Characterisation of CYP102A25 from Bacillus marmarensis and CYP102A26 from Pontibacillus halophilus: P450 Homologues of BM3 with Preference towards Hydroxylation of Medium‐Chain Fatty Acids

Cytochrome P450 monooxygenases are highly desired biocatalysts owing to their ability to catalyse a wide variety of chemically challenging C?H activation reactions. The CYP102A subfamily of enzymes are natural catalytically self‐sufficient proteins consisting of a haem and FMN‐FAD reductase domain fused in a single‐component system. They catalyse the oxygenation of saturated and unsaturated fatty acids to produce primarily ω?1, ω?2 and ω?3 hydroxy acids. These monooxygenases have potential applications in biotechnology; however, their substrate range is still limited and there is a continued need to add diversity to this class of biocatalysts. Herein, we present the characterisation of two new members of this class of enzymes, CYP102A25 (BMar) from Bacillus marmarensis and CYP102A26 (PHal) from Pontibacillus halophilus, both of which express readily in a recombinant bacterial host. BMar exhibits the highest activity toward myristic acid and shows moderate activity towards unsaturated fatty acids. PHal exhibits broader activity towards mid‐chain‐saturated (C₁₄–C₁₈) and unsaturated fatty acids. Furthermore, PHal shows good regioselectivity for the hydroxylation of myristic acid, targeting the ω?2 position for C?H activation.     

Cover Image,Volume 66, Issue 3

The cover image, by Katia Sparnacci et al., is based on the Research Article High temperature surface neutralization process with random copolymers for block copolymer self‐assembly, DOI: 10.1002/pi.5285 .

     

Effect of sol–gel layers obtained from GLYMO/MTES mixtures on the delamination of a cataphoretic paint on AA1050

In this study, the performance of different sol–gel layers produced from different mixtures of silicon alkoxides precursors (γ-glycidoxypropyltrimethoxysilane, GLYMO, and methyltriethoxysilane, MTES) applied on AA1050 aluminum alloy as a pretreatment prior to depositing an electrophoretic paint (polyether–polyamine polymeric blend) is investigated. The structure of the sol–gel coatings was characterized by means of ATR FTIR, while the corrosion protection properties were assessed by polarization curves. Accelerated laboratory tests, such as exposure in both neutral and acetic salt spray chambers and filiform corrosion tests, were employed to investigate the corrosion protection properties of the cataphoretic paint-coated samples. The failure mechanisms of the different coatings were investigated. The experiments revealed that the presence of GLYMO in the sol–gel coating seems not to be suitable for acting as a coupling agent between the paint and the aluminum substrate. On a positive note, this work shows that the filiform corrosion test seems to be the most appropriate test to evaluate the efficiency of sol–gel layers employed as pretreatment to enhance the corrosion protection provided by a paint on an aluminum substrate.     

Retardation of Crystallization through the Addition of Dairy Phospholipids

The objective of this work was to identify the effects that milk phospholipids (PL) have on crystallization of anhydrous milk fat (AMF). Three mixtures were prepared by adding 0%, 0.01%, and 0.1% PL to AMF. Each mixture was crystallized for 90 min at 24, 26, and 28 °C. The solid fat content was measured as a function of time and fitted to the Avrami equation. Melting point, thermal behavior, viscoelastic properties, and crystal morphology were all measured at 90 min. All assays were repeated, as well as hardness, after being stored at 5 °C for 48 hours. Samples containing PL showed slower crystallization as concentration increased especially at higher temperatures (26 and 28 °C). The addition of PL caused a difference in crystal morphology resulting in visibly larger crystals at 90 min. The elasticity and hardness at 90 min were influenced by the addition of PL at 24 °C with lower values obtained in samples with PL compared to the AMF alone. No differences in hardness nor in elasticity was observed for samples crystallized at 26 and 28 °C. A decrease in melting enthalpy was observed in samples with PL indicating a reduction in crystallization at all temperatures, which was supported by crystal morphology.     

