Extremely fast triplet formation by charge recombination in a Nile Red/fullerene flexible dyad

A donor/acceptor dyad was obtained by linking Nile Red and fullerene to a calix[4]arene scaffold. The dyad was spectroscopically characterized, both with steady-state and ultrafast transient absorption experiments, as well as with electrochemical and spectroelectrochemical techniques. We demonstrate extremely fast and efficient formation of a long-lived excited triplet localized on the fullerene moiety in this system, occurring in about 80 ps in toluene and 220 ps in chloroform. The mechanism of this process is investigated and discussed. The spectroscopic and electrochemical characterization suggests the occurrence of electron transfer from Nile Red to fullerene, leading to the formation of a charge-separated state. This state lives very briefly and, because of the small interaction between the electron donor and acceptor, promotes a singlet/triplet state mixing, inducing charge recombination and efficient triplet formation

Sintesi di sistemi multicromoforici a base calixarenica per lo studio del trasferimento di energia e di carica

The work presented in this thesis describes the synthesis and the spectroscopic characterization of chromophore-equipped calix[4]arenes designed for two different purposes: the development of bichromophoric model systems for the investigation of photoinduced energy and electron transfer processes, and the preparation of antenna ligands for the sensitization of lanthanoid ions. The calix[4]arene represents a versatile scaffold that can be functionalized with several chromophores and ligating units, can adopt different conformations, offering control over the distance and reciprocal orientation of the dyes, and is endowed of a residual flexibility that can be modulated according to the medium. After an introductory chapter, the second chapter describes the synthesis of a bichromophoric dyad obtained by anchoring a Nile Red dye and a fullerene C60 on the upper rim of a cone calix[4]arene and the steady-state spectroscopic studies aimed at investigating the energy and charge transfer phenomena occurring after photoexcitation of Nile Red. In the third chapter is reported the functionalization of a cone and a 1,3-alternate calix[4]arene with two different BODIPY dyes specifically selected to study the occurrence of coherent phenomena in the energy transfer process. The use of different conformations of the scaffold allowed us to investigate the influence of the interchromophore distance on the transfer efficiency. The fourth chapter deals with the exploration of synthetic pathways to obtain a small library of calix[4]arene-based antenna ligands for the photosensitization of lanthanoid ions. The library was designed with the aim of analyzing the role of different factors, such as the antenna structure, the distance between the antenna and the lanthanoid and the number of antennae, on the efficiency of the sensitization. Three different antennae, absorbing in the UV and visible region, were thus synthesized to be linked either at the upper or at the lower rim of three different calix[4]arene scaffolds. One of them is a redox-reversible antenna that can be exploited to investigate the potential of on-off switching of lanthanoid luminescence

Heme binding and peroxidase activity of a secreted minicatalase

Microbial pathogens often require efficient and robust H2 O2 scavenger activities to survive in the presence of reactive oxygen species generated by inflammatory responses. In addition to catalases and peroxidases, enzymes known to scavenge H2 O2 , a novel class of secreted minicatalases has been described in diderm bacteria. Here, we characterize the Helicobacter pylori (Hp) minicatalase: a monomeric hemoprotein with catalase core homology. Overexpression of Hp minicatalase rescued a catalase/peroxidase deficient E. coli phenotype under aerobic conditions and limited H2 O2 stress. The purified enzyme lacks catalase activity, but has strong (kcat >100 s(-1) ) H2 O2 -dependend peroxidase activity towards a variety of organic substrates. Our investigations into heme binding revealed that the heme cofactor is assembled in the periplasm to form the functional holoprotein. Furthermore, we observed the presence of a disulfide bond near the heme cavity of Hp minicatalase, which is conserved in secreted minicatalases and, therefore, may play a role in heme binding. This article is protected by copyright. All rights reserved

Molecular Architecture and Symmetry Properties of 1,3-Alternate Calix[4]arenes with Orientable Groups at the Para Position of the Phenolic Rings

Two glycoclusters constituted by four fully acetylated β-acetylmannosamine residues linked through trimethylenethioureido spacers to a calix[4]­arene core and differing for the presence of methoxy or propoxy groups at the lower rim were synthesized. One of the two compounds is fixed in the 1,3-alternate geometry by the presence of the propoxy groups, while the other is potentially free to assume one of the different geometries allowed in calix[4]­arene. Their similar NMR spectra in chloroform clearly suggest the same 1,3-alternate geometry. Both compounds were submitted to a conformational investigation with the DFT approach at the standard B3LYP/6-31G­(d) level. The two glycocalixarenes showed a large conformational preference for the same geometry that put the mannosamine moiety of one substituent close to the thioureido group of the opposite substituent. This allows the formation of intramolecular hydrogen bonds and originates a series of through-space close contacts. A comparison with the NOESY maps evidence an excellent correspondence between experimental and theoretical data, thus giving an experimental validation of the highly symmetrical conformation that the two glycocalixarenes assume in apolar solvents

