Cu-ZSM-5: A biomimetic inorganic model for methane oxidation

The present work highlights recent advances in elucidating the methane oxidation mechanism of inorganic Cu-ZSM-5 biomimic and in identifying the reactive intermediates that are involved. Such molecular understanding is important in view of upgrading abundantly available methane, but also to comprehend the working mechanism of genuine Cu-containing oxidation enzymes

Oxygen precursor to the reactive intermediate in methanol synthesis by Cu-ZSM-5

The reactive oxidizing species in the selective oxidation of methane to methanol in oxygen activated Cu-ZSM-5 was recently defined to be a bent mono(μ-oxo)dicopper(II) species, [Cu_2O]^(2+). In this communication we report the formation of an O_2-precursor of this reactive site with an associated absorption band at 29,000 cm^(-1). Laser excitation into this absorption feature yields a resonance Raman (rR) spectrum characterized by ^(18)O_2 isotope sensitive and insensitive vibrations, νO-O and νCu-Cu, at 736 (Δ^(18)O_2 = 41 cm^(-1)) and 269 cm^(-1), respectively. These define the precursor to be a μ-(η^2:η^2) peroxo dicopper(II) species, [Cu_2(O_2)]^(2+). rR experiments in combination with UV-vis absorption data show that this [Cu_2(O_2)]^(2+) species transforms directly into the [Cu_2O]^(2+) reactive site. Spectator Cu^+ sites in the zeolite ion-exchange sites provide the two electrons required to break the peroxo bond in the precursor. O_2-TPD experiments with ^(18)O_2 show the incorporation of the second ^(18)O atom into the zeolite lattice in the transformation of [Cu_2(O_2)]^(2+) into [Cu_2O]^(2+). This study defines the mechanism of oxo-active site formation in Cu-ZSM-5

A Case of Occipital Neuralgia in the Greater and Lesser Occipital Nerves Treated with Neurectomy by Using Transcranial Doppler Sonography: Technical Aspects

Occipital neuralgia is usually defined as paroxysmal stabbing pain in the greater or lesser occipital nerve (GON or LON) distribution. In occipital neuralgia patients, surgical considerations are carefully taken into account if medical management is ineffective. However, identification of the occipital artery by palpation in patients with thick necks or small occipital arteries can be technically difficult. Therefore, we established a new technique using transcranial Doppler (TCD) sonography for more accurate and rapid identification. The patient was a 64-year-old man who had undergone C1-C3 screw fixation and presented with intractable stabbing pain in the bilateral GON and LON distributions. In cases in which pain management was performed using medication, physical therapy, nerve block, or radiofrequency thermocoagulation, substantial pain relief was not consistently achieved, and recurrence of pain was reported. Therefore, we performed occipital neurectomy of the bilateral GON and LON by using TCD sonography, which helped detect the greater occipital artery easily. After the operation, the patient's headache disappeared gradually, although he had discontinued all medication except antidepressants. We believe that this new technique of occipital neurectomy via a small skin incision performed using TCD sonography is easy and reliable, has a short operative time, and provides rapid pain relief

Prediction of functional outcome after acute ischemic stroke : comparison of the CT-DRAGON score and a reduced features set

Background and Purpose:The CT-DRAGON score was developed to predict long-term functional outcome after acute stroke in the anterior circulation treated by thrombolysis. Its implementation in clinical practice may be hampered by its plethora of variables. The current study was designed to develop and evaluate an alternative score, as a reduced set of features, derived from the original CT-DRAGON score. Methods:This single-center retrospective study included 564 patients treated for stroke, in the anterior and the posterior circulation. At 90 days, favorable [modified Rankin Scale score (mRS) of 0-2] and miserable outcome (mRS of 5-6) were predicted by the CT-DRAGON in 427 patients. Bootstrap forests selected the most relevant parameters of the CT-DRAGON, in order to develop a reduced set of features. Discrimination, calibration and misclassification of both models were tested. Results:The area under the receiver operating characteristic curve (AUROC) for the CT-DRAGON was 0.78 (95% CI 0.74-0.81) for favorable and 0.78 (95% CI 0.72-0.83) for miserable outcome. Misclassification was 29% for favorable and 13.5% for miserable outcome, with a 100% specificity for the latter. National Institutes of Health Stroke Scale (NIHSS), pre-stroke mRS and age were identified as the strongest contributors to favorable and miserable outcome and named the reduced features set. While CT-DRAGON was only available in 323 patients (57%), the reduced features set could be calculated in 515 patients (91%) (p < 0.001). Misclassification was 25.8% for favorable and 14.4% for miserable outcome, with a 97% specificity for miserable outcome. The reduced features set had better discriminative power than CT-DRAGON for both outcomes (both p < 0.005), with an AUROC of 0.82 (95% CI 0.79-0.86) and 0.83 (95% CI 0.77-0.87) for favorable and miserable outcome, respectively. Conclusions:The CT-DRAGON score revealed acceptable discrimination in our cohort of both anterior and posterior circulation strokes, receiving all treatment modalities. The reduced features set could be measured in a larger cohort and with better discrimination. However, the reduced features set needs further validation in a prospective, multicentre study

Mechanism of selective benzene hydroxylation catalyzed by iron-containing zeolites

