Reversible switching between hydrophilic and hydrophobic superparamagnetic iron oxide microspheres via one-step supramolecular dynamic dendronization: exploration of dynamic wettability

Janus and Amphiphilic MoS2 2D Sheets for Surface-Directed Orientational Assemblies toward Ex Vivo Dual Substrate Release

The two-dimensional (2-D) Janus and amphiphilic molybdenum disulfide (MoS2) nanosheet with opposite optical activities on each side (amphichiral) is synthesized by modifying sandwich-like bulk MoS2 with tannic acid and cholesterol through biphasic emulsion method. This new type of amphichiral Janus MoS2 nanosheet consists of a hydrophilic and positive optical activity tannic acid side as well as a hydrophobic and negative optical activity cholesterol side thereby characterized by circular dichroism. Surface-directed orientational differentiation assemblies are performed for the as-synthesized 2D material and are characterized by contact angle, infrared spectroscopy, X-ray photoelectron, and circular dichroism spectroscopies. The amphiphilic nature of the materials is demonstrated by the pre-organization of the nanosheets on either hydrophobic or hydrophilic surfaces, providing unprecedented properties of circular dichroism signal enhancement and wettability. Selective detachment of the surface organic groups (cholesterol and tannic acid fragments) is realized by matrix-assisted laser desorption/ionisation - time-of-flight (MALDI-TOF) mass spectrometry, and the dual substrate release in tissue is detected by ex vivo mass spectrometry imaging.

Synthesis of Functional Building Blocks for Type III-B Rotaxane Dendrimer

Second-generation type III-B rotaxane dendrons, equipped with succinimide and acetylene functional groups, were synthesized successfully and characterized by NMR spectroscopy and mass spectrometry. A cell viability study of a dendron with a normal cell line of L929 fibroblast cells revealed no obvious cytotoxicity at a range of 5 to 100 μM. The nontoxic properties of the sophisticated rotaxane dendron building blocks provided a choice of bio-compatible macromolecular machines that could be potentially developed into polymeric materials.

π-Stacking Stopper-Macrocycle Stabilized Dynamically Interlocked [2]Rotaxanes

The synthesis of mechanically interlocked molecules is valuable due to their unique topologies. With π-stacking intercomponent interaction, e.g., phenanthroline and anthracene, novel [2]rotaxanes have been synthesized by dynamic imine clipping reaction. Their X-ray crystal structures indicate the π-stackings between the anthracene moiety (stopper) on the thread and the (hetero)aromatic rings at the macrocycle of the rotaxanes. Moreover, the length of glycol chains affects the extra π-stacking intercomponent interactions between the phenyl groups and the dimethoxy phenyl groups on the thread. Dynamic combinatorial library has shown at best 84% distribution of anthracene-threaded phenanthroline-based rotaxane, coinciding with the crystallography in that the additional π-stacking intercomponent interactions could increase the thermodynamic stability and selectivity of the rotaxanes.

Optimizing green ferrate (VI) modification towards flotation separation of waste polyvinylchloride and acrylonitrile-butadiene-styrene mixtures

The recycling of waste plastics is of considerable significance with environmental and economic benefits, while available separation approaches have been considered as a major bottleneck for its widespread application. Thus, we proposed a simple method, flotation along with surface modification, to separate waste acrylonitrile-butadienestyrene and polyvinylchloride mixtures. Single-factor experiment was conducted to determine the critical parameters in surface modification. Surface response methodology using Box-Behnken Design was performed to optimize separation performance. The quadratic models were generated to predict the floatability of acrylonitrile-butadienestyrene and the difference between the floatability of polyvinylchloride and acrylonitrile-butadienestyrene. The model was also utilized to determine optimized conditions by desirability approaches. The optimized conditions were: concentration = 0.18 M, temperature = 75.00 °C, treatment time = 11.50 min along with stirring rate = 200 rpm. The efficient separation of acrylonitrile-butadienestyrene and polyvinylchloride was achieved, yielding recovery of 98.40% and purity of 98.43%. The experimental responses well agreed with predicted values, demonstrating the accuracy of the prediction model. The formed hydrophilic groups, coated iron oxide, and signs of corrosion were confirmed as the major mechanism for the selective surface hydrophilization of acrylonitrile-butadienestyrene. Consequently, this method is feasible for separation of waste acrylonitrile-butadienestyrene and polyvinylchloride mixtures, and can be expected to promote the sustainable recycling of waste plastics.

