The Photochemical Mediated Ring Contraction of 4H-1,2,6-Thiadiazines To Afford 1,2,5-Thiadiazol-3(2H)-one 1-Oxides

1,2,6-Thiadiazines treated with visible light and 3O2 under ambient conditions are converted into difficult-to-access 1,2,5-thiadiazole 1-oxides (35 examples, yields of 39-100%). Experimental and theoretical studies reveal that 1,2,6-thiadiazines act as triplet photosensitizers that produce 1O2 and then undergo a chemoselective [3 + 2] cycloaddition to give an endoperoxide that ring contracts with selective carbon atom excision and complete atom economy. The reaction was optimized under both batch and continuous-flow conditions and is also efficient in green solvents.

Exploring how changes to the steroidal core alter oleogelation capability in sterol: γ-oryzanol blends

Oleogels based on sterols such as β-sitosterol blended with the sterol ester γ-oryzanol are a very interesting class of systems, but there are aspects of their formation and structure that remain elusive. It has previously been shown that a methyl group on the C30 position of the sterol-ester plays an important role in gelation. This work explored the effect that having C30 methyl groups on both the sterol and the sterol-ester had on the gelation process and subsequent gel structure. Lanosterol and saponified γ-oryzanol (which was synthesized as part of this study) were identified as materials of interest, as both feature a methyl group on the C30 position of their steroidal cores. It was observed that both sterols formed gels when blended with γ-oryzanol, and also that lanosterol gelled sunflower oil without the addition of γ-oryzanol. All of these gels were significantly weaker than that formed by β-sitosterol blended with γ-oryzanol. To explore why, molecular docking simulations along with AFM and SAXS were used to examine these gels on a broad range of length scales. The results suggest that saponified γ-oryzanol-γ-oryzanol gels have a very similar structure to that of β-sitosterol-γ-oryzanol gels. Lanosterol-γ-oryzanol gels and pure lanosterol gel, however, form with a totally different structure facilitated by the head-to-tail stacking motif exhibited by lanosterol. These results give further evidence that relatively slight changes to the molecular structure of gelators can result in significant differences in subsequent gel properties.

8,8'-(Benzo[c][1,2,5]thiadiazole-4,7-diyl)bis(quinolin-4(1H)-one): a twisted photosensitizer with AIE properties

A new benzothiadiazole (BTZ) luminogen is prepared via the Suzuki-Miyaura Pd-catalysed C-C cross-coupling of 8-iodoquinolin-4(1H)-one and a BTZ bispinacol boronic ester. The rapid reaction (5 min) affords the air-, thermo-, and photostable product in 97% yield as a yellow precipitate that can be isolated by filtration. The luminogen exhibits aggregated-induced emission (AIE) properties, which are attributed to its photoactive BTZ core and nonplanar geometry. It also behaves as a molecular heterogeneous photosensitizer for the production of singlet oxygen under continuous flow conditions.

Targetable Mechanical Properties by Switching between Self-Sorting and Co-assembly with In Situ Formed Tripodal Ketoenamine Supramolecular Hydrogels

A new family of supramolecular hydrogelators are introduced in which self-sorting and co-assembly can be utilised in the tuneability of the mechanical properties of the materials, a property closely tied to the nanostructure of the gel network. The in situ reactivity of the components of the gelators allows for system chemistry concepts to be applied to the formation of the gels and shows that molecular properties, and not necessarily the chemical identity, determines some gel properties in these family of gels.

Molecular Interactions behind the Self-Assembly and Microstructure of Mixed Sterol Organogels

In this work, we have employed docking and atomistic molecular dynamics (MD) simulations supported by complementary experiments using atomic force microscopy, rheology, and spectroscopy to investigate the self-assembled structure of β-sitosterol and γ-oryzanol molecules into cylindrical tubules in a nonaqueous solvent. Docking models of several phytosterols, including sitosterol, with oryzanol and other sterol esters demonstrate that for systems to form tubules, the phytosterol sterane group must be stacked in a wedge shape with the ester sterane group and a hydrogen bond must form between the hydroxyl group of the phytosterol and the carbonyl group of the ester. MD of the self-assembled structure were initiated with the molecules in a roughly cylindrical configuration, as suggested from previous experimental studies, and the configurations were found to be stable during 50 ns simulations. We performed MD simulations of two tubules in proximity to better understand the aggregation of these fibrils and how the fibrils interact in order to stick together. We found that an interfibril network of noncovalent bonds, in particular van der Waals and π-π contacts, which is formed between the ferulic acid groups of oryzanol through the hydroxyl, methoxy, and aromatic groups, is responsible for the surface-to-surface interactions between fibrils; an observation supported by molecular spectroscopy. We believe that these interactions are of primary importance in creating a strong organogel network.

