Wantai Yang

Metal–Organic Frameworks with Incorporated Carbon Nanotubes: Improving Carbon Dioxide and Methane Storage Capacities by Lithium Doping

Reduction of the anthropogenic emission of CO2 is currently a top priority because CO2 emission is closely associated with climate change. Carbon capture and storage (CCS) and the development of renewable and clean energy sources are two approaches for the reduction of CO2 emission. One of the most promising alternative fuels is CH4, which is the major component of natural gas. The efficient storage of CH4 is still one of the main challenges for its widespread application. Accordingly, the development of more efficient approaches for CO2 capture and CH4 storage is critically important. Recently, metal–organic frameworks (MOFs, e.g., MOF210 and NU-100) have shown great potential for gas storage because of their high specific surface area (SSA) and functionalized pore walls. However, most MOF materials still show relatively low CO2 and CH4 uptakes. To enhance CO2 and CH4 adsorption, it is imperative to develop new materials, such as covalent organic frameworks (COFs), or to modify MOFs by using postsynthetic approaches. Herein, we focus on the latter strategy. One of the modification approaches is incorporation of carbon nanotubes (CNTs) into MOFs in order to achieve enhanced composite performance, because of the unusual mechanical and hydrophobicity properties of CNTs. Another approach is doping MOFs or COFs with electropositive metals. Recent studies indicate that the surface carboxylate functional groups of a substrate could act as nucleation sites to form MOFs by heterogeneous nucleation and crystal growth. Both experimental and theoretical investigations indicate that the H2 adsorption capacities of MOFs can be enhanced significantly by doping alkali-metal ions, in particular Li ions, to the frameworks, owing to the strong affinity of Li ions towards H2 molecules. [3d, 7] Similarly, Lan et al. also showed theoretically that doping of COFs with Li ions can significantly enhance the CH4 uptake of COFs. [8] Most recently, the multiscale simulations performed by Lan et al. indicate that Li is the best surface modifier of COFs for CO2 capture among a series of metals (Li, Na, K, Be, Mg Ca, Sc and Ti). Furthermore, their simulations show that the excess CO2 uptakes of the lithium-doped COFs can be enhanced by four to eight times compared to the undoped COFs at 298 K and 1 bar. Motivated by these experimental and theoretical results, we synthesized hybrid MOF materials by using the two modification techniques outlined above, that is, 1) incorporation of CNTs into [Cu3(C9H3O6)2(H2O)3]·x H2O ([Cu3(btc)2], HKUST-1; btc = 1,3,5-benzenetricarboxylate), which is an important MOF material owing to its open metal sides and high thermal stabilities, as well as its sorption properties, 10] and 2) doping [Cu3(btc)2] with Li + ions. We used lithium naphthalenide (LiC10H8 ) to introduce Li ions into the [Cu3(btc)2] frameworks. These frameworks have Cu 2+

Helix‐Sense‐Selective Polymerization of Achiral Substituted Acetylenes in Chiral Micelles

Helix-sense-selective polymerizations have been developed to control the screw sense of helices, by which optically active helical polymers can be formed from achiral monomers. The current methodologies for helix-sense-selective polymerizations can be grouped into three categories: 1) by using chiral initiators or chiral catalysts (cocatalysts), well exemplified by the leading studies from the groups of Okamoto, Nakano, Masuda, Novak, Chen, and Aoki; 2) by using a chiral structure-directing agent, as demonstrated by the excellent work from Meijer and co-workers; and 3) by using external asymmetric field effects creatively developed by the Akagi and Shirakawa groups. Chiral micelles 12] have been widely applied for chiral recognition, chiral separation, and enantioselective synthesis. The latter is of particular significance and promise, as chiral micelles provide an alternative for effectively controlling chiral stereostructures, and thus they can be expected to provide asymmetric environments for performing helix-sense-selective polymerizations. To confirm this hypothesis, we prepared optically active nanoparticles consisting of substituted helical polyacetylenes by asymmetric polymerization of achiral monomers in chiral micelles, whereas nonasymmetric polymerizations occurred in achiral micelles and provided nanoparticles without optical activity. Unfortunately, in the asymmetric polymerizations, even though the helical polymers forming the nanoparticles adopted one predominant handedness, they lost optical activity in solution. In the present study, a novel strategy was created by which helicalsense-selective polymerizations were achieved in chiral micelles; moreover, the as-prepared helical polymers kept their preferential helicity even in solution. The strategy for helix-sense-selective polymerizations in chiral micelles is outlined schematically in Scheme 1. A chiral emulsifier, dodecylphenylalanine (dor l-DPA), was synthesized from phenylalanine and dodecanoyl chloride. 22] DPA

