Nanoimprint Lithography-Directed Self-Assembly of Bimetallic Iron-M (M=Palladium, Platinum) Complexes for Magnetic Patterning

Self-assembly of d⁸ metal polypyridine systems is a well-established approach for the creation of 1D organometallic assemblies but there are still challenges for the large-scale construction of nanostructured patterns from these building blocks. We describe herein the use of high-throughput nanoimprint lithography (NIL) to direct the self-assembly of the bimetallic complexes [4'-ferrocenyl-(2,2':6',2''-terpyridine)M(OAc)]⁺ (OAc)^- (M=Pd or Pt; OAc=acetate). Uniform nanorods are fabricated from the molecular self-organization and evidenced by morphological characterization. More importantly, when top-down NIL is coupled with the bottom-up self-assembly of the organometallic building blocks, regular arrays of nanorods can be accessed and the patterns can be controlled by changing the lithographic stamp, where the mold imposes a confinement effect on the nanorod growth. In addition, patterns consisting of the products formed after pyrolysis are studied. The resulting arrays of ferromagnetic FeM alloy nanorods suggest promising potential for the scalable production of ordered magnetic arrays and fabrication of magnetic bit-patterned media.

DNase I-Responsive Calixpyridinium-Mediated DNA Aggregation

In this work, cationic macrocyclic calixpyridinium was employed as a new strategy to condense DNA. Moreover, the degradation of DNA by DNase I could lead to the calixpyridinium-DNA supramolecular aggregates being dissipated. Therefore, the present system is potentially applicable as the targeted drug delivery model at DNase I-overexpressed sites.

Aggregation and Tunable Color Emission Behaviors of l-Glutamine-Derived Platinum(II) Bipyridine Complexes by Hydrogen-Bonding, π-π Stacking and Metal-Metal Interactions

An l-glutamine-derived functional group was introduced to the bis(arylalkynyl)platinum(II) bipyridine complexes 1-4. The emission could be switched between the ³ MLCT excited state and the triplet excimeric state through solvent or temperature changes, which is attributed to the formation and disruption of hydrogen-bonding, π-π stacking, and metal-metal interactions. Different architectures with various morphologies, such as honeycomb nanostructures and nanospheres, were formed upon solvent variations, and these changes were accompanied by ¹ H NMR and distinct emission changes. Additionally, yellow and red emissive metallogels were formed at room temperature due to the different aggregation behaviors introduced by the substituent groups on bipyridine. The thermoresponsive metallogel showed emission behavior with tunable colors by controlling the temperature. The negative Gibbs free-energy change (ΔG) and the large association constant for excimer formation have suggested that the molecules undergo aggregation through hydrogen-bonding, π-π, and metal-metal interactions, resulting in triplet excimeric emission.

A hyaluronidase/temperature dual-responsive supramolecular assembly based on the anionic recognition of calixpyridinium

We have successfully constructed a supramolecular assembly based on the anionic recognition of calixpyridinium for the first time employing native biocompatible polysaccharide hyaluronan as the guest, which showed hyaluronidase-responsive disassembly and temperature-responsive morphological conversion from a nanosphere to a nanosquare upon increasing the temperature.

Preparation and Formation Process of Zn(II)-Coordinated Nanovesicles

Mixing a glycylglycine lipid and zinc acetate has been reported to form novel supramolecular Zn(II)-coordinated nanovesicles in ethanol. In this study, we investigate in detail the formation of nanovesicles by using three lipids at different temperatures and discuss their formation process. The original lipids show extremely low solubilities and appear as plate structures in ethanol. Within a small window of lipid solubility, the formation of lipid-Zn(II) complexes occurs mainly on the solid surfaces of plate structures. Controlling of the lipid solubility by temperature affects the kinetics of complex formation and the subsequent transformation of the complexes into nanovesicles and nanotubes. An improved method of two-step control of temperature is developed for preparing all the three kinds of nanovesicles. We provide new insights into the formation process of nanovesicles based on several control experiments. A tetrahedral lipid-cobalt(II) complex similarly produces nanovesicles, whereas an octahedral complex gives sheet structures. Mixing of zinc acetate with a β-alanyl-β-alanine lipid can only give sheet structures, which lack a polyglycine II hydrogen-bond network and induce no morphological changes. We conclude that the formation of the lipid-Zn(II) complexes on solid plate structures, tetrahedral geometry, and polyglycine II hydrogen-bond network in the complexes shall work cooperatively for the formation of Zn(II)-coordinated nanovesicles.

Binuclear alkynylplatinum(ii) terpyridine complexes with flexible bridges behave as organogelators for several organic solvents

New binuclear alkynylplatinum(ii) terpyridyl complexes with flexible bridges have been synthesized and characterized by ¹H NMR, mass spectra and elemental analysis.

Multiphase transition of supramolecular metallogels triggered by temperature

Multiphase transition: a new class of supramolecular alkynylplatinum(ii) metallogels, which displayed reversible multiphase transition induced by temperature, were successfully constructed.

