Advanced Solid-state NMR Techniques Research Articles

Atomic-Scale Resolution Insights into Structural and Dynamic Differences between Ofloxacin and Levofloxacin.

This study employs advanced solid-state NMR techniques to investigate the atomic-level structure and dynamics of two enantiomers: ofloxacin and levofloxacin. The investigation focuses on critical attributes, such as the principal components of the chemical shift anisotropy (CSA) tensor, the spatial proximity of 1H and 13C nuclei, and site-specific 13C spin-lattice relaxation time, to reveal the local electronic environment surrounding specific nuclei. Levofloxacin, the levo-isomer of ofloxacin, exhibits higher antibiotic efficacy than its counterpart, and the dissimilarities in the CSA parameters indicate significant differences in the local electronic configuration and nuclear spin dynamics between the two enantiomers. Additionally, the study employs the 1H-13C frequency-switched Lee-Goldburg heteronuclear correlation (FSLGHETCOR) experiment to identify the presence of heteronuclear correlations between specific nuclei (C15 and H7 nuclei and C13 and H12 nuclei) in ofloxacin but not in levofloxacin. These observations offer insights into the link between bioavailability and nuclear spin dynamics, underscoring the significance of NMR crystallography approaches in advanced drug design.

Compositions, Structures, and Properties of Mesoporous-Fe,N-Containing Carbon Materials for Oxygen- and Sulfur-Reduction Electrocatalysts

Mesoporous N- and Fe,N-carbon materials, prepared by polymerization of small molecule precursors and subsequent pyrolysis, exhibit high and accessible surface areas, high electrical conductivities, and high electrocatalytic activities that are comparable to more expensive activated-carbon-supported precious-metal (Pt) fuel cell electrocatalysts. Their favorable properties are due to a combination of factors, including high nitrogen contents that increase the number of active moieties, selective formation of certain types of N moieties at surface sites, relatively large (3 nm) mesopores to promote facile diffusion, and sufficient electron conductivity to surface N environments where the reactions occur. The resulting materials exhibit electrocatalytic properties that are comparable to a standard catalyst containing 20 wt% Pt supported on activated carbon. This is evident in Figure 1a, which shows current-voltage plots associated with the reduction of oxygen for 20 wt% Pt-C and for various N- and Fe,N-mesoporous carbon materials that were prepared identically except for the use of different mesostructured porogen templates. These results show that the oxygen reduction activities of the mesoporous N-carbons are significantly higher when a ZnCl2/NaCl salt mixture is used to produce mesoporosity, compared to mesoporous silica. In addition, the incorporation of a small amount (0.5 wt%) of Fe in the mesoporous N-carbon greatly improves oxygen reduction reactivity, which is shown to be superior to the commercial 20 wt% Pt-C. Similarly favorable activities and trends are observed for these materials as electrocatalysts for sulfur reduction.While the inclusion of N heteroatoms has previously been demonstrated to improve the reduction activities of carbon-based electrocatalysts,1 the atomic-level origins of such properties have remained elusive. This has been due to the multicomponent and non-stoichiometric compositions of these porous graphitic solids, their complicated distributions of disordered and ordered regions, and their paramagnetic and/or conductive properties. Nevertheless, advanced solid-state NMR techniques, in combination with Raman spectroscopy, X-ray diffraction, electron microscopy, and DFT modeling, yield detailed new insights on the atomic environments and interactions of N heteroatoms in mesoporous N-carbon electrocatalysts.2 Most importantly, two-dimensional (2D) 13C-15N correlation NMR spectra resolve distinct signals that enable the types and distributions of different N heteroatom environments to be established and correlated with electrocatalytic properties. For example, as shown in Figure 1b, the distributions of correlated of 15N and 13C signals in the 2D contour-plot spectrum of the salt-templated mesoporous N-carbon material manifest at least four distinct types of N-heteroatom environments: pyrrolic (purple), graphitic (blue), edge/isolated pyridinic (yellow), and pyrazinic/pyridinic (red) moieties. Green-shaded regions indicate correlated signals that arise from atomically proximate (<1 nm) moieties. These assignments are corroborated by DFT calculations to determine the chemical shieldings of different N-carbon moieties, which are shown as points overlaying the experimental 2D spectrum. Similar 2D spectra acquired for silica-templated mesoporous N-carbons yield different quantities and distributions of these N-carbon moieties, which account for the significantly different (lower) macroscopic oxygen reduction activities (Figure 1a). Furthermore, 1D 15N{1H} CP-MAS NMR spectra enable surface N species to be selectively distinguished from interior moieties (e.g., graphitic N) by the formers’ interactions with adsorbed water. In combination, these powerful multi-nuclear NMR analyses unambiguously establish that certain types of N-carbon moieties are more important to electrocatalytic performance than others.Incorporation of non-precious transition metals, such as Fe, significantly increases electrocatalytic activity.3,4 This is similarly the case for mesoporous N-carbon materials investigated here that were synthesized under otherwise identical conditions, except for the addition of a small (0.5 wt%) Fe (Figure 1a). The important role(s) of Fe, however, are challenging to establish, due to its generally dilute loading and its paramagnetic (and possibly ferromagnetic) properties. Nevertheless, 57Fe Mössbauer spectra, solid-state 15N NMR spectra, and 15N spin-lattice (T 1) relaxation time analysesresolve 15N signals from 15N species that are proximate to paramagnetic Fe heteroatoms, from which 15N-Fe distances are estimated. These analyses provide detailed new insights into the types, atomic environments, and distributions of 15N heteroatoms in mesoporous N- and Fe,N-carbon materials, which, until now, have been infeasible to distinguish by scattering or other spectroscopic techniques. Understanding the roles of these moieties in the catalytic reduction of oxygen or sulfur is expected to yield new design criteria for syntheses of high performance non-precious-metal electrocatalysts for diverse fuel cell and battery applications. References (1) Gong, K.; et al. Science 2009, 323, 760–764.(2) Becwar, S. M.; et al. submitted.(3) Donghun, K.; et al. ACS Appl. Mater. Interfaces 2018, 10, 25337−25349.(3) Al-Zoubi, T.; et al. J. Am. Chem. Soc. 2020, 142, 5477–5481. Figure 1

