Investigation of non-precious metal cathode catalysts for direct borohydride fuel cells.

Borohydride crossover in anion exchange membrane (AEM) based direct borohydride fuel cells (DBFCs) impairs their performance and induces cathode catalyst poisoning. This study evaluates three non-precious metal catalysts, namely LaMn0.5Co0.5O3 (LMCO) perovskite, MnCo2O4 (MCS) spinel, and Fe-N-C, for their application as cathode catalysts in DBFCs. The rotating disk electrode (RDE) testing shows significant borohydride tolerance of MCS. Moreover, MCS has exhibited exceptional stability in accelerated durability tests (ADTs), with a minimal reduction of 10 mV in half-wave potential. DFT calculations further reveal that these catalysts predominantly adsorb over , unlike commercial Pt/C which preferentially adsorbs . In DBFCs, MCS can deliver a peak power density of 1.5 W cm-2, and a 3% voltage loss after a 5 hours durability test. In contrast, LMCO and Fe-N-C have exhibited significantly lower peak power density and stability. The analysis of the TEM, XRD, and XPS results before and after the single-cell stability tests suggests that the diminished stability of LMCO and Fe-N-C catalysts is due to catalyst detachment from carbon supports, resulting from the nanoparticle aggregation during the high-temperature preparation process. Such findings suggest that MCS can effectively mitigate the fuel crossover challenge inherent in DBFCs, thus enhancing its viability for practical application.

High-Performance Zinc-Air Batteries Based on Bifunctional Hierarchically Porous Nitrogen-Doped Carbon.

Active and durable bifunctional electrocatalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) on the cathode are required for high-performance rechargeable metal-air batteries. Herein, the synthesis of hierarchically porous nitrogen-doped carbon (HPNC) with bifunctional oxygen electrocatalysis for Zn-air batteries is reported. The HPNC catalyst possesses a large surface area of 1459 m2 g-1 and exhibits superior electrocatalytic activity toward ORR and OER simultaneously with a low OER/ORR overpotential of 0.62 V, taking the difference between the potential at 10 mA cm-2 for OER and half-wave potential for ORR in 0.1 m KOH. Adopting HPNC as the air cathode, primary and rechargeable Zn-air batteries are fabricated. The primary batteries demonstrate a high open-circuit potential of 1.616 V, a specific capacity of 782.7 mAh gZn -1 and a superb peak power density of 201 mW cm-2 . The rechargeable batteries can be cycled stably for over 360 cycles or 120 h at the current density of 5 mA cm-2 . As elucidated by density functional theory, N-doping is preferred on defective sites with pentagon configuration and on the edge in the form of pyridinic-N-type. The high content of these two motifs in HPNC leads to the superior ORR and OER activities, respectively.

Construction of multilayer films with bactericidal and long-term antitumor drug release properties as a non-vascular stent coating for therapy in obstruction.

The construction of antibacterial and antitumor coatings could offer effective routes to improve the therapeutic effects of non-vascular stents for unresectable obstructions caused by malignant tumours. Herein, polyelectrolyte multilayers have been explored as bactericidal coatings with controlled antitumor drug release. To solve the challenges of loading and controlled release of small-molecule chemotherapeutic drugs in polyelectrolyte multilayers, the antitumor drug doxorubicin (DOX) was chemically conjugated onto polyethylenimine via cis aconitic anhydride (pH-sensitive linker), thus obtaining the polycation prodrug PEI-CA-DOX. Alginate sodium was oxidized (O-Alg) and mixed with DOX to prepare the O-Alg-DOX complex as a polyanion. QCM-D and contact angle tests were used to monitor and verify the progressive build-up of the PEI-CA-DOX/O-Alg-DOX multilayer films, which show a linear growth. The in vitro antibacterial tests indicated that the PEI-CA-DOX-terminated PEI-CA-DOX/O-Alg-DOX multilayers could kill the bacteria effectively. As-such multilayers also presented a long-term sustained DOX release behaviour in PBS due to the combination of slow release in PEI-CA-DOX and fast release in the O-Alg-DOX complex. The as-designed PEI-CA-DOX/O-Alg-DOX multilayers with combined antibacterial and antitumor properties may have great potential for applications in non-vascular stent coatings for palliative treatment of obstruction caused by malignant tumours.

Diameter of Carbon Nanotube-Directed Self-Assembly of Amphiphilic Block Copolymers.

