Metal-Free Electrocatalytic Alkaline Water Splitting by Porous Macrocyclic Proton Sponges.

Macrocycles are unique as they encapsulate and transfer guest molecules or ions and facilitate catalytic processes. Although metalated macrocycles are pivotal in electrocatalytic processes, using metal-free analogs has been rare. Following the strategy of Kanbara et al.

Pyrolytic Depolymerization of Polyolefins Catalysed by Zirconium-based UiO-66 Metal-Organic Frameworks.

Polyolefins such as polyethylenes and polypropylenes are the most-produced plastic waste globally, yet are difficult to convert into useful products due to their unreactivity. Pyrolysis is a practical method for large-scale treatment of mixed, contaminated plastic, allowing for their conversion into industrially-relevant petrochemicals. Metal-organic frameworks (MOFs), despite their tremendous utility in heterogeneous catalysis, have been overlooked for polyolefin depolymerization due to their perceived thermal instabilities and inability of polyethylenes and polypropylenes to penetrate their pores.

Probing Short-Range Interactions in Isostructural Hydrate and Perhydrate of Dabrafenib by Magic-Angle Spinning Solid-State NMR.

Dabrafenib (), an anticancer drug, exhibits isostructural properties in its hydrate () and perhydrate () forms, as revealed by single-crystal X-ray diffraction. Despite the HO and HO solvent molecules occupying identical locations, the two polymorphs have different thermal behaviors. In general, determination of stoichiometry of HO in the perhydrate crystals is difficult due to the presence of both HO and HO in the same crystal voids.

Lithiophilic Dibenzamide Linkages to Impart Lithium Storage Capacity in Porous Polybenzamides.

Polymer-based organic cathode materials have shown immense promise for lithium storage, owing to their structural diversity and functional group tunability. However, designing appropriate high-performance cathode materials with a high-rate capability and long cycle life remains a significant challenge. It is quintessential to design polymer-based electrodes with lithiophilic linkages.

High-resolution heteronuclear correlations between spin-1/2 and half-integer quadrupolar nuclei under fast MAS solid-state NMR.

High isotropic resolution is essential for the structural elucidation of samples with multiple sites. In this study, utilizing the benefits of TRAPDOR-based heteronuclear multiple quantum coherence (T-HMQC) and a pair of one rotor period long cosine amplitude modulated low-power (cos-lp) pulse-based symmetric-split-t multiple-quantum magic angle spinning (MQMAS) methods, we have developed a proton-detected 2D Cl/H T-HMQC-MQMAS pulse sequence under fast MAS (70 kHz) to achieve high-resolution in the indirect dimension of the spin-3/2 (Cl) nuclei connected via protons. As T-HMQC polarizes not only single-quantum central transition (SQ) but also triple-quantum (TQ) coherences, the proposed 2D pulse sequence is implemented via selection of two coherence pathways (SQ→TQ →SQ and TQ → SQ→TQ) resulting in the Cl isotropic dimension and is superior to the existing double-quantum satellite-transition (DQ) T-HMQC in terms of resolution.

Modular Design of Highly Stable Semiconducting Porous Coordination Polymer for Efficient Electrosynthesis of Ammonia.

Developing highly stable porous coordination polymers (PCPs) with integrated electrical conductivity is crucial for advancing our understanding of electrocatalytic mechanisms and the structure-activity relationship of electrocatalysts. However, achieving this goal remains a formidable challenge because of the electrochemical instability observed in most PCPs. Herein, we develop a "modular design" strategy to construct electrochemically stable semiconducting PCP, namely, Fe-pyNDI, which incorporates a chain-type Fe-pyrazole metal cluster and π-stacking column with effective synergistic effects.

NMR crystallography of amino acids.

The development of NMR crystallography methods requires a reliable database of chemical shifts measured for systems with known crystal structure. We measured and assigned carbon and hydrogen chemical shifts of twenty solid natural amino acids of known polymorphic structure, meticulously determined using powder X-ray diffraction. We then correlated the experimental data with DFT-calculated isotropic shieldings.

Synthesis of 3,3'-dihydroxy-2,2'-diindan-1,1'-dione derivatives for tautomeric organic semiconductors exhibiting intramolecular double proton transfer.

To investigate potential applications of the 3,3'-dihydroxy-2,2'-biindan-1,1'-dione (BIT) structure as an organic semiconductor with intramolecular hydrogen bonds, a new synthetic route under mild conditions is developed based on the addition reaction of 1,3-dione to ninhydrin and the subsequent hydrogenation of the hydroxyl group. This route affords several new BIT derivatives, including asymmetrically substituted structures that are difficult to access by conventional high-temperature synthesis. The BIT derivatives exhibit rapid tautomerization by intramolecular double proton transfer in solution.

