14 research outputs found

    Ab Initio and DFT Modeling of Stereoselective Deamination of Aziridines by Nitrosyl Chloride

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    ABSTRACT: The stereochemical course of the deamination of cis-2,3-dimethylaziridine by nitrosyl chloride was investigated at the QCISD/6-31G(d) level. Calculations reveal that the reaction takes place in two steps. In the first step, the reactants form a pre-reactive complex, followed by a spiro-type bicyclic transition state, which on dissociative cycloelimination gives the N-nitrosoaziridine intermediate. In the second step, this intermediate undergoes cycloreversion through a slightly asynchronous concerted transition state to form an alkene with the same stereochemistry, which is in total agreement with experiment. In the whole reaction, the denitrosation step is found to be rate-determining. For comparison, geometry optimizations and energies were also obtained at the B3LYP/6-31

    Structure and Reactivity of Pd Complexes in Various Oxidation States in Identical Ligand Environments with Reference to C–C and C–Cl Coupling Reactions: Insights from Density Functional Theory

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    Bonding and reactivity of [(<sup>R</sup>N4)­Pd<sup><i>n</i></sup>CH<sub>3</sub>X]<sup>(<i>n</i>−2)+</sup> complexes have been investigated at the M06/BS2//B3LYP/BS1 level. Feasible mechanisms for the unselective formation of ethane and methyl chloride from mono-methyl Pd<sup>III</sup> complexes and selective formation of ethane or methyl chloride from Pd<sup>IV</sup> complexes are reported here. Density functional theory (DFT) results indicate that Pd<sup>IV</sup> is more reactive than Pd<sup>III</sup> and Pd in different oxidation states that follow different mechanisms. Pd<sup>III</sup> complexes react in three steps: (i) conformational change, (ii) transmetalation, and (iii) reductive elimination. In the first step a five-coordinate Pd<sup>III</sup> intermediate is formed by the cleavage of one Pd–N<sub>ax</sub> bond, and in the second step one methyl group is transferred from the Pd<sup>III</sup> complex to the above intermediate via transmetalation, and subsequently a six-coordinate Pd<sup>IV</sup> intermediate is formed by disproportion. In this step, transmetalation can occur on both singlet and triplet surfaces, and the singlet surface is lying lower. Transmetalation can also occur between the above intermediate and [(<sup>R</sup>N4)­Pd<sup>II</sup>(CH<sub>3</sub>)­(CH<sub>3</sub>CN) ]<sup>+</sup>, but this not a feasible path. In the third step this Pd<sup>IV</sup> intermediate undergoes reductive elimination of ethane and methyl chloride unselectively, and there are three possible routes for this step. Here axial–equatorial elimination is more facile than equatorial–equatorial elimination. Pd<sup>IV</sup> complexes react in two steps, a conformational change followed by reductive elimination, selectively forming ethane or methyl chloride. Thus, Pd<sup>III</sup> complex reacts through a six-coordinate Pd<sup>IV</sup> intermediate that has competing C–C and C–Cl bond formation, and Pd<sup>IV</sup> complex reacts through a five-coordinate Pd<sup>IV</sup> intermediate that has selective C–C and C–Cl bond formation. Free energy barriers indicate that iPr, in comparison to the methyl substituent in the <sup>R</sup>N4 ligand, activates the cleaving of the Pd–N<sub>ax</sub> bond through electronic and steric interactions. Overall, reductive elimination leading to C–C bond formation is easier than the formation of a C–Cl bond

    Unraveling the reaction mechanism, enantio and diastereoselectivities of selenium ylide promoted epoxidation

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    1001-1009The reaction between chiral selenium ylide and benzaldehyde leads to the formation of (2S,3S)-trans-epoxide with high enantio- and diastereoselectivity. Density functional theory and Hartree-Fock calculations using 6-31G(d) basis set have been performed to understand the reaction mechanism and factors associated with enantio- and diastereoselectivities. Conformation of chiral selenium ylide has been found to have a strong influence on the stability of the initial addition transition state between ylide and benzaldehyde. Calculated enantio- and diastereoselectivities from the energy differences between B3LYP/6-31G(d) addition TSs are in good agreement with the experimental data. The rate and diastereoselectivity are controlled by the <i style="mso-bidi-font-style: normal">cisoid-transoid rotational transition state. Analysis of transition state geometries clearly reveals that unfavorable eclipsing interaction between phenyl groups of the benzaldehyde and ylidic substituents mainly governs the energy differences between the enantio and diastereomeric transition states. The favourable reactivity is also explained through Fukui function calculations

