The catecholase activities were routinely modeled using transition metal complexes as catalyst and in some case basic pH were used as a reaction condition. In this article, the catalytic aerobic ...oxidation of proxy substrate 3,5‐di‐tert‐butylcatechol (DTBC) in methanol using triethylamine/diethylamine as catalyst was demonstrated as a functional mimic of catecholase activity. The kinetic manifestation of DTBC oxidation was explained as enzymatic substrate inhibition pattern in Michaelis‐Menten kinetic model. The mechanistic insight of the aerobic oxidation of DTBC was further validated using various spectroscopic techniques and DFT methods.
Catalytic aerobic oxidation of 3,5‐di‐tert‐butylcatechol (DTBC) in methanol using triethyl amine was follow enzymatic substrate inhibition pattern. The lowering of one electron oxidation potential in presence of triethylamine was the key mechanistic insight for this aerobic oxidation which was validated using various spectroscopic techniques and DFT methods.
A mixed-valence hexanuclear Cu cluster, (Cu(DSB)(CBT))2(Cu2Br)2PPh42 (where DSB = 2,3-disulfidobenzoate and CBT = 3-carboxybenzene- 1,2-bis(thiolate)) with four tetrahedral Cu(I) and two square ...planer Cu(III) centers, was constructed with an unprecedented topologic architecture of a zigzag patterned infinite sheet through unique intermolecular H-bonding interactions in solid state.
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► Hexanuclear mix valance Cu(I/II) cluster with asymmetric dithiolene ligand. ► 2,3-dimercaptobenzoic acid served as bi and tridentate ligand under controlled acetate buffer. ► 2D H-bonding network afforded unique topologic architecture of a zigzag patterned infinite sheet. ► DFT calculation explained mix valence state of Cu atom which is well agreement with experimental results.
A homoleptic hexanuclear Cu cluster, (Cu(DSB)(CBT))
2(Cu
2Br)
2PPh
4
2 (
1-PPh
4
) DSB
=
2,3-disulfidobenzoate; CBT
=
3-carboxybenzene-1,2-bis(thiolate) was synthesized as dark green crystals by the reaction of CuCl
2 with 2,3-dimercaptobenzoic acid in acetate buffer solution. The X-ray crystal study of
1-PPh
4
revealed its unique structural features: (1) one of two types of crystallographically distinct Cu centers adopted a square planer geometry and the other center had a tetrahedral geometry, and (2) intermolecular H-bonding interactions connected between carboxylic acid group of CBT and the carboxylate group of DSB led to the construction of an unprecedented topologic architecture of a zigzag patterned infinite sheet. In addition, taking into account the total charge of the molecule, which contained 2,3-disulfidobenzoate and 3-carboxybenzene-1,2-bis(thiolate), and the diamagnetic nature of
1-PPh
4
,
1-PPh
4
led to it is assignment as a mixed-valence Cu(I)/Cu(III) cluster. Such mixed valence states of Cu atoms were also examined by density functional theory calculation.
