Molecular tweezers are open-ended, cavity-possessing U-shaped molecular architectures with high potential for various applications in supramolecular chemistry. Their covalent synthesis, however, is ...often tedious and the structures obtained lack structural responsiveness beyond the limited conformational flexibility of the scaffold. Herein we present a proof-of-concept study on the design, synthesis, assembly, and transformations of a novel supramolecular constructa fully noncovalent molecular tweezer. The supramolecular tweezer was assembled from a set of four building blocks, composed of two identical molecular angle bars and two flat aromatic extension wings, using hydrogen bonding only. The chirality-assisted aggregation process was utilized to ensure scaffold bending directionality using enantiomerically pure bicyclic angle bars. To address the challenges associated with shifting of the equilibrium from strong cooperative narcissistic self-sorting of self-complementary angle bars in cyclic aggregates toward integrative self-sorting in molecular tweezers, a rational desymmetrization strategy was applied. The dynamic supramolecular tweezer has been shown to display rich supramolecular chemistry, allowing for stimuli-responsive change in aggregate topology and solvent-responsive supramolecular polymerization.
The structure, stability, and intermolecular interactions in SO.sub.3-(H.sub.2O)n (n = 1-7) clusters were investigated using density functional and wave functional methods. The putative global ...minimum shows the SO.sub.3 molecule tends to be on the surface water clusters. The increase in the number of water molecules chalcogen bond distance between water molecules and SO.sub.3 decreases, while the maximum number of water molecules coordinated to the SO.sub.3 molecule remains at three. The calculated solvation energy increases with the increase in the number of water molecules, and it does not saturate, which indicates that the addition of water molecules can add up to the existing water cluster network. The interaction energy between water molecules and SO.sub.3 was less than the solvation energy conforming to the cluster forming of water molecules. The Gibbs free energy and entropy values decrease with the increase in cluster size, signifying the amount of water molecule decide the sequential hydration process. Thermochemistry data at various temperatures show that low-temperature regions found in the upper part of the troposphere favor hydration formation. Molecular electrostatic potentials (MESP) show reduced V.sub.s,max value of pi-hole on sulfur atom and increased value on hydrogens of water molecules which results in the addition of water which leads to the sequential addition of water molecules to the water network. The quantum theory of atoms in molecules (QTAIM) shows the presence of S···O, O···H interactions between SO.sub.3 and water molecules. Between water molecules O···H, H-bonding interactions were observed, and in larger clusters, O···O interaction was also noticed. QTAIM analysis shows that the water-water HBs in these clusters are weak H-bond, while the SO.sub.3-water interaction can be classified as medium H-bonds which was further supported by the NCI and 2D RDG plots.
Diarylamines possess two potentially atropisomeric C–N axes; however, there are few examples of atropisomerically stable diarylamines in the literature, as the contiguous axes can allow for low ...energy racemization pathways via concerted bond rotations. Herein, we describe highly atropisomerically stable diarylamines that possess barriers to racemization of 30–36 kcal/mol, corresponding to half-lives to racemization on the decade to century time scale at room temperature. Investigation of the factors that led to the high stereochemical stability suggests that increased conjugation of the aniline lone pair of electrons into a more electron-deficient aryl ring, coupled with intramolecular hydrogen-bonding, locked the corresponding axis into a defined planar conformation, disfavoring the lower energy racemization pathways.
A para-substituted triphenylphosphine oxide with terminal vanadocene centers has been prepared and is, to our knowledge, the first example of an untethered C3v-symmetric triarylphosphine oxide in the ...solid state. Crystallographic and DFT studies suggest this locked conformation is due to intermolecular H-bonding interactions. Electrochemical measurements suggest these interactions may persist in solution. A monometallic variant, adopting the standard C3 propeller geometry, has also been synthesized for comparison.
