Visualizing Chiral Interactions in Carbohydrates Adsorbed on Au(111) by High-Resolution STM Imaging

Carbohydrates are the most abundant organic material on Earth and the structural “material of choice” in many living systems. Nevertheless, design and engineering of synthetic carbohydrate materials presently lag behind that for protein and nucleic acids. Bottom-up engineering of carbohydrate materials demands an atomic-level understanding of their molecular structures and interactions in condensed phases. Here, high-resolution scanning tunneling microscopy (STM) is used to visualize at submolecular resolution the three-dimensional structure of cellulose oligomers assembled on Au(1111) and the interactions that drive their assembly. The STM imaging, supported by ab initio calculations, reveals the orientation of all glycosidic bonds and pyranose rings in the oligomers, as well as details of intermolecular interactions between the oligomers. By comparing the assembly of D- and L-oligomers, these interactions are shown to be enantioselective, capable of driving spontaneous enantioseparation of cellulose chains from its unnatural enantiomer and promoting the formation of engineered carbohydrate assemblies in the condensed phases.     

Polymerization Induced Microphase Separation for the Fabrication of Nanostructured Materials

Polymerization induced microphase separation (PIMS) is a strategy used to develop unique nanostructures with highly useful morphologies through the microphase separation of emergent block copolymers during polymerization. In this process, nanostructures are formed with at least two chemically independent domains, where at least one domain is composed of a robust crosslinked polymer. Crucially, this synthetically simple method is readily used to develop nanostructured materials with the highly coveted co-continuous morphology, which can also be converted into mesoporous materials by selective etching of one domain. As PIMS exploits a block copolymer microphase separation mechanism, the size of each domain can be tightly controlled by modifying the size of block copolymer precursors, thus providing unparalleled control over nanostructure and resultant mesopore sizes. Since its inception 11 years ago, PIMS has been used to develop a vast inventory of advanced materials for an extensive range of applications including biomedical devices, ion exchange membranes, lithium-ion batteries, catalysis, 3D printing, and fluorescence-based sensors, among many others. In this review, we provide a comprehensive overview of the PIMS process, summarize latest developments in PIMS chemistry, and discuss its utility in a wide variety of relevant applications.     

Two Calcium Coordination Polymers with Multi-Stimuli-Responsive Properties

Two skeleton isomers, [CaL(H₂O)(DMF)₂]•DMF ( 1 ) (H₂L=5-(1,3-dioxo-1H-benzo[de]isoquinolin-2(3H)-yl)isophthalic acid) with a 1 dimensional chain structure and [CaL(DMF)_1.72]• (DMF)_0.28 ( 2 ) with a 2 dimensional layer structure were synthesized. Mechanochromic luminescence studies reveal that 1 and 2 exhibit luminescent red-shift and blue-shift respectively under grinding stimuli. The different influence of grinding stimuli on the π⋅⋅⋅π interaction in the two structures are proposed to be the main reason for such different responses. In addition, 1 has a rare broad sensing ability for halogenated hydrocarbons and can distinguish seven halogenated hydrocarbons out of 17 solvents. 1 can also be used for rapid detection of trace water in DMF with a calculated detection limit of 0.0078 v/v %. The relevant recognition mechanism is the decomposition of the structure during the recognition process due to the water instability of the ionic bond. The above results reveal that both compounds have the potential to be used as multi-stimulus-responsive materials.     

Transient and Dissipative Host–Guest Hydrogels Regulated by Consumption of a Reactive Chemical Fuel

The transient self-assembly of molecules under the direction of a consumable fuel source is fundamental to biological processes such as cellular organization and motility. Such biomolecular assemblies exist in an out-of-equilibrium state, requiring continuous consumption of high energy molecules. At the same time, the creation of bioinspired supramolecular hydrogels has traditionally focused on associations occurring at the thermodynamic equilibrium state. Here, hydrogels are prepared from cucurbit[7]uril host–guest supramolecular interactions through transient physical crosslinking driven by the consumption of a reactive chemical fuel. Upon action from this fuel, the affinity and dynamics of CB[7]–guest recognition are altered. In this way, the lifetime of transient hydrogel formation and the dynamic modulus obtained are governed by fuel consumption, rather than being directed by equilibrium complex formation.     

