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Aryldiazonium cation undergoes C–C coupling reactions through instant formation of PdIV aryldiazenido complex with the precursor [(Tp*)PdIIMe2]- complex (Tp* = tris(3,5-dimethyl-1-pyrazolyl)borate). This PdIV arylazenido complex is the first high-valent PdIV complex in C–C coupling reactions which can decompose further into aryldiazonium cation and PdII complex and follow a series of reactions via a two-electron or ionic path. Alternatively, it can decompose into aryl radical (AniR) and follow one-electron or radical path forming the C–C coupled product. The possibility of these two mechanisms were proposed by Fekl and co-workers [Dalton Trans. 2017, 46, 4004–4008] and in this work, DFT calculations have been performed to clarify the mechanism as well as to probe the competitive role of aryldiazonium cation and aryl radical (AniR) in this reaction. In the two-electron pathway the process follows sequentially oxidative addition, transmetallation, oxidative addition and dinitrogen extrusion, and reductive elimination to form the C–C coupled product 4,4′-dimethoxybiphenyl (P1) and 4-methoxy toluene (P3). In the one-electron or radical pathway, 4-methoxyphenyl radicals are formed directly and they recombine to give P1. There are other products including [(Tp*)PdIVMe3] (P2) and ethane (P4) formed in the reaction. QTAIM calculations reveal that methyl group migrates as a cation in the transmetallation step of the two-electron path. N2 extrusion passes through a six membered cyclic transition state involving orbital and CH--.π interactions, and reductive elimination passes through a three-membered cyclic transition state. NBO calculations explain the nature of metal-ligand bonding of the species involved in the reaction path. A close inspection of the activation barriers shows the one-electron pathway seems to be favoured over two-electron path because it is low lying and everything becomes irreversible once aryl radical is formed, which quickly undergoes completely irreversible coupling, whereas the first several steps of the two-electron pathway are all reversible. This is in agreement with the experiment and calculations further clarify that the proposed PdIV diaryldiazenido complex is not feasible. Computations thus reveal that aryldiazonium cation starts the reaction by forming [(Tp*)PdIVMe2(pmbd)](RC) complex and this complex reacts favourably through aryl radical to form the products. Aryldiazonium cation readily reacts with the precursor PdII complex to give PdIV aryldiazenido complex and this complex undergoes C–C coupling reaction via radical pathway through aryl radical and forms 4, 4′-dimethoxybiphenyl as a major product, and ethane and 4-methoxytoluene as minor products following PdII/PdIV catalytic cycle. [ABSTRACT FROM AUTHOR]

Nickel-based catalysts are employed in organometallic transformations such as C–C/C–heteroatom cross-coupling reactions. The work presented here describes the reactivity of high valent nickel complexes using DFT computations performed at the B3LYP/BS1 level. The calculated bond parameters shed light on how the ligand flexibility changes the reactivity of the nickel centre in various oxidation states of nickel. The reactivity of NiIII-center (2+) and NiIV-center (32+) complexes reveals that direct reductive elimination leading to the C–C coupled product of 1,1-dimethylbenzocyclobutene (P1) is more feasible than the path via five-coordinate intermediates (2+-Int1 and 32+-Int1) as the latter path involves ligand-conformation-change transition states that demand high energy. However, the five-coordinate 32+-Int1 intermediate reacts with MeCN in the sixth position of NiIV-center to generate the 32+-Int2 intermediate that readily undergoes barrierless reductive elimination leading to the product (P1) and this also explains the high yield under blue LED illumination that is observed experimentally. Solvent participation and ligand flexibility are essential for reductive elimination pathways. The Kohn–Sham energy levels of d-orbitals are progressively stabilized when going from the NiII to NiIII to NiIV oxidation states. The HOMO–LUMO gaps (ΔEH–L) show that the overall reactivity decreases in the order 32+ > 2+ > 1. Finally, the reaction of the NiIV-center 32+ complex in the presence of the Cl− nucleophile is investigated. This shows that the reductive elimination of C–C/C–heteroatom coupling can occur through three pathways with almost similar activation barriers (∼18.0 kcal mol−1). This agrees well with the experimental observation that the three products are formed in the reaction almost in the same percentages. QTAIM pictures reveal that the transition-state structures of 32+-TS6, 32+-TS7 and 32+-TS8 relating to reductive elimination from the NiIV-center complex involves a three-membered cyclic transition state. [ABSTRACT FROM AUTHOR]