Solid-state NMR study of adsorbed water molecules in covalent organic framework materials

Abstract This study investigates the locations and interactions of adsorbed water molecules within a porous COF material, TpPa-1. The TpPa-1 samples include the as-synthesized powder samples and the samples first subjected to compression at high pressure and then ground into a powder form. The investigation applies a variety of advanced solid-state NMR techniques. The results indicate that the adsorbed water molecules in the as-synthesized and compressed samples can exist in different locations and bonding states. Here, the adsorbed water molecules in the as-synthesized samples are found to be mainly located in the pore spaces and interact only loosely with the chemical groups of the material. In contrast, a proportion of the water molecules in the compressed samples enter into the interstices between the layers and interact with the amino groups and the carbonyl groups of the material. The relocation of the water molecules in the compressed samples provides a plausible explanation for the molecular origin of the water adsorption capability of TpPa-1. In addition, the revealed weak interactions between the water molecules and the chemical groups of TpPa-1 are correlated with the molecular origin of the high water permeance.

A Multi-Technique Experimental and Computational Approach To Study the Dehydration Processes in the Crystals of Endomorphin Opioid Peptide Derivative

When molecular crystals undergo partial dehydration, determining the crystal contents and precise localization of the remaining water in the crystal lattice becomes challenging, especially when the quality of crystals after dehydration is not suitable for X-ray diffraction studies. In this work, we describe a methodology that allows the determination and refinement of the structures of partially dehydrated crystals employing complementary experimental (advanced solid-state NMR techniques, differential scanning calorimetry, elemental analysis) and computational (gauge-including projector-augmented wave density functional theory) techniques. We present the power of the methodology using an opioid peptide derivative, endomorphin-2-OH (EM2-OH) heptahydrate. The advanced solid state NMR techniques 2D-PASS, inv-HETCOR, and cross polarization variable contact (CP-VC) carried out with very fast magic angle spinning were used as a source of the constraints showing differences and similarities in the structures and local molecular dynamics for crystallized and dehydrated samples. A crystal structure prediction employing the gauge-including projector-augmented wave (GIPAW) method was used for the determination and refinement of dehydrated EM2-OH. After dehydration, three out of the initial seven water molecules remain in the lattice of the EM2-OH crystals, with two water molecules located in the pockets made by the pseudocyclic conformations and one forming a bridge between two independent EM2-OH molecules.