A set of new generation N/O donors, maleonitrile tethered, tetradentate heteroscorpionate modified Schiff base type ligands, 2-((E)-2-hydroxybenzylideneamino)-3-(pyridin-2-ylmethylamino)maleonitrile ...(H2LH), 2-((E)-2-hydroxy-5-nitrobenzylideneamino)-3-(pyridin-2-ylmethylamino)maleonitrile (H2LNO2), and 2-((E)-2-hydroxy-3-methoxybenzylideneamino)-3-(pyridin-2-ylmethylamino)maleonitrile (H2LOMe) were synthesized. These ligands were reacted with a stoichiometric amount of zinc acetate to afford corresponding mononuclear Zn complexes Zn(LH) (1H), Zn(LNO2) (1NO2), and Zn(LOMe) (1OMe) with excellent yields. All metal complexes and ligands were fully characterized using all possible spectroscopic tools, including single-crystal X-ray structure analysis in some cases. The 1H NMR spectral feature was well explained in terms of the electronic effect of the ligand's substitution at the phenyl ring. Novel monomeric Zn complexes supported by heteroscorpionate ligands were explored as effective catalysts to convert CO2 and CS2 to cyclic carbonates and thiocarbonates, respectively, via epoxide ring opening under mild and solvent-free conditions where tetrabutylammonium bromide (TBAB) was used as co-catalyst. The synthesized catalyst activates CO2 and CS2 at ambient conditions, whereas most of the reported catalysts require harsh conditions. Electronically, the Zn center in 1H was found to have the highest Lewis acidity, enabling better catalytic activity with respect to other Zn complexes. The probable mechanisms of catalytic activity for CO2 and CS2 activation were also explained. Mechanistically, the {Zn–Br} unit serves as a Lewis acidic platform that stabilizes the activated epoxide intermediate after ring opening by bromide ion and provides suitable nucleophiles for a further attack at the CO2/CS2 center. Exclusive cyclic carbonate/thiocarbonate formation was explained as the cyclization of activated CO2/CS2 product occurring at the Zn center before it is released as an acyclic intermediate.
Abstract
The Event Horizon Telescope has recently observed the images and shadows of the compact objects M87* and Sgr A* at the centres of the galaxies Messier 87 and Milky Way. This has opened up a ...new window in observational astronomy to probe and test gravity and fundamental physics in the strong-field regime. In this paper, we construct a rotating version of a modified Janis-Newman-Winicour metric obtained through the Simpson-Visser regularisation procedure and constrain the metric parameters using the observed shadows of M87* and Sgr A*. Depending on parameter values, the spacetime metric represents either a naked singularity or a wormhole. We find that the naked singularity case is not consistent with observations, as it casts a shadow that is much smaller than the observed ones. On the other hand, the shadow formed by the wormhole branch, depending on the parameter values, is consistent with the observations. We put constraints on the wormhole throat radius by comparing the shadow with the observed ones of M87* and Sgr A*.
Synthesizing hydrosulfido Cu thiolate complexes is quite challenging. In this report, two new and rare hydrosulfido Cu thiolate complexes, Et4N2(mnt)Cu-SH (2, mnt = maleonitrile dithiolene = ...S2C2(CN)2) and Et4N3(mnt)Cu-(μ-SH)-Cu(mnt) (3), have been synthesized. Coordination sites and O2 activation by complex 2 resemble the formylglycine generating enzyme (FGE), an enzyme recently crystallographically characterized with sulfur-only coordination around Cu (three thiolate ligands). The function of this enzyme (and complex 2) is surprising because vulnerable thiolates should not be well suited for O2 activation rationally. Indeed, activation of oxygen by such an all-sulfur-coordinated Cu complex 2 is lacking in the literature. Aerial O2 (ambient O2 from the air) activation by complex 2 could proceed through a superoxide radical intermediate and a sulfur radical intermediate detected by resonance Raman (rR) spectroscopy and electron paramagnetic resonance (EPR) spectroscopy, respectively. The chemistry of 2 has been examined by its reactivity, crystal structure, and spectroscopic and cyclic voltammetric analyses. In addition, the results have been complemented with density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations.
