Synthesis of Amino Acids by Base-Enhanced Photoredox Decarboxylative Alkylation of Aldimines.

A photoredox decarboxylative coupling of N-hydroxyphthalimide esters with aldimines is reported for synthesizing α-amino esters. A broad scope of alkyl radicals generated under visible light irradiation adds to glyoxylate aldimines in reliably good to excellent yields. Adding inorganic bases such as potassium carbonate significantly enhanced the yields by suppressing the umpolung side reaction. The computation study suggests that the base facilitates hydrogen atom transfer from the radical cation of Hantzsch ester to the N-centered radical intermediates. Introducing amino acid side chains into natural products and drug molecules by this method is demonstrated.

Iron(II)-Catalyzed Radical Addition to Aldimines with Hantzsch Ester as a Two-Hydrogen Atom Donor.

The first Fe(OTf)2-catalyzed radical addition to aldimines with Hantzsch ester as a two-hydrogen atom donor is reported. The tin-free reaction works well for electron-deficient substrates and provides a potentially useful approach to α-branched amines and α-amino acids.

Force and deformation transmission characteristics of a compliant tendon-sheath actuation system based on Hill-type muscle model.

Artificial muscle is a kind of transmission actuator widely used in rehabilitation robots and wearable devices. However, there are some restrictions on the usage of these artificial muscles, including the short stroke length, complex structure, special power sources, and high nonlinear characteristics. Inspired by Hill-type muscle model, in this article, a new kind of artificial muscle using tendon-sheath and compliant springs is proposed to perform muscle-like characteristics. Force and deformation transmission models are proposed and validated by simulations and experiments. The experimental and simulation output results show nice goodness-of-fit and the R-square values are 0.9876 and 0.9046, respectively. Moreover, experiments are carried out in groups to analyze the transmission characteristics using different parameters, including variations of series springs, velocities, tendon diameters, and bending angles. The best R-square value of force-elongation curve and fitness curve could reach 0.9845, which indicates that the transmission model of the compliant artificial muscle can be used to express the transmission characteristics of the skeleton muscles.