Stabilized nanoparticles of phytosterol by rapid expansion from supercritical solution into aqueous solution

The basic objective of this work was to form stable suspensions of submicron particles of phytosterol, a water-insoluble drug, by rapid expansion of supercritical solution into aqueous solution (RESSAS). A supercritical phytosterol/CO2 mixture was expanded into an aqueous surfactant solution. In these experiments 4 different surfactants were used to impede growth and agglomeration of the submicron particles resulting from collisions in the free jet. The concentration of the drug in the aqueous surfactant solution was determined by high-performance liquid chromatography, while the size of the stabilized particles was measured by dynamic light scattering. Submicron phytosterol particles (<500 nm) were stabilized and in most cases a bimodal particle size distribution was obtained. Depending on surfactant and concentration of the surfactant solution, suspensions with drug concentrations up to 17 g/dm3 could be achieved, which is 2 orders of magnitude higher than the equilibrium solubility of phytosterol. Long-term stability studies indicate modest particle growth over 12 months. Thus, the results demonstrate that RESSAS can be a promising process for stabilizing submicron particles in aqueous solutions

Experiments and simulations show how long-range contacts can form in expanded unfolded proteins with negligible secondary structure

The sizes of unfolded proteins under highly denaturing conditions scale as N(0.59) with chain length. This suggests that denaturing conditions mimic good solvents, whereby the preference for favorable chain–solvent interactions causes intrachain interactions to be repulsive, on average. Beyond this generic inference, the broader implications of N(0.59) scaling for quantitative descriptions of denatured state ensembles (DSEs) remain unresolved. Of particular interest is the degree to which N(0.59) scaling can simultaneously accommodate intrachain attractions and detectable long-range contacts. Here we present data showing that the DSE of the N-terminal domain of the L9 (NTL9) ribosomal protein in 8.3 M urea lacks detectable secondary structure and forms expanded conformations in accord with the expected N(0.59) scaling behavior. Paramagnetic relaxation enhancements, however, indicate the presence of detectable long-range contacts in the denatured-state ensemble of NTL9. To explain these observations we used atomistic thermal unfolding simulations to identify ensembles whose properties are consistent with all of the experimental observations, thus serving as useful proxies for the DSE of NTL9 in 8.3 M urea. Analysis of these ensembles shows that residual attractions are present under mimics of good solvent conditions, and for NTL9 they result from low-likelihood, medium/long-range contacts between hydrophobic residues. Our analysis provides a quantitative framework for the simultaneous observation of N(0.59) scaling and low-likelihood long-range contacts for the DSE of NTL9. We propose that such low-likelihood intramolecular hydrophobic clusters might be a generic feature of DSEs that play a gatekeeping role to protect against aggregation during protein folding

The ExaNeSt Project:Interconnects, Storage, and Packaging for Exascale Systems

ExaNest is one of three European projects that support a ground-breaking computing architecture for exascale-class systems built upon power-efficient 64-bit ARM processors. This group of projects share an 'everything-close' and 'share-anything' paradigm, which trims down the power consumption - by shortening the distance of signals for most data transfers - as well as the cost and footprint area of the installation - by reducing the number of devices needed to meet performance targets. In ExaNeSt, we will design and implement: (i) a physical rack prototype and its liquid-cooling subsystem providing ultra-dense compute packaging, (ii) a storage architecture with distributed (in-node) non-volatile memory (NVM) devices, (iii) a unified, low-latency interconnect, designed to efficiently uphold desired Quality-of-Service guarantees for a mix of storage with inter-processor flows, and (iv) efficient rack-level memory sharing, where each page is cacheable at only a single node . Our target is to test alternative storage and interconnect options on actual hardware, using real-world HPC applications. The ExaNeSt consortium brings together technology, skills, and knowledge across the entire value chain, from computing IP, packaging, and system deployment, all the way up to operating systems, storage, HPC, big data frameworks, and cutting-edge applications

Experimental Parameterization of an Energy Function for the Simulation of Unfolded Proteins

The determination of conformational preferences in unfolded and disordered proteins is an important challenge in structural biology. We here describe an algorithm to optimize energy functions for the simulation of unfolded proteins. The procedure is based on the maximum likelihood principle and employs a fast and efficient gradient descent method to find the set of parameters of the energy function that best explain the experimental data. We first validate the method by using synthetic reference data, and subsequently apply the algorithms to data from nuclear magnetic resonance spin-labeling experiments on the Δ131Δ fragment of Staphylococcal nuclease. A significant strength of the procedure that we present is that it directly uses experimental data to optimize the energy parameters, without relying on the availability of high resolution structures. The procedure is fully general and can be applied to a range of experimental data and energy functions including the force fields used in molecular dynamics simulations

Native and nonnative conformational preferences in the urea-unfolded state of barstar

The refolding of barstar from its urea-unfolded state has been studied extensively using various spectroscopic probes and real-time NMR, which provide global and residue-specific information, respectively, about the folding process. Here, a preliminary structural characterization by NMR of barstar in 8 M urea has been carried out at pH 6.5 and 25°C. Complete backbone resonance assignments of the urea-unfolded protein were obtained using the recently developed three-dimensional NMR techniques of HNN and HN(C)N. The conformational propensities of the polypeptide backbone in the presence of 8 M urea have been estimated by examining deviations of secondary chemical shifts from random coil values. For some residues that belong to helices in native barstar, 13Cα and 13CO secondary shifts show positive deviations in the urea-unfolded state, indicating that these residues have propensities toward helical conformations. These residues are, however, juxtaposed by residues that display negative deviations indicative of propensities toward extended conformations. Thus, segments that are helical in native barstar are unlikely to preferentially populate the helical conformation in the unfolded state. Similarly, residues belonging to β-strands 1 and 2 of native barstar do not appear to show any conformational preferences in the unfolded state. On the other hand, residues belonging to the β-strand 3 segment show weak nonnative helical conformational preferences in the unfolded state, indicating that this segment may possess a weak preference for populating a helical conformation in the unfolded state

Axial power monitor rod issues and resolution for K-14.1

A recent concern arose over the treatment of uncertainty associated with the K-Reactor axial power monitors (APMs). There are nine axial power monitor rods located at various positions in the K-Reactor core. By comparing the output of one sensor near the top of the rod to the output of another sensor near the bottom of the rod, the relative ratio of the neutron flux from the top to the bottom of the core can be determined. This ratio is called the roof-top-ratio (RTR) and is the output of a top sensor (Sensor 2) divided by the output of a bottom sensor (Sensor 6). The RTR is important to the safety analyses because when the RTR is maintained within certain ranges, the severity of reactivity transients is limited. There are uncertainties associated with the equipment`s ability to measure the true roof top ratio. It was determined recently that sufficient uncertainty was not accounted for either in reactor operation or in the safety analyses. The concern about uncertainty was addressed for three separate issues. One issue dear with the linear response of the sensors for power ranges planned for K-Reactor operation. The second issue dear with overall uncertainty in the RTR channel. The third issue dear with apparent large ranges in confidence bands for the RTR at low reactor powers as represented by original vendor data. Plots of sparse vendor data indicated unacceptably large uncertainties in RTR would have to be accounted for at the power ranges planned for K-Reactor operation. These concerns were brought to management`s attention through the existing procedures for notification, irrespective of their potential impact on the restart schedule. Analyses have been completed to resolve the APM issues described above, and work is progressing to take the needed steps to change operational procedures