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PE and EVOH compatibilization is investigated upon functionalization of PE with ODIN, a fluorescent molecule forming multiple H-bonds with EVOH. Two-photon microscopy is exploited to monitor the polymer blending before and after reprocessing.

Auxetics are materials characterized by a negative Poisson’s ratio (NPR), an uncommon mechanical behavior corresponding to a transversal deformation tendency opposite to the traditional materials. Here we present the first example of a 3D synthetic molecular auxetic polymer, obtained by embedding a conformationally expandable cavitand as crosslinker into a rigid polymer of intrinsic microporosity (PIM). The rigidity and microporosity of the polymeric matrix are pivotal to maximize the expansion effect of the cavitand that, under mechanical stress, can assume two different conformations: a compact vase one and an extended kite form. The auxetic behavior and the corresponding NPR of the proposed material is predicted by a specific micromechanical model that considers the cavitand volume expansion ratio, the fraction of the cavitand crosslinker in the polymer, and the mechanical characteristics of the polymer backbone. The reversible auxetic behavior of the material is experimentally verified via Digital Image Correlation technique (DIC) performed during the mechanical tests on films obtained by blending the auxetic crosslinked polymer with pristine PIM. Two specific control experiments prove that the mechanically driven conformational expansion of the cavitand crosslinker is the sole responsible of the observed NPR of the polymer.

Nanohybrids prepared by self-assembly of tetraphopshonate cavitands on silica nanoparticles enable selective detection of N-methylated amines at micromolar concentrations via STD-based NMR experiments.

Mechanochemical synthesis is an attractive preparative method that combines a green approach with versatility, efficiency, and rapidity of reaction. However, it often yields microcrystalline materi...

The dynamic behavior of supramolecular organic frameworks (SOFs) based on the rigid tetra-4-(4-pyridyl)phenylmethane (TPPM) organic tecton has been elucidated through 3D electron diffraction, X-ray powder diffraction and differential scanning calorimetry (DSC) analysis. The SOF undergoes a reversible single-crystal-to-single-crystal transformation when exposed to vapours of selected organic solvents, moving from a closed structure with isolated small voids to an expanded structure with solvated channels along the b axis. The observed selectivity is dictated by the fitting of the guest in the expanded SOF, following the degree of packing coefficient. The effect of solvent uptake on TPPM solid-state fluorescence was investigated, evidencing a significant variation in the emission profile only in the presence of chloroform.

We report a strategy for the realization of NMR chemosensors based on the spontaneous self-assembly of lower rim pyridinium-functionalized tetraphopshonate cavitands on commercial silica nanoparticles. These nanohybrids enable the selective detection of physiologically relevant

The unique temperature, solvent and pH drivenvase to kite equilibrium in quinoxaline cavitands allows the reversible uptake and release of guests. However, the cavity breathing associated with this...

The secondary structures of nucleic acids have an important influence on their cellular functions but can be difficult to identify and classify quickly. Here, we show that an arrayed suite of synthetic hosts and dyes is capable of fluorescence detection of oligonucleotide secondary structures. Multivariate analysis of different fluorescence enhancements-generated using cationic dyes that show affinity for both DNA G-quadruplexes and the synthetic hosts-enables discrimination between G-quadruplex structures of identical length and highly similar topological types. Different G-quadruplexes that display the same folding topology can also be easily differentiated by the number of G-quartets and sequence differences at the 3' or 5' ends. The array is capable of both differentiation and classification of the G-quadruplex structures at the same time. This simple non-invasive sensing method does not require the discovery and synthesis of specific G-quadruplex binding ligands, but employs a simple multicomponent approach to ensure wide applicability.

The formation of supramolecular structural units through self-assembly is a powerful method to design new architectures and materials endowed with specific properties. With the aim of adding a group of versatile tectons to the toolkit of crystal engineers, we have devised and synthesized four new V-shaped building blocks characterized by an aryl acetylene scaffold comprising three substituted pyridine rings connected by two triple bonds. The judicious choice of different substituents on the pyridine rings provides these tectons with distinctive steric, electrostatic and self-assembly properties, which influence their crystal structures and their ability of forming co-crystals. Co-crystals of the tectons with tetraiododifluorobenzene were obtained both via traditional and mechanochemical crystallization strategies, proving their potential for their use in crystal engineering. The energetic contributions of the supramolecular interactions at play in the crystal lattice have also been evaluated to better understand their nature and strength and rationalize their role in designing molecular crystals.