The cooperative self-assembly of nanoparticles and amphiphilic block copolymers has attracted increasing interests as it offers effective routes to achieve nanocomposite supramolecular structures with desired structure and properties. The incorporation of nanoparticles usually tunes the self-assembly structure of block copolymers, as the copolymer-nanoparticle interactions may change the relative volume ratio of hydrophobic block/hydrophilic block copolymers. It should be noted that the micro-size length and the strong nonpolar feature of carbon nanotubes (CNTs) may cause the block copolymer-CNT interactions to differ from the the block copolymer-nanoparticle interactions. Herein, we show that the diameter of CNTs and the copolymer/CNT ratio have a profound effect on the self-assembly behavior of amphiphilic block copolymers. Upon the addition of carboxylated multi-walled carbon nanotubes (c-MWCNTs, diameter <8 nm,) to the methoxy polyethylene glycol-poly (D,L-lactic acid) (MPEG-PDLLA) solution, it is difficult to observe the c-MWCNTs directly in TEM images. However, it has been found that they form supramolecular nanocomposite structures with MPEG-PDLLA. Moreover, these supramolecular structures transform from core-shell spherical micelles into rod-like micelles and then into large composite aggregates with the increase of the c-MWCNT addition. However, in the case of the addition of c-MWCNTs with a diameter of 30-50 nm, the dispersed c-MWCNTs and spherical core-shell micelles could be observed simultaneously in the TEM images at a low c-MWCNT addition, and then the micelle structure disappeared and only well-dispersed c-MWNTs were observed in TEM images at a high c-MWCNT addition. A possible model was proposed to explain the rule of CNTs participating in the formation of copolymer/CNT nanocomposite structures. It was also shown that as-prepared copolymer/CNT supramolecular nanocomposites could be used as drug carriers, enabling the adjustment of the drug loading and release time.

Preparation and Investigation of Amphiphilic Block Copolymers/Fullerene Nanocomposites as Nanocarriers for Hydrophobic Drug.

Biopolymer/inorganic material nanocomposites have attracted increasing interest as nanocarriers for delivering drugs owing to the combined advantages of both biopolymer and inorganic materials. Here, amphiphilic block copolymer/fullerene nanocomposites were prepared as nanocarriers for hydrophobic drug by incorporation of C60 in the core of methoxy polyethylene glycol-poly(d,l-lactic acid) (MPEG-PDLLA) micelles. The structure and morphology of MPEG-PDLLA/C60 nanocomposites were characterized using transmission electron microscopy, dynamic light scattering, high-resolution transmission electron microscopy, and thermal gravimetric analysis. It was found that the moderate amount of spherical C60 incorporated in the MPEG-PDLLA micelles may cause an increase in the molecular chain space of PDLLA segments in the vicinity of C60 and, thus, produce a larger cargo space to increase drug entrapment and accelerate the drug release from nanocomposites. Furthermore, sufficient additions of C60 perhaps resulted in an aggregation of C60 within the micelles that decreased the drug entrapment and produced a steric hindrance for DOX released from the nanocomposites. The results obtained provide fundamental insights into the understanding of the role of C60 in adjusting the drug loading and release of amphiphilic copolymer micelles and further demonstrate the future potential of the MPEG-PDLLA/C60 nanocomposites used as nanocarriers for controlled drug-delivery applications.

Atomic-Scale Insight into Tautomeric Recognition, Separation, and Interconversion of Guanine Molecular Networks on Au(111).

Although tautomerization may directly affect the chemical or biological properties of molecules, real-space investigation on the tautomeric behaviors of organic molecules in a larger area of molecular networks has been scarcely reported. In this paper, we choose guanine (G) molecule as a model system. From the interplay of high-resolution scanning tunneling microscopy (STM) imaging and density functional theory (DFT) calculations, we have successfully achieved the tautomeric recognition, separation, and interconversion of G molecular networks (formed by two tautomeric forms G/9H and G/7H) with the aid of NaCl on the Au(111) surface in ultrahigh vacuum (UHV) conditions. Our results may serve as a prototypical system to provide important insights into tautomerization related issues, which should be intriguing to biochemistry, pharmaceutics, and other related fields.

Controllable Scission and Seamless Stitching of Metal-Organic Clusters by STM Manipulation.