A set of new generation N/O donors, maleonitrile tethered, tetradentate heteroscorpionate modified Schiff base type ligands, 2-(( E ...)-2-hydroxybenzylideneamino)-3-(pyridin-2-ylmethylamino)maleonitrile (H2LH), 2-(( E )-2-hydroxy-5-nitrobenzylideneamino)-3-(pyridin-2-ylmethylamino)maleonitrile (H2LNO2), and 2-(( E )-2-hydroxy-3-methoxybenzylideneamino)-3-(pyridin-2-ylmethylamino)maleonitrile (H2LOMe) were synthesized. These ligands were reacted with a stoichiometric amount of zinc acetate to afford corresponding mononuclear Zn complexes Zn(LH) (1H), Zn(LNO2) (1NO2), and Zn(LOMe) (1OMe) with excellent yields. All metal complexes and ligands were fully characterized using all possible spectroscopic tools, including single-crystal X-ray structure analysis in some cases. The 1 H NMR spectral feature was well explained in terms of the electronic effect of the ligand's substitution at the phenyl ring. Novel monomeric Zn complexes supported by heteroscorpionate ligands were explored as effective catalysts to convert CO 2 and CS 2 to cyclic carbonates and thiocarbonates, respectively, via epoxide ring opening under mild and solvent-free conditions where tetrabutylammonium bromide (TBAB) was used as co-catalyst. The synthesized catalyst activates CO 2 and CS 2 at ambient conditions, whereas most of the reported catalysts require harsh conditions. Electronically, the Zn center in 1H was found to have the highest Lewis acidity, enabling better catalytic activity with respect to other Zn complexes. The probable mechanisms of catalytic activity for CO 2 and CS 2 activation were also explained. Mechanistically, the {Zn–Br} unit serves as a Lewis acidic platform that stabilizes the activated epoxide intermediate after ring opening by bromide ion and provides suitable nucleophiles for a further attack at the CO 2 /CS 2 center. Exclusive cyclic carbonate/thiocarbonate formation was explained as the cyclization of activated CO 2 /CS 2 product occurring at the Zn center before it is released as an acyclic intermediate.
A set of new generation N/O donors, maleonitrile tethered, tetradentate heteroscorpionate modified Schiff base type ligands, 2-((
E
...)-2-hydroxybenzylideneamino)-3-(pyridin-2-ylmethylamino)maleonitrile
(H
2
L
H
)
, 2-((
E
)-2-hydroxy-5-nitrobenzylideneamino)-3-(pyridin-2-ylmethylamino)maleonitrile
(H
2
L
NO2
)
, and 2-((
E
)-2-hydroxy-3-methoxybenzylideneamino)-3-(pyridin-2-ylmethylamino)maleonitrile
(H
2
L
OMe
)
were synthesized. These ligands were reacted with a stoichiometric amount of zinc acetate to afford corresponding mononuclear Zn complexes
Zn(L
H
)
(
1
H
),
Zn(L
NO2
)
(
1
NO2
), and
Zn(L
OMe
)
(
1
OMe
) with excellent yields. All metal complexes and ligands were fully characterized using all possible spectroscopic tools, including single-crystal X-ray structure analysis in some cases. The
1
H NMR spectral feature was well explained in terms of the electronic effect of the ligand's substitution at the phenyl ring. Novel monomeric Zn complexes supported by heteroscorpionate ligands were explored as effective catalysts to convert CO
2
and CS
2
to cyclic carbonates and thiocarbonates, respectively,
via
epoxide ring opening under mild and solvent-free conditions where tetrabutylammonium bromide (TBAB) was used as co-catalyst. The synthesized catalyst activates CO
2
and CS
2
at ambient conditions, whereas most of the reported catalysts require harsh conditions. Electronically, the Zn center in
1
H
was found to have the highest Lewis acidity, enabling better catalytic activity with respect to other Zn complexes. The probable mechanisms of catalytic activity for CO
2
and CS
2
activation were also explained. Mechanistically, the {Zn-Br} unit serves as a Lewis acidic platform that stabilizes the activated epoxide intermediate after ring opening by bromide ion and provides suitable nucleophiles for a further attack at the CO
2
/CS
2
center. Exclusive cyclic carbonate/thiocarbonate formation was explained as the cyclization of activated CO
2
/CS
2
product occurring at the Zn center before it is released as an acyclic intermediate.
Electronically varied Zn complexes as a common catalytic platform to activate CO
2
and CS
2
under mild and solvent-free conditions, which selectively yielded cyclic carbonates or cyclic thiocarbonates.
