Epoxides, Cyclic Sulfites, and Sulfate from Natural Pentacyclic Triterpenoids:  Theoretical Calculations and Chemical Transformations

2003 ◽  
Vol 68 (12) ◽  
pp. 4833-4844 ◽  
Author(s):  
Andrés García-Granados ◽  
Pilar E. López ◽  
Enrique Melguizo ◽  
Juan N. Moliz ◽  
Andrés Parra ◽  
...  
Keyword(s):  
Theoretical Calculations ◽  
Chemical Transformations ◽  
Pentacyclic Triterpenoids ◽  
Cyclic Sulfites

scholarly journals Recent Developments in the Functionalization of Betulinic Acid and Its Natural Analogues: A Route to New Bioactive Compounds

Molecules ◽  
2019 ◽  
Vol 24 (2) ◽  
pp. 355 ◽  
Author(s):  
Joana L. C. Sousa ◽  
Carmen S. R. Freire ◽  
Armando J. D. Silvestre ◽  
Artur M. S. Silva
Keyword(s):  
Betulinic Acid ◽  
Antitumor Agents ◽  
Aldol Condensation ◽  
Antimalarial Activity ◽  
Biological Activities ◽  
Chemical Transformations ◽  
Pentacyclic Triterpenoids ◽  
Natural Analogues ◽  
Palladium Catalyzed ◽  
Aldol Condensation Reactions

Betulinic acid (BA) and its natural analogues betulin (BN), betulonic (BoA), and 23-hydroxybetulinic (HBA) acids are lupane-type pentacyclic triterpenoids. They are present in many plants and display important biological activities. This review focuses on the chemical transformations used to functionalize BA/BN/BoA/HBA in order to obtain new derivatives with improved biological activity, covering the period since 2013 to 2018. It is divided by the main chemical transformations reported in the literature, including amination, esterification, alkylation, sulfonation, copper(I)-catalyzed alkyne-azide cycloaddition, palladium-catalyzed cross-coupling, hydroxylation, and aldol condensation reactions. In addition, the synthesis of heterocycle-fused BA/HBA derivatives and polymer‒BA conjugates are also addressed. The new derivatives are mainly used as antitumor agents, but there are other biological applications such as antimalarial activity, drug delivery, bioimaging, among others.

Thermally induced mineral and chemical transformations in calcareous mudstones around a basaltic dyke (Perthus Pass, southern Massif Central, France). Possible implications as a natural analogue of nuclear waste disposal

Clay Minerals ◽  
2007 ◽  
Vol 42 (2) ◽  
pp. 213-231 ◽  
Author(s):  
C. Henry ◽  
J.-Y. Boisson ◽  
A. Bouchet ◽  
A. Meunier
Keyword(s):  
Theoretical Calculations ◽  
Heat Diffusion ◽  
Large Temperature ◽  
Chemical Transformations ◽  
X Ray Diffraction ◽  
Experimental Conditions ◽  
Retention Capacity ◽  
Massif Central ◽  
Thermally Induced ◽  
X Ray

AbstractA mixed-layer illite-smectite, illite-rich calcareous mudstone intruded by a basaltic dyke at the Perthus Pass (southern Massif Central, France) allows us to study the transformation of clays subjected to a brief thermal gradient. X-ray diffraction, scanning electron microscopy, electron microprobe and atomic absorption spectroscopy analyses were performed on samples at variable distances from the mudstone-dyke contacts.A roughly similar evolution is seen on both sides of the dyke: quartz, calcite, kaolinite and illite disappear; Ca-silicates, albite and saponite-beidellite form, late meteoric halloysite crystallizes in open fractures.Chemical and mineralogical transformations are related to heat diffusion from the dyke. Theoretical calculations highlight the influence of the dyke orientation. The mineralogical reactions observed in rocks are similar to those observed in experimental conditions. The formation of new swelling phases with a high retention capacity linked to a short duration, large-temperature increase, should constitute a positive process for Repository Performance Assessment.

Regioselective Enzymatic Acylations of Polyhydroxylated Eudesmanes:  Semisynthesis, Theoretical Calculations, and Biotransformation of Cyclic Sulfites

2000 ◽  
Vol 65 (24) ◽  
pp. 8214-8223 ◽  
Author(s):  
Andrés García-Granados ◽  
Enrique Melguizo ◽  
Andrés Parra ◽  
Yolanda Simeó ◽  
Beatriz Viseras ◽  
...  
Keyword(s):  
Theoretical Calculations ◽  
Cyclic Sulfites

scholarly journals A merged copper(I/II) cluster isolated from Glaser coupling

2019 ◽  
Vol 10 (1) ◽  
Author(s):  
Siqi Zhang ◽  
Liang Zhao
Keyword(s):  
Theoretical Calculations ◽  
Mixed Valence ◽  
Hydrogen Atom Transfer ◽  
Chemical Transformations ◽  
Oxidation Reactions ◽  
High Hydrogen ◽  
Copper Acetylide ◽  
Back Donation ◽  
Glaser Coupling

Abstract Ubiquitous copper-oxygen species are pivotal in enabling multifarious oxidation reactions in biological and chemical transformations. We herein construct a macrocycle-protected mixed-valence cluster [(tBuC≡CCuI3)-(μ2-OH)-CuII] by merging a copper acetylide cluster with a copper-oxygen moiety formed in Glaser coupling. This merged Cu(I/II) cluster shows remarkably strong oxidation capacity, whose reduction potential is among the most positive for Cu(II) and even comparable with some Cu(III) species. Consequently, the cluster exhibits high hydrogen atom transfer (HAT) reactivity with inert hydrocarbons. In contrast, the degraded [CuII-(μ2-OH)-CuII] embedded in a small macrocyclic homologue shows no HAT reactivity. Theoretical calculations indicate that the strong oxidation ability of Cu(II) in [(tBuC≡CCuI3)-(μ2-OH)-CuII] is mainly ascribed to the uneven charge distribution of Cu(I) ions in the tBuC≡CCuI3 unit because of significant [dCu(I) → π*(C≡C)] back donation. The present study on in situ formed metal clusters opens a broad prospect for mechanistic studies of Cu-based catalytic reactions.

