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Your search keyword '"Forbes, Malcolm D. E."' showing total 292 results
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292 results on '"Forbes, Malcolm D. E."'

1. AB569, a nontoxic chemical tandem that kills major human pathogenic bacteria

Author

McDaniel, Cameron T., Panmanee, Warunya, Winsor, Geoffrey L., Gill, Erin, Bertelli, Claire, Schurr, Michael J., Dongare, Prateek, Paul, Andrew T., Ko, Seung-Hyun B., Lau, Gee W., Dasgupta, Nupur, Bogue, Amy L., Miller, William E., Mortensen, Joel E., Haslam, David B., Dexheimer, Phillip, Muruve, Daniel A., Aronow, Bruce J., Forbes, Malcolm D. E., Danilczuk, Marek, Brinkman, Fiona S. L., Hancock, Robert E. W., Meyer, Thomas J., and Hassett, Daniel J.

Published
2020

6. Photochemical [2+4]‐Dimerization Reaction from the Excited State.

Author

Ahuja, Sapna, Baburaj, Sruthy, Valloli, Lakshmy Kannadi, Rakhimov, Sarvar Aminovich, Manal, Kavyasree, Kushwaha, Aakrati, Jockusch, Steffen, Forbes, Malcolm D. E., and Sivaguru, Jayaraman

Subjects
EXCITED states, PHOTODIMERIZATION, VISIBLE spectra, ENERGY transfer, STEREOCHEMISTRY
Abstract

Aryl‐maleimides undergo a novel [2+4]‐photodimerization instead of the expected [2+2]‐photodimerization under both direct irradiation with visible light and under sensitized energy transfer conditions. This new excited state reactivity in aryl‐maleimides is deciphered through photochemical, photophysical, and spectroscopic studies. The stereochemistry of the photodimer depends on the type of non‐bonding interactions prevalent during photodimerization which is in turn dictated by the substituents on the maleimide ring. More importantly, the stereochemistry of the photodimer formed is complementary to the product observed under thermal conditions. [ABSTRACT FROM AUTHOR]

Published
2024
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9. Modulating Photochemical Properties to Enhance the Stability of Electronically Dimmable Eye Protection Devices†.

Author

Baburaj, Sruthy, Parthiban, Jayachandran, Rakhimov, Sarvar Aminovich, Johnson, Rasheedah, Sukhomlinova, Ludmila, Luchette, Paul, Jockusch, Steffen, Forbes, Malcolm D. E., and Sivaguru, Jayaraman

Subjects
LIQUID crystals, PHOTODEGRADATION
Abstract

The study evaluates compatibility of stabilizers with dye doped liquid crystal (LC) scaffolds that are used in electronically dimmable materials. The photodegradation of the materials was investigated and suitable stabilizers were evaluated to slow the degradation process. Various types of benzotriazole‐based stabilizers were evaluated for stabilizing the liquid crystals. Based on spin trapping experiments, radicals generated upon UV exposure is likely responsible for the degradation of the system. The radical generation is competitively inhibited by the addition of stabilizers. [ABSTRACT FROM AUTHOR]

Published
2023
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15. Anomalous chemically induced electron spin polarization in proton-coupled electron transfer reactions: insight into radical pair dynamics† †Dedicated to Professor Michael R. Wasielewski on the occasion of his 70th birthday

Author

Brugh, Alexander M. and Forbes, Malcolm D. E.

Subjects
Chemistry
Abstract

Time-resolved electron paramagnetic resonance (TREPR) spectroscopy has been used to study the proton coupled electron transfer (PCET) reaction between a Ruthenium complex (Ru(bpz)(bpy)2) and several substituted hydroquinones (HQ)., Time-resolved electron paramagnetic resonance (TREPR) spectroscopy has been used to study the proton coupled electron transfer (PCET) reaction between a ruthenium complex (Ru(bpz)(bpy)2) and several substituted hydroquinones (HQ). After excitation at 355 nm, the HQ moiety forms a strong hydrogen bond to the exposed N atoms in the bpz heterocycle. At some point afterwards, a PCET reaction takes place in which an electron from the O atom of the hydrogen bond transfers to the metal center, and the proton forming the hydrogen bond remains on the bpz ligand N atom. The result is a semiquinone radical (HQ˙), whose TREPR spectrum is strongly polarized by the triplet mechanism (TM) of chemically induced dynamic electron spin polarization (CIDEP). Closer examination of the CIDEP pattern reveals, in some cases, a small amount of radical pair mechanism (RPM) polarization. We hypothesize that when the HQ moiety has electron donating groups (EDGs) substituted on the ring, S–T– RPM polarization is observed in HQ˙. These anomalous intensities are accounted for by spectral simulation using polarization from S–T– mixing. The generation of S–T– RPM is attributed to slow radical separation after PCET due to stabilization of the positive charge on the ring by EDGs. Results from a temperature dependence support the hypothesis.

Published
2020

26. Chemically induced multiplet electron-nuclear polarization in zero and low magnetic fields

Author

Bagryanskaya, Elena G., Yashiro, Haruhiko, Fedin, Matvei, Purtov, Peter, and Forbes, Malcolm D. E.

