Diversity in supramolecular chemistry can showcase itself in many ways. This includes the diversity of thought and topics covered in research (from fundamental science to applications in biology and materials), as well as the diversity of people (e.g., diversity in race, gender, sexual orientation, country of origin, type of higher education institute, career stage,…). At the North American Supramolecular Chemistry (NASC) meetings, we aim to bring together the best that supramolecular chemistry has to offer in North America, create a sense of community and provide a platform for researchers at any stage of their career to present their work. NASC 2023 was the successful second edition of the NASC meeting series, and this proceedings article highlights the research and impressions of some of the speakers at NASC 2023.

Supramolecular macrocyclic forces have been used to trap phytate, myo-inositol-1,2,3,4,5,6-hexakisphosphate, a key bioanion with multiple roles in metabolic processes. Due to the complex chemistry of six multivalent phosphates surrounding the small, cyclic inositol framework, crystallographic information of simple phytate salts has been elusive. This report represents a combined crystallographic, theoretical, and solution binding investigation of a supramolecular macrocyclic complex of phytate. Together, the results provide significant insight to phytate's intramolecular and intermolecular interactions at the microenvironment level. The macrocycle-phytate aggregates consist of phytate anionic pairs, each partly sandwiched by two 24-membered, amide/amine-based cationic macrocycles. The phytate ion pairs hold the tetrameric macrocyclic array together by six strong intermolecular hydrogen bonds. Both phytates crystallize in 1a5e phosphate conformations (one axial (P2) and five equatorial phosphates). Solution NMR binding studies in 1 : 1 DMSO-d6 : D2O indicate 2 : 1 macrocycle:phytate associations, suggesting that the sandwich-like nature of the complex holds together in solution. DFT studies indicate the likely occurrence of dynamic intramolecular interchange of phosphate protons, as well as important roles for the axial (P2) phosphate in both intramolecular and intermolecular hydrogen bonding interactions. Phytate, myo-inositol-1,2,3,4,5,6-hexakisphosphate (depicted by the turtle), is an important bioanion that plays multiple roles in metabolic processes. Supramolecular macrocyclic forces have been used to trap phytate, resulting in insight to its intramolecular and intermolecular interactions at the microenvironment level. Results indicate that an axial phosphate and proton interchange play important structural roles with changing environment.image

Thirty-six-membered ring macrocycles form sandwich-like channels for oligomeric chains of hexaphosphate clusters.

The bis[squaramido]ferrocene scaffold is introduced and shown to selectively bind and electrochemically report sulfate in competitive water/DMSO mixtures.

Hydrophobic and hydrophilic, monotopic and ditopic carboxamide pincer hosts containing ethyl, hexyl, 2-hydroxyethyl and 2-hydroxyethyl ethyl ether pendant arms were synthesized. Solubility trends indicated that solubilities in water or hydrocarbon solvents varied depending on the nature of the pendant arms. Binding constants for hydrophilic pincers were larger in general than their hydrophobic analogs. Significant synergistic binding effects for the ditopic hosts were not observed.

Supramolecular insight to intra- and inter-ionic interactions in two inositol hexaphosphate conformers as a function of pH was enabled by NMR and crystallographic studies. These findings also shed light on the complex interactive roles of extended salt-water arrays through the crystal "solution" lattice.

An unsymmetrical semirigid tetraurea macrocycle, 1, selectively traps SO42- with high affinity in a 0.5% water:DMSO-d(6) solution (K-a = 90,500 M-1). The macrocycle displays somewhat less affinity for HSO4- (Ka = 68,600 M-1), while Kas for OAc- and H2PO4- are approximately half that seen for SO42- (49,800 and 52,600 M-1, respectively). Cl- binds weakly (K-a = 3430 M-1), and essentially no affinity is observed for NO3-. Structural results for the SO42- and Cl- complexes indicate 1:1 1:anion complexes, with encapsulation of the SO42- but not for Cl-ion, which hovers at the macrocyclic periphery. For the ditopic biphenyl-4,4 '-dicarboxylate, each carboxylate binds to its own macrocycle in a sandwich-like mode, which shows a 2:1 1:dianion association. Binding studies indicate 1:1 binding for the monotopic anions in the 0.5% water:DMSO-d(6) solutions, but as the water content of the solvent is increased, the binding mode changes to a 2:1 1:anion association according to the binding studies in solution. Binding studies indicate that 1 maintains a significant tolerance for water up to 1:1 mixtures of water:DMSO-d(6).

Structurally elusive inositol hexakisphosphates have been trapped in host-guest sandwiches between two picolinamide macrocycles that remain intact in solution, aided by hydrogen bonds and electrostatic interactions. This first report of macrocyclic complexes of inositol hexakisphosphates provides structural insight to significant biosources of phosphorus that impact the global phosphorus cycle.

Carbon-hydrogen bonds in a cryptand cage boost chloride entrapment to ultrahigh affinity

An important biomolecule found in plant seeds and tissues, and in eukaryotic cells is myo ‐inositol‐1,2,3,4,5,6‐hexakisphosphate (phytate, IP 6 ). Phytate has many roles, including phosphate, myo ‐inositol, and mineral storage and retrieval in plants, and a number of metabolic roles, not all of which are known. Despite the importance of phytate in biology, structural information is limited. Aside from this report of the potassium phytate structure, K 3 [H 9 IP 6 ] · 2H 2 O, only the structures of the sodium and zinc salts have appeared. The potassium structure reveals the importance of metal ion chelation in stabilizing the conformation, and the two previously reported structures support this finding. Potassium ion and hydrogen bond bridges link the interwoven phytate networks throughout the lattice. 1 H NMR (800 MHz) titrations show the conformation crossover from the 1a5e to the 5a1e conformation between pH 9 and 10, and detailed 1 H deconvolution studies at low pH reveal the underlying pattern assignments for individual protons.

The Front Cover shows an overhead view of myo-inositol-1,2,3,4,5,6-hexakisphosphate, known as phytate. Along with it (clockwise from the top) are almonds, walnuts, pine nuts, selected beans, pecans, and cashews, with green peas at the center. Phytate plays a major role in mineral storage and retrieval in plant seeds and grains and is found in significant quantities in nuts and legumes. Despite its strong interaction with metal ions, this potassium structure is only the third crystal structure of a metal salt. This structure, along with the earlier Na and Zn structures, reveals the important role that chelation plays in phytate–metal interactions. More information can be found in the Communication by K. Bowman-James et al. For more on the story behind the cover research, see the Cover Profile.