Infiltration of chitin by protein coacervates defines the squid beak mechanical gradient.

The beak of the jumbo squid Dosidicus gigas is a fascinating example of how seamlessly nature builds with mechanically mismatched materials. A 200-fold stiffness gradient begins in the hydrated chitin of the soft beak base and gradually increases to maximum stiffness in the dehydrated distal rostrum. Here, we combined RNA-Seq and proteomics to show that the beak contains two protein families. One family consists of chitin-binding proteins (DgCBPs) that physically join chitin chains, whereas the other family comprises highly modular histidine-rich proteins (DgHBPs). We propose that DgHBPs play multiple key roles during beak bioprocessing, first by forming concentrated coacervate solutions that diffuse into the DgCBP-chitin scaffold, and second by inducing crosslinking via an abundant GHG sequence motif. These processes generate spatially controlled desolvation, resulting in the impressive biomechanical gradient. Our findings provide novel molecular-scale strategies for designing functional gradient materials.

Biohybrid glycopolymer capable of ionotropic gelation.

Ionotropic gelation is particularly appealing for the formation of hydrogels because it takes place under mild conditions, is not thermoreversible, and does not involve toxic chemicals. A well-known example is the gelation of alginate in the presence of calcium ions, which is at the base of numerous applications involving this polymer. In this study, alginate-derived oligosaccharides were converted into acrylamide- and methacrylamide-type macromonomers in two steps without resorting to protective group chemistry. They were then copolymerized with 2-hydroxyethylmethacrylamide in aqueous solution to yield high molar mass biohybrid glycopolymers containing between 25 and 52% by mass of oligosaccharide graft chains. A comparative kinetic study showed that both acrylamide- and methacrylamide-type macromonomers reacted since the early stages of the copolymerization, but that the mole fraction in the polymer was smaller than in the feed up to 50-60% conversion and increased markedly afterward. This effect was slighter for the methacrylamide-type macromonomer though. Copolymers carrying oligosaccharide chains with 16-20 repeating units were synthesized and used for a gelation experiment: When dialyzed against CaCl(2) 0.5 mol L(-1), the polymer carrying (1→4)-α-l-guluronan residues led to a soft isotropic self-standing transparent hydrogel, while the polymer carrying (1→4)-ß-d-mannuronan residues gave a loose opaque gel. This study demonstrates that alginate-extracted oligosaccharides and aqueous radical polymerization can be combined for the flexible design of biohybrid glycopolymers capable of ionotropic gelation under very mild conditions.

Fast and Green Synthesis of an Oligo-Hydrocaffeic Acid-Based Adhesive.

A green, mussel-inspired bioadhesive based on oligomerization of hydrocaffeic acid was synthesized in water by an ultrafast one-step reaction in the presence of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide as an activating agent. The resulting oligomers exhibited strong wet adhesion when applied to different substrates including glass, stainless steel, and aluminum. Compared to most commercial adhesives, this bioinspired adhesive is produced via a sustainable and green process, i.e., aqueous-based synthesis, one-step reaction, and in the absence of any purification step to obtain the final functional adhesive.

Bioinspired pH and magnetic responsive catechol-functionalized chitosan hydrogels with tunable elastic properties.

We have developed pH- and magnetic-responsive hydrogels that are stabilized by both covalent bonding and catechol/Fe(3+) ligands. The viscoelastic properties of the gels are regulated by the complexation valence and can be used to tune drug release profiles. The stable incorporation of magnetic nanoparticles further expands control over the mechanical response and drug release, in addition to providing magnetic stimuli-responsivity to the gels.

Synthesis of ß-D-glucopyranuronosylamine in aqueous solution: kinetic study and synthetic potential.

A systematic study of the synthesis of ß-D-glucopyranuronosylamine in water is reported. When sodium D-glucuronate was reacted with ammonia and/or volatile ammonium salts in water a mixture of ß-D-glucopyranuronosylamine and ammonium N-ß-D-glucopyranuronosyl carbamate was obtained at a rate that strongly depended on the experimental conditions. In general higher ammonia and/or ammonium salt concentrations led to a faster conversion of the starting sugar into intermediate species and of the latter into the final products. Yet, some interesting trends and exceptions were observed. The use of saturated ammonium carbamate led to the fastest rates and the highest final yields of ß-D-glucopyranuronosylamine/carbamate. With the exception of 1 M ammonia and 0.6 M ammonium salt, after 24 h of reaction all tested protocols led to higher yields of ß-glycosylamine/carbamate than concentrated commercial ammonia alone. The mole fraction of α-D-glucopyranuronosylamine/carbamate at equilibrium was found to be 7-8% in water at 30°C. Concerning bis(ß-D-glucopyranuronosyl)amine, less than 3% of it is formed in all cases, with a minimum value of 0.5% in the case of saturated ammonium carbamate. Surprisingly, the reaction was consistently faster in the case of sodium D-glucuronate than in the case of D-glucose (4-8 times faster). Finally, the synthetic usefulness of our approach was demonstrated by the synthesis of three N-acyl-ß-D-glucopyranuronosylamines and one N-alkylcarbamoyl-ß-D-glucopyranuronosylamine directly in aqueous-organic solution without resorting to protective group chemistry.