Theoretical Investigation of Linear Relationships between the Dihedral Torsion Angles and Diosmium Bond Distances in Diosmium Sawhorse Complexes.

Strong linear relationships between their Ceq-Os-Os-Ceq dihedral angles and their Os-Os bond distances in diosmium sawhorse complexes Os2(u-O2CR)2(CO)4L2 (L = CO and/or PR3) form two trendlines depending upon the presence or absence of terminal phosphines. These trends appear unrelated to the basicity of the bridging ligand or the number of phosphines. The mathematical derivation of the relationship between the O-Os-Os-O dihedral angle and the Os-Os bond distance shows how the other geometric parameters affect this relationship. Optimized density functional theory (DFT) structures reveal a similar strong linear correlation, where more electron-donating ligands render shorter Os-Os bond distances and larger dihedral angles, but these results form a single trendline. Computational scans of individual parameters show that the Os-Os bond responds strongly to changes in the dihedral angles, but the dihedral angles only respond weakly to changes in the Os-Os bond distance because the Os-Os-O bond angle links and modifies their direct coupling. Solid-state analysis of their structures, including DFT geometry optimizations, shows that phosphines protect the Os-Os bond distance from packing influences along the Os-Os axis, while in complexes without phosphines, packing compresses the Os-Os bond and the weak dihedral responses create the second trendline.

Essential nutrients and cerebral small vessel diseases: a two-sample Mendelian randomization study.

Background: Previous studies have suggested a potential association between nutrients and cerebral small vessel disease (CSVD), but this association has not been fully addressed. Object: We intended to clarify the causal associations between four categories of essential nutrients (amino acids, polyunsaturated fatty acids, minerals and vitamins) and two acute manifestations of CSVD (intracerebral hemorrhage and small vessel stroke) using two-sample Mendelian randomization (MR) analysis. Method: We obtained European-based large-scale genome-wide association studies (GWASs) related to CSVD (6,255 cases and 233,058 controls) and nutrient concentrations. Causality evaluation mainly included the results of the inverse variance-weighted (IVW) method. The simple median method, the weighted median method and the MR-Egger method were adopted for sensitivity analyses. Results: For ICH or SVS, increased levels of phenylalanine (OR = 1.188, p < 0.001) and dihomo-gamma-linolenic acid (DGLA) (OR = 1.153, p = 0.001) showed risk effects, while docosapentaenoic acid (DPA) (OR = 0.501, p < 0.001), zinc (OR = 0.919, p < 0.001), and arachidonic acid (OR = 0.966, p = 0.007) showed protective effects. For lobar hemorrhage or SVS, AA (OR = 0.978, p < 0.001), zinc (OR = 0.918, p < 0.001), and retinol (OR = 0.753, p < 0.001) showed risk effects; DPA (OR = 0.682, p = 0.022), gamma-linolenic acid (OR = 0.120, p = 0.033) and 25(OH)D (OR = 0.874, p = 0.040) showed protective effects. For nonlobar hemorrhage or SVS, DGLA (OR = 1.088, p < 0.001) and phenylalanine (OR = 1.175, p = 0.001) showed risk effects. Conclusion: Our study analyzed the effect of nutrients on CSVD risk from a genetic perspective, with implications for CSVD prevention through nutrient supplementation.

Simultaneous profiling of dust aerosol mass concentration and optical properties with polarized high-spectral-resolution lidar.

Dust particles originating from arid desert regions can be transported over long distances, presenting severe risks to climate, environment, social economics, and human health at the source and downwind regions. However, there has been a dearth of continuous diurnal observations of vertically resolved mass concentration and optical properties of dust aerosols, which hinders our understanding of aerosol mixing, stratification, aerosol-cloud interactions, and their impacts on the environment. To fill the gap of the insufficient observations, to the best of our knowledge, this work presents the first high-spectral-resolution lidar (HSRL) observation providing days of continuous profiles of the mass concentration, along with particle linear depolarization ratio (PLDR), backscattering coefficient, extinction coefficient and lidar ratio (LR), simultaneously. We present the results of two strong dust events observed by HSRL over Beijing in 2021. The maximum particle mass concentrations reached (1.52 ± 3.5) x103 µg/m3 and (19.48 ± 0.36) x103 µg/m3 for the two dust events, respectively. The retrieved particle mass concentrations and aerosol optical depth (AOD) agree well with the observation from the surface PM10 concentrations and sun photometer with correlation coefficients of 0.90 and 0.95, respectively. The intensive properties of PLDR and LR of the dust aerosols are 0.31 ± 0.02 and 39 ± 7 sr at 532 nm, respectively, which are generally close to those obtained from observations in the downwind areas. Moreover, inspired by the observations from HSRL, a universal analytical relationship is discovered to evaluate the proportion of dust aerosol backscattering, extinction, AOD, and mass concentration using PLDR. The universal analytical relationship reveals that PLDR can directly quantify dust aerosol contribution, which is expected to further expand the application of polarization technology in dust detection. These valuable observations and findings further our understanding of the contribution of dust aerosol to the environment and help supplement dust aerosol databases.

