De novo protein design is delivering new peptide and protein structures at a rapid pace. Many of these synthetic polypeptides form well-defined and hyperthermal-stable structures. Generally, however, less is known about the dynamic properties of the de novo designed structures. Here, we explore one aspect of dynamics in a series of de novo coiled-coil peptide assemblies: namely, peptide exchange within and between different oligomers from dimers through to heptamers. First, we develop a fluorescence-based reporter assay for peptide exchange that is straightforward to implement, and, thus, would be useful to others examining similar systems. We apply this assay to explore both homotypic exchange within single species, and heterotypic exchange between coiled coils of different oligomeric states. For the former, we provide a detailed study for a dimeric coiled coil, CC-Di, finding a half-life for exchange of 4.2 +/- 0.3 minutes at a peptide concentration of 200 mu M. Interestingly, more broadly when assessing exchange across all of the oligomeric states, we find that some of the designs are faithful and only undergo homotypic strand exchange, whereas others are promiscuous and exchange to form unexpected hetero-oligomers. Finally, we develop two design strategies to improve the orthogonality of the different oligomers: (i) using alternate positioning of salt bridge interactions; and (ii) incorporating non-canonical repeats into the designed sequences. In so doing, we reconcile the promiscuity and deliver a set of faithful homo-oligomeric de novo coiled-coil peptides. Our findings have implications for the application of these and other coiled coils as modules in chemical and synthetic biology.

Trifluoroacetic acid (TFA) is a known and persistent pollutant in the environment. Although several direct anthropogenic sources exist, production from the atmospheric degradation of fluorocarbons such as some hydrofluorocarbons (HFCs) has been a known source for some time. The current transition from HFCs to HFOs (hydrofluoroolefins) is beneficial from a global warming viewpoint because HFOs are much shorter-lived and pose a much smaller threat in terms of warming, but the fraction of HFOs converted into TFA is higher than seen for the corresponding HFCs and the region in which TFA is produced is close to the source. Therefore, it is timely to review the role of TFA in the Earth's environment. This review considers its toxicity, sources and removal processes, measurement in a variety of environments, and future prospects. New global model integrations are used to quantify the impacts of uncertainties on TFA levels using the Henry's Law constant for TFA and the range of gas-phase kinetic parameters chosen for the reaction of OH radicals with a representative HFO (HFO-1234yf). Model runs suggest that TFA surface concentrations vary by up to 10% based on Henry's Law data but could be up to 25% smaller than previously modelled values suggest depending on the kinetic analysis adopted. Therefore, future estimates of TFA surface concentrations based on HFO removal require updating and the kinetic analysis of TFA production warrants further investigation. The toxicity of TFA appears to be low, but further studies of a much wider range of animal and plant types are required.

ADVERTISEMENT RETURN TO ISSUEEditorialNEXTCollection on the Spectroscopy, Structure, and Reactivity of Stabilized Criegee IntermediatesAndrew J. Orr-Ewing*Andrew J. Orr-EwingSchool of Chemistry, University of Bristol, Bristol BS8 1TS, United Kingdom*Email: [email protected]More by Andrew J. Orr-Ewinghttps://orcid.org/0000-0001-5551-9609 and David L. Osborn*David L. OsbornCombustion Research Facility, Mail Stop 9055, Sandia National Laboratories, Livermore, California 94551-0969, United StatesDepartment of Chemical Engineering, University of California, Davis, California 95616, United States*Email: [email protected]More by David L. Osbornhttps://orcid.org/0000-0003-4304-8218Cite this: J. Phys. Chem. A 2024, 128, 15, 2909–2911Publication Date (Web):April 18, 2024Publication History Received5 March 2024Published online18 April 2024Published inissue 18 April 2024https://doi.org/10.1021/acs.jpca.4c01459Copyright © 2024 American Chemical Society. This publication is available under these Terms of Use. Request reuse permissions This publication is free to access through this site. Learn MoreArticle Views-Altmetric-Citations-LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail PDF (936 KB) Get e-AlertscloseSUBJECTS:Absorption,Isomerization,Organic reactions,Oxides,Volatile organic compounds Get e-Alerts