Selective Metal-Free CO Photoreduction in Water Using Porous Nanostructures with Internal Molecular Free Volume.

The conversion of CO to a sole carbonaceous product using photocatalysis is a sustainable solution for alleviating the increasing levels of CO emissions and reducing our dependence on nonrenewable resources such as fossil fuels. However, developing a photoactive, metal-free catalyst that is highly selective and efficient in the CO reduction reaction (CORR) without the need for sacrificial agents, cocatalysts, and photosensitizers is challenging. Furthermore, due to the poor solubility of CO in water and the kinetically and thermodynamically favored hydrogen evolution reaction (HER), designing a highly selective photocatalyst is challenging.

Molecular Design of Organic Ionic Plastic Crystals Consisting of Tetracyanoborate with Ultralow Phase Transition Temperature.

Organic ionic plastic crystals (OIPCs) are a ductile soft material where the composing ions are in isotropic free rotation, while their positions are aligned in order. The rotational motion in its plastic phase promotes ion conduction by decreasing the activation energy. Here, we report novel OIPCs comprised of tetracyanoborate ([TCB]) and various organic cations.

Synthesizing Interpenetrated Triazine-based Covalent Organic Frameworks from CO.

Crystalline triazine-based covalent organic frameworks (COFs) are aromatic nitrogen-rich porous materials. COFs typically show high thermal/chemical stability, and are promising for energy applications, but often require harsh synthesis conditions and suffer from low crystallinity. In this work, we propose an environmentally friendly route for the synthesis of crystalline COFs from CO molecules as a precursor.

Design of a robust and strong-acid MOF platform for selective ammonium recovery and proton conductivity.

Metal-organic frameworks (MOFs) are potential candidates for the platform of the solid acid; however, no MOF has been reported that has both aqueous ammonium stability and a strong acid site. This manuscript reports a highly stable MOF with a cation exchange site synthesized by the reaction between zirconium and mellitic acid under a high concentration of ammonium cations (NH). Single-crystal XRD analysis of the MOF revealed the presence of four free carboxyl groups of the mellitic acid ligand, and the high first association constant (p) of one of the carboxyl groups acts as a monovalent ion-exchanging site.

Bottom-Up Synthesis of Crystalline Covalent Organic Framework Nanosheets, Nanotubes, and Kippah Vesicles: An Odd-Even Effect Induction.

Few-layer organic nanosheets are becoming increasingly attractive as two-dimensional (2D) materials due to their precise atomic connectivity and tailor-made pores. However, most strategies for synthesizing nanosheets rely on surface-assisted methods or top-down exfoliation of stacked materials. A bottom-up approach with well-designed building blocks would be the convenient pathway to achieve the bulk-scale synthesis of 2D nanosheets with uniform size and crystallinity.

Determination of the mutual orientation between proton CSA tensors mediated through band-selective H-H recoupling under fast MAS.

The mutual orientation of nuclear spin interaction tensors provides critical information on the conformation and arrangement of molecules in chemicals, materials, and biological systems at an atomic level. Proton is a ubiquitous and important element in a variety of substances, and its NMR is highly sensitive due to their virtually 100% natural abundance and large gyromagnetic ratio. Nevertheless, the measurement of mutual orientation between the H CSA tensors has remained largely untouched in the past due to strong H-H homonuclear interactions in a dense network of protons.

Hyperpolarization of Biomolecules in Eutectic Crystals at Room Temperature Using Photoexcited Electrons.

The hyperpolarization of biomolecules at room temperature could facilitate highly sensitive magnetic resonance imaging for metabolic studies and nuclear magnetic resonance (NMR)-based screenings for drug discovery. In this study, we demonstrate the hyperpolarization of biomolecules in eutectic crystals using photoexcited triplet electrons at room temperature. Eutectic crystals composed of the domains of benzoic acid doped with the polarization source and analyte domains were prepared using a melting-quenching process.

Determination of the relative orientation between N-H dipolar coupling and H chemical shift anisotropy tensors under fast MAS solid-state NMR.

In this work, we have proposed a proton-detected three-dimensional (3D) N-H dipolar coupling (DIP)/H chemical shift anisotropy (CSA)/H chemical shift (CS) correlation experiment to measure the relative orientation between the N-H dipolar coupling and the H CSA tensors under fast magic angle spinning (MAS) solid-state NMR. In the 3D correlation experiment, the N-H dipolar coupling and H CSA tensors are recoupled using our recently developed windowless C-symmetry-based C3-ROCSA (recoupling of chemical shift anisotropy) DIPSHIFT and C3-ROCSA pulse-based methods, respectively. The 2D N-H DIP/H CSA powder lineshapes extracted using the proposed 3D correlation method are shown to be sensitive to the sign and asymmetry of the H CSA tensor, a feature that allows the determination of the relative orientation between the two correlating tensors with improved accuracy.

