Crystal chemistry and single-phase synthesis of Gd3+ substituted Co–Zn ferrite nanoparticles for enhanced magnetic properties

Rare earth (RE) ions are known to improve the magnetic interactions in spinel ferrites if they are accommodated in the lattice, whereas the formation of a secondary phase leads to the degradation of the magnetic properties of materials. Therefore, it is necessary to solubilize the RE ions in a spinel lattice to get the most benefit. In this context, this work describes the synthesis of Co–Zn ferrite nanoparticles and the Gd³⁺ doping effect on the tuning of their magnetic properties. The modified sol–gel synthesis approach offered a facile way to synthesize ferrite nanoparticles using water as the solvent. X-ray diffraction with Rietveld refinement confirmed that both pure Co–Zn ferrite and Gd³⁺ substituted Co–Zn ferrite maintained single-phase cubic spinel structures. Energy dispersive spectroscopy was used to determine the elemental compositions of the nanoparticles. Field and temperature dependent magnetic characteristics were measured by employing a vibration sample magnetometer in field cooled (FC)/zero field cooled (ZFC) modes. Magnetic interactions were also determined by Mössbauer spectroscopy. The saturation magnetization and coercivity of Co–Zn ferrite were improved with the Gd³⁺ substitution due to the Gd³⁺ (4f⁷)–Fe³⁺ (3d⁵) interactions. The increase in magnetization and coercivity makes these Gd³⁺ substituted materials applicable for use in magnetic recording media and permanent magnets.

Rare earth (RE) ions are known to improve the magnetic interactions in spinel ferrites if they are accommodated in the lattice, whereas the formation of a secondary phase leads to the degradation of the magnetic properties of materials.     

Corrosion resistance of Ni–P/SiC and Ni–P composite coatings prepared by magnetic field-enhanced jet electrodeposition

To extend the working life of 45# steel, Ni–P and Ni–P/SiC composite coatings were prepared on its surface by magnetic field-enhanced jet electrodeposition. This study investigated the effect of magnetic field on the corrosion resistance of Ni–P and Ni–P/SiC composite coatings prepared by conventional jet electrodeposition. The surface and cross-sectional morphologies, microstructure, and composition of the composite coatings were determined by scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), and X-ray diffraction (XRD), respectively. The corrosion resistance was studied using a LEXT4100 laser confocal microscope. The introduction of a stable magnetic field was found to improve the surface morphology of the coatings, increase the growth rate, and reduce the agglomeration of nano-SiC (3 g L⁻¹, 40 nm) particles, thus significantly improving the corrosion resistance of the coatings. The corrosion potential of the Ni–P coating increased from −0.78 V (0 T) to −0.46 V (0.5 T), and the corrosion current density decreased from 9.56 × 10⁻⁶ A dm⁻² (0 T) to 4.31 × 10⁻⁶ A dm⁻² (0.5 T). The corrosion potential of the Ni–P/SiC coating increased from −0.59 V (0 T) to −0.28 V (0.5 T), and the corrosion current density decreased from 6.01 × 10⁻⁶ A dm⁻² (0 T) to 2.90 × 10⁻⁶ A dm⁻² (0.5 T).

We investigated the effect of magnetic field on Ni–P and Ni–P/SiC composite coatings prepared by jet electrodeposition.     

Facile preparation of porous sheet–sheet hierarchical nanostructure NiO/Ni–Co–Mn–Ox with enhanced specific capacity and cycling stability for high performance supercapacitors

NiO, Ni–Co–Mn–O_x and NiO/Ni–Co–Mn–O_x on nickel foam substrates were prepared via a chemical bath deposition–calcination. The thermodynamic behavior was observed by TG/DTA. The chemical structure and composition, phase structure and microstructures were tested by XPS, XRD, FE-SEM and TEM. The electrochemical performance was measured by CV, GCD and EIS. The mechanism for formation and enhancing electrochemical performance is also discussed. Firstly, the precursors such as NiOOH, CoOOH and MnOOH grow on nickel foam substrates from a homogeneous mixed solution via chemical bath deposition. Thereafter, these precursors are calcined and decomposed into NiO, Co₃O₄ and MnO₂ respectively under different temperatures in a muffle furnace. Notably, NiO/Ni–Co–Mn–O_x on nickel foam substrates reveals a high specific capacity with 1023.50 C g⁻¹ at 1 A g⁻¹ and an excellent capacitance retention with 103.94% at 5 A g⁻¹ after 3000 cycles in 2 M KOH, its outstanding electrochemical performance and cycling stability are mainly attributed to a porous sheet–sheet hierarchical nanostructure and synergistic effects of pseudo-capacitive materials and excellent redox reversibility. Therefore, this research offers a facile synthesis route to transition metal oxides for high performance supercapacitors.

NiO, Ni–Co–Mn–O_x and NiO/Ni–Co–Mn–O_x on nickel foam substrates were prepared via a chemical bath deposition–calcination.     

Structural,mechanical, dielectric properties and magnetic interactions in Dy3+-substituted Co–Cu–Zn nanoferrites

Sol–gel-synthesized Co–Cu–Zn ferrite nanoparticles diluted with Dy³⁺ ions were investigated in terms of their structural, morphological, elastic, magnetic and dielectric properties. X-ray diffraction patterns showed the formation of a single-phase cubic spinel structure. As the concentration of Dy³⁺ ions was increased, the lattice length gradually increased from 8.340 to 8.545 Å, obeying Vegard''s law. The Williamson–Hall (W–H) method was employed to observe the change in the lattice strain. Crystallite size obtained from W–H plots followed a pattern similar to that observed using the Scherrer equation. The cation distribution suggested a strong preference of Dy³⁺ ions for the octahedral B site while Cu²⁺ and Fe³⁺ ions were distributed over both A and B sites. The microstructures of the samples were visualized using transmission electron microscopy. Mechanical properties such as stiffness constant, longitudinal and transverse wave velocities, Young''s modulus, bulk modulus, rigidity modulus, Poisson''s ratio and Debye temperature were investigated by acquiring infrared spectra recorded in the range of 300 to 800 cm⁻¹. Replacement of Fe³⁺ ions with the strongly magnetic Dy³⁺ ions increased the saturation magnetization and coercivity. Dielectric constant increased with Dy³⁺ substitution but decreased with applied frequency.

Improvement in various properties of Co–Cu–Zn ferrite upon Dy substitution.     

Fulvic–polyphosphate composite embedded in ZnO nanorods (FA–APP@ZnO) for efficient P/Zn nutrition for peas (Pisum sativum L.)