The synergistic use of (organo)photoredox catalysts with hydrogen-atom transfer (HAT) cocatalysts has emerged as a powerful strategy for innate C(sp3)-H bond functionalization, particularly for C-H bonds α- to nitrogen. Azide ion (N3-) was recently identified as an effective HAT catalyst for the challenging α-C-H alkylation of unprotected, primary alkylamines, in combination with dicyanoarene photocatalysts such as 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene (4CzIPN). Here, time-resolved transient absorption spectroscopy over sub-picosecond to microsecond timescales provides kinetic and mechanistic details of the photoredox catalytic cycle in acetonitrile solution. Direct observation of the electron transfer from N3- to photoexcited 4CzIPN reveals the participation of the S1 excited electronic state of the organic photocatalyst as an electron acceptor, but the N3• radical product of this reaction is not observed. Instead, both time-resolved infrared and UV-visible spectroscopic measurements implicate rapid association of N3• with N3- (a favorable process in acetonitrile) to form the N6•- radical anion. Electronic structure calculations indicate that N3• is the active participant in the HAT reaction, suggesting a role for N6•- as a reservoir that regulates the concentration of N3•.

ADVERTISEMENT RETURN TO ISSUEEditorialNEXTVirtual Issue on Photodissociation: From Fundamental Dynamics and Spectroscopy to Photochemistry in Planetary Atmospheres and in SpaceClaire Vallance*Claire VallanceChemistry Research Laboratory, Department of Chemistry, University of Oxford, 12 Mansfield Road, Oxford OX1 3TA, United Kingdom*Email: [email protected]More by Claire Vallancehttps://orcid.org/0000-0003-3880-8614 and Andrew J. Orr-Ewing*Andrew J. Orr-EwingSchool of Chemistry, University of Bristol, Bristol BS8 1TS, United Kingdom*Email: [email protected]More by Andrew J. Orr-Ewinghttps://orcid.org/0000-0001-5551-9609Cite this: J. Phys. Chem. A 2023, 127, 28, 5767–5771Publication Date (Web):July 20, 2023Publication History Received12 June 2023Published online20 July 2023Published inissue 20 July 2023https://doi.org/10.1021/acs.jpca.3c03975Copyright © Published 2023 by American Chemical SocietyRequest reuse permissions This publication is free to access through this site. Learn MoreArticle Views442Altmetric-Citations-LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (1 MB) Get e-AlertscloseSUBJECTS:Bond cleavage,Molecules,Photodissociation,Quantum mechanics,Solvents Get e-Alerts

Thermally activated delayed fluorescence (TADF) emitters are molecules of interest as homogeneous organic photocatalysts (OPCs) for photoredox chemistry. Here, three classes of OPC candidates are studied in dichloromethane (DCM) or N,N-dimethylformamide (DMF) solutions, using transient absorption spectroscopy and time-resolved fluorescence spectroscopy. These OPCs are benzophenones with either carbazole (2Cz-BP and 2tCz-BP) or phenoxazine/phenothiazine (2PXZ-BP and 2PTZ-BP) appended groups and the dicyanobenzene derivative 4DP-IPN. Dual lifetimes of the S1 state populations are observed, consistent with reverse intersystem crossing (RISC) and TADF emission. Example fluorescence lifetimes in DCM are (5.18 ± 0.01) ns and (6.22 ± 1.27) μs for 2Cz-BP, (1.38 ± 0.01) ns and (0.32 ± 0.01) μs for 2PXZ-BP, and (2.97 ± 0.01) ns and (62.0 ± 5.8) μs for 4DP-IPN. From ground state bleach recoveries and time-correlated single photon counting measurements, triplet quantum yields in DCM are estimated to be 0.62 ± 0.16, 0.04 ± 0.01, and 0.83 ± 0.02 for 2Cz-BP, 2PXZ-BP, and 4DP-IPN, respectively. 4DP-IPN displays similar photophysical behavior to the previously studied OPC 4Cz-IPN. Independent of the choice of solvent, 4DP-IPN, 2Cz-BP, and 2tCz-BP are shown to be TADF emitters, whereas emission by 2PXZ-BP and 2PTZ-BP depends on the molecular environment, with TADF emission enhanced in aggregates compared to monomers. Behavior of this type is representative of aggregation-induced emission luminogens (AIEgens).

