The physicochemical properties of phosphate glasses are strongly influenced by the modifier cation-oxygen bonding interaction and the spatial distribution of modifier cations, yet direct experimental insight into these structural-chemical aspects remains limited. In this work, we present a comprehensive multinuclear (31P and 17O) NMR study of single- and mixed-modifier metaphosphate glasses containing alkali (Li, Na, Rb) and alkaline-earth (Mg, Ca, Ba) cations with identical nominal network connectivity. The 31P magic-angle-spinning (MAS) NMR spectra confirm that the network structure of these glasses is dominated by Q2 phosphate units, while 17O MAS and triple-quantum MAS (3QMAS) NMR provide an oxygen-centric view of bridging (BO) and nonbridging oxygen (NBO) environments and elucidate their interactions with the modifier cations. A relationship between the 17O quadrupolar asymmetry parameter and the P-O-P bond angle is established using ab initio calculations, enabling extraction of the bond-angle distribution (BAD) directly from experimental 17O 3QMAS NMR data. These distributions show increased disorder in the P-O-P BAD with increasing modifier field strength, consistent with enhanced chain folding/coiling effects. Analysis of 17O 3QMAS isotropic line shapes in single- vs mixed- modifier glasses in conjunction with bond-valence considerations indicates that the mixing between alkali and alkaline-earth cations are more uniform, while that between dissimilar alkali cations is more random. Such cation mixing behavior appears to be controlled by the structural preference to maximize a uniform spatial charge distribution and to play a key role in controlling the dependence of the glass transition and ionic transport behavior on the modifier compositional makeup.

Cryptococcus neoformans and Cryptococcus gattii are fungal pathogens that cause life-threatening infections, including cryptococcal meningitis. A distinctive feature of the cryptococcal cell wall is the extensive deacetylation of chitin to chitosan, a modification that is essential for virulence but whose structural role in cell-wall organization remains poorly understood. Here, we analyzed the cell walls of wild-type strains of both species and their avirulent chitosan-deficient mutants, which serve as vaccine candidates. Loss of chitosan disrupted cell morphology and altered cell-wall ultrastructure, with more pronounced defects in C. neoformans. Solid-state NMR revealed that aggregated α-1,3-glucans form the principal rigid domain of the cell wall in both species and are closely associated with chitin microfibrils, whereas surrounding β-glucans and mannoproteins constitute a more dynamic matrix. Chitosan modulates hydration and flexibility, and its loss increases chitin exposure and triggers species-specific remodeling of the polysaccharide network. In C. neoformans, chitosan depletion increased α-1,3-glucan content and reduced β-glucan levels, whereas C. gattii selectively lost one α-1,3-glucan subtype while maintaining β-glucan levels. Although capsule production remained intact, chitosan deficiency altered glucuronoxylomannan linkage patterns and mannoprotein composition. These findings reveal how chitosan organizes cryptococcal cell-wall architecture and highlight distinct structural adaptation strategies among pathogenic Cryptococcus species.

Metal-organic frameworks (MOFs) are promising drug carriers due to their high porosity and diverse functionalities. The interactions between MOFs and drug molecules play a crucial role in drug delivery, influencing both the loading capacity and release kinetics. In this work, we report the design and synthesis of a zirconium-based MOF (Zr-IDA), obtained by replacing the hydrophobic 2,6-naphthalenedicarboxylate (NDC) ligand in DUT-52 with a hydrophilic indole-2,5-dicarboxylate (IDA) linker. Zr-IDA exhibits a structure similar to that of DUT-52 but achieves a significantly higher loading of 5-fluorouracil (5-Fu), reaching 0.676 g/g, an increase of 100.5% compared to DUT-52 (0.337 g/g) under identical conditions. Moreover, Zr-IDA provides a much slower release profile: complete release of 5-Fu requires 6 days, whereas DUT-52 releases the same payload in only 1.5 days. To elucidate the enhanced host-guest interactions in 5-Fu@Zr-IDA, multinuclear solid-state NMR (SSNMR) experiments were conducted to probe the local structure. One-dimensional 19F, 13C, and 1H MAS SSNMR spectra confirm successful incorporation of 5-Fu within the pores of Zr-IDA. Two-dimensional 1H-1H SQ-SQ and 1H-19F HETCOR SSNMR reveal that 5-Fu molecules reside near the IDA linkers and Zr metal centers, stabilized by cooperative hydrogen bonding between the fluorine atom of 5-Fu molecules and Zr-coordinated hydroxyl groups, as well as IDA NH sites. Density functional theory calculations further support the experimental findings, identifying two major preferred 5-Fu adsorption sites within the octahedral and tetrahedral pores.