Current synthetic elastomers suffer from the well‐known trade‐off between toughness and stiffness. By a combination of multiscale experiments and atomistic simulations, a transparent unfilled ...elastomer with simultaneously enhanced toughness and stiffness is demonstrated. The designed elastomer comprises homogeneous networks with ultrastrong, reversible, and sacrificial octuple hydrogen bonding (HB), which evenly distribute the stress to each polymer chain during loading, thus enhancing stretchability and delaying fracture. Strong HBs and corresponding nanodomains enhance the stiffness by restricting the network mobility, and at the same time improve the toughness by dissipating energy during the transformation between different configurations. In addition, the stiffness mismatch between the hard HB domain and the soft poly(dimethylsiloxane)‐rich phase promotes crack deflection and branching, which can further dissipate energy and alleviate local stress. These cooperative mechanisms endow the elastomer with both high fracture toughness (17016 J m−2) and high Young's modulus (14.7 MPa), circumventing the trade‐off between toughness and stiffness. This work is expected to impact many fields of engineering requiring elastomers with unprecedented mechanical performance.
A bioinspired multifunctional elastomer with both high fracture toughness and high Young's modulus is designed, breaking through the current trade‐off present in the state‐of‐the‐art. The octuple hydrogen bonding promotes the formation of ultrastrong nanodomains, which, together with a soft poly(dimethylsiloxane)‐rich phase, form a bicontinuous network structure. Such hierarchical networks with ultrastrong nanodomains enhance the mechanical properties.
Acetonitrile and water are miscible solvents. This study compares their separation by betaine and betaine hydrochloride. Acetonitrile is a hydrogen (H) bond acceptor and so is betaine, because of its ...-CO and -CO- groups. Therefore, betaine competes with acetonitrile for interactions with the hydrogens of water molecules, as indicated by attenuated total reflectance - Fourier transform infrared spectroscopy (ATR-FTIR). Therefore, when added to acetonitrile-water mixtures, betaine displaces acetonitrile. Separation into bulk phases occurs with 5–10 wt% betaine (relative to water), for acetonitrile concentrations between 50 and 80 wt% (relative to the aqueous phase). At lower acetonitrile concentrations (e.g., 1 wt%), betaine separates acetonitrile from water to yield emulsified acetonitrile droplets, detected by light scattering. With 1 wt% acetonitrile and betaine, acetonitrile droplets in water are negatively charged due to the -CO- group of betaine, as shown by electrophoretic measurements. In the case of betaine hydrochloride, the negative charge of the -CO- group is shielded by a proton, and interactions with water are weaker. As a result, bulk separation is not observed. Nonetheless, betaine hydrochloride also competes against acetonitrile for interactions with hydrogen atoms of water molecules, albeit not as effectively as betaine. This is shown by ATR-FTIR. Therefore, betaine hydrochloride emulsifies acetonitrile in water into sub-micron droplets. These droplets are positively charged, owing to the positively charged nitrogen atom of betaine hydrochloride. Acidifying mixtures of betaine, acetonitrile and water (with HCl) impedes bulk separation. This result confirms the importance of electrostatic interactions between the hydrogens of water and the unshielded, negative -CO- group of betaine.
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Deep eutectic solvents (DESs) are an emerging class of mixtures characterized by significant depressions in melting points compared to those of the neat constituent components. These materials are ...promising for applications as inexpensive “designer” solvents exhibiting a host of tunable physicochemical properties. A detailed review of the current literature reveals the lack of predictive understanding of the microscopic mechanisms that govern the structure–property relationships in this class of solvents. Complex hydrogen bonding is postulated as the root cause of their melting point depressions and physicochemical properties; to understand these hydrogen bonded networks, it is imperative to study these systems as dynamic entities using both simulations and experiments. This review emphasizes recent research efforts in order to elucidate the next steps needed to develop a fundamental framework needed for a deeper understanding of DESs. It covers recent developments in DES research, frames outstanding scientific questions, and identifies promising research thrusts aligned with the advancement of the field toward predictive models and fundamental understanding of these solvents.
