Calibration of the CMS hadron calorimeters using proton-proton collision data at root s=13 TeV

Methods are presented for calibrating the hadron calorimeter system of theCMSetector at the LHC. The hadron calorimeters of the CMS experiment are sampling calorimeters of brass and scintillator, and are in the form of one central detector and two endcaps. These calorimeters cover pseudorapidities vertical bar eta vertical bar ee data. The energy scale of the outer calorimeters has been determined with test beam data and is confirmed through data with high transverse momentum jets. In this paper, we present the details of the calibration methods and accuracy.Peer reviewe

Using the pulsed nature of staircase cyclic voltammetry to determine interfacial electron-transfer rates of adsorbed species.

Staircase cyclic voltammetry (SCV) is the digital counterpart of analog cyclic voltammetry (CV). However, when the redox-active species is adsorbed at the electrode surface, the voltammetric peak shapes (width, height, area, and to a lesser extent the reduction potentials) obtained with SCV can be very different from those of CV, even when small potential steps are used. Like analog CV, SCV provides a straightforward method to estimate and subtract the background and charging currents from the desired Faradaic current, while the pulsed nature of SCV provides the time-dependent decay of the Faradaic current, similar to chronoamperometry. Thus, electron-transfer rate constants can be directly measured as a function of applied potential, and no a priori model is required. An SCV equivalent of the square wave "quasi-reversible maximum" of observed peak height versus sampling moment and step size is predicted. The SCV response can only become independent of potential step size and similar to CV at high scan rates (ν > 10 k(0)E(step)), if the current is sampled at half the step interval. The applicability of SCV to studies of redox centers in proteins is illustrated for the two-electron oxidation/reduction of yeast cytochrome c peroxidase, adsorbed at a pyrolytic graphite edge-plane electrode

Direct detection and measurement of electron relays in a multicentered enzyme: Voltammetry of electrode-surface films of E-coli fumarate reductase, an iron-sulfur flavoprotein

Intramolecular electron relays operating in a multicentered enzyme are revealed by protein film voltammetry. The membrane-extrinsic catalytic domain of E. coli fumarate reductase (FrdAB) adsorbs to electroactive monolayer coverage at a rotating pyrolytic graphite edge electrode, giving characteristic voltammetric signals that are resolved and assigned to redox-active sites. At pH 7.3 (2°C), signals attributable to Centers 1 ([2Fe-2S) and 3 ([3Fe-4S]) and FAD are envelop together around -50 mV, while Center 2 ([4Fe-4S]) appears as a weaker signal at -305 mV. At pH 9.5, similar voltammetry is observed, the main difference being that the FAD component shifts to the negative edge of the envelope. The prominence of the two-electron FAD signal enables active-site redox transformations to be tracked and examined over a range of conditions. Scans at rates up to 20 V s-1 in the absence of fumarate show that electrons are relayed to the FAD, most obviously by Centers 1 and 3. Upon adding fumarate, the signals undergo transformations as specific centers engage in catalytic electron transport. A sigmoidal wave originating in the FAD envelope region is joined by a second wave close to the potential of Center 2. This is particularly evident under conditions optimizing enzyme catalytic control (as opposed to mass-transport control), i.e. high fumarate levels, high rotation rate, and pH 9.0 at which the enzyme is less active than at pH 7.0. Intramolecular electron transport is partitioned between different relay systems depending on catalytic demand and proficiency of the FAD as electron acceptor. At high pH, the less favorable driving force for electron transfer from Centers 1 and 3 places at greater burden on Center 2. Catalytic voltammograms show hysteresis in the presence of oxalacetate, an inhibitor binding preferentially to oxidized FAD. Reductive activation is slow but accelerates sharply below the potential of Center 2, showing that this cluster is much more effective than the others in reducing the inhibitor-bound active site. The results demonstrate how voltammetry can be used to quantify intramolecular electron transfer among multiple sites in complex enzymes

Interpreting the catalytic voltammetry of electroactive enzymes adsorbed on electrodes