Radiolytic degradation of a new diglycol-diamide ligand for actinide and lanthanide co-extraction from spent nuclear fuel

Within the Partitioning and Transmutation strategies, great efforts have been devoted in the last decades to the development of lipophilic ligands able to co-extract trivalent Lanthanides (Ln) and Actinides (An) from spent nuclear fuel. Because of the harsh working conditions these ligands undergo, it is important to prove their chemical and radiolytic stability during the counter-current multi-stage extraction process. In the present work the hydrolytic and radiolytic resistance of the freshly prepared and aged organic solutions containing the new ligand (2,6-bis[(N-methyl-N-dodecyl)carboxamide]-4-methoxy-tetrahydro-pyran) were investigated in order to evaluate the impact on the safety and efficiency of the process. Liquid-liquid extraction tests with spiked solutions showed that the ligand extracting performances are strongly impaired by storing the samples at room temperature and in the light. Moreover, the extracting efficiency of the irradiated samples resulted to be influenced by gamma irradiation, while selectivity remains unchanged. Preliminary mass spectrometric data showed that degradation is mainly due to the acid-catalysed reaction of the ligand carboxamide and ether groups with the 1-octanol present in the diluent

A calixarene-based fluorescent ratiometric temperature probe

We report the first macrocycle-based ratiometric molecular thermometer exploiting the conformational thermosensitivity of a calixarene functionalized with two different fluorophores. Thanks to the dependence on temperature of the efficiency of excitation energy transfer between the organic fluorophores, the thermometer works over a 60 °C-wide temperature range with a sensitivity of 4% °C-1

Development of a Selective Americium Separation Process using H4TPAEN as Water-Soluble Stripping Agent

Recycling americium from spent nuclear fuel is considered as an important option for a future sustainable nuclear fuel cycle. The PUREX solvent extraction process allows to separate uranium and plutonium from a solution of spent fuel dissolved in nitric acid. In a second step, it would be desirable to separate americium from fission products, and especially lanthanides, but also from curium in order to further transmute americium in future fast neutron reactors. For this purpose, we report the investigation of a new solvent extraction process based on the use of TODGA as an extractant in the organic phase and H4TPAEN as a selective Am(III) stripping agent in the aqueous phase. With this promising system it is possible to co-extract Am, Cm and lanthanides at high acidity and then selectively strip americium from the loaded organic phase at pH around 1 with H4TPAEN. Batch extraction data were acquired to evaluate best conditions to develop a liquid-liquid extraction flow sheet. The influence of several parameters like concentration of ligand, cations and temperature on Am(III)/Cm(III) and Am/lanthanides separation was evaluated. Especially, the ability of H4TPAEN complexing agent to strip macro-concentrations of Am was demonstrated

Actinide–lanthanide co-extraction by rigidified diglycolamides

<p>Within the actinide and lanthanide co-extraction strategy, three rigidified diglycolamides, namely 2,6-bis (<i>N</i>-dodecyl-carboxamide)-4-oxo-4<i>H</i>-pyran (<b>1</b>), 2,6-bis-[<i>N</i>-(4-<i>tert</i>-butylphenyl)carboxamide]-4-oxo-4<i>H</i>-pyran (<b>2</b>), 2,6-​bis[(<i>N</i>-docecyl-<i>N</i>-methyl)carboxamide]-​4-methoxy-​tetrahydro-pyran (<b>3</b>), were synthesized. Moreover, the effect of structural rigidification on Am(III) and Eu(III) extraction under different conditions was investigated. The carboxamide extractant <b>3</b> resembles the extracting behavior of <i>N,N,N</i>′,<i>N</i>′‐tetraoctyl diglycolamide (TODGA) in terms of efficiency and affinity within the lanthanide family, together with fast kinetics and satisfactory cation back-extraction. The presence of 1-octanol in the diluent mixture strongly affects the ligand stability. Moreover, despite the low extraction efficiency showed by <b>1</b> and <b>2</b>, all the three ligands exhibit a higher affinity for Am with respect to TODGA, resulting in a lower lanthanide/Americium separation factor, of around 4 for ligand <b>3</b> and close to 1 for ligands <b>1</b> and <b>2</b>.</p