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1.
J Fluoresc ; 2021 Oct 02.
Artigo em Inglês | MEDLINE | ID: mdl-34599730

RESUMO

Tetracyanoquinodimethane (TCNQ) on reaction with primary/secondary amines sequels in mono/di-substituted TCNQ adducts known as diaminodicyanoquinodimethanes (DADQ's) possessing astounding optical or non-linear optical characteristics. Crucially, the subtle choice of amine contributes to the outcome of molecular material aspects. Herein, we present a comprehensive investigation of 7,7-bis(N,N-diethylethylenediamino)-8,8-dicyanoquinodimethane (BDEDDQ); manifesting the impact of ethyl group (existing on the di-substituted nitrogen of N,N-diethylethylenediamine (DEED)); on the crystal structure, optical property and thermal stability. Crystallography study revealed supramolecular self-assemblies among molecular dipoles emanating fluorescence enhancement in the solid state compared to solutions. Quantum yields were primarily ~0.2 to 0.4% in solutions and ~56% in the solid. Stokes shift was noticed to be more in solutions (~90 nm) than solid (~67 nm), suggesting excess vibrational relaxations in solutions. Differential scanning calorimetry revealed ~182 °C as the melting temperature. The heat capacity of solid was found to be 5.03 mJs-1. Thermogravimetric analysis conveyed single stage decomposition process initiated by the two amine side chains. Scanning electron microscopy of films prepared by drop casting solutions imparted divergent morphological features, due to different rates of evaporation accompanied by varied growth kinetics. Accordingly, in this paper we have demonstrated the utilization of simple N,N-diethylethylenediamine (DEED) to successfully generate a noteworthy blue emissive molecular material exhibiting semiconducting feature besides reasonable thermal stability.

2.
J Biomol Struct Dyn ; : 1-15, 2021 Sep 27.
Artigo em Inglês | MEDLINE | ID: mdl-34569409

RESUMO

Pomegranate peel, the waste product generated from pomegranate fruit, has prophylactic properties, such as antimicrobial, anti-malarial, and controls respiratory infections and influenza. Based on the previous literature and need of the hour, molecular docking was performed to evaluate the inhibitory effects of major pomegranate peel polyphenols against COVID-19. Among the 44 studied compounds, 37 polyphenols show interaction with the catalytic dyad of the Mpro protease and 18 polyphenols have a higher binding affinity than that of the Mpro protease inhibitor (N3), indicating their high probability of binding at ACE2: SARS-CoV-2 interface. Furthermore, several polyphenols studied in this work are found to have higher binding affinity as compared to those of hydroxychloroquine, lopinavir, nelfinavir, and curcumin, some of which have been earlier tested against COVID-19. Further, molecular dynamics simulations (200 ns) for Mpro-polyphenols including pelargonidin3-glucoside, quercetin3-O-rhamnoside, cyanidin3-glucoside and punicalin revealed highly stable complexes with less conformational fluctuations and similar degree of compactness. Estimation of total number of intermolecular hydrogen bonds and binding free energy confirmed the stability of these Mpro-polyphenol complexes over Mpro-curcumin complex. Based on the greater binding affinity of polyphenols of pomegranate peel towards Mpro as compared to that of curcumin, pomegranate peel may be considered in any herbal medicinal formulation or may be incorporated into daily diets for prevention of COVID-19.Communicated by Ramaswamy H. Sarma.

