1,725 research outputs found
Nitrosonium complexation by the tetraphosphonate cavitand 5,11,17,23-tetramethyl-6,10:12,16:18,22:24,4-tetrakis(phenylphosphonato-κ2O,O)resorcin(4)arene
No full textThe crystal structure of a new supramolecular complex between the tetraphosphonate cavitand 5,11,17,23-tetramethyl-6,10:12,16:18,22:24,4-tetrakis(phenylphosphonato-κ2O,O′)resorcin(4)arene and the nitrosyl cation NO+, as the BF4− salt, is reported. The complex, of general formula [(C56H44P4O12)(NO)]BF4·CH2Cl2 or NO@Tiiii[H, CH3, C6H5] BF4·CH2Cl2, crystallizes in the space group P-1. The nitrosyl cation is disordered over two equivalent positions, with occupancies of 0.503 (2) and 0.497 (2), and interacts with two adjacent P=O groups at the upper rim of the cavitand through dipole–charge interactions. In the lattice, the cavitands are connected through a series of C—H...π interactions involving the methyl and methylenic H atoms and the aromatic rings of the macrocycle. The structure is further stabilized by the presence of C—H...F interactions between the hydrogen atoms of the cavitands and the F atoms of the tetrafluoridoborate anion. As a result of the disorder, the lattice dichloromethane molecules could not be modelled in terms of atomic sites, and were treated using the PLATON SQUEEZE procedure [Spek (2015). Acta Cryst. C71, 9–18]. The complexation process has also been studied in solution through NMR titrations
Supramolecular Sensing with Phosphonate Cavitands
No full textMolecular recognition is a recurrent theme in chemical sensing because of the importance of selectivity for sensor performances. The popularity of molecular recognition in chemical sensing has resulted from the progress made in mastering weak interactions, which has enabled the design of synthetic receptors according to the analyte to be detected.
However, the availability of a large pool of modular synthetic receptors so far has not had a significant impact on sensors
used in the real world. This technological gap has emerged because of the difficulties in transferring the intrinsic molecular
recognition properties of a given receptor from solution to interfaces and in finding high fidelity transduction modes for the
recognition event. This Account focuses on the ways to overcome these two bottlenecks, and we recount our recent efforts to
produce highly selective supramolecular sensors using phosphonate cavitands as receptors. Through two examples, we
present an overview of the different operating strategies that are implemented depending on whether the interface is vapor-solid or liquid-solid.
First we describe the selective detection of short chain aliphatic alcohols in the vapor phase. In this example, we solved a key
issue common to all sensors for organic vapors: the dissection of the specific interaction (between cavitand and the alcohol) from
ubiquitous nonspecific dispersion interactions (between the analytes and interferents in the solid layer). We removed responses resulting from the nonspecific interactions of the analytes with interferents by directly connecting the recognition event at the interface to the transduction mechanism (photoinduced charge transfer).
The second example addresses the specific detection of sarcosine in urine. Recent research has suggested that sarcosine can serve as reliable biomarker of the aggressive forms of prostate cancer. Tetraphosphonate cavitands can complex N-methyl ammonium salts with impressive selectivity in solution, and we used this property as a starting point.
The sensor implementation requires that we first graft the cavitand onto silicon and gold surfaces as monolayers. The
exclusive recognition of sarcosine by these supramolecular sensors originates from their operation in aqueous environments, where synergistic multiple interactions with the phosphonate cavitand are possible only for N-methyl ammonium derivatives. We couple that selectivity with detection modes that probe the strength of the complexation either directly (microcantilever) or via exchange with molecules that have comparable affinity for the cavity (fluorescence dye dispacement)
Environmental Gas Sensing with Cavitands
No full textEnvironmental gas sensing needs stringent sensor requirements in terms of sensitivity, selectivity and ruggedness. One of the major issues to be addressed is combining in a single device the conflicting requirements of molecular-level selectivity and low-ppb sensitivity. The exploitation of synthetic molecular receptors as sensing materials is particularly attractive to address the selectivity issue, to single out the desired analytes in the presence of overwhelming amounts of interferents. This minireview summarizes the strategies in environmental gas and vapor sensing using molecular receptors as selective hosts for specific analytes, with the main focus on cavitands. In particular, we highlight the use of these macrocycles as selective preconcentrator units to be integrated into portable devices for environmental monitoring. Depending on the class of analytes to be detected, the molecular recognition properties of cavitands can be manipulated through the proper choice of the bridging groups at the upper rim, and their transducer integration can be implemented through the manifold functionalization options at the lower rim
Cavitands at Work: From Molecular Recognition to Supramolecular Sensors
No full textExploitation of the molecular recognition properties of a given receptor in analytical applications requires mastering of specific host-guest interactions at interfaces. This review outlines the issues involved in turning P-V-bridged cavitands into selective layers for mass sensors, as a case study for gas-solid interfaces. The specific interactions operating at each phase level can be ferreted out by use of MS and crystallographic analyses, respectively. Their influence on sensor selectivity can be enhanced by exposure of the guest (analyte) to a network of cooperative interactions encoded in a single cavitand receptor. On the other hand, high layer permeability - necessary to achieve fast and reversible sensor responses - increases non-specific dispersion interactions. Shifting of the balance towards selectivity without loss of reversibility represents the major challenge facing those wishing to venture into the field of supramolecular sensors
Impiego di un Sistema Olfattivo Artificiale (SOA ) per il controllo della conservabilità della carne di lumaca
No full textLa richiesta sul mercato di prodotti a base di carne di lumaca è aumentata in maniera rilevante in questi ultimi 10 anni; in particolare tale aumento è ascrivibile a lumache commercializzate vive. Il controllo ufficiale di questo prodotto si avvale tuttora della valutazione organolettica della freschezza, facilmente applicabile dagli operatori sanitari ma con il limite di essere soggettiva. In questo lavoro si descrive l’impiego di un Sistema Olfattivo Artificiale (SOA) allo scopo di monitorare, in maniera obiettiva, lo sviluppo dell’odore durante la conservazione di carne di lumaca a +5°C per
14 giorni. Sottoponendo i dati così ottenuti ed elaborandoli con la tecnica dell’analisi multivariate (PCA), è stato possibile separare i dati in tre classi, con un tasso di discriminazione anche del 99,5%.
