Search

Your search keyword '"Knowles, Robert R."' showing total 274 results
Start Over Author "Knowles, Robert R."
274 results on '"Knowles, Robert R."'

1. Diamond Surface Functionalization via Visible Light-Driven C-H Activation for Nanoscale Quantum Sensing

Author

Rodgers, Lila V. H., Nguyen, Suong T., Cox, James H., Zervas, Kalliope, Yuan, Zhiyang, Sangtawesin, Sorawis, Stacey, Alastair, Jaye, Cherno, Weiland, Conan, Pershin, Anton, Gali, Adam, Thomsen, Lars, Meynell, Simon A., Hughes, Lillian B., Jayich, Ania C. Bleszynski, Gui, Xin, Cava, Robert J., Knowles, Robert R., and de Leon, Nathalie P.

Subjects
Condensed Matter - Materials Science, Quantum Physics
Abstract

Nitrogen-vacancy centers in diamond are a promising platform for nanoscale nuclear magnetic resonance sensing. Despite significant progress towards using NV centers to detect and localize nuclear spins down to the single spin level, NV-based spectroscopy of individual, intact, arbitrary target molecules remains elusive. NV molecular sensing requires that target molecules are immobilized within a few nanometers of NV centers with long spin coherence time. The inert nature of diamond typically requires harsh functionalization techniques such as thermal annealing or plasma processing, limiting the scope of functional groups that can be attached to the surface. Solution-phase chemical methods can be more readily generalized to install diverse functional groups, but they have not been widely explored for single-crystal diamond surfaces. Moreover, realizing shallow NV centers with long spin coherence times requires highly ordered single-crystal surfaces, and solution-phase functionalization has not yet been shown to be compatible with such demanding conditions. In this work, we report a versatile strategy to directly functionalize C-H bonds on single-crystal diamond surfaces under ambient conditions using visible light. This functionalization method is compatible with charge stable NV centers within 10 nm of the surface with spin coherence times comparable to the state of the art. As a proof of principle, we use shallow ensembles of NV centers to detect nuclear spins from functional groups attached to the surface. Our approach to surface functionalization based on visible light-driven C-H bond activation opens the door to deploying NV centers as a broad tool for chemical sensing and single-molecule spectroscopy.

Published
2023
Full Text
View/download PDF

2. Radical Redox Annulations: A General Light-Driven Method for the Synthesis of Saturated Heterocycles

Author

Murray, Philip RD, Leibler, Isabelle Nathalie-Marie, Hell, Sandrine M, Villalona, Eris, Doyle, Abigail G, and Knowles, Robert R

Subjects
Generic health relevance, annulation, photocatalysis, PCET, heterocycles, carbocations, Inorganic Chemistry, Organic Chemistry, Chemical Engineering
Abstract

We introduce here a two-component annulation strategy that provides access to a diverse collection of five- and six-membered saturated heterocycles from aryl alkenes and a family of redox-active radical precursors bearing tethered nucleophiles. This transformation is mediated by a combination of an Ir(III) photocatalyst and a Brønsted acid under visible-light irradiation. A reductive proton-coupled electron transfer generates a reactive radical which undergoes addition to an alkene. Then, an oxidative radical-polar crossover step leading to carbocation formation is followed by ring closure through cyclization of the tethered nucleophile. A wide range of heterocycles are easily accessible, including pyrrolidines, piperidines, tetrahydrofurans, morpholines, δ-valerolactones, and dioxanones. We demonstrate the scope of this approach through broad structural variation of both reaction components. This method is amenable to gram-scale preparation and to complex fragment coupling.

Published
2022

9. Diamond surface functionalization via visible light-driven C-H activation for nanoscale quantum sensing.

Author

Rodgers, Lila V. H., Suong T. Nguyen, Cox, James H., Zervas, Kalliope, Zhiyang Yuan, Sangtawesin, Sorawis, Stacey, Alastair, Jaye, Cherno, Weiland, Conan, Pershin, Anton, Gali, Adam, Thomsen, Lars, Meynell, Simon A., Hughes, Lillian B., Bleszynski Jayich, Ania C., Xin Gui, Cava, Robert J., Knowles, Robert R., and de Leon, Nathalie P.

