Redox-regulated ethylene binding to a rhenium-thiolate complex.

This thesis reports the reactivity of the rhenium-thiolate complex, tris(2-diphenylphosphinobenzenethiolato)rhenium(III), [Re(DPPBT) 3 ] ( 1 ) and its oxidized derivatives with ethylene. The reactivity has been studied by electrochemical, spectroelectrochemical, and chemical methods. Based on the cyclic voltammetric data, ( 1 ) shows two reversible one electron oxidations and a single reduction. The three redox events are observed at potentials of 420, -340 and -1620 mV versus a ferrocene reference. The events span formal oxidation states from Re(II) to Re(V) although significant ligand participation in the redox events makes these formal assignments misleading with respect to the electronic structure of the complexes. Bulk oxidation of ( 1 ) (E applied = +23 mV) in the presence of ethylene yields {[(ethane-1,2-diylbis(thio-2,1-phenylene)diphenyl-phosphino)(2-diphenylphosphinobenzenethiolato)]rhenium(III)} ( 6 ) from the addition of the alkene across cis sulfur sites. Electronic spectra recorded during the oxidation reveal two stages. The first stage is assigned as the one electron oxidation of ( 1 ) to tris(2-diphenylphosphinobenzenethiolato)rhenium(IV) ( 3 ), which is indicated by the intensity increases at 390 and 581 nm. During the second stage, a reaction occurs between ( 3 ) and ethylene that yields {[(ethane-1,2-diylbis(thio-2,1-phenylene)diphenyl-phosphino)(2-diphenylphosphinobenzenethiolato)]rhenium(II)} ( 5 ), which is oxidized to ( 6 ) as shown by the intensity loss at 390 and 581 nm and simultaneous intensity gain at 484 nm. The formal Re(III)/Re(II) reduction potential of ( 6 ) is shifted approximately +1520 mV consistent with the formation of two thioether donors. Complex ( 6 ) is stable in solution, but reduction at an applied potential of -977 mV initiates C-S bond cleavage and release of ethylene. The spectroscopic results reveal the pathway to be the reverse of the C-S bond formation. Oxidation of ( 1 ) using AgPF 6 followed by an ethylene purge yields (6)[PF 6 ] . The +ESI-MS of (6)[PF 6 ] shows a parent ion peak at m/z = 547.0710 (z = 2). The complex (6)[PF 6 ] crystallizes as a long thin orange plate in the monoclinic space group C2/c with unit cell dimensions of a = 29.009(18) Å; b = 22.577(18) Å; c = 43.99(3) Å; and ß = 96.182(17)°. The kinetic and equilibrium parameters associated with C-S bond formation/cleavage were extracted from cyclic voltammograms at multiple scan rates using the DigiSim software package. The rate constants for C-S formation between ( 3 ) and ethylene, k f , and for C-S bond cleavage for ( 5 ), k r , were extracted from simulation of the CV data at 7 scan rates ranging from 100 to 1000 mV/s for 3 independent trials. Average values for k f and k r are (1.2 ± 0.2) × 10 -1 M -1 s -1 and (3.0 ± 0.4) × 10 -2 s -1 , respectively. From these, K 2 was calculated as 4.0 ± 0.8 in agreement with predictions from the UV-visible study. K 1 and K 3 are equilibrium constants for ethylene binding/release between ( 1 ) and {[(ethane-1,2-diylbis(thio-2,1-phenylene)diphenyl-phosphino)(2-diphenyl-phosphinobenzenethiolato)]rhenium(I)} ( 8 ), and tris(2-diphenylphosphinobenzenethiolato)rhenium(V) ( 4 ) and ( 6 ), respectively. From the redox potentials and the equilibrium constant K 2 , values for K 1 and K 3 were determined. K 1 has a calculated value of (1.9 ± 0.4) × 10 -11 consistent with observation of an unstable C-S bond. In contrast, the calculated value of K 3 , (2.5 ± 0.9) × 10 9 , is large and is consistent with the observed stability of ( 6 ). The large differences in equilibrium constants as a function of oxidation state provide a means to easily gate ethylene addition/release

Carbon-sulfur bond formation/cleavage reactions of metal-stabilized thiyl radicals by electrochemical and chemical methods.

The oxidation of metallothiolates is complicated by non-innocence or potential redox activity of sulfur to yield thiyl (RS•) radicals. In some instances, the one-electron oxidation of metal thiolates yields a product with the unpaired electron nearly equally delocalized between metal and sulfur such that, a specific site of oxidation cannot be defined. We refer to these complexes as metal-stabilized thiyl radicals. This dissertation explores reversible carbon-sulfur bond formation between metal-stabilized thiyl radicals and unsaturated hydrocarbons. Oxidation of the metal thiolate precursors [Ru(DPPBT)3]- Ru-l, and Re(DPPBT)3, Re-l, (DPPBT = diphenylphosphino-benzenethiolato), generates reactive species add with alkenes, alkynes, and dienes to yield metal-dithioether products. The electrochemical experiment reveals the addition of alkenes to [Ru-l]+ as an irreversible process. The oxidized intermediate [Re-l]+ binds alkenes reversibly with equilibrium binding constants that vary with complex charge. This dissertation employs the complex, [Ru-l]- to investigate metal-stabilized thiyl radical reactivity with alkenes, alkynes, and dienes. The successful works allow us to establish the scope and limits of these reactions. The rate constants of substrates are obtained through digital simulation of cyclic voltammograms at multiple scan rates. The electronic effects provide a measure of the relative reactivity of the substituted styrenes toward the metal-coordinated thiyl radicals, which yields a Hammett correlation (p = -0.7(1)) consistent with an electrophilic character for our thiyl radical complexes. Experimentally determined rate constants range from 4.6(5) x 107 M-1 S-l for electron-rich alkenes to 2.7(2) x 104 M-1 S-l for electron-poor alkenes. For cyclic alkenes, the rate of addition correlates with ring strain; knorbornene \u3e kcyclopentene \u3e kcyclohexene. The rate constant of alkyne addition are found to be approximately 100 times lower than alkenes as well-known. The dienes are obtained the addition rate in range between alkenes and alkynes. Crystalline samples of the ethylene addition products [Ru-l•C2H4]+ and [Re-l•C2H4]+ are obtained from preparative scale reactions using chemical oxidants. Chemical oxidation of [Ru-l]¨ in the presence of m-methylstyrene, pmethyl styrene, cyclohexene, and l-octyne yields the dithioether complexes [Ru-l• m-methylstyrenet]+, [Ru-l•p-methylstyrene]+, [Ru-l•cyclohexenet]+, and [Ru-l•octynet]+. All chemically synthesized complexes were fully characterized including 31P NMR and mass spectrometry

