Search results for "molecule"
showing 10 items of 5162 documents
Surface-anchored counterions on weak chiral anion-exchangers accelerate separations and improve their compatibility for mass-spectrometry-hyphenation
2017
In the present work we propose new variants of chiral stationary phases (CSP) with tert-butylcarbamoylquinine (tBuCQN) as chiral selector molecule. Four tBuCQN-CSPs with distinct bonding chemistries are compared in terms of their pH-dependent surface charge by ζ-potential determinations, by achiral and chiral liquid chromatographic tests and LC-ESI-MS hyphenation. In one embodiment tBuCQN was immobilized on 3-mercaptopropylmethylsilyl-modified silica by thiol-ene click reaction (brush type CSP with selector coverage of 0.38mmol/g). In another embodiment, poly-(3-mercaptopropyl)-methylsiloxane was coated onto vinylized silica particles in presence of tBuCQN and radical initiator. The tBuCQN …
Anion Recognition by a Bioactive Diureidodecalin Anionophore: Solid-State, Solution, and Computational Studies
2018
Recent work has identified a bis-(p-nitrophenyl)ureidodecalin anion carrier as a promising candidate for biomedical applications, showing good activity for chloride transport in cells yet almost no cytotoxicity. To underpin further development of this and related compounds, a detailed structural and binding investigation is reported. Crystal structures of the transporter as five solvates confirm the diaxial positioning of urea groups while revealing a degree of conformational flexibility. Structures of complexes with Cl−, Br−, NO3 −, SO4 2− and AcO−, supported by computational studies, show how the binding site can adapt to accommodate these anions. 1H NMR binding studies revealed exception…
N-Heterocyclic Carbene Catalyzed Asymmetric Synthesis of Dihydropyranothiazoles via Azolium Enolate Intermediates
2017
A highly diastereo- and enantiostereoselective synthesis of bicyclic dihydropyranothiazoles combining a thiazole and δ-lactone skeleton via NHC-catalyzed [4+2] annulation of 5-alkenylthiazolones and α-chloroaldehydes has been developed. The heterocyclic products are formed via azolium enolate intermediates in good yields with high diastereo- and enantistereoselectivities.
Synthesis, characterization and the first crystal structure of the Zn(II) complex of 4,6-O-ethylidine-N-(2-hydroxybenzylidene)-β-D-glucopyranosylamine
2001
4,6-O-Ethylidine-N-(2-hydroxybenzylidene)-β-D-glucopyranosylamine (H3L1) and N-(5-bromo-2-hydroxybenzylidene-4,6-O-ethylidine-β-D-glucopyranosylamine (H3L2) molecules possessing a–C-1–N=C(H)–moiety for metal-ion binding were synthesized by condensing the 4,6–O–ethylidene–β–D–glucopyranosylamine with salicylaldehyde or 5–bromosalicylaldehyde. Complexes of these ligands with Zn(II) were isolated and characterized using elemental analysis, FTIR, UV–Vis absorption, NMR spectroscopic and FAB mass spectrometric techniques. The structure of the Zn(II) complex derived from H3L1 was established for the first time by a single-crystal X-ray diffraction study. The anomeric nature of the saccharide moie…
Biomimetic diels–alder cyclizations for the construction of the brevianamide, paraherquamide, sclerotamide, asperparaline and VM55599 ring systems
1998
Abstract A potentially bio-mimetic Diels–Alder cyclization to construct the bicyclo[2.2.2] ring system common to the paraherquamides, marcfortines, sclerotamides, brevianamides, VM55599, and asperparaline is reported. Epi-deoxybrevianamide E (22) is converted into the corresponding lactim ether (23) and then oxidized with DDQ to provide an azadiene (24) which is tautomerized in the presence of base to azadiene 25 which, spontaneously cyclizes to give a 2:1 mixture of cycloadducts 26 and 27. These cycloadducts are each in turn, converted into d , l -C-19-epi-brevianamide A (20) and d , l -brevianamide B (6). The stereochemical implications of the [4+2] cycloaddition is discussed in the conte…
Monoradicals and Diradicals of Dibenzofluoreno[3,2-b]fluorene Isomers: Mechanisms of Electronic Delocalization
2020
The preparation of a series of dibenzo- and tetrabenzo-fused fluoreno[3,2-b]fluorenes is disclosed, and the diradicaloid properties of these molecules are compared with those of a similar, previously reported series of anthracene-based diradicaloids. Insights on the diradical mode of delocalization tuning by constitutional isomerism of the external naphthalenes has been explored by means of the physical approach (dissection of the electronic properties in terms of electronic repulsion and transfer integral) of diradicals. This study has also been extended to the redox species of the two series of compounds and found that the radical cations have the same stabilization mode by delocalization…
Sequestering aromatic molecules with a spin-crossover Fe(II) microporous coordination polymer.
