Water Chains in Hydrophobic Crystal Channels: Nanoporous Materials as Supramolecular Analogues of Carbon Nanotubes

Understanding the Wettability of C1N1 (Sub)Nanopores: Implications for Porous Carbonaceous Electrodes

Understanding how water interacts with nanopores of carbonaceous electrodes is crucial for energy storage and conversion applications. A high surface area of carbonaceous materials does not necessarily need to translate to a high electrolyte-solid interface area. Herein, we study the interaction of water with nanoporous C1N1 materials to explain their very low specific capacitance in aqueous electrolytes despite their high surface area. Water was used to probe chemical environments, provided by pores of different sizes, in 1H MAS NMR experiments. We observe that regardless of their high hydrophilicity, only a negligible portion of water can enter the nanopores of C1N1, in contrast to a reference pure carbon material with a similar pore structure. The common paradigm that water easily enters hydrophilic pores does not apply to C1N1 nanopores below a few nanometers. Calorimetric and sorption experiments demonstrated strong water adsorption on the C1N1 surface, which restricts water mobility across the interface and impedes its penetration into the nanopores.

Energy-Efficient Iodine Uptake by a Molecular Host⋅Guest Crystal

Recently, porous organic crystals (POC) based on macrocycles have shown exceptional sorption and separation properties. Yet, the impact of guest presence inside a macrocycle prior to adsorption has not been studied. Here we show that the inclusion of trimethoxybenzyl-azaphosphatrane in the macrocycle cucurbit[8]uril (CB[8]) affords molecular porous host⋅guest crystals (PHGC-1) with radically new properties. Unactivated hydrated PHGC-1 adsorbed iodine spontaneously and selectively at room temperature and atmospheric pressure. The absence of (i) heat for material synthesis, (ii) moisture sensitivity, and (iii) energy-intensive steps for pore activation are attractive attributes for decreasing the energy costs. 1 H NMR and DOSY were instrumental for monitoring the H2 O/I2 exchange. PHGC-1 crystals are non-centrosymmetric and I2 -doped crystals showed markedly different second harmonic generation (SHG), which suggests that iodine doping could be used to modulate the non-linear optical properties of porous organic crystals.

Intrinsic Contributions of 2'-Hydroxyl to the Hydration of Nucleosides at the Monomeric Level

Although many reports have revealed structural differences between DNA and RNA at the polymeric level, there are no comparative studies with 2'-deoxyribonucleoside and ribonucleoside to explore the role of the 2'-OH group at the monomeric level under the same conditions. Inspired by this, herein, the intrinsic contributions of the 2'-OH group in the nucleoside have been systematically investigated by directly solving the single-crystal structures of 2'-deoxy-2-aminoadenosine (1), 2-aminoadenosine (2), and 2-aminoarabinofuranosyladenine (3) in water. The 2'-OH group not only influenced the conformation and base-pair pattern of the single-nucleoside molecule, but also played a fundamental role in the entire supramolecular structure. Interestingly, compound 1, which did not contain the 2'-OH group, displayed strong hydration, whereas 2 and 3 (with the 2'-OH group in the opposite direction) exhibited no hydration, which was completely different from that observed in nucleic acids. Meanwhile, compound 1 trapped water molecules to form unique trihydrol moieties, which further served as the backbone to construct the simplest double-chain DNA-like structures. To this end, to investigate the effect of the biological environment on these unique structures, the solvent was changed from water to phosphate-buffered saline (PBS). Surprisingly, such a subtle adjustment led to entirely different superstructures, consisting of 2D lamellar structures in water and 3D porous structures in PBS. These large morphological differences could be attributed to delicate ion hydration, which was also confirmed through variable-temperature X-ray analysis, SEM, and intermolecular interaction energy calculations. In summary, this study comprehensively investigated the intrinsic contributions of 2'-hydroxyl to the hydration of nucleosides at the monomeric level; this is helpful to further understand the differences in DNA/RNA and the impact of their surrounding environment.

A Chiral Bis-Naphthylated Tetrandrine Dibromide: Synthesis, Self-Assembly into an Organic Framework Based On Nanosized Spherical Cages, and Inclusion Studies

Crystalline framework materials have gained interest because of their many potential applications. A novel chiral tetrandrine salt (DNT) has been synthesized and characterized by conventional analytical techniques and single-crystal X-ray diffraction analysis, and its self-assembly behavior studied. In the solid state, 48 molecules of the compound self-assemble into an organic framework based on nanospherical aggregates formed exclusively through weak noncovalent interactions. Additionally, it was demonstrated by UV-vis spectroscopy and TGA that assembled DNT can include the Nile Red dye, giving a fluorescent material. To the best of our knowledge, these spherical assemblies are the largest among the purely synthetic organic self-assembled molecular crystals reported to date.