The eligibility of tetraquinoxaline cavitands (QxCav) as molecular grippers relies on their unique conformational mobility between a closed (vase) and an open (kite) form, triggered in solution by conventional stimuli like pH, temperature and ion concentration. In the present paper, the mechanochemical conformational switching of ad hoc functionalized QxCav covalently embedded in an elastomeric polydimethylsiloxane and in a more rigid polyurethane matrix is investigated. The rigid polymer matrix is more effective in converting mechanical force into a conformational switch at the molecular level, provided that all four quinoxaline wings are covalently connected to the polymer., Controlled switch: The Vase‐kite conformational switching of polymer embedded tetraquinoxaline cavitands is triggered by mechanical force.

Inclusion of polymethine cyanine dyes in the cavity of macrocyclic receptors is an effective strategy to alter their absorption and emission behavior in aqueous solution. In this paper, the effect of the host-guest interaction between cucurbit[8]uril (CB[8]) and a model trimethine indocyanine (Cy3) on dye spectral properties and aggregation in water is investigated. Solution studies, performed by a combination of spectroscopic and calorimetric techniques, indicate that the addition of CB[8] disrupts Cy3 aggregates, leading to the formation of a 1 : 1 host-guest complex with an association constant of 1.5×106 M-1 . At concentrations suitable for NMR experiments, the slow formation of a supramolecular polymer was observed, followed by precipitation. Single crystals X-ray structure elucidation confirmed the formation of a polymer with 1 : 1 stoichiometry in the solid state.

The removal of toxic and carcinogenic polycyclic aromatic hydrocarbons (PAHs) from water is one of the most intractable environmental problems nowadays, because of their resistance to remediation. This work introduces a highly efficient, regenerable membrane for the removal of PAHs from water, featuring excellent filter performance and pH-driven release, thanks to the integration of a cavitand receptor in electrospun polyacrylonitrile (PAN) fibers. The role of the cavitand receptor is to act as molecular gripper for the uptake/release of PAHs. To this purpose, the deep cavity cavitand BenzoQxCav is designed and synthetized and its molecular structure is elucidated via X-Ray diffraction. The removal efficiency of the new adsorbent material toward the 16 priority PAHs is demonstrated via GC-MS analyses at ng L-1 concentration. A removal efficiency in the 32%, to 99% range is obtained. The regeneration of the membrane is performed by exploiting the pH-driven conformational switching of the cavitand between the vase form, where the PAHs uptake takes place, to the kite one, where the PAHs release occurs. The absorbance and regeneration capability of the membrane are successfully tested in four uptake/release cycles and the morphological stability.

The ability to detect early damage is of great significance in load bearing composite materials used for high performance applications. Microdamages if left unchecked can grow under subsequent stress, leading to catastrophic structural failure. The sensing of early stage damage via nondestructive methods is therefore critically important for the safe use of these materials. Herein a supramolecular approach to self-diagnosis of early stage damage in a carbon fiber epoxy composite material, via the incorporation of a CB[8] based ternary complex as an additive is reported. The complex comprising a fluorescent probe and a quencher encapsulated by the CB[8] is introduced into the epoxy resin of the composite as a supramolecular cross-linking agent, whose stress-induced dissociation results in the turn on of fluorescence of the probe. In this way, detection of irreversible mechanical strain and fatigue at an early stage is attainable, enabling the assessment of microdamage in the material.