A direct, catalytic conversion of benzene to phenol would have wide-reaching economic impacts. Fe zeolites exhibit a remarkable combination of high activity and selectivity in this conversion, leading to their past implementation at the pilot plant level. There were, however, issues related to catalyst deactivation for this process. Mechanistic insight could resolve these issues, and also provide a blueprint for achieving high performance in selective oxidation catalysis. Recently, we demonstrated that the active site of selective hydrocarbon oxidation in Fe zeolites, named α-O, is an unusually reactive Fe(IV)=O species. Here, we apply advanced spectroscopic techniques to determine that the reaction of this Fe(IV)=O intermediate with benzene in fact regenerates the reduced Fe(II) active site, enabling catalytic turnover. At the same time, a small fraction of Fe(III)-phenolate poisoned active sites form, defining a mechanism for catalyst deactivation. Density-functional theory calculations provide further insight into the experimentally defined mechanism. The extreme reactivity of α-O significantly tunes down (eliminates) the rate-limiting barrier for aromatic hydroxylation, leading to a diffusion-limited reaction coordinate. This favors hydroxylation of the rapidly diffusing benzene substrate over the slowly diffusing (but more reactive) oxygenated product, thereby enhancing selectivity. This defines a mechanism to simultaneously attain high activity (conversion) and selectivity, enabling the efficient oxidative upgrading of inert hydrocarbon substrates

[Cu_2O]^(2+) active site formation in Cu-ZSM-5: geometric and electronic structure requirements for N_2O activation

Understanding the formation mechanism of the [Cu_2O]^(2+) active site in Cu-ZSM-5 is important for the design of efficient catalysts to selectively convert methane to methanol and related value-added chemicals and for N_2O decomposition. Spectroscopically validated DFT calculations are used here to evaluate the thermodynamic and kinetic requirements for formation of [Cu_2O](2+) active sites from the reaction between binuclear Cu(I) sites and N_2O in the 10-membered rings Cu-ZSM-5. Thermodynamically, the most stable Cu^I center prefers bidentate coordination with a close to linear bite angle. This binuclear Cu^I site reacts with N_2O to generate the experimentally observed [Cu_2O]^(2+) site. Kinetically, the reaction coordinate was evaluated for two representative binuclear Cu^I sites. When the Cu-Cu distance is sufficiently short (5.0 Å), N_2O binds in a "terminal" η^1-O fashion to a single Cu^I site of the dimer and the resulting E_a for N_2O activation is significantly higher (16 kcal/mol). Therefore, bridging N_2O between two Cu^I centers is necessary for its efficient two-electron activation in [Cu_2O]^(2+) active site formation. In nature, this N_2O reduction reaction is catalyzed by a tetranuclear Cu_Z cluster that has a higher E_a. The lower E_a for Cu-ZSM-5 is attributed to the larger thermodynamic driving force resulting from formation of strong Cu^(II)-oxo bonds in the ZSM-5 framework

[Cu_2O]^(2+) active site formation in Cu-ZSM-5: geometric and electronic structure requirements for N_2O activation

Understanding the formation mechanism of the [Cu_2O]^(2+) active site in Cu-ZSM-5 is important for the design of efficient catalysts to selectively convert methane to methanol and related value-added chemicals and for N_2O decomposition. Spectroscopically validated DFT calculations are used here to evaluate the thermodynamic and kinetic requirements for formation of [Cu_2O](2+) active sites from the reaction between binuclear Cu(I) sites and N_2O in the 10-membered rings Cu-ZSM-5. Thermodynamically, the most stable Cu^I center prefers bidentate coordination with a close to linear bite angle. This binuclear Cu^I site reacts with N_2O to generate the experimentally observed [Cu_2O]^(2+) site. Kinetically, the reaction coordinate was evaluated for two representative binuclear Cu^I sites. When the Cu-Cu distance is sufficiently short (5.0 Å), N_2O binds in a "terminal" η^1-O fashion to a single Cu^I site of the dimer and the resulting E_a for N_2O activation is significantly higher (16 kcal/mol). Therefore, bridging N_2O between two Cu^I centers is necessary for its efficient two-electron activation in [Cu_2O]^(2+) active site formation. In nature, this N_2O reduction reaction is catalyzed by a tetranuclear Cu_Z cluster that has a higher E_a. The lower E_a for Cu-ZSM-5 is attributed to the larger thermodynamic driving force resulting from formation of strong Cu^(II)-oxo bonds in the ZSM-5 framework

Performance of CMS muon reconstruction in pp collision events at sqrt(s) = 7 TeV

The performance of muon reconstruction, identification, and triggering in CMS has been studied using 40 inverse picobarns of data collected in pp collisions at sqrt(s) = 7 TeV at the LHC in 2010. A few benchmark sets of selection criteria covering a wide range of physics analysis needs have been examined. For all considered selections, the efficiency to reconstruct and identify a muon with a transverse momentum pT larger than a few GeV is above 95% over the whole region of pseudorapidity covered by the CMS muon system, abs(eta) < 2.4, while the probability to misidentify a hadron as a muon is well below 1%. The efficiency to trigger on single muons with pT above a few GeV is higher than 90% over the full eta range, and typically substantially better. The overall momentum scale is measured to a precision of 0.2% with muons from Z decays. The transverse momentum resolution varies from 1% to 6% depending on pseudorapidity for muons with pT below 100 GeV and, using cosmic rays, it is shown to be better than 10% in the central region up to pT = 1 TeV. Observed distributions of all quantities are well reproduced by the Monte Carlo simulation.Comment: Replaced with published version. Added journal reference and DO