3.
J Biol Inorg Chem ; 26(5): 569-582, 2021 08.
Artigo em Inglês | MEDLINE | ID: mdl-34241683

RESUMO

Metalloenzymes are ubiquitous in nature catalyzing a number of crucial biochemical processes in animal and plant kingdoms. For better adaptation to the relative abundance of different metal ions in different cellular fluids, many of these enzymes exhibit metal promiscuity. The microbial enzyme DapE, an essential enzyme for bacterial growth and survival and a potentially safe target for antibiotics, continues to show enzyme activity when the two zinc ions in its active site are replaced by other transition metal ions. The effect of metal-ion substitution at the second metal-binding site of DapE on its substrate affinity and catalytic efficiency is investigated by QM/MM treatment of the enzyme-substrate complex, by modelling the enzyme with Mn(II), Co(II), Ni(II), or Cu(II) ion in place of Zn(II) at its second metal-binding site, while retaining Zn(II) ion at the first metal-binding site. On the basis of substrate binding energy and activation energy barrier for the chemical catalysis, it is found that Zn-Mn DapE shows poor binding affinity as well as inefficient chemical catalysis. Although Zn-Cu and Zn-Ni DapEs show activation energy barriers comparable to that of wild-type Zn-Zn DapE, their weaker substrate affinity renders these mixed-metal enzymes less efficient. On the other hand, Zn-Co DapE is found to outperform the naturally occurring Zn-Zn DapE, both in terms of substrate affinity and chemical catalysis. The observed metal promiscuity may have played an important role in the survival of bacteria even in those cellular media where Zn ions are in limited supply. Metal nonspecificity in the catalysis of DapE enzyme allows bacteria to thrive in different cellular media.


Assuntos
Amidoidrolases/metabolismo , Metais Pesados/metabolismo , Amidoidrolases/química , Sítios de Ligação , Teoria da Densidade Funcional , Metais Pesados/química , Modelos Moleculares , Conformação Molecular
4.
Dalton Trans ; 50(23): 8036-8044, 2021 Jun 15.
Artigo em Inglês | MEDLINE | ID: mdl-34013307

RESUMO

The reaction between 2,5-bis(diphenylphosphinomethyl)pyrrole and Me3SiN3 gave the new pyrrole-based bis(phosphinimine) L1H in an excellent yield. L1H reacts with [CuCl(COD)]2, AgBF4, or AgOTf to give the corresponding two-coordinate mononuclear ionic complex formulated as [M{(L1H)-κ2N,N}]+[X]- where M = Cu and Ag; X = [CuCl2], BF4 or OTf. Their single crystal X-ray diffraction studies confirmed the two-coordinate geometry formed by the chelate bonding mode of L1H. These 10-membered metalacycles exhibit planar chirality and were also characterized by spectroscopic methods. In addition, in all three structures, there exists a hitherto unknown π-interaction between the pyrrole ring atoms and metal, represented as η2-(Cα-N) in the copper(i) complex, and η3-(Cα-N-Cα') in the silver(i) complexes. These weak interactions were supported by DFT calculations in terms of their electron densities, non-covalent interaction plots and the decrease in the aromaticity of the pyrrole ring.

5.
ACS Omega ; 6(4): 3090-3105, 2021 Feb 02.
Artigo em Inglês | MEDLINE | ID: mdl-33553926

RESUMO

Tetracyanoquinodimethane (TCNQ) is known to react with various amines to generate substituted TCNQ derivatives with remarkable optical and nonlinear optical characteristics. The choice of amine plays a crucial role in the outcome of molecular material attributes. Especially, mono/di-substituted TCNQ's possessing strong fluorescence in solutions than solids are deficient. Furthermore, cation recognition in the solid-state TCNQ derivatives is yet undetermined. In this article, we present solution-enhanced fluorescence and exclusive solid-state recognition of K+ ion achieved through the selection of 4-(4-aminophenyl)morpholin-3-one (APM) having considerable π-conjugation and carbonyl (C=O) functionality, particularly in the ring. TCNQ when reacted with APM, in a single-step reaction, resulted in two well-defined distinct compounds, namely, 7,7-bis(4-(4-aminophenyl)morpholin-3-ono)dicyanoquinodimethane (BAPMDQ [1], yellow) and 7,7,8-(4-(4-aminophenyl)morpholin-3-ono)tricyanoquinodimethane (APMTQ [2], red), with increased fluorescence intensity in solutions than their solids. Crystal structure investigation revealed extensive C-H-π interactions and strong H-bonding in [1], whereas moderate to weak interactions in [2]. Surprisingly, simple mechanical grinding during KBr pellet preparation with [1, 2] triggered unidentified cation recognition with a profound color change (in ∼1 min) detected by the naked eye, accompanied by a drastic enhancement of fluorescence, proposed due to the presence of carbonyl functionality, noncovalent intermolecular interactions, and molecular assemblies in [1, 2] solids. Cation recognition was also noted with various other salts as well (KCl, KI, KSCN, NH4Cl, NH4Br, etc.). Currently, the recognition mechanism of K+ ion in [1, 2] is demonstrated by the strong electrostatic interaction of K+ ion with CO and simultaneously cation-π interaction of K+ with the phenyl ring of APM, supported by experimental and computational studies. Computational analysis also revealed that a strong cation-π interaction occurred between the K+ ion and the phenyl ring (APM) in [2] than in [1] (ΔG binding calculated as ∼16.3 and ∼25.2 kcal mol-1 for [1] and [2], respectively) providing additional binding free energy. Thus, both electrostatic and cation-π interactions lead to the recognition. Scanning electron microscopy of drop-cast films showed microcrystalline "roses" in [1] and micro/nano "aggregates" in [2]. Optical band gap (∼3.565 eV) indicated [1, 2] as wide-band-gap materials. The current study demonstrates fascinating novel products obtained by single-pot reaction, resulting in contrasting optical properties in solutions and experiencing cation recognition capability exclusively in the solid state.