Biocleavable comb-shaped gene carriers from dextran backbones with bioreducible ATRP initiation sites.

It is of crucial importance to design reduction-sensitive polysaccharide-based copolymers for intracellular triggered gene and drug delivery. In this work, a simple two-step method involving the reaction of hydroxyl groups of dextran with cystamine was first developed to introduce reduction-sensitive disulfide linked initiation sites of atom transfer radical polymerization (ATRP) onto dextran. Well-defined biocleavable comb-shaped vectors consisting of nonionic dextran backbones and disulfide-linked cationic P(DMAEMA) side chains were subsequently prepared via ATRP for highly efficient gene delivery. The P(DMAEMA) side chains can be readily cleavable from the dextran backbones under reducible conditions. Moreover, the bioreducible P(DMAEMA) side chains can be functionalized by poly(poly(ethylene glycol)ethyl ether methacrylate) (P(PEGEEMA)) end blocks to reduce the cytotoxicity and further enhance the gene transfection efficiency. This present study demonstrated that properly grafting short bioreducible polycation side chains from a nonionic polysaccharide backbone with biocleavable ATRP initiation sites is an effective means to produce a class of polysaccharide-based gene delivery vectors.

In vivo treatment of tumors using host-guest conjugated nanoparticles functionalized with doxorubicin and therapeutic gene pTRAIL

The combination of gene therapy and chemotherapy may increase the therapeutic efficacy in the treatment of patients. In this work, the anti-cancer drug Dox and therapeutic gene pTRAIL-loaded host-guest co-delivery system was assayed for the possibility of in vivo synergistically treating tumors. The introduced Dox could act as an auxiliary component to human tumor necrosis factor-related apoptosis-inducing ligand-encoding plasmid gene pTRAIL. Such delivery system possessed the good ability of in vivo retention of chemotherapeutic drugs, achieved good therapeutic effects in the inhibition of tumor growth and significantly prolonged the survival time of tumor-bearing mice. With the efficient ability to co-deliver drug and gene, such host-guest assembly should have great potential applications in cancer therapy.

Surface Chemoselective Phototransformation of C–H Bonds on Organic Polymeric Materials and Related High-Tech Applications

