Search results for "isomeria"
showing 10 items of 20 documents
Experimental Confirmation of a Topological Isomer of the Ubiquitous Au25(SR)18 Cluster in the Gas Phase
2021
High-resolution electrospray ionization ion mobility mass spectrometry has revealed a gas-phase isomer of the ubiquitous, extremely well-studied Au25(SR)18 cluster both in anionic and cationic form. The relative abundance of the isomeric structures can be controlled by in-source activation. The measured collision cross section of the new isomer agrees extremely well with a recent theoretical prediction (Matus, M. F.; et al. Chem. Commun. 2020, 56, 8087) corresponding to a Au25(SR)18– isomer that is energetically close and topologically connected to the known ground-state structure via a simple rotation of the gold core without breaking any Au–S bonds. The results imply that the structural d…
Raman spectroscopy of glycolic acid complexes with N2
2019
High overtone excitation induced conformational isomerization of glycolic acid – nitrogen complex in an argon matrix was investigated by Raman spectroscopy. The interaction between glycolic acid and nitrogen change the green light (532 nm) induced isomerization processes compared to non-complexed glycolic acid. The 180° rotation around of the Csingle bondC bond and stabilization of carboxyl Odouble bondCsingle bondOsingle bondH dihedral angle to trans position were the main conformational changes observed in the complex of the lowest energy conformer and nitrogen. Interestingly, only one stable light-induced conformational product was observed, which isomerises back to the lowest energy con…
New β-decaying state in 214Bi
2021
A new β-decaying state in 214Bi has been identified at the ISOLDE Decay Station at the CERN-ISOLDE facility. A preferred Iπ = (8−) assignment was suggested for this state based on the β-decay feeding pattern to levels in 214Po and shell-model calculations. The half-life of the Iπ = (8−) state was deduced to be T1/2 = 9.39(10) min. The deexcitation of the levels populated in 214Po by the β decay of this state was investigated via γ -γ coincidences and a number of new levels and transitions was identified. Shell-model calculations for excited states in 214Bi and 214Po were performed using two different effective interactions: the H208 and the modified Kuo-Herling particle interaction. Both ca…
Detailed spectroscopy of 195Bi
2017
An experiment focused on the study of shape coexistence and new high-spin structures in 195 Bi has been performed. The nucleus is in a transitional region of the bismuth isotope chain. A large number of new states have been found, resulting in a significant extension of the previously known level scheme. Several new collective structures have been identified. A strongly coupled rotational band built upon the 13 / 2 + isomeric state was extended up to I π = ( 49 / 2 + ) and an energy of 5706 keV. The I π = 31 / 2 + member of the π i 13 / 2 band was also found to feed a new long-lived isomeric state with an excitation energy of 2616 keV and a spin and parity of I π = 29 / 2 + . The half-life …
Angular Regioselectivity in the Reactions of 2-Thioxopyrimidin-4-ones and Hydrazonoyl Chlorides : Synthesis of Novel Stereoisomeric Octahydro[1,2,4]t…
2020
The regioselective synthesis of cis and trans stereoisomers of variously functionalized octahydro[1,2,4]triazolo[4,3-a]quinazolin-5-ones was performed. The 2-thioxopyrimidin-4-ones used in the synthesis reacted with hydrazonoyl chlorides in a regioselective manner to produce the angular regioisomers [1,2,4]triazolo[4,3-a]quinazolin-5-ones rather than the linear isomers [1,2,4]triazolo[4,3-a]quinazolin-5-ones. The synthesis process took place with electronic control. The angular regiochemistry of the products was confirmed by X-ray experiments and two-dimensional NMR studies.