6.
J Phys Chem Lett ; 11(20): 8585-8591, 2020 Oct 15.
Artigo em Inglês | MEDLINE | ID: mdl-32931285

RESUMO

Amyloid polymorphism has emerged as an important topic of research in recent years to identify the particular species responsible for several neurodegenerative disorders, whereas the concept is overlooked in the case of the simplest building block, that is, l-phenylalanine (l-Phe) self-assembly. Here, we report the first evidence of l-Phe polymorphism and the conversion of metastable helical fibrillar to thermodynamically stable rodlike crystalline morphologies with increasing time and temperature. Furthermore, only the fibrillar l-Phe polymorph shows a significant modulation of the model membrane. In addition, the l-Phe molecules prefer to arrange in a multilayered rodlike fashion than in a lateral arrangement, which reduces the membrane binding ability of the l-Phe polymorph due to the decrease in the partial charge of the N-terminal of l-Phe units. The present work exemplifies a different approach to understanding l-Phe self-assembly and provides an effective strategy for the therapy of phenylketonuria by scrutinizing the discrete membrane activity of different l-Phe polymorphs.


Assuntos
Amiloide/química , Fenilalanina/química , Fenilcetonúrias/metabolismo , Fatores Etários , Cristalização , Humanos , Ligação de Hidrogênio , Imagem Óptica , Ligação Proteica , Conformação Proteica , Dobramento de Proteína , Multimerização Proteica , Temperatura , Termodinâmica
7.
Chem Asian J ; 15(20): 3304-3313, 2020 Oct 16.
Artigo em Inglês | MEDLINE | ID: mdl-32790947

RESUMO

A series of organometallic complexes [Cl(dppe)2 Ru-C≡C-(3-R-C4 H2 S)-C≡C-Ru(dppe)2 Cl] (3-R-C4 H2 S=3-substituted thienyl moiety; R=-H, -C2 H5 , -C3 H7 , -C4 H9 , -C6 H13 , -OMe, -CN in 5 a-5 g respectively) have been synthesized by systematic variation of 3-substituents at the thienylethynyl bridging unit. The diruthenum(II) wire-like complexes (5 a-5 g) have been achieved by the reaction of thienylethynyl bridging units, HC≡C-(3-R-C4 H2 S)-C≡CH (4 a-4 g) with cis-[Ru(dppe)2 Cl2 ]. The wire-like diruthenium(II) complexes undergo two consecutive electrochemical oxidation processes in the potential range of 0.0 - 0.8 V. Interestingly, the wave separation between the two redox waves is greatly influenced by the substituents at the 3-position of the thienylethynyl. Thus, the substitution on 3-position of the thienylethynyl bridging unit plays a pivotal role for tuning the electronic properties. To understand the electronic behavior, density functional theory (DFT) calculations of the selected diruthenium wire-like complexes (5 a-5 e) with different alkyl appendages are performed. The theoretical data demonstrate that incorporation of alkyl groups to the thienylethynyl entity leaves unsymmetrical spin densities, thus affecting the electronic properties. The voltammetric features of the other two Ru(II) alkynyl complexes 5 f and 5 g (with -OMe and -CN group respectively) show an apparent dependence on the electronic properties. The electronic properties in the redox conjugate, (5 a+ ) with Kc of 3.9×106 are further examined by UV-Vis-NIR and FTIR studies, showing optical responses in NIR region along with changes in "-Ru-C≡C-" vibrational stretching frequency. The origin of the observed electronic transition has been assigned based on time-dependent DFT (TDDFT) calculations.