hydrogen atoms from the polymer surface and the phenolic hydroxyl groups of HQ. As a result, HQ is grafted on the polymer surface without any obvious side reactions. By using a HQ derivative with a para-substituent R group, a strategy has been further developed to incorporate a broad range of functional R groups onto the polymeric surface. Eventually, a series of R groups, including SO3H, NH2, SH, and COOH were grafted onto the polymer surface with an R spacer. Improved hydrophilicity and self-assembly of gold nanoparticles are achieved on modified surfaces on which different functional groups have been grafted. 3.4.3. Aryl Ketones. Aryl ketones contain a benzene ring connected to a carbonyl group. Aromatic ketones have been the subject of numerous photochemical studies. Some typical compounds that have been used for C−H phototransformation on surfaces or interfaces are listed in Table 4. The presence of a carbonyl group induces Norrish II type photochemical reactions under UV irradiation. As a result, the n,π* triplet state is formed by ISC of the singlet state, and this has been recognized as a highly active biradical intermediate with a lifetime on the order of 10−7 to 10−8 s. It should be noted that Figure 27. The proposed reaction routes for phototransformation of C−H bonds by acetone and the subsequent use of the product as a polymersupported inhibitor. Reprinted with permission from ref 160a. Copyright 2004 WILEY-VCH Verlag GmbH & Co. KGaA. Table 4. The Aryl Ketones Used in the Phototransformation of C−H Bonds on Surfaces or Interfaces Chemical Reviews Review dx.doi.org/10.1021/cr300246p | Chem. Rev. 2013, 113, 5547−5594 5563 such a lifetime value of the photoexcited state can be affected markedly by some solution parameters such as concentration, the type of media, pH, and other secondary interactions in solution. This intermediate can behave like alkoxy radicals and abstract hydrogen from C−H bonds. Aryl ketones are first used in biomimetic chemistry in the 1970s, including the first quantitative inactivation of chymotrypsin. The benzene ring in aryl ketones can be conveniently functionalized to attach a variety of functional groups or molecular linkers through specific reactions such as Friedel−Crafts acylation or alkylation. 3.4.3.1. Acetophenone. Although acetophenone (AcP) has an unpleasant odor and more volatility than the benzophenone, it possesses similar photochemical reactivity to benzophenone in solution. AcP has a weak n−π* transition at 315−320 nm and a π−π* transition at 280 nm. This molecule has a molar absorption coefficient of 1.5 × 10 mol−1 cm−1 at 254 nm, the wavelength of a commonly used UV source. Successful applications of AcP as a PAL reagent have been achieved under UV irradiation at 320 nm. By UV irradiation, AcP is activated to its excited singlet state, followed by ISC to its triplet state, which can subsequently abstract hydrogen atoms from C−H or N−H bonds from organic substances and functional molecules. Finally, the resulting surface radicals couple with surrounding functional molecular radicals to complete the grafting (Figure 28A). With this method, biologically active molecules including 2-aminopyridine (AP), N′-(2-pyridylaminomethyl)-1,2,4-triazole (TA),and benzocaine (BC) have been implanted on HDPE surfaces to enhance the surface hydrophilicity. The modified HDPE surface grafted with TA has a substantially decreased water contact angle below 20°. Besides the normal reaction routes observed in the case of grafting AP and TA, it is found that in the case of grafting BC, the reaction mechanism is based on the energy transfer from the triplet state of AcP to BC due to the photosensitivity of the carbonyl group contained in BC molecules (Figure 28B). Such energy transfer first converts the ground state of BC to a triplet state, which can further react with C−H bonds from the HDPE surface to form surface macroradicals and is itself converted to the corresponding radical intermediate. Photo-cross-linking has also been achieved on LDPE films by using molecules containing one or two AcP groups and their precursors. 3.4.3.2. Isopropyl Thioxanthone. Isopropyl thioxanthone (ITX) is a xanthone (XT) derivative where an oxygen atom in the ether bridge is replaced by sulfur atom and the aromatic ring is functionalized with an isopropyl group (Chart 1). XT has a structure quite similar to benzophenone and a typical triplet energy almost identical to that of AcP. Nonetheless, XT does show some interesting differences from other aromatic ketones. For example, it has been found that the nature of the lowest lying triplet state has a strong dependence on the temperature and polarity of the media; the reaction rate with hydrogen donor in solution and self-quenching rate are markedly correlated to the hydrogen-bonding properties of the solvent, showing an extremely enhanced reaction rate for hydrogen abstraction in nonpolar solvents. From the viewpoint of molecular structure and thermodynamics, the high self-quenching and hydrogen abstraction rates in nonpolar media are due to the reactivity at the ether bridge of XT and a combination of increased electrophilic character of the triplet state as well as a more favorable enthalpy change. In the report on the use of ITX for surface C−H bond transformation, activated ITX is first formed under UV irradiation (e.g., 254 nm), which then can abstract hydrogen from C−H bonds on polymer surfaces after ISC from a singlet to a triplet state. If exogenous reagents are not added, the resulting surface radical can couple with ITX-semipinacol Figure 28. The reaction mechanism for AcP-mediated phototransformation of C−H bonds on surfaces: (A) hydrogen abstraction by the AcP triplet state; (B) hydrogen abstraction through energy transfer from the AcP triplet state to other molecules. Chart 1. The Molecular Structure of XT and ITX Chemical Reviews Review dx.doi.org/10.1021/cr300246p | Chem. Rev. 2013, 113, 5547−5594 5564 (ITXSP) to obtain a functionalized surface grafted with ITXSP. The grafted ITXSP structure has a large stereohindrance and has a maximum absorption in the range from 380 to 420 nm (in the visible region), and it thus can further undergo a novel visible light-induced living surface grafting polymerization through reactivation under visible light (Figure 29). With glycidyl methacrylate (GMA) and LDPE films as models, this green living chemical process has been demonstrated to show a linear dependence on monomer concentration in both the surface grafting chain length and the grafting polymerization rate. It is therefore possible to accurately control the thickness of the grafted layer by simply altering the irradiation time and using environmentally friendly, energy-saving green chemistry. This visible light-induced living surface grafting polymerization can be used for biosensitive material systems where UV light cannot be used because of its strong denaturing action on biospecies. 3.4.3.3. Benzophenone. Because of its high chemical stability, commercial availability, and photochemical properties, benzophenone (BP) has been widely used in photopolymerization and PAL where H-abstraction from C−H bonds is utilized to produce active radical species for further radical polymerization of monomers or radical coupling-based molecular conjugation. BP has an n−π* transition near 330− 360 nm that is well-separated from the π−π* transition, and the resultant triplet state formed from the singlet state is responsible for hydrogen abstraction from C−H bonds. The excitation occurs with long wavelength UV (typically 365 nm), which is favorable for biomolecule immobilization because of low UV damage to biological substances with long wavelength UV. Except having a shorter triplet lifetime in organized media (e.g., 10−100 ns in cyclodextrin complexes), BP (and also ITX mentioned in section 3.4.3.2) normally can afford a long lifetime (7.7 × 10−3 s for BP and 8.0 × 10−3 s for ITX). The chemoselective modification of C−H bonds mediated by BP can be divided into three main routes. The first one involves attaching a functional R group onto the benzene ring of BP and then introducing R onto the polymer surface by the coupling of BP onto the surface (I); the second route involves using free BP to form surface radicals that can subsequently react with the surrounding reactive groups to give functionalization (II); the final one entails attaching the benzene ring of BP onto surfaces and then using this immobilized BP to attack molecules carrying the functional R groups (III) (Figure 30). Here, R can be a variety of structures ranging from small functional groups to amino acids, lipids, peptides, or macromolecules. The polymer radicals generated by BP photochemistry also probably undergo photodegradation through radical-initiated chain scission, and such photodegradation can result in advanced applications in for instance the field of liquid crystal alignement. 3.4.3.3.1. Small Molecular Groups. BP itself can be used to convert C−H to C−BP by a radical coupling process, and the resulting BP-terminated surface has been used to develop photolamination, photo-cross-linking, and hyperbranched polymer synthesis, as well as living photoinitiated or thermally initiated radical surface graft polymerization. For example, when BP is conjugated onto a surface by route I, the resulting Figure 29. A mechanism and schematic illustration of the reaction process introducing ITX as “dormant” groups onto a LDPE film by ITX-mediated phototransformation of C−H bonds. The grafted ITX further undergoes reversible photosensitive dissociation to initiate free radical polymerization of GMA by visible light irradiation.. Figure 30. Three typical reaction routes to convert C−H to C−R bonds by BP-mediated photochemical transformation. Chemical Reviews Review dx.doi.org/10.1021/cr300246p | Chem. Rev. 2013, 113, 5547−5594 5565 grafted BP can develop a reversible dissociation/recombination equilib