Homogeneous glass formation in binary rare-earth silicate systems has thus far been precluded due to the presence of extensive liquid-liquid immiscibility and a strong tendency of these liquids toward crystallization. In this study, we demonstrate homogeneous glass formation in the Sc2O3-SiO2 binary system within a narrow compositional window (37-39 mol% Sc2O3) near a deep eutectic between the compounds Sc2Si2O7 and Sc2SiO5, using containerless laser melting under aerodynamic levitation. The atomic structure of these unusual glasses is investigated using multinuclear (29Si, 45Sc, 17O) solid-state nuclear magnetic resonance (NMR) and Raman spectroscopy. The spectroscopic results, when taken together, provide a comprehensive picture of the structure of these glasses characterized by pyrosilicate [Si2O7]6- anionic units interconnected by Sc cations in ScO6 coordination polyhedra, via Si-O-Sc linkages. A significant fraction (similar to 6%) of the oxygen atoms in the structure is present as free oxide (FO) ions in Sc-O-Sc linkages, providing connectivity between the ScO6 polyhedra. The formation of the FO species via oxygen disproportionation reaction is promoted by the uniquely high field strength of the Sc3+ ions, and the resulting structural frustration is hypothesized to suppress crystallization of the stable pyrosilicate phase in these liquids, enabling glass formation in an otherwise non-glass-forming binary system. These findings highlight the critical role of rare-earth cation field strength in controlling oxygen speciation, structure, and glass-forming ability in this binary silicate system.

In this study, we have established an empirical 25Mg chemical shift scale for silicates based on experimentally determined isotropic shift δiso values for Mg sites in crystalline compounds spanning coordination numbers from four to eight. These data reveal a robust linear correlation between δiso and the average Mg-O bond distance in the coordination polyhedra, defining approximate δiso ranges of 50 to 30, 27 to 17, 17 to -5, and ≤ -15 ppm for MgIV, MgV, MgVI, and MgVIII environments, respectively. This scale is applied to a comprehensive slice-by-slice analysis of previously reported ultra-high field (35.2 T) 25Mg 3QMAS NMR spectra of three glasses of composition CaMgSi2O6, Na2MgSi3O8, and K2MgSi5O12, revealing a positive correlation between the quadrupolar coupling constant CQ and δiso within two structurally distinct Mg environments assignable to MgVI and MgIV. Quantitative analysis indicates that ∼70-75% of Mg is present as MgIV in all three glasses, yielding an average Mg-O coordination number of ∼4.6 for CaMgSi2O6 glass, in close agreement with the value of ∼4.4 reported in a recent isotope-substituted neutron diffraction study. The finding of the lack of any significant dependence of the Mg-O coordination number on the field strength of the second network modifying cation in these glasses is in sharp contrast with previous reports of a preference of Mg for fourfold coordination in silicate glasses containing low field strength alkali cations.

The A beta peptide contributes to Alzheimer's disease through various mechanisms, including cell membrane disruption. While the fibrillar structure of A beta(1-42) in aqueous medium has been elucidated, its oligomer structure remains elusive. We have combined Fourier transform infrared (FTIR) spectroscopy, transmission electron microscopy (TEM), solid-state NMR (ssNMR), and molecular dynamics (MD) approaches to achieve a structural model for A beta(1-42) octamer in lipid bilayers. FTIR data identify conformational transitions of A beta(1-42) to a stable beta-sheet structure. ssNMR analysis allows assignment of 38 out of 42 A beta(1-42) residues, with three additional inter-residue contacts to define the tertiary fold. Combined, MD simulations produce a structural model of A beta(1-42) octamers in a novel sushi-roll fold of in-register cross-beta motif with a lipid-filled internal cavity. The membrane-embedded structure of A beta(1-42) and the mode of peptide-lipid interactions provide a better understanding of A beta neurotoxicity.

