12 research outputs found
Role of Anation on the Mechanism of Proton Reduction Involving a Pentapyridine Cobalt Complex: A Theoretical Study
Kinetic
and thermodynamic aspects of proton reduction involving pentapyridine
cobaltÂ(II) complex were investigated with the help of quantum chemical
calculations. Free energy profile of all possible mechanistic routes
for proton reduction was constructed with the consideration of both
anation and solvent bound pathways. The computed free energy profile
shows that acetate ion plays a significant role in modulating the
kinetic aspects of CoÂ(III)âhydride formation which is found
to be the key intermediate for proton reduction. Upon replacing solvent
by acetate ion, one electron reduction and protonation of Co<sup>I</sup> species become more rapid along with slow displacement reaction.
Most favorable pathways for hydrogen evolution from CoÂ(III)âhydride
species is also investigated. Among the four possible pathways, reduction
followed by protonation of CoÂ(III)âhydride (RPP) is found to
be the most feasible pathway. On the basis of QTAIM and NBO analyses,
the electronic origin of most favorable pathway is explained. The
basicity of cobalt center along with thermodynamic stability of putative
Co<sup>III/II</sup>âH species is essentially a prime factor
in deciding the most favorable pathway for hydrogen evolution. Our
computed results are in good agreement with experimental observations
and also provided adequate information to design cobalt-based molecular
electrocatalysts for proton reduction in future
Unraveling the reaction mechanism, enantio and diastereoselectivities of selenium ylide promoted epoxidation
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
Structure and Reactivity of Pd Complexes in Various Oxidation States in Identical Ligand Environments with Reference to CâC and CâCl Coupling Reactions: Insights from Density Functional Theory
Bonding
and reactivity of [(<sup>R</sup>N4)ÂPd<sup><i>n</i></sup>CH<sub>3</sub>X]<sup>(<i>n</i>â2)+</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 PdâN<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)ÂPd<sup>II</sup>(CH<sub>3</sub>)Â(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 axialâequatorial elimination is
more facile than equatorialâequatorial 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 CâC and CâCl
bond formation, and Pd<sup>IV</sup> complex reacts through a five-coordinate
Pd<sup>IV</sup> intermediate that has selective CâC and CâCl
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 PdâN<sub>ax</sub> bond through electronic
and steric interactions. Overall, reductive elimination leading to
CâC bond formation is easier than the formation of a CâCl
bond
Quantum mechanical study on complexation phenomenon of pillar[5]arene towards neutral dicyanobutane
Based on density functional theory calculations, we have addressed the electronic structure, binding and nature of non-covalent interactions between alkylated pillar[5]arene (P[5]A) and 1,4-dicyanobutane (DCB)-based host-guest macrocycles. Neutral 1,4-dicyanobutane-based alkylated DCB_ProP[5]A is found to show higher binding energy when compared to the other three host-guest macrocycles. These complexes are largely stabilised by non-covalent interactions, which are ascertained through NCI and QTAIM analyses. Furthermore, the second-order perturbation energy of NBO analysis show that LP (N) â Ď*(C-H) interactions predominate in DCB_ProP[5]A complex. Particularly, alkyl substituents (-methyl, -ethyl and -propyl) are playing a vital role in stabilising the host-guest complexes. In summary, the present work not only exhibits an efficient strategy to build a new family of alkylated P[5]A inclusion complexes but also providing deeper understanding on various non-covalent interactions towards 1,4-dicyanobutane (DCB) guest molecules inside the host environment.</p
Halogen-Based 17β-HSD1 Inhibitors: Insights from DFT, Docking, and Molecular Dynamics Simulation Studies
The high expression of 17β-hydroxysteroid dehydrogenase type 1 (17β-HSD1) mRNA has been found in breast cancer tissues and endometriosis. The current research focuses on preparing a range of organic molecules as 17β-HSD1 inhibitors. Among them, the derivatives of hydroxyphenyl naphthol steroidomimetics are reported as one of the potential groups of inhibitors for treating estrogen-dependent disorders. Looking at the recent trends in drug design, many halogen-based drugs have been approved by the FDA in the last few years. Here, we propose sixteen potential hydroxyphenyl naphthol steroidomimetics-based inhibitors through halogen substitution. Our Frontier Molecular Orbitals (FMO) analysis reveals that the halogen atom significantly lowers the Lowest Unoccupied Molecular Orbital (LUMO) level, and iodine shows an excellent capability to reduce the LUMO in particular. Tri-halogen substitution shows more chemical reactivity via a reduced HOMOâLUMO gap. Furthermore, the computed DFT descriptors highlight the structureâproperty relationship towards their binding ability to the 17β-HSD1 protein. We analyze the nature of different noncovalent interactions between these molecules and the 17β-HSD1 using molecular docking analysis. The halogen-derived molecules showed binding energy ranging from â10.26 to â11.94 kcal/mol. Furthermore, the molecular dynamics (MD) simulations show that the newly proposed compounds provide good stability with 17β-HSD1. The information obtained from this investigation will advance our knowledge of the 17β-HSD1 inhibitors and offer clues to developing new 17β-HSD1 inhibitors for future applications
Pyrene Schiff Base: Photophysics, Aggregation Induced Emission, and Antimicrobial Properties
Pyrene
containing Schiff base molecule, namely 4-[(pyren-1-ylmethylene)Âamino]Âphenol
(KB-1), was successfully synthesized and well characterized by using <sup>1</sup>H, <sup>13</sup>C NMR, FT-IR, and EI-MS spectrometry. UVâvisible
absorption, steady-state fluorescence, time-resolved fluorescence,
and transient absorption spectroscopic techniques have been employed
to elucidate the photophysical processes of KB-1. It has been demonstrated
that the absorption characteristics of KB-1 have been bathochromatically
tuned to the visible region by extending the Ď-conjugation.
The extended Ď-conjugation is evidently confirmed by DFT calculations
and reveals that ĎâĎ* transition is the major factor
responsible for electronic absorption of KB-1. The photophysical property
of KB-1 was carefully examined in different organic solvents at different
concentrations and the results show that the fluorescence of this
molecule is completely quenched due to photoinduced electron transfer.
Intriguingly, the fluorescence intensity of KB-1 increases enormously
by the gradual addition of water up to 90% with concomitant increase
in fluorescence lifetime. This clearly signifies that this molecule
has aggregation-induced emission (AIE) property. The mechanism of
AIE of this molecule is suppression of photoinduced electron transfer
(PET) due to hydrogen bonding interaction of imine donor with water.
A direct evidence of PET process has been presented by using nanosecond
transient absorption measurements. Further, KB-1 was successfully
used for antimicrobial and bioimaging studies. The antimicrobial studies
were carried out through disc diffusion method. KB-1 is used against
both Gram-positive (<i>Rhodococcus rhodochrous</i> and <i>Staphylococcus aureus</i>) and Gram-negative (<i>Escherichia
coli</i> and <i>Pseudomonas aeruginosa</i>) bacterial
species and also fungal species (<i>Candida albicans</i>). The result shows KB-1 can act as an excellent antimicrobial agent
and as a photolabeling agent. <i>S. aureus</i>, <i>P. aeruginosa</i>, and <i>C. albicans</i> were found
to be the most susceptible microorganisms at 1 mM concentration among
the bacteria used in the present investigation