Subjects
DIAMOND surfaces, NUCLEAR spin, THERMAL plasmas, PLASMA materials processing, FUNCTIONAL groups, MELT spinning
Abstract

Nitrogen-vacancy (NV) centers in diamond are a promising platform for nanoscale NMR sensing. Despite significant progress toward using NV centers to detect and localize nuclear spins down to the single spin level, NV-based spectroscopy of individual, intact, arbitrary target molecules remains elusive. Such sensing requires that target molecules are immobilized within nanometers of NV centers with long spin coherence. The inert nature of diamond typically requires harsh functionalization techniques such as thermal annealing or plasma processing, limiting the scope of functional groups that can be attached to the surface. Solution-phase chemical methods can be readily generalized to install diverse functional groups, but they have not been widely explored for single-crystal diamond surfaces. Moreover, realizing shallow NV centers with long spin coherence times requires highly ordered single-crystal surfaces, and solution-phase functionalization has not yet been shown with such demanding conditions. In this work, we report a versatile strategy to directly functionalize C--H bonds on single-crystal diamond surfaces under ambient conditions using visible light, forming C--F, C--Cl, C--S, and C--N bonds at the surface. This method is compatible with NV centers within 10 nm of the surface with spin coherence times comparable to the state of the art. As a proof-of-principle demonstration, we use shallow ensembles of NV centers to detect nuclear spins from surface-bound functional groups. Our approach to surface functionalization opens the door to deploying NV centers as a tool for chemical sensing and single-molecule spectroscopy. [ABSTRACT FROM AUTHOR]

Published
2024
Full Text
View/download PDF

15. Proton-Coupled Electron Transfer in Organic Synthesis: Fundamentals, Applications, and Opportunities

Author

Miller, David C., Tarantino, Kyle T., Knowles, Robert R., Bayley, Hagan, Editorial board, Houk, Kendall N., Editorial board, Hughes, Greg, Editorial board, Hunter, Christopher A., Series editor, Ishihara, Kazuaki, Series editor, Krische, Michael J, Series editor, Lehn, Jean-Marie, Series editor, Lehn, J.-M., Editorial board, Luque, Rafael, Editorial board, Olivucci, Massimo, Editorial board, Siegel, Jay S., Editorial board, Thiem, Joachim, Editorial board, Venturi, Margherita, Editorial board, Wong, Chi-Huey, Editorial board, Wong, Henry N.C., Editorial board, Wing-Wah Yam, Vivian, Editorial board, Wong, Wai-Yeung, Editorial board, Yam, Vivian Wing-Wah, Series editor, Yan, Chunhua, Series editor, You, Shu-Li, Series editor, Guillena, Gabriela, editor, and Ramón, Diego J., editor

Published
2016
Full Text
View/download PDF

17. Radical Redox Annulations: A General Light-Driven Method for the Synthesis of Saturated Heterocycles

Author

Murray, Philip R. D., Leibler, Isabelle Nathalie-Marie, Hell, Sandrine M., Villalona, Eris, Doyle, Abigail G., and Knowles, Robert R.

Subjects
carbocations, Inorganic Chemistry, heterocycles, Organic Chemistry, General Chemistry, Generic health relevance, Chemical Engineering, annulation, PCET, photocatalysis, Catalysis, annulation, photocatalysis, PCET, heterocycles, carbocations
Abstract

We introduce here a two-component annulationstrategy that provides access to a diverse collection of five- and six- membered saturated heterocycles from aryl alkenes and a family ofredox-active radical precursors bearing tethered nucleophiles. This transformation is mediated by a combination of an Ir(III)photocatalyst and a Brønsted acid under visible-light irradiation. A reductive proton-coupled electron transfer generates a reactiveradical which undergoes addition to an alkene. Then, an oxidative radical-polar crossover step leading to carbocation formation isfollowed by ring closure through cyclization of the tethered nucleophile. A wide range of heterocycles are easily accessible,including pyrrolidines, piperidines, tetrahydrofurans, morpholines, δ-valerolactones, and dioxanones. We demonstrate the scope of this approach through broad structural variation of both reaction components. This method is amenable to gram-scale preparation and to complex fragment coupling.

Published
2022

26. Photochemical and Electrochemical Applications of Proton-Coupled Electron Transfer in Organic Synthesis

Author

Murray, Philip R. D., primary, Cox, James H., additional, Chiappini, Nicholas D., additional, Roos, Casey B., additional, McLoughlin, Elizabeth A., additional, Hejna, Benjamin G., additional, Nguyen, Suong T., additional, Ripberger, Hunter H., additional, Ganley, Jacob M., additional, Tsui, Elaine, additional, Shin, Nick Y., additional, Koronkiewicz, Brian, additional, Qiu, Guanqi, additional, and Knowles, Robert R., additional

Published
2021
Full Text
View/download PDF

29. Interference of nuclear wavepackets in a pair of proton transfer reactions.

Author

Xinzi Zhang, Schwarz, Kyra N., Luhao Zhang, Fassioli, Francesca, Bo Fu, Nguyen, Lucas Q., Knowles, Robert R., and Scholes, Gregory D.

