Quantification of photooxidative defects in weathered microplastics using ¹³C multiCP NMR spectroscopy

Weathering of microplastics made of commodity plastics like polystyrene, polypropylene and polyethylene introduces polar polymer defects as a result of photooxidation and mechanical stress. Thus, hydrophobic microplastic particles gradually become hydrophilic, consisting of polar oligomers with a significant amount of oxygen-bearing functional groups. This turnover continuously changes interactions between microplastics and natural colloidal matter. To be able to develop a better understanding of this complex weathering process, quantification of the corresponding defect proportions is a first and essential step. Using polystyrene, (13)C enriched at the α position to 23%, we demonstrate that (13)C cross polarisation (CP) NMR spectroscopy allows for probing the typical alcohol, peroxo, keto and carboxyl defects. Even the discrimination between in- and end-chain ketones, carboxylic acids and esters as well as ketal functions was possible. Combined with multiCP excitation, defect proportions could be determined with excellent accuracy down to 0.1%. For materials with (13)C in natural abundance, this accounts for a detection limit of roughly 1%. The best trade-off between measurement time and accuracy for the quantification of the defect intensities for multiCP excitation was obtained for CP block lengths shorter than 250 μs and total build-up times longer than 2 ms. Further measurement time reduction is possible by using multiCP excitation to calibrate intensities obtained from series of (13)C CP MAS NMR spectra. As photooxidation is an important degradation mechanism for microplastics in the environment, we expect these parameters to be transferable for probing defect proportions of weathered microplastics in general

Oxygen Vacancy Ordering in Aluminous Bridgmanite in the Earth's Lower Mantle

Oxygen vacancies (OVs), that charge-balance the replacement of octahedrally coordinated Si4+ by Al3+ in the mineral bridgmanite, will influence transport properties in the lower mantle but little is known about their stability and local structure. Using 27Al nuclear magnetic resonance (NMR) spectroscopy we have characterized OVs within six aluminous bridgmanite samples. In the resulting NMR spectra sixfold, fivefold, and fourfold coordinated Al species are resolved, in addition to near eightfold coordinated Al substituting for Mg. Fivefold coordinated Al is formed by single OV sites but fourfold coordination must result from short range ordering of OVs, producing OV clusters that may form through migration into twin domain walls. Characterizing the occurrence of such OV structures is an important prerequisite for understanding how transport properties change with depth and composition in the lower mantle

Water dynamics in solutions of linear poly (N-isopropyl acrylamide) studied by ²H NMR field-cycling relaxometry

We use ²H nuclear magnetic resonance to study the dynamics of deuterated water in a solution of linear poly (N-isopropyl acrylamide) (pNIPAM, 4 wt%) across its coil-to-globule transition at a lower critical solubility temperature (LCST) around 32°C. In agreement with previous studies, we find that the ²H spin-lattice (T₁) and, in particular, spin-spin (T₂) relaxation times abruptly decrease when heating through the LCST, indicating that the polymer collapse causes an emergence of a water fraction with strongly reduced mobility. To quantify the dynamics of this slow water fraction, we exploit the fact that ²H field-cycling relaxometry allows us to measure the spectral density of the water reorientation in a broad frequency range. We find that the slow water fraction is characterised by a broad logarithmic Gaussian distribution of correlation times (σ LG = 2.3), which is centred about τ LG ≈ 10⁻⁹ s near the LCST. Hence, the common assumption of a Debye spectral density does not apply. We argue that a minor water fraction, which is located inside the pNIPAM globules and shows dynamics governed by the disordered polymer matrix, accompanies a major water fraction with bulk-like dynamics above the LCST. The former fraction amounts to about 0.4 water molecules per NIPAM monomer. Several findings indicate fast exchange between these bound and free water fractions on the T₁ and T₂ time scales

Porous Salts Containing Cationic Al24-Hydroxide-Acetate Clusters from Scalable, Green and Aqueous Synthesis Routes

The solution chemistry of aluminum is highly complex and various polyoxocations are known. Here we report on the facile synthesis of a cationic Al24 cluster that forms porous salts of composition [Al24 (OH)56 (CH3 COO)12 ]X4 , denoted CAU-55-X, with X=Cl- , Br- , I- , HSO4 - . Three-dimensional electron diffraction was employed to determine the crystal structures. Various robust and mild synthesis routes for the chloride salt [Al24 (OH)56 (CH3 COO)12 ]Cl4 in water were established resulting in high yields (>95 %, 215 g per batch) within minutes. Specific surface areas and H2 O capacities with maximum values of up to 930 m2  g-1 and 430 mg g-1 are observed. The particle size of CAU-55-X can be tuned between 140 nm and 1250 nm, permitting its synthesis as stable dispersions or as highly crystalline powders. The positive surface charge of the particles, allow fast and effective adsorption of anionic dye molecules and adsorption of poly- and perfluoroalkyl substances (PFAS)