Understanding the optical properties of micrometer-scale light-absorbing aerosol particles is of paramount importance in addressing key challenges in atmospheric and physical chemistry. For example, the absorption of solar radiation by atmospheric aerosols represents one of the largest uncertainties in climate models. Moreover, reaction acceleration within the unique environments of aerosol droplets cannot be replicated in bulk solutions. The causes of these reaction rate enhancements remain controversial, but ultrasensitive spectroscopic measurements of evolving aerosol optical properties should provide new insights. We demonstrate a new approach using cavity ring-down spectroscopy that allows the first direct spectroscopic quantification of the continuously evolving absorption and scattering cross sections for single, levitated, micrometer-scale particles as their size and chromophore concentration change. For two-component droplets composed of nigrosin and 1,2,6-hexanetriol, the unprecedented sensitivity of our measurements reveals the evolving real and imaginary components of the refractive index caused by changes in concentration as 1,2,6-hexanetriol slowly evaporates.

We study charge transfer in dissociating molecules of 2-iodopropane (C3H7I) in a UV pump – XUV probe regime at the SACLA free-electron laser. Signatures of charge transfer from the recently dissociated iodine atom to the neutral propyl radical are observed in recorded 3D ion momentum distributions. This signature has evaded observation in previous related experiments. Detailed analysis of these signatures allows the identification of a region of internuclear separation where charge transfer occurs.

Dennis Milesevic opened discussion of the paper by Marsha Lester: The formation of the tert-butyl hydroperoxide (TBHP) radicals has been discussed in detail in the paper (https://doi.org/10.1039/d2fd00008c). However, you are forming primary radicals, which are not particularly stable. Therefore

Enantioenriched seven-membered carbocycles are motifs in many molecules of structural and biological interest. We report a simple, practical, transition metal-free and mechanistically unusual method for the enantioselective synthesis of substituted cycloheptatrienes. By forming a coloured enolate with an appropriate absorption band and selectively irradiating in situ, we to initiate a tandem, asymmetric anionic and photochemical ring expansion of readily accessible N-benzylbenzamides. The cascade of reactions leading to the products entails enantioselective benzylic deprotonation with a chiral lithium amide, dearomatizing cyclization of the resulting configurationally defined organolithium to give an extended amide enolate, and photochemically induced formal [1,7]-sigmatropic rearrangement and 6π-electrocyclic ring-opening - the latter all evidently being stereospecific - to deliver enantioenriched cycloheptatrienes with embedded benzylic stereocentres.

Although ultraviolet (UV)-induced photochemical cleavage of carbon-halogen bonds in gaseous halocarbons is mostly homolytic, the photolysis of chlorobenzene in solution has been proposed to produce a phenyl cation, c-C6H5+, which is a highly reactive intermediate of potential use in chemical synthesis and N2 activation. Any evidence for such a route to phenyl cations is indirect, with uncertainty remaining about the possible mechanism. Here, ultrafast transient absorption spectroscopy of UV-excited (λ = 240 and 270 nm) chlorobenzene solutions in fluorinated (perfluorohexane) and protic (ethanol and 2,2,2-trifluoroethanol) solvents reveals a broad electronic absorption band centered at 540 nm that is assigned to an isomer of chlorobenzene with both charge-separated and triplet-spin carbene character. This spectroscopic feature is weaker, or absent, when experiments are conducted in cyclohexane. The intermediate isomer of chlorobenzene has a solvent-dependent lifetime of 30-110 ps, determined by reaction with the solvent or quenching to a lower-lying singlet state. Evidence is presented for dissociation to ortho-benzyne, but the intermediate could also be a precursor to phenyl cation formation.

