conditions coexist, supporting CND. In effluent-irrigated soils, the predicted NO2- formation rate in small aggregates is enhanced when compared to freshwater-irrigated soils. The difference vanishes with increasing aggregate size as anaerobic NO2- consumption exceeds aerobic NO2- formation due to the coupling of nitrification and denitrification.     

Impact of dietary fibers on the properties and proteolytic digestibility of lactoferrin nano-particles

The application and development of biopolymer-based particulate delivery systems is receiving considerable attention from scientists and manufacturers seeking to engineer healthier and safer foods. Present work focused on the fabrication and proteolysis of bovine lactoferrin nano-particles onto which pectins, alginate and carrageenan were electrostatically deposited. DLS, CD and AFM were used to ascertain the formation of spherical structures with varying zeta potentials and modified protein folding. SDS-PAGE analyses of samples collected during simulated human gastro-duodenal digestion revealed that in the case of high and low methoxy pectin particle zeta potential values (−35.4 mV and −50.3 mV respectively) were found to be inversely linked to lactoferrin digestion rate. Moreover, the electrostatic binding of food grade iota-carrageenan onto lactoferrin nano-particles was found to yield highly charged particles (zeta = −69.2 mV) with low surface roughness and to enable a proportion of the lactoferrin to resist 1 h of simulated gastric digestion. Overall, these findings suggest that electrostatic biopolymer interactions may modulate protein digestion and possibly facilitate controlled protein delivery to the upper gastrointestinal tract or have implications to protein nutritional value.     

A predictive synchronizer for periodic clock domains

An adaptive predictive clock synchronizer for systems on chip incorporating multiple clock domains is presented. The synchronizer takes advantage of the periodic nature of clocks in order to predict potential conflicts in advance, and to conditionally employ an input sampling delay to avoid such conflicts. The result is conflict-free synchronization with maximal throughput and minimal latency. The adaptive predictive synchronizer adjusts automatically to a wide range of clock frequencies, regardless of whether the transmitter is faster or slower than the receiver. The synchronizer also avoids sampling duplicate data or missing any input. A novel method is presented for formal treatment of synchronizers and metastability. Correct operation of the synchronizer is formally proven and verified.     

Energy as a determinant of investment behaviour

Studies of the determinants of investment behaviour have so far failed to consider the effects of changing energy prices. This paper aims to remedy this omission. After reviewing the theory of investment analysis, the author presents an econometric examination of the role of energy prices in US investment activity. He finds that the price of energy is an important factor in adequately explaining investment decisions and that its importance is likely to grow.     

Forecasting electric utility fossil-fuel consumption

The objective of this analysis is to develop a model to forecast the consumption of fossil fuels by electric utilities on a month-to-month basis. A scheme is devised and implemented that attributes fossil-fuel generation (exclusive of coal) to the consumption of residual fuel oil, distillate fuel oil, crude oil, and natural gas. A multinomial logit specification is used whereby the share of each of these fuels is a function of relative prices, weather, time, seasonal factors, and extraneous influences (e.g. a coal strike). The results agree well with actual shares.     

Synthesis and size-dependent properties of zinc-blende semiconductor quantum rods

Dimensionality and size are two factors that govern the properties of semiconductor nanostructures. In nanocrystals, dimensionality is manifested by the control of shape, which presents a key challenge for synthesis. So far, the growth of rod-shaped nanocrystals using a surfactant-controlled growth mode, has been limited to semiconductors with wurtzite crystal structures, such as CdSe (ref. 3). Here, we report on a general method for the growth of soluble nanorods applied to semiconductors with the zinc-blende cubic lattice structure. InAs quantum rods with controlled lengths and diameters were synthesized using the solution-liquid-solid mechanism with gold nanocrystals as catalysts. This provides an unexpected link between two successful strategies for growing high-quality nanomaterials, the vapour-liquid-solid approach for growing nanowires, and the colloidal approach for synthesizing soluble nanocrystals. The rods exhibit both length- and shape-dependent optical properties, manifested in a red-shift of the bandgap with increased length, and in the observation of polarized emission covering the near-infrared spectral range relevant for telecommunications devices.