The effect of the backscattered energetic atoms on the stress generation and the surface morphology of reactively sputtered vanadium nitride films

During the reactive magnetron sputtering of transition metal nitrides in an Ar-N₂ ambient, Ar⁺ and N₂⁺ plasma ions are neutralized upon impingement on the target and are backscattered towards the growing film as neutral Ar and N species, respectively. Based on simulations, as well as on plasma and on film characterization techniques we manifest the relationship between the bombardment by the backscattered energetic atoms and the properties of reactively sputtered vanadium nitride (VN) films. Depending on the N₂ flow (q_N2) two bombardment regimes are established. In the first regime, (q_N2 < 20 sccm) the contribution of the N species to the energetic bombardment is insignificant. The major bombarding species in this regime are the backscattered Ar species, as well as positive plasma ions and sputtered atoms. These species have relatively low energies and subplantation ratios and thus, their energy is transferred to the surface of the growing film. In the second regime (q_N2 > 20 sccm) the backscattered N atoms are the major bombarding species and their flux to the growing film increases with increasing the N₂ flow. We argue that the backscattered N atoms have higher energy and subplantation ratio in comparison to the other bombarding species. As a result, a higher part of their energy is dissipated in the bulk of the film. The two bombarding regimes correlate well with the residual compressive stresses and the surface roughness of the films. Films grown at q_N2 < 20 sccm exhibit low compressive stresses and their roughness drops when q_N2 is increased. This consistent with the low subplantation ratio and the transfer of the energy of the bombarding species to surface the growing film. The compressive stresses of films grown at q_N2 > 20 sccm are higher, than those of the films grown in the first regime, and increase with increasing N₂ flow. This is attributed to the subplantation of the bombarding N species in the growing film.     

High‐Throughput Feasible Screening Tool for Determining Enzyme Stabilities against Organic Solvents Directly from Crude Extracts

Biotransformations in organic chemistry frequently suffer from limitations caused by low water‐solubility of substrates and product inhibition. Both, usually are addressed by the addition of organic cosolvents, which often accompanies at the expense of enzyme stability. A common method for measuring enzyme stability is to determine the melting temperature (T_m) of the enzyme. However, current methods are limited to the application of purified enzymes. Herein, for the first time, an easy and fast (<1 h) high‐throughput feasible method to determine enzyme stabilities directly from crude extracts is reported. In pure buffer, the T_m value measured in the crude extract was identical to that obtained for the purified enzyme. Through the addition of different organic compounds, the T_m values in the crude extract differed by up to 2.4 °C from that of the purified enzymes due to the presence of the host‐cell proteins. Thus, the measurement of enzyme stabilities in crude extracts appears to represent conditions in whole‐cell catalysts even better. The applied nano differential scanning fluorimetry technology is further proven to be suitable for whole‐cell catalysts with two overexpressed enzymes; thus representing a tool for the rapid screening of natural and mutant enzyme libraries in terms of process stability for challenging biotransformations.     

Mechanical and chemical characteristics of hermetically coated silica optical fibre

The mechanical strength of carbon hermetically coated fibres, compared to standard single mode silica optical fibre, has been investigated through chemical exposure to fluorinated vapour reagents, known as the harshest reagents for silica. Two reagents were used: ammonium hydrogenofluoride and hydrofluoric acid.Dynamic fatigue tests for different stress rates were implemented using a two-point bending testing device in order to determine n-stress corrosion parameter from Weibull statistics. As-received and chemically etched fibres were compared.Hermetically coated fibres appeared extremely durable in harsh chemical conditions. No significant change in the Weibull distribution and the mean fibre strength was observed after 6 days of chemical exposure to hydrofluoric vapours. In the same conditions, the mechanical strength of the epoxy-acrylate polymer coated standard fibres has decreased to nearly 50% of the initial strength value. SEM observations revealed crystal deposition on the chemical exposed fibres. Chemical analysis provides partial information on the complex mechanisms of fibre corrosion.     

