Oxygenolysis reaction mechanism of copper-dependent quercetin 2,3-dioxygenase: A density functional theory study

The mechanism of the action of copper-dependent quercetin 2,3-dioxygenase(2,3QD) has been investigated by means of hybrid density functional theory.The 2,3QD enzyme cleaves the O-heterocycle of a quercetin by incorporation of both oxygen atoms into the substrate and releases carbon monoxide.The calculations show that dioxygen attack on the copper complex is energetically favorable.The adduct has a possible near-degeneracy of states between [Cu 2+-(substrate-H +)] and [Cu +-(substrate-H).],and in addition the pyramidalized C 2 atom is ideally suited for forming a dioxygen-bridged structure.In the next step,the C 3-C 4 bond is cleaved and intermediate Int 5 is formed via transition state TS 4.Finally,the O a-O b and C 2-C 3 bonds are cleaved,and CO is released in one concerted transition state(TS 5) with the barrier of 63.25 and 61.91 kJ/mol in the gas phase and protein environments,respectively.On the basis of our proposed reaction mechanism,this is the rate-limiting step of the whole catalytic cycle and is strongly driven by a relatively large exothermicity of 100.86 kJ/mol.Our work provides some valuable fundamental insights into the behavior of this enzyme.     

Renormalized dynamics in charge qubit measurements by a single electron transistor

We investigate charge qubit measurements using a single electron transistor, with focus on the backaction-induced renormalization of qubit parameters. It is revealed the renormalized dynamics leads to a number of intriguing features in the detector's noise spectra, and therefore needs to be accounted for to properly understand the measurement result. Noticeably, the level renormalization gives rise to a strongly enhanced signal-to-noise ratio, which can even exceed the universal upper bound imposed quantum mechanically on linear-response detectors.     

Lewis acid-catalyzed nucleophilic ring-opening/intramolecular Conia-ene reactions of methylenecyclopropane 1,1-diesters with propargyl alcohols

We presented a Lewis acid-catalyzed nucleophilic ring opening of methylenecyclopropane (MCP) 1,1-diesters with propargyl alcohols. Unlike the proximal-bond cleavage mode observed in cases of unactivated MCPs, the intrinsic characteristic of MCP 1,1-diesters gave a regiospecific distal-bond cleavage under attack of propargyl alcohols as nucleophiles. By combining a subsequent intramolecular Conia-ene reaction, 3,5-dimethylenetetrahydropyrans could be obtained in either a stepwise or a one-pot strategy.     

Quantum Efficiency of Charge Qubit Measurements Using a Single Electron Transistor

The quantum efficiency, which characterizes the quality of information gain against information loss, is an important figure of merit for any realistic quantum detectors in the gradual process of collapsing the state being measured. In this work we consider the problem of solid-state charge qubit measurements with a single-electron-transistor (SET). We analyze two models: one corresponds to a strong response SET, and the other is a tunable one in response strength. We find that the response strength would essentially bound the quantum efficiency, making the detector non-quantum-limited. Quantum limited measurements, however, can be achieved in the limits of strong response and asymmetric tunneling. The present study is also associated with appropriate justifications for the measurement and backaction-dephasing rates, which were usually evaluated in controversial methods.     

Coulomb blockade double-dot Aharonov–Bohm interferometer: Giant fluctuations

Electron transport through two parallel quantum dots is a kind of solid-state realization of double path interference. We demonstrate that the inter-dot Coulomb correlation and quantum coherence would result in strong current fluctuations with a divergent Fano factor at zero frequency. We also provide physical interpretation for this surprising result, which displays its generic feature and allows us to recover this phenomenon in more complicated systems.