A nano-fertilizer (FA–APP@ZnO) was designed and prepared based on the copolymer of fulvic acid (FA) and ammonium polyphosphate (APP) with ZnO nanorods embedded, to tackle the antagonism between phosphorus (P) and zinc (Zn) in fertilization. FA–APP@ZnO was confirmed to revert the precipitability of H₂PO₄⁻ and Zn²⁺ into a synergistic performance, where FA and APP can disperse ZnO nanorods, and in return, ZnO catalyzes the hydrolysis of the absorbed APP. The hydrolysis rate constant of pyrophosphates consequently increased 8 times. The dry biomass of pea (Pisum sativum L.) under the FA–APP@ZnO hydroponics for 7 days increased by 119%, as compared with the situation employing the conventional NH₄H₂PO₄ and ZnSO₄ compound fertilizer. Moreover, the uptake of seedlings for P and Zn was enhanced by 54% and 400%, respectively. The accelerated orthophosphate release due to ZnO catalysis and the well-dispersed ZnO nanorods enabled by APP met the urgent demand for P and Zn nutrients for peas, especially at their vigorous seedling stage. This work would provide a new idea for constructing nano-platforms to coordinate the incompatible P and Zn nutrients for the improvement of agronomic efficiency.

Phyto-nanotechnology can improve the nutrient efficiency and alleviate the environmental stress caused by eluvial agricultural chemicals, contributing to sustainable agriculture.     

New advances on Au–magnetic organic hybrid core–shells in MRI,CT imaging,and drug delivery

Magnetic nanoparticles have been widely studied for various scientific and technological applications such as magnetic storage media, contrast agents for magnetic resonance imaging (MRI), biolabelling, separation of biomolecules, and magnetic-targeted drug delivery. A new strategy on Au–magnetic nano-hybrid core–shells was applied in MRI, CT imaging, and drug delivery, which has been received much attention nowadays. Herein, the designing of different magnetic core–shells with Au in MRI and cancer treatment is studied.

Magnetic nanoparticles have been studied for scientific and technological applications such as magnetic storage media, contrast agents for magnetic resonance imaging, biolabelling, separation of biomolecules, and magnetic-targeted drug delivery.     

The pH-triggered drug release and simultaneous carrier decomposition of effervescent SiO2–drug–Na2CO3 composite nanoparticles: to improve the antitumor activity of hydrophobic drugs

To achieve a better release effect of hydrophobic drugs and spontaneous nanocarrier disintegration by dissolution as well as the CO₂ production of Na₂CO₃ further, improving the therapeutic effect of hydrophobic drugs, and thereby avoiding the accumulation of the nanocarrier in vivo to produce organ toxicity, effervescent SiO₂–drug–Na₂CO₃ composite nanoparticles (ESNs) were prepared in this study using a tetraethyl orthosilicate hydrolysis method. Sodium carbonate was used as the effervescent disintegrant to respond to the acidic microenvironment of the tumor. The properties of ESNs were assessed and TEM images were taken to verify the self-disintegration characteristics of nanocarrier materials. The in vitro anticancer efficacy of ESNs was evaluated in human breast cancer MCF-7 cells. ESNs loaded with hydrophobic drugs were successfully constructed, and showed high entrapment efficiency and drug loading. The nanocarrier successfully achieved self-disintegration in a PBS environment of pH value at 5.0, and showed excellent antitumor effect in vitro. ESNs can effectively load hydrophobic drugs and achieve self-disintegration, while avoiding toxicity from the accumulation of the nanocarrier. These results suggest that ESNs are a promising drug delivery system capable of maximizing the anticancer therapeutic efficacy and minimizing the systemic toxicity.

Effervescent SiO₂–drug–Na₂CO₃ composite nanoparticles were prepared in this study using a tetraethyl orthosilicate hydrolysis method to achieve a better release effect of hydrophobic drugs and spontaneous nanocarrier disintegration by dissolution.     

Characterization and osteogenic evaluation of mesoporous magnesium–calcium silicate/polycaprolactone/polybutylene succinate composite scaffolds fabricated by rapid prototyping

The properties of scaffolds for bone tissue engineering, including their biocompatibility, highly interconnected porosity, and mechanical integrity, are critical for promoting cell adhesion, proliferation, and osteoinduction. We used various physical and biological assays to obtain in vitro confirmation that the proposed composite scaffolds are potentially suitable for applications to bone tissue engineering. The proposed new composite scaffolds, which we fabricated by a rapid prototyping technique, were composed of mesoporous magnesium–calcium silicate (m_MCS), polycaprolactone (PCL), and polybutylene succinate (PBSu). We systematically evaluated the characteristics of the composite scaffolds, such as the hydrophilicity and bioactivity. We also investigated the proliferation and osteogenic differentiation of human mesenchymal stem cells (MSCs) scaffolded on the m_MCS/PCL/PBSu composite. Our results showed that, compared to the m_MCS/PCL scaffold, the m_MCS/PCL/PBSu scaffold has improved water absorption, in vitro degradability, biocompatibility, and bioactivity in simulated body fluid, while its mechanical strength is reduced. Moreover, the results of the cytotoxicity tests specified in ISO 10993-12 and ISO 10993-5 clearly indicate that the m_MCS/PCL scaffold is not toxic to cells. In addition, we obtained significant increases in initial cell attachment and improvements to the osteogenic MSC differentiation by replacing the m_MCS/PCL scaffold with the m_MCS/PCL/PBSu scaffold. Our results indicate that the m_MCS/PCL/PBSu scaffold achieves enhanced bioactivity, degradability, cytocompatibility, and osteogenesis. As such, this scaffold is a potentially promising candidate for use in stem cell-based bone tissue engineering.

A new composite scaffold consisting of mesoporous magnesium–calcium silicate (m_MCS), polycaprolactone (PCL), and polybutylene succinate (PBSu) was manufactured by a rapid prototyping technique, for stem cell-based bone tissue engineering.     

Influence of shell compositions of solution blown PVP/PCL core–shell fibers on drug release and cell growth

Developing a facile means of controlling drug release is of utmost interest in drug delivery systems. In this study, core–shell structured nanofibers containing a water-soluble porogen were fabricated via solution blow spinning, to be used as drug-loaded bioactive tissue scaffolds. Hydrophilic polyvinylpyrrolidone (PVP) and hydrophobic poly(ε-caprolactone) (PCL) were chosen to produce the core and the shell compartments of the fiber, respectively. In the core, a hydrophilic sulforhodamine B (SRB) dye was loaded as a model drug. In the PCL shell, two kinds of PVP with different molecular weights (40 kDa and 1300 kDa) were added, and the influence of PVP leaching on the SRB release and cell growth was investigated. The monolithic PCL-shelled fibers displayed a sustained SRB release with a weak burst effect. The addition of PVP in the shell induced a phase separation, forming microscale PVP domains. The PVP domain, acting as a porogen, was leached out in the medium and, as a result, the burst release of SRB was promoted. This burst effect was more prominent with the lower molecular weight PVP. The biocompatibility of the core–shell fibers was evaluated with human epidermal keratinocytes (HEK) by a cell viability assay and microscopic observation of cell proliferation. The HEK cells on fibers with a PVP/PCL composite shell formed self-assembled spherical clusters, displaying higher cell viability and proliferation than those on the monolithic PCL-shelled fibers that induced HEK cell growth in two-dimensional monolayers. The results demonstrate that the presence of hydrophilic porogens on tissue scaffolds can accelerate drug release and enhance cell proliferation by increasing surface wettability, roughness and porosity. The findings of this study provide a basic insight into the construction of bioactive three-dimensional tissue scaffolds.

The presence of hydrophilic porogens on the surface of core–shell fibers can accelerate drug release and enhance cell proliferation.     