8.
Phys Chem Chem Phys ; 22(28): 16013-16022, 2020 Jul 22.
Artigo em Inglês | MEDLINE | ID: mdl-32632422

RESUMO

Lipoxygenases are non-heme iron containing enzymes that catalyze oxygenation of poly-unsaturated fatty acids in different animal and plant species with extremely high regio- and stereospecificity. Nature employs 8-lipoxygenase to produce 8R-hydroperoxide from the oxygenation of arachidonic acid. A single-point L434F mutation of 8-lipoxygenase alters the regio- and stereospecificity of the final products, with a product ratio of 66 : 34 for 8R- and 12S-hydroperoxide, respectively. A molecular level explanation of this flipped regiospecificity is presented in this work on the basis of molecular dynamics simulations and transition network analysis of oxygen migration in the protein matrix. Phe434 is shown to exist in two conformations, the so-called open and closed conformations. In the closed conformation, the phenyl group of Phe434 shields the C8 site of the substrate, thereby preventing access of the oxygen molecule to this site, which leads to a quenching of the 8R-product. On the other hand, both closed and open conformations of Phe434 allow the oxygen molecule to approach the pro-S face of the C12 site of the substrate, which enhances the propensity of the 12S-hydroperoxide.


Assuntos
Araquidonato Lipoxigenases/genética , Animais , Araquidonato Lipoxigenases/química , Araquidonato Lipoxigenases/metabolismo , Cristalografia por Raios X , Simulação de Dinâmica Molecular , Mutação , Conformação Proteica
9.
Phys Chem Chem Phys ; 22(2): 628-641, 2020 Jan 02.
Artigo em Inglês | MEDLINE | ID: mdl-31822879

RESUMO

The valence shell photoelectron spectrum of OsO4 has been calculated from the wave functions of the ejected photoelectrons responsible for the formation of the lowest five cationic states, whose vertical ionization energies have been estimated using the equation of motion coupled cluster with singles and doubles (EOM-CCSD) and multi-configurational self consistent field (MCSCF) based methods. These non-relativistic states when coupled via the spin-orbit operator result in the spin-orbit states, which are compared with the results from synchrotron measurements. The lowest three cationic states could be described by both the EOM-CCSD and MCSCF based methods, whereas the multi-reference character of the closely spaced fourth and fifth cationic states was suitably described by the latter method. The photoelectron spectral intensities of different ionization channels, calculated using the Dyson orbital formalism within the sudden approximation, reproduced the experimental spectrum by capturing all of its essential features, including the detailed vibronic structure of the first band, which shows the presence of fundamental, overtone and combination bands of a1 and e modes. The kinetic energy dependence of the photoionization parameters, such as the photoionization cross section and asymmetry parameters, has been calculated for each of the photoionization channels and the complex interplay of multiple partial waves that define the wave function of the ejected electron at different photon energies has been analyzed to explain the resonance structures observed in the experimental cross section profiles.