A new, deep tetra­quinoxaline-based cavitand has been synthesized, and its solid-state complex with benzene has been studied through X-ray diffraction analysis., We report the synthesis of a new macrocyclic receptor, namely 2,8,14,20-tetra­hexyl-4,24:6,10:12,16:18,22-O,O′-tetra­kis­[2,3-di­hydro-[1,4]dioxino[2,3-g]quinoxalin-7,8-di­yl]resorcin[4]arene, DeepQxCav, obtained by the addition of ethyl­ene glycol di­tosyl­ate to an octa­hydroxy quinoxaline cavitand. A 1:1 supra­molecular complex of this cavitand with benzene has been obtained and analysed through X-ray diffraction analysis. The complex, of general formula C92H88O16N8·C6H6, crystallizes in the space group C2/c, with the cavitand host located about a twofold rotation axis. The benzene guest, which is held inside the cavity by C—H⋯π inter­actions and dispersion forces, is disordered over two equivalent sites, one in a general position and one lying on a twofold axis. The crystal structure features C—H⋯O hydrogen bonds and C—H⋯π inter­actions involving the alkyl chains, the aromatic rings, and the O atoms of the dioxane moiety of the resorcinarene scaffold. The crystal studied was refined as a two-component twin.

© 2019 The Royal Society of Chemistry. Stimuli-responsive supramolecular assemblies are dynamic systems that can reversibly switch between different states upon external stimuli. In this context, metal coordination offers a reliable strategy for the preparation of stimuli responsive supramolecular architectures. Herein we report the preparation of a solvent-responsive cavitand-lanthanum coordination complex. A tetra-phosphonate cavitand has been functionalized with four hydroxyl moieties at the upper rim to form a pre-organized octadentate ligand capable of binding lanthanum salts. Exploiting the orthogonal recognition sites, two different complex architectures are formed in acetonitrile and acetone, respectively. The complexes have been characterized in solution by NMR spectroscopy, ITC experiments, while at the solid state, the single crystal structure of the acetonitrile derivative has been determined. Furthermore, as observed by DOSY-NMR spectroscopy, small quantities of acetone in acetonitrile are sufficient to trigger assembly interconversion.

The host-guest inclusion complexes of cucurbiturils with alkyl viologen have interesting architectures, chemical properties, and potential applications in sensors and nanotechnology. A highly hydrated triclinic crystal of cucurbit[8]uril (CB[8]) complexed by methyl hexadecyl viologen (MVC16) is characterized by the unprecedented coexistence in the crystal of three host-guest complexes with 3:2, 2:2, and 1:1 stoichiometries. In all these complexes, the hook-shaped alkyl chain of the MVC16 is hosted in the CB[8] macrocycles, while the methyl viologen moieties have various environments. In the Z-shaped 3:2 complex, a central CB[8] unit hosts two viologen heads in the cavity, while the 2:2 complex is held together by π-stacking interactions between two viologen units. In the square 2D tiling crystal packing of CB[8] macrocycles, the same site which favors the dimerization observed in the 2:2 complex is also statistically occupied by a single methyl viologen moiety of the 1:1 complex. The rational interpretation of the crystal structure represented an intriguing challenge, due to the complicated statistical disorder in the alkyl chains hosted in CB[8] units and in the methyl viologen moieties of 2:2 and 1:1 complexes. In contrast with the solution behavior dominated by the 2:1 complex, the coexistence of three host-guest complexes with 3:2, 2:2, and 1:1 ratios highlights the fundamental importance of packing effects in the crystallized supramolecular complexes. Therefore, the crystallization process has permitted us to capture different host-guest systems in a single crystal, revealing a supramolecular landscape in a single photo.

There is considerable interest in dynamic materials featuring modular components with nano-scale dimensions and controlled responsiveness to external stimuli. Supramolecular polymers are a class of materials that fulfil all these conditions well. Here, we present a family of host–guest supramolecular polymers that combine the outstanding complexing properties of tetraphosphonate cavitands toward N-methylpyridinium guests with molecular switching. The designed monomer is a cavitand featuring four inward facing PO groups at the upper rim and a single N-methylpyridinium unit at the lower rim, forming instantaneously a polymeric species in solution, thanks to the high complexation constants measured for these host–guest interactions. This system has been analyzed by NMR spectroscopy and electrochemical techniques. In order to interpret the results of diffusion-sensitive experiments, we took advantage of the X-ray crystal structure obtained for the polymeric species and developed an original treatment for the PGSE data by non-linear fitting. The analysis of the experimental data identified an isodesmic polymerization model at a monomer concentration below 20 mM, driven by intrachain host–guest interactions, and an additional level of tetrameric bundle aggregation above 20 mM, due to interchain dipolar and quadrupolar interactions. Two orthogonal disassembly procedures have been implemented: electrochemical reduction for the linear chains and solvent-driven dissolution for the bundles.

