Kinetic and DFT Studies on the Mechanism of C−S Bond Formation by Alkyne Addition to the [Mo3S4(H2O)9]4+ Cluster

Reaction of [Mo3(μ3-S)(μ-S)3] clusters with alkynes usually leads to formation of two C−S bonds between the alkyne and two of the bridging sulfides. The resulting compounds contain a bridging alkenedithiolate ligand, and the metal centers appear to play a passive role despite reactions at those sites being well illustrated for this kind of cluster. A detailed study including kinetic measurements and DFT calculations has been carried out to understand the mechanism of reaction of the [Mo3(μ3-S)(μ-S)3(H2O)9]4+ (1) cluster with two different alkynes, 2-butyne-1,4-diol and acetylenedicarboxylic acid. Stoppedflow experiments indicate that the reaction involves the appearance in a single kinetic step of a band at 855 or 875 nm, depending on the alkyne used, a position typical of clusters with two C−S bonds. The effects of the concentrations of the reagents, the acidity, and the reaction medium on the rate of reaction have been analyzed. DFT and TD-DFT calculations provide information on the nature of the product formed, its electronic spectrum and the energy profile for the reaction. The structure of the transition state indicates that the alkyne approaches the cluster in a lateral way and both C−S bonds are formed simultaneously

Bias and Precision in Magnetic Resonance Imaging-Based Estimates of Renal Blood Flow: Assessment by Triangulation

Background Renal blood flow (RBF) can be measured with dynamic contrast enhanced-MRI (DCE-MRI) and arterial spin labeling (ASL). Unfortunately, individual estimates from both methods vary and reference-standard methods are not available. A potential solution is to include a third, arbitrating MRI method in the comparison. Purpose To compare RBF estimates between ASL, DCE, and phase contrast (PC)-MRI. Study Type Prospective. Population Twenty-five patients with type-2 diabetes (36% female) and five healthy volunteers (HV, 80% female). Field Strength/Sequences A 3 T; gradient-echo 2D-DCE, pseudo-continuous ASL (pCASL) and cine 2D-PC. Assessment ASL, DCE, and PC were acquired once in all patients. ASL and PC were acquired four times in each HV. RBF was estimated and split-RBF was derived as (right kidney RBF)/total RBF. Repeatability error (RE) was calculated for each HV, RE = 1.96 × SD, where SD is the standard deviation of repeat scans. Statistical Tests Paired t-tests and one-way analysis of variance (ANOVA) were used for statistical analysis. The 95% confidence interval (CI) for difference between ASL/PC and DCE/PC was assessed using two-sample F-test for variances. Statistical significance level was P  1) and results with outliers removed were presented. Results In patients, the mean RBF (mL/min/1.73m2) was 618 ± 62 (PC), 526 ± 91 (ASL), and 569 ± 110 (DCE). Differences between measurements were not significant (P = 0.28). Intrasubject agreement was poor for RBF with limits-of-agreement (mL/min/1.73m2) [−687, 772] DCE-ASL, [−482, 580] PC-DCE, and [−277, 460] PC-ASL. The difference PC-ASL was significantly smaller than PC-DCE, but this was driven by a single-DCE outlier (P = 0.31, after removing outlier). The difference in split-RBF was comparatively small. In HVs, mean RE (±95% CI; mL/min/1.73 m2) was significantly smaller for PC (79 ± 41) than for ASL (241 ± 85). Conclusions ASL, DCE, and PC RBF show poor agreement in individual subjects but agree well on average. Triangulation with PC suggests that the accuracy of ASL and DCE is comparable. Evidence Level 2 Technical Efficacy Stage

New heterometallic cubane-like clusters [{(η5-Cp)Mo}3S4{M‘(CO)3}](pts) (M‘ = Cr, Mo, W; pts =p-toluenesulfonate) obtained by ligand substitution reactions and Insertion of {M‘(CO)3} fragments

A series of group 6 heterometallic sulfide clusters have been prepared to establish a route to potential models of hydrodesulfurization catalysts suitable for application in nonaqueous media. The cluster compound [{(H2O)3Mo}3S4](pts)4·9H2O (pts = p-toluenesulfonate) was treated with triethyl orthoformate in the presence of a catalytic amount of Hpts to yield an ethanol complex of the [Mo3S4]4+ cluster core. The complex was subsequently converted in situ to acetonitrile and tetrahydrofuran complexes before treatment with thallium cyclopentadienide to yield the new cluster compound [{(η5-Cp)Mo}3S4](pts) (1). Insertion of {M‘(CO)3} fragments into 1 afforded the series of cubane-like, heterometallic clusters [{(η5-Cp)Mo}3S4{M‘(CO)3}](pts) (M‘ = Cr (2a), Mo (2b), W (2c)). Single-crystal X-ray analysis established the heterometallic S4-capped tetrahedral cluster core in the structure of 2c·1/2CH3OH