Zn2+ removal from the aqueous environment using a polydopamine/hydroxyapatite/Fe3O4 magnetic composite under ultrasonic waves

In this study, an easily magnetically recoverable polydopamine (PDA)-modified hydroxyapatite (HAp)/Fe₃O₄ magnetic composite (HAp/Fe₃O₄/PDA) was suitably synthesized to exploit its adsorption capacity to remove Zn²⁺ from aqueous solution, and its structural properties were thoroughly examined using different analytical techniques. The effect of multiple parameters like pH, ultrasonic power, ultrasonic time, adsorbent dose, and initial Zn²⁺ concentration on the adsorption efficiency was assessed using RSM-CCD. According to the acquired results, by increasing the adsorbent quantity, ultrasonic power, ultrasonic time, and pH, the Zn²⁺ adsorption efficiency increased and the interaction between the variables of ultrasonic power/Zn²⁺ concentration, pH/Zn²⁺ concentration, pH/absorbent dose, and ultrasonic time/adsorbent dose has a vital role in the Zn²⁺ adsorption. The uptake process of Zn²⁺ onto PDA/HAp/Fe₃O₄ followed Freundlich and pseudo-second order kinetic models. The maximum capacity of Zn²⁺ adsorption (q_m) obtained by PDA/HAp/Fe₃O₄, HAp/Fe₃O₄, and HAp was determined as 46.37 mg g⁻¹, 40.07 mg g⁻¹, and 37.57 mg g⁻¹, respectively. Due to its good performance and recoverability (ten times), the HAp/Fe₃O₄/PDA magnetic composite can be proposed as a good candidate to eliminate Zn²⁺ ions from a water solution.

A magnetically recoverable polydopamine (PDA)-modified hydroxyapatite (HAp)/Fe₃O₄ magnetic composite (HAp/Fe₃O₄/PDA) was synthesized to exploit its adsorption capacity to remove Zn²⁺ from aqueous solution and the structural properties were examined.     

Microstructure,mechanical properties,and electrical conductivity of Mg–8Li–2Y–Zn/Al multilayered composites fabricated by cross asynchronous accumulative roll bonding

Mg–Li alloy is a material with great potential for development but its application in multiple fields is limited due to disadvantages, such as low strength and poor molding properties. In this study, Mg–8Li–2Y–Zn/Al multilayered composites were prepared by the Al layer cladding Mg–Li alloys using a cross asynchronous accumulative roll banding (CAARB) method, and the changes in microstructural characterization, mechanical properties, and electrical conductivity after rolling were evaluated. The results showed that the asynchronous rolling introduced additional shear variables, which provided the conditions for the aluminum layers to fracture to form wave patterns and improve the formability of the composites. The change in the rolling direction caused the grain orientation to be dispersed along the TD direction. The microhardness and tensile strength of the Mg–8Li–2Y–Zn/Al composites increased during the CAARB and reached a maximum after four cycles. In addition, calculations based on the skin depth indicate that the addition of Al layers benefits the composites in terms of improved electrical conductivity. Overall, the addition of Al layers allows more flexibility in the design and extension of Mg–Li alloys, and these findings provide insights into the control of microstructure and improvement of properties of Al/Mg–Li multilayered composites using the CAARB process.

Mg–8Li–2Y–Zn/Al multilayered composites were successfully fabricated by the CAARB process, and have excellent mechanical properties and electrical conductivity, expanding their applications.     

Conversion of methane to C2 and C3 hydrocarbons over TiO2/ZSM-5 core–shell particles in an electric field

Catalytic conversion of methane (CH₄) to light olefins is motivated by increasing recoverable reserves of methane resources, abundantly available in natural gas, shale gas, and gas hydrates. The development of effective processes for conversion of CH₄ to light olefins is still a great challenge. The interface of ZSM-5 zeolite and TiO₂ nanoparticles is successfully constructed in their core–shell particles via mechanochemical treatment with high shear stress. The oxidative coupling of methane at a low temperature under application of an electric field may be induced by the O₂ activation via electrons running through the surface of TiO₂ located at the interface of TiO₂ and zeolite particles. Moreover, C₃H₆ was also produced by the ethylene to propylene (ETP) reaction catalyzed by Brønsted acid sites in the ZSM-5 zeolite within core–shell particles.

A TiO₂/ZSM-5 composite catalyst efficiently works for the oxidative coupling of methane and the subsequent ethylene-to-propylene reactions in an electric field.     

Preparation and characterization of an edible metal–organic framework/rice wine residue composite

In this communication, using rice wine residue (RWR) as the support, an edible γ-cyclodextrin-metal–organic framework/RWR (γ-CD-MOF/RWR) composite with a macroscopic morphology was synthesized. The obtained edible composite is promising for applications in drug delivery, adsorption, food processing, and others.

An edible metal–organic framework/rice wine residue composite was made with large surface area for potential applications in drug delivery, adsorption, food processing, and others.