Conformation-Controlled Diplatinum(II)-Ferrocene Dyads to Achieve Long-Lived Charge-Separated States

Square-planar polypyridyl platinum(II) complexes possess a rich range of structural and spectroscopic properties that are ideal for designing artificial photosynthetic centers. Taking advantage of the directionality in the charge-transfer excitation from the metal to the polypyridyl ligand, we describe here diplatinum(II)-ferrocene dyads, open-butterfly-like dyad 1 and closed-butterfly-like dyad 2, which were designed to understand the conformation and orientation effects to prolong the lifetime of charge-separated state. In contrast to the open-butterfly-like dyad 1, the closed-butterfly-like dyad 2 shows three-times long lifetime of charge separated state upon photoexcitation, demonstrating that the orientation in the rigid structure of dyad 2 is a very important issue to achieve long-lived charge separated state.

Dual-Responsive Lipid Nanotubes: Two-Way Morphology Control by pH and Redox Effects

Lipid nanotubes are the preferred structures for many applications, especially biological ones, and thus have attracted much interest recently. However, there is still a significant need for developing more lipid nanotubes that are reversibly controllable to improve their functionality and usability. Here, we presented a two-way reversible morphology control of the nanotubes formed by the recently designed molecule AQUA (C25H29NO4). Because of its special design, the AQUA has both pH-sensitive and redox-active characters provided by the carboxylic acid and anthraquinone groups. Upon chemical reduction, the nanotubes turned into thinner ribbons, and this structural transformation was significantly reversible. The reduction of the AQUA nanotubes also switched the nanotubes from electrically conductive to insulative. Nanotube morphology can additionally be altered by decreasing the pH below the pKa value of the AQUA, at ∼4.9. Decreasing the pH caused the gradual unfolding of the nanotubes, and the interlayer distance in the nanotube's walls increased. This morphological change was fast and reversible at a wide pH range, including the physiological pH. Thus, the molecular design of the AQUA allowed for an unprecedented two-way and reversible morphology control with both redox and pH effects. These unique features make AQUA a very promising candidate for many applications, ranging from electronics to controlled drug delivery.

Our Expedition in Linear Neutral Platinum-Acetylide Complexes: The Preparation of Micro/nanostructure Materials, Complicated Topologies, and Dye-Sensitized Solar Cells

During the past few decades, the construction of various kinds of platinum-acetylide complexes has attracted considerable attention, because of their wide applications in photovoltaic cells, non-linear optics, and bio-imaging materials. Among these platinum-acetylide complexes, the linear neutral platinum-acetylide complexes, due to their attractive properties, such as well-defined linear geometry, synthetic accessibility, and intriguing photoproperties, have emerged as a rising star in this field. In this personal account, we will discuss how we entered the field of linear neutral platinum-acetylide chemistry and what we found in this field. The preparation of various types of linear neutral platinum-acetylide complexes and their applications in the areas of micro/nanostructure materials, complicated topologies, and dye-sensitized solar cells will be summarized in this account.

Dual-responsive vesicles formed by an amphiphile containing two tetrathiafulvalene units in aqueous solution

The first example of tetrathiafulvalene (TTF)-based vesicle fabricated in water solution with 1 vol.% tetrahydrofuran that could be prevented by chemical oxidant Fe(ClO4)3 or electron-deficient cyclobis(paraquat-p-phenylene) tetracation cyclophane (CBPQT(4+)) is described.

Amphiphilic polymeric micelles as microreactors: improving the photocatalytic hydrogen production of the [FeFe]-hydrogenase mimic in water

An amphiphilic polymeric micelle is utilized as a microreactor to load a hydrophobic [FeFe]-hydrogenase mimic for photocatalytic hydrogen production in water.

Nanopatterned L10-FePt nanoparticles from single-source metallopolymer precursors for potential application in ferromagnetic bit-patterned media magnetic recording

A new single-source metallopolymer precursor P was applied for the synthesis of magnetic FePt nanoparticles, which was also suitable for patterning by high-throughput nanoimprint lithography to obtain ferromagnetic nanolines.

Supramolecular polymeric vesicles formed by p-sulfonatocalix[4]arene and chitosan with multistimuli responses

Supramolecular polymeric vesicles are constructed by the complexation of p-sulfonatocalix[4]arene and chitosan, where the multivalent electrostatic interactions between the anionic sulfonate tetramer and cationic polyammoniums served as the dominant driving force. The supra-amphiphilic assemblies are disassembled upon exposure to a pH stimulus since the partial deprotonation of chitosan accompanied by a pH increase. Adding a competitive guest can also disrupt the assembly, representing the host-guest inclusion response. Interestingly, an abnormal temperature-response is observed, possibly as a result of the temperature-directed fusion process.

