Structure of a cyclodextrin functionalized anionic clay: XRD analysis, spectroscopy, and computer simulations

Bioapplication of cyclodextrin-containing montmorillonite

Recent progresses in the integration of CDs and montmorillonite, as well as applications of CD-containing montmorillonite hybrid host systems are summarized in this review. Several efficient synthesis strategies, such as ion exchange, metal coordination, supramolecular strategies, polymerizations and organic synthesis methods, have been discussed during the preparation of CDs/montmorillonite hybrid composites. In particular, diverse instrumental techniques were highly recommended for characterizing the as-obtained hybrid systems, including their chemical composition and structures, crystallinity, surface/self-assembled morphologies, as well as other particular physiochemical properties, providing a direct guide for promoting the desired structures and exploring various applications. It should be noted that the introduction of functional groups, as well as the integration of CDs and montmorillonite granted the thus obtained CD-containing montmorillonite hybrid host systems a lot of unique features, providing great opportunities for expanding the practical applications to a series of biological and environmental areas, such as biosensors, sorption and decontamination of bio/environmental hazardous materials, biostudies about aqueous dispersity, stability and biocompatibility, drug loading and target delivery, controlled and sustained drug release, as well as antibacterial.

Construction of Crowning β-cyclodextrin with Temperature Response and Efficient Properties of Host-Guest Inclusion

Promoting a drug inclusion proportion in hydrophobic cavity of β-cyclodextrin using simple methods is a highly ambitious task. Herein, we report the crowning β-cyclodextrins formed by intramolecular hydrogen bonding interaction, which has greatly prolonged the cavity depth of β-cyclodextrin, and therefore further efficiently improved the inclusion proportion to complex drug molecule (vitamin E). Furthermore, the self-assembly behaviors, controllable release, and antioxidant properties of vitamin E embedded into the cavity of crowning β-cyclodextrins was investigated, and host-guest inclusions exhibited temperature-responsive controlled release, excellent antioxidant activity, and photostability.

Energy and structure of bonds in the interaction of organic anions with layered double hydroxide nanosheets: A molecular dynamics study

The application of hybrid and hierarchical nanomaterials based on layered hydroxides and oxyhydroxides of metals is a swiftly progressing field in biomedicine. Layered double hydroxides (LDH) possess a large specific surface area, significant surface electric charge and biocompatibility. Their physical and structural properties enable them to adsorb various kinds of anionic species and to transport them into cells. However, possible side effects resulting from the interaction of LDH with anions of the intercellular and intracellular medium need to be considered, since such interaction can potentially disrupt ion transport, signaling processes, apoptosis, nutrition and proliferation of living cells. In the present paper molecular dynamics is used to determine the energies of interaction of organic anions (aspartic acid, glutamic acid and bicarbonate) with a fragment of layered double hydroxide Mg/Al-LDH. The average number of hydrogen bonds between the anions and the hydroxide surface and characteristic binding configurations are determined. Possible effects of LDH on the cell resulting from binding of protein fragments and replacement of native intracellular anions with delivered anions are considered.

Fabrication of poly(β-cyclodextrin-co-citric acid)/bentonite clay nanocomposite hydrogel: thermal and absorption properties

A β-cyclodextrin (β-CD)/bentonite clay (BNC) nanocomposite hydrogel was prepared through combining in situ intercalative polymerization and melt intercalation methods.

Accommodating unwelcome guests in inorganic layered hosts: inclusion of chloranil in a layered double hydroxide

The host-guest chemistry of most inorganic layered solids is limited to ion-exchange reactions. The guest species are either cations or anions to compensate for the charge deficit, either positive or negative, of the inorganic layers. Here, we outline a strategy to include neutral molecules like ortho- and para-chloranil, that are known to be good acceptors in donor-acceptor or charge-transfer complexes, within the galleries of a layered solid. We have succeeded in including neutral ortho- and para-chloranil molecules within the galleries of an Mg-Al layered double hydroxide (LDH) by using charge-transfer interactions with preintercalated p-aminobenzoate ions as the driving force. The p-aminobenzoate ions are introduced in the Mg-Al LDH via ion exchange. The intercalated LDH can adsorb ortho- and para-chloranil from chloroform solutions by forming charge-transfer complexes with the p-aminobenzoate anions present in the galleries. We use X-ray diffraction, spectroscopy, and molecular dynamics simulations to establish the nature of interactions and arrangement of the charge-transfer complex within the galleries of the layered double hydroxide.

Controllable photoluminescence properties of an anion-dye-intercalated layered double hydroxide by adjusting the confined environment

This article reports a novel method to tune the photoluminance properties of ammonium 1-anilinonaphthalene-8-sulfonate (ANS) in a 2D matrix of layered double hydroxide (LDH) by changing the interlayer microenvironment. ANS and a series of surfactants with different alkyl chain lengths (pentanesulphonate (PES), hexanesulphonate (HES), heptanesulphonate (HPS), decanesulphonate (DES), and dodecylsulphonate (DDS)) were respectively cointercalated into the galleries of ZnAl-LDH by the anion exchange method. Thin films of ANS/surfactant-LDHs obtained by the solvent evaporation method possess good c orientation as revealed by XRD and SEM. It was found that the ANS/HPS-LDH film showed the maximum fluorescence efficiency and the longest intensity-average lifetime among these ANS/surfactant-LDH composites owing to the "size-matching" rule between the organic dye and surfactant. Moreover, the fluorescence properties can be tuned by changing the relative molar ratio of ANS/HPS, and the film containing 20% ANS (molar percentage, expressed as ANS(20%)/HPS-LDH) exhibits the maximum fluorescence efficiency, the longest average lifetime, and significantly enhanced photo and thermal stability. In addition, the composite films show fluorescence anisotropy, attributed to the preferential orientation of ANS in the LDH gallery. Therefore, this work demonstrates a feasible approach to tuning the photoluminescence properties of a dye confined in an inorganic 2D matrix via changing the interlayer microenvironment, which may be considered to be a good candidate for solid photoluminescence materials, nonlinear optics, and polarized luminescence materials.

