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156 results on '"Clark, Ewan R."'

1. Himic Anhydride: A Retro Diels-Alder Reaction for the Organic Laboratory and an Accompanying NMR Study

Author

Birchall, Lee T., Shehata, Sara, Serpell, Christopher J., Clark, Ewan R., and Biagini, Stefano C. G.

Abstract

The thermal equilibration of himic anhydride [IUPAC (2-"endo,"3-"endo")-bicyclo[2.2.1]hept-5-ene-2,3-dicarboxylic acid anhydride] to (2-"exo,"3-"exo")-bicyclo[2.2.1]hept-5-ene-2,3-dicarboxylic acid anhydride and subsequent recrystallization of the "exo"-product can be performed as a standard undergraduate laboratory experiment requiring minimal equipment. The interpretation of the [superscript 1]H NMR spectra for these norbornene carboxylic anhydride molecules promotes an appreciation of constrained ring systems and factors that affect chemical shifts and coupling constants.

Published
2021
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2. Competitive Intramolecular Hydrogen Bonding: Offering Molecules a Choice.

Author

Sun, Yu, Morton, Evelyn R., Bhabha, Hunaida, Clark, Ewan R., Bučar, Dejan‐Krešimir, Barros‐Metlova, Victoria, Gould, Jamie A., Aliev, Abil E., and Haynes, Cally J. E.

Subjects
DRUG design, CONFORMATIONAL analysis, DENSITY functional theory, HYDROGEN bonding, SOLVENT analysis
Abstract

The conformational preferences of N‐((6‐methylpyridin‐2‐yl)carbamothioyl)benzamide were studied in solution, the gas phase and the solid state via a combination of NMR, density functional theory (DFT) and single crystal X‐ray techniques. This acyl thiourea derivative can adopt two classes of low energy conformation, each stabilized by a different 6‐membered intramolecular hydrogen bond (IHB) pseudoring. Analysis in different solvents revealed that the conformational preference of this molecule is polarity dependent, with increasingly polar environments yielding a higher proportion of the minor conformer containing an NH⋅⋅⋅N IHB. The calculated barrier to interconversion is consistent with dynamic behaviour at room temperature, despite the propensity of 6‐membered IHB pseudorings to be static. This work demonstrates that introducing competitive IHB pathways can render static IHBs more dynamic and that such systems could have potential as chameleons in drug design. [ABSTRACT FROM AUTHOR]

Published
2024
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4. Contrasting reactivity of B–Cl and B–H bonds at [Ni(IMes)2] to form unsupported Ni-boryls.

Author

Audsley, Gabrielle, Carpentier, Ambre, Pécharman, Anne-Frédérique, Wright, James, Roseveare, Thomas M., Clark, Ewan R., Macgregor, Stuart A., and Riddlestone, Ian M.

Subjects
OXIDATIVE addition, SCISSION (Chemistry)
Abstract

[Ni(IMes)2] reacts with chloroboranes via oxidative addition to form rare unsupported Ni-boryls. In contrast, the oxidative addition of hydridoboranes is not observed and products from competing reaction pathways are identified. Computational studies relate these differences to the mechanism of oxidative addition: B–Cl activation proceeds via nucleophilic displacement of Cl−, while B–H activation would entail high energy concerted bond cleavage. [ABSTRACT FROM AUTHOR]

Published
2024
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7. Quantum Spin‐ Dimers in a Low‐Dimensional Tetrabromocuprate Magnet

Author

Sampson, Gavin, Bristowe, Nicholas C., Carr, Sam T., Saib, Asad, Stenning, Gavin B. G., Clark, Ewan R., and Saines, Paul J.

Abstract

This work describes a homometallic spin ½ tetrabromocuprate adopting a bilayer structure. Magnetic susceptibility measurements show a broad maximum centered near 70 K, with fits to this data using a Heisenberg model consistent with strong antiferromagnetic coupling between neighboring Cu in different layers of the bilayer. There are further weak intralayer ferromagnetic interactions between Cu cations in neighboring dimers. First principles calculations are consistent with this but suggest there is only significant magnetic coupling within one direction of a layer; this would suggest the presence of a spin-ladder within the bilayer with antiferromagnetic rung and weaker ferromagnetic rail couplings.

Published
2022

9. Establishing the selective phospholipid membrane coordination, permeation and lysis properties for a series of ‘druggable’ supramolecular self-associating antimicrobial amphiphiles (accepted)

Author

Boles, Jessica E., Bennett, C., Baker, J., Hilton, Kira L.F., Kotak, H. A., Clark, Ewan R., Long, Y, White, Lisa J., Lai, H. Y., Hind, C. K., Sutton, J. Mark, Garrett, Michelle D., Cheasty, A, Ortega-Roldan, Jose L., Charles, Mark, Haynes, Cally J. E., and Hiscock, Jennifer R.

