Marina Caporaso

Microwave-assisted flash conversion of non-edible polysaccharides and post-harvest tomato plant waste to levulinic acid

A microwave-assisted protocol for the conversion of non-edible polysaccharides and tomato plant waste to levulinic acid has been developed. Full conversion has been achieved in all cases at 2 min irradiation and clean levulinic acid was obtained without any purification in high yields (63–95%).

Pd/C-catalyzed aerobic oxidative esterification of alcohols and aldehydes: a highly efficient microwave-assisted green protocol.

Summary We herein describe an environmentally friendly microwave-assisted oxidative esterification of alcohols and aldehydes in the presence of molecular oxygen and a heterogeneous catalysis (Pd/C, 5 mol %). This efficient and ligandless conversion procedure does not require the addition of an organic hydrogen acceptor. The reaction rate is strongly enhanced by mild dielectric heating. Furthermore, it is a versatile green procedure which generally enables the isolation of esters to be carried out by simple filtration in almost quantitative yields.

Enabling technologies built on a sonochemical platform: challenges and opportunities.

Scientific and technological progress now occurs at the interface between two or more scientific and technical disciplines while chemistry is intertwined with almost all scientific domains. Complementary and synergistic effects have been found in the overlay between sonochemistry and other enabling technologies such as mechanochemistry, microwave chemistry and flow-chemistry. Although their nature and effects are intrinsically different, these techniques share the ability to significantly activate most chemical processes and peculiar phenomena. These studies offer a comprehensive overview of sonochemistry, provide a better understanding of correlated phenomena (mechanochemical effects, hot spots, etc.), and pave the way for emerging applications which unite hybrid reactors.

Design and Synthesis of a γ1β8‐Cyclodextrin Oligomer: A New Platform with Potential Application as a Dendrimeric Multicarrier

We report the synthesis and characterization of a water-soluble, star-shaped macromolecular platform consisting of eight β-cyclodextrin (β-CD) units anchored to the narrower rim of a γ-CD core through bis(triazolyl)alkyl spacers. The efficient synthetic protocol is based on the microwave (MW)-promoted Cu-catalyzed 1,3-dipolar cycloaddition of CD monoazides to CD monoacetylenes. The ligand-hosting capability of the construct has been assessed by relaxometric titration and nuclear magnetic relaxation dispersion (NMRD) profiling, which showed it to be good, and this was supported by molecular dynamics simulations. To demonstrate the feasibility of obtaining supramolecular structures with high hosting ability, we designed a dimeric platform, formed by joining two nonamers through the γ-CD cores through a bis(lithocholic acid) linker. With a view to the potential biological applications, cytotoxicity and extent of binding to human serum albumin were assessed. The properties of this dendrimeric multicarrier make it suitable for pharmaceutical and diagnostic purposes, ranging from targeted drug delivery to molecular imaging.

Enabling technologies and green processes in cyclodextrin chemistry

Summary The design of efficient synthetic green strategies for the selective modification of cyclodextrins (CDs) is still a challenging task. Outstanding results have been achieved in recent years by means of so-called enabling technologies, such as microwaves, ultrasound and ball mills, that have become irreplaceable tools in the synthesis of CD derivatives. Several examples of sonochemical selective modification of native α-, β- and γ-CDs have been reported including heterogeneous phase Pd- and Cu-catalysed hydrogenations and couplings. Microwave irradiation has emerged as the technique of choice for the production of highly substituted CD derivatives, CD grafted materials and polymers. Mechanochemical methods have successfully furnished greener, solvent-free syntheses and efficient complexation, while flow microreactors may well improve the repeatability and optimization of critical synthetic protocols.