10.
J Phys Chem B ; 123(50): 10605-10621, 2019 12 19.
Artigo em Inglês | MEDLINE | ID: mdl-31775504

RESUMO

Lipoxygenases (lox's) are a group of non-heme iron containing enzymes that catalyze oxygenation of polyunsaturated fatty acids with precise regio- and stereoselectivities. The origin of regio- and stereospecific catalysis by 8-lox is explored in its wild-type (wt) form and in three mutants (Arg185Ala, Ala592Met, and Ala623His). The catalytic action of this enzyme progresses in two steps, namely, hydrogen abstraction from one double allylic carbon atom of substrate followed by oxygen insertion at the resulting prochiral carbon radical of the substrate. It is shown that the positional specificity of the hydrogen abstraction is a result of conformational dynamics of the bound substrate. While the C10 atom of the substrate is found to be the most probable site of hydrogen abstraction in the wt-lox, hydrogen abstraction from C13 is more favorable in the mutants. The present study discovers the presence of an interconnected network of a three-channel migration pathway operating in the protein matrix for efficient oxygen transport. Each migration channel is bestowed with a pocket at the peripheral region of protein as an oxygen access site, which transfers the oxygen to the active site through a well-connected migration path on a time scale of a few hundred picoseconds. By a careful geometric analysis of the oxygen pockets near the substrate binding cleft, the present study identifies the launching sites for oxygenation at the prochiral carbon centers C8, C11, C12, and C15 and the stereochemistry (R/S) of the corresponding products. It is found that the dominating 8R product in the wt-lox is due to the presence of the aromatic ring pair of Tyr181 and Phe173 acting as a gatekeeper for efficient delivery of oxygen at the pro-R face of C8. The change in the stereochemistry of the products in mutants is explained in terms of dynamic interactions between substrate and the surrounding residues.


Assuntos
Araquidonato Lipoxigenases/metabolismo , Biocatálise , Simulação de Dinâmica Molecular , Araquidonato Lipoxigenases/química , Araquidonato Lipoxigenases/genética , Mutação , Conformação Proteica , Estereoisomerismo , Especificidade por Substrato
11.
J Phys Chem A ; 123(46): 9883-9892, 2019 Nov 21.
Artigo em Inglês | MEDLINE | ID: mdl-31663743

RESUMO

(PMe3)2FeCl3 is an Fe(III) complex that exists in the intermediate-spin ground state in a distorted trigonal bipyramidal geometry. An electronic state with high-spin configuration lies in close vicinity to the ground state, making it a potential spin crossover candidate. A mechanistic account of the spin crossover from the lowest quartet state (Q0) to the lowest sextet state (S1) of this complex is provided by exploring both thermal and light-induced pathways. The presence of a large barrier between the two spin states suggests a possible thermal spin crossover at a rather high temperature. The light-induced spin crossover is investigated by employing complete active space self-consistent field calculations together with dynamic correlation and spin-orbit coupling for the lowest seven quartet and lowest five sextet states. The system in the Q0 state upon light absorption is excited to the optically bright Q4 LMCT state. By following minimum energy pathways along the electronic states, two light-induced pathways for spin crossover are identified. From the Q4 state, the system can photo-regenerate the ground intermediate-spin state (Q0) through an internal conversion of Q4/Q3 followed by Q3/S1 and S1/Q0 intersystem crossings. In an alternate route, through Q4/S2 intersystem crossing followed by S2/S1 internal conversion, the system can complete the spin crossover from the Q0 to S1 state.

12.
J Chem Phys ; 151(13): 134103, 2019 Oct 07.
Artigo em Inglês | MEDLINE | ID: mdl-31594344

RESUMO

The Renner vibronic-coupling problem in 4Π electronic states of linear molecules is analyzed with rigorous and systematic inclusion of spin-orbit (SO) coupling. The 8 × 8 Hamiltonian matrix of a 4Π state in the diabatic electronic representation has been constructed by a Taylor expansion in the bending normal mode up to second order. As previously found for 2Π states and 3Π states, SO-induced vibronic-coupling terms that are linear in the bending amplitude exist in addition to the quadratic electrostatic Renner coupling. The effects of the linear and quadratic Renner coupling on the four Kramers-degenerate potential energy surfaces of the 4Π state are discussed. The spectroscopic effects of the linear SO-vibronic-coupling mechanism have been analyzed by numerical calculations of vibronic spectra.