In this paper we report the synthesis and characterization of biocompatible multi-functional magnetic nanoparticles (MNPs) able to enhance the intracellular transport of N-methylated drugs. The Fe3O4 magnetic core was first functionalized with a mixed monolayer consisting of two different phosphonic acids having terminal acetylenic and amino groups, which provide an active platform for further functionalization with organic molecules. Then, a tetraphosphonate cavitand receptor (Tiiii) bearing an azide moiety and the N-hydroxysuccinimide (NHS) activated forms of poly(ethylene glycol) (PEG), folic acid (FA) and carboxy-X-rhodamine (Rhod) were covalently anchored on alkyne and amine moieties respectively, through 1,3-dipolar cycloaddition and EDC/NHS coupling reactions. The obtained MNPs are biocompatible and possess magnetic, luminescence and recognition properties which make them suitable for multimodal theranostic applications. In particular, combined confocal microscopy and cytotoxicity experiments showed that these multi-functional MNPs are able to recognize a specific drug "in situ'' and promote its cellular internalization, thus enhancing its efficiency.

Functional polyethylene (PE) bearing pendant hydroxyl groups was dynamically crosslinked via reactive extrusion using commercially available N,N′-Bis[3-(trimethoxysilyl)propyl] ethylenediamine (TMSPEDA). This fast and efficient way allowed to produce PE vitrimers without synthetic effort or use of solvents, which makes the process environmentally friendly and easy to upscale. The dynamic crosslinking transformed thermoplastic PE into an elastic solid with greatly improved melt strength as revealed by DMTA and rheology. Mechanical properties could be tuned by varying the amount of TMSPEDA crosslinker. All prepared vitrimers were sparingly soluble in xylene and were not affected by moisture demonstrating crosslinked character, improved solvent resistance and excellent hydrolysis resistance which is of great importance for industrial applications. Despite the crosslink nature of the material, the dynamic silyl ether exchange enabled processability and recyclability of this system using industrially relevant techniques like injection and compression molding.

A study leading to the development of a piezoelectric sensing device for environmental monitoring of aromatic micropollutants in water is reported. A Piezoelectric Quartz Crystal (PQC) was functionalized through electropolymerization of a quinoxaline cavitand, known to possess remarkable capabilities in selectively trapping aromatic compounds through multiple π-π and CH-π interactions. The obtained film was characterized via X-ray Photoelectron spectroscopy (XPS) to elucidate its chemical composition. The design and synthesis of the new quinoxaline cavitand functionalized at the upper rim with a bithiophene moiety suitable for electropolymerization is described. The molecular structure of the new receptor was elucidated via X-ray diffraction analysis. The performance of the obtained sensor towards selected chlorinated and not chlorinated hydrocarbons in water was tested. Excellent limit of detection (0.17 ppm), below the present stringent Italian value, was achieved for 1,2,4-trichlorobenzene, outperforming conventional systems. The frequencymetric sensor showed high reproducibility from independent functionalized PQCs, with RSD values lower than 5%.

Multiple hydrogen bonding motifs are promising tools for polymer functionalization to obtain adaptable networks combining advantages of permanently cross-linked systems with processability of thermoplastics. Here we describe the use of a new multiple hydrogen bonding motif to impart increased tensile strength, stiffness, barrier properties, and a plateau modulus after melting to functional polyolefins, while retaining adaptability of the polymer network. The cross-linked nature of these polymers was elucidated by thermal and mechanical analysis, revealing a raised glass transition and rheology similar to permanently cross-linked polymer matrices. The apolar polymer matrix was found to stabilize the new hydrogen bonding motif at elevated temperatures. The resulting polymer showed thermal resistance superior to ureidopyrimidone (UPy) motif functionalized materials, the most commonly employed synthetic multiple hydrogen bonding motif to date.