Scanning tunneling microscopy (STM) manipulation techniques have proven to be a powerful method for advanced nanofabrication of artificial molecular architectures on surfaces. With increasing complexity of the studied systems, STM manipulations are then extended to more complicated structural motifs. Previously, the dissociation and construction of various motifs have been achieved, but only in a single direction. In this report, the controllable scission and seamless stitching of metal-organic clusters have been successfully achieved through STM manipulations. The system presented here includes two sorts of hierarchical interactions where coordination bonds hold the metal-organic elementary motifs while hydrogen bonds among elementary motifs are directly involved in bond breakage and re-formation. The key to making this reversible switching successful is the hydrogen bonding, which is comparatively facile to be broken for controllable scission, and, on the other hand, the directional characteristic of hydrogen bonding makes precise stitching feasible.

Solventless Formation of G-Quartet Complexes Based on Alkali and Alkaline Earth Salts on Au(111).

Template cations have been extensively employed in the formation, stabilization and regulation of structural polymorphism of G-quadruplex structures in vitro. However, the direct addition of salts onto solid surfaces, especially under ultra-high-vacuum (UHV) conditions, to explore the feasibility and universality of the formation of G-quartet complexes in a solventless environment has not been reported. By combining UHV-STM imaging and DFT calculations, we have shown that three different G-quartet-M (M: Na/K/Ca) complexes can be obtained on Au(111) using alkali and alkaline earth salts as reactants. We have also identified the driving forces (intra-quartet hydrogen bonding and electrostatic ionic bonding) for the formation of these complexes and quantified the interactions involved. Our results demonstrate a novel route to fabricate G-quartet-related complexes on solid surfaces, providing an alternative feasible way to bring metal elements to surfaces for constructing metal-organic systems.

Dehydrogenative homocoupling of terminal alkenes on copper surfaces: a route to dienes.

Homocouplings of hydrocarbon groups including alkynyl (sp(1) ), alkyl (sp(3) ), and aryl (sp(2) ) have recently been investigated on surfaces with the interest of fabricating novel carbon nanostructures/nanomaterials and getting fundamental understanding. Investigated herein is the on-surface homocoupling of an alkenyl group which is the last elementary unit of hydrocarbons. Through real-space direct visualization (scanning tunneling microscopy imaging) and density functional theory calculations, the two terminal alkenyl groups were found to couple into a diene moiety on copper surfaces, and is contrary to the common dimerization products of alkenes in solution. Furthermore, detailed DFT-based transition-state searches were performed to unravel this new reaction pathway.

On-surface formation of two-dimensional polymer via direct C-H activation of metal phthalocyanine.

From high-resolution UHV-STM imaging and DFT calculations we successfully obtained a 2D polymer structure formed through direct C-H activation followed by an aryl-aryl coupling of a metal-phthalocyanine (CoPc) on Ag(110).

Formation of polyphenyl chains through hierarchical reactions: Ullmann coupling followed by cross-dehydrogenative coupling.

From an interplay of UHV-STM imaging and DFT calculations, we have illustrated on-surface formation of polyphenyl chains through a hierarchical reaction pathway involving two different kinds of reactions (Ullmann coupling and cross-dehydrogenative coupling), which will provide a deeper understanding of on-surface chemical reactions and an alternative and efficient strategy to fabricate desired surface molecular nanostructures.

On-surface synthesis of organometallic complex via metal-alkene interactions.

From the interplay of high-resolution scanning tunneling microscopy (STM) imaging/manipulation and density functional theory (DFT) calculations, we have shown that the spontaneous formation of an organometallic complex by copper-alkene interactions can be successfully achieved, where the specific molecular adsorption geometry is revealed to be the key for facilitating such interaction.

Formation of a G-quartet-Fe complex and modulation of electronic and magnetic properties of the Fe center.

Although the G-quartet structure has been extensively investigated due to its biological importance, the formation mechanism, in particular, the necessity of metal centers, of an isolated G-quartet on solid surfaces remains ambiguous. Here, by using scanning tunneling microscopy under well-controlled ultra-high-vacuum conditions and density functional theory calculations we have been able to clarify that besides the intraquartet hydrogen bonding a metal center is mandatory for the formation of an isolated G-quartet. Furthermore, by subtly perturbing the local coordination bonding schemes within the formed G-quartet complex via local nanoscale scanning tunneling microscopy manipulations, we succeed in modulating the d orbitals and the accompanying magnetic properties of the metal center. Our results demonstrate the feasibility of forming an isolated G-quartet complex on a solid surface and that the strategy of modulating electronic and magnetic properties of the metal center can be extended to other related systems such as molecular spintronics.