Abstract

The rise of antimicrobial resistance remains one of the greatest global health threats facing humanity. Furthermore, the development of novel antibiotics has all but ground to a halt due to a collision of intersectional pressures. Herein we determine the antimicrobial efficacy for 14 structurally related supramolecular self-associating amphiphiles against clinically relevant Gram-positive methicillin resistant Staphylococcus aureus and Gram-negative Escherichia coli. We establish the ability of these agents to selectively target phospholipid membranes of differing compositions, through a combination of computational host:guest complex formation simulations, synthetic vesicle lysis, adhesion and membrane fluidity experiments, alongside our novel 1H NMR CPMG nanodisc coordination assays, to verify a potential mode of action for this class of compounds and enable the production of evermore effective next-generation antimicrobial agents. Finally, we select a 7-compound subset, showing two lead compounds to exhibit ‘druggable’ profiles through completion of a variety of in vivo and in vitro DMPK studies., Author's Accepted Manuscript

Published
2022
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10. Diverse Cooperative Reactivity at a Square Planar Aluminium Complex and Catalytic Reduction of CO2.

Author

Shaves, Chloe L., Villegas-Escobar, Nery, Clark, Ewan R., and Riddlestone, Ian M.

Subjects
CATALYTIC reduction, ALUMINUM, SQUARE, LEWIS acids
Abstract

The use of a sterically demanding pincer ligand to prepare an unusual square planar aluminium complex is reported. Due to the constrained geometry imposed by the ligand scaffold, this four-coordinate aluminium centre remains Lewis acidic and reacts via differing metal-ligand cooperative pathways for activating ketones and CO2. It is also a rare example of a single-component aluminium system for the catalytic reduction of CO2 to a methanol equivalent at room temperature. [ABSTRACT FROM AUTHOR]

Published
2023
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11. Establishing the selective phospholipid membrane coordination, permeation and lysis properties for a series of ‘druggable’ supramolecular self-associating antimicrobial amphiphiles

Author

Boles, Jessica E., primary, Bennett, Charlotte, additional, Baker, Jennifer, additional, Hilton, Kira L. F., additional, Kotak, Hiral A., additional, Clark, Ewan R., additional, Long, Yifan, additional, White, Lisa J., additional, Lai, Hin Yuk, additional, Hind, Charlotte K., additional, Sutton, J. Mark, additional, Garrett, Michelle D., additional, Cheasty, Anne, additional, Ortega-Roldan, Jose L., additional, Charles, Mark, additional, Haynes, Cally J. E., additional, and Hiscock, Jennifer R., additional

Published
2022
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16. Towards the prediction of global solution state properties for hydrogen bonded, self-associating amphiphiles

Author

White, Lisa J., Tyuleva, Stilyana N., Wilson, Ben, Shepherd, H.J., Ng, Kendrick K. L., Holder, Simon J., Clark, Ewan R., and Hiscock, Jennifer R.

Abstract

Through this extensive structure-property study we show that critical micelle concentration correlates with self-associative hydrogen bond complex formation constant, when combined with outputs from low level, widely accessible, computational models. Herein, we bring together a series of 39 structurally related molecules obtained through stepwise variation of a hydrogen bond donor-acceptor amphiphilic salt. The self-associative and corresponding global properties for this family of compounds have been studied in the gas, solid and solution states. Within the solution state we have shown the type of self-associated structure present to be solvent dependent. In DMSO, this class of compound show a preference for hydrogen bonded dimer formation, however moving into aqueous solutions the same compounds are found to form larger self-associated aggregates. This observation has allowed us the unique opportunity to investigate and begin to predict selfassociation events at both the molecular and extended aggregate level.

Published
2018

17. Metal-free electrocatalytic hydrogen oxidation using frustrated Lewis pairs and carbon-based Lewis acids† †Electronic supplementary information (ESI) available. See DOI: 10.1039/c5sc04564a Click here for additional data file

Author

Lawrence, Elliot J., Clark, Ewan R., Curless, Liam D., Courtney, James M., Blagg, Robin J., Ingleson, Michael J., and Wildgoose, Gregory G.

Subjects
Chemistry
Abstract

The synergistic interaction of a carbon-centred Lewis acid and borane “hydride shuttle” offers a metal-free, CO tolerant pathway to hydrogen oxidation., Whilst hydrogen is a potentially clean fuel for energy storage and utilisation technologies, its conversion to electricity comes at a high energetic cost. This demands the use of rare and expensive precious metal electrocatalysts. Electrochemical-frustrated Lewis pairs offer a metal-free, CO tolerant pathway to the electrocatalysis of hydrogen oxidation. They function by combining the hydrogen-activating ability of frustrated Lewis pairs (FLPs) with electrochemical oxidation of the resultant hydride. Here we present an electrochemical–FLP approach that utilises two different Lewis acids – a carbon-based N-methylacridinium cation that possesses excellent electrochemical attributes, and a borane that exhibits fast hydrogen cleavage kinetics and functions as a “hydride shuttle”. This synergistic interaction provides a system that is electrocatalytic with respect to the carbon-based Lewis acid, decreases the required potential for hydrogen oxidation by 1 V, and can be recycled multiple times.

