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The structures of magnesium chloride dimer-water clusters, (MgCl2)2(H2O)n−/0, were investigated with size-selected anion photoelectron spectroscopy and theoretical calculations to understand the dissolution of magnesium chloride in water. The most stable structures were confirmed by comparing vertical detachment energies (VDEs) with the experimental measurements. A dramatic drop of VDE at n = 3 has been observed in the experiment, which is in accordance with the structural change of (MgCl2)2(H2O)n−. Compared to the neutral clusters, the excess electron induces two significant phenomena in (MgCl2)2(H2O)n−. First, the planar D2h geometry can be converted into a C3v structure at n = 0, making the Mg–Cl bonds easier to be broken by water molecules. More importantly, a negative charge-transfer-to-solvent process occurs after adding three water molecules (i.e., at n = 3), which leads to an obvious deviation in the evolution of the clusters. Such electron transfer behavior was noticed at n = 1 in monomer MgCl2(H2O)n−, indicating that the dimerization between two MgCl2 molecules can make the cluster more capable of binding electron. In neutral (MgCl2)2(H2O)n, this dimerization provides more sites for the added water molecules, which can stabilize the entire cluster and maintain its initial structure. Specifically, filling the coordination number to be 6 for Mg atoms can be seen as a link between structural preferences in the dissolution of the monomers, dimers, and extended bulk-state of MgCl2. This work represents an important step forward into fully understanding the solvation of MgCl2 crystals and other multivalent salt oligomers. [ABSTRACT FROM AUTHOR]

Particulate Matter 2.5 (PM2.5) is a significant risk factor for frailty and chronic diseases. Studies on the associations between PM2.5 and frailty, chronic diseases, and multimorbidity are scarce, especially from large cohort studies. We aimed to explore the potential association between PM2.5 exposure and the risk of frailty, chronic diseases, and multimorbidity. We collected data from a national cohort (CHARLS) with a follow-up period of 11–18 years, totaling 13,366 participants. We obtained PM2.5 concentration data from the Atmospheric Composition Analysis Group at Dalhousie University. PM2.5 exposure is based on the average annual concentration in the prefecture-level city where residents live. We define frailty as the comprehensive manifestation of declining various body functions, characterized by a frailty index of 0.25 or greater, and multimorbidity as the presence of at least two or more chronic conditions. Cox proportional hazards regression was used to estimate the hazard ratio (HR) with its 95% confidence interval (95%CI). A 10-μg/m3 increase for PM2.5 was significantly associated with an increased risk of frailty (HR = 1.289, 95%CI = 1.257–1.322, P < 0.001). A 10-μg/m3 increase for PM2.5 was significantly associated with the elevated risk for most chronic diseases. Compared to those with no morbidity or only single morbidity, a 10-μg/m3 increase for PM2.5 was significantly associated with the elevated risk for multimorbidity (HR = 1.220, 95%CI = 1.181–1.260, P < 0.001). Ambient PM2.5 exposure is a significant risk factor for frailty, chronic diseases, and multimorbidity, and some measures need to be taken to reduce PM2.5 concentration and prevent frailty and chronic diseases. [ABSTRACT FROM AUTHOR]