13.
Mol Neurobiol ; 56(9): 6551-6565, 2019 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-30868446

RESUMO

The amyloid cascade hypothesis dealing with the senile plaques is until date thought to be one of the causative pathways leading to the pathophysiology of Alzheimer's disease (AD). Though many aggregation inhibitors of misfolded amyloid beta (Aß42) peptide have failed in clinical trials, there are some positive aspects of the designed therapeutic peptides for diseases involving proteinaceous aggregation. Here, we evaluated a smart design of side chain tripeptide (Leu-Val-Phe)-based polymeric inhibitor addressing the fundamental hydrophobic amino acid stretch "Lys-Leu-Val-Phe-Phe-Ala" (KLVFFA) of the Aß42 peptide. The in vitro analyses performed through the thioflavin T (ThT) fluorescence assay, infrared spectroscopy, isothermal calorimetry, cytotoxicity experiments, and so on evinced a promising path towards the development of new age AD therapeutics targeting the inhibition of misfolded Aß42 peptide fibrillization. The in silico simulations done contoured the mechanism of drug action of the present block copolymer as the competitive inhibition of aggregate-prone hydrophobic stretch of Aß42. Graphical abstract The production of misfolded Aß42 peptide from amyloid precursor protein initiates amyloidosis pathway which ends with the deposition of fibrils via the oligomerization and aggregation of Aß42 monomers. The side chain tripeptide-based PEGylated polymer targets these Aß42 monomers and oligomers inhibiting their aggregation. This block copolymer also binds and helps degrading the preformed fibrils of Aß42.


Assuntos
Doença de Alzheimer/tratamento farmacológico , Polietilenoglicóis/química , Peptídeos beta-Amiloides/química , Peptídeos beta-Amiloides/metabolismo , Peptídeos beta-Amiloides/ultraestrutura , Morte Celular , Linhagem Celular Tumoral , Sobrevivência Celular , Humanos , Ligantes , Simulação de Dinâmica Molecular , Polietilenoglicóis/síntese química , Eletricidade Estática
14.
Org Lett ; 21(6): 1578-1582, 2019 03 15.
Artigo em Inglês | MEDLINE | ID: mdl-30816718

RESUMO

2,4-Dienones undergo visible-light-promoted, photocatalyst-free dimerization in neat conditions to provide cyclohexene derivatives stereoselectively through cascade rearrangement pathways, whereas regioselective E → Z isomerization of the more dienophilic double bond takes place exclusively in nitromethane. On the basis of intermediate isolation and computational DFT studies, the dimerization reaction is proposed to proceed via s-trans to s-cis isomerization/regioselective E → Z isomerization/Diels-Alder cycloaddition.

15.
Inorg Chem ; 58(2): 1155-1166, 2019 Jan 22.
Artigo em Inglês | MEDLINE | ID: mdl-30614701

RESUMO

A series of heterobimetallic wire-like organometallic complexes [( tpy-C6H4-R)(PPh3)2Ru-C≡C-Fc]+ ( tpy-C6H4-R = 4'-(aryl)-2,2':6',2''-terpyridyl, Fc = [(η5-Cp)2Fe], R = -H, -Me, -F, -NMe2 in complexes 5-8, respectively) featuring ferrocenyl and 4'-(aryl)-2,2':6',2''-terpyridyl ruthenium(II) complexes as redox active metal termini, have been synthesized. Various spectroscopic tools, such as multinuclear NMR, IR spectra, HRMS, CHN analyses, and single crystal X-ray crystallography have been utilized to characterize the heterobimetallic complexes. The electrochemical and UV-vis-NIR spectroscopic studies have been investigated to evaluate the electronic delocalization across the molecular backbones of the Ru(II)-Fe(II) heterobinuclear organometallic dyads. Electrochemical studies reveal two well-separated reversible redox waves as a result of successive oxidation of the ferrocenyl and Ru(II) redox centers. The spin density distribution analyses reveal that the initial oxidation process is associated with the Fe(II)/Fe(III) couple followed by one electron oxidation of the ruthenium(II) center. The high Kc value (0.11-1.73 × 1012) and intense NIR absorption, with molar absorption coefficient (in the order of 103 M-1 cm-1) for the RuIIFeIII mixed-valence species, signify strong electronic communication between the two metal termini. The electronic coupling constant ( Hab) has been estimated to be 492 and 444 cm-1 for the structurally characterized complexes 6 and 7, respectively. The redox and NIR absorption features indicate that the mixed-valence system of the heterobinuclear dyads belongs to a Robin and Day "class II" system.