Novel Phenanthrene Sorption Mechanism by Two Pollens and Their Fractions.

A pair of pollens (Nelumbo nucifera and Brassica campestris L.) and their fractions were characterized by elemental analysis and advanced solid-state (13)C NMR techniques and used as biosorbents for phenanthrene (Phen). Their constituents were largely aliphatic components (including sporopollenin), carbohydrates, protein, and lignin as estimated by (13)C NMR spectra of the investigated samples and the four listed biochemical classes. The structure of each nonhydrolyzable carbon (NHC) fraction is similar to that of sporopollenin. The sorption capacities are highly negatively related to polar groups largely derived from carbohydrates and protein but highly positively related to alkyl carbon, poly(methylene) carbon, and aromatic carbon largely derived from sporopollenin and lignin. The sorption capacities of the NHC fractions are much higher than previously reported values, suggesting that they are good sorbents for Phen. The Freundlich n values significantly decrease with increasing concentrations of poly(methylene) carbon, alkyl C, aromatic moieties, aliphatic components, and the lignin of the pollen sorbents, suggesting that aliphatic and aromatic structures and constituents jointly contribute to the increasing nonlinearity. To our knowledge, this is the first investigation of the combined roles of alkyl and aromatic moiety domains, composition, and accessibility on the sorption of Phen by pollen samples.

Advanced solid-state NMR techniques for characterization of membrane protein structure and dynamics: Application to Anabaena Sensory Rhodopsin

Studies of the structure, dynamics, and function of membrane proteins (MPs) have long been considered one of the main applications of solid-state NMR (SSNMR). Advances in instrumentation, and the plethora of new SSNMR methodologies developed over the past decade have resulted in a number of high-resolution structures and structural models of both bitopic and polytopic α-helical MPs. The necessity to retain lipids in the sample, the high proportion of one type of secondary structure, differential dynamics, and the possibility of local disorder in the loop regions all create challenges for structure determination. In this Perspective article we describe our recent efforts directed at determining the structure and functional dynamics of Anabaena Sensory Rhodopsin, a heptahelical transmembrane (7TM) protein. We review some of the established and emerging methods which can be utilized for SSNMR-based structure determination, with a particular focus on those used for ASR, a bacterial protein which shares its 7TM architecture with G-protein coupled receptors.

Study of the Mechanism of Thermal Chemical Processes in the Crystals of YAF Tripeptides by Means of Mass Spectrometry and Solid State NMR

Thermal reactions in two Tyr-Ala-Phe (YAF) tripeptide crystals with different molecular packing (monoclinic and hexagonal), distinct stereochemistry of central amino acid (D or L alanine) and specific arrangement of molecules in the crystal lattice (head-to-tail) were investigated. Samples were heated up to 180 °C, while the melting point for YAF crystals is above the 220 °C. Below the melting temperature, in both cases the chemical reactions leading to formation of cyclic dipeptides (YA diketopiperazine) and leaving of phenylalanine were observed. Two possible mechanisms of chemical reaction in the crystal lattice assuming intra- and/or intermolecular pathways were considered. (13)C and (15)N enriched YAF samples were employed to study of mechanism of solid state reactivity using mass spectrometry and advanced solid state NMR techniques (2D DARR (Dipolar Assisted Rotational Resonance) and 2D Double CP (Cross-Polarization) correlations).