Questa classificazione ha permesso di determinare la qualità del campione analizzato in funzione del tempo e delle condizioni di conservazione
Cavitand-Based Coordination Cages: Achievements and Current Challenges
No full textThe research results obtained in the self-assembly of cavitand-based coordination cages are presented. Cavitands are ideal multidentate ligands for the creation of coordination cages due to their structural rigidity, concave structure, and great versatility in terms of synthetic modularity. The introduction of the ligand moieties on the resorcinarene building block proceeds at the upper rim of the cavity, to take full advantage of the structural rigidity of the cavitand scaffold. Two different synthetic strategies are employed for the formation of multidentate cavitand ligands: (a) functionalization at the apical positions and (b) introduction of the ligands as bridging units. The key features to control the cage self-assembly process emerging from this overview are the preorganization, for the cavitands, and kinetic versus thermodynamic stability of the resulting complexes, for the connecting metal. The versatility of this class of coordination cages is demonstrated by the formation of their heterotopic and heteronuclear versions, as well as their self-assembly on gold and silicon surfaces. Desymmetrization of the cages is appealing because of the resulting differentiation of the inner cavities in terms of shape and interactivity, while surface self-assembly represents an important opportunity to expand the application range of these objects
Biochemical sensing with macrocyclic receptors
No full textPreventive 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
Formaggio a pasta dura a basso contenuto di sale
No full textL’eccessiva assunzione di sodio con la dieta è stata
documentata recentemente, su basi scientifiche, come
tra i fattori di rischio per le patologie cardiovascolari. Il
Regno Unito è tra i principali Paesi che stanno adottando
diverse strategie per la riduzione di sodio negli alimenti
a più largo consumo. Tuttavia la riduzione di sale
comporta inevitabilmente un effetto sfavorevole sulle
qualità organolettiche e sul sapore. Anche nei formaggi
a pasta dura e a lunga stagionatura il sale gioca un
ruolo importante oltre che nella conservazione anche
e soprattutto nel determinare le caratteristiche legate
alla gradevolezza. In questo studio vengono riportate
le analisi effettuate su campioni di formaggio a pasta
dura (GranSpeciale) con un contenuto di sale normale
e campioni dello stesso formaggio a contenuto ridotto
(-35%). L’impiego di un Sistema Artificiale Olfattivo (SOA)
ha permesso di verificare che il profilo aromatico dei
campioni presi in esame risulta pressoché sovrapponibile
(livello di discriminazione del 62,1%)
Probing the structural determinants of amino acid recognition: X-ray studies of crystalline ditopic host-guest complexes of the positively charged amino acids, ARg, Lys, and His with a cavitand molecule
No full textCrystallization of tetraphosphonate cavitand Tiiii[H, CH3, CH3] in the presence of positively charged amino acids, namely arginine, lysine, or histidine, afforded host-guest complex structures. The X-ray structure determination revealed that in all three structures, the fully protonated form of the amino acid is ditopically complexed by two tetraphosphonate cavitand molecules. Guanidinium, ammonium, and imidazolium cationic groups of the amino acid side chain are hosted in the cavity of a phosphonate receptor, and are held in place by specific hydrogen bonding interactions with the P=O groups of the cavitand molecule. In all three structures, the positively charged α-ammonium groups form H-bonds with the P=O groups, and with a water molecule hosted in the cavity of a second tetraphosphonate molecule. Furthermore, water-assisted dimerization was observed for the cavitand/histidine ditopic complex. In this 4:2 supramolecular complex, a bridged water molecule is held by two carboxylic acid groups of the dimerized amino acid. The structural information obtained on the geometrical constrains necessary for the possible encapsulation of the amino acids are important for the rational design of devices for analytical and medical applications
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