16.
J Chem Phys ; 149(20): 204308, 2018 Nov 28.
Artigo em Inglês | MEDLINE | ID: mdl-30501231

RESUMO

The valence shell photoelectron spectrum of ICN has been simulated using the equation-of-motion coupled-cluster method to calculate the ionization energies and the norms of the Dyson orbitals to describe the intensity of the photoelectron bands. The simulated spectrum not only reproduces the position and intensity of the four main bands observed in the experimental photoelectron spectrum, but the vibronic structure present in the individual photoelectron bands is also reproduced to a reasonable extent. The agreement between the experimental and simulated vibronic structures at higher energies corresponding to the à and B ̃ states is particularly noteworthy. Additionally, the photoionization cross section and asymmetry parameter have been calculated for the ionization of four outermost valence molecular orbitals in the photon energy range of 0-50 eV. The computed asymmetry parameters are found to provide a qualitative description of the corresponding experimental measurements. The shape-resonance seen in the experimental asymmetry parameters and the trends seen in the calculated cross section for the four ionization channels have been explained by the partial wave analysis of the contribution of the individual angular momentum channels to the photoelectron.

17.
J Chem Phys ; 149(23): 234302, 2018 Dec 21.
Artigo em Inglês | MEDLINE | ID: mdl-30579306

RESUMO

Mononuclear Fe(iii) complexes commonly exist in high-spin or low-spin states, whereas their occurrence in the intermediate-spin state (S = 3/2) is scarce. The magnetic anisotropy in two trigonal-bipyramidal mononuclear Fe(iii) complexes, ( P M e 3 ) 2 F e C l 3 (1) and ( P M e 2 P h ) 2 F e C l 3 (2), in their intermediate-spin ground state has been examined by ab initio electronic structure calculations. The calculations successfully reproduce the experimental magnetic anisotropic barrier, U eff in 1 (81 cm-1) and 2 (42 cm-1), which is shown to arise due to thermally assisted quantum tunneling of magnetization from the second Kramer's doublets. The magnetic anisotropy in both the complexes is found to be significantly influenced by the axial ligands, while the equatorial ligands have negligible contribution. The large reduction in U eff of 2 has been shown to arise due to the phenyl groups, which results in the lifting of orbital degeneracy of e″ and e' frontier orbitals and leads to a net quenching of the orbital angular momentum of the metal center causing a diminished spin-orbit splitting in 2. While the crystal structure of 2 shows two phenyl rings out of plane to each other, the present study discovered another stable conformation of 2, where the two phenyl rings are in the same plane (2a). Unlike 2, the planarity of the two phenyl rings in 2a restores the degeneracy of the frontier orbitals, thereby increasing the spin-orbit splitting and a consequent rise in U eff from 42 to 80 cm-1 in 2a.