On-surface aryl-aryl coupling via selective C-H activation.

Through the interplay of high-resolution scanning tunneling microscopy (STM) imaging/manipulation and density functional theory (DFT) calculations, we have demonstrated that an unprecedented selective aryl-aryl coupling via direct C-H bond activation can be successfully achieved on Cu(110). These findings present a simple and generalized route for preparing low dimensional carbon nanomaterials.

Oxygen-induced self-assembly of quaterphenyl molecules on metal surfaces.

From high-resolution UHV-STM imaging and DFT calculations we have demonstrated a novel method to construct well-ordered molecular nanostructures of an unfunctionalized aromatic molecule (4Ph) on both Ag(110) and Cu(110) by introducing oxygen molecules.

Adsorption-geometry induced transformation of self-assembled nanostructures of an aldehyde molecule on Cu(110).

From an interplay of high-resolution STM imaging/manipulation and DFT calculations, we have revealed that different self-assembled nanostructures of BA molecules on Cu(110) are attributable to specific molecular adsorption geometries, and thus the corresponding intermolecular hydrogen bonding patterns. The STM manipulations demonstrate the feasibility of switching such weak-hydrogen-bonding patterns.

Ni-induced supramolecular structural transformation of cytosine on Au(111): from one-dimensional chains to zero-dimensional clusters.

Interplay between high-resolution STM imaging and DFT calculations demonstrates that through introduction of Ni atoms the self-assembled structures of cytosine could undergo a structural transformation from 1-D chains to 0-D clusters on Au(111). Interestingly, the 0-D clusters formed are separately distributed on the surface.

Atomic-scale investigation on the facilitation and inhibition of guanine tautomerization at Au(111) surface.

Nucleobase tautomerization might induce mismatch of base pairing. Metals, involved in many important biophysical processes, have been theoretically proven to be capable of affecting tautomeric equilibria and stabilities of different nucleobase tautomers. However, direct real-space evidence on demonstrating different nucleobase tautomers and further revealing the effect of metals on their tautomerization at surfaces has not been reported to date. From the interplay of high-resolution STM imaging and DFT calculations, we show for the first time that tautomerization of guanine from G/9H to G/7H is facilitated on Au(111) by heating, whereas such tautomerization process is effectively inhibited by introducing Ni atoms due to its preferential coordination at the N7 site of G/9H. These findings may help to elucidate possible influence of metals on nucleobase tautomerization and provide from a molecular level some theoretical basis on metal-based drug design.

Investigation of thermo-sensitive amphiphilic micelles as drug carriers for chemotherapy in cholangiocarcinoma in vitro and in vivo.

Cholangiocarcinoma is an epithelial cancer of the bile ducts with poor prognosis and, in recent years, a rapidly increasing incidence. In this study, nano-sized thermo-sensitive micelles were investigated as drug carriers to improve chemotherapy in cholangiocarcinoma. Thermo-sensitive amphiphilic block copolymer, P-(N,N-isopropylacrylamide-co-N-hydroxymethylacrylamide)-b-caprolactone [P-(NIPAAm-co-NHMAAm)-b-PCL] with lower critical solution temperature (LCST) at about 38°C was synthesized. Doxorubicin (DOX)-loaded micelles were prepared by dialysis method. The micelles exhibited a sustained and temperature-dependent DOX release. Toxicity of the blank micelles for human cholangiocarcinoma (QBC939) cells was minimal both in vitro and in vivo. In contrast, the DOX-loaded micelles effectively inhibited proliferation and induced apoptosis of QBC939 cells in vitro (p<0.05) and inhibited tumor growth in nude mice by 21.49%. These results indicated that thermo-sensitive amphiphilic micelles are a promising and effective drug carrier, and show potential for improving chemotherapy for cholangiocarcinoma.

Surface-assisted cis-trans isomerization of an alkene molecule on Cu(110).

From the interplay of STM imaging and DFT calculations we have investigated the isomerization of an alkene molecule on Cu(110) under ultrahigh vacuum conditions. We show that the on-surface cis-trans isomerization could efficiently occur well below room temperature, in which the copper surface is speculated to play a key role.