Early structural evolution of native cytochrome c after solvent removal

Electrospray ionization transfers thermally labile biomolecules, such as proteins, from solution into the gas phase, where they can be studied by mass spectrometry. Covalent bonds are generally preserved during and after the phase transition, but it is less clear to what extent noncovalent interactions are affected by the new gaseous environment. Here, we present atomic-level computational data on the structural rearrangement of native cytochrome c immediately after solvent removal. The first structural changes after desolvation occur surprisingly early, on a timescale of picoseconds. For the time segment of up to 4.2 ns investigated here, we observed no significant breaking of native noncovalent bonds; instead, we found formation of new noncovalent bonds. This generally involves charged residues on the protein surface, resulting in transiently stabilized intermediate structures with a global fold that is essentially the same as that in solution. Comparison with data from native electron capture dissociation experiments corroborates both its mechanistic postulations and our computational predictions, and suggests that global structural changes take place on a millisecond timescale not covered by our simulations.     

Reversible pH lability of cross-linked vault nanocapsules

Vaults are ubiquitous, self-assembled protein nanocapsules with dimension in the sub-100 nm range that are conserved across diverse phyla from worms to humans. Their normal presence in humans at a copy number of over 10,000/cell makes them attractive as potential drug delivery vehicles. Toward this goal, bifunctional amine-reactive reagents are shown to be useful for the reversible cross-linking of recombinant vaults such that they may be closed and opened in a controllable manner.     

The influence of crosslinking and fumed silica nanoparticles on mixed gas transport properties of poly[1-(trimethylsilyl)-1-propyne]

Crosslinking poly[1-(trimethylsilyl)-1-propyne] (PTMSP) films with 3,3′-diazidodiphenylsulfone, a bis(azide) crosslinker, rendered the films insoluble in common solvents for PTMSP such as toluene. At all temperatures, mixed gas CH₄ and n-C₄H₁₀ permeabilities of crosslinked PTMSP were less than those of uncrosslinked PTMSP, which correlates with lower free volume in the crosslinked material. The presence of fumed silica (FS) nanoparticles in both uncrosslinked PTMSP and crosslinked PTMSP increased mixed gas CH₄ and n-C₄H₁₀ permeabilities, consistent with the disruption of polymer chain packing by such nanoparticles. Mixed gas CH₄ permeabilities of all films were significantly less than their corresponding pure gas CH₄ permeabilities. For example, at 35 °C, the mixed gas CH₄ permeabilities were approximately 60–80% less than their pure gas values. The greatest decrease was observed for uncrosslinked PTMSP, while nanocomposite PTMSP films showed the least decrease. The mixed gas n-C₄H₁₀/CH₄ selectivities of crosslinked PTMSP and nanocomposite PTMSP films were less than those of uncrosslinked PTMSP at all temperatures. For example, at 35 °C, the mixed gas n-C₄H₁₀/CH₄ selectivities of uncrosslinked PTMSP, crosslinked PTMSP containing 10 wt% crosslinker, and uncrosslinked PTMSP containing 30 wt% FS were 33, 27, and 17, respectively, when the feed gas contained 2 mol% n-C₄H₁₀ and the total upstream mixture fugacity was 11 atm. For all films, as temperature decreased, mixed gas n-C₄H₁₀ permeabilities increased, and mixed gas CH₄ permeabilities decreased. Consequently, the mixed gas n-C₄H₁₀/CH₄ selectivities increased substantially as temperature decreased and the mixed gas selectivity of uncrosslinked PTMSP increased from 33 to 170 as temperature decreased from 35 °C to ?20 °C when the feed gas contained 2 mol% n-C₄H₁₀ and the total upstream mixture fugacity was 11 atm.     

Fire resistance tests and differentiated design procedures — The Building Code: Aims and means

Every building should be executed and arranged in such a way or by the use of such materials that, taking into consideration its purpose and location, it will give reasonable fire safety for persons staying in the building, including proper facilities for saving the occupants and for fire extinguishment to be carried out, and also to give reasonable safety against spread of fire to adjoining buildings and activities on adjoining sites. — Danish Building Code, Chapter 6.1.1 Note: The material properties of the compartments are defined in References 3 and 4. A black furnace refers to a furnace in which the incident flux is equal toT _gas ⁴.     

Wide-angle chromatic aberration corrector for the human eye

The human eye is affected by large chromatic aberration. This may limit vision and makes it difficult to see fine retinal details in ophthalmoscopy. We designed and built a two-triplet system for correcting the average longitudinal chromatic aberration of the eye while keeping a reasonably wide field of view. Measurements in real eyes were conducted to examine the level and optical quality of the correction. We also performed some tests to evaluate the effect of the corrector on visual performance.     

Safer energetic materials by a nanotechnological approach

Energetic materials - explosives, thermites, populsive powders - are used in a variety of military and civilian applications. Their mechanical and electrostatic sensitivity is high in many cases, which can lead to accidents during handling and transport. These considerations limit the practical use of some energetic materials despite their good performance. For industrial applications, safety is one of the main criteria for selecting energetic materials. The sensitivity has been regarded as an intrinsic property of a substance for a long time. However, in recent years, several approaches to lower the sensitivity of a given substance, using nanotechnology and materials engineering, have been described. This feature article gives an overview over ways to prepare energetic (nano-)materials with a lower sensitivity.     