As a typical class of porous materials, metal–organic frameworks (MOFs) have attracted increasing attention since being first proposed by Yaghi and co-workers.¹ Over the past two decades, owing to their large surface area, ultrahigh porosity and tunable pore size,² MOFs have exhibited great prospects for gas storage and separation,^3,4 catalysis,^5–8 sensors,⁹ drug delivery,^10–12etc. Among numerous reported MOFs, γ-cyclodextrin-MOF (γ-CD-MOF), which is connected by the (γ-CD)₆ units of alkaline earth metal ions, was initially synthesized and reported by Stoddart et al.^13,14 in the 2010s. Owing to the –OCCO– groups derived from γ-CD, this kind of MOF is edible and therefore opens a new path for preparing green, biocompatible and edible MOF materials.^13,15,16 For example, Stoddart et al.¹¹ reported a co-crystallization approach to trap ibuprofen and lansoprazole inside γ-CD-MOF, and the resultant composite microspheres can be used for sustained drug delivery. Zhang et al.¹⁷ proposed a strategy to graft cholesterol over the surface of γ-CD-MOF to form a protective hydrophobic layer to improve its water stability. Many researchers succeeded in preparing oral delivery medicine with high drug loading and an enhanced therapeutic effect by combining the drug molecules with γ-CD-MOF.^16,18–20 These works present the excellent application prospects of γ-CD-MOF in the medical field.Since MOFs possess so many attractive advantages, extensive studies have focused on combining MOFs with many other functional materials (metal nanoparticles, quantum dots, carbon matrices and polyoxometalates, etc.) by means of the synergistic effect, leading to the formation of novel composites designed for targeted applications.^21–28 However, these reported composites were still presented as loose powders, which may not be convenient for the applications. Therefore, the question of how to prepare MOFs-based composites for larger particles at low cost is of great significance. On the other hand, as a traditional alcoholic beverage, rice wine has been popular in southern China and some other Asian nations for thousands of years.²⁹ The rice wine lees or rice wine residue (RWR) is a by-product of the fermentation process of rice wine. It is a mixture of proteins, amino acids and polysaccharides. It is traditionally a health food in some Asian nations.³⁰ The edibility, extensive source, low cost and specific macroscopic shape make RWR a potential functional material for further use of MOFs.Herein, a facile and environmental-friendly strategy has been developed to realize the growth of γ-CD-MOF on rice wine residue, resulting in the formation of an edible MOF/RWR composite in the shape of rice grains. The material characterization confirmed the obtained composite possesses the characteristics of MOF. Except for the edible γ-CD-MOF/RWR, other MOF/RWR composites (HKUST-1, ZIF-67 and MIL-100(Fe)/RWR composites; shown in Fig. S1^†) were prepared to demonstrate the universality of this synthesis strategy.The synthesis procedure of the γ-CD-MOF/RWR composite is schematically illustrated in Fig. 1. The rice wine residue was soaked in deionized water for 12 h and then washed with deionized water three times before vacuum freeze-drying. Similar to the synthesis of γ-CD-MOF powder,¹⁵ KOH was dissolved into water. Then certain amounts of the aforementioned dry rice wine residue were soaked into the K⁺-containing solution for 2 h in order to absorb the sufficient potassium ions. K⁺ was then linked by the coordination of –OCCO– units in γ-CD and RWR with the three-dimensional interconnected network. After vapor diffusion of MeOH and some other procedures described in the synthesis of γ-CD-MOF powder (seen in ESI), the γ-CD-MOF/RWR composite (Fig. 2) was obtained. This method is convenient as no extra binders are needed during the whole process. The same procedure was employed to prepare the RWR composites with other MOFs (HKUST-1, ZIF-67 and MIL-100(Fe)). And the syntheses are briefly described in the ESI. The images of the obtained composites are shown in Fig. S1.^†Open in a separate windowFig. 1Schematic illustration of the synthesis procedure of γ-CD-MOF/RWR composite.Open in a separate windowFig. 2Digital photo of the γ-CD-MOF/RWR composite.The rice wine residue, of which the elemental analysis is shown in Table S1,^† is mainly composed of polysaccharides and proteins. Thus, a broad peak at around 22.2° in the XRD patterns of rice wine residue can be observed (Fig. S2^†), which is due to its poor crystallinity.³¹ The XRD patterns of γ-CD-MOF and γ-CD-MOF/RWR composite samples are shown in Fig. 3a. The characteristic peaks at 5.6°, 6.9°, 13.3°, 16.6°, 20.6° and 23.2°, observed from the XRD patterns of γ-CD-MOF, agree with the previously reported works.^32,33 Meanwhile, compared with γ-CD-MOF, the γ-CD-MOF/RWR composite shows similar characteristic peaks with lower intensity, indicating a lower crystallinity of the MOF within the composite. Fig. 3b shows the FT-IR spectra of different samples. Compared with the rice wine residue, the peaks in regions 1 and 2 of γ-CD-MOF and γ-CD-MOF/RWR can be ascribed to the stretching vibration of –CH₂ and –C–O–C– of the MOF, respectively.^15,34 These results further confirm the formation of the γ-CD-MOF in the γ-CD-MOF/RWR composite.Open in a separate windowFig. 3XRD patterns (a) and FT-IR spectra (b) of γ-CD-MOF/RWR composite, γ-CD-MOF and RWR.The SEM images were collected to further investigate the micromorphology of the as-prepared samples. As shown in Fig. 4a, a three-dimensional layered network structure and rich macropores of the rice wine residue rough surface can be seen. γ-CD-MOF (Fig. 4b) exhibits a uniform body-centered cubic shape with an average size of 4.27 μm, which is in accordance with the reported works.^15,35,36 Meanwhile, the images of the γ-CD-MOF/RWR composite (Fig. 4c and d) show that the cubic γ-CD-MOF crystals are well dispersed on the surface of the rice wine residue and even partially integrated into the framework of the rice wine residue. Compared with the pristine γ-CD-MOF, some γ-CD-MOF in γ-CD-MOF/RWR is not an intact cubic structure, exhibiting a significantly different morphology. This suggests a synergistic effect between the MOF crystals and the rice wine residue during the growth of MOF crystals, rather than a simple physical mixture of the two materials. The thermal stability of the γ-CD-MOF/RWR composite was investigated via TGA analysis. As shown in Fig. S3,^† the decomposition temperature of γ-CD-MOF/RWR composite slightly increased compared with those of pristine γ-CD-MOF and rice wine residue. Moreover, the γ-CD-MOF/RWR composite was stable in water, methanol and ethanol (shown in Fig. S4^†) even under mild stirring. These results indicate an improved physiochemical stability of γ-CD-MOF after the incorporation of rice wine residue. This finding further confirms the synergistic effect between them.Open in a separate windowFig. 4SEM images of rice wine residue (a), γ-CD-MOF (b) and γ-CD-MOF/RWR composite (c and d). Fig. 5a shows the nitrogen sorption isotherms of the γ-CD-MOF and γ-CD-MOF/RWR composite. Both pristine γ-CD-MOF and γ-CD-MOF/RWR exhibit typical type-I isotherms, demonstrating their microporous structures. The pore size distributions of pure γ-CD-MOF and γ-CD-MOF/RWR (Fig. 5b) confirm the existence of micropores (between 1 and 2 nm). The calculated Brunauer–Emmett–Teller (BET) surface areas, micropore volume and total pore volume are listed in 35,37 The specific surface area of the γ-CD-MOF/RWR composite is 651 m² g⁻¹, which is significantly higher than that of the pure rice wine residue (10.8 m² g⁻¹). Thus, the increase in the specific surface area of γ-CD-MOF/RWR composite can be attributed to the growth of γ-CD-MOF on the RWR support. Therefore, γ-CD-MOF/RWR composite inherits both the high porosity of γ-CD-MOF and the macroscopic morphology of rice wine residue, which should contribute to its practical applications.Open in a separate windowFig. 5N₂ adsorption and desorption isotherms (a) and pore size distributions (b) of γ-CD-MOF/RWR composite and corresponding comparative samples.Summary of the BET areas (S_BET), micropore volume (V_micro) and total pore volume (V_tot) of γ-CD-MOF, γ-CD-MOF/RWR composite and pure rice wine residue

A pH-sensitive and sustained-release oral drug delivery system: the synthesis,characterization, adsorption and release of the xanthan gum-graft-poly(acrylic acid)/GO–DCFP composite hydrogel