2012
All in a spin: A series of three-dimensional porous coordination polymer {Fe(dpe)[Pt(CN)(4)]}⋅G (dpe = 1,2-di(4-pyridyl)ethylene; G = phenazine, anthracene, or naphthalene) exhibiting spin crossover and host-guest functions is reported. The magnetic properties of the framework are very sensitive to the chemical nature (aromatic or hydroxilic solvents) and the size of the included guest molecules.
New acridinium trifluoromethanesulfonate stacks induced in the presence of organotin(IV) complexes
2013
Abstract Three new crystalline architectures based on acridinium trifluoromethanesulfonate salts [C13H10N]+[CF3SO3]– have been isolated as single crystals from the reaction of the dimeric hydroxo di-n-butylstannane trifluoromethanesulfonato complex [n-Bu2Sn(OH)(H2O)(CF3SO3)]2 (1) with acridine (C13H9N, Acr), in dichloromethane at room temperature. When an equimolar mixture of anthracene (C14H10, Ant) and acridine is initially used, the crystallization of a sandwich-type arrangement occurs, leading to the intercalation of one molecule of anthracene between two acridium trifluoromethanesulfonate salt molecules. In the three X-ray structures reported, the crystal packing involves the contribut…
Organotin(IV) trifluoromethanesulfonates chemistry: Isolation and characterization of a new di-n-butyl derivative presenting a Sn3O3 core
2012
Abstract Reaction of the dimeric hydroxo di-n-butylstannane trifluoromethanesulfonato complex [n-Bu2Sn(OH)(H2O)(CF3SO3)]2 (1) with a mixture of anthracene (C14H10, Ant) and phenazine (C12H8N2, Phz) in dichloromethane at room temperature yielded the novel di-n-butyltin(IV) trifluoromethanesulfonate salt {[n-Bu2Sn(H2O)]2O·n-Bu2Sn(OH)2}(CF3SO3)2 (2), together with the co-crystallization of phenazinium trifluoromethanesulfonate salts ([C12H9N2][CF3SO3], PhzH) collected in the solid state in two distinct self-assembled architectures, 3 and 4, showing π–π stacking interactions, and involving the intercalation of free molecules of phenazine and anthracene, respectively. Complex 2 is a cationic tri…
Profile of leukocyte-endothelial cell interactions induced in venules and arterioles by nucleoside reverse-transcriptase inhibitors in vivo.
2013
Background There is controversy regarding cardiovascular (CV) toxicity of the nucleoside reverse-transcriptase inhibitors used to treat human immunodeficiency virus infection. Methods We evaluated the effects of nucleoside reverse-transcriptase inhibitors on leukocyte-endothelium interactions, a hallmark of CV diseases, in rat mesenteric vessels using intravital microscopy and in human arterial cells using a flow chamber system. Results Abacavir and didanosine increased rolling, adhesion and emigration in rat vessels. These effects were reversed with antibodies against Macrophage-1 antigen (Mac-1) or intercellular adhesion molecule 1 and were reproduced in human cells. Lamivudine, zidovudin…