Biocatalytic Strategies towards [4+2] Cycloadditions

Long sought after [4+2] cyclases have sprouted up in numerous biosynthetic pathways in recent years, raising hopes for biocatalytic solutions to cycloaddition catalysis, an important problem in chemical synthesis. In a few cases, detailed pictures of the inner workings of these catalysts have emerged, but intense efforts to gain deeper understanding are underway by means of crystallography and computational modelling. This Minireview aims to shed light on the catalytic strategies that this highly diverse family of enzymes employs to accelerate and direct the course of [4+2] cycloadditions with reference to small-molecule catalysts and designer enzymes. These catalytic strategies include oxidative or reductive triggers and lid-like movements of enzyme domains. A precise understanding of natural cycloaddition catalysts will be instrumental for customizing them for various synthetic applications.     

An Ancestral Member of the Polysaccharide Lyase Family 2 Displays Endolytic Activity and Magnesium Dependence

Polysaccharide lyases (PLs) are enzymes that cleave glycosidic linkages in hexuronate polysaccharides, such as homogalacturonan (HG), using a β-elimination mechanism. Traditionally, PL activities on HG have been associated with catalytic calcium cofactors, unusually high pH optima, and arginine Brønstead bases. Recently, however, PL families that harness transition metal cofactors, utilize lysine and histidine Brønstead bases, and display more neutral pH optima have been described. One such family is PL2, which has members found primarily in phytopathogenic (e.g., Dickeya spp. and Pectobacterium spp.) or enteropathogenic (e.g., Yersinia spp.) bacterial species. PL2 is divided into two major subfamilies that are correlated with either an endolytic or exolytic activity. This study has focused on the activity of a PL2 member, which is not classified within either subfamily and helps to illuminate the origin of enzyme activities within the family. In addition, the role of Mg²⁺ as a preferential catalytic metal for an intracellular PL2 (PaePL2) is described. The implications for the relationship between catalytic metal selectivity and the cellular location of pectate lyase-mediated catalysis are discussed.     

A Tunable,Fullerene-Based Molecular Amplifier for Vibrational Circular Dichroism

Vibrational circular dichroism (VCD) studies are reported on a chiral compound in which a fullerene C₆₀ moiety is used as an electron acceptor and local VCD amplifier for an alanine-based peptide chain. Four redox states are investigated in this study, of which three are reduced species that possess low-lying electronic states as confirmed by UV/Vis spectroelectrochemistry. VCD measurements in combination with (TD)DFT calculations are used to investigate (i) how the low-lying electronic states of the reduced species modulate the amplification of VCD signals, (ii) how this amplification depends on the distance between oscillator and amplifier, and (iii) how the spatial extent of the amplifier influences amplification. These results pave the way for further development of tailored molecular VCD amplifiers.     

On the optimal strategy of stochastic-based reliability assessment of railway bridges for high-speed trains

Meccanica - The scope of this paper is to evaluate the performance and computational efficiency of various stochastic simulation methods for a stochastic based reliability assessment of railway...     

Optimization of Fishing Strategies in Space and Time as a Non-convex Optimal Control Problem

The behavior of a fishing fleet and its impact onto the biomass of fish can be described by a nonlinear parabolic diffusion–reaction equation. Looking for an optimal fishing strategy leads to a non-convex optimal control problem with a bilinear control action. In this work, we present such an optimal control formulation, prove its well-posedness and derive first- and second-order optimality conditions. These results provide a basis for tailored finite element discretization as well as for Newton type optimization algorithms. First numerical test problems show typical features as so-called No-Take-Zones and maximal fishing quota (total allowable catches) as parts of an optimal fishing strategy.