Water Cloud Detection with Circular Polarization Lidar: A Semianalytic Monte Carlo Simulation Approach.

This work presents polarization property studies of water clouds using a circular polarization lidar through a simulation approach. The simulation approach is based on a polarized, semianalytic Monte Carlo method under multiple-scattering conditions and considers three types of water clouds (namely homogeneous, inhomogeneous and partially inhomogeneous). The simulation results indicate that the layer-integrated circular depolarization ratios show similar variation trends as those of layer-integrated linear depolarization ratios. The Mishchenko-Hovenier relationship is validated to correlate the simulated layer-integrated circular and linear depolarization ratios. In addition, the cloud droplet effective radius, extinction coefficient, lidar field-of-view (FOV) and height of the cloud bottom are all found to affect the layer-integrated depolarization ratio. The current work theoretically indicates that a circular polarization lidar can efficiently perform measurements of water clouds, enjoying the advantage of higher sensitivity compared to a traditional linear polarization lidar. Hence, it should be of interest to researchers in fields of polarization lidar applications.

Validation of the dual field-of-view polarization LIDAR technique for the retrieval of homogeneous water cloud microphysical properties: a study based on a polarimetric Monte Carlo simulation.

This article highlights the validation of the dual fields-of-view (FOVs) polarization lidar technique for the retrieval of cloud droplet effective radius in conjunction with cloud extinction coefficient of homogeneous water cloud via simulation approach. The simulation is based on polarimetric Monte Carlo method incorporated with semianalytic features under multiple-scattering conditions. The simulation results show that the depolarization ratio measured at dual-FOVs is a function of the cloud droplet effective radius and cloud extinction coefficient. Using the method of standard deviation on extensive simulation results and then by applying the polynomial regression, two polynomial relationships are obtained expressing the retrieval of the cloud droplet effective radius and cloud extinction coefficient from the layer integrated depolarization ratio at low optical depths close to the cloud bottom. Eventually, the results those presented by Ref.[1] are validated. The water cloud microphysical properties, liquid water content and cloud droplet number concentration are the functions of these two parameters and thus can be found numerically.

Kinetic and Computational Analysis of CO Substitution in a Dinuclear Osmium Carbonyl Complex: Intersection between Dissociative and Dissociative-Interchange Mechanisms.

The mechanism for the CO substitution reaction involving the diosmium carbonyl sawhorse complex Os2(µ-O2CH)2(CO)6, which contains an Os-Os single bond, two axial CO ligands, and four equatorial CO ligands, was investigated experimentally and theoretically. Kinetic measurements show 13CO axial substitution proceeding by a dissociative reaction that is first-order in the complex and zero-order in 13CO but with an unexpectedly negative entropy of activation. The corresponding electronic structure calculations yield an enthalpy of activation for axial CO dissociation that is much larger than that determined by the kinetic experiments, but in agreement with the complex's stability with respect to CO loss. Additional calculations yield a dissociative interchange transition state whose free energy, enthalpy, and entropy of activation are in good agreement with those obtained from the kinetic measurements for the apparently dissociative substitution. These results point to an exchange reaction mechanism that is surprisingly close to the poorly understood transition from a dissociative mechanism with a CO-loss intermediate to a dissociative interchange mechanism with a transition state involving both the entering and the leaving COs. The key to explain these findings is provided by the vibrational analysis, which shows very low energy wagging motions for the axial COs. Thus, the incoming CO only displaces the outgoing CO when the complex has an outgoing CO near the wag's turning point. This dissociative interchange mechanism predicted by the calculation explains the unexpected combination of kinetics and stability characteristics. Kinetics reveals that the reaction is first-order in the Os dimer with a negative Eyring entropy, while a stability study shows that the Os dimer's decomposition rate is several orders of magnitude slower than CO exchange.