Hydrogen bond interaction and dynamics in PMMA/PVPh polymer blends as revealed by advanced solid-state NMR

The hydrogen bond interactions and dynamics of the poly (methyl methacrylate) (PMMA) and poly (4-vinyl phenol) (PVPh) polymer blends were studied by a variety of advanced solid-state NMR techniques. The possible hydrogen bond interactions between the carbonyl group of PMMA and hydroxyl group of PVPh were successfully elucidated by two-dimensional 1H–1H spin-exchange 13C–1H heteronuclear chemical-shift correlation (HETCOR) NMR experiment. The 13C 2D separation of undistorted powder patterns by effortless recoupling (SUPER) experiments combined with quantum chemical calculations for the theoretical predictions of chemical-shift anisotropy (CSA) parameters were utilized to investigate the intermolecular hydrogen-bonding interactions and molecular conformation of the blends. 13C–1H PISEMA (polarization inversion and spin-exchange at magic angle) experiments at different temperatures were used to reveal the heterogeneous dynamics resulting from the cooperative motion associated with the hydrogen bond interaction. PISEMA analysis shows that the motion of aromatic group in PVPh is affected by the rotating motions of methyl in PMMA.

Characterization of Wood Chars Produced at Different Temperatures Using Advanced Solid-State 13C NMR Spectroscopic Techniques

Temperature is one of the controlling factors determining the chemical structure of char. We employed advanced solid-state 13C NMR techniques to characterize maple wood and its chars produced under...

Defect Structures in Aluminosilicate Single-Walled Nanotubes: A Solid-State Nuclear Magnetic Resonance Investigation

We report a detailed investigation of the defect structures in aluminosilicate single-walled nanotubes via multiple advanced solid-state NMR techniques. A combination of 1H–29Si and 1H–27Al FSLG-HETCOR, 1H CRAMPS, and 1H–29Si CP/MAS experiments were employed to evaluate the proton environments around Al and Si atoms in the final nanotube structure. The 1H CRAMPS spectra of dehydrated aluminosilicate nanotubes revealed the proton environments in great detail. Integration of these results with the findings from the 1H–29Si and 1H–27Al FSLG-HETCOR and 1H–29Si CP/MAS data allows the structural assignment of all the chemical shifts and the identification of various types of defect structures in the aluminosilicate nanotube wall. In particular, we identify five main types of defect structures arising from specific atomic vacancies in the nanotube structure. It is estimated that ∼16% of Si atoms in the nanotube inner wall are involved in a defect structure. The characterization of the detailed structure of the n...

Structural changes of humic acids from sinking organic matter and surface sediments investigated by advanced solid-state NMR: Insights into sources, preservation and molecularly uncharacterized components

Knowledge of the structural changes that particulate organic matter (POM) undergoes in natural systems is essential for determining its reactivity and fate. In the present study, we used advanced solid-state NMR techniques to investigate the chemical structures of sinking particulate matter collected at different depths as well as humic acids (HAs) extracted from these samples and underlying sediments from the Saguenay Fjord and the St. Lawrence Lower Estuary (Canada). Compared to bulk POM, HAs contain more non-polar alkyls, aromatics, and aromatic C–O, but less carbohydrates (or carbohydrate-like structures). In the two locations studied, the C and N contents of the samples (POM and HAs) decreased with depth and after deposition onto sediments, leaving N-poor but O-enriched HAs and suggesting the involvement of partial oxidation reactions during POM microbial degradation. Advanced NMR techniques revealed that, compared to the water-column HAs, sedimentary HAs contained more protonated aromatics, non-protonated aromatics, aromatic C–O, carbohydrates (excluding anomerics), anomerics, OC q, O–C q–O, OCH, and OCH 3 groups, but less non-polar alkyls, NCH, and mobile CH 2 groups. These results are consistent with the relatively high reactivity of lipids and proteins or peptides. In contrast, carbohydrate-like structures were selectively preserved and appeared to be involved in substitution and copolymerization reactions. Some of these trends support the selective degradation (or selective preservation) theory. The results provide insights into mechanisms that likely contribute to the preservation of POM and the formation of molecules that escape characterization by traditional methods. Despite the depletion of non-polar alkyls with depth in HAs, a significant portion of their general structure survived and can be assigned to a model phospholipid. In addition, little changes in the connectivities of different functional groups were observed. Substituted and copolymerized carbohydrates and fused-ring aromatics detected in the present study likely represented an important part of molecularly uncharacterized components (MUC).