In this study, graphene oxide (GO) was successfully prepared using the improved Hummers method, and the prepared GO powder was dissolved in distilled water and subjected to ultrasonic stripping. Diclofenac potassium (DCFP) was selected as a model drug to systematically evaluate the adsorption mechanism of DCFP by GO. Different reaction models were constructed to fit the adsorption kinetics and adsorption isotherms of DCFP on GO, in order to further explore the underlying adsorption mechanism. The results demonstrated that the pseudo-second-order kinetic model and Freundlich model could better delineate the adsorption process of DCFP by GO. Both π–π stacking and hydrophobic interaction were mainly involved in the adsorption process, and there were electrostatic interaction and hydrogen bonding at the same time. Then, the xanthan gum-graft-poly(acrylic acid)/GO (XG-g-PAA/GO) composite hydrogel was synthesized by in situ polymerization as a slow-release drug carrier. For this reason, a XG-g-PAA/GO–DCFP composite hydrogel was synthesized, and its in vitro drug release and pharmacokinetic data were assessed. The results showed that the synthesized XG-g-PAA/GO composite hydrogel had a certain mechanical strength and uniform color, indicating that GO is evenly distributed in this composite hydrogel. Moreover, the results of a swelling ratio test demonstrated that the swelling ratios of the XG-g-PAA/GO composite hydrogel were significantly increased with increasing pH values, implying that this material is sensitive to pH. The in vitro drug release experiment showed that the cumulative release of DCFP after 96 h was significantly higher in artificial intestinal fluid than in artificial gastric fluid. These findings indicate that the XG-g-PAA/GO–DCFP composite hydrogel exhibits pH sensitivity under physiological conditions. Besides, the results of in vivo pharmacokinetic analysis revealed that the t_1/2 of DCFP group was 2.03 ± 0.35 h, while that of the XG-g-PAA/GO–DCFP composite hydrogel group was 10.71 ± 2.04 h, indicating that the synthesized hydrogel could effectively prolong the drug action time. Furthermore, the AUC_(0–t) of the DCFP group was 53.99 ± 3.18 mg L⁻¹ h⁻¹, while that of the XG-g-PAA/GO–DCFP composite hydrogel group was 116.79 ± 14.72 mg L⁻¹ h⁻¹, suggesting that the bioavailability of DCFP is greatly enhanced by this composite hydrogel. In conclusion, this study highlights that the XG-g-PAA/GO–DCFP composite hydrogel can be applied as a sustained-release drug carrier.

In this study, graphene oxide (GO) was successfully prepared using the improved Hummers method, and the prepared GO powder was dissolved in distilled water and subjected to ultrasonic stripping.     

Synthesis of a novel magnetic Caragana korshinskii biochar/Mg–Al layered double hydroxide composite and its strong adsorption of phosphate in aqueous solutions

Phosphate pollution of aquatic ecosystems is of great concern and requires the development of high-performance materials for effective pollution treatment. To realize efficient phosphate removal from aqueous solution, an easily separable magnetic (Fe₃O₄) Caragana korshinskii biochar/Mg–Al layered double hydroxide composite (denoted as FCB/MAC) was synthesized via two-step electro-assisted modification for the first time. Subsequently, the physical and chemical properties of FCB/MAC were characterized. Furthermore, the sorption mechanism for phosphate removal was investigated in detail. The results indicated that Fe₃O₄ and the Mg–Al layered double hydroxide were successfully embedded in the biochar matrix. Moreover, FCB/MAC exhibited a high phosphate adsorption capacity and excellent magnetic properties for easy recovery. The maximum phosphate sorption capacity of FCB/MAC was 252.88 mg g⁻¹, which is much higher than the capacities of most magnetic phosphate adsorbents. In addition, the adsorption kinetics and isotherms indicated that phosphate adsorption by FCB/MAC was controlled by the pseudo-second-order kinetic model and the Langmuir–Freundlich isotherm model. The phosphate adsorption mechanism involves anion exchange, electrostatic attraction, and ligand exchange. After five adsorption–desorption cycles, the phosphate adsorption capacity of FCB/MAC was 25.71 mg g⁻¹ with 51.43% removal efficiency and high recyclability. Thus, the composite prepared in this study is a promising adsorbent for phosphate removal from aqueous solution, and this work provides an excellent reference for constructing novel biochar-based phosphate adsorbents.

This study describes an optimized two-step electro-assisted modification process for the preparation of biochar modified with Fe₃O₄ and Mg–Al layered double hydroxide.     

Control of drug release from polymer matrices impregnated with magnetic beads —a proposed mechanism and model for enhanced release

The need to regulate drug release rates in applications such as suppression of diabetic symptoms and birth control has previously led to the development of delivery systems containing small magnetic beads uniformly imbedded within drug-laden polymer matrices. An oscillating magnetic field imposed on such systems triggers a significant increase in release rate. A mechanism for enhanced release is proposed here, which draws upon the similarity between the observed increase in mass transfer by pulsation, e.g., promotion of axial diffusion in a cylinder with pulsed (but zero net) flow and enhanced drug release by the oscillating field. A mathematical model is derived based on this analogy. Its predictions are consistent with general observations and provide correlations of release rates with the frequency and amplitude of the oscillating magnetic field and the intrinsic drug diffusivity.     

Switchable conformational changes of DNA nanogel shells containing disulfide–DNA hybrids for controlled drug release and efficient anticancer action

Oligonucleotide strands containing dithiol (–SS–) groups were used as the co-crosslinkers in PNIPA–AAc based nanogels (NGs). They hybridized with PEG–oligonucleotides introduced into the gels. The specific DNA hybrid formed in the nanogel/nanocarrier was involved in highly efficient accumulation of intercalators. The presence of –SS– groups/bridges improved the storing efficiency of doxorubicin (Dox) in DNA hybrids by 53, 40 and 20% compared to regular, single stranded and regular double stranded DNA crosslinkers, respectively. The explicit arrangement of the hybrids in the carrier enabled their reduction by glutathione and an effective cancer treatment while the side toxicity could be reduced. Compared to the NGs with traditional crosslinkers and those containing typical dsDNA-based hybrids, an improved, switchable and controlled drug release occurred in the novel NGs. Since the novel NGs can release the oligonucleotide strands during their degradation, this gives an opportunity for a combined drug-gene therapy.

Switchable conformational changes of multiresponsive nanogels containing disulfide/DNA hybrid shells for pulsative drug release.     

MIL-101(Cr)–cobalt ferrite magnetic nanocomposite: synthesis,characterization and applications for the sonocatalytic degradation of organic dye pollutants

In this study, for the first time, a novel magnetically recyclable MIL-101(Cr)/CoFe₂O₄ nanocomposite was prepared via a facile solvothermal method. The morphology, structural, magnetic and optical properties of the nanocomposite were characterized via field emission scanning electron microscopy (FE-SEM), transmission electron microscope (TEM), energy dispersive X-ray (EDX) spectroscopy, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), vibrating sample magnetometer (VSM), UV-visible spectroscopy (UV-visible) and BET surface area analysis. Furthermore, the sonocatalytic activity of the MIL-101(Cr)-based magnetic nanocomposite was explored for the degradation of organic dye pollutants such as Rhodamine B (RhB) and methyl orange (MO) under ultrasound irradiation in the presence of H₂O₂. Under optimized conditions, the degradation efficiency reached 96% for RhB and 88% for MO. The sonocatalytic activity of MIL-101(Cr)/CoFe₂O₄ was almost 12 and 4 times higher than that of the raw MIL-101(Cr) and pure CoFe₂O₄, respectively. The improved sonocatalytic performance of the as-prepared binary nanocomposite can be attributed to the relatively high specific surface area of MIL-101(Cr) and magnetic property of CoFe₂O₄, as well as the fast generation and separation of charge carriers (electrons and holes) in MIL-101(Cr) and CoFe₂O₄. In addition, the trapping tests demonstrated that ·OH radicals are the main active species in the dye degradation process. Moreover, the most influencing factors on the sonocatalytic activity such as the H₂O₂ amount, initial dye concentration and catalyst dosage were investigated. Finally, the nanocomposite was magnetically separated and reused without any observable change in its structure and performance even after four consecutive runs.

