Multifunctional heterogeneous catalysts are an effective strategy to drive chemical cascades, with attendant time, resource and cost efficiencies by eliminating unit operations arising in normal multistep processes. Despite advances in the design of such catalysts, the fabrication of proximate, chemically antagonistic active sites remains a challenge for inorganic materials science. Hydrogen-bonded organocatalysts offer new opportunities for the molecular level design of multifunctional structures capable of stabilising antagonistic active sites. We report the catalytic application of a charge-assisted, hydrogen-bonded crystalline material, bis(melaminium)adipate (BMA), synthesised from melamine and adipic acid, which possesses proximate acid-base sites. BMA exhibits high activity for the cascade deacetalisation-Knoevenagel condensation of dimethyl acetals to form benzylidenemalononitriles under mild conditions in water; BMA is amenable to large-scale manufacture and recycling with minimal deactivation. Computational modelling of the melaminium cation in protonated BMA explains the observed catalytic reactivity, and identifies the first demethoxylation step as rate-limiting, in good agreement with time-dependent 1H NMR and kinetic experiments. A broad substrate scope for the cascade transformation of aromatic dimethyl acetals is demonstrated.

Therapeutic deep eutectic solvents (THEDES) have been attracting increasing attention in the pharmaceutical literature as a promising enabling technology capable of improving physicochemical and biopharmaceutical properties for difficult-to-deliver drug compounds. The current literature has explored amide local anaesthetics and carboxylic acid nonsteroidal anti-inflammatories (NSAIDs) as commonly used THEDES formers for their active hydrogen-bonding functionality. However, little is known about what happens within the \"deep eutectic\" region where a range of binary compositions present simply as a liquid with no melting events detectable across experimentally achievable conditions. There is also very limited understanding of how parent compounds\' physicochemical properties could impact upon the formation, interaction mechanism, and stability of the formed liquid systems, despite the significance of these information in dose adjustment, industrial handling, and scaling-up of these liquids. In the current work, we probed the \"deep eutectic\" phenomenon by investigating the formation and physicochemical behaviours of some chosen lidocaine-NSAID systems across a wide range of composition ratios. Our data revealed that successfully formed THEDES exhibited composition dependent Tg variations with strong positive deviations from predicted Tg values using the Gordon-Taylor theory, suggesting substantial interactions within the formed supramolecular structure. Interestingly, it was found that the parent compound\'s glass forming ability had a noticeable impact upon such profound interaction and hence could dictate the success of THEDES formation. It has also been confirmed that all successful systems were formed based on charge-assisted hydrogen bonding within their THEDES network, affirming the significant role of partial protonisation on achieving a profound melting point depression. More importantly, the work found that within the \"deep eutectic\" region there was still an ideal, or thermodynamically preferrable \"THEDES point\", which would exhibit excellent stability upon exposure to stress storage conditions. The discoveries of this study bring the literature one step closer to fully understanding the \"therapeutic deep eutectic\" phenomenon. Through correlation between parent reagents\' physicochemical properties and the synthesised products\' characteristics, we establish a more educated process for the prediction and engineering of THEDES.

The widespread coexistence of hydrophilic organic compounds and microplastics (MPs) in the environment has greatly increased their associated environmental problems. To evaluate the potential carrier effect of oxygen-containing MPs on coexisting pollutants, adsorption behaviors of four hydrophilic organic compounds (benzoic acid, sulfamethoxazole, sulfamerazine and ciprofloxacin) on MPs (pristine and weathered polyamide (PA)) were studied in the aquatic environment. The results showed that the surface morphology, size, oxygen content, molecular structure, surface charge and crystallinity of PA were changed after weathering, and the weathering degree of PA treated with heat-activated potassium persulfate was the highest. The main adsorption mechanisms included hydrogen bonding, hydrophobic interaction, charge-assisted hydrogen bonding, and electrostatic interaction. Hydrogen bonding and hydrophobic interaction contributed to the adsorption, while electrostatic interaction weakened the adsorption under the specific pH conditions. The formation of charge-assisted hydrogen bonding (CAHB) was also verified through pH influence experiments, and this force can overcome the electrostatic repulsion. The high adsorption of KPA (PA weathered by K2S2O8) under alkaline conditions was well explained by the formation of homonuclear CAHB due to the increase of oxygen-containing functional groups compared to the other three PA. Additionally, weathering did not always enhance the adsorption of hydrophilic organic compounds on PA, which was related to the changes in surface charge, crystallinity and hydrophilicity of PA. Overall, the physical and chemical properties (e.g., specific surface area, oxygen content, molecular structure) of PA after weathering and its trend of adsorption were different from other oxygen-free MPs in this study. This work can provide basic data for environmental risk of MPs and contribute to clarify and understand the processes of oxygenated MPs in the aquatic environment.

