Formation of TbPc₂ Single-Molecule Magnets’ Covalent 1D Structures via Acyclic Diene Metathesis

We present here a reaction scheme to connect TbPc₂ single-molecule magnets into 1D architectures using acyclic diene metathesis. To investigate the impact of the bonding through aliphatic chains on the magnetic properties of TbPc₂, we isolate and characterize the dimeric species obtained as one of the products of the reaction. Remarkably, the magnetic properties are only slightly modified after the formation of the bond between molecules, enlightening the great potential of this reaction scheme

Cavitands Endow All-Dielectric Beads With Selectivity for Plasmon-Free Enhanced Raman Detection of <i>N</i>_ε‑Methylated Lysine

SiO₂/TiO₂ microbeads (T-rex) are promising materials for plasmon-free surface-enhanced Raman scattering (SERS), offering several key advantages in biodiagnostics. In this paper we report the combination of T-rex beads with tetraphosphonate cavitands (Tiiii), which imparts selectivity toward <i>N</i>_ε<i>-</i>methylated lysine. SERS experiments demonstrated the efficiency and selectivity of the T-rex-Tiiii assays in detecting methylated lysine hydrochloride (<i>N</i>_ε<i>-</i>Me-Lys-Fmoc) from aqueous solutions, even in the presence of the parent Lys-Fmoc hydrochloride as interferent. The negative results obtained in control experiments using TSiiii ruled out any other form of surface recognition or preferential physisorption. MALDI-TOF analyses on the beads exposed to <i>N</i>_ε<i>-</i>Me-Lys-Fmoc revealed the presence of the Tiiii•<i>N</i>_ε<i>-</i>Me-Lys-Fmoc complex. Raman analyses based on the intensity ratio of <i>N</i>_ε<i>-</i>Me-Lys-Fmoc and cavitand-specific modes resulted in a dose–response plot, which allowed for estimating the concentration of <i>N</i>_ε<i>-</i>methylated lysine from initial solutions in the 1 × 10^–3 to 1 × 10^–5 M range. These results can set the basis for the development of new Raman assays for epigenetic diagnostics

Design and synthesis of a cavitand pillar for MOFs

<div><p>In this paper, we report the first example of a tetramethylene bridged cavitand with two distal methylbenzoate legs at the lower rim, adopting a unique and unprecedented equatorial equatorial (<b>ee</b>) configuration both in solution and in the solid state, as confirmed by NMR and single crystal X-ray diffraction. The presence of functional groups, which are potential metal binding sites in the <b>ee</b> configuration, makes these cavitands suitable candidates to be used as pillars in metal-organic frameworks (MOF) as specific molecular recognition units.</p></div

Probing Molecular Recognition at the Solid–Gas Interface by Sum-Frequency Vibrational Spectroscopy

Molecular recognition is among the most important chemical events in living systems and has been emulated in supramolecular chemistry, driven by chemical and biochemical sensing potential. Identifying host–guest association in situ at the interface, between the substrate-bound receptors and the analyte-containing media, is essential to predict complexation performances in term of the receptor conformation, orientation and organization. Herein, we report the first sum-frequency vibrational spectroscopy study of molecular recognition at the solid–gas interface. The binding capability of tetraquinoxaline cavitands toward volatile aromatic and aliphatic compounds, namely benzonitrile and acetonitrile, is investigated as test system. We prove the selective complexation of the receptors, organized in a solid-supported hybrid bilayer, toward aromatic compounds. Quantitative analysis allows to correlate the average orientations of the guest molecules and the host binding pockets, establishing “on-axis” complexation of benzonitrile within the cavitand cavity. The study is readily applicable to other receptors, molecular architectures, interfaces and analytes

Polymer Blending through Host–Guest Interactions

In this work, a supramolecular approach, based on molecular recognition, was used to direct the blending of immiscible polymers toward compatibility and even molecular miscibility. A slight modification of the two immiscible polymers polystyrene (PS) and poly­(butyl methacrylate) (PBMA), with the introduction of the two recognition groups tetraphosphonate cavitand (HOST) and methylpyridinium (GUEST), respectively, led to the formation of compatible mixtures between them, characterized by a single <i>T</i>_g and by an homogeneous texture at the surface level, as evidenced by AFM measurements. The energetically favorable host–guest interactions among polymeric chains overcome their repulsive interfacial energy, leading to the suppression of phase segregation at the level of material. The complexation between PS–HOST and PBMA–GUEST copolymers has been demonstrated to be reversible by the action of a specific external stimulus in the form of guest exchange with the competitive <i>N</i>-methylbutyl ammonium chloride

Cavitand-Functionalized Porous Silicon as an Active Surface for Organophosphorus Vapor Detection