scholarly journals Formation of complex hydrocarbon systems from methane at the upper mantle thermobaric conditions

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Aleksandr Serovaiskii ◽  
Vladimir Kutcherov
Keyword(s):  
Upper Mantle ◽  
Theoretical Calculations ◽  
Extreme Temperature ◽  
Hydrocarbon Mixture ◽  
Chemical Transformations ◽  
Product Systems ◽  
Thermobaric Conditions ◽  
Diamond Anvil ◽  
Temperature And Pressure ◽  
Hydrocarbons Synthesis

AbstractThe existence of methane in the Earth’s mantle does not cause any doubt, however, its possible chemical transformation under the mantle thermobaric conditions is not enough known. Investigation of methane at the upper mantle thermobaric conditions, using diamond anvil cells, demonstrated the possible formation of ethane, propane and n-butane from methane, however, theoretical calculations of methane behaviour at extreme temperature and pressure predicted also heavier hydrocarbons. We experimentally investigated the chemical transformations of methane at the upper mantle thermobaric conditions, corresponding to the depth of 70–80 km (850–1000 K, 2.5 GPa), using “Toroid”-type Large reactive volume device and gas chromatography. The experimental results demonstrated the formation of the complex hydrocarbon mixture up to C7 with linear, branched and cycled structures and benzene. Unsaturated hydrocarbons were detected on the trace level in the products mixture. The increasing of exposure time leaded to growth of heavier components in the product systems. The data obtained suggest possible existence of complex hydrocarbon mixtures at the upper mantle thermobaric conditions and provide a new insight on the possible pathways of the hydrocarbons synthesis from methane in the upper mantle.

XUV Absorption Spectra of Carbon Ions

1988 ◽  
Vol 102 ◽  
pp. 71-73
Author(s):  
E. Jannitti ◽  
P. Nicolosi ◽  
G. Tondello
Keyword(s):  
Absorption Spectra ◽  
Cross Section ◽  
Theoretical Calculations ◽  
Photoionization Cross Section ◽  
Carbon Ions

AbstractThe photoabsorption spectra of the carbon ions have been obtained by using two laser-produced plasmas. The photoionization cross-section of the CV has been absolutely measured and the value at threshold, σ=(4.7±0.5) × 10−19cm2, as well as its behaviour at higher energies agrees quite well with the theoretical calculations.

Relative Intensities in ED Patterns From Thin Gold Films

1972 ◽  
Vol 30 ◽  
pp. 636-637
Author(s):  
R. H. Morriss ◽  
J. D. C. Peng ◽  
C. D. Melvin
Keyword(s):  
Theoretical Calculations ◽  
Diffraction Theory ◽  
Gold Films ◽  
Reasonable Accuracy ◽  
Experimental Conditions ◽  
Crystal Perfection ◽  
Heavy Atoms ◽  
Fine Focus ◽  
Convergent Beam ◽  
Beam Diffraction

Although dynamical diffraction theory was modified for electrons by Bethe in 1928, relatively few calculations have been carried out because of computational difficulties. Even fewer attempts have been made to correlate experimental data with theoretical calculations. The experimental conditions are indeed stringent - not only is a knowledge of crystal perfection, morphology, and orientation necessary, but other factors such as specimen contamination are important and must be carefully controlled. The experimental method of fine-focus convergent-beam electron diffraction has been successfully applied by Goodman and Lehmpfuhl to single crystals of MgO containing light atoms and more recently by Lynch to single crystalline (111) gold films which contain heavy atoms. In both experiments intensity distributions were calculated using the multislice method of n-beam diffraction theory. In order to obtain reasonable accuracy Lynch found it necessary to include 139 beams in the calculations for gold with all but 43 corresponding to beams out of the [111] zone.

Effects of Higher-Order Laue Zone reflections on structure images

1993 ◽  
Vol 51 ◽  
pp. 450-451
Author(s):  
H. S. Kim ◽  
S. S. Sheinin
Keyword(s):  
Wave Vector ◽  
Theoretical Calculations ◽  
Reciprocal Lattice ◽  
Image Plane ◽  
Bloch Wave ◽  
Dynamical Theory ◽  
Higher Order ◽  
Lattice Image ◽  
Lattice Vector ◽  
Image Position

The importance of image simulation in interpreting experimental lattice images is well established. Normally, in carrying out the required theoretical calculations, only zero order Laue zone reflections are taken into account. In this paper we assess the conditions for which this procedure is valid and indicate circumstances in which higher order Laue zone reflections may be important. Our work is based on an analysis of the requirements for obtaining structure images i.e. images directly related to the projected potential. In the considerations to follow, the Bloch wave formulation of the dynamical theory has been used.The intensity in a lattice image can be obtained from the total wave function at the image plane is given by: where ϕg(z) is the diffracted beam amplitide given by In these equations,the z direction is perpendicular to the entrance surface, g is a reciprocal lattice vector, the Cg(i) are Fourier coefficients in the expression for a Bloch wave, b(i), X(i) is the Bloch wave excitation coefficient, ϒ(i)=k(i)-K, k(i) is a Bloch wave vector, K is the electron wave vector after correction for the mean inner potential of the crystal, T(q) and D(q) are the transfer function and damping function respectively, q is a scattering vector and the summation is over i=l,N where N is the number of beams taken into account.

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