Search

Halloysite surface was modified with tetrabutylammonium iodide, and then the obtained nanomaterial was used as support for ZnO nanoparticles. After characterization, the nanomaterial was used as a catalyst for fatty acid methyl esters (FAMEs) production. The recyclability of the nanomaterial was also investigated, and the optimization of reaction conditions by the design of experiments approach was performed as well. In addition, the synthesized nanomaterial was tested as a catalyst for FAME production from a series of waste lipids affording biodiesel in moderate to good yields (35–95%), depending on the matrix. To fully exploit the feasibility of clay minerals as catalysts in biodiesel formation, a screening of different clays and clay minerals with different morphologies and compositions, such as sepiolite, palygorskite, bentonite, and hectorite was also performed in the esterification of FFAs (a mixture of 1:1 palmitic and stearic acids). Finally, hectorite, chosen as a model of 2:1 clay minerals, was covalently modified, and tested as a catalyst in the esterification of FFAs.

Halloysite 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.

© 2017 Future Science Ltd. Clays for drug delivery have been used from ancient time due to the large availability of clay minerals and their unprecedented properties. The empirical use of nanoclays from the past is converted in a stimulating scientific task aimed at building up nanoarchitectonic vehicles for drug delivery in a targeted and stimuli-responsive fashion. Here the historical aspects are discussed; next the modern examples of applications of different clay-based materials are discussed. A special focus is given to halloysite clay nanotubes, which are an emerging and very promising nanomaterial for drug-delivery purposes due to its special morphology and unique chemical properties. Advantages and limitations of these natural nanomaterials are critically discussed pointing out the future perspectives and directions for further research.

Halloysite nanotubes (HNTs) are natural nanomaterials that are biocompatible and available in large amounts at low prices. They are emerging nanomaterials with appealing properties for applications like support for metal nanoparticles (NPs). The potential environmental impacts of NPs can be understood in terms of phytotoxicity. Current research has been focusing on HNT applications in cell or animal models, while their use in plants is limited so their ecotoxicological impact is poorly documented. To date there are no studies on the phytotoxic effects of functionalized halloysites (functionalized-HNTs). To develop a quantitative risk assessment model for predicting the potential impact of HNT-supported palladium nanoparticles (HNT-PdNPs) on plant life, an investigation was undertaken to explore their effects on seed germination, seedling development, and mitotic division in root tip cells of 2 lots of Raphanus sativus L. with different vigor. The results showed that exposure to 1500mg/L of HNTs, functionalized-HNTs, and HNT-PdNPs had no significant influence on germination, seedling development, xylem differentiation, or mitotic index in both lots. Cytogenetic analyses revealed that treatments with functionalized-HNT significantly increased the number of aberrations in low-vigor seeds. These results suggest that low-vigor seeds represent a model for a stress test that would be useful to monitor the effects of NPs. Moreover the present study offers scientific evidence for the use of halloysite for environmental purposes, supporting the biological safety of HNT-PdNPs.

Nanotechnologies 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.

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.

Halloysite nanotubes (HNTs) represent a versatile core structure for the design of functional nanosystems of biomedical interest. However, the development of selective methodologies for the site-controlled functionalization of the nanotubes at specific sites is not an easy task. This study aims to accomplish a procedure for the site-selective/specific, “pin-point”, functionalization of HNTs with polydopamine (HNTs@PDA). This goal was achieved, at pH 6.5, by exploiting the basicity of ZnO nanoparticles anchored on the HNTs external surface (HNTs@ZnO) to induce a punctual polydopamine polymerization and coating. The morphology and the chemical composition of the nanomaterial was demonstrated by several techniques. Turbidimetric analysis showed that PDA coating affected the aqueous stability of HNTs@PDA compared to both HNTs@ZnO and HNTs. Notably, hyperthermia studies revealed that the nanomaterial induced a local thermic rise, up to 50 °C, under near-infrared (NIR) irradiation. Furthermore, secondary functionalization of HNTs@PDA by selective grafting of biotin onto the PDA coating followed by avidin binding was also accomplished.

Scientific research has been invigorated by a new class of biodegradable materials as alternatives to polymers derived from fossils. Such biomaterials can also offer economic advantages because they are derived from renewable resources. Several biopolymers (gelatin, chitin, chitosan, starch, pectin, cellulose and its modified versions, etc.) have been exploited to produce films and formulations. Their use is limited because of fast degradation, predominant hydrophilic character, and, in some cases, unsatisfactory mechanical properties. However, the properties of these polymers can be improved by using inorganic fillers such as additives. Halloysite nanotube is a promising green filler for this purpose.