This paper reports on the preparation of a porous silicon-based material covalently functionalized with cavitand receptors suited for the detection of organophosphorus vapors. Two different isomeric cavitands, both containing one acid group at the upper rim, specifically designed for covalent anchoring on silicon, were grafted on H-terminated porous silicon (PSi) by thermal hydrosilylation. The covalently functionalized surfaces and their complexation properties were characterized by combining different analytical techniques, namely X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), and mass spectroscopy analysis coupled with thermal desorption experiments. Complexation experiments were performed by exposing both active surfaces and a control surface consisting of PSi functionalized with a structurally similar but inactive methylene-bridged cavitand (MeCav) to dimethyl methylphosphonate (DMMP) vapors. Comparison between active and inactive surfaces demonstrated the recognition properties of the new surfaces. Finally, the nature of the involved interactions, the energetic differences between active and inactive surfaces toward DMMP complexation, and the comparison with a true nerve gas agent (sarin) were studied by DFT modeling. The results revealed the successful grafting reaction, the specific host–guest interactions of the PSi-bonded receptors, and the reversibility of the guest complexation

Switching from Separated to Contact Ion-Pair Binding Modes with Diastereomeric Calix[4]pyrrole Bis-phosphonate Receptors

We describe the design, synthesis and conformational assignment of three diasteromeric bis-phosphonate cavitands based on an aryl extended calix[4]­pyrrole tetrol scaffold. The diastereoisomers differ in the relative spatial orientation of the PO groups installed at their upper rims. We demonstrate that these compounds act as heteroditopic receptors for ion pairs forming ion-paired 1:1 complexes with alkylammonium (quaternary and primary) chloride salts in dichloromethane (DCM) solution and in the solid-state. ¹H NMR titrations indicate that the complexes are highly stable thermodynamically and kinetically. In the case of tetraalkyl-phosphonium/ammonium chloride guests, the host featuring the two PO groups directed outwardly with respect to the aromatic cavity, <b>4oo</b>, produces the most thermodynamically stable complexes. Conversely, for the primary alkyl ammonium chloride, the most effective receptor is the diastereoisomer <b>4ii</b> with the two PO groups converging on top of the aromatic cavity. In the nonpolar DCM solvent, the size of the quaternary cation has a strong impact in the thermodynamic stability of the complexes and their binding geometry. We use 2D-ROESY experiments to map out the binding geometries of the 1:1 complexes formed in solution. The 1:1 complexes of the <b>4oo</b> host with the chloride salts have a <i>separated</i> arrangement of the bound ion-pair. In contrast, those of the <b>4ii</b> host display a <i>close-contact</i> arrangement. We also investigate the same complexation processes in acetonitrile (ACN) solution. Both the salt and the initially formed anionic complex are fully dissociated in this more polar solvent. The receptors show an analogous trend in their binding affinities for quaternary phosphonium/ammonium chloride salts to the one seen in DCM solution. However, in ACN solution, the magnitudes of the binding affinities are reduced significantly and the size of the cation does not play a role. In addition, the inversion in the trend of relative binding affinities of the complexes, which was revealed in DCM solution, is eradicated in ACN when changing the cation substitution from quaternary to primary

Switching from Separated to Contact Ion-Pair Binding Modes with Diastereomeric Calix[4]pyrrole Bis-phosphonate Receptors

We describe the design, synthesis and conformational assignment of three diasteromeric bis-phosphonate cavitands based on an aryl extended calix[4]­pyrrole tetrol scaffold. The diastereoisomers differ in the relative spatial orientation of the PO groups installed at their upper rims. We demonstrate that these compounds act as heteroditopic receptors for ion pairs forming ion-paired 1:1 complexes with alkylammonium (quaternary and primary) chloride salts in dichloromethane (DCM) solution and in the solid-state. ¹H NMR titrations indicate that the complexes are highly stable thermodynamically and kinetically. In the case of tetraalkyl-phosphonium/ammonium chloride guests, the host featuring the two PO groups directed outwardly with respect to the aromatic cavity, <b>4oo</b>, produces the most thermodynamically stable complexes. Conversely, for the primary alkyl ammonium chloride, the most effective receptor is the diastereoisomer <b>4ii</b> with the two PO groups converging on top of the aromatic cavity. In the nonpolar DCM solvent, the size of the quaternary cation has a strong impact in the thermodynamic stability of the complexes and their binding geometry. We use 2D-ROESY experiments to map out the binding geometries of the 1:1 complexes formed in solution. The 1:1 complexes of the <b>4oo</b> host with the chloride salts have a <i>separated</i> arrangement of the bound ion-pair. In contrast, those of the <b>4ii</b> host display a <i>close-contact</i> arrangement. We also investigate the same complexation processes in acetonitrile (ACN) solution. Both the salt and the initially formed anionic complex are fully dissociated in this more polar solvent. The receptors show an analogous trend in their binding affinities for quaternary phosphonium/ammonium chloride salts to the one seen in DCM solution. However, in ACN solution, the magnitudes of the binding affinities are reduced significantly and the size of the cation does not play a role. In addition, the inversion in the trend of relative binding affinities of the complexes, which was revealed in DCM solution, is eradicated in ACN when changing the cation substitution from quaternary to primary