A magnetically separable MIL-101(Cr)/CoFe₂O₄ binary nanocomposite was prepared via a hydrothermal route and applied as a sonocatalyst for the efficient degradation of organic dyes.     

Iodine-catalyzed synthesis of benzoxazoles using catechols,ammonium acetate,and alkenes/alkynes/ketones via C–C and C–O bond cleavage

An efficient metal-free synthesis strategy of benzoxazoles was developed via coupling catechols, ammonium acetate, and alkenes/alkynes/ketones. The developed methodology represents an operationally simple, one-pot and large-scale procedure for the preparation of benzoxazole derivatives using molecular iodine as the catalyst.

A metal-free one-pot multi-component method for the efficient synthesis of 2-aryl benzoxazoles via coupling of catechols, ammonium acetate and alkenes/alkynes/ketones using an I₂–DMSO catalyst system is illustrated.     

A fluorescent calixarene-based dimeric capsule constructed via a MII–terpyridine interaction: cage structure,inclusion properties and drug release

Two analogues of capsule-like fluorescent cages have been constructed by dimerization of terpyridine-containing calixarene derivatives utilizing a M^II–terpyridine (M = Zn and Cd) interaction. ¹H NMR spectral studies show that the self-assembled molecular capsules Zn₄L1₂ and Cd₄L1₂ have a highly symmetrical D_4h-structure. The encapsulation of the anticancer drug mercaptopurine in their cavities has been documented by NMR, ESI-TOF-MS, fluorescence switching, and molecular simulation, indicating that strong S–π and π–π interactions between drug and cage are of importance for the host–guest binding. The nanoscale cages exhibit excellent behaviors to control the release of mercaptopurine in phosphate buffered saline solution (pH = 7.4). These results further highlight the potential of self-assembled Zn₄L1₂ cages for drug-carrier applications.

A fluorescent calixarene-based dimeric capsule has been constructed via a M^II–terpyridine interaction, and can capture mercaptopurine in solution and crystalline state and control drug release in PBS accompanied with fluorescence recovery.