Solidification and Simultaneous Dual-Wavelength Emission of Rhodamine 6G and Coumarin 102 Codoped in AlPO4 Mesoporous Glass

Transparent AlPO4 mesoporous glasses codoped with different amounts, as well as different molar ratios, of Rhodamine 6G (Rh6G) and Coumarin 102 (Cou102) were fabricated by a dipping method. Solidification of dyes in mesoporous AlPO4 glasses was probed by 27Al and 31P solid state NMR techniques. The interaction of dyes with the glassy AlPO4 network has been characterized by a new six-coordinated aluminum species (Al(6)) environment in 27Al MAS spectra, combined with advanced solid state NMR techniques probing 27Al−1H and 27Al−31P internuclear dipole couplings. Optical excitation and simultaneous dual-wavelength emission spectra of both series of samples show significant dependences on the Rh6G and Cou102 concentration and Cou102/Rh6G molar ratio. Efficient simultaneous dual-wavelength emission was observed at low dye concentration ( 10−3 M), quenching of the fluorescence of Cou102 happened, but the fluorescence intensity was dependent on the Cou102/Rh6G molar ratio.

Chemical Structures of Corn Stover and Its Residue after Dilute Acid Prehydrolysis and Enzymatic Hydrolysis: Insight into Factors Limiting Enzymatic Hydrolysis

Advanced solid-state NMR techniques and wet chemical analyses were applied to investigate untreated corn stover (UCS) and its residues after dilute acid prehydrolysis (DAP) and enzymatic hydrolysis (RES) to provide evidence for the limitations to the effectiveness of enzyme hydrolysis. Advanced solid-state NMR spectral-editing techniques as well as 1H-13C two-dimensional heteronuclear correlation NMR (2D HETCOR) were employed. Our results indicated that dilute acid prehydrolysis selectively removed amorphous carbohydrates, increased aromatic CH/other protonated -C═C- and enriched alkyl CH and CH2 components. Cinnamic acids were increased, and proteinaceous materials and N-containing degradation or condensation compounds were absorbed or coprecipitated in RES. 2D HETCOR experiments indicated a close association between lignin and the residual carbohydrates. Ketones/aldehydes were not detected in the DAP, in contrast to a report in which an appreciable amount of ketones/aldehydes was generated from the acid pretreatment of a purified cellulose in the literature. This suggested that acid pretreatment may modify the structure of purified cellulose more than biomass and that biomass may be a better substrate than model biopolymers and compounds for assessing structural changes that occur with industrial processing. On the basis of NMR and wet chemical analyses, we found the following factors could cause the limitations to the effectiveness of enzymatic hydrolysis: (1) chemical modification of carbohydrates limited the biologically degradable carbohydrates available; (2) cinnamic acids in the residue accumulated; (3) accessibility was potentially limited due to the close association of carbohydrates with lignin; and (4) proteinaceous materials and N-containing degradation or condensation compounds were absorbed or coprecipitated.

Fluorescent AlPO 4 gels and glasses doped with Rhodamine 6G: Preparation, structural and optical characterization

Fluorescent AlPO 4 xerogels doped with different amounts of Rhodamine 6G (Rh6G) laser dye were prepared by a one-step sol–gel process. In addition, mesoporous AlPO 4 glasses obtained from undoped gels were loaded with different amounts of Rh6G by wet impregnation. Optical excitation and emission spectra of both series of samples show significant dependences on Rh6G concentration, revealing the influence of dye molecular aggregation. At comparable dye concentrations the aggregation effects are found to be significantly stronger in the gels than in the mesoporous glasses. This effect might be attributed to stronger interactions between the dye molecules and the glass matrix, resulting in more efficient dye dispersion in the latter. The interaction of Rh6G with the glassy AlPO 4 network has been probed by 27Al and 31P solid-state NMR techniques. New five- and six-coordinated aluminum environments have been observed and characterized by advanced solid-state NMR techniques probing 27Al– 1H and 27Al– 31P internuclear dipole couplings. The fractional area of these new Al sites is correlated with the combined fractional area of two new Q (0) 3Al and Q (0) 2Al phosphate species observed in the 31P MAS NMR spectra. Based on this correlation as well as detailed composition dependent studies, we suggest that the new signals arise from the breakage of Al–O–P linkages associated with the insertion process.

