Recent Updates on the Barrier Properties of Ethylene Vinyl Alcohol Copolymer (EVOH): A Review

The gas barrier properties of ethylene vinyl alcohol copolymer (EVOH) against oxygen, carbon dioxide and water vapor have been widely investigated in relation to different material characteristics, environmental conditions and new processing technologies. Recently, EVOH is gaining more attention as a barrier material against other gases and organic substances such as aromas, flavors, fuels, chemicals (e.g., BTEX), and as a functional barrier, e.g., to avoid mineral oil migration. This review contains an update on permeability data of EVOH emphasizing its potential as a barrier material for new and versatile applications in food and pharmaceutical packaging, agriculture, construction, automotive, etc.     

Active Esters as Pseudostoppers for Slippage Synthesis of [2]Pseudorotaxane Building Blocks: A Straightforward Route to Multi‐Interlocked Molecular Machines

The efficient synthesis and very easy isolation of dibenzo[24]crown‐8‐based [2]pseudorotaxane building blocks that contain an active ester motif at the extremity of the encircled molecular axle and an ammonium moiety as a template for the dibenzo[24]crown‐8 is reported. The active ester acts both as a semistopper for the [2]pseudorotaxane species and as an extensible extremity. Among the various investigated active ester moieties, those that allow for the slippage process are given particular focus because this strategy produces fewer side products. Extension of the selected N‐hydroxysuccinimide ester based pseudorotaxane building block by using either a mono‐ or a diamino compound, both containing a triazolium moiety, is also described. These provide a pH‐dependent two‐station [2]rotaxane molecular machine and a palindromic [3]rotaxane molecular machine, respectively. Molecular machinery on both interlocked compounds through variation of pH was studied and characterized by means of NMR spectroscopy.     

A TPA-caged precursor of (imino)coumarin for “turn-on” fluorogenic detection of Cu

We strategize to utilize the precursors of (imino)coumarin fluorophores to deliver novel reactive Cu⁺ probes, where tris[(2-pyridyl)-methyl] amine (TPA) works as a reactive receptor towards Cu⁺. To verify this strategy, CP1, a representative probe and relevant sensing behaviors towards Cu⁺ are presented here. CP1 features good solubility and fast response for monitoring labile copper in aqueous solution and live cells. The sensing mechanism of CP1 is determined by HPLC titration and mass spectrometric analysis. The probe CP1 exhibits a 60-fold fluorescence enhancement and a detection limitation of 10.8 nM upon the detection of Cu⁺. CP1 is further applied for imaging labile copper in live cells. This work provides a starting point for future development of Cu⁺ probes, based on in situ formation of (imino)coumarin scaffolds, as well as their further investigations of copper signaling and biological events.     

Recombinant Cyanobacteria for the Asymmetric Reduction of C=C Bonds Fueled by the Biocatalytic Oxidation of Water

A recombinant enoate reductase was expressed in cyanobacteria and used for the light‐catalyzed, enantioselective reduction of C=C bonds. The coupling of oxidoreductases to natural photosynthesis allows asymmetric syntheses fueled by the oxidation of water. Bypassing the addition of sacrificial cosubstrates as electron donors significantly improves the atom efficiency and avoids the formation of undesired side products. Crucial factors for product formation are the availability of NADPH and the amount of active enzyme in the cells. The efficiency of the reaction is comparable to typical whole‐cell biotransformations in E. coli. Under optimized conditions, a solution of 100 mg prochiral 2‐methylmaleimide was reduced to optically pure 2‐methylsuccinimide (99 % ee, 80 % yield of isolated product). High product yields and excellent optical purities demonstrate the synthetic usefulness of light‐catalyzed whole‐cell biotransformations using recombinant cyanobacteria.     

Aminosilane Functionalized Aligned Fiber PCL Scaffolds for Peripheral Nerve Repair

Silane modification is a simple and cost-effective tool to modify existing biomaterials for tissue engineering applications. Aminosilane layer deposition has previously been shown to control NG108-15 neuronal cell and primary Schwann cell adhesion and differentiation by controlling deposition of ─NH₂ groups at the submicron scale across the entirety of a surface by varying silane chain length. This is the first study toreport depositing 11-aminoundecyltriethoxysilane (CL11) onto aligned Polycaprolactone (PCL) scaffolds for peripheral nerve regeneration. Fibers are manufactured via electrospinning and characterized using water contact angle measurements, atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS). Confirmed modified fibers are investigated using in vitro cell culture of NG108-15 neuronal cells and primary Schwann cells to determine cell viability, cell differentiation, and phenotype. CL11-modified fibers significantly support NG108-15 neuronal cell and Schwann cell viability. NG108-15 neuronal cell differentiation maintains Schwann cell phenotype compared to unmodified PCL fiber scaffolds. 3D ex vivo culture of Dorsal root ganglion explants (DRGs) confirms further Schwann cell migration and longer neurite outgrowth from DRG explants cultured on CL11 fiber scaffolds compared to unmodified scaffolds. Thus, a reproducible and cost-effective tool is reported to modify biomaterials with functional amine groups that can significantly improve nerve guidance devices and enhance nerve regeneration.     