The proton transport mechanism in superprotonic phases of solid acids has been a subject of experimental and theoretical studies for a number of years. Despite this, details of the mechanism still ...need further clarification. In particular in the M3H(AO4)2 family of crystals, where M = NH4, K, Rb, Cs, and A = S, Se, the proton diffusion is mostly considered in the (001) plane, whereas it is relatively high in the 001 direction as well. In this paper, we report the results of our ab initio molecular dynamics simulations of the Cs3H(SeO4)2 superprotonic phase and propose an atomic-level mechanism of proton transport and pathways both in the (001) plane and along the 001 direction. It turned out that structural configurations formed by hydrogen-bonded tetrahedral anions during the proton diffusion are more complicated and diverse than those considered so far in the literature. Our predicted values of the proton conductivity and activation energy agree well with available experimental data. This validates the reliability of the computational results obtained.
The human body contains 60–70% water, depending on age. As a body fluid, it is not only a medium in which physical and chemical processes take place, but it is also one of the active mediators. Water ...is the richest substance with non-covalent hydrogen bonds. Water molecules, by themselves (in vacuum), are diamagnetic but when organized into clusters, they become diamagnetic or paramagnetic. Also, biomolecules (DNA, collagen, clathrin, and other proteins) have non-covalent hydrogen bonds in their structure. The interaction, as well as signal transmission, between water and biomolecules is achieved through the vibrations of covalent and non-covalent hydrogen bonds, which determine the state and dynamics of conformational changes in biomolecules. Disruptive conformational changes in biomolecules, cells, and tissues lead to their dysfunctionality, so they are a frequent cause of many disorders and diseases. For example, the rearrangement of hydrogen bonding due to mitochondrial disease mutation in cytochrome bc1 disturbs heme bH redox potential and spin state. In order to prevent and repair the dysfunctional conformational changes, a liquid substance was developed based on the second derivative of the Csub.60 molecule (SD-Csub.60), which has classical and quantum properties. The characterization of SD-Csub.60 by UV-VIS-NIR, FTIR, TEM, and AFM/MFM was performed and it is shown that SD-Csub.60 water layers generate vibrations with near-zero phase dispersion which are transmitted through Fibonacci’s water chains to biomolecules. In comparison with previously published SD-Csub.60 derivate (3HFWC, size until 10 nm, and 1–5 water layers), the improved formulation (3HFWC-W, size 10–25 nm, and 6–9 water layers) showed multiplied cytotoxic activity against melanoma cell lines of different aggressiveness. Apart from this, the mode of action was preserved and based on an induction of senescence rather than cell death. Importantly, high selectivity towards malignant phenotypes was detected. Observed effects can be ascribed to a machinery of hydrogen bonds, which are generated in SD-Csub.60 and transmitted through water to biomolecules. This approach may open a new field in science and healthcare—a “water-based nanomedicine”.
We show that the cooperative reinforcement between hydrogen bonds in guanine quartets is not caused by resonance‐assisted hydrogen bonding (RAHB). This follows from extensive computational analyses ...of guanine quartets (G4) and xanthine quartets (X4) based on dispersion‐corrected density functional theory (DFT‐D). Our investigations cover the situation of quartets in the gas phase, in aqueous solution as well as in telomere‐like stacks. A new mechanism for cooperativity between hydrogen bonds in guanine quartets emerges from our quantitative Kohn–Sham molecular orbital (MO) and corresponding energy decomposition analyses (EDA). Our analyses reveal that the intriguing cooperativity originates from the charge separation that goes with donor–acceptor orbital interactions in the σ‐electron system, and not from the strengthening caused by resonance in the π‐electron system. The cooperativity mechanism proposed here is argued to apply, beyond the present model systems, also to other hydrogen bonds that show cooperativity effects.
Separation leads to cooperation: Quantum chemical analyses show that telomere structures receive additional stabilization from cooperativity effects in guanine quartets (see graphic). This cooperativity derives directly from the charge separation across guanine bases, induced by the unidirectional donor–acceptor orbital interactions in the hydrogen bonds.
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