In Situ Observations of the Microstructural Evolution during Heat Treatment of a PH 13-8 Mo Maraging Steel

The standard heat treatment of PH 13-8 Mo maraging steels consists of solution annealing and subsequent aging. Herein, it is investigated how an additional intercritical annealing step prior to aging affects the microstructure, and, consequently, the mechanical properties of a PH 13-8 Mo maraging steel. In situ techniques by means of high-temperature electron backscatter diffraction and high-temperature X-ray diffraction are applied to study the microstructural changes during intercritical annealing and subsequent aging. In addition, high-resolution investigation methods, such as transmission electron microscopy and atom probe tomography supplemented by transmission Kikuchi diffraction, are used for an in-depth characterization of the microstructure. The results reveal that a diffusion-controlled martensite to austenite transformation accompanied by partitioning of the substitutional atoms Cr, Ni, and Mo takes place during intercritical annealing. As a result of partitioning during intercritical annealing, an inhomogeneous distribution of Ni remains in the microstructure after the martensitic transformation. Consequently, the formation of reverted austenite is facilitated during subsequent aging due to existing Ni-enriched zones in martensite. Since the fracture toughness is significantly enhanced compared to the standard heat treatment, it is suggested that this improvement is related to the increased phase fraction of reverted austenite.     

Elastic properties of intermingled hybrid composites

The combination of different types of fibers in a common matrix, known as a hybrid composite, has the potential of achieving a balance between composite strength and ductility, as well as a more cost-effective use of expensive fibers, not re-alized in a single-fiber compostie. The elastic properties of a continuous Kevlar®/glass intermingled hybrid composite have been investigated. Theoretical predictions utilizing a self-consistent model and a bound approach are compared to the influence of the relative Kevlar®/glass fiber volume fraction on the elasstic material properties.     

Non‐Racemic Halohydrins via Biocatalytic Hydrogen‐Transfer Reduction of Halo‐Ketones and One‐Pot Cascade Reaction to Enantiopure Epoxides

Biocatalytic hydrogen‐transfer reduction of α‐chloro‐ketones furnished non‐racemic chlorohydrins by employing either Rhodococcus ruber as lyophilized cell catalyst or an alcohol dehydrogenase preparation from Pseudomonas fluorescens DSM 50106 (PF‐ADH). For all substrates investigated, Rhodococcus ruber gave strictly the “Prelog” product, whereas PF‐ADH showed scattered stereopreference. One possibility for a follow‐up reaction of halohydrins is the ring closure to the corresponding epoxide. A novel “one pot‐one step strategy” was employed to obtain the enantiopure epoxide from the α‐chloro‐ketone in a cascade like fashion at pH>12 involving biocatalytic hydrogen transfer reduction and in situ chemo‐catalyzed ring closure.     

Engineering TM1459 for Stabilisation against Inactivation by Amino Acid Oxidation

Oxidative alkene cleavage is a highly interesting reaction to obtain aldehydes and ketones. The Mn-dependent protein TM1459 from Thermotoga maritima can catalyse alkene cleavage of styrene derivatives in the presence of tert-butyl hydroperoxide. Despite the high thermal stability of the enzyme, it gets inactivated during the reaction. The data reported here indicate that auto-oxidation is responsible for the low stability of TM1459 in the oxidative environment required for the alkene cleavage reaction. By targeting the exchange of residues prone to oxidation, this phenomenon was successfully prevented. Importantly, the stability to oxidation conveyed by the amino acid exchanges led to increased enzyme activity. However, the exchanges resulted in slightly modified positions of two of the four metal-binding amino acids, thereby strongly impacting metal binding.     

Ligand-Directed Chemistry on Glycoside Hydrolases – A Proof of Concept Study

Selective covalent labelling of enzymes using small molecule probes has advanced the scopes of protein profiling. The covalent bond formation to a specific target is the key step of activity-based protein profiling (ABPP), a method which has become an indispensable tool for measuring enzyme activity in complex matrices. With respect to carbohydrate processing enzymes, strategies for ABPP so far involve labelling the active site of the enzyme, which results in permanent loss of activity. Here, we report in a proof of concept study the use of ligand-directed chemistry (LDC) for labelling glycoside hydrolases near – but not in – the active site. During the labelling process, the competitive inhibitor is cleaved from the probe, departs the active site and the enzyme maintains its catalytic activity. To this end, we designed a building block synthetic concept for small molecule probes containing iminosugar-based reversible inhibitors for labelling of two model β-glucosidases. The results indicate that the LDC approach can be adaptable for covalent proximity labelling of glycoside hydrolases.