In the recent times metal complexes with dual mechanisms of action, anti-cancer and anti-angiogenic, have gained substantial interest in the field of medicinal chemistry. In the present work, cobalt(iii) complexes containing tetradentate Schiff bases [Co(acacen)(HA)2](ClO4) [1], [Co(acacen)(DA)2](ClO4) [2], [Co(Ph-acacen)(HA)2](ClO4) [3] and [Co(Ph-acacen)(DA)2](ClO4) [4] (where acacen: N,N′-bis(acetylacetone)ethylenediamine and Ph-acacen: N,N′-bis(1-phenylbutane-1,3-dione)ethylenediamine, HA: heptylamine and DA: dodecylamine) were synthesised and characterized by elemental analysis, ESI-MS, NMR and IR spectroscopy. The interaction between these cobalt complexes and CT-DNA was investigated by various spectroscopic measurements. The results suggest that complexes containing “Ph-acacen” Schiff base show strong binding affinity for DNA compared to the corresponding “acacen” Schiff base-containing complexes. Further, the binding of all the complexes to BSA is strong, as evaluated by UV-visible, fluorescence and circular dichroism spectroscopy. Molecular docking analysis has been performed to obtain more insights into the interaction between bio-molecules (DNA and BSA) and the cobalt complexes. The theoretical results agreed well with the experimental results. The cytotoxic potential of all the cobalt complexes was screened by an in vitro method against A549 and VERO cells. The IC50 values indicate that all the cobalt complexes are as active as cisplatin, the standard drug, against A549 cells but the VERO cells were unaffected even at the highest dose. Various staining techniques such as acridine orange (AO)/ethidium bromide (EB), HOECHST 33248, and Annexin V/6-CFDA and cell cycle analysis of A549 cells revealed that the mode of cell death is apoptosis. All the cobalt complexes showed an inhibitory effect on angiogenesis as revealed by in vivo chicken chorio-allantoic membrane assay. [ABSTRACT FROM AUTHOR]

In this study, a 1,8-dimethyl-1,3,6,8,10,13-hexaazacyclotetradecane nickel(ii) complex was encapsulated in the supercages of zeolite Y for the photocatalytic removal of methylene blue under visible light. The nickel(ii) macrocyclic complex catalysts are known for their photooxidation property. Heterogenization of the homogenous catalyst is essential for their outstanding activity and reusability. The flexible ligand method was adopted for the encapsulation of the complex into the zeolite Y. The neat complex and encapsulated complex were characterized by DRS UV-vis, FTIR, powder XRD, cyclic voltammetry, BET and FESEM. The energy levels and transition probability of the encapsulated metal complex were varied due to the constrained environment of the zeolite. Density Functional Theory (DFT) calculations were performed to correlate with the experimental results for both the neat and encapsulated complexes. The DFT results reveal that the changes in the structural parameters and HOMO–LUMO energies offer useful insights into the nature of the host–guest complex and its reactivity. Besides this, the zeolite encapsulated complex shows photocatalytic activity towards the degradation of methylene blue under visible light irradiation with reusability. The mechanistic details on the photocatalytic activity were also proposed. [ABSTRACT FROM AUTHOR]