A fast and effective approach for reversible wetting-dewetting transitions on ZnO nanowires

Here, we demonstrate a facile approach for the preparation of ZnO nanowires (NWs) with tunable surface wettability that can be manipulated reversibly in a controlled manner from a superhydrophilic state to a superhydrophobic state. The as-synthesized ZnO NWs obtained by a chemical vapor deposition method are superhydrophilic with a contact angle (CA) value of ~0°. After H₂ gas annealing at 300 °C for 90 minutes, ZnO NWs display superhydrophobic behavior with a roll-off angle less than 5°. However, O₂ gas annealing converts these superhydrophobic ZnO NWs into a superhydrophilic state. For switching from superhydrophobic to superhydrophilic state and vice versa in cyclic manner, H₂ and O₂ gas annealing treatment was used, respectively. A model based on density functional theory indicates that the oxygen-related defects are responsible for CA switching. The water resistant properties of the ZnO NWs coating is found to be durable and can be applied to a variety of substrates including glass, metals, semiconductors, paper and even flexible polymers.

Dynamic Covalent Nanoparticle Building Blocks

Rational and generalisable methods for engineering surface functionality will be crucial to realising the technological potential of nanomaterials. Nanoparticle-bound dynamic covalent exchange combines the error-correcting and environment-responsive features of equilibrium processes with the stability, structural precision, and vast diversity of covalent chemistry, defining a new and powerful approach for manipulating structure, function and properties at nanomaterial surfaces. Dynamic covalent nanoparticle (DCNP) building blocks thus present a whole host of possibilities for constructing adaptive systems, devices and materials that incorporate both nanoscale and molecular functional components. At the same time, DCNPs have the potential to reveal fundamental insights regarding dynamic and complex chemical systems confined to nanoscale interfaces.

Spatially nanoscale-controlled functional surfaces toward efficient bioactive platforms

Interest in well-defined surface architectures has shown a steady increase, particularly among those involved in biological applications where the reactivity of functional groups on the surface is desired to be close to that of the solution phase. Recent research has demonstrated that utilizing the self-assembly process is an attractive and viable choice for the fabrication of two-dimensional nanoscale-controlled architectures. This review highlights representative examples for controlling the spatial placement of reactive functional groups in the optimization of bioactive surfaces. While the selection is not comprehensive, it becomes evident that surface architecture is one of the key components in allowing efficient biomolecular interactions with surfaces and that the optimized lateral spacing between the immobilized molecules is crucial and even critical in some cases.

Recovering Magnetic Fe3O4-ZnO Nanocomposites from Algal Biomass Based on Hydrophobicity Shift under UV Irradiation

Magnetic separation, one of the promising bioseparation technologies, faces the challenges in recovery and reuse of magnetic agents during algal harvesting for biofuel extraction. This study synthesized a steric acid (SA)-coated Fe3O4-ZnO nanocomposite that could shift hydrophobicity under UV365 irradiation. Our results showed that with the transition of surface hydrophobicity under UV365 irradiation, magnetic nanocomposites detached from the concentrated algal biomass. The detachment was partially induced by the oxidation of SA coating layers due to the generation of radicals (e.g., •OH) by ZnO under UV365 illumination. Consequently, the nanocomposite surface shifted from hydrophobic to hydrophilic, which significantly reduced the adhesion between magnetic particles and algae as predicted by the extended Derjaguin and Landau, Verwey, and Overbeek (EDLVO) theory. Such unique hydrophobicity shift may also find many other potential applications that require recovery, recycle, and reuse of valuable nanomaterials to increase sustainability and economically viability.

Fabrication of electromagnetic Fe3O4@polyaniline nanofibers with high aspect ratio

High aspect ratio Fe₃O₄@polyaniline nanofibers prepared show better magnetization saturation and conductivity value compared to Fe₃O₄@polyaniline microspheres.

Type III-B rotaxane dendrimers

Type III-B first generation [3]rotaxane and second generation [4]rotaxane dendrimers have been synthesized via (1) a modified copper-catalyzed alkyne-azide cycloaddition (CuAAC), (2) Glaser-Hay's acetylenic oxidative homo-coupling, and (3) amide formation. The dendron does not reveal obvious cytotoxicities in L929 fibroblast cells. The rotaxane dendrimers can capture ammonia and are switchable both in solution and on surfaces.

Surface molecular tailoring using pH-switchable supramolecular dendron-ligand assemblies

The rational design of materials with tailored properties is of paramount importance for a wide variety of biological, medical, electronic and optical applications. Here we report molecular level control over the spatial distribution of functional groups on surfaces utilizing self-assembled monolayers (SAMs) of pH-switchable surface-appended pseudorotaxanes. The supramolecular systems were constructed from a poly(aryl ether) dendron-containing a dibenzo[24]crown-8 (DB24C8) macrocycle and a thiol ligand-containing a dibenzylammonium recognition site and a fluorine end group. The dendron establishes the space (dendritic effect) that each pseudorotaxane occupies on the SAM. Following SAM formation, the dendron is released from the surface by switching off the noncovalent interactions upon pH stimulation, generating surface materials with tailored physical and chemical properties.

