Converting disulfide bridges in native peptides to stable methylene thioacetals

Disulfide bridges play a crucial role in defining and rigidifying the three-dimensional structure of peptides. However, disulfides are inherently unstable in reducing environments. Consequently, the development of strategies aiming to circumvent these deficiencies - ideally with little structural disturbance - are highly sought after. Herein, we report a simple protocol converting the disulfide bond of peptides into highly stable methylene thioacetal. The transformation occurs under mild, biocompatible conditions, enabling the conversion of unprotected native peptides into analogues with enhanced stability. The developed protocol is applicable to a range of peptides and selective in the presence of a multitude of potentially reactive functional groups. The thioacetal modification annihilates the reductive lability and increases the serum, pH and temperature stability of the important peptide hormone oxytocin. Moreover, it is shown that the biological activities for oxytocin are retained

Alkali base-initiated Michael addition/alkyne carbocyclization cascades.

A new cascade reaction involving an intramolecular Michael addition followed by an alkyne carbocyclization is presented. The reaction is promoted by a substoichiometric amount of KHMDS and represents one of the rare examples where the carbocyclization of an unactivated alkyne is mediated by an alkali metal base, under mild conditions. The reaction allows the generation of functionally dense, stereochemically defined, tricyclic structures possessing three adjacent stereocenters in good yields and with high stereoselectivity

Ageing analysis and asymmetric stress considerations for small format cylindrical cells for wearable electronic devices

Performance assessments on miniature cylindrical cells used in Fitbit Flex 2 fitness trackers have been performed to understand the dominant ageing modes and small format implications. We utilise electrochemical testing, x-ray photoelectron Spectroscopy (XPS), x-ray computed tomography (XCT) and scanning electron microscopy (SEM), to reveal device and component structural features and changes. The cell maintains 82% cell capacity retention after 500 continuous charging and discharging cycles at 3.0–4.35 V, 0.75C rate at 20 °C. The anode shows severe delamination due to high bending stress exerted on the cell components, however this seemingly has minimum impact on the electrochemical performance if the coating is sufficiently compressed in the jelly roll with a good electrical contact. After ageing, the surface layers continue to grow, with more LiF found on the cathode and anode. The formation of LiF is discussed and we suggest the main ageing mechanism of the Fitbit cell is related to increasing charge transfer resistance due to the transportation of Li+ ions being inhibited by the thicker surface layer, which contains LiF. That preferential delamination on the inner sides of the electrode coatings was observed consistently opens up an interesting avenues for advances in cylindrical cell manufacturing at large