We present results from an experimental ion imaging study into the fragmentation dynamics of 1-iodopropane and 2-iodopropane following interaction with extreme ultraviolet intense femtosecond laser pulses with a photon energy of 95 eV. Using covariance imaging analysis, a range of observed fragmentation pathways of the resulting polycations can be isolated and interrogated in detail at relatively high ion count rates (∼12 ions shot-1). By incorporating the recently developed native frames analysis approach into the three-dimensional covariance imaging procedure, contributions from three-body concerted and sequential fragmentation mechanisms can be isolated. The angular distribution of the fragment ions is much more complex than in previously reported studies for triatomic polycations, and differs substantially between the two isomeric species. With support of simple simulations of the dissociation channels of interest, detailed physical insights into the fragmentation dynamics are obtained, including how the initial dissociation step in a sequential mechanism influences rovibrational dynamics in the metastable intermediate ion and how signatures of this nuclear motion manifest in the measured signals.

ADVERTISEMENT RETURN TO ISSUEPREVEditorialNEXTVirtual Issue on Atmospheric Aerosol ResearchFranz M. Geiger*Franz M. GeigerDepartment of Chemistry, Northwestern University, Evanston, Illinois 60208, United States*Email: [email protected]More by Franz M. Geigerhttps://orcid.org/0000-0001-8569-4045, V. Faye McNeill*V. Faye McNeillDepartment of Chemical Engineering and Department of Earth and Environmental Sciences, Columbia University, New York, New York 10027, United States*Email: [email protected]More by V. Faye McNeillhttps://orcid.org/0000-0003-0379-6916, and Andrew J. Orr-Ewing*Andrew J. Orr-EwingSchool of Chemistry, University of Bristol, Bristol BS8 1TS, United Kingdom*Email: [email protected]More by Andrew J. Orr-Ewinghttps://orcid.org/0000-0001-5551-9609Cite this: ACS Earth Space Chem. 2022, 6, 8, 1957–1959Publication Date (Web):August 18, 2022Publication History Received11 July 2022Published online18 August 2022Published inissue 18 August 2022https://pubs.acs.org/doi/10.1021/acsearthspacechem.2c00209https://doi.org/10.1021/acsearthspacechem.2c00209editorialACS PublicationsCopyright © 2022 American Chemical Society. This publication is available under these Terms of Use. Request reuse permissions This publication is free to access through this site. Learn MoreArticle Views578Altmetric-Citations-LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail PDF (906 KB) Get e-AlertscloseSUBJECTS:Aerosols,Atmospheric chemistry,Climate,Particles,Phase transitions Get e-Alerts

Robin J. Shannon opened discussion of the introductory lecture by Stephen J. Klippenstein: I was surprised and heartened by your success in using a statistical approach to treat roaming radical channels. Could you comment further on the reasons why statistical rate theory ap

ADVERTISEMENT RETURN TO ISSUEEditorialNEXTA Venue for Advances in Experimental and Theoretical Methods in Physical ChemistryAndrew J. Orr-Ewing*Andrew J. Orr-EwingSchool of Chemistry, University of Bristol, Cantock's Close, Bristol BS8 1TS, U.K.More by Andrew J. Orr-Ewinghttps://orcid.org/0000-0001-5551-9609, T. Daniel CrawfordT. Daniel CrawfordDepartment of Chemistry, Virginia Tech, Blacksburg, Virginia 24061, United StatesMolecular Sciences Software Institute, 1880 Pratt Drive, Suite 1100, Blacksburg, Virginia 24060, United StatesMore by T. Daniel Crawfordhttps://orcid.org/0000-0002-7961-7016, Martin T. ZanniMartin T. ZanniDepartment of Chemistry, University of Wisconsin─Madison, 1101 University Avenue, Madison, Wisconsin 53706, United StatesMore by Martin T. Zannihttps://orcid.org/0000-0001-7191-9768, Gregory HartlandGregory HartlandUniversity of Notre Dame, Notre Dame, Indiana 46556, United StatesMore by Gregory Hartlandhttps://orcid.org/0000-0002-8650-6891, and Joan-Emma SheaJoan-Emma SheaDepartment of Chemistry and Biochemistry, University of California, Santa Barbara, Santa Barbara, California 93106, United StatesDepartment of Physics, University of California, Santa Barbara, Santa Barbara, California 93106, United StatesMore by Joan-Emma Sheahttps://orcid.org/0000-0002-9801-9273Cite this: J. Phys. Chem. A 2022, 126, 2, 177–179Publication Date (Web):January 20, 2022Publication History Published online20 January 2022Published inissue 20 January 2022https://pubs.acs.org/doi/10.1021/acs.jpca.1c10457https://doi.org/10.1021/acs.jpca.1c10457editorialACS PublicationsCopyright © 2022 American Chemical Society. This publication is available under these Terms of Use. Request reuse permissions This publication is free to access through this site. Learn MoreArticle Views2082Altmetric-Citations-LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail PDF (602 KB) Get e-AlertscloseSUBJECTS:Computational chemistry,Lasers,Machine learning,Physical chemistry,Software Get e-Alerts