Natural hydrophobicity and reversible wettability conversion of flat anatase TiO₂ thin film

Flat anatase TiO2 thin film deposited at room temperature shows the natural hydrophobicity, which is destroyed by 400 °C vacuum annealing. On the basis of the analysis of surface composition and structure, the origin of hydrophobicity of the flat TiO2 film can be identified as (1) approximately fully stoichiometric TiO2 and (2) hydrocarbon adsorbates on the film surface. We further validate that interfacial water molecules near the surface of the as-prepared TiO2 film are oriented in the hydrophobic hydration structure via Fourier transform infrared/attenuated total reflection. Moreover, the as-prepared TiO2 film also shows a smart surface reversibly switched between hydrophobicity and super-hydrophilicity. During the recovery process of hydrophobicity, the irradiated films show the wettability with water contact angle of 107 ± 1.7, 72 ± 2.5, 80 ± 1.1, and 17 ± 1.3° corresponding to after a week of exposure to ambient air, O2, CF4, and Ar, respectively. It can be strongly reinforced that the stoichiometry and the adsorbates both play an important role in forming the hydrophobic TiO2 films.

Reversible superhydrophobic-superhydrophilic transition of ZnO nanorod/epoxy composite films

Tuning the surface wettability is of great interest for both scientific research and practical applications. We demonstrated reversible transition between superhydrophobicity and superhydrophilicity on a ZnO nanorod/epoxy composite film. The epoxy resin serves as an adhesion and stress relief layer. The ZnO nanorods were exposed after oxygen reactive ion etching of the epoxy matrix. A subsequent chemcial treatment with fluoroalkyl and alkyl silanes resulted in a superhydrophobic surface with a water contact angle up to 158.4° and a hysteresis as low as 1.3°. Under UV irradiation, the water contact angle decreased gradually, and the surface eventually became superhydrophilic because of UV induced decomposition of alkyl silanes and hydroxyl absorption on ZnO surfaces. A reversible transition of surface wettability was realized by alternation of UV illumination and surface treatment. Such ZnO nanocomposite surface also showed improved mechanical robustness.

Photocytotoxicity and magnetic relaxivity responses of dual-porous γ-Fe2O3@meso-SiO2 microspheres

Novel high magnetization microspheres with porous γ-Fe(2)O(3) core and porous SiO(2) shell were synthesized using a templating method, whereas the size of the magnetic core and the thickness of the porous shell can be controlled by tuning the experimental parameters. By way of an example, as-prepared γ-Fe(2)O(3)@meso-SiO(2) microspheres (170 nm) display excellent water-dispersity and show photonic characteristics under externally applied a magnetic field. The magnetic property of the γ-Fe(2)O(3) porous core enables the microspheres to be used as a contrast agent in magnetic resonance imaging with a high r(2) (76.5 s(-1) mM(-1) Fe) relaxivity. The biocompatible composites possess a large BET surface area (222.3 m(2)/g), demonstrating that they can be used as a bifunctional agent for both MRI and drug carrier. Because of the high substrate loading of the magnetic, dual-porous materials, only a low dosage of the substrate will be acquired for potential practical applications. Hydrophobic zinc(II) phthalocyanine (ZnPC) photosensitizing molecules have been encapsulated into the dual-porous microspheres to form γ-Fe(2)O(3)@meso-SiO(2)-ZnPC microspheres. Biosafety, cellular uptake in HT29 cells, and in vitro MRI of these nanoparticles have been demonstrated. Photocytotoxicity (λ > 610 nm) of the HT29 cells uptaken with γ-Fe(2)O(3)@meso-SiO(2)-ZnPC microspheres has been demonstrated for 20 min illumination.

Guided transport of water droplets on superhydrophobic-hydrophilic patterned Si nanowires

We present a facile method to fabricate hydrophilic patterns in superhydrophobic Si nanowire (NW) arrays for guiding water droplets. The superhydrophobic Si NW arrays were obtained by simple dip-coating of dodecyltrichlorosilane (DTS). The water contact angles (CAs) of DTS-coated Si NW arrays drastically increased and saturated at the superhydrophobic regime (water CA ≥ 150°) as the lengths of NWs increased. The demonstrated superhydrophobic surfaces show an extreme water repellent property and small CA hysteresis of less than 7°, which enable the water droplets to easily roll off. The wettability of the DTS-coated Si NW arrays can be converted from superhydrophobic to hydrophilic via UV-enhanced photodecomposition of the DTS, and such wettability conversion was reproducible on the same surfaces by repeating the DTS coating and photodecomposition processes. The resulting water guiding tracks were successfully demonstrated via selective patterning of the hydrophilic region on superhydrophobic Si NW arrays, which could enable water droplets to move along defined trajectories.