Acyclic Janus-AT Nucleoside Host Channels Precisely Lock Water into Single-File Wires with Local Rotational Flexibility

Confining polar water molecules to particular geometries demands sophisticated intermolecular interactions, and not many small synthetic molecules have accomplished such a task. Herein, regioisomeric acyclic Janus-AT nucleosides (1 and 2), with a self-complementary fused genetic alphabet and conformationally flexible side chains, have been selectively synthesized. 1 and 2 adopt disparate base-pair motifs from the π-π stacked hydrophobic base moieties and distinct hydrogen bond (HB) interconnections from the hydrophilic sugar residues, which in turn lead to divergent, intricate intermolecular interaction networks with different capacities to confine water molecules. Under the precise control of the host framework of the N⁸ -regioisomer, separate ordered single-file water wires can be locked through special three-HB clamps into unique inter- and intra-wire geometrical alignments. Localized dynamic synchronized rotations within the fixed framework coordinated by both the host hydroxy groups and guest water molecules were observed in a temperature-induced reversible single-crystal-to-single-crystal transition (SCSCT).

Dynamics of water in conical solvation shells around a benzene solute under different thermodynamic conditions

Water molecules in different parts of the anisotropic hydration shell of an aromatic molecule experience different interactions. In the present study, we investigate the anisotropic dynamics of water molecules in different non-overlapping conical shells around a benzene solute at sub- and supercritical conditions by means of molecular dynamics simulations using both non-polarizable and polarizable models. In addition to the dynamical properties, the effects of polarizability on the hydration structure of benzene at varying thermodynamic conditions are also investigated in the current study. The presence of πH-bonding in the solvation shell is found to be an important factor that influences the anisotropic dynamics of the benzene hydration shell. The water molecules located axial to the benzene plane are found to be maximally influenced by the πH-bonding. The extent of πH-bonding is found to be somewhat reduced on inclusion of polarizability. The πH-bonded water molecules are found to reorient through large-amplitude angular jumps where the jump-angle amplitude increases at higher temperatures and lower densities. For both non-polarizable and polarizable models, it is found that the water molecules in the axial conical shells possess faster orientational and hydrogen bond dynamics compared to those in the equatorial plane. Water molecules in the axial conical shells are also found to diffuse at a faster rate than bulk molecules due to the relatively weaker benzene-water πH-bonding interactions in the axial region of the hydration shell. The residence dynamics of water molecules in different conical solvation shells around the solute is also investigated in the current study.

Streams, cascades, and pools: various water cluster motifs in structurally similar Ni(ii) complexes

Hydrogen bonding (HB) interactions are well known to impact the properties of water in the bulk and within hydrated materials.

Selective Adsorption and Selective Transport Diffusion of CO2-CH4 Binary Mixture in Coal Ultramicropores

The adsorption and diffusion of the CO2-CH4 mixture in coal and the underlying mechanisms significantly affect the design and operation of any CO2-enhanced coal-bed methane recovery (CO2-ECBM) project. In this study, bituminous coal was fabricated based on the Wiser molecular model and its ultramicroporous parameters were evaluated; molecular simulations were established through Grand Canonical Monte Carlo (GCMC) and Molecular Dynamic (MD) methods to study the effects of temperature, pressure, and species bulk mole fraction on the adsorption isotherms, adsorption selectivity, three distinct diffusion coefficients, and diffusivity selectivity of the binary mixture in the coal ultramicropores. It turns out that the absolute adsorption amount of each species in the mixture decreases as temperature increases, but increases as its own bulk mole fraction increases. The self-, corrected, and transport diffusion coefficients of pure CO2 and pure CH4 all increase as temperature or/and their own bulk mole fractions increase. Compared to CH4, the adsorption and diffusion of CO2 are preferential in the coal ultramicropores. Adsorption selectivity and diffusivity selectivity were simultaneously employed to reveal that the optimal injection depth for CO2-ECBM is 800-1000 m at 308-323 K temperature and 8.0-10.0 MPa.

Anisotropic structure and dynamics of the solvation shell of a benzene solute in liquid water from ab initio molecular dynamics simulations

The anisotropic structure and dynamics of the hydration shell of a benzene solute in liquid water have been investigated by means of ab initio molecular dynamics simulations using the BLYP (Becke–Lee–Yang–Parr) and dispersion corrected BLYP-D functionals.

Porous organic hydrate crystals: structure and dynamic behaviour of water clusters

Infinite water clusters with a T5(2) motif were observed in porous crystals of 4-nitrostyrylpyridine hydrochloride, the behavior of which was revealed by solid-state ¹⁷O NMR spectroscopic analyses.

Assembly of encapsulated water in hybrid bisamides: helical and zigzag water chains

The addition of water promotes the self-assembly of hybrid bisamides by bridging between the molecules and stabilizes the helical or zigzag one-dimensional water chains.

The Dynamics, energetics and selectivity of water chain-containing aquapores created by the self-assembly of aquafoldamer molecules

Self-assembled hollow tubular aquapores were found to be stable, very dynamic yet highly selective toward recognition of water molecules.

What are preferred water-aromatic interactions in proteins and crystal structures of small molecules?