The pyrolysis of natural gas: A study of carbon deposition and the suitability of reactor materials

This study of methane pyrolysis was designed to look at carbon deposition on the internal reactor and wafer surface during CH₄ pyrolysis. The rate of carbon deposition on the internal reactor surfaces could be reduced with: lower methane/oxygen ratios, shorter residence times, and lower temperatures. The type of carbon formed appeared to have a significant effect on the pyrolysis process. Pyrolytic carbon with a lower order structure produces a higher selectivity for carbon formation compared to carbon with a higher order structure. Form a process perspective, there are two obvious means of addressing this: deposited carbon could be regularly removed; and/or pyrolysis conditions are selected that produce carbon with a higher order structure. From the results, it is very clear that any development of a commercial process for natural gas pyrolysis in ceramic reactor systems would have to carefully address the selection of reactor material. © 2018 American Institute of Chemical Engineers AIChE J, 65: 1035–1046, 2019     

Sorption of polar and nonpolar aromatic organic contaminants by plant cuticular materials: role of polarity and accessibility

In both forest and agricultural soils, plant derived cuticular materials can constitute a significant part of soil organic matter. In this study, the sorption of nonpolar (naphthalene and phenanthrene) and polar (phenol and 1-naphthol) aromatic organic pollutants to aliphatic-rich cuticularfractions of green pepper (Capsicum annuum) (i.e., bulk (PC1), dewaxed (PC2), nonsaponifiable (PC3), nonsaponifiable-nonhydrolyzable (PC4), and dewaxed-hydrolyzed residue (PC5)) were examined to better understand the influence of polarity and accessibility on their sorption behavior. The polarity and structures of cuticular fractions were characterized by elemental analysis, Fourier transform infrared spectroscopy, and solid-state 13C NMR. The sorption isotherms fit well to the Freundlich equation. Sorption of the tested organic compounds to PC4, which had more condensed domains, was nonlinear (Freundlich N(s) values of 0.766-0.966). For naphthalene and phenanthrene, the largest sorption capacity (K(oc)) occurred in PC5, which contained the highest paraffinic carbons (63%) and the lowest polarity: approximately 2 and aproximately 3 times higher than the respective carbon-normalized octanol-water partition coefficient (K(owc)), indicating that PC5 was a powerful sorption medium. For phenol and 1-naphthol, the largest K(oc) values occurred in PC4 with polar aromatic cores: approximattely 17 and approximately 7 times higher than the respective K(owc), suggesting that PC4 was much more accessible and compatible to polar aromatic pollutants than nonpolar aromatic pollutants. There was little or no correlation of K(oc) with either aliphatic or aromatic components of the tested aliphatic-rich sorbents because the polarity and accessibility apparently played a regulating role in the sorption of organic contaminants.     

PEG-based hydrogel membrane coatings

As a first step towards preparing fouling-resistant coatings for water purification membranes, three series of copolymer hydrogel networks were synthesized using poly(ethylene glycol) diacrylate (PEGDA) as the crosslinker and acrylic acid (AA), 2-hydroxyethyl acrylate (HEA), or poly(ethylene glycol) acrylate (PEGA) as comonomers. Copolymers containing varying amounts of PEGDA with each of these comonomers were prepared. Glass transition temperatures obeyed the Fox equation. Crosslink density strongly influenced water uptake and water permeability for materials of constant chemical composition. For example, the volume fraction of water sorbed by a 100 mol% PEGDA hydrogel was 0.61. However, introducing comonomers into the network reduced hydrogel crosslink density, and in hydrogels having the same ethylene oxide content, water sorption increased as crosslink density decreased. The highest water volume fraction observed was 0.72, obtained in a copolymer containing 80 mol% PEGA and 20 mol% PEGDA. Water permeability increased systematically with increasing water sorption, and water permeability coefficients ranged from 10 to 26 L μm/(m² h bar). NaCl partition coefficients ranged from 0.36 to 0.53 (g NaCl/cm³ hydrogel)/(g NaCl/cm³ solution). NaCl diffusion coefficients varied little with polymer composition; in this regard, diffusion coefficient values ranged from 4.3 × 10⁻⁶ to 7.4 × 10⁻⁶ cm²/s. Based on contact angle measurements using n-decane in water, oil exhibited a low affinity for the surfaces of these polymers, suggesting that coatings prepared from such materials might improve the fouling resistance of membranes towards oily wastewater.     

Optimizing headspace sampling temperature and time for analysis of volatile oxidation products in fish oil

Headspace-gas chromatography (HS-GC), based on adsorption to Tenax GR®, thermal desorption and GC, has been used for analysis of volatiles in fish oil. To optimize sampling conditions, the effect of heating the fish oil at various temperatures and times was evaluated from anisidine values (AV) and HS-GC. AV indicated sample degradations at 90°C but only small alterations between 60 and 75°C. HS-GC showed increasing response with temperature and time. Purging at 75°C for 45 min was selected as the preferred sampling condition for oxidized fish oil.