    Is corannulene a better diene or dienophile? A DFT analysis

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    Diels Alder reactivity of corannulene has been probed using density functional theory (DFT) at B3LYP/6-31G level by employing it both as a diene and a dienophile in cycloaddition with ethylene and 1,3-butadiene as typical partners. Computations reveal that corannulene acts better as a dienophile than as a diene and as a dienophile it undergoes normal electron demand type addition with 1,3-butadiene, and as a diene corannulene undergoes inverse electron demand type addition with ethylene. When employed as a dienophile the addition takes place preferentially in the rim position than in the spoke position due to strong steric and electronic reasons. Further in the rim addition rim exo approach is favored kinetically and thermodynamically. As a diene, corannulene shows regioselectivity for rim-spoke addition over spoke-spoke addition. Concerted type cycloadditions have been studied and the reactions are seen to take place preferentially on the convex face. The effect of substituents in butadiene on the reactivity and the reaction of butadiene-pentaindenocorannulene (an extended corannulene) system has been investigated for the most favorable rim exo positions

    Effect of coordination mode of thiosemicarbazone on the biological activities of its Ru(II)-benzene complexes: Biomolecular interactions and anticancer activity via ROS-mediated mitochondrial apoptosis

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    Ru(II)-benzene complexes (P1 and P2) were synthesized using a thiosemicarbazone ligand (L1) in two different coordination modes, monodentate S and bidentate N,S, through carefully adjusted reaction conditions. Comprehensive characterization of the complexes was achieved through single crystal X-ray diffraction, revealing a piano-stool geometry around the Ru(II) ion. To evaluate the binding capabilities of the complexes towards CT DNA and BSA, UV–Vis and/or hydrodynamic methods were utilized. Docking studies further validated the intercalative binding mode with DNA, in agreement with the experimental findings, and identified specific BSA amino acids involved in the binding interactions. Based on the results of binding studies, cytotoxicity of the ligand and complexes was appraised in various cancer and normal cell lines alongside the commercial pharmaceutics. Complexes P1 and P2 displayed a promising activity against MDA-MB-231 [IC50 = 5.11 (P1) and 3.48 μM (P2)] and PANC-1 [IC50 = 7.20 (P1) and 4.85 μM (P2)] cancer cells; with the bidentate system (P2) exhibiting a higher activity than its monodentate congener P1, although both of them showed superior activity than the reference drugs. Various bioassays including Western blot analysis revealed the mode of cell death to be apoptosis, which was further concluded to be via the ROS-mediated mitochondrial signaling pathway

    Surfactant–copper(II) Schiff base complexes: synthesis, structural investigation, DNA interaction, docking studies, and cytotoxic activity

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    <div><p>A series of surfactant–copper(II) Schiff base complexes (<b>1–6</b>) of the general formula, [Cu(sal-R<sub>2</sub>)<sub>2</sub>] and [Cu(5-OMe-sal-R<sub>2</sub>)<sub>2</sub>], {where, sal = salicylaldehyde, 5-OMe-sal = 5-methoxy- salicylaldehyde, and R<sub>2</sub> = dodecylamine (DA), tetradecylamine (TA), or cetylamine (CA)} have been synthesized and characterized by spectroscopic, ESI-MS, and elemental analysis methods. For a special reason, the structure of one of the complexes (<b>2</b>) was resolved by single crystal X-ray diffraction analysis and it indicates the presence of a distorted square-planar geometry in the complex. Analysis of the binding of these complexes with DNA has been carried out adapting UV-visible-, fluorescence-, as well as circular dichroism spectroscopic methods and viscosity experiments. The results indicate that the complexes bind via minor groove mode involving the hydrophobic surfactant chain. Increase in the length of the aliphatic chain of the ligands facilitates the binding. Further, molecular docking calculations have been performed to understand the nature as well as order of binding of these complexes with DNA. This docking analysis also suggested that the complexes interact with DNA through the alkyl chain present in the Schiff base ligands via the minor groove. In addition, the cytotoxic property of the surfactant–copper(II) Schiff base complexes have been studied against a breast cancer cell line. All six complexes reduced the visibility of the cells but complexes 2, 3, 5, and 6 brought about this effect at fairly low concentrations. Analyzed further, but a small percentage of cells succumbed to necrosis. Of these complexes (<b>6</b>) proved to be the most efficient aptotoxic agent.</p></div
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