Supramolecular pseudo-block gene carriers based on bioreducible star polycations

A series of supramolecular pseudo-block polycations (CD-SS-pDM/Ad-pPEGs) were realized by assembling bioreducible β-cyclodextrin-cored star poly (2-dimethyl amino)ethyl methacrylate with different molecular weight and an adamantine-ended linear poly(poly(ethylene glycol)ethyl ether methacrylate) (pPEGEEMA) via the host-guest interaction. The pseudo-block CD-SS-pDM/Ad-pPEG carriers were investigated in terms of DNA binding capability, cytotoxicity, gene transfection in HepG2 and COS7 cell lines, and in vivo anti-tumor activity. The pseudo-block carriers exhibited undiminished pDNA-condensing abilities compared with the starting star carriers. Meanwhile, the pseudo-block carriers displayed lower cytotoxicity and higher gene transfection efficiencies at various N/P ratios. These results are consistent with the favorable properties of pPEGEEMA as expected. Furthermore, cellular internalization results and in vivo anti-tumor activity analysis demonstrated that assembled pPEGEEMA could enhance the stability of pseudo-block carriers, thus improving their cellular internalization and gene transfection efficiency. The present study demonstrated that supramolecular pseudo-block polycations via the host-guest interaction is an effective means to produce new gene carriers.

