765 research outputs found
Crystal structure of (E)-pent-2-enoic acid
The molÂecule of the title compound, C5H8O2, a low-melting [alpha],[beta]-unsaturated carbÂoxyÂlic acid, is essentially planar [maximum displacement = 0.0239 (13) Ă
]. In the crystal, molÂecules are linked into centrosymmetric dimers via pairs of O-H...O hydrogen bonds
Photochemistry of Furyl- and Thienyldiazomethanes: Spectroscopic Characterization of Triplet 3-Thienylcarbene
Photolysis (λ \u3e 543 nm) of 3-thienyldiazomethane (1), matrix isolated in Ar or N2 at 10 K, yields triplet 3-thienylcarbene (13) and α-thial-methylenecyclopropene (9). Carbene 13 was characterized by IR, UV/vis, and EPR spectroscopy. The conformational isomers of 3-thienylcarbene (s-E and s-Z) exhibit an unusually large difference in zero-field splitting parameters in the triplet EPR spectrum (|D/hc| = 0.508 cmâ1, |E/hc| = 0.0554 cmâ1; |D/hc| = 0.579 cmâ1, |E/hc| = 0.0315 cmâ1). Natural Bond Orbital (NBO) calculations reveal substantially differing spin densities in the 3-thienyl ring at the positions adjacent to the carbene center, which is one factor contributing to the large difference in D values. NBO calculations also reveal a stabilizing interaction between the sp orbital of the carbene carbon in the s-Z rotamer of 13 and the antibonding Ï orbital between sulfur and the neighboring carbonâan interaction that is not observed in the s-E rotamer of 13. In contrast to the EPR spectra, the electronic absorption spectra of the rotamers of triplet 3-thienylcarbene (13) are indistinguishable under our experimental conditions. The carbene exhibits a weak electronic absorption in the visible spectrum (λmax = 467 nm) that is characteristic of triplet arylcarbenes. Although studies of 2-thienyldiazomethane (2), 3-furyldiazomethane (3), or 2-furyldiazomethane (4) provided further insight into the photochemical interconversions among C5H4S or C5H4O isomers, these studies did not lead to the spectroscopic detection of the corresponding triplet carbenes (2-thienylcarbene (11), 3-furylcarbene (23), or 2-furylcarbene (22), respectively)
Phenylalanine Ammonia-Lyase-Catalyzed Deamination of an Acyclic Amino Acid: Enzyme Mechanistic Studies Aided by a Novel Microreactor Filled with Magnetic Nanoparticles
Phenylalanine ammonia-lyase (PAL), found in many organisms,
catalyzes the deamination of l-phenylalanine (Phe) to (E)-cinnamate by the aid of its MIO prosthetic group. By using PAL immobilized on magnetic nanoparticles and fixed in a microfluidic reactor with an in-line UV detector, we demonstrated that PAL can catalyze ammonia elimination from the acyclic propargylglycine (PG) to yield (E)-pent-2-ene-4-ynoate. This highlights new opportunities to extend MIO enzymes towards acyclic substrates. As PG is acyclic, its deamination cannot involve a FriedelâCrafts-type attack at an aromatic ring. The reversibility of the PAL reaction, demonstrated by the ammonia addition to (E)-pent-2-ene-4-ynoate yielding enantiopure l-PG, contradicts the proposed highly exothermic single-step mechanism. Computations with the QM/MM models of the N-MIO intermediates from l-PG and l-Phe in PAL show similar arrangements within the active site, thus supporting a mechanism via the N-MIO intermediate
Possibility of [1,5] sigmatropic shifts in bicyclo[4.2.0]octa-2,4-dienes
The thermal equilibration of the methyl esters of endiandric acids D and E was subject to a computational study. An electrocyclic pathway via an electrocyclic ring opening followed by a ring flip and a subsequent electrocyclization proposed by Nicolaou [Nicolaou, K. C.; Chen, J. S. Chem. Soc. Rev. 2009, 38, 2993], was computationally explored. The free-energy barrier for this electrocyclic route was shown to be very close to the bicyclo[4.2.0]octa-2,4-diene reported by Huisgen [Huisgen, R.; Boche, G.; Dahmen, A.; Hechtl, W. Tetrahedron Lett. 1968, 5215]. Furthermore, the possibility of a [1,5] sigmatropic alkyl group shift of bicyclo[4.2.0]octa-2,4-diene systems at high temperatures was explored in a combined computational and experimental study. Calculated reaction barriers for an open-shell singlet biradical-mediated stepwise [1,5] sigmatropic alkyl group shift were shown to be comparable with the reaction barriers for the bicyclo[4.1.0]hepta-2,4-diene (norcaradiene) walk rearrangement. However, the stepwise sigmatropic pathway is suggested to only be feasible for appropriately substituted compounds. Experiments conducted on a deuterated analogous diol derivative confirmed the calculated (large) differences in barriers between electrocyclic and sigmatropic pathways
Fast method for the determination of short-chain-length polyhydroxyalkanoates (scl-PHAs) in bacterial samples by In Vial-Thermolysis (IVT)
none8siA new method based on the GCâMS analysis of thermolysis products obtained by treating bacterial
samples at a high temperature (above 270 C) has been developed. This method, here named âIn-Vial-
Thermolysisâ (IVT), allowed for the simultaneous determination of short-chain-length polyhydrox-
yalkanoates (scl-PHA) content and composition. The method was applied to both single strains and
microbial mixed cultures (MMC) fed with different carbon sources.