A thermochromic thin film based on host-guest interactions in a layered double hydroxide

Optically transparent thin films with thermochromic properties have been fabricated by means of cointercalation of different molar ratios of 4-(4-anilinophenylazo)benzenesulfonate (AO5) and sodium dodecylbenzene sulfonate (SDS) into the galleries of a ZnAl layered double hydroxide (LDH). The X-ray diffraction (XRD) patterns of these thin films show that they are assembled in a highly c-oriented manner, and the basal spacing ranges from 2.95 to 2.63 nm with varying AO5/SDS molar ratio. The preferential orientation of AO5 in the galleries of 10% AO5-LDH (AO5/SDS = 10:90, molar percentage) was evaluated by the fluorescence polarization technique; the results show that AO5 anions are accommodated between sheets of ZnAl-LDH as monomeric units with a tilt angle Psi (defined as the angle between the transition dipole moment of the AO5 anion with respect to the normal to the LDH layer) of 74 degrees. It was found that the composite film exhibits marked thermochromic behavior (light yellow <==> reddish-orange) in the temperature range of 35-65 degrees C, which is reversible over a number of heating-cooling cycles. It has been demonstrated that the thermochromic behavior results from tautomerism of interlayer AO5 and furthermore that both the host-guest and guest-guest interactions are key factors, since pristine AO5 shows no thermochromic performance. The 10% AO5-LDH film shows the highest thermochromic efficiency of all the films examined. Furthermore, a reversible contraction and expansion of the LDH basal spacing was also observed for this thin film over the same temperature range.

Preparation of stable exfoliated Pt-clay nanocatalyst

In this paper, we report a novel experimental protocol for the preparation of stable and exfoliated nano-Pt catalysts supported on layered silicate clay surfaces. Uniformly dispersed highly crystalline Pt nanoparticles with diameters between 2 and 5 nm were chemically adsorbed on to the layered silicate surfaces using a chemical vapor deposition (CVD) method employing organoclay as the initial support. The as-prepared catalysts were found to be extremely stable against both intensive mechanical agitation and high temperature treatment. No Pt loading or morphology changes were observed after ultrasonication under a sonication power density of 6 MW/m(3) for up to 72 h at room temperature or annealing at 700 degrees C for 1 h under Ar flow. On the other hand, Pt catalysts prepared using the inorganic clay as the initial support were found to be highly unstable against both mechanical agitation and high temperature treatment. Significant leaching and catalyst restructuring or sintering was observed. Exfoliation of catalysts and the nature of Pt adsorption were elucidated by systematic analysis using wide-angle X-ray diffraction (WAXD) analysis, Brunauer-Emmett-Teller (BET) surface area analysis, and time-of-flight secondary ion mass spectroscopy (ToF-SIMS) analysis. No low angle diffraction peak was observed in the WAXD pattern, and a 700% increase in BET surface area was observed after Pt deposition on clay surfaces. Depth profiling ToF-SIMS on Pt deposited on SiO(2) wafer surfaces showed the presence of PtSiO ion at the Pt and SiO(2) interface. This ion group was also detected in the bulk of Pt-OrC catalyst, confirming chemisorption of Pt on layered silicate clays. A much lower concentration of PtSiO ion was observed in the Pt-NaC with a similar Pt loading. In addition, X-ray photoelectron spectroscopy (XPS) shows that the binding energy of Pt4f(7/2) in Pt-OrC is much higher than that in the Pt-NaC. The protocol reported in this paper can also be applicable to other clay supported stable metallic catalysts.

Ion Binding to Cucurbit[6]uril: Structure and Dynamics

Molecular dynamics simulations are used to study the microscopic structure and dynamics of cations bound to cucurbit[6]uril (CB[6]) in water and in aqueous solutions of sodium, potassium, and calcium chloride. The molarities are 0.183 M for the salts and 0.0184 M for CB[6]. The cations bind only to CB[6] carbonyl oxygens. They are never found inside the CB[6] cavity. Complexes with Na(+) and K(+) mostly involve one cation, whereas with Ca(2+) single- and double-cation complexes are formed in similar proportions. The binding dynamics strongly depends on the type of cation. A smaller size or higher charge increases the residence time of a cation at a given carbonyl oxygen. When bound to CB[6], sodium and potassium cations jump mainly between nearest or second-nearest neighbors. Calcium shows no hopping dynamics. It is coordinated predominantly by one CB[6] oxygen. A few water molecules (zero to four) can occupy the CB[6] cavity, which is limited by the CB[6] oxygen faces. Their residence time is hardly influenced by sodium and potassium ions. In the case of calcium the residence time of the inner water increases notably. A simple structural model for the cation activity as "lids" over the CB[6] portal cannot, however, be identified. The slowing of the water exchange by the ions is a consequence of the generally slower dynamics in their presence and of their stable solvation shells.