1,721,121 research outputs found
Covalently Modified Halloysite Clay Nanotubes: Smart Nanomaterials for Drug Delivery Applications
No full textHalloysite nanoclays (HNTs) are promising nanomaterials because of their versatile properties, such as hollow tubular morphology and tunable surface chemistry. HNTs are biocompatible, no toxic and abundantly available at low cost. Due to these characteristics HNTs are suitable for development of hybrid sustainable materials, which are perspective for polymeric matrices reinforcement, active food packaging and drug delivery. HNTs are quite polydisperse in size with a length of ca. 1 m, while the external diameter and the lumen range between 50-80 nm and 10-15 nm, respectively. Chemically, halloysite is composed of gibbsite octahedral sheet (Al-OH) groups on the inner surface and siloxane (Si−O−Si) groups on the external surface. This different chemistry allows the selective modification of HNTs surfaces. We performed several chemical functionalization of HNTs materials to confer properties valuable in specific applications.
The introduction of chemical modification of both surfaces (inner lumen and outer surface) is a relevant strategy to tune the nanotube properties. Namely, chemical modification of HNT surfaces allows to obtain nanoarchitecture with targeted affinity through outer surface functionalization and drug cargo ability from the nanotube lumen
Organo-Clay Nanomaterials Based on Halloysite and Cyclodextrin as Carriers for Polyphenolic Compounds
Full text linkHybrid material based on halloysite covalently linked to a hyper-reticulated cyclodextrin network was investigated as a potential carrier for polyphenolic compounds. The absorption ability of the hybrid system was studied in different pH conditions as well as the kinetic release of curcumin, chosen as a drug model. A preliminary study was performed to assess the antioxidant capacity of the
obtained carrier. The obtained results highlighted that the curcumin molecule can have sustained release from the carrier over the time, retaining its antioxidant properties due to the combination of
two different host systems that give rise to an hyper-reticulated structure, allowing an increase in the drug loading and stabilization. Therefore, this work puts forward an efficient strategy to prepare
organic-inorganic hybrids with three different cavities that could encapsulate two or more drug molecules with different physico-chemical properties
Regioselective Epoxide Ring Opening. Steroselective Synthesis of a Tetrahydropyran Ring
No full textThe stereoselective synthesis of a 2-substituted tetrahydropyran with adjacent alkoxy-bearing stereogenic centre is described. The key steps of this synthesis were the stereoselective epoxidation of an allylic alcohol and the regioselective epoxide ring opening by lithium aluminum hydride. The regio and stereoselective synthesis of a trihydroxyselenide and a trihydroxysulfide is also described. The latter compounds are not suitable for cyclization to tetrahydrofuran ring
Nanoclays for Conservation
No full textWithin the conservation of artworks materials, this chapter describes innovative strategies based on clay nanoparticles that are promising for protective coating, surface cleaning, and consolidation. We present the preparation of polymer/montmorillonite nanocomposites, which are revealed as efficient protective coatings for highly porous stones, marbles, and bread-made artifacts. Anticorrosive films for metal substrates have been obtained by polymer filling with laponite and halloysite nanotubes (HNTs) containing corrosion inhibitors into their lumen. The dispersion of hydrophobically modified HNTs into chitosan matrix drives to fabricate biofilms with surface cleaning capacity. Rust stains have been removed from marble samples by using laponite/cellulose fibers. Regarding the preservation of lignocellulosic artworks, composite systems based on sustainable polymers (cellulose ethers and beeswax) and HNTs have been successfully employed as consolidants of archaeological woods. Encapsulation of Ca(OH)2 into an HNT cavity has been explored for paper deacidification. In conclusion, we have summarized the nanoclay-based protocols used in conservation issues. © 2019 Copyrigh
Phytotoxicity of halloysite-supported ionic liquid-like phase (HNT-SILLP) catalyst on Raphanus sativus L.