Pressure and mechanical forces during pharmaceutical manufacturing can induce solid-phase transformations of active pharmaceutical ingredients (APIs), posing risks to product quality. Here, we report the structural characterization of a metastable high-pressure polymorph of the multi-component GDC-0022 tosylate salt formed under applied pressure of 250 MPa. The crystal structure of the high-pressure polymorph is determined with a combination of 1H, 14N and 19F solid-state NMR (SSNMR) spectroscopy and crystal structure prediction (CSP). Distinct 1H and 19F SSNMR signals, longitudinal relaxation time (T 1) measurements, and 2D 19F spin-diffusion spectra confirm that the high- and low-pressure forms coexist as separate crystalline domains. 2D 19F{1H} hetero-nuclear correlation (HETCOR) and 1H double-quantum single-quantum (DQ-SQ) NMR spectra resolve key 1H NMR signals of each phase, while 1H{14N} J-HMQC experiments establish that the high-pressure form retains salt character, with one nitrogen atom remaining protonated. CSP combined with DFT GIPAW chemical shift calculations identifies a high-density polymorph consistent with the experimental 1H and 19F chemical shifts. These results demonstrate that NMR crystallography can deconvolute complex polymorphic mixtures and provide a practical framework for managing pressure-induced phase transitions in drug manufacturing.

Some metal organic-inorganic complexes (MOICs) are known for their glass-forming ability. However, the composition range of glass-forming MOICs is rather limited as the mechanism of MOIC glass formation has not been well understood. Here, we uncover the structural factors controlling MOIC glass formation and thereby develop new MOIC glass formers. MOIC glass formation relies on the creation of a hydrogen-bonded structural network. By properly choosing metal centers, anions, and organic ligands of MOICs, a supramolecular structural network can be constructed, thereby allowing property modulation. Furthermore, MOIC systems with mixed crystals are generated by ligand-mixing and then vitrified by melt-quenching. The glass-transition temperature (T g) of the derived glasses can be linearly tuned through the substitution of benzimidazole for imidazole. Interestingly, vitrification led to disordering of hydrogen-bonded networks in MOICs at short-, medium-, and long-range scales. This work enables the expansion of the composition range of MOIC glasses with various functionalities.

Some zeolitic imidazolate frameworks (ZIFs) represent a new family of glass formers, with hitherto unknown photonic functionalities. In this work, we report the discovery of broadband white light emission in ZIF-62, achieved through a vitrification-pressurization-annealing strategy. In this strategy, visible (blue) light emission was realized after the vitrification of ZIF-62,  subsequently enhanced and broadened upon pressurization. Additionally, a sharp redshift (37 nm) of the emission peak occurred in pressurized ZIF-62 glass as the annealing temperature exceeded a critical annealing temperature (1.07Tg). This implies that the photoluminescence of ZIF-62 can be precisely tailored. The photoluminescence quantum yield of ZIF-62 glass reached 12.2% after annealing at 1.13Tg for 30 min. The origin of the observed phenomena was revealed by conducting structural analyses. Based on the annealed ZIF-62 glass with the best photoluminescent performance, a white light-emitting diode (LED) was fabricated, which exhibited a luminous efficacy of 4.2 lm/W and a high operational stability, i.e., retaining 36.8% of the efficacy after 72 h of operation. This work demonstrated the feasibility of the development of one-component white LEDs by utilizing the annealed ZIF-62 glass.

Bismuth- and iodine-containing metal-organic frameworks (MOFs) are crucial in catalysis, gas adsorption, and luminescence, with local environments of Bi and I ions shaping their performance. Using 209Bi and 127I solid-state NMR (SSNMR) for characterization is extremely challenging due to the exceedingly large quadrupolar interactions in MOFs. Here, we present ultra-wideline (UW) SSNMR spectra of eight MOFs acquired at ultra-high magnetic fields up to 36 T, with breadths of 8-50 MHz, revealing very large quadrupolar couplings. These spectra uncover key structural details, including dehydration, guest adsorption, phase transitions, and disorder. This study establishes 209Bi and 127I UW SSNMR as powerful tools for probing Bi and I ions in weight-dilute systems, offering broad applications in catalysis, solar cells, biochemistry, and beyond.

Oxygen is an integral component of proteins and nucleic acids, but remains sparsely studied in such samples because its only NMR active isotope, 17O, is a low sensitivity and resolution species. These properties are a consequence of its low natural abundance (0.039%) and the fact that 17O is a S = 5/2 nuclide with large quadrupolar couplings (6-11 MHz). In this work, we address these issues with efficient isotopic labeling, high magnetic fields, fast magic-angle spinning and indirect 1H detection. This combination of refinements, in conjunction with multidimensional heteronuclear correlation experiments, improves sensitivity and permits observation of oxygen sites specific to each amino acid residue in a model dipeptide sample in a manner consistent with the goal of high resolution. In particular, double-quantum cross-polarization at high sample spinning frequencies is found to provide efficient polarization transfer between 13C and 17O nuclei. Notably, the use of 17O as the initial source of polarization for experiments, as opposed to 1H, is found to be advantageous in terms of sensitivity per unit time due to the short 17O T1 relaxation. Additionally, the second-order quadrupolar broadening in the 17O dimension is averaged by incorporation of a low-power multiple-quantum sequence to yield sharp isotropic peaks. Comparison of isotropic and anisotropic 17O spectra allows extraction of quadrupolar parameters for each oxygen site. Finally, the high 17O resolution obtained is used in 3D experiments in combination with 13C polarization transfers and subsequent 1H detection to demonstrate the potential to determine sequential assignments and long range distance restraints. Collectively, these results suggest that 17O correlation spectroscopy can become an essential tool in the repertoire of techniques for biomolecular structure determination with the backbone 17O that has not yet been fully utilized.

