Coherent short-pulse laser excitation has been used to control the approximate energy and relative proximity of two valence electrons within the same alkaline-earth atom, thereby providing insight into the dynamical evolution of a three-body Coulomb system. Our time-domain experiments enable direct experimental study of the electron dynamics at the classical limit of a two-electron atom. As an example, we look at the mechanism of autoionization for one two-electron configuration class and find that the doubly excited atom decays through a single violent electron-electron collision rather than a gradual exchange of energy between the electrons.
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http://dx.doi.org/10.1126/science.1092220 | DOI Listing |
Biochemistry
January 2025
Department of Chemistry, University of Florida, Gainesville, Florida 32611, United States.
Post-transcriptional modifications at the anticodon stem-loop of tRNAs are key to the translation function. Metabolic pathways to these modifications often incorporate complex enzymology. A notable example is the hypermodified nucleoside, queuosine, found at the wobble position of Asn, Asp, His, and Tyr encoding tRNAs.
View Article and Find Full Text PDFSci Rep
November 2024
School of Environmental Science and Engineering, Southwest Jiaotong University, Chengdu, 611756, China.
J Am Chem Soc
November 2024
Division of Chemistry and Chemical Engineering, California Institute of Technology (Caltech), Pasadena, California 91125, United States.
Reagents capable of concerted proton-electron transfer (CPET) reactions can access reaction pathways with lower reaction barriers compared to stepwise pathways involving electron transfer (ET) and proton transfer (PT). To realize reductive multielectron/proton transformations involving CPET, one approach that has shown recent promise involves coupling a cobaltocene ET site with a protonated arylamine Brønsted acid PT site. This strategy colocalizes the electron/proton in a matter compatible with a CPET step and net reductive electrocatalysis.
View Article and Find Full Text PDFJ Phys Chem B
November 2024
School of Chemistry, Chemical Engineering and Biotechnology, Nanyang Technological University, Singapore 637371, Singapore.
The electrochemical reduction of riboflavin (vitamin B) in a dimethyl sulfoxide solvent was examined under a CO atmosphere and compared with results under an argon atmosphere. Variable-scan-rate cyclic voltammetry combined with controlled potential electrolysis (CPE) and analysis by UV-vis and EPR spectroscopies provided insights into the nature of interactions of reduced flavins with dissolved CO. Reductive exhaustive CPE experiments under CO indicated an overall two-electron stoichiometry, compared to one-electron reduction under an argon atmosphere, due to the lowering of the formal one-electron reduction potential of the flavin radical anion to form the dianion, which can be rationalized by riboflavin-CO molecular interactions.
View Article and Find Full Text PDFInorg Chem
October 2024
Department of Chemistry and Chemical Biology, The University of New Mexico, MSC03 2060, 1 University of New Mexico, Albuquerque, New Mexico 87131-0001, United States.
A combination of X-ray absorption and low-temperature electronic absorption spectroscopies has been used to probe the geometric and electronic structures of the human mitochondrial amidoxime reducing component enzyme (hmARC1) in the oxidized Mo(VI) and reduced Mo(IV) forms. Extended X-ray absorption fine structure analysis revealed that oxidized enzyme possesses a 5-coordinate [MoO(S)(PDT)] (PDT = pyranopterin dithiolene) active site with a cysteine coordinated to Mo. A 5-coordinate geometry is retained in the reduced state, with the equatorial oxo being protonated.
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