Synthesis of biocompatible, mesoporous Fe(3)O(4) nano/microspheres with large surface area for magnetic resonance imaging and therapeutic applications

This article reports the fabrication of mesoporous Fe(3)O(4) nano/microspheres with a high surface area value (163 m(2)/g, Brunauer-Emmett-Teller) and demonstrates their use for drug loading, release, and magnetic resonance imaging (MRI). These monodispersed, mesoporous Fe(3)O(4) nano/microspheres with controllable average sizes ranging from 50 to 200 nm were synthesized using a Fe(3)O(4)/poly(acrylic acid) hybrid sphere template and subsequent silica shell formation and removal. We found that the SiO(2) coating is a crucial step for the successful synthesis of uniform mesoporous Fe(3)O(4) nano/microspheres. The as-synthesized mesoporous Fe(3)O(4) nanospheres show a high magnetic saturation value (M(s) = 48.6 emu/g) and could be used as MRI contrast agents (r(2) = 36.3 s(-1) mM(-1)). Trypan blue exclusion and MTT assay (see Supporting Information ) cytotoxicity analyses of the nanospheres based on HepG2 and MDCK cells showed that the products were biocompatible, with a lower toxicity than lipofectamine (positive control). Hydrophilic ibuprofen and hydrophobic zinc(II) phthalocyanine drug loading into mesoporous Fe(3)O(4) nanospheres and selected release experiments were successfully achieved. The potential use of mesoporous Fe(3)O(4) nanospheres in biomedical applications, in light of the nano/microspheres' efficient drug loading and release, MRI, and low cytotoxicity, has been demonstrated. It is envisaged that mesoporous Fe(3)O(4) nanospheres can be used as drug carriers and MRI contrast agents for the reticuloendothelial system; they can also be delivered locally, such as via a selective catheter.

Self-assembly, stability quantification, controlled molecular switching, and sensing properties of an anthracene-containing dynamic [2]rotaxane

The preparation of a novel anthracene-containing dynamic [2]rotaxane by a templating self-assembly process between a diamine and a dialdehyde to form a [24]crown-8 macrocyclic diimine, in the presence of a dumbbell containing a secondary dialkylammonium ion center as the template, which has been exploited for its sensing properties. By appealing to the ability of the anthracene ring system--one of the two stoppers associated with the dumbbell--to act as a fluorescent probe, the fluorescence and fluorescence-quenching nature of the dynamic rotaxane in an equilibrium mixture has been investigated and quantified in the presence of external stimuli such as water, acids, salts, and an amine. The stability, as expressed by the hydrolysis of the dynamic rotaxane has been monitored by following: (i) the anthracene fluorescence and (ii) the movements of the signals in the (1)H NMR spectra. The rate of hydrolysis (t(1/2) = 6.9 min) of the dynamic rotaxane in the presence of a small amount (1 equiv.) of acid was found to be very much faster than when the hydrolysis was carried out with a large amount (>100 equiv.) of water, when t(1/2) > 140 min. Furthermore, it has been established that the anthracene fluorescence of the dynamic rotaxane rises with an increasing amount of acid. Two acid sensors have been identified with different operating modes-namely, logarithmic and linear. The combination of different inputs involving water, acids, salts and an amine leads to different fluorescence outputs from the dynamic rotaxane, hence, producing a prototype for expressing molecular logic.

The stability of imine-containing dynamic [2]rotaxanes to hydrolysis

Large amounts (>100 mol equivalents) of water are required to effect by hydrolysis the partial disassembly of the rings from the dumbbell components of two dynamic [2]rotaxanes. The two dynamic [2]rotaxanes are comprised of [24]crown-8 rings-each of which incorporate two imine bonds-encircling a dumbbell component composed of a dibenzylammonium ion in which each of the two benzyl substituents carries two methoxyl groups attached to their 3- and 5-positions. A mechanism for the partial disassembly of the two dynamic [2]rotaxanes, involving the cleavage of the kinetically labile imine bonds by water molecules, is proposed. The most important experimental observation to be noted is the fact that the hydrolysis of the macrocyclic diimines, associated with the templating -CH(2)NH(2)(+)CH(2)-centres in the middle of their dumbbells, turns out to be an uphill task to perform in the face of the molecular recognition provided by strong [N(+)-HO] hydrogen bonds and weaker, yet not insignificant, [C-HO] interactions. The dynamic nature of the imine bond formation and hydrolysis is such that the acyclic components produced during hydrolysis of the imine bonds can be enticed to cyclise once again around the -CH(2)NH(2)(+)CH(2)-template, affording the [2]rotaxanes. The reluctance of imine bonds, present in substantial numbers in larger molecular and extended structures, is significant when it comes to exercising dynamic chemistry in compounds where multiple imine bonds are present.