While pH-driven interconversion of tetraquinoxaline cavitands (QxCav) from vase to kite conformation has been extensively studied both in solution and at interfaces, cavitands behavior in solid matrices is still unexplored. Therefore, the synthesis of a new class of quinoxaline cavitand based copolymers is here reported; a soluble linear poly(butyl methacrylate) (PBMA) and an insoluble cross-linked polydimethylsiloxane (PDMS), ensuring a convenient incorporation of the switchable unit, were chosen as polymer matrices. Conformational studies, performed both in solution and at the solid state, confirmed the retention of vase → kite switching behavior when moving from monomeric units to polymeric structures.

Here, we provide the first structural characterization of host-guest complexation between cucurbit[7]uril (Q7) and dimethyllysine (KMe2 ) in a model protein. Binding was dominated by complete encapsulation of the dimethylammonium functional group. While selectivity for the most sterically accessible dimethyllysine was observed both in solution and in the solid state, three different modes of Q7-KMe2 complexation were revealed by X-ray crystallography. The crystal structures revealed also entrapped water molecules that solvated the ammonium group within the Q7 cavity. Remarkable Q7-protein assemblies, including inter-locked octahedral cages that comprise 24 protein trimers, occurred in the solid state. Cucurbituril clusters appear to be responsible for these assemblies, suggesting a strategy to generate controlled protein architectures.

Active materials are those capable of giving some physical reaction under external stimuli coming from the environment such as temperature, pH, light, mechanical stress, etc. Reactive polymeric materials can be obtained through the introduction of switchable molecules in their network, i.e. molecules having two distinct stable conformations: if properly linked to the hosting polymer chains, the switching from one state to the other can promote a mechanical reaction of the material, detectable at the macroscale, and thus enables us to tune the response according to a desired functionality. In the present paper, the main aspects of the mechanical behavior of polymeric materials with embedded switchable molecules—properly linked to the polymer's chains—are presented and discussed. Starting from the micro mechanisms occurring in such active material, a continuum model is developed, providing a straightforward implementation in computational approaches. Finally, some experimental outcomes related to a switchable molecules (known as quinoxaline cavitands) added to an elastomeric PDMS under chemical stimuli, are presented and quantitatively discussed through the use of the developed mechanical framework.

Solid-phase microextraction and gas chromatography-mass spectrometry followed by multivariate data analysis were used to analyze lung tissues from both healthy and carcinogenic patients. A total of 78 volatile compounds belonging to different chemical classes were identified, seven of which were able to discriminate between the two groups. Discriminant analysis allowed to correctly classify 98.3% of the cases. By using the leave-one-method, 100% of the cross-validated samples belonging to the "tumor" group was correctly classified, whereas 2 cross-validated healthy samples out of 48 were erroneously allocated in the "tumor" group. Achieved results suggest the need of further investigation to assess the role of the seven identified compounds as lung cancer biomarkers in breath analysis, thus allowing the development of low-cost diagnostic devices.

In this work we report a comprehensive study leading to the fabrication of a prototype sensor for environmental benzene monitoring. The required high selectivity and ppb-level sensitivity are obtained by coupling a silicon-integrated concentration unit containing the specifically designed EtQxBox cavitand to a miniaturized PID detector. In the resulting stand-alone sensor, the EtQxBox receptor acts at the same time as highly sensitive preconcentrator for BTEX and GC-like separation phase, allowing for the selective desorption of benzene over TEX. The binding energies of the complexes between EtQxBox and BTX are calculated through molecular mechanics calculations. The examination of the corresponding crystal structures confirms the trend determined by computational studies, with the number of C-H···N and CH···? interactions increasing from 6 to 9 along the series from benzene to o-xylene. The analytical performances of EtQxBox are experimentally tested via SPME, using the cavitand as fiber coating for BTEX monitoring in air. The cavitand EFs are noticeably higher than those obtained by using the commercial CAR-DVB-PDMS. The LOD and LOQ are calculated in the ng/m range, outperforming the commercial available systems in BTEX adsorption. The desired selective desorption of benzene is achieved by applying a smart temperature program on the EtQxBox mesh, which starts releasing benzene at lower temperatures than TEX, as predicted by the calculated binding energies. The sensor performances are experimentally validated and ppb level sensitivity toward the carcinogenic target aromatic benzene was demonstrated, as required for environmental benzene exposure monitoring in industrial applications and outdoor environment.