Chromogenic probes based onoxidizedbis(indolyl)methanes have been synthesized with varying substituents (R = -Me [1], -OMe [2], -OH, [3]) on the central aryl ring. In addition to electronic influence, the involvement of substituents in ion-dipole and charge-assisted hydrogen bonding interactions significantly alters the solvatochromic response and pH-sensitive behavior. In polar aprotic solvents, like CH3CN, a concentration-dependent stepwise color change was observed with F- ions. In the case of2, a reversible hydrogen bonding interaction between the deprotonated probe and HF2- dimer might be responsible for that, while step-wise deprotonation caused by F- ions could be the probable reason with3. Since the formation of HF2- is energetically unfavorable in a polar protic solvent, the response of 2 with F- ions appears to be very different in EtOH medium. Interestingly, no such alteration in anion sensing behavior was noticed with3going from an aprotic to a protic solvent.

The crystal structures of two polymorphs of a phenazine hexacyanoferrate(II) salt/cocrystal, with the formula (Hphen)3[H2Fe(CN)6][H3Fe(CN)6]·2(phen)·2H2O, are reported. The polymorphs are comprised of (Hphen)2[H2Fe(CN)6] trimers and (Hphen)[(phen)2(H2O)2][H3Fe(CN)6] hexamers connected into two-dimensional (2D) hydrogen-bonded networks through strong hydrogen bonds between the [H2Fe(CN)6]2- and [H3Fe(CN)6]- anions. The layers are further connected by hydrogen bonds, as well as through π-π stacking of phenazine moieties. Aside from the identical 2D hydrogen-bonded networks, the two polymorphs share phenazine stacks comprising both protonated and neutral phenazine molecules. On the other hand, the polymorphs differ in the conformation, placement and orientation of the hydrogen-bonded trimers and hexamers within the hydrogen-bonded networks, which leads to different packing of the hydrogen-bonded layers, as well as to different hydrogen bonding between the layers. Thus, aside from an exceptional number of symmetry-independent units (nine in total), these two polymorphs show how robust structural motifs, such as charge-assisted hydrogen bonding or π-stacking, allow for different arrangements of the supramolecular units, resulting in polymorphism.

In the cation of the title salt, C9H12N3S+·Br-, the thia-zolidine ring adopts an envelope conformation with the C atom adjacent to the phenyl ring as the flap. In the crystal, N-H⋯Br hydrogen bonds link the components into a three-dimensional network. Weak π-π stacking inter-actions between the phenyl rings of adjacent cations also contribute to the mol-ecular packing. A Hirshfeld surface analysis was conducted to qu-antify the contributions of the different inter-molecular inter-actions and contacts.

The title salt, C16H15ClN3S+·Br-, is isotypic with (E)-3-[(4-fluoro-benzyl-idene)amino]-5-phenyl-thia-zolidin-2-iminium bromide [Khalilov et al. (2019 ▸). Acta Cryst. E75, 662-666]. In the cation of the title salt, the atoms of the phenyl ring attached to the central thia-zolidine ring and the atom joining the thia-zolidine ring to the benzene ring are disordered over two sets of sites with occupancies of 0.570 (3) and 0.430 (3). The major and minor components of the disordered thia-zolidine ring adopt slightly distorted envelope conformations, with the C atom bearing the phenyl ring as the flap atom. In the crystal, centrosymmetrically related cations and anions are linked into dimeric units via N-H⋯Br hydrogen bonds, which are further connected by weak C-H⋯Br contacts into chains parallel to the a axis. Furthermore, not existing in the earlier report of (E)-3-[(4-fluoro-benzyl-idene)amino]-5-phenyl-thia-zolidin-2-iminium bromide, C-H⋯π inter-actions and π-π stacking inter-actions [centroid-to-centroid distance = 3.897 (2) Å] between the major components of the disordered phenyl ring contribute to the stabilization of the mol-ecular packing. Hirshfeld surface analysis and two-dimensional fingerprint plots indicate that the most important contributions for the crystal packing are from H⋯H (30.5%), Br⋯H/H⋯Br (21.2%), C⋯H/H⋯C (19.2%), Cl⋯H/H⋯Cl (13.0%) and S⋯H/H⋯S (5.0%) inter-actions.