Subjects
Chemistry, Physical and theoretical -- Research, Magnetic fields -- Physiological aspects, Electrons -- Physiological aspects, Polarization (Nuclear physics) -- Physiological aspects, Acids -- Physiological aspects, Chemicals, plastics and rubber industries
Published
2002

27. Time-resolved CIDNP study of intramolecular charge transfer in the dipeptide tryptophan-tyrosine

Author

Morozova, Olga B., Yurkovskaya, Alexandra V., Tsentalovich, Yuri P., Forbes, Malcolm D. E., and Sagdeev, Renad Z.

Subjects
Chemistry, Physical and theoretical -- Research, Polarization (Nuclear physics) -- Physiological aspects, Charge transfer -- Research, Peptides -- Physiological aspects, Tryptophan -- Physiological aspects, Tyrosine -- Physiological aspects, Chemicals, plastics and rubber industries
Published
2002

28. Study of the rotational barrier in the hindered bisphenoxyl A radical

Author

Clancy, Christine M. R. and Forbes, Malcolm D. E.

Subjects
Chemistry, Physical and theoretical -- Research, Rotational motion -- Analysis, Radicals (Chemistry) -- Physiological aspects, Phenols -- Physiological aspects, Carbon -- Physiological aspects, Chemicals, plastics and rubber industries
Published
2001

31. Guest Inclusion Modulates Concentration and Persistence of Photogenerated Radicals in Assembled Triphenylamine Macrocycles

Author

Sindt, Ammon J., primary, DeHaven, Baillie A., additional, Goodlett, Dustin W., additional, Hartel, Johannes O., additional, Ayare, Pooja J., additional, Du, Yong, additional, Smith, Mark D., additional, Mehta, Anil K., additional, Brugh, Alexander M., additional, Forbes, Malcolm D. E., additional, Bowers, Clifford R., additional, Vannucci, Aaron K., additional, and Shimizu, Linda S., additional

Published
2019
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34. Synthesis and crystal structure of catena-poly-[[tetra-µ-acetato-copper(II)]-µ-6-ethoxy-N²,N4-bis[2-(pyridin-2-yl)ethyl]-1,3,5-triazine-2,4-diamine].

Author

Ayodele, Mayokun J., Green, Travis C., Chathuri, W. A., Warsapperuma, V., Forbes, Malcolm D. E., and Ostrowski, Alexis D.

Subjects
CRYSTAL structure, INTERMOLECULAR forces, COORDINATION polymers, HYDROGEN bonding, SPACE groups, TRIAZINE derivatives, DIAMINES, TRIAZINES
Abstract

The title compound, [Cu2(C19H23N7O)(C2H3O2)4]n, was obtained via reaction of copper(II) acetate with the coordinating ligand, 6-ethoxy-N²,N4-bis[2-(pyridin-2-yl)ethyl]-1,3,5-triazine-2,4-diamine. The crystallized product adopts the monoclinic P21/c space group. The metal core exhibits a paddle-wheel structure typical for dicopper tetraacetate units, with triazine and pyridyl nitrogen atoms from different ligands coordinating to the two axial positions of the paddle wheel in an asymmetric manner. This forms a coordination polymer with the segments of the polymer created by the c-glide of the P21/c setting of the space group. The resulting chains running along the c-axis direction are held together by intramolecular N--H…O hydrogen bonding. These chains are further packed by dispersion forces, producing an extended three-dimensional structure. [ABSTRACT FROM AUTHOR]

Published
2021
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37. Persistent Radicals of Self‐assembled Benzophenone bis ‐Urea Macrocycles: Characterization and Application as a Polarizing Agent for Solid‐state DNP MAS Spectroscopy

Author

DeHaven, Baillie A., primary, Tokarski, John T., additional, Korous, Arthur A., additional, Mentink‐Vigier, Frederic, additional, Makris, Thomas M., additional, Brugh, Alexander M., additional, Forbes, Malcolm D. E., additional, van Tol, Johan, additional, Bowers, Clifford R., additional, and Shimizu, Linda S., additional

Published
2017
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38. B 12 -Mediated, Long Wavelength Photopolymerization of Hydrogels

Author

Hughes, Robert M., Shell, Jennifer R., Lawrence, David S., Brugh, Alexander M., Forbes, Malcolm D. E., Rodgers, Zachary L., Molesky, Brian P., Moran, Andrew M., and Doherty, Laura M.

Abstract

Medical hydrogel applications have expanded rapidly over the past decade. Implantation in patients by non-invasive injection is preferred, but this requires hydrogel solidification from a low viscosity solution to occur in vivo via an applied stimuli. Transdermal photo-crosslinking of acrylated biopolymers with photoinitiators and lights offers a mild, spatiotemporally controlled solidification trigger. However, the current short wavelength initiators limit curing depth and efficacy because they do not absorb within the optical window of tissue (600 - 900 nm). As a solution to the current wavelength limitations, we report the development of a red light responsive initiator capable of polymerizing a range of acrylated monomers. Photo-activation occurs within a range of skin type models containing high biochromophore concentrations.