Published
2016

22. Germanium(II) and tin(II) complexes of a sterically demanding phosphanide ligand

Author

Izod, Keith, Stewart, John, Clark, Ewan R., Clegg, William, and Harrington, Ross W.

Subjects
Germanium -- Chemical properties, Nuclear magnetic resonance spectroscopy -- Usage, Organolithium compounds -- Structure, Organolithium compounds -- Chemical properties, Tetrahydrofuran -- Chemical properties, Tin -- Chemical properties, Chemistry
Published
2010

25. Highly nucleophilic dipropanolamine chelated boron reagents for aryl-transmetallation to iron complexes

Author

Dunsford, Jay J, Clark, Ewan R., and Ingleson, Michael J.

Subjects
inorganic chemicals
Abstract

New aryl- and heteroarylboronate esters chelated by dipropanolamine are synthesised directly from boronic acids. The corresponding anionic borates are readily accessible by deprotonation and demonstrate an increase in hydrocarbyl nucleophilicity in comparison to other common borates. The new borates proved competent for magnesium or zinc additive-free, direct boron-to-iron hydrocarbyl transmetallations with well-defined iron(II) (pre)catalysts. The application of the new borate reagents in representative Csp2–Csp3 cross-coupling led to almost exclusive homocoupling unless coupling is performed in the presence of a zinc additive.

Published
2015

26. [(acridine)BCl2]+: A Borenium Cation That Is a Strong Boron- and Carbon-Based Lewis Acid

Author

Clark, Ewan R. and Ingleson, Michael J.

Abstract

[(acridine)BCl2][AlCl4] was synthesized by halide abstraction from (acridine)BCl3with AlCl3. The hydride ion affinity of the C9 position in [(acridine)BCl2]+was calculated to be 14 kcal mol–1greater than that at boron. [(acridine)BCl2][AlCl4] reacts with 1 equiv of acridine to form the strained boronium cation [(acridine)2BCl2][AlCl4] and with P(mesityl)3by photoinduced one-electron transfer to form the 9,9′-biacridane moiety by radical coupling. A stable frustrated Lewis pair (FLP) was formed on combining [(acridine)BCl2][AlCl4] and 2,4,6-tri-tert-butylpyridine (TBP), which heterolytically activated H2at 100 °C. The ultimate location of the hydride from H2activation was the C9 position of acridine and not boron. Carbon Lewis acid based reactivity also occurred when thieno[3,2-b]thiophene was added to the [(acridine)BCl2][AlCl4]/TBP FLP or to [(acridine)2BCl2][AlCl4], with arylation of acridine at C9 observed for both.

Published
2024
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49. Direct C(sp2)-C(sp3) Cross-Coupling of Diaryl Zinc Reagents with Benzylic, Primary, Secondary, and Tertiary Alkyl Halides.

Author

Dunsford, Jay J., Clark, Ewan R., and Ingleson, Michael J.

Subjects
*CARBON compounds, *ZINC, *TRANSITION metals, *HALOALKANES, *SOLVENTS, *CATALYSTS
Abstract

The direct C(sp2)-C(sp3) cross-coupling of diaryl zinc reagents with benzylic, primary, secondary, and tertiary alkyl halides proceeded in the absence of coordinating ethereal solvents at ambient temperature without the addition of a catalyst. The C(sp2)-C(sp3) cross-coupling showed excellent functional-group tolerance, and products were isolated in high yields, generally without the requirement for purification by chromatography. This process represents an expedient, operationally simple method for the construction of new C(sp2)- C(sp3) bonds. [ABSTRACT FROM AUTHOR]

Published
2015
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50. Direct C(sp²)-C(sp³) Cross-Coupling of Diaryl Zinc Reagents with Benzylic, Primary, Secondary, and Tertiary Alkyl Halides.

Author

Dunsford, Jay J., Clark, Ewan R., and Ingleson, Michael J.

Subjects
DIARYL compounds, HALOALKANES, FUNCTIONAL groups, CARBON-carbon bonds, BENZYLIC group, CHROMATOGRAPHIC analysis
Abstract

The direct C(sp²)-C(sp³) cross-coupling of diaryl zinc reagents with benzylic, primary, secondary, and tertiary alkyl halides proceeded in the absence of coordinating ethereal solvents at ambient temperature without the addition of a catalyst. The C(sp²)-C(sp³) cross-coupling showed excellent functional-group tolerance, and products were isolated in high yields, generally without the requirement for purification by chromatography. This process represents an expedient, operationally simple method for the construction of new C(sp²)-C(sp³) bonds. [ABSTRACT FROM AUTHOR]

Published
2015
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