Bis[cyclic (alkyl)(amino)carbene] isomers : Stable trans-bis(CAAC) versus facile olefin formation for cis-bis(CAAC)
2022
Isomeric bis(aldiminium) salts with a 1,4-cyclohexylene framework were synthesized. The first isolable bis(CAAC) was prepared from the trans-stereoisomer and its ditopic ligand competency was proven by conversion to iridium(I) and rhodium(I) complexes. Upon deprotonation, the cis-isomer yielded an electron rich olefin via a classic, proton-catalyzed pathway. The C[double bond, length as m-dash]C bond formation from the desired cis-bis(CAAC) was shown to be thermodynamically very favorable and to involve a small activation barrier. Compounds that can be described as insertion products of the cis-bis(CAAC) into the E–H bonds of NH3, CH3CN and H2O were also identified. peerReviewed
Isomer dynamics of the [Au6(NHC-S)4]2+ nanocluster
2022
The use of metal nanoclusters is strongly reliant on their size and configuration; hence, studying the potential isomers of a cluster is extremely beneficial in understanding their performance. In general, the prediction and identification of isomer structures and their properties can be challenging and computationally expensive. Our work describes an investigation to find local isomers for the previously experimentally characterized small gold cluster [Au6(NHC-S)4]2+ protected by bidentate mixed carbene-thiolate ligands. We employ the molecular dynamics simulation method where the interatomic forces are calculated from density functional theory. We find several isomers that are more stable…
Avidiini-HABA-kompleksin karakterisointi ja kontrollointi
2011
Avidiini on tetrameerinen proteiini, jota on tutkittu ja käytetty paljon ligandien sitomiskykynsä ansiosta. Avidiinin luonnollinen ligandi on biotiini, jonka affiniteetti avidiiniin on erittäin voimakas (Kd=10-15 M). Avidiini kykenee sitomaan myös muita ligandeja, mutta pienemmällä affiniteetilla. Yksi avidiiniin sitoutuvista molekyyleistä on HABA (4’-hydroksiatsobentseeni-2-karboksyylihappo) -atsoväri, jota on käytetty avidiini-biotiiniteknologiassa hyväksi. HABA-molekyylillä on kaksi eri rakenteellista isomeerimuotoa, trans- ja cis-isomeerit. Yleensä se esiintyy tasomaisena molekyylinä eli trans-isomeerina, mutta se voi menettää tasomaisen rakenteensa ja ilmentyä tällöin cis-isomeerinä. A…
Experimental and Theoretical Investigations of Structural Isomers of Dichalcogenoimidodiphosphinate Dimers: Dichalcogenides or Spirocyclic Contact Io…
2007
A synthetic protocol for the tert-butyl-substituted dichalcogenoimidodiphosphinates [Na(tmeda){(EPtBu2)2N}] (3 a, E=S; 3 b, E=Se; 3 c, E=Te) has been developed. The one-electron oxidation of the sodium complexes [Na(tmeda){(EPR2)2N}] with iodine produces a series of neutral dimers (EPR2NPR2E[BOND])2 (4 b, E=Se, R=iPr; 4 c, E=Te, R=iPr; 5 a, E=S, R=tBu; 5 b, E=Se, R=tBu; 5 c, E=Te, R=tBu). Attempts to prepare 4 a (E=S, R=iPr) in a similar manner produced a mixture including HN(SPiPr2). Compounds 4 b, 4 c and 5 a–c were characterised by multinuclear NMR spectra and by X-ray crystallography, which revealed two alternative structures for these dimeric molecules. The derivatives 4 b, 4 c, 5 a an…
Carboxylate catalyzed isomerization of β,γ‐unsaturated N-acetylcysteamine thioesters
2022
We demonstrate herein the capacity of simple carboxylate salts – tetrametylammonium and tetramethylguanidinium pivalate – to act as catalysts in the isomerization of β,γ-unsaturated thioesters to α,β-unsaturated thioesters. The carboxylate catalysts gave reaction rates comparable to those obtained with DBU, but with fewer side reactions. The reaction exhibits a normal secondary kinetic isotope effect ( k 1H / k 1D = 1.065±0.026) with a β,γ−deuterated substrate. Computational analysis of the mechanism provides a similar value ( k 1H / k 1D = 1.05) with a mechanism where γ-reprotonation of the enolate intermediate is rate determining. peerReviewed