The distribution of water molecules around aromatic rings in the protein structures and crystal structures of small molecules shows quite a small number of the strongest OH-π interactions, a larger number of parallel interactions, and the largest number of the weakest CH-O interactions.

Parallel water/aromatic interactions of non-coordinated and coordinated water

The parallel interactions of non-coordinated and coordinated water molecules with an aromatic ring were studied by analyzing data in the Cambridge structural database (CSD) and by using quantum chemical calculations. The CSD data show that water/aromatic contacts prefer parallel to OH/π interactions, which indicates the importance of parallel interactions. The results reveal the influence of water coordination to a metal ion; the interactions of aqua complexes are stronger. Coordinated water molecules prefer a parallel-down orientation in which one OH bond is parallel to the aromatic ring, whereas the other OH bond points to the plane of the ring. The interactions of aqua complexes with parallel-down water/benzene orientation are as strong as the much better known OH/π orientations. The strongest calculated interaction energy is -14.89 kcal mol(-1) . The large number of parallel contacts in crystal structures and the quite strong interactions indicate the importance of parallel orientation in water/benzene interactions.

1D water chain stabilized by meso-expanded calix[4]pyrrole

A new core expanded calix[4]pyrrole is reported, in which the opposite bridging sp³-carbons are replaced by ethylene moieties.

Cholanamide components for organic alloys; expanding the scope of nanoporous steroidal ureas

Amide-linked side-chains can substitute for esters in crystalline nanoporous steroidal ureas (NSPUs). This efficient conjugation method increases the versatility of NPSUs, and should aid the inclusion of complex functional units in the crystal channels.

Simultaneous encapsulation of an infinite T4(0)A(0)6(0) water tape and discrete water hexamers in a hydrogen-bonded Ag(i) supramolecular framework

In a one-dimensional mixed-ligand Ag(i) coordination polymer, an infinite 1D T4(0)A(0)6(0) water tape and discrete water hexamers were simultaneously encapsulated.

Impeller-like dodecameric water clusters in metal–organic nanotubes

A triazole ligand, 3-amino-1,2,4-triazole-5-carboxylic acid (H₂atc), bearing carboxylate and amino groups, has been incorporated into a nanotubular copper(ii)–organic framework that displays an nbo-type topology in which the impeller-like (H₂O)₁₂ water clusters were trapped in the nanotubes that can be encapsulated reversibly and precisely.

Tunable porous organic crystals: structural scope and adsorption properties of nanoporous steroidal ureas

Previous work has shown that certain steroidal bis-(N-phenyl)ureas, derived from cholic acid, form crystals in the P6(1) space group with unusually wide unidimensional pores. A key feature of the nanoporous steroidal urea (NPSU) structure is that groups at either end of the steroid are directed into the channels and may in principle be altered without disturbing the crystal packing. Herein we report an expanded study of this system, which increases the structural variety of NPSUs and also examines their inclusion properties. Nineteen new NPSU crystal structures are described, to add to the six which were previously reported. The materials show wide variations in channel size, shape, and chemical nature. Minimum pore diameters vary from ~0 up to 13.1 Å, while some of the interior surfaces are markedly corrugated. Several variants possess functional groups positioned in the channels with potential to interact with guest molecules. Inclusion studies were performed using a relatively accessible tris-(N-phenyl)urea. Solvent removal was possible without crystal degradation, and gas adsorption could be demonstrated. Organic molecules ranging from simple aromatics (e.g., aniline and chlorobenzene) to the much larger squalene (M(w) = 411) could be adsorbed from the liquid state, while several dyes were taken up from solutions in ether. Some dyes gave dichroic complexes, implying alignment of the chromophores in the NPSU channels. Notably, these complexes were formed by direct adsorption rather than cocrystallization, emphasizing the unusually robust nature of these organic molecular hosts.

Size, separation, structural order, and mass density of molecules packing in water and ice

The structural symmetry and molecular separation in water and ice remain uncertain. We present herewith a solution to unifying the density, the structure order and symmetry, the size (H-O length dH), and the separation (d(OO) = d(L) + d(H) or the O:H length d(L)) of molecules packing in water and ice in terms of statistic mean. This solution reconciles: i) the d(L) and the d(H) symmetrization of the O:H-O bond in compressed ice, ii) the d(OO) relaxation of cooling water and ice and, iii) the d(OO) expansion of a dimer and between molecules at water surface. With any one of the d(OO), the density ρ(g·cm⁻³), the d(L), and the d(H), as a known input, one can resolve the rest quantities using this solution that is probing conditions or methods independent. We clarified that: i) liquid water prefers statistically the mono-phase of tetrahedrally-coordinated structure with fluctuation, ii) the low-density phase (supersolid phase as it is strongly polarized with even lower density) exists only in regions consisting molecules with fewer than four neighbors and, iii) repulsion between electron pairs on adjacent oxygen atoms dictates the cooperative relaxation of the segmented O:H-O bond, which is responsible for the performance of water and ice.