Covalently functionalized halloysite nanotubes (HNTs) were successfully employed as dual-responsive nanocarriers for curcumin (Cur). Particularly, we synthesized HNT-Cur prodrug with a controlled curcumin release on dependence of both intracellular glutathione (GSH) and pH conditions. In order to obtain HNT-Cur produgs, halloysite was firstly functionalized with cysteamine through disulphide linkage. Afterwards, curcumin molecules were chemically conjugated to the amino end groups of halloysite via Schiff's base formation. The successful functionalization of halloysite was proved by thermogravimetric analysis, FT-IR spectroscopy, dynamic light scattering and scanning electron microscopy. Experimental data confirmed the presence of curcumin on HNT external surface. Moreover, we investigated the kinetics of curcumin release by UV-vis spectroscopy, which highlighted that HNT-Cur prodrug possesses dual stimuli-responsive ability upon exposure to GSH-rich or acidic environment. In vitro antiproliferative and antioxidant properties of HNT-Cur prodrug were studied with the aim to explore their potential applications in pharmaceutics. This work puts forward an efficient strategy to prepare halloysite based nanocarriers with controlled drug delivery capacity through direct chemical grafting with stimuli-responsive linkage.

The development of systems able to deliver genetic material into a target site is a challenge for modern medicine. Single-stranded peptide nucleic acids have attracted attention as promising therapeutic molecules for diagnostic and gene therapy. However, their poor cell membrane permeability represents a drawback for biomedical applications. Halloysite nanotubes (HNTs) are emerging materials in drug delivery applications both for their ability to penetrate cell membranes and for enhancing the solubility of drugs in biological media. Herein, we report the first example of the use of a nanocarrier based on halloysite labelled with fluorescent switchable halochromic oxazine molecules, to deliver a single-stranded peptide nucleic acids tetramer (PNAts) into living cells. The PNAts is covalently attached to halloysite (HNTs-PNA), whereas the fluorescent probe supramolecularly interacts with HNTs. The ability of the nanomaterial to bind complementary single-stranded DNA was assessed by resonance light scattering measurements. Finally, studies of cellular uptake were carried out by confocal laser scanning microscopy on normal and tumoral cell lines. This work highlights the usefulness of the covalent approach to generate HNTs-PNA nanomaterials for the potential targeting of future specific nucleic acids in living cells, which could open the doorway to novel possibilities for theranostic and gene therapy applications.

Fluorescence imaging has become an indispensable tool in the biomedical laboratory to elucidate the fundamental dynamic and structural factors regulating cellular processes. The development of fluorescent nanoprobes represents a challenge to detect any cellular process under a microscope. Herein, a fluorescent nanomaterial was synthesized by exploiting the supramolecular interaction between a halochromic switch (1Cl) and halloysite nanotubes (HNTs). The successful synthesis of a HNTs/1Cl nanomaterial was confirmed by thermogravimetric analysis and Fourier transform infrared. The aqueous mobility was investigated by dynamic light scattering and ζ-potential measurements as well. Furthermore, the morphology was imaged by transmission electron microscopy, and the interaction of the clay with 1Cl was also studied by kinetic adsorption measurements. In addition, the spectroscopy properties of the resulting nanomaterial were studied in solution and the solid state by UV-vis and fluorescence measurements. Finally, the ability of our nanomaterial to detect cancer cells was assessed with confocal laser scanning microscopy measurements on normal (hTERT) and/or tumoral cell lines (MCF-7 and HL-60R).

The prodrug approach, as well as the development of specific systems able to deliver a chemotherapeutic agent in the target site, decreasing the side effects often associated with its administration, are still a challenging. In this context, both methotrexate drug molecules (MTX) and biotin ligand moieties, whose receptors are overexpressed on the surface of several cancer cells, were loaded on halloysite nanotubes (HNTs) to develop nanomaterial based on multifunctional and "smart" delivery systems. To highlight the crucial role played by biotin, carrier systems based on HNTs and MTX were also synthetized. In detail, several approaches were envisaged: i) a supramolecular interaction between the clay and the drug; ii) a covalent grafting of the drug onto the HNTs external surface and, iii) a combination of both approaches. The nanomaterials obtained were characterized by thermogravimetric analysis, FT-IR, and UV-vis spectroscopies, DLS and ζ-potential measurements and the morphologies were imaged by HAADF/STEM investigations. Kinetic release experiments at different pH conditions were also performed. Finally, as a proof-of-concept application of our pro-drug delivery systems based on HNTs in cancer therapy, the cytotoxic effects were evaluated on acute myeloid leukemia cell lines, HL60 and its multidrug resistance variant, HL60R. The obtained results showed that both the MTX prodrug system and the biotinylated ones played a crucial role in the biological activity and, they are promising agents for the cancer treatments.

The effect of beta-cyclodextrin (beta-CD) on the mononuclear heterocyclic rearrangement of the (Z)-phenylhydrazone of 3-benzoyl-5-phenyl-1,2,4-oxadiazole (1) in aqueous borate buffer at pH = 9.6 has been analyzed at temperatures ranging from 293.15 to 313.15 K. The trend of the absorption spectra of 1 as a function of time has been accounted for with the formation of two different 1:1 complexes between beta-CD and 1, the first, "unreactive" complex being formed faster than the "reactive" one. The occurrence of negative activation enthalpy values for the studied interconversion evidences the kinetic relevance of inclusion processes. Computational models elaborated using the MM2 molecular mechanics force field give an idea of the relative importance of the different complexes, additionally helping us to formulate a suitable reaction scheme.

