Spatiotemporal Regulation of Hydrogel Actuators by Autocatalytic Reaction Networks.

Regulating hydrogel actuators with chemical reaction networks is instrumental for constructing life-inspired smart materials. Herein, hydrogel actuators are engineered that are regulated by the autocatalytic front of thiols. The actuators consist of two layers. The first layer, which is regular polyacrylamide hydrogel, is in a strained conformation. The second layer, which is polyacrylamide hydrogel with disulfide crosslinks, maintains strain in the first layer. When thiols released by the autocatalytic front reduce disulfide crosslinks, the hydrogel actuates by releasing the mechanical strain in the first layer. The autocatalytic front is sustained by the reaction network, which uses thiouronium salts, disulfides of ß-aminothiols, and maleimide as starting components. The gradual actuation by the autocatalytic front enables movements such as gradual unrolling, screwing, and sequential closing of "fingers." This actuation also allows the transmission of chemical signals in a relay fashion and the conversion of a chemical signal to an electrical signal. Locations and times of spontaneous initiation of autocatalytic fronts can be preprogrammed in the spatial distribution of the reactants in the hydrogel. To approach the functionality of living matter, the actuators triggered by an autocatalytic front can be integrated into smart materials regulated by chemical circuits.

Kinetic Selection in the Out-of-Equilibrium Autocatalytic Reaction Networks that Produce Macrocyclic Peptides.

Autocatalytic reaction networks are instrumental for validating scenarios for the emergence of life on Earth and for synthesizing life de novo. Here, we demonstrate that dimeric thioesters of tripeptides with the general structure (Cys-Xxx-Gly-SEt)2 form strongly interconnected autocatalytic reaction networks that predominantly generate macrocyclic peptides up to 69 amino acids long. Some macrocycles of 6-12 amino acids were isolated from the product pool and were characterized by NMR spectroscopy and single-crystal X-ray analysis. We studied the autocatalytic formation of macrocycles in a flow reactor in the presence of acrylamide, whose conjugate addition to thiols served as a model "removal" reaction. These results indicate that even not template-assisted autocatalytic production combined with competing removal of molecular species in an open compartment could be a feasible route for selecting functional molecules during the pre-Darwinian stages of molecular evolution.

Synthesis and structural investigation of 2-aminomethyl-3-(4-methoxy-phenyl)-propionic acid containing a peptide analogue of the amyloidogenic AS(6-7) sequence: inhibition of fibril formation.

The incorporation of a single ß-amino acid moiety in a highly amyloidogenic peptide sequence resulted in the complete inhibition of amyloid fibril formation. The Boc-l-Phe-l-Leu-OMe sequence 1, which has sequence identity with the N-terminal AS(6-7) of the non-immunoglobulin amyloid fibril protein AS, which is responsible for rheumatoid arthritis, self-associates to produce fibrils. The d-Phe analogue peptide 2 shows an elongated ribbon-like morphology. However, the 2-aminomethyl-3-(4-methoxy-phenyl)-propionic acid containing analogue peptide 3 exhibits a polydisperse microsphere morphology. Moreover, fibrils from peptides 1 and 2 exhibit typical green-gold birefringence upon Congo red (CR) staining and show an amyloid-like morphological resemblance. However, the 2-aminomethyl-3-(4-methoxy-phenyl)-propionic acid modified peptide 3 does not respond to the Congo red assay. From X-ray crystallography, peptide 1 with the l-Phe residue adopts an extended structure, whereas the d-Phe analogue 2 adopts a kink-like structure. Both peptides 1 and 2 show twisted anti-parallel sheet-like structures at higher order assembly. However, peptide 3 adopts a nine-membered hydrogen bonded δ-turn-like structure in the solid state and self-associates to form a loop-like supramolecular structure through multiple intermolecular hydrogen bonds. The structural analysis presented herein may foster new studies for de novo design and therapeutics.

Porous organic material from discotic tricarboxyamide: side chain-core interactions.

The benzene-1,3,5-tricarboxyamide containing three l-methionine (1) self-assemble through 3-fold amide-amide hydrogen bonds and π-π stacking to fabricate one-dimensional nanorod like structure. However, the tyrosine analogue (2) carrying multiple H-bonding side chains lost the C3 symmetry and 3-fold amide-amide hydrogen bonds and developed a porous structure. The porous material exhibits ten times more N2 sorption (155 cc/g) than the columnar one, indicating that side chain-core interactions have a drastic effect on structure and function.

Halogen bond induced phosphorescence of capped γ-amino acid in the solid state.

The Boc and N,N'-dicyclohexylurea capped γ-amino acid upon monobromination showed phosphorescence in the solid state. The compound exhibited different photoluminescence intensity and lifetimes in crystals obtained from ethyl acetate and methanol. X-ray crystallography revealed that the intermolecular C=O…Br halogen bond directs the heavy atom effect to produce the phosphorescence.