A Computational Study of a Prebiotic Synthesis of the Steroid Progesterone (A and B Rings)

WSEAS TRANSACTIONS ON BIOLOGY AND BIOMEDICINE ◽

10.37394/23208.2020.17.2 ◽

2020 ◽

Vol 17 ◽

Keyword(s):

Double Bond ◽

Hydroxyl Radicals ◽

Computational Study ◽

Prebiotic Synthesis ◽

Magnesium Ion ◽

Methyl Substituent ◽

Trans Conformation ◽

Trans Orientation ◽

Metal Site ◽

Enthalpy Changes

The magnesium ion metalloporphyrin complex is shown to bind the ligands propyne (p) and ethyne (e) on the metal or nitrogen pyrrole sites as a two site catalyst in their copolymerization. The order of addition of the monomers is (pepeeepee). The steroid ring D (pep) is formed first from the propyne adduct bound to the metal site and the but-diene adduct bound to the N-site. The optimal orientation of these adducts determines the β-orientation of the 17-substituent. Further reaction with hydroxyl radicals allows this to be a 17 β- acetyl substituent. Further addition of three ethyne monomers forms a N-tri-ene cyclopentene derivative able to cyclise to form the steroid ring C (pee) with a trans conformation and a 13-β methyl substituent.. Further binding of propyne on the metal site together with the N-indenyl bound adduct enables the B-ring (eep) to form with a trans orientation and a 10-β-methyl substituent. Further addition of two ethyne monomers to the Mg.porphin.N-phenanthrenyl bound adduct allows cyclisation to form the A-ring (pee). The polymerization is curtailed by reaction with hydroxyl radical to form the 3-keto substituent. The cleavage of the Mg.porphin catalyst produces the double bond of pregnane-4,5-diene-3,20-dione. The reactions have been shown to be feasible from the overall enthalpy changes in the ZKE approximation at the HF and MP2 /6-31G* level, and with acceptable activation energies.

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A Computational Study of a Prebiotic Synthesis of the Steroid Progesterone (C and D Rings)

WSEAS TRANSACTIONS ON BIOLOGY AND BIOMEDICINE ◽

10.37394/23208.2020.17.3 ◽

2020 ◽

Vol 17 ◽

Keyword(s):

Hydroxyl Radicals ◽

Computational Study ◽

Prebiotic Synthesis ◽

Activation Energies ◽

Magnesium Ion ◽

Methyl Substituent ◽

Trans Conformation ◽

Metal Site ◽

Optimal Orientation ◽

Enthalpy Changes

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COMPUTING NARROW NANOTUBES AND THEIR DERIVATIVES

International Journal of Nanoscience ◽

10.1142/s0219581x0200019x ◽

2002 ◽

Vol 01 (03n04) ◽

pp. 303-312 ◽

Cited By ~ 5

Author(s):

ZDENĚK SLANINA ◽

FILIP UHLÍK ◽

LESZEK STOBINSKI ◽

HONG-MING LIN ◽

LUDWIK ADAMOWICZ

Keyword(s):

Computational Study ◽

Activation Barriers ◽

Enthalpy Changes ◽

Oxygen Addition

Very recently, narrow nanotubes have been observed with diameters of 5 or even 4 Å. In this report we survey calculations that have so far been performed on narrow model nanotubes, namely capped by fragments of D2d and D6h C 36 fullerene cages or by fragments of C 32 and C 16quasi-fullerene cages with two four-membered rings, or finally by a fragment of dodecahedral C 20. The computations can reproduce the observed diameters of the narrow nanotubes. The results also indicate that fragments of C 32, used as caps instead of C 36, can lead to quite competitive energetics. Thus, a novel possibility that some of the narrow nanotubes can contain four-membered rings at their tips seems plausible. The present paper also surveys computational study of oxygen additions to the narrow nanotubes, i.e., a problem frequently studied with fullerenes. Both thermodynamic enthalpy changes and kinetic activation barriers for oxygen addition to selected bonds are computed and analyzed. The lowest isomer (thermodynamically the most stable) is never of the 6/6 type, i.e., the thermodynamically most convenient structures are produced by oxygen additions to the nanotube tips. The computations show that narrow nanotubes should be relatively prone to additions of oxygen.

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H–Abstraction from Dimethyl Sulfide in the Presence of an Excess of Hydroxyl Radicals. A Quantum Chemical Evaluation of Thermochemical and Kinetic Parameters Unveil an Alternative Pathway to Dimethyl Sulfoxide.