Switching from Separated to Contact Ion-Pair Binding Modes with Diastereomeric Calix[4]pyrrole Bis-phosphonate Receptors

We describe the design, synthesis and conformational assignment of three diasteromeric bis-phosphonate cavitands based on an aryl extended calix[4]­pyrrole tetrol scaffold. The diastereoisomers differ in the relative spatial orientation of the PO groups installed at their upper rims. We demonstrate that these compounds act as heteroditopic receptors for ion pairs forming ion-paired 1:1 complexes with alkylammonium (quaternary and primary) chloride salts in dichloromethane (DCM) solution and in the solid-state. ¹H NMR titrations indicate that the complexes are highly stable thermodynamically and kinetically. In the case of tetraalkyl-phosphonium/ammonium chloride guests, the host featuring the two PO groups directed outwardly with respect to the aromatic cavity, <b>4oo</b>, produces the most thermodynamically stable complexes. Conversely, for the primary alkyl ammonium chloride, the most effective receptor is the diastereoisomer <b>4ii</b> with the two PO groups converging on top of the aromatic cavity. In the nonpolar DCM solvent, the size of the quaternary cation has a strong impact in the thermodynamic stability of the complexes and their binding geometry. We use 2D-ROESY experiments to map out the binding geometries of the 1:1 complexes formed in solution. The 1:1 complexes of the <b>4oo</b> host with the chloride salts have a <i>separated</i> arrangement of the bound ion-pair. In contrast, those of the <b>4ii</b> host display a <i>close-contact</i> arrangement. We also investigate the same complexation processes in acetonitrile (ACN) solution. Both the salt and the initially formed anionic complex are fully dissociated in this more polar solvent. The receptors show an analogous trend in their binding affinities for quaternary phosphonium/ammonium chloride salts to the one seen in DCM solution. However, in ACN solution, the magnitudes of the binding affinities are reduced significantly and the size of the cation does not play a role. In addition, the inversion in the trend of relative binding affinities of the complexes, which was revealed in DCM solution, is eradicated in ACN when changing the cation substitution from quaternary to primary

Switching from Separated to Contact Ion-Pair Binding Modes with Diastereomeric Calix[4]pyrrole Bis-phosphonate Receptors

We describe the design, synthesis and conformational assignment of three diasteromeric bis-phosphonate cavitands based on an aryl extended calix[4]­pyrrole tetrol scaffold. The diastereoisomers differ in the relative spatial orientation of the PO groups installed at their upper rims. We demonstrate that these compounds act as heteroditopic receptors for ion pairs forming ion-paired 1:1 complexes with alkylammonium (quaternary and primary) chloride salts in dichloromethane (DCM) solution and in the solid-state. ¹H NMR titrations indicate that the complexes are highly stable thermodynamically and kinetically. In the case of tetraalkyl-phosphonium/ammonium chloride guests, the host featuring the two PO groups directed outwardly with respect to the aromatic cavity, <b>4oo</b>, produces the most thermodynamically stable complexes. Conversely, for the primary alkyl ammonium chloride, the most effective receptor is the diastereoisomer <b>4ii</b> with the two PO groups converging on top of the aromatic cavity. In the nonpolar DCM solvent, the size of the quaternary cation has a strong impact in the thermodynamic stability of the complexes and their binding geometry. We use 2D-ROESY experiments to map out the binding geometries of the 1:1 complexes formed in solution. The 1:1 complexes of the <b>4oo</b> host with the chloride salts have a <i>separated</i> arrangement of the bound ion-pair. In contrast, those of the <b>4ii</b> host display a <i>close-contact</i> arrangement. We also investigate the same complexation processes in acetonitrile (ACN) solution. Both the salt and the initially formed anionic complex are fully dissociated in this more polar solvent. The receptors show an analogous trend in their binding affinities for quaternary phosphonium/ammonium chloride salts to the one seen in DCM solution. However, in ACN solution, the magnitudes of the binding affinities are reduced significantly and the size of the cation does not play a role. In addition, the inversion in the trend of relative binding affinities of the complexes, which was revealed in DCM solution, is eradicated in ACN when changing the cation substitution from quaternary to primary