| 1. |
- Banerjee, Ambar, 1985-, et al.
(författare)
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Accessing metal-specific orbital interactions in C–H activation with resonant inelastic X-ray scattering
- 2024
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Ingår i: Chemical Science. - : Royal Society of Chemistry. - 2041-6520 .- 2041-6539. ; 15:7, s. 2398-2409
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Tidskriftsartikel (refereegranskat)abstract
- Photochemically prepared transition-metal complexes are known to be effective at cleaving the strong C–H bonds of organic molecules in room temperature solutions. There is also ample theoretical evidence that the two-way, metal to ligand (MLCT) and ligand to metal (LMCT), charge-transfer between an incoming alkane C–H group and the transition metal is the decisive interaction in the C–H activation reaction. What is missing, however, are experimental methods to directly probe these interactions in order to reveal what determines reactivity of intermediates and the rate of the reaction. Here, using quantum chemical simulations we predict and propose future time-resolved valence-to-core resonant inelastic X-ray scattering (VtC-RIXS) experiments at the transition metal L-edge as a method to provide a full account of the evolution of metal–alkane interactions during transition-metal mediated C–H activation reactions. For the model system cyclopentadienyl rhodium dicarbonyl (CpRh(CO)2), we demonstrate, by simulating the VtC-RIXS signatures of key intermediates in the C–H activation pathway, how the Rh-centered valence-excited states accessible through VtC-RIXS directly reflect changes in donation and back-donation between the alkane C–H group and the transition metal as the reaction proceeds via those intermediates. We benchmark and validate our quantum chemical simulations against experimental steady-state measurements of CpRh(CO)2 and Rh(acac)(CO)2 (where acac is acetylacetonate). Our study constitutes the first step towards establishing VtC-RIXS as a new experimental observable for probing reactivity of C–H activation reactions. More generally, the study further motivates the use of time-resolved VtC-RIXS to follow the valence electronic structure evolution along photochemical, photoinitiated and photocatalytic reactions with transition metal complexes.
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| 2. |
- Barzgar Vishlaghi, Mahsa, et al.
(författare)
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Accelerating water oxidation on BiVO 4 photoanodes via surface modification with Co dopants
- 2023
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Ingår i: Journal of Materials Chemistry A. - 2050-7488 .- 2050-7496. ; 11:31, s. 16648-16658
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Tidskriftsartikel (refereegranskat)abstract
- Despite the vast investigations on improving the photoelectrochemical performance of BiVO4 for water splitting, charge recombination in the near-surface region remains a challenge. In this study, we showed that the diffusion of Co2+ ions into the BiVO4 subsurface boosted the water oxidation activity and charge injection efficiency remarkably. The increase in the concentration of oxygen vacancies upon the incorporation of cobalt ions was shown by electron paramagnetic resonance (EPR) spectroscopy and confirmed by density functional theory (DFT) calculations. DFT calculations revealed that vanadium sites in the subsurface region were the most favorable sites for substitution with cobalt ions. Charge localization at surface oxygen vacancies was found less favorable in the presence of cobalt in the subsurface layer, eliminating surface recombination. This resulted in 4.25 times larger charge injection efficiency and 6.2 times higher photocurrent density at the potential of ∼0.6 V, as compared to pristine BiVO4. This enhancement was significantly larger as compared to CoOx-loaded BiVO4, indicating that the suppressed recombination at the surface and improved charge transfer kinetics obtained solely by CoOx deposition are not sufficient for enhanced activity of BiVO4. A longer charge carrier lifetime obtained upon cobalt incorporation was observed by transient absorption spectroscopy and verified the reduced rate of recombination.
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| 3. |
- Jay, Raphael, et al.
(författare)
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Tracking C–H activation with orbital resolution
- 2023
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 380:6648, s. 955-960
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Tidskriftsartikel (refereegranskat)abstract
- Transition metal reactivity toward carbon-hydrogen (C-H) bonds hinges on the interplay of electron donation and withdrawal at the metal center. Manipulating this reactivity in a controlled way is difficult because the hypothesized metal-alkane charge-transfer interactions are challenging to access experimentally. Using time-resolved x-ray spectroscopy, we track the charge-transfer interactions during C-H activation of octane by a cyclopentadienyl rhodium carbonyl complex. Changes in oxidation state as well as valence-orbital energies and character emerge in the data on a femtosecond to nanosecond timescale. The x-ray spectroscopic signatures reflect how alkane-to-metal donation determines metal-alkane complex stability and how metal-to-alkane back-donation facilitates C-H bond cleavage by oxidative addition. The ability to dissect charge-transfer interactions on an orbital level provides opportunities for manipulating C-H reactivity at transition metals.
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| 4. |
- Reyna, Matthew A, et al.
(författare)
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Pathway and network analysis of more than 2500 whole cancer genomes
- 2020
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 11
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Tidskriftsartikel (refereegranskat)abstract
- The catalog of cancer driver mutations in protein-coding genes has greatly expanded in the past decade. However, non-coding cancer driver mutations are less well-characterized and only a handful of recurrent non-coding mutations, most notably TERT promoter mutations, have been reported. Here, as part of the ICGC/TCGA Pan-Cancer Analysis of Whole Genomes (PCAWG) Consortium, which aggregated whole genome sequencing data from 2658 cancer across 38 tumor types, we perform multi-faceted pathway and network analyses of non-coding mutations across 2583 whole cancer genomes from 27 tumor types compiled by the ICGC/TCGA PCAWG project that was motivated by the success of pathway and network analyses in prioritizing rare mutations in protein-coding genes. While few non-coding genomic elements are recurrently mutated in this cohort, we identify 93 genes harboring non-coding mutations that cluster into several modules of interacting proteins. Among these are promoter mutations associated with reduced mRNA expression in TP53, TLE4, and TCF4. We find that biological processes had variable proportions of coding and non-coding mutations, with chromatin remodeling and proliferation pathways altered primarily by coding mutations, while developmental pathways, including Wnt and Notch, altered by both coding and non-coding mutations. RNA splicing is primarily altered by non-coding mutations in this cohort, and samples containing non-coding mutations in well-known RNA splicing factors exhibit similar gene expression signatures as samples with coding mutations in these genes. These analyses contribute a new repertoire of possible cancer genes and mechanisms that are altered by non-coding mutations and offer insights into additional cancer vulnerabilities that can be investigated for potential therapeutic treatments.
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