10.26434/chemrxiv.11799096.v1 ◽

2020 ◽

Author(s):

Zoi Salta ◽

Jacopo Lupi ◽

Vincenzo Barone ◽

Oscar Ventura

Keyword(s):

Dimethyl Sulfoxide ◽

Hydroxyl Radicals ◽

Quantum Chemical ◽

Dimethyl Sulfide ◽

Computational Study ◽

Alternative Pathway ◽

Oxidation Mechanism ◽

State Theory ◽

Rate Coefficients ◽

Reduced Sulfur Compounds

<div> Elucidation of the oxidation mechanism of naturally emitted reduced sulfur compounds, especially dimethyl sulfide, plays a central role in understanding background acid precipitation in the natural environment. Most frequently, theoretical studies of the addition and H-elimination reactions of dimethyl sulfide with hydroxyl radicals are studied considering the presence of oxygen that further reacts with the radicals formed in the initial steps. Although the reaction of intermediate species with additional hydroxyl radicals has been considered as part of the global mechanism of oxidation, few if any attention has been dedicated to the possibility of reactions of the initial radicals with a second •OH molecule. In this work we performed a computational study using quantum-chemical methods, of the mechanism of H-abstraction from dimethyl sulfide under normal atmospheric conditions and in reaction chambers at different O2 partial pressure, including complete absence of oxygen. Additionally, important rate coefficients were computed using canonical and variational transition state theory. The rate coefficient for abstraction affords a 4.72 x 10-12 cm3 molecule1 s-1 value, very close to the most recent experimental one (4.13 x 10-12 cm3 molecule-1 s-1). According to our best results, the initial methyl thiomethyl radical was obtained at -25.2 kcal/mol (experimentally -22.4 kcal/mol), and four important paths were identified on the potential energy surface. From the interplay of thermochemical and kinetic arguments, it was possible to demonstrate that the preferred product of the reaction of dimethyl sulfide with two hydroxyl radicals, is actually dimethyl sulfoxide. </div><div> </div>

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Base-Catalyzed Self-Condensation of Arylacetaldehydes: Molecular Structures of (E)-2,4-Bis(9-Anthryl)but-2-enal and (E)-2,4-Diphenylbut-2-enal

Australian Journal of Chemistry ◽

10.1071/ch9880727 ◽

1988 ◽

Vol 41 (5) ◽

pp. 727 ◽

Cited By ~ 1

Author(s):

O Axelsson ◽

HD Becker ◽

BW Skelton ◽

H Sorenson ◽

AH White

Keyword(s):

Double Bond ◽

Single Crystal ◽

Structure Determination ◽

Molecular Structures ◽

Trans Conformation ◽

X Ray ◽

Olefinic Double Bond

Both 9-anthrylacetaldehyde and phenylacetaldehyde undergo stereoselective self-condensation in the presence of base to give (E)- 2,4-di(9-anthryl)but-2-enal (2a), and (E)-2,4-diphenylbut-2-enal (2b) respectively, as established by single-crystal X-ray structure determination. Crystals of (2a) are monoclinic, P21/n, Z 8, a 10.638(9), b 20.68(1), c 20.41(2)Ǻ, β 92.36(5)°; R was 0.061 for No 3476 'observed' reflections. Crystals of (2b) are monoclinic, P21/c, Z 4, a 5.781(2), b 23.163(8), c 9.297(5)Ǻ, β 91.54(4)°; R 0.037 for No 1174. In both compounds, the enal moiety assumes a virtually planar s-trans conformation, with the angles between the planes of the olefinic double bond and the adjacent aromatic π-system around 70°.

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High-capacity cathodes for magnesium lithium chlorine tri-ion batteries through chloride intercalation in layered MoS2: a computational study

Journal of Materials Chemistry A ◽

10.1039/c8ta01050a ◽

2018 ◽

Vol 6 (16) ◽

pp. 6830-6839 ◽

Cited By ~ 18

Author(s):

Zhuo Wang ◽

Guosheng Shao

Keyword(s):

Lithium Ion Batteries ◽

Computational Study ◽

High Capacity ◽

Lithium Ion ◽

Magnesium Ion ◽

Alternative Technology ◽

Resource Limited ◽

Magnesium Ion Batteries ◽

Layered Mos2

Rechargeable magnesium ion batteries (MIBs) have great potential as an alternative technology to substitute resource-limited lithium-ion batteries (LIBs), but rather difficult transportation of Mg2+ in cathodes and hence low cathode capacities loom as a major roadblock for their applications.

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Ionic and Radical Mechanisms in Olefinic Systems, with Special Reference to Processes of Double-Bond Displacement, Vulcanization and Photogelling

Rubber Chemistry and Technology ◽

10.5254/1.3543163 ◽

1942 ◽

Vol 15 (4) ◽

pp. 774-779

Author(s):

Ernest Harold Farmer

Keyword(s):

Double Bond ◽

Special Reference ◽

Methyl Substituent ◽

Benzene Nucleus ◽

Methyl Group ◽

Unsaturated System ◽

Alkyl Groups ◽

Electron Release

Abstract The α-methylenic reactions discussed in the preceding two papers recall a series of interesting observations by Baker and Nathan, which indicate that a p-methyl substituent attached to the benzene nucleus can permit electron release to the nucleus in a manner that appears only in lesser degree in higher alkyl groups, and may be absent in some (e.g., Buγ). Thus in p-methylbenzyl bromide, the suggested function of the methyl group (dotted arrows in (I) permits (see PDF for diagram) additional electron release at the C—Br bond, and so facilitates the anionization of the bromine. Baker and Nathan suggest that the electrons of the duplet constituting the C—H bond of the methyl group are less localized than those in a similarly placed C—C bond, and hence that a methyl group attached to the necessary conjugated unsaturated system is capable of electron-release by a mechanism similar to the tautomeric effect:

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