An official website of the United States government
Abstract Binding and activation of CO by nitrogenase is a topic of interest because CO is isoelectronic to N2, the physiological substrate of this enzyme. The catalytic relevance of one‐ and multi‐CO‐bound states (the lo‐CO and hi‐CO states) of V‐nitrogenase to C−C coupling and N2reduction was examined. Enzymatic and spectroscopic studies demonstrate that the multiple CO moieties in the hi‐CO state cannot be coupled as they are, suggesting that C−C coupling requires further activation and/or reduction of the bound CO entity. Moreover, these studies reveal an interesting correlation between decreased activity of N2reduction and increased population of the lo‐CO state, pointing to the catalytic relevance of the belt Fe atoms that are bridged by the single CO moiety in the lo‐CO state. Together, these results provide a useful framework for gaining insights into the nitrogenase‐catalyzed reaction via further exploration of the utility of the lo‐CO conformation of V‐nitrogenase.
more »
« less
Light‐driven Transformation of Carbon Monoxide into Hydrocarbons using CdS@ZnS : VFe Protein Biohybrids
Abstract Enzymatic Fisher‐Tropsch (FT) process catalyzed by vanadium (V)‐nitrogenase can convert carbon monoxide (CO) to longer‐chain hydrocarbons (>C2) under ambient conditions, although this process requires high‐cost reducing agent(s) and/or the ATP‐dependent reductase as electron and energy sources. Using visible light‐activated CdS@ZnS (CZS) core‐shell quantum dots (QDs) as alternative reducing equivalent for the catalytic component (VFe protein) of V‐nitrogenase, we first report a CZS : VFe biohybrid system that enables effective photo‐enzymatic C−C coupling reactions, hydrogenating CO into hydrocarbon fuels (up to C4) that can be hardly achieved with conventional inorganic photocatalysts. Surface ligand engineering optimizes molecular and opto‐electronic coupling between QDs and the VFe protein, realizing high efficiency (internal quantum yield >56 %), ATP‐independent, photon‐to‐fuel production, achieving an electron turnover number of >900, that is 72 % compared to the natural ATP‐coupled transformation of CO into hydrocarbons by V‐nitrogenase. The selectivity of products can be controlled by irradiation conditions, with higher photon flux favoring (longer‐chain) hydrocarbon generation. The CZS : VFe biohybrids not only can find applications in industrial CO removal for high‐value‐added chemical production by using the cheap, renewable solar energy, but also will inspire related research interests in understanding the molecular and electronic processes in photo‐biocatalytic systems.
more »
« less
- Award ID(s):
- 1904131
- PAR ID:
- 10439324
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- ChemSusChem
- Volume:
- 16
- Issue:
- 20
- ISSN:
- 1864-5631
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
null (Ed.)The electronic structure of the active-site metal cofactor (FeV-cofactor) of resting-state V-dependent nitrogenase has been an open question, with earlier studies indicating that it exhibits a broad S = 3/2 EPR signal (Kramers state) having g values of ∼4.3 and 3.8, along with suggestions that it contains metal-ions with valencies [1V 3+ , 3Fe 3+ , 4Fe 2+ ]. In the present work, genetic, biochemical, and spectroscopic approaches were combined to reveal that the EPR signals previously assigned to FeV-cofactor do not correlate with active VFe-protein, and thus cannot arise from the resting-state of catalytically relevant FeV-cofactor. It, instead, appears resting-state FeV-cofactor is either diamagnetic, S = 0, or non-Kramers, integer-spin ( S = 1, 2 etc. ). When VFe-protein is freeze-trapped during high-flux turnover with its natural electron-donating partner Fe protein, conditions which populate reduced states of the FeV-cofactor, a new rhombic S = 1/2 EPR signal from such a reduced state is observed, with g = [2.18, 2.12, 2.09] and showing well-defined 51 V ( I = 7/2) hyperfine splitting, a iso = 110 MHz. These findings indicate a different assignment for the electronic structure of the resting state of FeV-cofactor: S = 0 (or integer-spin non-Kramers state) with metal-ion valencies, [1V 3+ , 4Fe 3+ , 3Fe 2+ ]. Our findings suggest that the V 3+ does not change valency throughout the catalytic cycle.more » « less
-
Abstract Oxidative coupling of methane (OCM) can be performed electrocatalytically by utilizing solid oxide cells, which provide a readily controlled oxygen supply through dense electrolytes. La0.7Sr0.2Ni0.2Fe0.8O3(LSNF) perovskite is an effective anode for OCM. Its surface characteristics and electrocatalytic activity can be improved by reduction and the resultant exsolution of bimetallic NiFe nanoparticles from its bulk. X‐ray diffraction (XRD) and environmental transmission electron microscopy proved that the evolution of hetero‐phases under reducing environment resulted in bimetallic NiFe nanoparticles being formed on the surface. A 36 % improvement in C2+hydrocarbon production rate was achieved due to the reduction of LSNF with the exsolved NiFe nanoparticles. Co‐feeding of H2O enhanced selective conversion of CH4resulting in the production rate of C2+hydrocarbons being increased by 56 %. Analysis of impedance spectra and in‐situ DRIFTS under a CH4+H2O atmosphere provided an understanding for the enhancement on the electrocatalytic OCM.more » « less
-
Quantum information processing demands efficient quantum light sources (QLS) capable of producing high-fidelity single photons or entangled photon pairs. Single epitaxial quantum dots (QDs) have long been proven to be efficient sources of deterministic single photons; however, their production via molecular-beam epitaxy presents scalability challenges. Conversely, colloidal semiconductor QDs offer scalable solution processing and tunable photoluminescence but suffer from broader linewidths and unstable emissions. This leads to spectrally inseparable emission from exciton (X) and biexciton (XX) states, complicating the production of single photons and triggered photon pairs. Here, we demonstrate that colloidal semiconductor quantum shells (QSs) achieve significant spectral separation (~ 75-80 meV) and long temporal stability of X and XX emissive states, enabling the observation of exciton-biexciton bunching in colloidal QDs. Our low-temperature single-particle measurements show cascaded XX-X emission of single photon pairs for over 200 seconds, with minimal overlap between X and XX features. The X-XX distinguishability allows for an in-depth theoretical characterization of cross-correlation strength, placing it in perspective with photon pairs of epitaxial counterparts. These findings highlight a strong potential of semiconductor quantum shells for applications in quantum information processing.more » « less
-
null (Ed.)CO 2 -based enhanced oil recovery is widely practiced. The current understanding of its mechanisms largely focuses on bulk phenomena such as achieving miscibility or reducing oil density and viscosity. Using molecular dynamics simulations, we show that CO 2 adsorption on calcite surfaces impedes decane transport at moderate adsorption density but enhances decane transport when CO 2 adsorption approaches surface saturation. These effects change the decane permeability through 8 nm-wide pores by up to 30% and become negligible only in pores wider than several tens of nanometers. The strongly nonlinear, non-monotonic dependence of decane permeability on CO 2 adsorption is traced to CO 2 's modulation of interfacial structure of long-chain hydrocarbons, and thus the slippage between interfacial hydrocarbon layers and between interfacial CO 2 and hydrocarbon layers. These results highlight a new and critical role of CO 2 -induced interfacial effects in influencing oil recovery from unconventional reservoirs, whose porosity is dominated by nanopores.more » « less