The Mo-O coordination environment is probed in a series of simple and complex crystalline alkali molybdates as well as in mixed-alkali molybdate glasses using high-field (18.8 and 20.0 T) 95Mo magic-angle-spinning (MAS) and multiple-quantum MAS (MQMAS) nuclear magnetic resonance (NMR) spectroscopy. When taken together, the 95Mo NMR spectroscopic results indicate that somewhat contrary to the conventional wisdom the corner- and edge-shared MoO6 octahedral sites in these alkali molybdates are characterized by higher values of the isotropic shift (delta iso) and quadrupolar coupling constant (C Q) compared to the MoO4 tetrahedral sites. These trends are hypothesized to be related to the unusually strong distortion of MoO6 octahedra in corner- and edge-shared configurations and the resulting increase in the paramagnetic component of the chemical shift. While the 95Mo C Q of the MoO4 sites displays an approximately linear positive correlation with the degree of tetrahedral distortion, no such correlation is observed for the MoO6 sites. High-resolution 95Mo NMR spectra show the coexistence of tetrahedral and octahedral Mo-O environments in the structure of alkali molybdate glasses, with the relative fraction of the latter environment increasing with Mo content. The results presented in this study indicate that high-resolution 95Mo NMR spectroscopy at high magnetic fields (similar to 20 T or higher) may prove to be a promising tool for investigating the Mo-O coordination environments in nuclear waste glasses.

1,3-Diketone molecules existing in their cis-keto-enol tautomeric forms in the solid state are classic examples that contain low-barrier hydrogen bonds (LBHBs) of the O-H···O type. We report experimental observations of H/D isotope shifts in 13C and 17O solid-state nuclear magnetic resonance (NMR) spectra of three representative 1,3-diketone molecules: dibenzoylmethane, benzoylacetone, and curcumin. While there are several examples of H/D isotope shifts in solid-state 13C NMR spectra in the literature, this study reports on the first observation of such H/D isotope shifts in solid-state 17O NMR spectra. We found that the H/D isotope shifts in dibenzoylmethane are considerably larger than those in benzoylacetone and curcumin. To aid interpretation of the observed H/D isotope shifts, we performed direct 1H-17O distance measurement using two-dimensional 17O/1H quadrupole-dipole correlation NMR spectroscopy. The results of 1H-17O distance measurements provided direct evidence about the "location" of the enol hydrogen atom in the 17O···1H···17O LBHBs. We demonstrated that H/D isotope shifts in solid-state 17O NMR and 1H-17O distance measurement are two new ways of probing the nature of LBHBs. Our new solid-state 17O NMR results are discussed in connection to nuclear quantum effects (i.e., the potential energy curve, zero-point energy, and nuclear wave function) and high-quality structural data available for these compounds in the literature.

Defect engineering in metal-organic frameworks (MOFs) offers a promising approach to modify material properties by introducing controlled structural imperfections. Zr-based MOFs, particularly the well-known UiO-66, hold significant potential for diverse applications. Defects in UiO-66 can be generated using monocarboxylic acids as modulators, among other methods. However, resolving the atomic-level local structures of these defects remains a considerable challenge. In this study, the local structures of these defects are carefully characterized by multinuclear solid-state NMR spectroscopy (SSNMR) in combination with X-ray absorption fine structure (XAFS). In situ heating XAFS analyses at Zr K-edge reveal critical changes in the local structure of Zr during the removal of trifluoroacetic acid (TFA), including the decreased Zr-O coordination numbers and alterations in Zr-Zr bond distances. Multinuclear 1H, 13C, 19F, 35/37Cl, 17O solid-state NMR methods are used to identify capping species and defect-associated species. Subsequently, the engineered defects are found to significantly improve the catalytic performance of Pt nanoparticles (NPs) integrated into the defective UiO-66 framework. Pt-UiO-66 with defects exhibits much improved hydrogen evolution reaction (HER) activity and stability compared to the Pt-UiO-66 without defects.