Self-assembled coordination cages with well-defined geometries and cavities have attracted much attention due to their potential applications in molecular recognition, catalytic reactions, biochemistry, and medicine.¹ Concerning medicinal studies, metallocages are promising drug delivery carriers, which can interact with biomolecules, possess anticancer activity, and increase solubility in biological media.² Recent reports have demonstrated that coordination cages can act as effective hosts for medicinal guests and have interesting biological properties.³ For example, Therrien et al. reported the first coordination cage, an arene–ruthenium-based metallocage, used as drug-delivery system, which showed anticancer effects against human A2780 ovarian cancer cells upon encapsulation of Pd and Pt acetylacetonato complexes.^3a Lippard et al. developed a new strategy to use a hexanuclear supramolecular Pt^II cage as a drug delivery vehicle to deliver Pt^IV prodrugs to cancer cells.^3b Briken and Isaacs et al. described that metal–organic polyhedron capped with cucurbit[8]uril could deliver doxorubicin to cancer cells and enhance the cytotoxicity, which was ascribed to a combination of increased cellular uptake of cage and doxorubicin release.^3c Su and Jiang et al. investigated the binding behavior between drug molecule 5-fluorouracil and M₄L₄ type tetrahedral cages, and demonstrated that the porous cage nanoparticle could control release of 5-fluorouracil in simulated human body liquid of phosphate buffer solution.^3d Despite this growing interest on drug encapsulation into metallocages as drug-delivery systems, the research on the drug adsorption/release processes is still in its infancy, and further studies are necessary to explore their uses in medicinal chemistry. In addition, fluorescent coordination cages, especially for the cages that turn-on their fluorescence in response to external stimuli, are very attractive for both therapeutic and imaging applications in the medicinal chemistry field, because they allow in vitro or in vivo imaging without specific handling.⁴ Therefore, the design of self-assembled cages that ensure the fluorescence response upon the release of an active molecule is more desirable.Calixarenes are an important class of macrocyclic host molecules in supramolecular chemistry. Calixarene derivatives have been used for the recognition of various molecular species, such as sugars, amino acids, peptides, proteins, and nucleic acids,⁵ which are basic substrates in biological processes, and also used in drug delivery investigations.⁶ In terms of the calixarene cavity and cage cavity to encapsulate the guests, calixarene-based coordination cages may be employed as drug delivery systems through hydrophobic effects and/or ion-dipole or hydrogen bonding interactions.⁷ Moreover, compared with smaller sized coordination complexes studied previously (<1.5 nm), the larger sized calixarene-based supramolecular cages should exhibit slower renal clearance and longer circulation, which would be helpful for theranostic applications, because particle size influences the clearance rate of nanoparticles from the bloodstream.⁸ Only a few reports on the biological properties of calixarene-based nanoscale cages (>2.0 nm) have appeared.^7,9 Recently, Liao and Hu et al. synthesized an extra-large octahedral coordination cage based on Co₄-p-tert-butylsulfonyl calix[4]arene. The calixarene-based cage demonstrated good adsorption properties towards a small drug molecule, ibuprofen (Ibu), and the Ibu release experiment revealed that the cage exhibited a slow drug release behavior.⁹ Despite the remarkable size and well-known inclusion properties of calixarene-based cages, studies of their applications in drug delivery are rare.Therefore, in this work, in order to obtain fluorescent calixarene-based nanoscale cages, we designed two self-assembled nanocapsules Zn₄L1₂ and Cd₄L1₂ based on upper rim terkis-phenyl-terpyridine substituted calix[4]arene derivatives which showed fluorescence properties due to the coordination bond of terpyridine (tpy) and Zn²⁺/Cd²⁺ ions. In general, the connectivity of tpy–M(ii)–tpy (M = Zn, Cd, Fe, and Ru) is fixed at 180° and thus, limits the use of metal ions as cornered directing units. Therefore, a few previous studies of tpy–M(ii)–tpy only concentrated on 0-D and 3-D supramolecular cages and prisms¹⁰ compared to the numerous reports of linear and 2-D structures based on tpy.¹¹ On the other hand, to evaluate the capability of these cages as drug carriers, mercaptopurine was chosen as the drug guest. Mercaptopurine is a medication used for cancer and autoimmune diseases,¹² the interactions of which with cage have rarely been thorough studied in the field of host–guest chemistry.Herein, two highly symmetrical molecular capsules were constructed by dimerization of tpy-containing calixarene derivatives utilizing a Zn(ii)/Cd(ii)-tpy interaction for the first time. The D_4h-structures and binding property of two Zn₄L1₂ and Cd₄L1₂ cages with mercaptopurine drug were investigated by NMR spectra, ESI-TOF-MS, AFM, UV-Vis and fluorescent spectra, and DFT calculations. The releasing drug experiments were carried out, revealing that nanoscale Zn₄L1₂ and Cd₄L1₂ cages can significantly delay release of mercaptopurine into the simulated body liquids.In order to acquire capsules with nanoscale inner space, an upper rim terkis-terpyridine substituted calix[4]arene (L1) was used for constructing the capsules. Ligand 1 could be obtained according to our report.¹³The two nanocapsules Zn₄L1₂(OTf)₈ and Cd₄L1₂(OTf)₈ could be obtained as yellow precipitation by adding a THF solution of L1 to a THF solution of zinc(ii) or cadmium(ii) trifluoromethanesulfonate (OTf⁻) with ligand/metal molar ratio of 1 : 2 (Scheme 1). The counter-ions could be exchanged by adding a methanol of ammonium hexafluorophosphate (PF₆⁻) to the acetonitrile solution of Cd₄L1₂ to give Cd₄L1₂(PF₆)₈.Open in a separate windowScheme 1The synthesis of calix[4]arene based nanocapsules.All of the capsules were soluble in MeCN-d₃, and then their NMR spectra were measured and showed in Fig. 1 and S1.^† It could be seen that the signals in the ¹H NMR spectra of Cd-capsules were well resolved, while the NMR spectra of Zn-capsules exhibited broad ¹H signals. The ¹H NMR of Cd₄L1₂(PF₆)₈ (Fig. 1) showed the expected peaks of a tpy–metal complex. In the aromatic region, there were five sets of aromatic protons from tpy units, two sets from phenyl groups, and a single peak from calixarene, which were in agreement with the desired structure. The protons at 4,4′′, 5,5′′, and 6,6′′-position of tpy dramatically shifted upfield because the formation of complex led to the electron shielding effect. The ¹³C NMR of Zn₄L1₂ and Cd₄L1₂ showed only one series of clear and sharp peaks owing to the uniform and symmetrical architecture (Fig. S2^†), implying no by-products and uncomplexed tpy moieties existed. At the same time, their DOSY spectra (Fig. 2 and S3^†) confirmed only one species in the solution. The log D = −9.3 and −9.2 were observed and then diameter of 2.5 nm and 2.0 nm were determined in DOSY for Cd₄L1₂ and Zn₄L1₂, respectively, consistent with the following molecular modelling results. Cd₄L1₂(PF₆)₈ and Zn₄L1₂(OTf)₈ were further characterized by ESI-MS to determine the proposed structures, which have a molecular weight of 5366.0 Da and 5202.2 Da, respectively. It was found that a series of peaks at m/z 2538.0, 1643.7, 1196.5, 928.2, 749.3 and 621.6 with charge states from 2+ to 7+ were detected for Cd₄L1₂(PF₆)₈, which could be ascribed to the loss of a different number of counterion PF₆⁻ (Fig. 3). As shown in Fig. S4,^† the isotope pattern of each peak of Cd₄L1₂(PF₆)₈ was in good accordance with the corresponding simulated isotope distribution. Similarly, the peak series at m/z 2456.1, 1587.7, 1153.5, 893.0, 719.4 and 595.2 for [Zn₄L1₂(OTf⁻)_8−n]ⁿ⁺ (n = 2–7) verify formation of the same dimer cage (Fig. S5^†).Open in a separate windowFig. 1 ¹H NMR spectra (400 MHz, 298 K) of (a) ligand L1 (CDCl₃) and (b) Cd₄(L1)₂(PF₆)₈ MOC (CD₃CN).Open in a separate windowFig. 2 ¹H DOSY spectrum (400 MHz, CD₃CN, 298 K) of Cd₄(L1)₂(PF₆)₈ MOC.Open in a separate windowFig. 3ESI-MS spectrum of Cd₄(L1)₂(PF₆)₈ MOC.Several attempts to obtain diffraction quality single crystals of Zn₄L1₂ were unsuccessful. To incur further insight into the structural features, we obtained energy optimized structure of Zn₄L1₂ using DFT (B3LYP, LANL2DZ) calculations. As illustrated in Fig. 4a and Table S1,^† a cage in an approximate square bipyramid was constructed when the upper rims of two calix[4]arenes were close to each other and captured four Zn²⁺ ions. Six coordination bonds existed between each Zn²⁺ ion and each two terpyridine groups from two individual calix[4]arene arms. Four Zn²⁺ complex units were tightly interlocked into an approximate square through four π–π interactions between terpyridine groups of each adjacent Zn²⁺ complex unit. In fact, L1 was not favored for a dimer capsule and thus there was tension in the dimer capsules. Molecular modelling showed the structure distortion of the dimer was mostly neutralized by bending the phenyl group between calixarene and terpyridine. Therefore, the ligand bending was the major contribution to accommodate the strain. As additional evidence, the images from AFM showed the morphology of the dimer cage Zn₄L1₂ as cone-shape dots on the mica surface (Fig. S6^†). The measured height of these dots exhibited two different values: 3.9 ± 0.2 nm and 2.2 ± 0.3 nm, which were larger than cage height (3.1 nm) and length (2.0 nm) shown in molecular modelling, respectively, due to the unavoidable tip broadening effect.Open in a separate windowFig. 