A novel strategy for the recognition of anions in water using charge-neutral σ-hole halogen and chalcogen bonding acyclic hosts is demonstrated for the first time. Exploiting the intrinsic ...hydrophobicity of halogen and chalcogen bond donor atoms integrated into a foldamer structural molecular framework containing hydrophilic functionalities, a series of water-soluble receptors was constructed for an anion recognition investigation. Isothermal titration calorimetry (ITC) binding studies with a range of anions revealed the receptors to display very strong and selective binding of large, weakly hydrated anions such as I– and ReO4 –. This is achieved through the formation of 2:1 host–guest stoichiometric complex assemblies, resulting in an encapsulated anion stabilized by cooperative, multidentate, convergent σ-hole donors, as shown by molecular dynamics simulations carried out in water. Importantly, the combination of multiple σ-hole–anion interactions and hydrophobic collapse results in I– affinities in water that exceed all known σ-hole receptors, including cationic systems (β2 up to 1.68 × 1011 M–2). Furthermore, the anion binding affinities and selectivity trends of the first example of an all-chalcogen bonding anion receptor in pure water are compared with halogen bonding and hydrogen bonding receptor analogues. These results further advance and establish halogen and chalcogen bond donor functions as new tools for overcoming the challenging goal of anion recognition in pure water.
The unprecedented application of a chiral halogen‐bonding 3rotaxane host system for the discrimination of stereo‐ and E/Z geometric isomers of a dicarboxylate anion guest is described. Synthesised by ...a chloride anion templation strategy, the 3rotaxane host recognises dicarboxylates through the formation of 1:1 stoichiometric sandwich complexes. This process was analysed by molecular dynamics simulations, which revealed the critical synergy of halogen and hydrogen bonding interactions in anion discrimination. In addition, the centrally located chiral (S)‐BINOL motif of the 3rotaxane axle component facilitates the complexed dicarboxylate species to be sensed via a fluorescence response.
The discrimination between dicarboxylate stereo‐ and geometric isomers by a chiral halogen‐bonding 3rotaxane can be monitored in terms of the fluorescence response. Computational modelling studies revealed the critical synergy between the axle of the rotaxane host and macrocycle components in achieving dicarboxylate guest selectivity.
The application of chiral interlocked host molecules for discrimination of guest enantiomers has been largely overlooked, which is surprising given their unique three-dimensional binding cavities ...capable of guest encapsulation. Herein, we combined the stringent linear geometric interaction constraints of halogen bonding (XB), the noncovalent interaction between an electrophilic halogen atom and a Lewis base, with highly preorganized and conformationally restricted chiral cavities of 2rotaxanes to achieve enantioselective anion recognition. Representing the first detailed investigation of the use of chiral XB rotaxanes for this purpose, extensive 1H NMR binding studies and molecular dynamics (MD) simulation experiments revealed that the chiral rotaxane cavity significantly enhances enantiodiscrimination compared to the non-interlocked free axle and macrocycle components. Furthermore, by examining the enantioselectivities of a family of structurally similar XB 2rotaxanes containing different combinations of chiral and achiral macrocycle and axle components, the dominant influence of the chiral macrocycle in our rotaxane design for determining the effectiveness of chiral discrimination is demonstrated. MD simulations reveal the crucial geometric roles played by the XB interactions in orientating the bound enantiomeric anion guests for chiral selectivity, as well as the critical importance of the anions’ hydration shells in governing binding affinity and enantiodiscrimination.
Electron-deficient heavy chalcogen atoms contain Lewis acidic σ-holes which are able to form attractive supramolecular interactions, known as chalcogen bonding (ChB), with Lewis bases. However, their ...potential in solution-phase anion binding applications is only just beginning to be realized in simple acyclic systems. Herein, we explore the 5-(methylchalcogeno)-1,2,3-triazole (chalcogen = Se, Te) motif as a novel ChB donor for anion binding. Other than being chemically robust enough to be incorporated into macrocyclic structures, thereby significantly expanding the scope and complexity of ChB host systems, we also demonstrate, by 1H NMR and DFT calculations, that the chalcogen atoms oriented within the macrocycle cavity are able to chelate copper(I) endotopically. Exploiting this property, the first examples of mechanically interlocked 2rotaxanes containing ChB-donor groups are prepared via an active metal template strategy. Solution-phase 1H NMR and molecular modeling studies provide compelling evidence for the dominant influence of ChB in anion binding by these interlocked host systems. In addition, unprecedented charge-assisted ChB-mediated anion binding was also studied in aqueous solvent mixtures, which revealed considerable differences in anion recognition behavior in comparison with chalcogen-free host analogues. Moreover, DFT calculations and molecular dynamics simulations in aqueous solvent mixtures indicate that the selectivity is determined by the different hydrophilic characters of the anions allied to the hydration of the binding units in the presence of the anions. Exploiting the NMR-active nuclei of the ChB-donor chalcogen atoms, heteronuclear 77Se and 125Te NMR were used to directly study how anion recognition influences the local electronic environment of the chalcogen atoms in the mechanically bonded rotaxane binding sites in organic and aqueous solvent mixtures.