Published
2015
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39. Guest Inclusion Modulates Concentration and Persistence of Photogenerated Radicals in Assembled Triphenylamine Macrocycles

Author

Sindt, Ammon J., DeHaven, Baillie A., Goodlett, Rachel L., Hartel, Johannes O., Ayare, Pooja J., Du, Yong, Smith, Mark D., Mehta, Anil K., Brugh, Alexander M., Forbes, Malcolm D. E., Bowers, Clifford R., Vannucci, Aaron K., and Shimizu, Linda S.

Abstract

Substituted triphenylamine (TPA) radical cations show great potential as oxidants and as spin-containing units in polymer magnets. Their properties can be further tuned by supramolecular assembly. Here, we examine how the properties of photogenerated radical cations, intrinsic to TPA macrocycles, are altered upon their self-assembly into one-dimensional columns. These macrocycles consist of two TPAs and two methylene ureas, which drive the assembly into porous organic materials. Advantageously, upon activation the crystals can undergo guest exchange in a single-crystal-to-single-crystal transformation generating a series of isoskeletal host–guest complexes whose properties can be directly compared. Photoinduced electron transfer, initiated using 365 nm light-emitting diodes, affords radicals at room temperature as observed by electron paramagnetic resonance (EPR) spectroscopy. The line shape of the EPR spectra and the quantity of radicals can be modulated by both polarity and heavy atom inclusion of the encapsulated guest. These photogenerated radicals are persistent, with half-lives between 1 and 7 d and display no degradation upon radical decay. Re-irradiation of the samples can restore the radical concentration back to a similar maximum concentration, a feature that is reproducible over several cycles. EPR simulations of a representative spectrum indicate two species, one containing two N hyperfine interactions and an additional broad signal with no resolvable hyperfine interaction. Intriguingly, TPA analogues without bromine substitution also exhibit similar quantities of photogenerated radicals, suggesting that supramolecular strategies can enable more flexibility in stable TPA radical structures. These studies will help guide the development of new photoactive materials.

Published
2020
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40. Dynamics of spin-correlated radical pairs in non-ionic surfactant solutions

Author

Chaney, Erin E. and Forbes, Malcolm D. E.

Subjects
Electron paramagnetic resonance spectroscopy -- Research, Radicals (Chemistry) -- Research, Chemicals, plastics and rubber industries
Abstract

Time-resolved (CW) electron paramagnetic resonance spectroscopy (TREPR) was used to investigate the different dynamics of radical pairs created in micelles made from nonionic, poly (ethylene glycol) (PEG)- based surfactants (Brij-35, Triton X-100, and Cremophor EL). Spectral simulation and comparison to other PEG radicals show that H-atom abstraction is taking place in PEG outer shell of Brij-35 and Triton X-100micelles rather than in the alky chain core.

Published
2003

45. B12-Mediated, Long Wavelength Photopolymerization of Hydrogels

Author

Rodgers, Zachary L., primary, Hughes, Robert M., additional, Doherty, Laura M., additional, Shell, Jennifer R., additional, Molesky, Brian P., additional, Brugh, Alexander M., additional, Forbes, Malcolm D. E., additional, Moran, Andrew M., additional, and Lawrence, David S., additional

Published
2015
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46. Radical Reactions with Double Memory of Chirality ( 2 MOC) for the Enantiospecific Synthesis of Adjacent Stereogenic Quaternary Centers in Solution: Cleavage and Bonding Faster than Radical Rotation

Author

Garcia-Garibay, Miguel A., Family, Farnosh, Campos, Luis M., Khan, Saeed I., Resendiz, Marino J. E., Lebedeva, Natalia V., Forbes, Malcolm D. E., and Fuller, Kerrian

Abstract

The solution photochemistry of bis(phenylpyrrolidinonyl)ketones (R,R)-1b and (S,S)-1b exhibited a remarkably high memory of chirality. Stereospecific decarbonylation to products (R,R)-3b and (S,S)-3b, respectively, occurred with an ee of ca. 80%. The reaction is thought to occur along the single state manifold by sequential Norrish type-I α-cleavage decarbonylation, and radical–radical combination in a time scale that is comparable to that required for the radical intermediate to expose its other enantiotopic face by rotation about an axis perpendicular to that of the p orbital (ca. 3–7 ps). The absolute configuration of a key intermediate and that of ketone (R,R)-1b were determined by single-crystal X-ray diffraction and the ee values of the photochemical products with the help of chiral shift reagent (+)-Eu(tfc)3 and chiral LC-MS/ MS. On the basis of the ee and de values at 25 °C, it could be determined that ca. 70% of the bond forming events occur with double memory of chirality, ca. 21% occur after rotation of one radical to form the meso product (R,S)-3b, and only 9% occur after double rotation to form the opposite enantiomer. This report represents the first example of a doubly enantiospecific Norrish type-I and decarbonylation reaction in solution and illustrates potentially efficient ways to obtain compounds with adjacent stereogenic quaternary centers.

Published
2009
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