18.
Dalton Trans ; 47(40): 14304-14317, 2018 Oct 16.
Artigo em Inglês | MEDLINE | ID: mdl-29967914

RESUMO

Organometallic molecular wires with π-conjugation along their molecular backbones are of considerable interest for application in molecular-scale electronics. In this regard, thienylethynyl-based π-conjugated oligomers of three, five and seven thienylethynyl units with -C[triple bond, length as m-dash]C-H termini have been successfully synthesized through stepwise Pd(0)/Cu(i)-catalyzed Sonogashira coupling. The corresponding highly soluble diruthenium(ii) diacetylide complexes (O1-Ru2, O3-Ru2, O5-Ru2 and O7-Ru2, respectively) have been prepared by the reaction of cis-Ru(dppe)2Cl2 and NaPF6 in DCM with the corresponding rigid rod-like thienylethynyl oligomers with one, three, five and seven thienylethynyl π-conjugated segments containing alkynyl termini (O1, O3, O5 and O7). These Ru(ii)-Cl capped diacetylide complexes have been further functionalized by incorporating a phenylacetynyl moiety to afford [Ru(ii)-C[triple bond, length as m-dash]C-Ph]-capped diacetylide organometallic wires (O1-Ru2-Ph, O3-Ru2-Ph, O5-Ru2-Ph and O7-Ru2-Ph). The photophysical properties of the highly soluble thienylethynyl-based oligomers and Ru(ii)-organometallic wires have been explored to understand their electronic properties. Electrochemical studies of the binuclear ruthenium(ii)-alkynyl complexes showed highly interesting results, revealing long-range electrochemical communication between the two remote Ru(ii) termini connected even with five and seven thienylethynyl units. DFT computational studies further support the long range electrochemical communication between the redox active metal termini through heavy participation of the thienylethynyl bridge in the corresponding mono-oxidized mixed valence species of the organometallic wire-like complexes.

19.
Dalton Trans ; 47(29): 9877-9888, 2018 Jul 24.
Artigo em Inglês | MEDLINE | ID: mdl-29998273

RESUMO

A series of arylene-vinylene π-conjugated terpyridyl ruthenium(ii) complexes, [Ru(PPh3)2Cl(tpy-C6H4-CH[double bond, length as m-dash]CH-Ar)][PF6] (1-4; tpy = 2,2':6',2''-terpyridyl, where Ar = phenyl, tolyl, 1-naphthyl and 9-anthracenyl as substituents at the 4' position of tpy), have been synthesized and characterized by multinuclear NMR, IR, HRMS and single crystal X-ray crystallography. The influence of the electronic nature of arylene groups on their photophysical and electrochemical properties has been investigated to understand the electronic interaction between the metal-organic redox centers. Furthermore, a σ-donor phenylacetylide group has been incorporated to accomplish [Ph-C[triple bond, length as m-dash]C-Ru(PPh3)2(tpy-C6H4-CH[double bond, length as m-dash]CH-Ar)][PF6] (5-8) complexes by the substitution of a coordinated chloride ligand and to investigate the change in their redox and photophysical properties. DFT studies have been performed to gain an insight into their electronic properties by determining the HOMO-LUMO energy levels and frontier molecular orbitals of all the synthesized Ru(ii) complexes.

20.
J Mol Graph Model ; 84: 82-89, 2018 09.
Artigo em Inglês | MEDLINE | ID: mdl-29936366

RESUMO

The perils of antimicrobial drug resistance can be overcome by finding novel antibiotic targets and corresponding small molecule inhibitors. Microbial enzyme DapE is a promising antibiotic target due to its importance to the bacterial survival. The potency of L-Captopril, a well known angiotensin-converting enzyme inhibitor, as an inhibitor of DapE enzyme has been evaluated by analyzing its binding modes and binding affinity towards DapE enzyme. L-Captopril is found to bind the metal centers of DapE enzyme either via its thiolate group or through its carboxylate group. While the latter binding mode is found to be thermodynamically favorable, the former binding mode, also seen in the crystal structure, is kinetically favored. To optimize the binding affinity of the inhibitor towards DapE enzyme, a series of L-Captopril-based inhibitors have been modelled by changing the side groups of L-Captopril. The introduction of a bipolar functional group at the C4 position of the pyrrolidine ring of L-Captopril and the substitution of the thiol group with a carboxylate group, have been shown to provide excellent enzyme affinity that supersedes the binding affinity of DapE enzyme towards its natural substrate, thus making this molecule a potential inhibitor with great promise.


Assuntos
Amidoidrolases/química , Captopril/análogos & derivados , Captopril/química , Inibidores Enzimáticos/química , Amidoidrolases/metabolismo , Captopril/farmacologia , Avaliação Pré-Clínica de Medicamentos , Reposicionamento de Medicamentos , Inibidores Enzimáticos/farmacologia , Modelos Moleculares , Conformação Molecular , Ligação Proteica , Relação Quantitativa Estrutura-Atividade
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