18F-fluoro-deoxy-glucose focal uptake in very small pulmonary nodules: fact or artifact? Case reports

ABSTRACT: BACKGROUND: F-fluoro-deoxy-glucose (18F-FDG) positron emission tomography integrated/combined with computed tomography (PET-CT) provides the best diagnostic results in the metabolic characterization of undetermined solid pulmonary nodules. The diagnostic performance of 18F-FDG is similar for nodules measuring at least 1 cm and for larger masses, but few data exist for nodules smaller than 1 cm. CASE PRESENTATION: We report five cases of oncologic patients showing focal lung 18F-FDG uptake on PET-CT in nodules smaller than 1 cm. We also discuss the most common causes of 18F-FDG false-positive and false-negative results in the pulmonary parenchyma. In patient 1, contrast-enhanced CT performed 10 days before PET-CT did not show any abnormality in the site of uptake; in patient 2, high-resolution CT performed 1 month after PET showed a bronchiole filled with dense material interpreted as a mucoid impaction; in patient 3, contrast-enhanced CT performed 15 days before PET-CT did not identify any nodules; in patients 4 and 5, contrast-enhanced CT revealed a nodule smaller than 1 cm which could not be characterized. The 18F-FDG uptake at follow-up confirmed the malignant nature of pulmonary nodules smaller than 1 cm which were undetectable, misinterpreted, not recognized or undetermined at contrast-enhanced CT. CONCLUSION: In all five oncologic patients, 18F-FDG was able to metabolically characterize as malignant those nodules smaller than 1 cm, underlining that: 18F-FDG uptake is not only a function of tumor size but it is strongly related to the tumor biology; functional alterations may precede morphologic abnormalities. In the oncologic population, especially in higher-risk patients, PET can be performed even when the nodules are smaller than 1 cm, because it might give an earlier characterization and, sometimes, could guide in the identification of alterations missed on CT

Proposed Ligand-Centered Electrocatalytic Hydrogen Evolution and Hydrogen Oxidation at a Noninnocent Mononuclear Metal-Thiolate.

The noninnocent coordinatively saturated mononuclear metal-thiolate complex ReL3 (L = diphenylphosphinobenzenethiolate) serves as an electrocatalyst for hydrogen evolution or hydrogen oxidation dependent on the presence of acid or base and the applied potential. ReL3 reduces acids to H2 in dichloromethane with an overpotential of 380 mV and a turnover frequency of 32 ± 3 s(-1). The rate law displays a second-order dependence on acid concentration and a first-order dependence on catalyst concentration with an overall third-order rate constant (k) of 184 ± 2 M(-2) s(-1). Reactions with deuterated acid display a kinetic isotope effect of 9 ± 1. In the presence of base, ReL3 oxidizes H2 with a turnover frequency of 4 ± 1 s(-1). The X-ray crystal structure of the monoprotonated species [Re(LH)L2](+), an intermediate in both catalytic H2 evolution and oxidation, has been determined. A ligand-centered mechanism, which does not require metal hydride intermediates, is suggested based on similarities to the redox-regulated, ligand-centered binding of ethylene to ReL3

Predictors of infectious foci on FDG PET/CT in Staphylococcus aureus bacteremia

Abstract We looked for predicting factors for the detection of infectious foci on 18F-fluorodeoxyglucose-positron emission tomography in combination with computed tomography (FDG PET/CT) among patients with Staphylococcus aureus bacteremia (SAB) who participated in an interventional study that was conducted at Rambam Health Care Campus, between July 1, 2015 and February 1, 2019. The primary outcome was an infectious focus detected by FDG PET/CT. Independent predictors for detection of focal infection were identified using univariate followed by a logistic regression multivariate analysis. We included 149 patients with 151 separate episodes of SAB who underwent FDG-PET/CT. Focal infections were detected in 107 patients (70.8%). Independent predictors for focal infection detection were community acquisition of bacteremia with odds ratio (OR) 3.03 [95% confidence interval (CI) 1.04–8.77], p-0.042 and C reactive protein (CRP) with OR 1.09 [95% CI 1.04–1.14], p < 0.001. Primary bacteremia was inversely associated with focal infection detection with OR 0.27 [0.10–0.69], p = 0.007, as were the pre-scan blood glucose levels OR 0.9 [0.98–0.99], p-0.004. The latter stayed significant in the subgroup of patients with diabetes mellitus. To conclude, patients with community-acquired bacteremia or high CRP levels should be carefully investigated for focal infection. Patients who present with primary bacteremia seem to be at low risk for focal infection