The photoexcitation of α-diazocarbonyl compounds produces singlet carbene intermediates that react with nucleophilic solvent molecules to form ylides. The zwitterionic nature of these newly formed ylides induces rapid changes in their interactions with the surrounding solvent. Here, ultrafast time-resolved infrared absorption spectroscopy is used to study the ylide-forming reactions of singlet carbene intermediates from the 270 nm photoexcitation of ethyl diazoacetate in various solvents and the changes in the subsequent ylide–solvent interactions. The results provide direct spectroscopic observation of the competition between ylide formation and C–H insertion in reactions of the singlet carbene with nucleophilic solvent molecules. We further report the specific solvation dynamics of the tetrahydrofuran (THF)-derived ylide (with a characteristic IR absorption band at 1636 cm–1) by various hydrogen-bond donors and the coordination by lithium cations. Hydrogen-bonded ylide bands shift to a lower wavenumber by −19 cm–1 for interactions with ethanol, −14 cm–1 for chloroform, −10 cm–1 for dichloromethane, −9 cm–1 for acetonitrile or cyclohexane, and −16 cm–1 for Li+ coordination, allowing the time evolution of the ylide–solvent interactions to be tracked. The hydrogen-bonded ylide bands grow with rate coefficients that are close to the diffusional limit. We further characterize the specific interactions of ethanol with the THF-derived ylide using quantum chemical (MP2) calculations and DFT-based atom-centered density matrix propagation trajectories, which show preferential coordination to the α-carbonyl group. This coordination alters the hybridization character of the ylidic carbon atom, with the greatest change toward sp2 character found for lithium-ion coordination.

David Heathcote opened a general discussion of the paper by Jürgen Troe: In Fig. 2 of your paper (https://doi.org/10.1039/d2fd00018k), you show the 3A′′ potential energy surface (PES) of the N + OH system obtained both from your asymptotic theory, and from the ab initio calculations of Li et al

Trifluoroacetic acid (TFA), a highly soluble and stable organic acid, is photochemically produced by certain anthropogenically emitted halocarbons such as HFC-134a and HFO-1234yf. Both these halocarbons are used as refrigerants in the automobile industry, and the high global warming potential of HFC-134a has promoted regulation of its use. Industries are transitioning to the use of HFO-1234yf as a more environmentally friendly alternative. We investigated the environmental effects of this change and found a 33-fold increase in the global burden of TFA from an annual value of 65 tonnes formed from the 2015 emissions of HFC-134a to a value of 2220 tonnes formed from an equivalent emission of HFO-1234yf. The percentage increase in surface TFA concentrations resulting from the switch from HFC-134a to HFO-1234yf remains substantial with an increase of up to 250-fold across Europe. The increase in emissions greater than the current emission scenario of HFO-1234yf is likely to result in significant TFA burden as the atmosphere is not able to disperse and deposit relevant oxidation products. The Criegee intermediate initiated loss process of TFA reduces the surface level atmospheric lifetime of TFA by up to 5 days (from 7 days to 2 days) in tropical forested regions.