The design of multifunctional nanomaterials which can help the healing processes of skin, preventing the bacterial infections, is crucial for the development of suitable therapy for the treatment of chronic lesions. The use of clay minerals in wound healing applications is well documented since the prehistoric period and offers several advantages due to their intrinsic properties. Herein, we report the development of ciprofloxacin carrier systems based on hectorite/halloysite (Ht/Hal) hybrid hydrogels for potential wound healing applications. To achieve this objective firstly the ciprofloxacin molecules were loaded onto Hal by a supramolecular and covalent approach. The so obtained fillers were thoroughly investigated by several techniques and at molecular level by means of quantum mechanics calculations along with empirical interatomic potentials. Afterwards the modified Hal were used as filler for Ht hydrogels. The introduction of modified Hal, in hectorite hydrogel, helps the gel formation with an improvement of the rheological properties. The in vitro kinetic release from both the fillers and from the hybrid hydrogels was studied both at skin's pH (5.4) and under neutral conditions (pH 7.4); in addition, the factors controlling the ciprofloxacin release process were determined and discussed. Finally, the in vitro biocompatibility of the Hal fillers was evaluated by means of cytotoxic assays and laser scanning confocal microscopy on normal human dermal fibroblasts., The work was carried out in the frame of the PON “AIM: Attrazione e Mobilità Internazionale” No. 1808223-1 project. Authors are thankful to H.A. Duarte for providing atomic coordinates of halloysite, to the CSIC Computational Center and the University of Granada Computation Center for computation facilities, and the Andalusian project grants RNM-1897 and P18-RT-3786 , and the Spanish MINECO projects , PCIN-2017-098 , FIS2016-77692-C2-2-P and CGL2016-80833-R , for the financial support of this research.

Clays are used in various cosmetic formulations, such as sunscreens, toothpastes, deodorants, creams, hair cosmetics, makeups, nail polish, facial masks, and shampoos, among others, to improve the organoleptic and physicochemical characteristics, to increase the stability, or to facilitate elaboration. Together with their technological functionalities, clays are cosmetologically active ingredients with cleaning, anti-aging, anti-wrinkling, and sun-care functionalities. Talc, kaolinite, mica, and some smectites are the clay minerals used most frequently in cosmetic products, but several other phyllosilicates as well as modified and synthetic clays are also used. Sometimes, clays are useful in the design of cosmetics just because they are made of rigid, small, and anisometric particles. Kaolinite and mica are made of hard prismatic particles which are lightly abrasive over the skin, teeth, or hair. Electric charges in smectites result in ion-exchange capacities useful in the loading of active cosmetics but also adsorbing and cleaning waste substances. Intermediate net negative charges of smectites result in layer expansion in polar media and specific rheological properties that are very useful in cosmetic formulations. The absence of charged particles in talc and kaolin make them flow easily resulting in lubricant effects. Protection against radiation from the sun by clay particles and decorative effects complete the possibilities of clays in cosmetics. The nomenclature for clays used as ingredients in cosmetics follows historical use and the names of commercial products, rather than following strict compositional principles. In this sense, an effort was made here to correlate the names of the minerals that make up each of the clay-based cosmetic ingredients., The work has been supported by funding from the Spanish group CTS-946 and project P18-RT-3786.

The synthesis of a new biocompatible bichromophoric system (CURBO) was developed, by connecting the skeleton of the naturally occurring curcumin to a BODIPY derivative. The system exhibited an intense fluorescence band with maximum at about 510 nm in organic solvent, while its emission spectra in aqueous solution were more complicated and slightly red-shifted, due to the effect of aggregation for the poor solubility of the dyad. To overcome these problems, the bichomophoric system has been loaded into the halloysite nanotubes (HNT). The HNT/CURBO nanocomposite, suspended in aqueous solution, showed an intensity of emission in the red region of the spectrum higher than the one exhibited by the pristine CURBO. The biocompatibility and photophysical behavior of HNT/CURBO nanocomposite were studied using ASC52Telo, h-TERT immortalized adipose-derived mesenchymal stem cells. To investigate the localization of the CURBO alone and in HNT/CURBO, fluorescence epimicroscopy was performed. The HNT/CURBO nanocomposite showed a high propensity to cross cell membranes, resulting in a massive cell uptake around the cell nucleus. Moreover, it lighted up ASC52Telo cells both with intense green and red fluorescence while excited in the blue portion of the electromagnetic spectrum, a phenomenon that could not be observed for the free CURBO. Dual-channel emissions dyes and, in particular, materials, such as the HNT/CURBO nanocomposite, emitting in the red portion of the spectrum have become, in recent decades, particularly fascinating since they can minimize the autofluorescence detection of the cell medium and allow interesting microscopy applications.