The IVT procedure provided similar analytical performances compared to previous Py-GCâMS and Py-
GC-FID methods, suggesting a similar application for PHA quantitation in bacterial cells. Results from the
IVT procedure and the traditional methanolysis method were compared; the correlation between the
two datasets was
fit for the purpose, giving a R2 of 0.975. In search of further simplification, the rationale
of IVT was exploited for the development of a âfield methodâ based on the titration of thermolyzed
samples with sodium hydrogen carbonate to quantify PHA inside bacterial cells. The accuracy of the IVT
method was
fit for the purpose.
These results lead to the possibility for the on-line measurement of PHA productivity. Moreover, they
allow for the fast and inexpensive quantification/characterization of PHA for biotechnological process
control, as well as investigation over various bacterial communities and/or feeding strategies.mixedF. Abbondanzi; G. Biscaro; G. Carvalho; L. Favaro; P. Lemos; M. Paglione; C. SamorĂŹ; C. TorriF. Abbondanzi; G. Biscaro; G. Carvalho; L. Favaro; P. Lemos; M. Paglione; C. SamorĂŹ; C. Torr
Pennington to The American Friends Service Committee, November 25, 1947
Pennington writing to the American Friends Service Committee about the Heifers-for-Relief campaign explaining their inability to ship out Heifers despite having money in the bank and what he wants to do in the meantime.https://digitalcommons.georgefox.edu/levi_pennington/1210/thumbnail.jp
A liquid chromatographic method optimization for the assessment of low and high molar mass carbonyl compounds in wines.
Carbonyl compounds (CC) play an important role in beverage aroma since they may affect flavor of wines, brandies, and beers, among others
Gazetteer of New Hebrides place names/Nomenclature des noms geographiques des Nouvelles-Hebrides
Pd(0)-catalyzed arylation of O-carbamates via Negishi cross-coupling and intermolecular Pd(0)-catalyzed atroposelective Csp2-H bond activation
Over the past decades, the transition-metal catalyzed C-H bond functionalization has emerged as a powerful tool for the straightforward access to molecular complexity, while respecting the principles of atom- and step-economy.
The research at the Baudoin group mainly focuses on the activation and the functionalization of C-H bonds with palladium. The investigation led to the development of new methodologies including intramolecular Csp3-H bond activation, and the arylation of remote Csp3-H bond via migrative cross-couplings. These methodologies were applied in the synthesis of biologically active complex molecules.
The ligand-controlled regioselective arylation of cyclic and acyclic N-Boc-amines via Pd(0)-catalyzed migrative Negishi cross-coupling was recently developed within our group. In light of this work, the enantioselective a-arylation of O-carbamates was achieved by combining Hoppeâs sparteine-mediated enantioselective lithiation-deprotonation and Pd(0)-catalyzed Negishi cross-coupling.
We then focused on the ligand-controlled migrative arylation of O-carbamates. The attempts toward the selective b-arylation were unsuccessful but led us to the discovery of a ligand-controlled g-arylation of g,d-unsatured O-carbamates. The reaction proceeds via a non-canonical haptotropic rearrangement of the palladium intermediate.
As a follow-up, we examined the feasibility of an intermolecular Pd(0)-catalyzed atroposelective Csp2-H arylation. Our investigation led us to the discovery of a catalytic system involving newly introduced bifunctionnal ligands
Efficient syntheses of climate relevant isoprene nitrates and (1R,5S)-(â)-myrtenol nitrate
Here we report the chemoselective synthesis of several important, climate relevant isoprene nitrates using silver nitrate to mediate a âhalide for nitrateâ substitution. Employing readily available starting materials, reagents and HornerâWadsworthâEmmons chemistry the synthesis of easily separable, synthetically versatile âkey building blocksâ (E)- and (Z)-3-methyl-4-chlorobut-2-en-1-ol as well as (E)- and (Z)-1-((2-methyl-4-bromobut-2-enyloxy)methyl)-4-methoxybenzene has been achieved using cheap, âoff the shelfâ materials. Exploiting their reactivity we have studied their ability to undergo an âallylic halide for allylic nitrateâ substitution reaction which we demonstrate generates (E)- and (Z)-3-methyl-4-hydroxybut-2-enyl nitrate, and (E)- and (Z)-2-methyl-4-hydroxybut-2-enyl nitrates (âisoprene nitratesâ) in 66â80% overall yields. Using NOESY experiments the elucidation of the carbonâcarbon double bond configuration within the purified isoprene nitrates has been established. Further exemplifying our âhalide for nitrateâ substitution chemistry we outline the straightforward transformation of (1R,2S)-(â)-myrtenol bromide into the previously unknown monoterpene nitrate (1R,2S)-(â)-myrtenol nitrate
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