Cyclodextrin‐Grafted Silica‐Supported Pd Nanoparticles: An Efficient and Versatile Catalyst for Ligand‐Free C−C Coupling and Hydrogenation

Silica is an extremely versatile support, which is capable of hosting metal nanoparticles (NPs) and enhancing their stability and reactivity. In this study, a novel cyclodextrin/silica support for Pd NPs, which we have denoted Pd/Si‐CD, has been prepared. The highly efficient and homogeneous impregnation of small palladium nanoparticles on this support has been carried out under conventional conditions, and ultrasound irradiation has been shown to have a beneficial effect on catalyst preparation. The catalyst exhibited excellent activity in ligand‐free C−C Suzuki and Heck couplings with a large number of aryl iodide and bromides, in which microwave irradiation use cuts down reaction time. Pd/Si‐CD have shown high activity and selectivity in the hydrogenation reaction, and the semihydrogenation of phenyl acetylene was also studied with excellent results.

Efficient mechanochemical synthesis of regioselective persubstituted cyclodextrins

A number of per-6-substituted cyclodextrin derivative syntheses have been effectively carried out in a planetary ball mill under solvent-free conditions. The preparation of Bridion® and important per-6-amino/thiocyclodextrin intermediates without polar aprotic solvents, a source of byproducts and persistent impurities, could be performed. Isolation and purification processes could also be simplified. Considerably lower alkylthiol/halide ratio were necessary to reach the complete reaction in comparison with thiourea or azide reactions. While the presented mechanochemical syntheses were carried out on the millimolar scale, they are easily scalable.

Synthesis of water-soluble multidentate aminoalcohol β-cyclodextrin derivatives via epoxide opening

New highly soluble β-aminoalcohol β-cyclodextrin (β-CD) derivatives have been synthesized via nucleophilic epoxide opening reactions with mono-6-amino mono-6-deoxy-permethyl-β-CD and mono-6-amino mono-6-deoxy-β-CD. The binding properties of the β-CD were enhanced by linking aminoalcohol subunits which caused its solubility to improve markedly. The reaction conditions were optimised using microwave irradiation giving moderate-to-good yields with a series of epoxides. A regioselective epoxide opening reaction was observed in the reaction with styrene oxide while the stereoselectivity was strictly dependent on substrate structure.

Synthesis of Randomly Substituted Anionic Cyclodextrins in Ball Milling

A number of influencing factors mean that the random substitution of cyclodextrins (CD) in solution is difficult to reproduce. Reaction assembly in mechanochemistry reduces the number of these factors. However, lack of water can improve the reaction outcomes by minimizing the reagent’s hydrolysis. High-energy ball milling is an efficient, green and simple method for one-step reactions and usually reduces degradation and byproduct formation. Anionic CD derivatives have successfully been synthesized in the solid state, using a planetary ball mill. Comparison with solution reactions, the solvent-free conditions strongly reduced the reagent hydrolysis and resulted in products of higher degree of substitution (DS) with more homogeneous DS distribution. The synthesis of anionic CD derivatives can be effectively performed under mechanochemical activation without significant changes to the substitution pattern but the DS distributions were considerably different from the products of solution syntheses.

Organisation and complexation of mono- and bis-β-cyclodextrins without chromophores with a fluorescence-sensitive probe in aqueous solutions

The behaviour of mono- and bis-β-cyclodextrin (CD) derivatives, namely 6I-deoxy-6I-[4-(hept-6-ynyl)-1H-1,2,3-triazolyl]-β-CD and 1,5-bis((1-(6I-deoxy-β-CD-6I-yl)-1H-1,2,3-triazol-4-yl)methoxy) pentyl, whose appended groups and inter-CD linkers, respectively, do not contain any chromophore, and their complexation with dimethyl-2,6-naphthalenedicarboxylate (DMN), a fluorescent polarity-sensitive probe in aqueous solutions, were investigated. Steady-state, time-resolved fluorescence, circular dichroism techniques, molecular mechanics (MM) and molecular dynamics (MD) simulations were employed. DMN appeared to slightly interact with the mono-β-CD and only unstable non-covalent dimers were formed. On the contrary, stable 1:1 and 2:1 stoichiometry complexes were obtained with bis-β-CD and DMN. A certain cooperativity due to the presence of both cavities and the linker favoured the formation of the complex 2:1 DMN:CD. DMN appeared to be axially oriented inside both CD cavities. MM and MD calculations also demonstrated the stability of the 1:1 and 1:2 stoichiometry complexes.