Spin-ice physics in cadmium cyanide

Spin-ices are frustrated magnets that support a particularly rich variety of emergent physics. Typically, it is the interplay of magnetic dipole interactions, spin anisotropy, and geometric frustration on the pyrochlore lattice that drives spin-ice formation. The relevant physics occurs at temperatures commensurate with the magnetic interaction strength, which for most systems is 1–5 K. Here, we show that non-magnetic cadmium cyanide, Cd(CN)2, exhibits analogous behaviour to magnetic spin-ices, but does so on a temperature scale that is nearly two orders of magnitude greater. The electric dipole moments of cyanide ions in Cd(CN)2 assume the role of magnetic pseudospins, with the difference in energy scale reflecting the increased strength of electric vs magnetic dipolar interactions. As a result, spin-ice physics influences the structural behaviour of Cd(CN)2 even at room temperature.ISSN:2041-172

Shared heritability and functional enrichment across six solid cancers

Quantifying the genetic correlation between cancers can provide important insights into the mechanisms driving cancer etiology. Using genome-wide association study summary statistics across six cancer types based on a total of 296,215 cases and 301,319 controls of European ancestry, here we estimate the pair-wise genetic correlations between breast, colorectal, head/neck, lung, ovary and prostate cancer, and between cancers and 38 other diseases. We observed statistically significant genetic correlations between lung and head/neck cancer (r(g) = 0.57, p = 4.6 x 10(-8)), breast and ovarian cancer (r(g) = 0.24, p = 7 x 10(-5)), breast and lung cancer (r(g) = 0.18, p = 1.5 x 10(-6)) and breast and colorectal cancer (r(g) = 0.15, p = 1.1 x 10(-4)). We also found that multiple cancers are genetically correlated with non-cancer traits including smoking, psychiatric diseases and metabolic characteristics. Functional enrichment analysis revealed a significant excess contribution of conserved and regulatory regions to cancer heritability. Our comprehensive analysis of cross-cancer heritability suggests that solid tumors arising across tissues share in part a common germline genetic basis

Etudes de matériaux d'électrodes positives par résonance magnétique nucléaire

Plusieurs matériaux d'électrode positive de batteries lithium-ion ont été étudiés par RMN du solide. Les tenseurs quadrupolaires et de déplacement des polytypes O2 et O3 de LiCoO2 ont été déterminés par ajustement itératif des intensités des bandes de rotation des spectres RMN MAS dans trois champs magnétiques différents (4,7 T, 7,1 T et 11,7 T). Les interactions dipolaires nucléaires du 6,7Li ont été prises en compte par l'approche de la fonction mémoire. Le calcul du tenseur de déplacement chimique du lithium montre que la susceptibilité magnétique des phases O2 et O3 résulte entièrement du paramagnétisme de Van Vleck de l'ion Co3+ (dans l'approximation du dipôle ponctuel). De plus, le calcul du gradient de champ électrique au niveau du 59Co et du 7Li (relié à la constante de couplage quadrupolaire par le modèle des charges ponctuelles, i.e., supposant que le cristal est ionique) donnent des charges identiques pour les deux polytypes, en accord avec des calculs empiriques de valence de liaison. Une étude identique a été effectuée pour NaCoO2 et HCoO2 par RMN MAS du 23Na, 1H et 59Co. Toutefois, dans le cas de NaCoO2, nous avons dû tenir compte de l'interaction quadrupolaire au second ordre du fait de la valeur élevée de la constante de couplage quadrupolaire des deux noyaux étudiés. Pour ces deux matériaux, le calcul non concluant du gradient de champ électrique nous laisse supposer que ces cristaux seraient moins ioniques que LiCoO2. Différentes phases de VOPO4 (aII-, b- et g-VOPO4) ont également été étudiées par RMN MAS du 31P et 51V utilisant la même méthode. La détermination des tenseurs quadrupolaires et de déplacement du 51V montre que ces phases se différencient essentiellement par la valeur de leurs constantes de couplage quadrupolaire. Nous avons également suivi, par RMN MAS du 31P, 51V et 6,7Li en mode quantitatif, l'évolution de différentes phases au cours du processus d'intercalation/désintercalation du lithium de la phase aII-VOPO4.STRASBOURG-Sc. et Techniques (674822102) / SudocSudocFranceF