A Maillard reaction product enhances eNOS activity in human endothelial cells

Nitric oxide (NO) produced by the endothelial nitric oxide synthase (eNOS) is an important signaling molecule in the cardiovascular system. Although dietary factors can modulate eNOS activity, putative effects of processed food are barely investigated. We aimed to examine whether the model Maillard reaction product 3‐hydroxy‐2‐methyl‐1‐propyl‐4(1H)‐pyridone (HMPP), formed from maltol or starch and propylamine, affects the eNOS system. Incubation of EA.hy926 endothelial cells with 30–300 μM HMPP for 18 h enhanced endothelial NO release measured with the fluorescent probe diaminofluorescein‐2 and eNOS activity determined by the [14C]L‐arginine‐[14C]L‐citrulline conversion assay. HMPP increased NO production also in two different types of primary human endothelial cells. Protein levels of eNOS and inducible NO synthase remained unaltered by HMPP. HMPP inhibited eNOS activity within the first 2–4 h, whereas it potently increased eNOS activity after 12–24 h. Levels of eNOS phosphorylation, expression of heat‐shock protein 90, caveolin‐1 and various antioxidant enzymes were not affected. Intracellular reactive oxygen species remained unchanged by HMPP. This is the first study to demonstrate positive effects of a Maillard reaction product on eNOS activity and endothelial NO production, which is considered favourable for cardiovascular protection.     

Femtosecond laser machining for characterization of local mechanical properties of biomaterials: a case study on wood

Abstract

The standard preparation technique for micro-sized samples is focused ion beam milling, most frequently using Ga⁺ ions. The main drawbacks are the required processing time and the possibility and risks of ion implantation. In contrast, ultrashort pulsed laser ablation can process any type of material with ideally negligible damage to the surrounding volume and provides 4 to 6 orders of magnitude higher ablation rates than the ion beam technique. In this work, a femtosecond laser was used to prepare wood samples from spruce for mechanical testing at the micrometre level. After optimization of the different laser parameters, tensile and compressive specimens were produced from microtomed radial-tangential and longitudinal-tangential sections. Additionally, laser-processed samples were exposed to an electron beam prior to testing to study possible beam damage. The specimens originating from these different preparation conditions were mechanically tested. Advantages and limitations of the femtosecond laser preparation technique and the deformation and fracture behaviour of the samples are discussed. The results prove that femtosecond laser processing is a fast and precise preparation technique, which enables the fabrication of pristine biological samples with dimensions at the microscale.     

Supramolecular assemblies based on dative boron-nitrogen bonds

Dative boron-nitrogen bonds were found to be a useful binding motif in structural supramolecular chemistry. Crystalline cages were formed using a diboronate ester and 2,4,6-tri(4-pyridyl)-1,3,5-triazine. These cages can act as hosts for electron-rich planar aromatic systems such as triphenylene. Further, crystalline two-dimensional polymers were formed via dative B-N bonds between a triboronic ester and a ditopic pyridyl ligand. Use of an extended triboronate ester resulted in formation of a gel in toluene with a minimum gelation concentration of 0.5 wt%.     

Safety assessment of food-contact paper and board using a battery of short-term toxicity tests: European union BIOSAFEPAPER project

An European Union (EU)-funded project QLK1-CT-2001-00930 (BIOSAFEPAPER) involves the development, validation and intercalibration of a short-term battery of toxicological tests for the safety assessment of food-contact paper and board. Dissemination of the results to industry, legislators (e.g. DG Consumer Protection, DG Enterprises, DG Research), standardization bodies such as CEN, and consumers will create an agreed risk evaluation procedure. The project involves pre-normative research in order to establish a set of in-vitro cytotoxicity and genotoxicity tests that will be easily adaptable to food-contact fibre-based materials and have endpoints relevant to consumer safety, including sub-lethal cellular events. These tests will be performed on samples representing actual migration conditions from food-contact paper and board with respect to different foodstuffs, and should form an experimental basis for scientifically sound recommendations for a harmonized system of risk evaluation and product testing.     

COMPOSITIONAL ANALYSIS OF PETROLEUM WAXES BY ZEOLITE MOLECULAR SIEVE-GCMS

To investigate the composition of petroleum waxes, studies were carried out on the extraction of normal paraffins from petroleum waxes by zeolite molecular sieve type 5A. Time required for adsorption of different molecular weight n-paraffins from standard mixture and petroleum waxes has been ascertained. Un-adsorbed part of the waxes has been investigated by GC-MS technique. Recovery of adsorbed hydrocarbon from molecular sieve was done by supercritical fluid extraction.