Light‐Induced Porphyrin‐Based Spectroscopic Ruler for Nanometer Distance Measurements

We present a novel pulsed electron paramagnetic resonance (EPR) spectroscopic ruler to test the performance of a recently developed spin‐labeling method based on the photoexcited triplet state (S=1). Four‐pulse electron double resonance (PELDOR) experiments are carried out on a series of helical peptides, labeled at the N‐terminal end with the porphyrin moiety, which can be excited to the triplet state, and with the nitroxide at various sequence positions, spanning distances in the range 1.8–8 nm. The PELDOR traces provide accurate distance measurements for all the ruler series, showing deep envelope modulations at frequencies varying in a progressive way according to the increasing distance between the spin labels. The upper limit is evaluated and found to be around 8 nm. The PELDOR‐derived distances are in excellent agreement with theoretical predictions. We demonstrate that high sensitivity is acquired using the triplet state as a spin label by comparison with Cu(II)–porphyrin analogues. The new labeling approach has a high potential for measuring nanometer distances in more complex biological systems due to the properties of the porphyrin triplet state.     

A new approach to 4,6-disubstituted-3,4-dihydropyran-2-ones by Domino Michael addition-cyclization reaction under PTC conditions

Domino Michael addition-cyclization reactions of α,β-unsaturated carbonyl compounds with activated 1,3-dithiane-2-carbothioate esters under solid-liquid phase transfer catalysis conditions provide 4,6-disubstituted-3,4-dihydropyran-2-one-3,3-dithioacetals in good chemical yield. Desulfurization proceeds chemoselectively under mild conditions affording 3,4-dihydropyran-2-ones in high yields.     

Thermal behaviour of poly(dimethylsiloxane) hybrid silicas prepared by radiation grafting

This paper reports our investigation regarding the thermal properties of new polymer-silica hybrid materials obtained by radiation grafting. The polymer poly(dimethylsiloxane),bis(3-aminopropyl)terminated is γ-grafted on a silica gel surface. The thermal behaviour of γ-grafted hybrid materials reveals remarkable differences compared to the thermal behaviour of physically adsorbed polymers. These differences allow us to assess the ability of γ-rays to produce a polymer chemically bonded on a silica surface. The chemical bonds formed by irradiation give to the polymer a high conformational stability confirmed by DTA analysis.     

Supramolecular Functions Related to the Redox Activity of Transition Metals

Abstract

The combination of the properties of different subunits in a multicomponent system may give rise to a function which is defined supramolecular. The presence of transition metals in one or more subunits may induce inter-component processes related to their redox and electron transfer (eT) properties, which trigger the supramolecular function (SF). The following examples are considered: (1) a receptor for transition metals is covalently linked to a fluorescent fragment; following recognition, a metal-to-fluorophore eT process quenches the fluorescence. SF: fluorosensing. (2) an azacyclam macrocycle, hosting the Ni^II/Ni^III redox couple, is covalently linked to a photoactive fragment: the Ni^III state quenches the neighboring fluorophore through an eT mechanism, the Ni^II state does not. SF: redox switching of a fluorescent signal. (3) a Cu^II ion is coordinated by two 2,2′-bipyridine molecules, each bearing a cyclam subunit containing a nickel centre; when nickel is in the divalent state, an inorganic anion X^? (N₃ ^?,NCO^?,NCS^?) is bound to Cu^II; on oxidation, X^? moves to the Ni^III centre. SF: electrochemically triggered translocation of X^? from copper to nickel and vice versa.     

Rheological,mechanical, thermal and electrical properties of UHMWPE/CNC composites

Cellulose - In this work, composites of ultra high molecular weight polyethylene (UHMWPE) and various loadings of cellulose nanocrystals (CNCs) were prepared exploiting different methods. Besides,...     

The Cauchy numbers

We study many properties of Cauchy numbers in terms of generating functions and Riordan arrays and find several new identities relating these numbers with Stirling, Bernoulli and harmonic numbers. We also reconsider the Laplace summation formula showing some applications involving the Cauchy numbers.     

Assessment of reproducibility and uncertainty of food microbiology methods: statistical approach of a multi-site laboratory

The validation of food microbiology methods and assessment of measurement uncertainty are required for laboratories operating EN ISO/IEC 17025 accreditation systems. This paper aims to describes the statistical approach adopted by a multi-site laboratory to satisfy these requirements and to routinely check the performance of the methods. A validation protocol was performed, reflecting a great variability of experimental conditions, represented by the period of time during which determinations were made, the different laboratories concerned, the large number of technicians involved, the differences in the level of contamination of the matrix analyzed and the operating conditions (equipment, reagents, culture media, environmental conditions, etc.). Despite the very high variability of the experimental conditions, the values of repeatability and reproducibility obtained for the methods were lower than those stated in the respective regulations. In addition, the top-down approach adopted in this study is to be considered effective overtime and allows to randomize all variable factors, including the effects of sensitivity and specificity, in order to simulate the conditions of real reproducibility. A specific Excel spreadsheet was also developed for the routine expression of analytical results. This spreadsheet represents a very useful tool for operators to calculate and routinely check the results, as well as to assess the uncertainty of measurement. This particular quality assessment system is enabling the multi-site laboratory to implement the accuracy, reliability and comparability of the analytical results and to ensure the analytical control of data output.     

Nucleophilic aromatic substitutions on 4,5-dicyanopyridazine. Pyrrole and indole systems as carbon nucleophiles

4,5-Dicyanopyridazine was found to react with pyrrole and indole counterparts not only as heterocyclic azadiene in inverse electron-demand Hetero Diels–Alder reactions, as previously evidenced, but even as a very reactive heterocyclic electrophile at C-4 carbon, in formal S_NAr2 processes where a CN group acts as leaving group. In particular, operating in acetic acid as solvent, nucleophilic addition–elimination sequences allowed a facile access to pyrrolyl- and indolylpyridazines, through the corresponding 1,4-dihydropyridazine adducts.     

Selective mono-arylation and -alkylation of chlorophenyl alkyl sulfides by nickel catalysed cross-coupling with grignard reagents

Chlorophenyl alkyl sulfides are mono-arylated and -alkylated selectively with Grignard reagents, in the presence of Ni(PPh₃)₂Cl₂, to give aryl- and alkyl-phenyl alkyl sulfides.