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.

Ureidopyrimidinone (UPy) is introduced into various polyethylenes (PEs) bearing hydroxyl groups by solution grafting, affording physically cross-linked PE via multiple H-bonding. Utilizing low melting UPy where the methyl group is substituted with isopropyl (isopropyl UPy, IPR-UPy), a reactive extrusion process is developed that allows significant shortening of the reaction time and elimination of the use of solvents and catalysts. Chemical grafting is confirmed by Fourier Transform Infrared Spectroscopy (FT-IR) and proton Nuclear Magnetic Resonance (1H NMR). Differential Scanning Calorimetry (DSC), rheology and Dynamical Mechanical Thermal Analysis (DMTA) are employed to investigate the thermal stability of the obtained polymers and reveal that UPy functionalized PE can be safely processed via reactive extrusion below 150 °C. Introduction of UPy significantly improves the mechanical properties and alters the rheology, showing that quadruple hydrogen bonding interactions are present both in the solid state and in the PE melt.

A hierarchical hybrid inorganic–organic system suited for the recognition of aromatic volatile organic compounds on brushlike ZnO fibers was synthetized. The hybrid material was obtained by a multistep approach based on the growth of ZnO nanorods onto electrospun ZnO fibers (average diameter 200 nm). The obtained nanostructured ZnO brushlike fibers (overall diameter 2 μm) were functionalized through the grafting of a bifunctional phosphonic linker (12-azidododecylphosphonic acid) followed by the anchoring of a specific cavitand receptor. The linker was anchored on ZnO fibers through the phosphonic group while the azide terminations reacted with a quinoxaline-bridged cavitand (QxCav) having four alkyne groups via “click” reaction. The anchoring steps were monitored through the evolution of the FT-IR features in the 3200–2800 cm–1 region due to C–Hx stretches and in the 2200–2000 cm–1 region due to the azide and alkyne groups of the phosphonic linker and QxCav. The recognition properties of this hybrid nano...

Herein, we present a modular indicator-displacement assay able to selectively recognize small molecules with biological relevance under competitive conditions. The assay relies on the change in affinity of macrocyclic receptors, such as cavitands, cyclodextrins or calixarenes, for monolayer-protected gold nanoparticles upon complexation of the respective target analyte. This change affects the equilibrium between the nanoparticles and a fluorescent reporter leading to a change in intensity of the fluorescent output signal. The recognition modules can be changed in order to tune the selectivity of the assay without affecting the nature of the output signal. The combined use of recognition modules results in an assay able to detect multiple analytes simultaneously with high selectivity.

The complexation of L-lactic acid by two isomeric diphosphonate cavitands was studied, both in solution and in the solid state. 1H and 31P NMR experiments and X-ray diffraction analysis on single crystals evidenced the formation of a supramolecular host–guest adduct with both synthetic receptors, driven by a combination of H-bonding and C–H⋯π interactions.

Since their first appearance in the chemistry scene thirty years ago, resorcinarene-based cavitands have been recognized to be a highly versatile class of compounds. Endowed with a rigid cavity of molecular dimensions, which can be decorated at the upper and lower rims with a variety of functional groups, they are efficient molecular receptors for chemical sensing, as well as tunable building blocks in the formation of covalent and supramolecular architectures. In this paper, we highlight and discuss “classic” and recent results concerning their chemistry, applications and crystal structure.

This study focuses on the influence of biochar – a solid, porous, carbonaceous material product resulting from biomass gasification of wood waste – on mechanical properties of cement mortars. In order to investigate its effectiveness for structural purposes, biochar is added in cement mortar in increasing percentages, up to 2.5% by weight of cement. Experimental findings show that, by including a proper biochar percentage, compressive and flexural strengths comparable to those of control specimens are obtained, with a slight increase in fracture energy. The use of biochar in building materials as carbon sink is also part of a strategy for the development of more sustainable materials within the construction industry, since the dual aim of storing carbon in a stable form in buildings and promoting waste reutilization by increasing the recycling rate could be achieved.