Steady-state electrocatalytic waveforms displayed by redox enzymes adsorbed on electrodes are analyzed to reveal and quantify important mechanistic characteristics of the active sites involved in catalysis and to elucidate the contributions of different factors in determining the overall electron-transport rates. The shape, height, steepness, and potential of the voltammetric waves are functions of mass transport, interfacial electron-transfer rates, and the intrinsic kinetic and thermodynamic properties of the enzyme. A model is constructed first for the most simple realistic case, an enzyme containing a single two-electron active site, and then this is extended to include additional electron-transfer centers that serve as intramolecular relays. Equations are derived that predict the steady-state behavior expected for different conditions, and the models are used to assess recent experimental results. An alternative perspective on enzyme catalytic electron-transport is thus presented, in which kinetics and energetics are viewed and analyzed in the potential domain

Catalytic electron transport in Chromatium vinosum [NiFe]-hydrogenase: application of voltammetry in detecting redox-active centers and establishing that hydrogen oxidation is very fast even at potentials close to the reversible H+/H2 value.

The nickel-iron hydrogenase from Chromatium vinosum adsorbs at a pyrolytic graphite edge-plane (PGE) electrode and catalyzes rapid interconversion of H(+)((aq)) and H(2) at potentials expected for the half-cell reaction 2H(+) right arrow over left arrow H(2), i.e., without the need for overpotentials. The voltammetry mirrors characteristics determined by conventional methods, while affording the capabilities for exquisite control and measurement of potential-dependent activities and substrate-product mass transport. Oxidation of H(2) is extremely rapid; at 10% partial pressure H(2), mass transport control persists even at the highest electrode rotation rates. The turnover number for H(2) oxidation lies in the range of 1500-9000 s(-)(1) at 30 degrees C (pH 5-8), which is significantly higher than that observed using methylene blue as the electron acceptor. By contrast, proton reduction is slower and controlled by processes occurring in the enzyme. Carbon monoxide, which binds reversibly to the NiFe site in the active form, inhibits electrocatalysis and allows improved definition of signals that can be attributed to the reversible (non-turnover) oxidation and reduction of redox centers. One signal, at -30 mV vs SHE (pH 7.0, 30 degrees C), is assigned to the [3Fe-4S](+/0) cluster on the basis of potentiometric measurements. The second, at -301 mV and having a 1. 5-2.5-fold greater amplitude, is tentatively assigned to the two [4Fe-4S](2+/+) clusters with similar reduction potentials. No other redox couples are observed, suggesting that these two sets of centers are the only ones in CO-inhibited hydrogenase capable of undergoing simple rapid cycling of their redox states. With the buried NiFe active site very unlikely to undergo direct electron exchange with the electrode, at least one and more likely each of the three iron-sulfur clusters must serve as relay sites. The fact that H(2) oxidation is rapid even at potentials nearly 300 mV more negative than the reduction potential of the [3Fe-4S](+/0) cluster shows that its singularly high equilibrium reduction potential does not compromise catalytic efficiency

Fast voltammetric studies of the kinetics and energetics of coupled electron-transfer reactions in proteins.

A wealth of information on the reactions of redox-active sites in proteins can be obtained by voltammetric studies in which the protein sample is arranged as a layer on an electrode surface. By carrying out cyclic voltammetry over a wide range of scan rates and exploiting the ability to poise or pulse the electrode potential between cycles, data are obtained that are conveniently (albeit simplistically) analysed in terms of plots of peak potentials against scan rate. A simple reversible electron-transfer process gives rise to a 'trumpet'-shaped plot because the oxidation and reduction peaks separate increasingly at high scan rate; the electrochemical kinetics are then determined by fitting to Butler-Volmer or Marcus models. Much more interesting though are the ways in which this 'trumpet plot' is altered, often dramatically, when electron transfer is coupled to biologically important processes such as proton transfer, ligand exchange, or a change in conformation. It is then possible to derive particularly detailed information on the kinetics, energetics and mechanism of reactions that may not revealed clearly or even at all by other methods. In order to interpret the voltammetry of coupled systems, it is important to be able to define 'ideal behaviour' for systems that are expected to show simple and uncoupled electron transfer. Accordingly, this paper describes results we have obtained for several proteins that are expected to show such behaviour, and compares these results with theoretical predictions