Correlating Molecular Structure to the Behavior of Linear Styrene–Butadiene Viscosity Modifiers

The effect of linear styrene–butadiene polymer structure on the temperature–viscosity behavior of model polymer-base oil solutions is investigated using molecular dynamics simulations. Simulations of alternating, random, and block styrene–butadiene polymers in a dodecane solvent are used to calculate viscosity at 40 and 100 °C, reference temperatures for characterizing their function as viscosity modifiers. Mechanisms underlying this function are explored by quantifying the radius of gyration and intramolecular interactions of the polymers at the same reference temperatures. The block styrene–butadiene configuration exhibits the least change in viscosity with temperature, characteristic of a good viscosity modifier or viscosity index improver, and the behavior is correlated to the ability of this structure to form smaller coils with more intramolecular interactions at lower temperatures and then expand as temperature is increased. The results indicate that there is a correlation between styrene–butadiene polymer structure, additive function, and the mechanisms underlying that function.     

Design of a NURBS interpolator with minimal feed fluctuation and continuous feed modulation capability

With the growing demands to machine complex dies, moulds, aerospace, automotive, and biomedical parts in shorter cycle time, the utilization of Non-Uniform Rational B-Spline (NURBS) toolpaths has become more important than ever before. There are two challenges associated with realizing a successful NURBS trajectory generator—minimizing feedrate fluctuations and being able to modulate the feed continuously. This paper presents a robust and numerically efficient NURBS interpolation strategy. Unwanted feed fluctuations and sensitivity to round-off errors are avoided by applying the feed correction polynomial concept to NURBS toolpaths in an adaptive manner. A numerically efficient feedrate modulation strategy is developed, based on the trapezoidal acceleration profile, which guarantees that the final trajectory is jerk limited in all axes and kinematic continuity is achieved between connecting segments throughout the long toolpaths. The feed modulation strategy can be integrated with various feed optimization techniques as well. Effectiveness of the overall NURBS interpolation scheme is demonstrated in 3-axis machining of a complex sculptured surface.     

Use of microwave dielectric loss for characterisation of natural rubber/carbon black composites

Summary Microwave dielectric loss spectroscopy (MDS) has shown remarkable potential as a tool for the observation of changes in elastomer network structure within the interphase region of natural rubber/ carbon black composites. During crosslinking (non elemental sulphur system) the dielectric loss progressively increased. However, during ageing at high temperature the dielectric loss decreased. Parallel studies on the unfilled matrix yielded no such variation in dielectric loss. It was therefore concluded that the changes in microwave responses were related to the development of the interphase during curing and its subsequent destruction during ageing. The microwave response was related to the composite mechanical properties as a function of ageing time. The effect of stabiliser was also investigated. Received: 13 September 1999/Revised version: 7 February 2000/Accepted: 10 February 2000     

Influence of low molecular weight ABS species on properties of PC/ABS systems

Differential scanning calorimetry (DSC), scanning electron microscopy (SEM) rheological, mechanical and impact tests were performed on alloys consisting of polycarbonate (PC) and diverse acrylonitrile‐butadiene‐styrene copolymers (ABS), from which different amounts of low molecular (M) weight (W) species had been previously extracted in a Soxhlet apparatus by methanol. The influence on properties of the alloy composition and of the low MW species amount was investigated. The glass transition temperature (Tg) was found to be a useful probe for monitoring the migration trends of low MW ABS species towards the PC domains for the different alloys. In a morphological analysis it was found that the higher the ABS extraction extent the less the penetration of the etching agent into the surfaces of smoothed specimens. The blend rheological behavior showed that the capability of improving the PC processability, characteristic of commercial ABS's, was strongly lowered by the ABS extracted ones. The alloy modulus was higher when the ABS extraction extent was larger. The yield stress of alloys showed higher values than that of the PC one, particularly at low ABS content. The alloy composition, for which the impact resilience was at its maximum value, strongly depended on the extraction extent. All the above findings seem to suggest an increased adhesion between PC and ABS domains with enhanced extraction amounts of low MW species from the ABS component.