Molecular dynamics computer simulations of Mg/Al hydrotalcite with interlayer Cl- were performed to better understand the structure of layered double hydroxides and their hydration behavior. A set of models with variable numbers of interlayer water molecules was investigated, with the assumption of no constraints on the movements of any atoms or on the geometry of the simulation supercells. Crystallographic parameters and two components of the hydration energy were calculated. One of these components is related to the interaction of water molecules with the rest of the structure and is controlled primarily by formation of a hydrogen-bonding network in the interlayer. The other is related to expansion of the host structure itself and reflects decreasing electrostatic interactions as the c-axis expands upon swelling. The dependence of these two energy components on the degree of hydration provides useful insight into the nature of hydrotalcite swelling behavior. There are two stable hydration states with c-axis dimensions of 23.9 and 21.7 Å, corresponding to hydrotalcite with 2 water molecules per each chloride in the interlayer, and dehydrated hydrotalcite, respectively. The first state is observed experimentally under ambient atmospheric conditions. The simulations also reveal a distorted octahedral structure of the hydroxide layer similar to that of hydrocalumite, the related Ca/Al phase.

BackgroundIn the ongoing COVID-19 pandemic, the susceptibility of patients with rheumatic diseases to COVID-19 remains unclear. We aimed to investigate susceptibility to COVID-19 in patients with autoimmune rheumatic diseases during the ongoing COVID-19 pandemic. MethodsWe did a multicentre retrospective study of patients with autoimmune rheumatic diseases in Hubei province, the epicentre of the COVID-19 outbreak in China. Patients with rheumatic diseases were contacted through an automated telephone-based survey to investigate their susceptibility to COVID-19. Data about COVID-19 exposure or diagnosis were collected. Families with a documented history of COVID-19 exposure, as defined by having at least one family member diagnosed with COVID-19, were followed up by medical professionals to obtain detailed information, including sex, age, smoking history, past medical history, use of medications, and information related to COVID-19. FindingsBetween March 20 and March 30, 2020, 6228 patients with autoimmune rheumatic diseases were included in the study. The overall rate of COVID-19 in patients with an autoimmune rheumatic disease in our study population was 0•43% (27 of 6228 patients). We identified 42 families in which COVID-19 was diagnosed between Dec 20, 2019, and March 20, 2020, in either patients with a rheumatic disease or in a family member residing at the same physical address during the outbreak. Within these 42 families, COVID-19 was diagnosed in 27 (63%) of 43 patients with a rheumatic disease and in 28 (34%) of 83 of their family members with no rheumatic disease (adjusted odds ratio [OR] 2•68 [95% CI 1•14-6•27]; p=0•023). Patients with rheumatic disease who were taking hydroxychloroquine had a lower risk of COVID-19 infection than patients taking other disease-modifying anti-rheumatic drugs (OR 0•09 [95% CI 0•01-0•94]; p=0•044). Additionally, the risk of COVID-19 was increased with age (adjusted OR 1•04 [95% CI 1•01-1•06]; p=0•0081).Interpretation Patients with autoimmune rheumatic disease might be more susceptible to COVID-19 infection than the general population.

No abstract

Investigation of a series of synthetic alkali silicate gels and gels produced by the alkali silica reaction (ASR) in field concrete using 29Si NMR spectroscopy, X‐ray diffraction, and bulk chemical analysis shows that local structures of the synthetic and field gels are quite similar. The most abundant Si sites for the field and synthetic gels with similar compositions have Q3 polymerization, and the number of non‐bridging oxygens per Si is similar for these samples. These samples also yield a basal X‐ray diffraction peak near 8–12 Å, suggesting that the structure is dominated by sheet‐like units, consistent with the dominant Q3 polymerization. Calculations based on the relative site abundances of the sites observed by 29Si NMR and the bulk chemical compositions indicate that there is insufficient alkali to charge‐balance all the non‐bridging oxygens and that there is a significant concentration of Si–OH linkages. The results provide strong support for the basic structural concepts of the so‐called kanemite model for ASR gel proposed by Wieker and coworkers, although the overall gel structure is likely to be more complex.