1,721,049 research outputs found
Cyclodextrins functionalized with nitroxyl persistent radicals: synthesis, magnetic behaviour and applications
No full textMagnetic behavior of cyclodextrin-based nanosponges bearing nitroxyl persistent radicals
No full textParamagnetic organic materials are attracting an increasing interest due to their potential use in nanomedicine. In particular, it has been reported that polymeric matrices containing TEMPO radical moieties are capable to combine drug delivery properties with intracellular scavenging action of reactive oxygen species.
Paramagnetic cyclodextrin nanosponges (pmCDNS) are a new class of nanodevices with potential application in nanomedicine, due to the following properties: a) adsorption and release capability of bioactive molecules; b) detectability by EPR and MRI spectroscopies during in vitro and in vivo experiments thanks to the presence of spin labels. Moreover, they may open the way to the synthesis of metal-free organic magnets.
pmCDNS were prepared by reaction in anhydrous DMSO of a mono-functionalized β-cyclodextrin (βCD), bearing a TEMPO radical moiety, with suitable cross-linkers (CL) like EDTA or pyromellitic dianhydride (PMA), with variable βCD/CL molar ratio. An alternative approach consisted into the one-pot reaction between pristine βCD, CL and a phthalic anhydride derivative bearing a TEMPO radical unit. The paramagnetic behavior of the obtained materials was investigated by EPR spectroscopy and SQUID magnetometry. Magnetic measurements, corrected for the diamagnetic contribution of the nanosponge matrix, displayed a Curie-Weiss behaviour with a negative paramagnetic Curie temperature (p = -4.3 K), suggesting that antiferromagnetic interactions were predominant in this system. The isothermal magnetisation at 2K was well fitted by the Brillouin function with a single spin moment (J=1⁄2), as expected by the TEMPO radical. A quantitative evaluation of the magnetic data suggested that around 50 mg of TEMPO radicals were present per gram of material
Metal-free aerobic oxidations mediated byN-hydroxyphthalimide. A concise review
No full textSince the beginning of the century, N-hydroxyphthalimide and related compounds have been revealed to be efficient organocatalysts for free-radical processes and have found ample application in promoting the aerobic oxidation of a wide range of organic substrates. When combined with different co-catalysts, they are activated to the corresponding N-oxyl radical species and become able to promote radical chains, involving molecular oxygen, directly or indirectly. Most of the examples reported in the literature describe the use of these N-hydroxy derivatives in the presence of transition-metal complexes. However, eco-friendly standards, including the demand for highly selective transformations, impose the development of metal-free processes, especially for largescale productions, as in the case of the oxygenation of hydrocarbons. For this reason, many efforts have been devoted in the past decade to the design of new protocols for the activation of N-hydroxy imides in the presence of nonmetal initiators. Herein we provide a concise overview of the most significant and successful examples in this field, with the final aim to furnish a useful instrument for all scientists actively involved in the O2-mediated selective oxidation of organic compounds and looking for environmentally safe alternatives to metal catalysis
Aerobic oxidation of alkylaromatics using a lipophilic n-hydroxyphthalimide: Overcoming the industrial limit of catalyst solubility
No full text4,4′-(4,4′-Isopropylidenediphenoxy)bis(N-hydroxyphthalimide), which is a new lipophilic analogue of N-hydroxyphthalimide, can act as an effective catalyst in the aerobic oxidation of alkylaromatics under reduced amounts of polar cosolvent. The catalyst was selected on the basis of an in-depth study of the influence that substituents on the aromatic ring of N-hydroxyphthalimide exert on determining the NO[BOND]H bond dissociation energy (BDE). BDE values for a range of model molecules are calculated by DFT and measured by EPR spectroscopy. The new catalyst can be successfully employed in the aerobic oxidation of cumene, ethylbenzene, and cyclohexylbenzene, affording, in all cases, good conversions and high selectivity for the corresponding hydroperoxide. The effect of solvent, catalyst, and temperature has also been investigated
RGD-derivatized PEI-PEG copolymers: Influence of the degree of substitution on the targeting behavior
No full textPEGylation is widely used to improve the stability of gene delivery vectors through the decrease of non-specific binding to serum proteins. In order to provide “stealth” vectors with targeting properties, the grafting of specific ligands is mandatory. For instance, the tripeptide arginine-glycine-aspartic acid (RGD) has been shown to confer selectivity towards some integrin-overexpressing tumor cells. Unfortunately, owing to the different RGD grafting degrees, some difference in starting materials and experimental conditions, the literature displays contradictory findings about the efficacy of this strategy.
Starting from branched poly(ethylene imine) (bPEI) transfectant and the heterobifunctional linker N-hydroxy-succinimide-poly(ethylene glycol)-maleimide, a series of variably substituted PEI-PEGs were synthesized and functionalized with linear and cyclic RGDs. bPEI-PEG-RGDs were as effective as bPEI in complexing DNA while derivatization did affect the physicochemical properties of polyplexes. A degree of substitution of 1.31% led to enhanced targeting of cognate receptor-expressing cells without impairing the transfection efficiency of bPEI, even in the presence of serum. Of note, both RGDs were equally effective to confer selectivity to polyplexes.
These results highlight the key role of the degree of substitution on the effectiveness and selectivity of bPEI-PEG-RGDs, suggesting that a systematic approach is needed for the development of more effective targeted transfectants
Catalizzatori di ossidazione di alchilaromatici
No full textLa presente invenzione riguarda nuovi catalizzatori per l’ossidazione aerobica di alchilaromatici e, in particolare, catalizzatori per convertire idrocarburi aromatici nei corrispondenti idroperossidi. Gli idroperossidi di idrocarburi aromatici possono poi essere trasformati, mediante un processo catalizzato da acidi, in fenolo e composti carbonilici, aldeidi o chetoni
Dip in colorimetric fluoride sensing by a chemically engineered polymeric cellulose/bPEI conjugate in the solid state
No full textThe cross-linking, via amide bond formation, of TEMPO-oxidized cellulose nanofibers with branched-polyethyleneimine functionalized with pNO2-phenyl urea units generates a novel polymeric conjugate material, with a sponge-like morphology, which can be successfully used for the heterogeneous sensing of fluoride anions in DMSO solution
Phase change material cellulosic composites for the cold storage of perishable products: From material preparation to computational evaluation
No full textWarm temperature spikes represent one of the main spoilage causes of perishable good-stuffs. The development of packaging materials with thermal buffering properties represents a powerful solution to address the problems arising from an uncontrollable interruption during cold-chain logistic.
Here, we propose the use of phase change material (PCM) composites for the design of cold storage packaging. Two different concentrations (25 and 50% w/w) of commercially available micro-encapsulated PCM were homogeneously dispersed in paper matrix via conventional negative filtration techniques. The possibility of obtaining composites with different latent heats in the 4-10 degrees C range has been demonstrated via differential scanning calorimetry measurements. Heat transmission tests, simulating the heating processes typical of the removal from a cold room, were performed on a suitable multilayer configuration. The obtained materials show the ability to maintain the inner temperature for a duration up to 10-fold longer in time, when compared to a similar cellulose material with a thickness of 2 cm. Experimental results have been numerically assessed by considering the material thermal parameters as homogeneous.
Both experimental and computational approaches here discussed offer an easy way for the design of micro-encapsulated PCM-cellulose composite as building blocks in cold storage packaging design
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