Supramolecular chemistry of metal complexes in solution

Building on established supramolecular chemistry, metal coordination and organometallic chemistry have been widely explored for supramolecular polymers and nanostructures. Increasingly, research has demonstrated that this approach is promising for the synthesis of novel materials with functions and properties derived from metal elements and their coordination structures. Unique self-assembling behaviour and unexpected supramolecular structures are frequently discovered due to multiple non-covalent interactions in addition to metal coordination. However, an explicit understanding of the synergistic effects of non-covalent interactions for designed synthesis of metal containing assemblies with structure correlated properties remains a challenge to be addressed. Recent literature in the area is highlighted in this review in order to illustrate newly explored concepts and stress the importance of developing well understood and controlled supramolecular chemistry for designed synthesis.

Smart nanovehicles based on pH-triggered disassembly of supramolecular peptide-amphiphiles for efficient intracellular drug delivery

A novel type of nanovehicle (NV) based on stimuli-responsive supramolecular peptide-amphiphiles (SPAs, dendritic poly (L-lysine) non-covalently linked poly (L-leucine)) is developed for intracellular drug delivery. To determine the pH-dependent mechanism, the supramolecular peptide-amphiphile system (SPAS) is investigated at different pH conditions using a variety of physical and chemical approaches. The pH-triggered disassembly of SPAS can be attributed to the disappearance of non-covalent interactions within SPAs around the isoelectric point of poly (L-leucine). SPAS is found to encapsulate guest molecules at pH 7.4 but release them at pH 6.2. In this way, SPAS is able to act as a smart NV to deliver its target to tumor cells using intracellular pH as a trigger. The DOX-loaded NVs are approximately 150 nm in size. In vitro release profiles and confocal laser scanning microscopy (CLSM) images of HepG2 cells confirm that lower pH conditions can trigger the disassembly of NVs and so achieve pH-dependent intracellular DOX delivery. In vitro cytotoxicity of the DOX-loaded NVs to HepG2 cells demonstrate that the smart NVs enhance the efficacy of hydrophobic DOX. Fluorescence-activated cell sorting (FACS) and CLSM results show that the NVs can enhance the endocytosis of DOX into HepG2 cells considerably and deliver DOX to the nuclei.

5-Ferrocenyl-2,2′-bipyridine ligands: synthesis, palladium(ii) and copper(i) complexes, optical and electrochemical properties

Two 5-ferrocenyl-2,2′-bipyridine ligands were synthesised using the palladium(0) catalysed Suzuki–Miyaura cross-coupling reaction. Palladium(ii) and copper(i) complexes of these ligands were synthesised and the optical and electrochemical properties of the complexes were compared to those of the “free” ligands.

Remarkable luminescence enhancement of chloroplatinum(ii) complexes of hexaethylene glycol methyl ether substituted 2,6-bis(benzimidazol-2′-yl)pyridine in water triggered by PF6−

Upon addition of hexafluorophosphate salts, the nonemissive aqueous solution of a chloroplatinum(ii) complex showed a remarkable luminescence enhancement.

Construction of redox-active multilayer film for electrochemically controlled release

An electrochemically controlled drug release from a redox-active multilayer film is reported. The multilayer film is fabricated by alternate assembly of the electrochemical redox-active micelles and DNA. The buildup of multilayer films is monitored by spectroscopic ellipsometry, UV-vis spectroscopy, and fluorescence spectroscopy. A ferrocene-modified poly (ethyleneimine) (PEI-Fc) is used to form a hydrophobic ferrocene core and hydrophilic PEI shell micelle, showing the electrochemical redox-active properties. Hydrophobic pyrene (Py) molecules are then incorporated into the micelles. The PEI-Fc@Py micelles are assembled into the (PEI-Fc@Py/DNA) multilayer film by layer-by-layer assembly. Thanks to ferrocene groups with the properties of the hydrophilic-to-hydrophobic switch based on the electrical potential trigger, pyrene molecules can be control released from the multilayer film. The electrochemically controlled release of pyrene is investigated and confirmed by electrochemical quartz crystal microbalance and electrochemistry workstation. The (PEI-Fc@drug/DNA) multilayer film may have potential applications in the field of biomedical and nanoscale devices.

Smart wormlike micelles

A major scientific challenge of the past decade pertaining to the field of soft matter has been to craft 'adaptable' materials, inspired by nature, which can dynamically alter their structure and functionality on demand, in response to triggers produced by environmental changes. Amongst these, 'smart' surfactant wormlike micelles, responsive to external stimuli, are a particularly recent area of development, yet highly promising, given the versatility of the materials but simplicity of the design-relying on small amphiphilic molecules and their spontaneous self-assembly. The switching 'on' and 'off' of the micellar assembly structures has been reported using electrical, optical, thermal or pH triggers and is now envisaged for multiple stimuli. The structural changes, in turn, can induce major variations in the macroscopic characteristics, affecting properties such as viscosity and elasticity and sometimes even leading to a spontaneous and effective 'sol-gel' transition. These original smart materials based on wormlike micelles have been successfully used in the oil industry, and offer a significant potential in a wide range of other technological applications, including biomedicine, cleaning processes, drag reduction, template synthesis, to name but a few. This review will report results in this field published over the last few years, describe the potential and practical applications of stimuli-responsive wormlike micelles and point out future challenges.