Organocatalizzatori e liquidi ionici supportati: nuovi materiali in sintesi organica

Nell’ultimo decennio l’organocatalisi e i liquidi ionici hanno rappresentato due campi di grande interesse scientifico. Gli organocatalizzatori hanno trovato particolare impiego in sintesi enantioselettive conducendo a prodotti finali con alte rese e selettività. I liquidi ionici sono stati estensivamente utilizzati come solventi alternativi e, opportunamente modificati, come catalizzatori o loro supporti. Uno sviluppo attuale che accomuna questi due campi di ricerca consiste nella possibilità di immobilizzazione di organocatalizzatori e liquidi ionici per trasformarli in materiali riciclabili con ampie capacità di utilizzo in chimica organica. Negli ultimi anni, il nostro gruppo di ricerca si è occupato di organocatalizzatori e liquidi ionici supportati. E’ stata sviluppata una metodologia sintetica per l’ancoraggio di organocatalizzatori su resine polistireniche attraverso una reazione tiolo-ene, permettendo di ottenere un largo numero di materiali catalitici che sono stati impiegati in reazioni aldoliche, di -selenenilazione e di Michael (Figura 1).1-2 Nel campo dei liquidi ionici supportati (SILP) ci siamo occupati del loro uso nel campo delle reazioni catalizzate da metalli che in organocatalisi. Inoltre, i SILP sono stati efficacemente impiegati in reazioni di apertura di epossidi in CO2 supercritica per fornire carbonati ciclici.3-4 In questo campo abbiamo sviluppato due tipi di materiali, monostrato e multistrato (Figura 2)

Halloysite nanotubes: a green resource for materials and life sciences

Clay minerals are considered one of the materials of the 20th century for their peculiar physico-chemical features. Among them, halloysite nanotubes (HNTs) are an emerging nanomaterial with a particular tubular structure that makes them a low cost and valuable alternative to the most common carbon nanotubes. Due to their tubular morphology, HNTs are employed in several fields acting as nanocontainers for different compounds for applications in drug carrier and delivery fields, catalysis, and as filler for polymeric matrices. The modification of HNTs’ surfaces allows to the synthesis of different nanoarchitectures that can improve the mechanical and thermal performance of polymer as well as they can enhance the use for the loading and release of chemicals. In this review, we summarize our recent results on halloysite functionalization, both supramolecular and covalent, and the application aforementioned fields

The Gelling Ability of Some Diimidazolium Salts: Effect of Isomeric Substitution of the Cation and Anion

The gelling ability of some geminal imidazolium salts was investigated both in organic solvents and in water solution. Organic salts differing either in the cation or anion structure were taken into account. In particular, the effects on the gelphase formation of isomeric substitution on the cation or anion as well as of the use of mono- or dianions were evaluated. As far as the cation structure is concerned, isomeric cations, such as 3,3’-di-n-octyl-1,1’-(1,4-phenylenedimethylene)diimidazolium and 3,3’-di-n-octyl-1,1’-(1,3-phenylenedimethylene) diimidazolium, were used. On the other hand, in addition to the bromide anion, isomeric dianions, such as the 1,5- and 2,6-naphthalenedisulfonate anions, were also examined. After preliminary gelation tests, different factors affecting the obtained gel phases, such as the nature of the solvent, organogelator concentrations, and action of external stimuli, were analyzed. The gel-phase formation was also studied as a function of time, by using resonance light scattering measurements. Gel morphologies were analyzed by scanning electron microscopy. To further support the understanding of the different behavior shown by the isomeric cations, some representative ion pairs were analyzed by DFT-based investigations. The collected data underline the significant role played by isomeric substitution of both cation and anion structures in determining the gelling capability of the investigated salts, as well as the properties of the gel phases. Finally, DFT investigations were helpful in the identification of the structural features affecting the self-assembly

Fluorescent naphthalimide-imidazolium hydrogels for biomedical applications

Bioimaging and in vivo imaging are cornerstone technologies in support of biomedical diagnosis. However, in some cases imaging methods have increased cancer risks for patients. Moreover, the most widely used diagnostic medical imaging technique, X-ray imaging, is the largest man-made source of radiation exposure to the general population. Thus, the research of new efficient and less invasive materials for imaging is quite urgent. Supramolecular hydrogels have recently proved to be promising biological carriers to load versatile bioimaging agents for in vitro or in vivo bioimaging, thanks to the ability to undergo reversible swelling and gel–sol transition in response to various physiological stimuli. In addition, the biodegradability and biocompatibility allowed the use of supramolecular gels also for cancer diagnosis, as they can be facilely endocytosed into cells [1]. Remembering the good biological response of some imidazolium derived hydrogels [2], fluorescent imidazolium organic salts, that should own the double function of gelator and bioimaging agent, have been synthesized. New fluorescent hydrogels with interesting physico-chemical properties (rheology, gel-sol temperature transition and optical properties) have been tested for anti-proliferative activity, in vitro bioimaging on cancer cells and controlled release of gelator in physiological medium. Results evidence how these hydrogels can be potentially investigated as new theranostic media for anticancer researc

A competitive reactivity study on the oxidative cyclization of thiosemicarbazones into 1,3,4-thiadiazolidines

Abstract In order to obtain useful insights on the mechanism of formation of 2(3H)-imino-1,3,4-thiadiazoles by oxidative cyclization of aldehyde thiosemicarbazones with Cu(II) or Fe(III) salts, a competitive reactivity study was performed on a suitable set of diversely substituted substrates, by means of HPLC techniques. This approach enabled to exploit Hammett\u2019s equation without performing otherwise difficult-to-run kinetic experiments. The results presented herein support the hypothesis that the formation of the thiadiazole ring is induced by the attack of the oxidizing Lewis acid metal cation onto the imine-like nitrogen atom of the thiosemicarbazone substrate. Beyond mechanistic interpretation, the paper particularly focuses onto the methodological issues implied

Lipase-catalyzed resolution of anti-substituted 1,3-dioxepan-5-ols

Several anti-6-substituted 1,3-dioxepan-5-ols were kinetically resolved using an immobilized lipase (Amano PS–C II) in toluene in the presence of vinyl acetate at 30 C. This approach provided, in some cases, the alcohol and the acetate in high enantiomeric purity, depending on the nature of the substituent (R = N3, SePh, I, OBn) and the acetal group (unsubstituted or dimethyl). The role of the size of substituents is also discussed. Enantiopure anti-6-substituted 1,3-dioxepan-5-ols are useful building blocks