Epoxidation and hydroxylation of Flav-3-enes, and synthesis of 2,3-trans-Flavan-3-ols

1974 ◽  
Vol 27 (4) ◽  
pp. 865 ◽  
Author(s):  
JW Clark-Lewis ◽  
EJ McGarry ◽  
AH Ilsley
Keyword(s):  
Chemical Shift ◽  
Oxygen Atom ◽  
Peracetic Acid ◽  
Accidental Coincidence ◽  
Virtual Coupling ◽  
Acetyl Group

Flav-3-ene epoxides cannot be prepared by the reaction of peracetic acid with a flavene, which leads mainly to the 2,3-trans-3,4-cis-4-acetoxyflavan-3-ols. The epoxides of flav-3-enes lacking electron releasing substituents in ring A may be prepared under weakly basic conditions, and on reduction give 2,3-trans-flavan-3-ols. Flavenes with electron-releasing substituents in conjugated positions in the A ring do not give epoxides under acidic or basic conditions, but the 2,3-trans-flavan-3-ols can be prepared by hydrogenolysis of the products obtained by interaction with peracetic acid. Mechanisms are proposed to account for the products obtained in the peroxidation reactions, and N.M.R. was used to establish the configurations of all the products. Migration of the acetyl group from the 4- to the 3-oxygen atom was observed in two cases, and the resultant 2,3-trans-3,4-cis-3-acetoxyflavan-4-ols showed virtual coupling of the 2- and 4-protons because of the accidental coincidence in chemical shift of the 2- and 3-protons. 2,3-cis-3,4-trans-3-Bromo-4,4'-dimethoxyflavan showed similar virtual coupling owing to near equivalence in the chemical shift of the 3- and the 4-protons.

Deshielding γ–gauche effects in 13C magnetic resonance: a comparison of the conformational behaviour of the acetyl group in cyclohexane and 5-substituted-1,3-dioxane systems

1984 ◽  
Vol 62 (7) ◽  
pp. 1308-1311 ◽  
Author(s):  
G. W. Buchanan ◽  
S. H. Preusser ◽  
V. L. Webb
Keyword(s):  
Magnetic Resonance ◽  
Chemical Shift ◽  
Low Temperature ◽  
Direct Measurement ◽  
Carbonyl Carbon ◽  
Acetyl Group ◽  
Carbon Chemical Shift ◽  
Reported Data

Low temperature (173 K) 13C spectra of acetylcyclohexane, 1-acetyl-1-methylcyclohexane, and 5-acetyl-5-methyl-1,3-dioxane are reported. Data permit the first direct measurement of −ΔG0 for the acetyl group bonded to cyclohexane. The value obtained, 1.02 ± 0.05 kcal/mol in CS2–CD2Cl2 solution, is considerably lower than that determined by equilibration methods. Factors contributing to observed axial–equatorial carbonyl carbon chemical shift differences for substituted cyclohexanes and 1,3-dioxanes are discussed.

scholarly journals Detecting Zn(II) Ions in Live Cells with Near-Infrared Fluorescent Probes

Molecules ◽  
2019 ◽  
Vol 24 (8) ◽  
pp. 1592 ◽  
Author(s):  
Fang ◽  
Xia ◽  
Bi ◽  
Wigstrom ◽  
Valenzano ◽  
...  
Keyword(s):  
Detection Limit ◽  
Oxygen Atom ◽  
Membrane Permeability ◽  
Fluorescent Probes ◽  
Near Infrared ◽  
Emission Spectra ◽  
Live Cells ◽  
Phenolic Oxygen ◽  
Acetyl Group ◽  
Low Cytotoxicity

Two near-infrared fluorescent probes (A and B) containing hemicyanine structures appended to dipicolylamine (DPA), and a dipicolylamine derivative where one pyridine was substituted with pyrazine, respectively, were synthesized and tested for the identification of Zn(II) ions in live cells. In both probes, an acetyl group is attached to the phenolic oxygen atom of the hemicyanine platform to decrease the probe fluorescence background. Probe A displays sensitive fluorescence responses and binds preferentially to Zn(II) ions over other metal ions such as Cd2+ ions with a low detection limit of 0.45 nM. In contrast, the emission spectra of probe B is not significantly affected if Zn(II) ions are added. Probe A possesses excellent membrane permeability and low cytotoxicity, allowing for sensitive imaging of both exogenously supplemented Zn(II) ions in live cells, and endogenously releases Zn(II) ions in cells after treatment of 2,2-dithiodipyridine.

A study of twinning in YBa2Cu3O7−x by large-angle convergent-beam electron diffraction

1990 ◽  
Vol 48 (4) ◽  
pp. 20-21
Author(s):  
P.A. Midgley ◽  
R. Vincent ◽  
D. Cherns
Keyword(s):  
Electron Diffraction ◽  
Oxygen Atom ◽  
Strain Field ◽  
Large Angle ◽  
Convergent Beam Electron Diffraction ◽  
Orthorhombic Distortion ◽  
Beam Electron ◽  
Resultant Powder ◽  
Convergent Beam ◽  
Mesh Grid

The oxygenation of YBa2Cu3O7−x (YBCO) leads to an orthorhombic distortion of the unit cell to accommodate the extra oxygen atom. This makes the formation of twins energetically favourable with CuO4 planar unit chains running alternately along the a and b axes of the parent tetragonal structure. The geometry of this twinning is such that four possible twin variants may co-exist with the twin boundaries lying in the (110) or (110) planes of the deformed structure. The traces of these planes are not mutually perpendicular and thus the crystal is strained to allow for the mismatch. It is to the nature of this strain field that this work has been addressed.Sintered samples were prepared by crushing and dispersing the resultant powder onto a very fine Cu mesh grid. Single crystals were chemically thinned to perforation. No discernible artefacts were seen and similar results were obtained with either method.

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