Discovery of the Lanthipeptide Curvocidin and Structural Insights into its Trifunctional Synthetase CuvL

Lanthipeptides are ribosomally-synthesized natural products from bacteria featuring stable thioether-crosslinks and various bioactivities. Herein, we report on a new clade of tricyclic class-IV lanthipeptides with curvocidin from Thermomonospora curvata as its first representative. We obtained crystal structures of the corresponding lanthipeptide synthetase CuvL that showed a circular arrangement of its kinase, lyase and cyclase domains, forming a central reaction chamber for the iterative substrate processing involving nine catalytic steps. The combination of experimental data and artificial intelligence-based structural models identified the N-terminal subdomain of the kinase domain as the primary site of substrate recruitment. The ribosomal precursor peptide of curvocidin employs an amphipathic α-helix in its leader region as an anchor to CuvL, while its substrate core shuttles within the central reaction chamber. Our study thus reveals general principles of domain organization and substrate recruitment of class-IV and class-III lanthipeptide synthetases.     

Polymorph selection during the crystallization of softly repulsive spheres: the inverse power law potential

Using hybrid Monte Carlo molecular simulations, we study crystallization from the melt of softly repulsive spheres interacting through an inverse power law potential. We work at fixed supercooling (i.e., at a temperature 25% below the melting temperature) and consider three systems, defined by different values for the inverse power exponent n: n = 5, n = 6.67, and n = 10. Modifying the value of n allows us to study the onset of crystallization in the domain of stability of the body-centered cubic (bcc) phase (n = 5 and n = 6.67) and in the domain of stability of the face-centered cubic (fcc) phase (n = 10). We show that, for the three systems, polymorph selection does not take place during crystal nucleation since the structure of the critical nuclei obtained for the three systems is not well defined. However, our results demonstrate that polymorph selection takes place during the growth step since growth proceeds either into the stable bcc phase for the two smaller values of n (n = 5 and n = 6.67) or into the stable fcc phase for the larger value of n (n = 10). We also show that we did not achieve complete control of polymorphism for n = 10. The growth step gives rise to either slowly growing crystallites composed of two blocks of different structures (the stable fcc form and the metastable bcc form) or rapidly growing crystallites of the metastable bcc form.     

Mycolactones: immunosuppressive and cytotoxic polyketides produced by aquatic mycobacteria

Mycolactones are a family of highly related macrocyclic polyketides that exhibit immunosuppressive and cytotoxic properties. First discovered in 1999, they are the primary virulence factors produced by the environmental human pathogen Mycobacterium ulcerans, the causative agent of Buruli ulcer, and by some closely-related aquatic mycobacteria that cause disease in fish and frogs. Mycolactones are characterized by a common 12-membered lactone core to which is appended an unsaturated fatty acyl side-chain of variable length and oxidation state. This Highlight summarizes recent progress in understanding the structural diversity of the mycolactones, their biological activity and mode of action in mammalian cells, and the genetics, evolution, and enzymology of their biosynthesis.     

Selective ortho methylation of nitroheteroaryls by vicarious nucleophilic substitution

An efficient and scalable three-step one-pot approach to 6-methyl-5-nitroisoquinoline (1) from inexpensive 5-nitroisoquinoline, utilizing the vicarious nucleophilic substitution (VNS) as a key step, is described. The optimized reaction conditions can be applied to a limited number of other aromatic and heteroaromatic nitro compounds. Attempts to understand the observed selectivity in the VNS step led to the discovery of two new reaction pathways under VNS conditions, one leading to an isoxazole and the other resulting in the formal cyclopropanation of an aromatic nitro compound.     

The Bip method, based on the induced circular dichroism of a flexible biphenyl probe in terminally protected -Bip-Xaa*- dipeptides, for assignment of the absolute configuration of beta-amino acids

An induced axial chirality of the biphenyl core of the Bip (2',1':1,2;1',2':3,4-dibenzcyclohepta-1,3-diene-6-amino-6-carboxylic acid) residue in the terminally protected dipeptides Boc-Bip-beta-Xaa*-OMe (beta-Xaa* = L-beta(3)-HAla, L-beta(3)-HVal, L-beta(3)-HLeu, L-beta(3)-HPro, trans-(1S,2S)-ACHC, trans-(1R,2R)-ACHC, trans-(1S,2S)-ACPC, trans-(1R,2R)-ACPC) resulted in an induced circular dichroism, revealing the usefulness of the Bip method for a reliable and fast assignment of the absolute configuration of chiral beta-amino acids. Remarkably, the Bip method was also applied to the unique spin-labeled, cyclic, beta-amino acids cis/trans-beta-TOAC and trans-POAC. In particular, this study allowed the assignment of the unknown absolute configurations of the enantiomers of the latter compound.