| 1. |
- Terenin, V. I., et al.
(författare)
-
1-(Trifluoromethyl)-3,4-dihydropyrrolo-[1,2-a] pyrazines: synthesis and reactions with O- and N-nucleophiles
- 2011
-
Ingår i: Chemistry of Heterocyclic Compounds. - : Springer Science and Business Media LLC. - 0009-3122 .- 1573-8353. ; 46:10, s. 1271-1278
-
Tidskriftsartikel (refereegranskat)abstract
- The method of synthesis has been developed and reactions of 1-(trifluoromethyl)-3,4-dihydro-pyrrolo[1,2-a]pyrazines with O- and N-nucleophiles have been studied. It was found that reactions of nucleophiles with 1-(trifluoro-methyl)pyrrolo[1,2-a]pyrazines transforms the trifluoromethyl group to amide and amidine groups together with aromatization of the pyrrolo[1,2-a]pyrazine system as a result of the formal elimination of a molecule of hydrogen fluoride.
|
|
| 2. |
|
|
| 3. |
- Gruhl, T., et al.
(författare)
-
Ultrafast structural changes direct the first molecular events of vision
- 2023
-
Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 615, s. 939-944
-
Tidskriftsartikel (refereegranskat)abstract
- Vision is initiated by the rhodopsin family of light-sensitive G protein-coupled receptors (GPCRs)(1). A photon is absorbed by the 11-cis retinal chromophore of rhodopsin, which isomerizes within 200 femtoseconds to the all-trans conformation(2), thereby initiating the cellular signal transduction processes that ultimately lead to vision. However, the intramolecular mechanism by which the photoactivated retinal induces the activation events inside rhodopsin remains experimentally unclear. Here we use ultrafast time-resolved crystallography at room temperature(3) to determine how an isomerized twisted all-trans retinal stores the photon energy that is required to initiate the protein conformational changes associated with the formation of the G protein-binding signalling state. The distorted retinal at a 1-ps time delay after photoactivation has pulled away from half of its numerous interactions with its binding pocket, and the excess of the photon energy is released through an anisotropic protein breathing motion in the direction of the extracellular space. Notably, the very early structural motions in the protein side chains of rhodopsin appear in regions that are involved in later stages of the conserved class A GPCR activation mechanism. Our study sheds light on the earliest stages of vision in vertebrates and points to fundamental aspects of the molecular mechanisms of agonist-mediated GPCR activation.
|
|
| 4. |
- Banerjee, Ambar, 1985-, et al.
(författare)
-
Accessing metal-specific orbital interactions in C–H activation with resonant inelastic X-ray scattering
- 2024
-
Ingår i: Chemical Science. - : Royal Society of Chemistry. - 2041-6520 .- 2041-6539. ; 15:7, s. 2398-2409
-
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.
|
|
| 5. |
- Jay, Raphael, et al.
(författare)
-
Tracking C–H activation with orbital resolution
- 2023
-
Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 380:6648, s. 955-960
-
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.
|
|
