Kinetic Control of Complexity in Multiple Dynamic Libraries

Multiple dynamic libraries of compounds are generated when more than one reversible reaction comes into play. Commonly, two or more orthogonal reversible reactions are used, leading to non-communicating dynamic libraries which share no building blocks. Only a few examples of communicating libraries have been reported, and in all those cases, building blocks are reversibly exchanged from one library to the other, constituting an antiparallel dynamic covalent system. Herein we report that communication between two different dynamic libraries through an irreversible process is also possible. Indeed, alkyl amines cancel the dynamic regime on the nucleophilic substitution of tetrazines, generating kinetically inert compounds. Interestingly, such amine can be part of another dynamic library, an imine-amine exchange. Thus, both libraries are interconnected with each other by an irreversible process which leads to kinetically inert structures that contain parts from both libraries, causing a collapse of the complexity. Additionally, a latent irreversible intercommunication could be developed. In such a way, a stable molecular system with specific host-guest and fluorescence properties, could be irreversibly transformed when the right stimulus was applied, triggering the cancellation of the original supramolecular and luminescent properties and the emergence of new ones.

Tailorable and Biocompatible Supramolecular-Based Hydrogels Featuring two Dynamic Covalent Chemistries

Dynamic covalent chemistry (DCC) has proven to be a valuable tool in creating fascinating molecules, structures, and emergent properties in fully synthetic systems. Here we report a system that uses two dynamic covalent bonds in tandem, namely disulfides and hydrazones, for the formation of hydrogels containing biologically relevant ligands. The reversibility of disulfide bonds allows fiber formation upon oxidation of dithiol-peptide building block, while the reaction between NH-NH₂ functionalized C-terminus and aldehyde cross-linkers results in a gel. The same bond-forming reaction was exploited for the "decoration" of the supramolecular assemblies by cell-adhesion-promoting sequences (RGD and LDV). Fast triggered gelation, cytocompatibility and ability to "on-demand" chemically customize fibrillar scaffold offer potential for applying these systems as a bioactive platform for cell culture and tissue engineering.

Injectable self-healing hydrogels formed via thiol/disulfide exchange of thiol functionalized F127 and dithiolane modified PEG

An injectable thermo-responsive hydrogel with excellent mechanical properties which can self-heal under mildly acidic to basic conditions was prepared.

Ion-gated synthetic photosystems

Herein, molecular strings of ions built along charge-transporting channels are shown to dramatically increase photocurrents and enable charge transport over long distances, thus confirming the existence and significance of ion-gated photosystems. For their synthesis, ordered and oriented stacks of naphthalenediimides were grown on indium tin oxide by ring-opening disulfide-exchange polymerization. To these charge-transporting channels, coaxial strings of anions or cations-fixed, mobile, complete, partial, pure, or mixed-were added by orthogonal hydrazone exchange. The presence of partially protonated carboxylates was found to most significantly increase activity, implying that they both attract holes and repel electrons, that is, facilitate photoinduced charge separation and hinder charge recombination at the same time. As a result of this quite remarkable situation, photocurrents increased rather than decreased with increasing charge stabilization on their "stepping stones." The presence of mobile anions facilitated long-distance charge transport through thick films. Turned off by inhibited anion mobility, that is, proton hopping, hole/proton antiport is identified to account for long-distance charge transport in ion-gated photosystems.

Chemical designs of functional photoactive molecular assemblies

Molecular assemblies with defined structures capable of photo-induced electron transfer or photochemical reactions are reviewed, emphasizing their supramolecular features.

25th anniversary article: reversible and adaptive functional supramolecular materials: "noncovalent interaction" matters

Supramolecular materials held together by noncovalent interactions, such as hydrogen bonding, host-guest interactions, and electrostatic interactions, have great potential in material science. The unique reversibility and adaptivity of noncovalent intreractions have brought about fascinating new functions that are not available by their covalent counterparts and have greatly enriched the realm of functional materials. This review article aims to highlight the very recent and important progresses in the area of functional supramoleuclar materials, focusing on adaptive mechanical materials, smart sensors with enhanced selectivity, soft luminescent and electronic nanomaterials, and biomimetic and biomedical materials with tailored structures and functions. We cannot write a complete account of all the interesting work in this area in one article, but we hope that it can in a way reflect the current situation and future trends in this prosperously developing area of functional supramolecular materials.

Reversible control over molecular recognition in surface-bound photoswitchable hydrogen-bonding receptors: towards read-write-erase molecular printboards

The synthesis of an anthracene-bearing photoactive barbituric acid receptor and its subsequent grafting onto azide-terminated alkanethiol/Au self-assembled monolayers by using an Cu(I) -catalyzed azide-alkyne reaction is reported. Monolayer characterization using contact-angle measurements, electrochemistry, and spectroscopic ellipsometry indicate that the monolayer conversion is fast and complete. Irradiation of the receptor leads to photodimerization of the anthracenes, which induces the open-to-closed gating of the receptor by blocking access to the binding site. The process is thermally reversible, and polarization-modulated IR reflection-absorption spectroscopy indicates that photochemical closure and thermal opening of the surface-bound receptors occur in 70 and 100 % conversion, respectively. Affinity of the open and closed surface-bound receptor was characterized by using force spectroscopy with a barbituric-acid-modified atomic force microscope tip.

Comparison of lipoic and asparagusic acid for surface-initiated disulfide-exchange polymerization

Bring it on: Organic chemistry on surfaces and in solution is not the same; this study offers a perfect example that small changes (from 27 to 35°; see graphic) can result in big consequences. Strained cyclic disulfides from asparagusic, but not lipoic acid, are ideal for growing functional architectures directly on surfaces; for the substrate-initiated synthesis of cell-penetrating poly(disulfide)s in solution, exactly the contrary is true.