In the cation of the title salt, C15H15N4S+·Br-·H2O, the central thia-zolidine ring adopts an envelope conformation with puckering parameters Q(2) = 0.279 (4) Å and φ(2) = 222.5 (9)°. The mean plane of the thia-zolidine ring makes dihedral angles of 12.4 (2) and 66.8 (3)° with the pyridine and phenyl rings, respectively. The pyridine ring in the title mol-ecule is essentially planar (r.m.s deviation = 0.005 Å). In the crystal, the cations, anions and water mol-ecules are linked into a three-dimensional network, which forms cross layers parallel to the (120) and (20) planes via O-H⋯Br, N-H⋯Br and N-H⋯N hydrogen bonds. C-H⋯π inter-actions also help in the stabilization of the mol-ecular packing. Hirshfeld surface analysis and 2D (two-dimensional) fingerprint plots indicate that the most important contributions to the crystal packing are from H⋯H (35.5%), C⋯H/H⋯C (23.9%), Br⋯H/H⋯Br (16.4%), N⋯H/H⋯N (10.6%) and S⋯H/H⋯S (7.9%) inter-actions.

The title Schiff base compounds, C20H16ClNO2 (I) and C24H22N2O2 (II), were synthesized via the condensation reaction of 2-amino-4-chloro-phenol for (I), and 2-(2,3-di-hydro-1H-indol-3-yl)ethan-1-amine for (II), with 4-benz-yloxy-2-hy-droxy-benzaldehyde. In both compounds, the configuration about the C=N imine bond is E. Neither mol-ecule is planar. In (I), the central benzene ring makes dihedral angles of 49.91 (12) and 53.52 (11)° with the outer phenyl and chloro-phenyl rings, respectively. In (II), the central benzene ring makes dihedral angles of 89.59 (9) and 72.27 (7)°, respectively, with the outer phenyl ring and the mean plane of the indole ring system (r.m.s. deviation = 0.011 Å). In both compounds there is an intra-molecular hydrogen bond forming an S(6) ring motif; an O-H⋯O hydrogen bond in (I), but a charge-assisted N+-H⋯O- hydrogen bond in (II). In the crystal of (I), mol-ecules are linked by C-H⋯π inter-actions, forming slabs parallel to plane (001). In the crystal of (II), mol-ecules are linked by pairs of N-H⋯O hydrogen bonds, forming inversion dimers. The dimers are linked by C-H⋯O hydrogen bonds, C-H⋯π inter-actions and a weak N-H⋯π inter-action, forming columns propagating along the a-axis direction. The anti-oxidant capacity of the synthesized compounds was determined by cupric reducing anti-oxidant capacity (CUPRAC) for compound (I) and by 2,2-picrylhydrazyl hydrate (DPPH) for compound (II).

By the solvothermal reaction under acidic conditions of Cu(NO3)2·3H2O, Na2C2O4 and the N,N\'-ditopic organic coligands 1-(pyridin-4-yl)piperazine (ppz) and 1,2-bis(pyridin-4-yl)ethane (bpa), two novel anionic copper(II) coordination compounds were obtained, namely the one-dimensional coordination polymer catena-poly[4-(pyridin-1-ium-4-yl)piperazin-1-ium [[(oxalato-κ2O1,O2)copper(II)]-μ-oxalato-κ3O1,O2:O1\']], {(C9H15N3)[Cu(C2O4)2)]}n or {(H2ppz)[Cu(C2O4)2]}n, (I), and the discrete ionic complex 4,4\'-(ethane-1,2-diyl)dipyridinium bis(oxalato-κ2O1,O2)copper(II), (C12H14N2)[Cu(C2O4)2] or (H2bpa)[Cu(C2O4)2], (II). The products were characterized by single-crystal X-ray diffraction, elemental analysis, powder X-ray diffraction, thermogravimetric analyses and UV and IR spectroscopic techniques. The [Cu(C2O4)2]2- units for (I) and (II) are stabilized by H2ppz2+ and H2bpa2+ cations, respectively, via charge-assisted hydrogen bonds. Also, a study of the pH-controlled synthesis of this system shows that (I) was obtained at pH values of 2-4. When using bpa, a two-dimensional square-grid network of [Cu(C2O4)(bpa)]n was obtained at a pH of 4. This indicates that the pH of the reaction also plays a key role in the structural assembly and coordination abilities of oxalate and N,N\'-ditopic coligands.