The design and construction of neutral interlocked host molecules for anion recognition are rare. Using an active‐metal template approach, the preparation of a family of neutral halogen bonding (XB) ...rotaxanes containing two, three and four iodotriazole groups integrated into the macrocycle and axle components is achieved. In spite of the interlocked hosts’ neutrality, such rotaxane systems are capable of binding halide anions strongly and selectively in wet organic solvent mixtures. Importantly, halide‐binding strength and selectivity can be modulated by varying the number and position of the halogen bond donor iodotriazole groups within the interlocked cavity; the rotaxane containing the largest number of halogen bond donor groups exhibits the highest halide anion‐binding affinities. By varying the percentage of water content in the solvent, neutral XB donor‐mediated anion‐binding strength is also demonstrated to be highly sensitive to solvent polarity.
A family of neutral halogen‐bonding rotaxanes have been prepared that show remarkably strong binding and selectivity for halides in water–acetone solvent mixtures. Halide binding strength and selectivity can be modulated by varying the number and position of the halogen bond donor iodotriazole groups within the interlocked host cavity, as well as by changing the solvent polarity.
Chiral halogen bonding (S)-BINOL-based receptors are demonstrated to enhance the enantioselective recognition and sensing of chiral anions compared to their hydrogen bonding analogues. Computational ...studies attribute this behaviour to the strict linearity of halogen bonding (XB) and steric environment conferred by the XB donor groups bridged by the (S)-BINOL motif.
A neutral redox‐active acyclic halogen bonding (XB) receptor with a ferrocene core functionalised at the 1,3‐positions of a cyclopentadienyl ring with iodotriazole motifs is prepared. Owing to ...favourable host‐guest size‐complementarity, the receptor was found to be selective for azide over a diverse range of anions with different geometries. Voltammetric studies revealed the unique ability of the XB ferrocene receptor to selectively sense azide via a significant cathodic shift of its ferrocene/ferrocenium redox couple. Notably, much weaker binding of azide was observed for the hydrogen bonding 1,3‐bis‐prototriazole ferrocene receptor analogue, which also displayed a poorer electrochemical response, suggesting that halogen bonding interactions play crucial roles in the binding and sensing of azide.
The first halogen bonding redox‐active ferrocene receptor that binds and electrochemically senses azide selectively in solution is reported, which shows greatly improved sensitivity and discrimination compared to its hydrogen bonding analogue.
Polylactide (PLA) is a fully biodegradable and recyclable plastic, produced from a bio‐derived monomer: it is a circular economy plastic. Its properties depend upon its stereochemistry and isotactic ...PLA shows superior thermal‐mechanical performances. Here, a new means to control tacticity by exploiting rotaxane conformational dynamism is described. Dynamic achiral 2rotaxanes can show high isoselectivity (Pi=0.8, 298 K) without requiring any chiral additives and enchain by a chain end control mechanism. The organocatalytic dynamic stereoselectivity is likely applicable to other small‐molecule and polymerization catalyses.
Circular economy: Polylactide (PLA) is a fully biodegradable and recyclable plastic, produced from a bio‐derived monomer. By exploiting the conformational dynamism of an achiral rotaxane catalyst, the tacticity of the PLA product can be controlled without requiring any chiral additive.
Novel chiral halogen and chalcogen bonding receptors exhibit different selectivities for stereo- and geometric dicarboxylate isomers compared to a hydrogen bonding analogue. The unique geometric and ...electronic properties of the chalcogen bonding receptor facilitate the diagnostic fluorescence sensing of geometric dicarboxylate isomer guest species.
Strong global demand for tropical timber and agricultural products has driven large-scale logging and subsequent conversion of tropical forests. Given that the majority of tropical landscapes have ...been or will likely be logged, the protection of biodiversity within tropical forests thus depends on whether species can persist in these economically exploited lands, and if species cannot persist, whether we can protect enough primary forest from logging and conversion. However, our knowledge of the impact of logging and conversion on biodiversity is limited to a few taxa, often sampled in different locations with complex land-use histories, hampering attempts to plan cost-effective conservation strategies and to draw conclusions across taxa. Spanning a land-use gradient of primary forest, once- and twice-logged forests, and oil palm plantations, we used traditional sampling and DNA metabarcoding to compile an extensive data set in Sabah, Malaysian Borneo for nine vertebrate and invertebrate taxa to quantify the biological impacts of logging and oil palm, develop cost-effective methods of protecting biodiversity, and examine whether there is congruence in response among taxa. Logged forests retained high species richness, including, on average, 70% of species found in primary forest. In contrast, conversion to oil palm dramatically reduces species richness, with significantly fewer primary-forest species than found on logged forest transects for seven taxa. Using a systematic conservation planning analysis, we show that efficient protection of primary-forest species is achieved with land portfolios that include a large proportion of logged-forest plots. Protecting logged forests is thus a cost-effective method of protecting an ecologically and taxonomically diverse range of species, particularly when conservation budgets are limited. Six indicator groups (birds, leaf-litter ants, beetles, aerial hymenopterans, flies, and true bugs) proved to be consistently good predictors of the response of the other taxa to logging and oil palm. Our results confidently establish the high conservation value of logged forests and the low value of oil palm. Cross-taxon congruence in responses to disturbance also suggests that the practice of focusing on key indicator taxa yields important information of general biodiversity in studies of logging and oil palm.
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