Detachable Porous Organic Polymers Responsive to Light and Heat

Stimuli-responsive porous materials have captured much attention due to the on-demand tunable properties. Most reported stimuli-responsive porous materials are based on molecule isomerism or host-guest interaction, and it is highly desired to develop new types based on different responsive mechanism. Herein, inspired by natural cells which have the ability to fuse and divide induced by external stimulation, we report a new type of stimuli-responsive porous material based on detachment mechanism. A detachable porous organic polymer, namely DT-POP-1, is fabricated from the polymerization of anthracene-containing monomer (AnMon) when irradiated by 365 nm UV light. DT-POP-1 can detach into the monomer AnMon when irradiated with 275 nm UV light or heat. Such polymerization/detachment is reversible. The detachment results in a big difference in porosity and adsorption capacity, making the present detachable porous polymer highly promising in adsorptive separation and drug delivery.     

Photo-controllable Luminescence from Radicals Leading to Ratiometric Emission Switching via Dynamic Intermolecular Coupling

The development of photoinduced luminescent radicals with dynamic emission color is still challenging. Herein we report a novel molecular radical system (TBIQ) that shows photo-controllable luminescence, leading to a wide range of ratiometric color changes via light excitation. The conjugated skeleton of TBIQ is decorated with steric-demanding tertiary butyl groups that enable appropriate intermolecular interaction to make dynamic intermolecular coupling possible for controllable behaviors. We reveal that the helicenic pseudo-planar conformation of TBIQ experiences a planarization process after light excitation, leading to more compactly stacked supermolecules and thus generating radicals via intermolecular charge transfer. The photo-controllable luminescent radical system is employed for a high-level information encryption application. This study may offer unique insight into molecular dynamic motion for optical manufacturing and broaden the scope of smart-responsive materials for advanced applications.     

Compartmentalized Polyampholyte Microgels by Depletion Flocculation and Coacervation of Nanogels in Emulsion Droplets

In pH-responsive drug carriers, the distribution of charges has been proven to affect delivery efficiency but is difficult to control and verify. Herein, we fabricate polyampholyte nanogel-in-microgel colloids (NiM−C) and show that the arrangement of the nanogels (NG) can easily be manipulated by adapting synthesis conditions. Positively and negatively charged pH-responsive NG are synthesized by precipitation polymerization and labelled with different fluorescent dyes. The obtained NG are integrated into microgel (MG) networks by subsequent inverse emulsion polymerization in droplet-based microfluidics. By confocal laser scanning microscopy (CLSM), we verify that depending on NG concentration, pH value and ionic strength, NiM−C with different NG arrangements are obtained, including Janus-like phase-separation of NG, statistical distribution of NG, and core–shell arrangements. Our approach is a major step towards uptake and release of oppositely charged (drug) molecules.     

Burning Graphite Faster than Carbon Black: A Case of Diffusion Control

External diffusion may be exploited as a tool to purify materials in a way thought to be inaccessible from a chemical reactivity point of view. A mixture of two carbonaceous materials, graphite and carbon black, are thermally oxidized in either i) outside total diffusion-limited regime or ii) total diffusion-limited regime. Depending on the treatment applied it is possible to purify either graphite, a trivial task, or carbon black, a task thought impossible. Introducing geometrical selectivity, controlled total diffusion-limited chemistry exceeds by far the field of carbon materials and can be used as an engineering tool for many materials purification, original synthesis, or to introduce asymmetry in a system. Several examples for direct applications of the findings are mentioned.     

Colossal Anisotropic Thermal Expansion through Coupling Spin Crossover and Rhombus Deformation in a Hexanuclear {FeIII4FeII2} Compound

Colossal and anisotropic thermal expansion is a key function for microscale or nanoscale actuators in material science. Herein, we present a hexanuclear compound of [(Tp*)Fe^III(CN)₃]₄[Fe^II(Ppmp)]₂⋅2 CH₃OH ( 1 , Tp*=hydrotris(3,5-dimethyl-pyrazol-1-yl)borate and Ppmp=2-[3-(2′-pyridyl)pyrazol-1-ylmethyl]pyridine), which has a rhombic core structure abbreviated as {Fe^III₂Fe^II₂}. Magnetic susceptibility measurements and single-crystal X-ray diffraction analyses revealed that 1 underwent thermally-induced spin transition with the thermal hysteresis. The Fe^II site in 1 behaved as a spin crossover (SCO) unit, and significant deformation of its octahedron was observed during the spin transition process. Moreover, the distortion of the Fe^II centers actuated anisotropic deformation of the rhombic {Fe^III₂Fe^II₂} core, which was spread over the whole crystal through the subsequent molecular rearrangements, leading to the colossal anisotropic thermal expansion. Our results provide a rational strategy for realizing the colossal anisotropic thermal expansion and shape memory effects by tuning the magnetic bistability.