Supramolecular Amino Acid Based Hydrogels: Probing the Contribution of Additive Molecules using NMR Spectroscopy

Supramolecular hydrogels are composed of self-assembled solid networks that restrict the flow of water. l-Phenylalanine is the smallest molecule reported to date to form gel networks in water, and it is of particular interest due to its crystalline gel state. Single and multi-component hydrogels of l-phenylalanine are used herein as model materials to develop an NMR-based analytical approach to gain insight into the mechanisms of supramolecular gelation. Structure and composition of the gel fibres were probed using PXRD, solid-state NMR experiments and microscopic techniques. Solution-state NMR studies probed the properties of free gelator molecules in an equilibrium with bound molecules. The dynamics of exchange at the gel/solution interfaces was investigated further using high-resolution magic angle spinning (HR-MAS) and saturation transfer difference (STD) NMR experiments. This approach allowed the identification of which additive molecules contributed in modifying the material properties.

Halogen effects on the solid-state packing of phenylalanine derivatives and the resultant gelation properties

Phenylalanine is an important amino acid both biologically, essential to human health, and industrially, as a building block of artificial sweeteners. Our interest in this particular amino acid and its derivatives lies with its ability to form gels in a number of solvents. We present here the studies of the influence of halogen addition to the aromatic ring on the gelation properties and we analyse the crystal structures of a number of these materials to elucidate the trends in their behaviour based on the halogen addition to the aromatic group and the interactions that result.

Gelation Landscape Engineering Using a Multi-Reaction Supramolecular Hydrogelator System

Simultaneous control of the kinetics and thermodynamics of two different types of covalent chemistry allows pathway selectivity in the formation of hydrogelating molecules from a complex reaction network. This can lead to a range of hydrogel materials with vastly different properties, starting from a set of simple starting compounds and reaction conditions. Chemical reaction between a trialdehyde and the tuberculosis drug isoniazid can form one, two, or three hydrazone connectivity products, meaning kinetic gelation pathways can be addressed. Simultaneously, thermodynamics control the formation of either a keto or an enol tautomer of the products, again resulting in vastly different materials. Overall, this shows that careful navigation of a reaction landscape using both kinetic and thermodynamic selectivity can be used to control material selection from a complex reaction network.

Supramolecular assembly in a Janus-type urea system

A pyrazolyl urea ligand exhibits marked conformational polymorphism, with the balance in conformer preference tipped by metallosupramolecular cluster assembly.

Use of in situ atomic force microscopy to follow phase changes at crystal surfaces in real time

AFM of cocrystals: Atomic force microscopy can be used to observe phase changes at crystal surfaces where the transformation is accompanied by a change in the spacing between layers of molecules. The conversion of a metastable polymorph of the caffeine-glutaric acid cocrystal into the thermodynamically stable form was analyzed continuously in situ using intermittent-contact-mode atomic force microscopy.

Cocrystal dissociation and molecular demixing in the solid state

A new cocrystal containing caffeine and theophylline was found to dissociate on heating, with caffeine and theophylline molecules spontaneously demixing and recrystallizing as separate phases, in a solid-solid transition likely driven by an increase in entropy. The morphology and composition of the resulting crystals was determined by transmission electron microscopy.

On crystal versus fiber formation in dipeptide hydrogelator systems

Naphthalene dipeptides have been shown to be useful low-molecular-weight gelators. Here we have used a library to explore the relationship between the dipeptide sequence and the hydrogelation efficiency. A number of the naphthalene dipeptides are crystallizable from water, enabling us to investigate the comparison between the gel/fiber phase and the crystal phase. We succeeded in crystallizing one example directly from the gel phase. Using X-ray crystallography, molecular modeling, and X-ray fiber diffraction, we show that the molecular packing of this crystal structure differs from the structure of the gel/fiber phase. Although the crystal structures may provide important insights into stabilizing interactions, our analysis indicates a rearrangement of structural packing within the fibers. These observations are consistent with the fibrillar interactions and interatomic separations promoting 1D assembly whereas in the crystals the peptides are aligned along multiple axes, allowing 3D growth. This observation has an impact on the use of crystal structures to determine supramolecular synthons for gelators.

Monofunctionalised cucurbit[6]uril synthesis using imidazolium host-guest complexation

Monohydroxylated cucurbit[6]uril was prepared for the first time through the controlled oxidation of CB[6] in the presence of a tailor-made bisimidazolium guest, as verified by (1)H NMR, ESI-MS and X-ray crystallography. Further chemical modification of monohydroxylated CB[6] was also readily achieved.

A cocrystal strategy to tune the luminescent properties of stilbene-type organic solid-state materials

The one- and two-photon luminescence of stilbene-type solid-state materials can be tuned and controlled from blue to yellow color by a supramolecular cocrystal method.