Structural and Morphological Transformations of Covalent Organic Nanotubes.

Covalent organic nanotubes (CONTs) are porous one-dimensional frameworks connected through imine bonds via Schiff base condensation between aldehydes and amines. The presence of two amine groups at the ortho position in the structurally demanding tetraaminotriptycene (TAT) building block leads to multiple reaction pathways between the ditopic aldehyde and the tetratopic amine. We have synthesized five different monomers of CONT-1 by the Schiff base condensation reaction between TAT and o-anisaldehyde.

Internuclear distance measurements between H and N in multi-component rigid solids at fast MAS.

H-N internuclear distances are readily and accurately measured using the symmetry-based phase-modulated resonance-echo saturation-pulse double-resonance (PM-S-RESPDOR) method in rigid solids. The fraction curve, (S - S')/S, is represented by a single variable of a H-N heteronuclear dipolar coupling, where S and S' are the PM-S-RESPDOR signal intensity with and without N PM saturation pulse, respectively. Analytical equation of the fraction curve easily provides H-N couplings.

Morphology Tuning via Linker Modulation: Metal-Free Covalent Organic Nanostructures with Exceptional Chemical Stability for Electrocatalytic Water Splitting.

The development of synthetic routes for the formation of robust porous organic polymers (POPs) with well-defined nanoscale morphology is fundamentally significant for their practical applications. The thermodynamic characteristics that arise from reversible covalent bonding impart intrinsic chemical instability in the polymers, thereby impeding their overall potential. Herein, a unique strategy is reported to overcome the stability issue by designing robust imidazole-linked POPs via tandem reversible/irreversible bond formation.

Ultrafast Magic Angle Spinning Solid-State NMR Spectroscopy: Advances in Methodology and Applications.

Solid-state NMR spectroscopy is one of the most commonly used techniques to study the atomic-resolution structure and dynamics of various chemical, biological, material, and pharmaceutical systems spanning multiple forms, including crystalline, liquid crystalline, fibrous, and amorphous states. Despite the unique advantages of solid-state NMR spectroscopy, its poor spectral resolution and sensitivity have severely limited the scope of this technique. Fortunately, the recent developments in probe technology that mechanically rotate the sample fast (100 kHz and above) to obtain "solution-like" NMR spectra of solids with higher resolution and sensitivity have opened numerous avenues for the development of novel NMR techniques and their applications to study a plethora of solids including globular and membrane-associated proteins, self-assembled protein aggregates such as amyloid fibers, RNA, viral assemblies, polymorphic pharmaceuticals, metal-organic framework, bone materials, and inorganic materials.

Fine Pore-Structure Engineering by Ligand Conformational Control of Naphthalene Diimide-Based Semiconducting Porous Coordination Polymers for Efficient Chemiresistive Gas Sensing.

Exploring new porous coordination polymers (PCPs) that have tunable structure and conductivity is attractive but remains challenging. Herein, fine pore structure engineering by ligand conformation control of naphthalene diimide (NDI)-based semiconducting PCPs with π stacking-dependent conductivity tunability is achieved. The π stacking distances and ligand conformation in these isoreticular PCPs were modulated by employing metal centers with different coordination geometries.

Three-Dimensional Metal-Organic Network Glasses from Bridging MF Anions and Their Dynamic Insights by Solid-State NMR.

Glassy-state coordination polymers (CPs) are a new class of network-forming glasses. In this work, we constructed glass-forming CPs composed of both anionic and neutral ligands as network formers. With the use of hexafluoro anions (MF) and 1,3-bis(4-pyridyl)propane (bpp), two isostructural CP crystals, [Zn(SiF)(bpp)] () and [Zn(TiF)(bpp)] (), were synthesized.

Proton Hyperpolarization Relay from Nanocrystals to Liquid Water.

Dynamic nuclear polarization (DNP) using transient electron spin polarization generated by photoexcitation can improve nuclear magnetic resonance (NMR) sensitivity far beyond the thermal equilibrium limit for analysis in life science and drug discovery. However, DNP of liquid water at room temperature remains an important challenge. Here, we propose a new method called hyperpolarization relay, in which the nonequilibrium polarization of electron spins is transferred to proton spins in the nanocrystals and then to proton spins in bulk water.