Understanding hydrogen-bond interactions in self-assembled lattice materials is crucial for preparing such materials, but the role of hydrogen bonds (H bonds) remains unclear. To gain insight into H-bond interactions at the materials’ intrinsic spatial scale, we investigated ultrafast H-bond dynamics between water and biomimetic self-assembled lattice materials (composed of sodium dodecyl sulfate and β-cyclodextrin) in a spatially resolved manner. To accomplish this, we developed an infrared pump, vibrational sum-frequency generation (VSFG) probe hyperspectral microscope. With this hyperspectral imaging method, we were able to observe that the primary and secondary OH groups of β-cyclodextrin exhibit markedly different dynamics, suggesting distinct H-bond environments, despite being separated by only a few angstroms. We also observed another ultrafast dynamic reflecting a weakening and restoring of H bonds between bound water and the secondary OH of β-cyclodextrin, which exhibited spatial uniformity within self-assembled domains, but heterogeneity between domains. The restoration dynamics further suggest heterogeneous hydration among the self-assembly domains. The ultrafast nature and meso- and microscopic ordering of H-bond dynamics could contribute to the flexibility and crystallinity of the material––two critically important factors for crystalline lattice self-assemblies––shedding light on engineering intermolecular interactions for self-assembled lattice materials.

VSFG (vibrational sum frequency generation) microscopy was used to study the SDS@2β-CD system, a synthetic capsid-like self-assembled material. We found because of strong hydrogen-bond interactions between water and the assemblies, water molecules are template to adopt the local mesoscopic ordering of the self-assemblies, which allows VSFG to probe water on nonflat interfaces. We show that the origin of the VSFG signal from the self-assembly is a combination of individual molecular chirality and highly coordinated ordering of the self-assembly, which gives rise of anisotropic signals, e.g., under SSS polarization. A similar strategy could be applied to other self-assembled materials composed by molecules without inversion symmetry. Using an imaging process, VSFG spectra of different self-assembly sheets were spatially resolved. We found heterogeneity among different domains, which can be attributed to variations in the hydration level of different domains. Since the SDS@2β-CD system is a synthetic lattice self-assembly, such heterogeneity could also exist in other natural lattice assemblies such as a virus and tubulin.

In nanoporous materials, guest-host interactions affect the properties and function of both adsorbent and adsorbate molecules. Due to their structural and chemical diversity, metal-organic frameworks (MOFs), a common class of nanoporous materials, have been shown to be able to efficiently and, often, selectively adsorb various types of guest molecules. In this study, we characterize the structure and dynamics of water confined in ZIF-90. Through the integration of experimental and computational infrared (IR) spectroscopy, we probe the structure of heavy water (D 2 O) adsorbed in the pores, disentangling the fundamental framework-water and water-water interactions. The experimental IR spectrum of D 2 O in ZIF-90 displays a blue-shifted OD-stretch band compared to liquid D 2 O. The analysis of the IR spectra simulated at both classical and quantum levels indicates that the D 2 O molecules preferentially interact with the carbonyl groups of the framework and highlights the importance of including nuclear quantum effects and taking into account Fermi resonances for a correct interpretation of the OD-stretch band in terms of the underlying hydrogen-bonding motifs. Through a systematic comparison with the experimental spectra, we demonstrate that computational spectroscopy can be used to gain quantitative, molecular-level insights into framework-water interactions that determine the water adsorption capacity of MOFs as well as the spatial arrangements of the water molecules inside the MOF pores which, in turn, are key to the design of MOF-based materials for water harvesting.File list (2) download file view on ChemRxiv water_in_zif90.pdf (4.99 MiB) download file view on ChemRxiv supporting_information.pdf (4.44 MiB)

Water capture mechanisms of zeolitic imidazolate framework ZIF-90 are revealed by differentiating the water clustering at interior interfaces of ZIF-90 and the center pore filling step, using vibrational sum-frequency generation spectroscopy (VSFG) at a one-micron spatial resolution. Spectral lineshapes of VSFG and IR spectra suggest that OD modes of heavy water in both water clustering and center pore filling steps experience similar environments, which is unexpected as weaker hydrogen bond interactions are involved in initial water clustering at interior surfaces. VSFG intensity shows similar dependence on the relative humidity as the adsorption isotherm, suggesting that water clustering and pore filling occur simultaneously. MD simulations based on MB-pol corroborate the experimental observations, indicating that water clustering and center pore filling happen nearly simultaneously within each pore, with water filling the other pores sequentially. The integration of nonlinear optics with computational simulations provides critical mechanistic insights into the pore filling mechanism that could be applied to the rational design of future MOFs.

<div> <div> <div> <p>In nanoporous materials, guest–host interactions affect the properties and function of both adsorbent and adsorbate molecules. Due to their structural and chemical diversity, metal-organic frameworks (MOFs), a common class of nanoporous materials, have been shown to be able to efficiently and, often, selectively adsorb various types of guest molecules. In this study, we characterize the structure and dynamics of water confined in ZIF-90. Through the integration of experimental and computational infrared (IR) spectroscopy, we probe the structure of heavy water (D₂O) adsorbed in the pores, disentangling the fundamental framework–water and water–water interactions. The experimental IR spectrum of D₂O in ZIF-90 displays a blue-shifted OD-stretch band compared to liquid D₂O. The analysis of the IR spectra simulated at both classical and quantum levels indicates that the D₂O molecules preferentially interact with the carbonyl groups of the framework and highlights the importance of including nuclear quantum effects and taking into account Fermi resonances for a correct interpretation of the OD-stretch band in terms of the underlying hydrogen-bonding motifs. Through a systematic comparison with the experimental spectra, we demonstrate that computational spectroscopy can be used to gain quantitative, molecular-level insights into framework–water interactions that determine the water adsorption capacity of MOFs as well as the spatial arrangements of the water molecules inside the MOF pores which, in turn, are key to the design of MOF-based materials for water harvesting.</p> </div> </div> </div>