Structural Features of a Bituminous Coal and Their Changes during Low-Temperature Oxidation and Loss of Volatiles Investigated by Advanced Solid-State NMR Spectroscopy

Quantitative and advanced 13C solid-state NMR techniques were employed to investigate (i) the chemical structure of a high volatile bituminous coal, as well as (ii) chemical structural changes of this coal after evacuation of adsorbed gases, (iii) during oxidative air exposure at room temperature, and (iv) after oxidative heating in air at 75 °C. The solid-state NMR techniques employed in this study included quantitative direct polarization/magic angle spinning (DP/MAS) at a high spinning speed of 14 kHz, cross polarization/total sideband suppression (CP/TOSS), dipolar dephasing, CH, CH2, and CHn selection, 13C chemical shift anisotropy (CSA) filtering, two-dimensional (2D) 1H−13C heteronuclear correlation NMR (HETCOR), and 2D HETCOR with 1H spin diffusion. With spectral editing techniques, we identified methyl CCH3, rigid and mobile methylene CCH2C, methine CCH, quaternary Cq, aromatic CH, aromatic carbons bonded to alkyls, small-sized condensed aromatic moieties, and aromatic C−O groups. With direct polarization combined with spectral-editing techniques, we quantified 11 different types of functional groups. 1H−13C 2D HETCOR NMR experiments indicated spatial proximity of aromatic and alkyl moieties in cross-linked structures. The proton spin diffusion experiments indicated that the magnetization was not equilibrated at a 1H spin diffusion time of 5 ms. Therefore, the heterogeneity in spatial distribution of different functional groups should be above 2 nm. Recoupled C−H long-range dipolar dephasing showed that the fraction of large charcoal-like clusters of polycondensed aromatic rings was relatively small. The exposure of this coal to atmospheric oxygen at room temperature for 6 months did not result in obvious chemical structural changes of the coal, whereas heating at 75 °C in air for 10 days led to oxidation of coal and generated some COO groups. Evacuation removed most volatiles and caused a significant reduction in aliphatic signals in its DP/MAS spectrum. DP/MAS, but not CP/MAS, allowed us to detect the changes during low-temperature oxidation and loss of volatiles. These results demonstrate the applicability of advanced solid-state NMR techniques in chemical characterization of coal.

Structural Characterization of Hydrothermal Carbon Spheres by Advanced Solid-State MAS 13C NMR Investigations

The local structure of carbon spheres obtained via the hydrothermal carbonization process is characterized by using a combination of advanced solid-state 13C NMR techniques. Glucose was chosen as the starting product because it offers the possibility of 13C isotopic enrichment and is regarded as a model compound for more complex polysaccharides and biomass, as reported in recent studies. A number of 13C solid-state MAS NMR techniques (single-pulse, cross-polarization, inversion recovery cross-polarization, INEPT, 13C−13C proton-driven magnetization exchange, and 13C−13C double-quantum−single-quantum correlation experiments) were combined to retrieve information about binding motifs and C−C closest neighbor relations. We found that the core of the carbonaceous scaffold is composed of furan rings cross-linked by domains containing short keto-aliphatic chains instead of otherwise expected graphene-type sheets, as mainly reported either for hydrothermal carbon spheres or for biomass-related carbons obtained b...

Advanced Solid State NMR Techniques for the Investigation of the Organic-Mineral Interfaces in Biomaterials

AbstractHigh resolution solid state NMR experiments were carried out on several compounds, to see how this technique can now be used to investigate in detail the surface structure of different biomaterials. First, because the surface of titanium implants can be functionalized by phosphonic acids, for instance to prevent bacterial adhesion,17O NMR experiments were performed on model TiO2 surfaces functionalized by 17O enriched phosphonic acids, to look at the mode of grafting of these coupling agents. Results bring clear evidence of the formation of Ti-O-P bridges and of the presence of residual P=O and P-OH groups. Second, given that calcium phosphates are widely present in biological hard tissues and synthetic biomaterials, 43Ca correlation experiments were performed on 43Ca enriched materials (hydroxyapatite and calcium benzoate), to see how the proximities between this nucleus and neighbouring atoms can be analyzed. Results show that both Ca…C and Ca…H proximities can be evidenced, and could thus help elucidate interface structures. All in all, these studies should pave the way to future investigations of biomaterials, and in particular of the structure of organic-inorganic interfaces.