Two synthetic protocols for the introduction of fluorine atoms into resorcinarene-based cavitands, at the lower and upper rim, respectively, are reported. Cavitand 1, bearing four fluorocarbon tails, and cavitand 2, which presents a fluorine atom on the para position of a diester phosphonate phenyl substituent, were synthesized and their complexation abilities toward the model guest sarcosine methyl ester hydrochloride were evaluated via NMR titration experiments. The effect of complexation on the 19F NMR resonance of the probe is evident only in the case of cavitand 2, where the inset of the cation-dipole and H-bonding interactions between the P=O bridges and the guest is reflected in a sizable downfield shift of the fluorine probe.

Preventive healthcare asks for the development of cheap, precise and non-invasive sensor devices for the early detection of diseases and continuous population screening. The actual techniques used for diagnosis, e.g. MRI and PET, or for biochemical marker sensing, e.g. immunoassays, are not suitable for continuous monitoring since they are expensive and prone to false positive responses. Synthetic supramolecular receptors offer new opportunities for the creation of specific, selective and cheap sensor devices for biological sensing of specific target molecules in complex mixtures of organic substances. The fundamental challenges faced in developing such devices are the precise transfer of the molecular recognition events at the solid–liquid interface and its transduction into a readable signal. In this review we present the progress made so far in turning synthetic macrocyclic hosts, namely cyclodextrins, calixarenes, cucurbiturils and cavitands, into effective biochemical sensors and the strategies utilized to solve the above mentioned issues. The performances of the developed sensing devices based on these receptors in detecting specific biological molecules, drugs and proteins are critically discussed.

Reliable chemical sensors with high selectivity and sensitivity toward specific target molecules require rational synthesis of receptors, in-depth characterization of their complexation abilities and highly efficient transduction of the molecular recognition event. Here we report a steady-state and time-resolved fluorescence investigation of EtQxBox, a fluorescent conformationally blocked quinoxaline-based cavitand, aimed at assessing its selectivity toward aromatic versus non-aromatic analytes in solution. Fluorescence quenching of the EtQxBox in acetone is observed at increasing concentration of both aromatic (i.e. benzonitrile) and aliphatic (i.e. acetonitrile) compounds. The combination with fluorescence lifetime measurements permits to discriminate the predominantly static quenching of the aromatic analyte, due to non-fluorescent host–guest complex formation, from the mostly dynamic quenching of the non-aromatic compound, resulting from aspecific diffusive collisions between the fluorophore and the quencher. The equilibrium association constants for both the complexes have been estimated using Stern–Volmer model.

A micro-electro-mechanical system (MEMS) based pre-concentrator filled with a standard Tenax TA adsorbent as well as with a synthetic receptor designed to adsorb 3-hydroxy-3-methylhexanoic acid (3H3MHA), a particular metabolite only available from human beings, was adapted to a custom made ion mobility spectrometer with gas-chromatographic pre-separation (GC-IMS). This combination was compared to a traditional sample loop GC-IMS. The application of a pre-concentrator is highly beneficial for the GC-IMS as analysing technique. By variation of the adsorbed sample volume, the system can be adapted to changing sample concentration ranges easily, thus increasing sensitivity significantly. Detection limits of few hundred ppqV could be obtained in this work for eucalyptol and 3 human metabolites (benzaldehyde, 2-ethyl-1-hexanol and decanal) as exemplary analytes. Moreover, the appropriate choice of selective pre-concentration phases in the pre-concentrator enables an adaptation of sampling to the composition of the mixture. Relevant compounds in very low concentrations can be amplified by using specially designed cavitands while interfering substances could be suppressed. This was successfully demonstrated by detecting 3H3MHA, a compound exclusively available in human sweat, which can be used to locate trapped or hidden individuals.

The complexation between 2-ureido-4[1H]-pyrimidinone (UPy) and 2,7-diamido-1,8-naphthyridine (NaPy) is used to promote the mild chemisorption of a UPy-functionalized terbium(III) double decker system on a silicon surface. The adopted strategy allows the single-molecule magnet behavior of the system to be maintained unaltered on the surface.