Subjects
PROTON transfer reactions, WAVE packets, QUANTUM theory, QUANTUM correlations, QUANTUM mechanics
Abstract

Quantum mechanics revolutionized chemists' understanding of molecular structure. In contrast, the kinetics of molecular reactions in solution are well described by classical, statistical theories. To reveal how the dynamics of chemical systems transition from quantum to classical, we study femtosecond proton transfer in a symmetric molecule with two identical reactant sites that are spatially apart. With the reaction launched from a superposition of two local basis states, we hypothesize that the ensuing motions of the electrons and nuclei will proceed, conceptually, in lockstep as a superposition of probability amplitudes until decoherence collapses the system to a product. Using ultrafast spectroscopy, we observe that the initial superposition state affects the reaction kinetics by an interference mechanism. With the aid of a quantum dynamics model, we propose how the evolution of nuclear wavepackets manifests the unusual intersite quantum correlations during the reaction. [ABSTRACT FROM AUTHOR]

Published
2022
Full Text
View/download PDF

32. Intermolecular Crossed [2 + 2] Cycloaddition Promoted by Visible-Light Triplet Photosensitization: Expedient Access to Polysubstituted 2-Oxaspiro[3.3]heptanes

Author

Murray, Philip R. D., primary, Bussink, Willem M. M., additional, Davies, Geraint H. M., additional, van der Mei, Farid W., additional, Antropow, Alyssa H., additional, Edwards, Jacob T., additional, D’Agostino, Laura Akullian, additional, Ellis, J. Michael, additional, Hamann, Lawrence G., additional, Romanov-Michailidis, Fedor, additional, and Knowles, Robert R., additional

Published
2021
Full Text
View/download PDF

33. Catalytic alkylation of remote CH bonds enabled by proton-coupled electron transfer

Author

Choi, Gilbert J., Zhu, Qilei, Miller, David C., Gu, Carol J., and Knowles, Robert R.

Subjects
Chemical bonds -- Observations, Electron transport -- Observations, Environmental issues, Science and technology, Zoology and wildlife conservation
Abstract

Author(s): Gilbert J. Choi [1]; Qilei Zhu [1]; David C. Miller [1]; Carol J. Gu [1]; Robert R. Knowles (corresponding author) [1] Despite advances in hydrogen atom transfer (HAT) catalysis [...]

Published
2016
Full Text
View/download PDF

40. C–H Alkylation via Multisite-Proton-Coupled Electron Transfer of an Aliphatic C–H Bond

Author

UCL - SST/IMCN/MOST - Molecular Chemistry, Materials and Catalysis, Morton, Carla M., Zhu, Qilei, Ripberger, Hunter, Troian-Gautier, Ludovic, Toa, Zi S. D., Knowles, Robert R., Alexanian, Erik J., UCL - SST/IMCN/MOST - Molecular Chemistry, Materials and Catalysis, Morton, Carla M., Zhu, Qilei, Ripberger, Hunter, Troian-Gautier, Ludovic, Toa, Zi S. D., Knowles, Robert R., and Alexanian, Erik J.

Abstract

The direct, site-selective alkylation of unactivated C(sp3)–H bonds in organic substrates is a long-standing goal in synthetic chemistry. General approaches to the activation of strong C–H bonds include radical-mediated processes involving highly reactive intermediates, such as heteroatom-centered radicals. Herein, we describe a catalytic, intermolecular C–H alkylation that circumvents such reactive species via a new elementary step for C–H cleavage involving multisite-proton-coupled electron transfer (multisite-PCET). Mechanistic studies indicate that the reaction is catalyzed by a noncovalent complex formed between an iridium(III) photocatalyst and a monobasic phosphate base. The C–H alkylation proceeds efficiently using diverse hydrocarbons and complex molecules as the limiting reagent and represents a new approach to the catalytic functionalization of unactivated C(sp3)–H bonds.

Published
2019

41. Discovery and mechanistic study of a photocatalytic indoline dehydrogenation for the synthesis of elbasvir† †Electronic supplementary information (ESI) available: Detailed experimental procedures and characterization data for all new compounds. See DOI: 10.1039/c5sc03350k

Author

Yayla, Hatice G., Peng, Feng, Mangion, Ian K., McLaughlin, Mark, Campeau, Louis-Charles, Davies, Ian W., DiRocco, Daniel A., and Knowles, Robert R.

Subjects
Chemistry, viruses, virus diseases, biochemical phenomena, metabolism, and nutrition, digestive system diseases
Abstract

Elbasvir is a potent NS5A antagonist for the treatment of chronic hepatitis C., Elbasvir is a potent NS5A antagonist for the treatment of chronic hepatitis C. A seemingly trivial indoline oxidation en route to the target compound was complicated by epimerization of a stereogenic hemiaminal center under most standard oxidation conditions. To address this issue, a novel visible light photoredox process for indoline oxidation was developed involving an iridium photosensitizer and environmentally-benign perester oxidant. The reaction was discovered through a high-throughput experimentation campaign and the optimized process was demonstrated on 100 g scale in flow to afford a key intermediate towards the target compound. A battery of kinetic, electrochemical, and spectroscopic studies of this process indicates a radical chain mechanism of dehydrogenation involving selective HAT from the substrate by an alkoxy radicals. Notably, isotope effects were used to validate the chain mechanism when quantum yield data proved ambiguous.

Published
2015

Catalog

Books, media, physical & digital resources
See catalog results