4The optimized structures of Zn₄L1₂ (a) and 4(mercaptopurine)@Zn₄L1₂ (b). The interactions are colored in dotted lines: coordination bond in gray, S–π interaction in green, S–H–π interaction in yellow and π–π interaction in pink. All hydrogens are omitted for clarity.The host–guest properties of the dimer capsules and mercaptopurine were evaluated in solution. After the dimer capsules were dissolved in an aqueous acetonitrile solution (MeCN/H₂O = 2/1), excessive mercaptopurine solids were added and stirred at room temperature for 2 h, and then the filtrate was separated for NMR and ESI-TOF-MS measurement. Considering the Cd-capsules had well-resolved signals and similar inclusion ability to Zn-capsules, Cd₄L1₂ were substituted for Zn₄L1₂ to study the binding interaction between the dimer capsules and mercaptopurine by ¹H NMR (Fig. S7^†) and ¹H DOSY spectra (Fig. S8^†). Mercaptopurine guests were observed to interact with cage Cd₄L1₂ and were in slow exchange between cavity and bulk solution on the NMR time scale. Two proton signals of the mercaptopurine guests experienced an upfield shift when compared with their free ¹H resonances measured in the solvent mixture of MeCN-d₃ and D₂O (2 : 1 v/v). This provided strong evidence for mercaptopurine binding within the cavities of the cages. Meanwhile, ¹H NMR peaks of cage host corresponding to 3,3′′, 4,4′′, 5,5′′ and 3′,5′-H were observed to shift upfield, whereas 6,6′′-H shifted downfield. ¹H DOSY measurements gave similar diffusion coefficients for ¹H signals of host and guest, which further supported the formation of an inclusion complex. Integration of the guest peaks indicated the cages could accommodate about four mercaptopurine guests (Fig. S8^†). These observations were consistent with what has been observed in other cases of hydrophobic guest binding in water.¹⁴ In addition, we tried to obtain further information on the stoichiometry of the host–guest interaction from ESI-MS experiments of the host–guest mixtures. As seen in Fig. S9 and S10,^† the MS signals showed a series of binding species between Cd₄L1₂/Zn₄L1₂ and mercaptopurine with a general formula of [n(mercaptopurine)@Cd₄L1₂/Zn₄L1₂] (n ≤ 7), which exhibited higher stoichiometries than that observed for ¹H NMR measurements (n ≈ 4). This suggested that the host–guest interaction of mercaptopurine and cage was strong. In addition to observing tightly bound mercaptopurine guests, the presumably weaker association of mercaptopurine with the exohedral binding sites on the exterior surface of the dimer cages could be detected because in the gas phase charged metallocages might produce ions related to extracage association of guests to the metal ions under the conditions of the mass spectral analysis. Similar mass spectra results were also observed in the reported literature.¹⁵ The control experiments of association of mercaptopurine with Zn(ii)(phenyl-tpy)₂(CF₃SO₃)₂ and 25,26,27,28-tetrabutoxycalix[4] arene have been performed. As seen from Fig. S11,^† no obvious shifts were observed in ¹H NMR spectra of the mixture, compared with that of 25,26,27,28-tetrabutoxycalix[4]arene, mercaptopurine, and Zn(ii)(phenyl-tpy)₂(CF₃SO₃)₂, respectively, supporting encapsulation of the guest molecules inside of the Zn₄L1₂ cage.From ¹H NMR spectra (Fig. S8^†), we speculated four mercaptopurine molecules could be encapsulated into the Zn₄L1₂ cage. To further clarify stoichiometry of the mercaptopurine@Zn₄L1₂ complex and explore their interaction modes, molecular simulation was executed in this drug-cage supramolecular system of mercaptopurine@Zn₄L1₂ and the results of their geometry optimization were shown in Fig. 4b and Tables S2 and S3.^† As illustrated in Fig. 4b, each pyramid unit encapsulated two mercaptopurine molecules. In one pyramid unit, one mercaptopurine orientated to cavity was captured by calix[4]arene cavity and two arms of the cage with three S–π interactions (3.93, 4.08 and 4.37 Å), one S–H–π interaction (4.37 Å) and one π–π interaction (4.55 Å). The other mercaptopurine was caught by the adjacent mercaptopurine and two arms of the cage with one S–π interactions (4.08 Å) and three π–π interactions (4.08, 4.47 and 4.76 Å). In another pyramid unit, there were similar interactions between the two encapsulated mercaptopurine molecules and the cage. There are two S–π interactions (3.95 and 4.25 Å), one S–H–π interaction (4.25 Å) and three π–π interactions (4.20, 4.55 and 4.58 Å) between the cage and the one mercaptopurine deepened into calix[4]arene cavity. And there are one S–π interactions (4.12 Å) and three π–π interactions (4.20, 4.27 and 4.52 Å) between the cage and the other mercaptopurine caught by the neighboring mercaptopurine. No coordination interaction appeared between mercaptopurine and Zn²⁺. Correspondingly, the symmetric geometrical structure of the cage was remarkably distorted in order to match the interactions with mercaptopurine. Moreover, the π–π interactions between adjacent terpyridine groups partially disappeared although the coordination interactions between terpyridine groups and Zn²⁺ still existed. Meanwhile, the stabilization energy −45.3 kcal mol⁻¹ (see Table S3^†) of 4(mercaptopurine)@Zn₄L1₂ complex also confirmed the fact that four mercaptopurines can be stably captured by the cage.It is well known that UV/Vis and fluorescent spectra are powerful methods for host–guest inclusion study. Therefore, the UV/Vis and fluorescent spectra of the Zn-capsules upon the addition of mercaptopurine were measured. In the absorption spectra, the titration of Zn₄L1₂ with mercaptopurine resulted in the decrease of the absorption intensity at 256 nm and 366 nm, respectively, and increase of the intensity at 236 nm and 328 nm with a blue-shift, respectively, while the three isosbestic points at 247 nm, 285 nm, and 350 nm appeared, indicating complex formation (Fig. 5a). Interestingly, the Zn₄L1₂ cage exhibited excellent fluorescent properties. In the fluorescent spectrum of Zn₄L1₂, the maximum excitation and emission wavelengths were observed at 340 and 600 nm, respectively. The fluorescence titration of Zn₄L1₂ with mercaptopurine showed a gradual decrease in the emission band at 600 nm with a slight blue-shift within 5 nm over mercaptopurine concentrations range of 6 × 10⁻⁴ to 7 × 10⁻² mM, which confirmed the interaction between Zn₄L1₂ and mercaptopurine further (Fig. 5b). Moreover, the interaction provided a fluorescence quenching pathway by the excitation energy transfer or charge transfer from Zn₄L1₂ to the mercaptopurine guests. It is desirable that the Zn₄L1₂ cages can make a fluorescence turn-on response upon the release of mercaptopurine.Open in a separate windowFig. 5(a) UV-Vis and (b) fluorescent titrations of Zn₄L1₂ (1.23 × 10⁻⁶ mol L⁻¹) with mercaptopurine in MeCN and H₂O (2 : 1 v/v). From a to u: 0, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, 6.0, 6.5 equiv.; from a to h: 0, 0.5, 1.0, 1.5, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, 10.0, 11.0, 15.0, 19.0, 23.0, 28.0, 38.0, 48.0, 58.0 equiv.Since Zn₄L1₂ has lower toxicity in comparison to Cd₄L1₂, Zn₄L1₂ was chosen as candidate to test its drug delivery property. It is known that drug-carrying materials with the nanometer size can achieve effective drug delivery. Nanoscale mercaptopurine@Zn₄L1₂ cages have been prepared by the method described above, and the loading amount was determined by ¹H NMR. As seen from Fig. S12,^† the loading amount of mercaptopurine encapsulated in Zn₄L1₂ cages was estimated to be 13.0 ± 0.2 wt%, corresponding to [4(mercaptopurine)@Zn₄L1₂].To simulate drug sustained-release in human body liquid, the release of mercaptopurine from the mercaptopurine@Zn₄L1₂ nanoparticles was performed in phosphate buffer solution (PBS, pH = 7.4) with dialysis bag and detected by UV/Vis spectrum. The release amount was calculated according to the calibration plots of standard curve of pure mercaptopurine in PBS. The mercaptopurine-loaded Zn₄L1₂ samples used for the release experiments weighed 10.0 mg and 0.61 mg of Ibu was released from the sample. The release process was considered in two stages within 45 hours (Fig. 6). In the first stage (8 h), 0.35 mg of Ibu was released in the first stage and in the second stage 0.26 mg in the next 37 hours. The drug release became very slow after 45 hours. These release behaviors were similar to those for the reported coordination cages.^9,16 For comparison, the pure mercaptopurine in solid state was dialyzed as a control-experiment which indicated that up to 95% of the total mercaptopurine was quickly released within 3 hours. These results suggested that the cage structures of Zn₄L1₂ protracted the release of mercaptopurine. The slow release may be due to the slow diffusion rate of mercaptopurine from the windows of the cavities owing to the strong interaction of S–π and the π–π interactions between mercaptopurine and the aromatic skeleton of Zn₄L1₂.Open in a separate windowFig. 6The release of mercaptopurine from control (red circle) and mercaptopurine@Zn₄L1₂ (black square).