Methyl Hexadecyl Viologen Inclusion in Cucurbit[8]uril: Coexistence of Three Host-Guest Complexes with Different Stoichiometry in a Highly Hydrated Crystal

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 \u3c0-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

The Role of Chain Length in Cucurbit[8]uril Complexation of Methyl Alkyl Viologens

Viologens are among the most studied guests for cucurbit[8]uril (CB[8]) and their complexation is usually driven by bipyridyl core inclusion inside the cavity to maximize both hydrophobic and cation-dipole interactions. The presence of alkyl substituents on the guest alters this complexation mode, switching to aliphatic chain inclusion in U-folded conformation. Herein, we report a thorough study of the influence of the alkyl chain length on the binding mode of methyl alkyl viologens. The chain length of the studied guests was increased by two methylene groups starting from methyl dodecyl viologen (MVC12) to the octadecyl analogue (MVC18). Complexation in water, investigated by NMR spectroscopy and ITC, revealed a clear switch from 1 : 1 to 2 : 1 host/guest stoichiometry moving from 12 to 16 carbon atoms, as a consequence of the chain folding of the major portion of the longer alkyl chain in one CB[8] cavity and the inclusion of the full viologen unit by another host molecule. The CB[8]2.MVC18 complex crystal structure evidences the unprecedented 2 : 1 stoichiometry and quantified in 12 the number of carbon atoms necessary to fill the CB[8] cavity in U-shaped conformation

Thresholds of Toxicological Concern for Cosmetics-Related Substances: New Database, Thresholds, and Enrichment of Chemical Space

A new dataset of cosmetics-related chemicals for the Threshold of Toxicological Concern (TTC) approach has been compiled, comprising 552 chemicals with 219, 40, and 293 chemicals in Cramer Classes I, II, and III, respectively. Data were integrated and curated to create a database of No-/Lowest-Observed-Adverse-Effect Level (NOAEL/LOAEL) values, from which the final COSMOS TTC dataset was developed. Criteria for study inclusion and NOAEL decisions were defined, and rigorous quality control was performed for study details and assignment of Cramer classes. From the final COSMOS TTC dataset, human exposure thresholds of 42 and 7.9 μg/kg-bw/day were derived for Cramer Classes I and III, respectively. The size of Cramer Class II was insufficient for derivation of a TTC value. The COSMOS TTC dataset was then federated with the dataset of Munro and colleagues, previously published in 1996, after updating the latter using the quality control processes for this project. This federated dataset expands the chemical space and provides more robust thresholds. The 966 substances in the federated database comprise 245, 49 and 672 chemicals in Cramer Classes I, II and III, respectively. The corresponding TTC values of 46, 6.2 and 2.3 μg/kg-bw/day are broadly similar to those of the original Munro dataset

Supramolecular Sensing with Phosphonate Cavitands

Molecular 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)

Formaggio a pasta dura a basso contenuto di sale

L’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%)

Impiego di un Sistema Olfattivo Artificiale (SOA ) per il controllo della conservabilità della carne di lumaca

La 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

Cavitands at Work: From Molecular Recognition to Supramolecular Sensors

Exploitation 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

Introduction of Water-solubilizing Groups at the Lower Rim of Tolylpyridine-bridged Cavitands

In this paper the preparation of water-soluble methylene-bridged cavitands presenting either positively or negatively charged groups at the lower rim following three different synthetic routes is reported. Moreover, four anionic sulphate functions have been successfully inserted on a tolylpyridine-bridged cavitand in order to carry out the self-assembly of coordination cages in water

Differentiation of mushrooms from three different geographic origins by Artificial Olfactory System(AOS).

An Artificial Olfactory Systems (oas) based on Metal Oxide Semiconductor Sensors (mos) was used to analyse samples of Boletus edulis (king bolete) mushrooms. The samples were from three different origins: Borgo Val di Taro (Italy), North China and South China. The Artificial Olfactory System together with statistical analysis were able to differentiate the geographical origin of the samples. Differential Function Analysis (Dfa) were more effective than Principal component analysis (pca) for the differentiation of samples