No full textNanotechnologies and nanomaterials are increasingly involved in the production of fillers, opacifiers, catalysts, semiconductors, cosmetics, microelectronic components and drug carriers with improved properties. Nevertheless, the production, use and disposal of nanomaterials, will inevitably lead to their release into the soil, with potential phytotoxicity on plants and negative impacts on economy, society and environment (1). In the last years halloysite nanotubes (HNT) emerged as promising materials with appealing perspective for technological applications. We have recently reported the generation of HNT derivatives carrying octylimidazolium moieties on the external surface (HNT supported ionic liquid-like phase, HNT-SILLP) and employed them as supports for palladium catalyst (HNT-SILLP/Pd) (2, 3). These studies have shown that these materials are good catalysts and encourage their potential application in large-scale industrial processes.
The present research aimed to investigate the potential phytotoxicity of HNT, HNT-SILLP and HNT-SILLP/Pd, by considering different endpoints as seed germination physiology and cytogenetic analyses (4).
Raphanus sativus L. seeds were imbibed in distilled water (control) or in HNT, HNT-SILLP and HNT-SILLP/Pd, incubated at 25°C in the dark, under continuous agitation up to 72 h. Germination percentage and mean germination time, together with fresh and dry weights were evaluated in control and HNTs-treated seeds. To further rule out possible impacts of these nanomaterials on genetic stability, the accumulation of nanotubes during seedling development by means of thermogravimetric analysis, IR spectroscopy and cytogenetical analysis on radical meristems were performed.
The preliminary results here presented show that these nanomaterials do not affect the germinative process and the development of the seedling. Thermogravimetric analysis and IR spectroscopy studies additionally showed that exposure to the investigated nanomaterials does not lead to an accumulation into the seedling organs since the plant cell wall might act as a barrier, efficiently preventing entry of these nanoparticles into the cell
Synthesis of 2,4,6-trisubstituted tetrahydropyrans via 6-exo selenoetherification of unsaturated alcohols
No full textStereoselectivity, regioselectivity and yields in the 6-exo selenoetherification of four unsaturated diols were found to depend on the stereochemistry of the diols and on the presence of an oxygen atom close to the intermediate seleniranium ring. Silica gel was useful in order to obtain good yields. Reactions performed both under kinetic and thermodynamic control led to the same products.
Stereoselectivity, regioselectivity and yields in the 6-exo selenoetherification of four unsaturated diols were found to depend on several factors such as the stereochemistry of the diols, the nature of the R group, the nature of the counter anion of the PhSe+ species and the presence of silica gel
Cutaneous antihistaminic action of cetirizine and dose-related EEG concomitants of sedation in man.
No full textPast, present and future perspectives on halloysite clay minerals
Full text linkHalloysite nanotubes (HNTs), clay minerals belonging to the kaolin groups, are emerging nanomaterials which have attracted the attention of the scientific community due to their interesting features, such as low-cost, availability and biocompatibility. In addition, their large surface area and tubular structure have led to HNTs’ application in different industrial purposes. This review reports a comprehensive overview of the historical background of HNT utilization in the last 20 years. In particular it will focus on the functionalization of the surfaces, both supramolecular and covalent, following applications in several fields, including biomedicine, environmental science and catalysis
Halloysite Nanotubes: Smart Nanomaterials in Catalysis
Full text linkThe use of clay minerals as catalyst is renowned since ancient times. Among the different clays used for catalytic purposes, halloysite nanotubes (HNTs) represent valuable resources for industrial applications. This special tubular clay possesses high stability and biocompatibility, resistance against organic solvents, and most importantly be available in large amounts at a low cost. Therefore, HNTs can be efficiently used as catalysts themselves or supports for metal nanoparticles in several catalytic processes. This review reports a comprehensive overview of the relevant advances in the use of halloysite in catalysis, focusing the attention on the last five years
Covalently modified nanoclays: synthesis, properties and applications
No full textClay minerals are phyllosilicates of nanoscale dimensions. According to their ability to entrap and release organic moieties, they have found applications in several fields, such as drug carrier and delivery, support for catalyst, environmental remediation and filler for polymeric matrices.
The possibility to modify, by covalent linkage, their surfaces gives the possibility to form new nanomaterials with improved properties respect to the pristine clay minerals.
In this chapter, the modifications of the siloxane surfaces of the most representative clay minerals, namely montmorillonite, sepiolites, laponite and halloysite were reviewed and discussed
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