Well-Defined Poly(2-hydroxyl-3-(2-hydroxyethylamino)propyl methacrylate) Vectors with Low Toxicity and High Gene Transfection Efficiency

Successful gene delivery vectors for clinical translation should have high transfection efficiency and minimal toxicity. In this work, well-defined poly(2-hydroxyl-3-(2-hydroxyethylamino)propyl methacrylate) (PGEA) vectors with flanking cationic secondary amine and nonionic hydroxyl units were prepared via the ring-opening reaction of the pendant epoxide groups of poly(glycidyl methacrylate) with the amine moieties of ethanolamine. It was found that PGEA carriers possess very low toxicity (<10% of the toxicity of branched polyethylenimine (PEI, 25 kDa), while exhibiting surprisingly excellent transfection efficiency (higher than or comparable to that of PEI (25 kDa)) in different cell lines. A series of transfection and cytotoxicity assays revealed that PGEAs are highly promising as a new class of safe and efficient gene delivery vectors for future clinical gene therapies.

High performance nitrogen-doped porous graphene/carbon frameworks for supercapacitors

Nitrogen-doped porous graphene/carbon (NPGC) framework electrode materials have been synthesized via chemical activation of graphene oxide/polypyrrole (GOP) composites with KOH. The effects of the mass ratio of KOH/GOP and activation temperature on the electrochemical performance of NPGC have been discussed. It is found that the NPGC prepared by activating GOP (GO : Py = 1 : 40) with 3.5 times mass of KOH at 650 °C (NPGC650) exhibits the highest specific capacitance of 405 F g−1 at a current density of 0.2 A g−1. Particularly, the specific capacitance still remains at 249 F g−1 even at a current density as high as 10 A g−1. Moreover, 96% of the capacitance can be retained after 1000 cycles even under a high operation current of 10 A g−1. The present work provides a novel strategy to synthesize NGPC electrode material for supercapacitors.

Auto-initiating performance of styrene on surface photografting polymerization

Investigating the surface photografting polymerization of styrene (St), it was found that in the absence of photoinitiator and at high temperatures, a remarkable amount the St-grafted polymer is formed. The initiation performance of St was further confirmed by surface photografting polymerization of acrylic acid, where St was used as the photoinitiator. This finding is useful to investigate the reaction mechanism of aromatic compounds under UV radiation and develop photoinitiator-free polymerization systems.

New Star-Shaped Carriers Composed of β-Cyclodextrin Cores and Disulfide-Linked Poly(glycidyl methacrylate) Derivative Arms with Plentiful Flanking Secondary Amine and Hydroxyl Groups for Highly Efficient Gene Delivery

The biocleavable star-shaped vectors (CD-SS-PGEAs) consisting of nonionic β-cyclodextrin (β-CD) cores and disulfide-linked low-molecular-weight poly(glycidyl methacrylate) (PGMA) derivative arms with plentiful flanking secondary amine and hydroxyl groups were successfully proposed for highly efficient gene delivery. A simple two-step method was first adopted to introduce reduction-sensitive disulfide-linked initiation sites of atom transfer radical polymerization (ATRP) onto β-CD cores. The disulfide-linked PGMA arms prepared subsequently via ATRP were functionalized via the ring-opening reaction with ethanolamine (EA) to produce the cationic EA-functionalized PGMA (PGEA) arms with plentiful secondary amine and nonionic hydroxyl units. The cationic PGEA arms can be readily cleavable from the β-CD cores under reducible conditions. Such biocleavable star-shaped CD-SS-PGEA vectors possessed the good pDNA condensation ability, low cytotoxicity, and efficient gene delivery ability.