Solid-state NMR methods with high resolution and sensitivity are presented for identification and charaterization of hydrogen-bonded 15N/17O atomic pairs in peptide samples. Indirect 1H detection under fast magic-angle spinning, and the stronger 1H-15N and 1H-17O couplings are leveraged to significantly improve sensitivity over previous methods that use direct 15N-17O interactions.

Zeolitic imidazolate framework (ZIF) glasses represent a newly emerged class of melt-quenched glasses, characterized by their intrinsic nanoporous structure, good processability, and multifunctionalities such as gas separation and energy storage. However, creating photonic functionalities in Zn-based ZIF glasses remains elusive. Here we show a remarkable broadband white light-emitting behavior in a Zn-based ZIF glass, which can be enhanced by annealing. Furthermore, we discovered a sharp red shift upon increasing annealing temperature above the critical temperature of 1.07Tg, where Tg is the glass transition temperature, for a short duration of 30 min. Finally, we achieved a high absolute internal photoluminescence quantum yield of 12.2

Metal inorganic-organic complex (MIOC) crystals are a new category of hybrid glass formers. However, the glass-forming compositions of MIOC crystals are limited due to lack of both a general design principle for such compositions and a deep understanding of the structure and formation mechanism for MIOC glasses. This work reports a general approach for synthesizing glass-forming MIOC crystals. In detail, the principle of this approach is based on the creation of hydrogen-bonded structural network by substituting acid anions for imidazole or benzimidazole ligands in the tetrahedral units of zeolitic imidazolate framework crystals. By tuning the metal centers, anions, and organic ligands of MIOCs, supramolecular unit structures can be designed to construct supramolecular networks and thereby enable property modulation. Furthermore, mixed-ligand synthesis yielded a mixed-crystal system in which the glass-transition temperature (Tg) can be linearly tuned from 282 K to 360 K through gradual substitution of benzimidazole for imidazole. Interestingly, upon vitrification, MIOCs were observed to undergo reorganization of hydrogen-bonded networks, with retention of tetrahedral units, short-range disorder, and the freezing of multiple conformations. This work offers a new strategy to systematically expand the glass-forming compositional range of MIOCs and to develop functional MIOC glasses.

An efficient experiment for 1H/17O heteronuclear correlation is presented, combining forward-and-back cross-polarization and low-power cosine multiple-quantum magic-angle spinning methods. Double cross-polarization (DCP) is compared with the heteronuclear multiple-quantum correlation (HMQC) method. Both experiments are applicable in instances of enhanced proton polarization such as with dynamic nuclear polarization. Under fast magic-angle spinning, cross-polarization becomes a viable method for polarization transfer and provides an order of magnitude enhancement over HMQC. In particular, it is observed that faster sample spinning opens up regions of rf fields optimal for spin-locking and cross-polarization with much less T2 signal loss. The incorporation of multiple-quantum magic-angle spinning enables high 17O isotropic resolution via proton detection.

Nuclear magnetic resonance (NMR) spectroscopy is an integral structure determination technique for chemists, biologists and materials scientists. The determination of atomic-level structures using solid-state NMR spectroscopy in concert with other experimental and computational approaches is dubbed NMR crystallography. This chapter provides an overview of experimental solid-state NMR approaches with a specific emphasis on fundamental one-dimensional (1D) and advanced double resonance solid-state NMR methods including two-dimensional (2D) heteronuclear correlation spectroscopy and measurement of heteronuclear dipolar and scalar couplings that are commonly used for determining the structures of organic compounds and materials.

Characterization of metal centers in metal-organic frameworks (MOFs) is critical for rational design and further understanding of structure-property relationships. The short-range structure about Zr atoms is challenging to properly elucidate in many Zr MOFs, particularly when local disorder is present. Static 91Zr solid-state NMR spectra of the seven zirconium MOFs UiO-66, UiO-66-NH2, UiO-67, MOF-801, MOF-808, DUT-68 and DUT-69 have been acquired at high magnetic fields of 35.2 T and 19.6 T, yielding valuable information on the local structure, site symmetry and order about Zr. 91Zr NMR is very sensitive to differences in MOF short-range structure caused by guest molecules, linker substitution and post-synthetic treatment. Complementary density functional theory (DFT) calculations assist in the interpretation and assignment of 91Zr solid-state NMR spectra, lend insight into structural origins of 91Zr NMR parameters and enable determination of local Zr coordination environments. This approach can be extended to many other materials containing zirconium.