The Knoevenagel condensation between active methylene compounds and aromatic carobonyl compounds has been developed using quinine as an organocatalyst to afford various electrophilic alkenes in ...excellent yields (up to 90%). In the presence of a catalytic amount of quinine (15 mol%), the reaction proceeded at room temperature (RT) under solvent-free conditions. In this green approach, the organocatalyst was recovered and recycled for up to four cycles without appreciable loss of activity.
Two sets of maleonitrile-tethered, N-atom-donor tridentate ligands which are configurationally isomeric, 2-(( E )-(aryl-methylene)amino)-3-((pyridin-2-ylmethyl)amino)maleonitrile (HL1-Ar) and ...2-((aryl-methyl)amino)-3-(( E )-(pyridin-2-ylmethylene)amino)maleonitrile (HL2-Ar) have been synthesized and fully characterized (where the aryl groups are 4-methoxyphenyl (HL1-OMe/HL2-OMe), 4-(trifluoromethyl)phenyl (HL1-CF3/HL2-CF3) and 2,4,6-trimethylphenyl (HL1-Mes/HL2-Mes)). The competitive role of the ligand's electronic effect and the type of metal ion were explored on the reactivity of Co( ii ) and Ni( ii ) metal ions with differently electronically tuned ligands. An Ni( ii ) metal ion was found to be effective towards the irreversible transformation of HL1-Ar to HL2-Ar (for all substitutions on the aryl group) where the simultaneous oxidation of amine and reduction of imine take place within a single conjugated maleonitrile-tethered ligand. Whereas, Co( ii ) interacted differently with each member of HL1-Ar. With the presence of an electron-donating group (EDG), a methyl group (at ortho and para positions) in the phenyl ring of HL1-Mes, Co( ii ) could selectively perform the ligand transformation. On the other hand, HL1-CF3 and HL1-OMe (with the presence of less EDG in the phenyl ring in comparison to HL1-Mes) did not respond to the amine–imine interconversion process. The isolated Co( ii ) and Ni( ii ) complexes were fully characterized using crystallography, cyclic voltammetry, NMR and UV-Vis spectroscopy and the correlation of spectral data changes with the different electronic environments of the ligands was well explained. The redox instability of Co( ii ) complexes with HL2-Ar towards aerobic oxidation was studied using spectro-electrochemical analysis. Finally, a mechanism for the amine–imine interconversion process was proposed based on experimentally identified intermediates as well as DFT calculations.
The serotonin receptor subtype 5-HTR
1B
is widely distributed in the brain with an important role in various behavioral implications including neurological conditions and psychiatric disorders. The ...neuromodulatory action of 5-HTR
1B
largely depends upon its arrestin mediated signaling pathway. In this study, we tried to investigate the role of unusually long intracellular loop 3 (ICL3) region of the serotonin receptor 5-HTR
1B
in interaction with β-arrestin1 (Arr2) to compensate for the absence of the long cytoplasmic tail. Molecular modeling and docking tools were employed to obtain a suitable molecular conformation of the ICL3 region in complex with Arr2 which dictates the specific complex formation of 5-HTR
1B
with Arr2. This reveals the novel molecular mechanism of phosphorylated ICL3 mediated GPCR-arrestin interaction in the absence of the long cytoplasmic tail. The in-cell disulfide cross-linking experiments and molecular dynamics simulations of the complex further validate the model of 5-HTR
1B
-ICL3-Arr2 complex. Two serine residues (Ser281 and Ser295) within the 5-HTR
1B
-ICL3 region were found to be occupying the electropositive pocket of Arr2 in our model and might be crucial for phosphorylation and specific Arr2 binding. The alignment studies of these residues showed them to be conserved only across 5-HTR
1B
mammalian species. Thus, our studies were able to predict a molecular conformation of 5-HTR
1B
-Arr2 and identify the role of long ICL3 in the signaling process which might be crucial in designing targeted drugs (biased agonists) that promote GPCR-Arr2 signaling to deter the effects of stress and anxiety-like disorders.