Characterization of sinking particles from the northwest Mediterranean Sea using advanced solid-state NMR

Sinking particles are the major transporter of organic carbon from surface to the deep ocean, and their chemical composition changes dramatically with depth. However, the exact mechanism controlling the chemical transformation as particles sink is not well understood, and little detail is known about the structural changes. This is mainly due to the paucity of techniques available to analyze the major macromolecular components of sinking particles. Here we applied advanced solid-state NMR techniques, including cross polarization/magic angle spinning (CPMAS), direct polarization/magic angle spinning (DPMAS), two-dimensional 1H– 13C heteronuclear correlation (2D HETCOR) and 1H T 1 inversion recovery, on sinking particles collected in the northwest Mediterranean Sea. The CPMAS 13C NMR spectrum of the 200-m particles is significantly different from that of the DPMAS 13C NMR spectrum: CPMAS overestimates the NCH and CHO groups, but underestimates the aliphatic components, which is attributed to the high mobility of polymethylene units. Thus DPMAS is more suitable for quantifying organic composition of sinking particles. Using 2D HETCOR with 1H spin diffusion, we estimated that the size of domains (similar structural entities either physically or chemically grouped together) in the 200-m sinking particles can be as large as tens of nanometers. The results of CPMAS 13C NMR and 1H inversion recovery on sinking particles from 200, 520 and 920 m indicate that the macromolecular heterogeneity observed in surface particles virtually disappears as particles sink into the deep ocean. This suggests that the macromolecular components at depth are different in structural composition than those in surface waters, and may be compositionally homogenized as particles sink.

Structure of hydrous aluminosilicate glasses along the diopside–anorthite join: A comprehensive one- and two-dimensional 1H and 27Al NMR study

We have taken a systematic approach utilizing advanced solid-state NMR techniques to gain new insights into the controversial issue concerning the dissolution mechanisms of water in aluminosilicate melts (glasses). A series of quenched anhydrous and hydrous (∼2 wt% H 2O) glass samples along the diopside (Di, CaMgSi 2O 6)—anorthite (An, CaAl 2Si 2O 8) join with varying An components (0, 20, 38, 60, 80, and 100 mol %) have been studied. A variety of NMR techniques, including one-dimensional (1D) 1H and 27Al MAS NMR, and 27Al → 1H cross-polarization (CP) MAS NMR, as well as two-dimensional (2D) 1H double-quantum (DQ) MAS NMR, 27Al triple-quantum (3Q) MAS NMR, and 27Al → 1H heteronuclear correlation NMR (HETCOR) and 3QMAS/HETCOR NMR, have been applied. These data revealed the presence of SiOH, free OH ((Ca,Mg)OH) and AlOH species in the hydrous glasses, with the last mostly interconnected with Si and residing in the more polymerized parts of the structure. Thus, there are no fundamental differences in water dissolution mechanisms for Al-free and Al-bearing silicate melts (glasses), both involving two competing processes: the formation of SiOH/AlOH that is accompanied by the depolymerization of the network structure, and the formation of free OH that has an opposite effect. The latter is more important for depolymerized compositions corresponding to mafic and ultramafic magmas. Aluminum is dominantly present in four coordination (Al IV), but a small amount of five-coordinate Al (Al V) is also observed in all the anhydrous and hydrous glasses. Furthermore, six-coordinate Al (Al VI) is also present in most of the hydrous glasses. As Al of higher coordinations are favored by high pressure, Al VIOH and Al VOH may become major water species at higher pressures corresponding to those of the Earth’s mantle.

Advanced Solid State NMR Techniques for the Characterization of Sol—Gel‐Derived Materials

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