The influence of phenols upon the fluorescence quenching of 9-aminoacridine (9-AA) was examined in acetonitrile solution by employing steady state and time-resolved fluorescence measurements. On increasing the concentration of quencher molecules the absorption spectra of 9-AA change with significant bathochromic shift. The fluorescence intensity of 9-AA change in presence of quencher molecules were measured at various temperatures as a function of the quencher concentrations. The observed bimolecular quenching rate constant (kq) depends on the nature and electronic effect of substituent present in the quencher molecules. The bimolecular quenching rate constant (kq) decreases on increasing the oxidation potential of quencher molecules. To examine the quenching behavior, kq values were correlated with the free energy change (ΔG). To get forthcoming in the quenching process, fluorescence quenching experiments were carried out in different solvents of varying polarities. The observed result suggest the involvement of charge-transfer quenching mechanism. Lifetime measurements support static quenching. Further, the radical scavenging potential is calculated from density functional theory (DFT) calculations to address the quenching behavior of the quencher molecules. DFT result reveals that electronic features are important in tuning the quenching ability of the quencher molecules and found to agree with the obtained experiment result. [ABSTRACT FROM AUTHOR]

Designing new and innovative receptors for the selective binding of radionuclides is central to nuclear waste management processes. Recently, a new multi-topic ion-pair receptor was reported which binds a variety of cesium salts. Due to the large size of the receptor, quantum chemical calculations on the full ion-pair receptors are restricted, thus the binding mechanisms are not well understood at the molecular level. We have assessed the binding strengths of various cesium salts to the recently synthesized multi-topic ion-pair receptor molecule using density functional theory based calculations. Our calculations predict that the binding of cesium salts to the receptor predominantly occurs via the cooperative binding mechanism. Cesium and the anion synergistically assist each other to bind favorably inside the receptor. Energy decomposition analysis on the ion-pair complexes shows that the Cs salts are bound to the receptor mainly through electrostatic interactions with small contribution from covalent interactions for large ionic radius anions. Further, QTAIM analysis characterizes the importance of different inter-molecular interactions between the ions and the receptor inside the ion-pair complexes. The role of the crystallographic solvent molecule contributes significantly by ∼10 kcal mol−1 to the overall binding affinities which is quite significant. Further, unlike the recent molecular mechanics (MM) calculations, our calculated binding affinity trends for various Cs ion-pair complexes (CsF, CsCl and CsNO3) are now in excellent agreement with the experimental binding affinity trends. [ABSTRACT FROM AUTHOR]

The electronic structure and spectroscopic properties of a series of rhenium(i) terpyridine complexes were investigated using density functional theory (DFT) and time dependent density functional theory (TD-DFT) methods. The influence of different substituent groups on the optical and electronic properties of Re(i) terpyridine complexes has also been explored. The reorganization energy calculations show that the substituted Re(i) terpyridine complexes are better electron transport materials with high quantum efficiency in OLED devices due to their high electron transport mobility and low λelectron values, whereas the unsubstituted complex shows relatively balanceable charge transfer abilities with the higher efficiency in organic light emitting devices (OLEDs). An NBO analysis reveals that n→σ* interactions are mainly responsible for the ground state stabilization of all the complexes. QTAIM results show that in all cases, Re–CO bonds are shared type transient interactions as reported in the other metal ligand complexes. The absorption is associated with 1MLCT/1LLCT/1ILCT character while the emission transition has 3MLCT/3LLCT/3ILCT character as revealed by a natural transition orbital (NTO) analysis. The higher quantum yields reported for the complexes 4–6 are found to be closely related to both its smaller ΔES1–T1, higher μS1, ET1 and moderate 3MLCT character. The calculated results show that Re(i) terpyridine complexes, particularly complexes 4–6, are suitable candidates for OLED materials. [ABSTRACT FROM AUTHOR]

The synthesis of the tetradentate dianionic ligand, H2 L (2,2'-(1E,1'E)-(2,2-dimethylpropane-1,3-dyl)bis(azanylylidene) bis(methanylylidene)diphenol), from 2,2-dimethyl-1,3-diaminopropane and its reaction with UO2(CH3COO)2-2H2O in a 1:1 molar ratio in methanol to produce the complex [UO2(L)(CH3OH)] are reported. The isolated compounds have been characterized by elemental analysis, ionization mass spectrometry (ESI-MS), UV/Vis, FT-IR, 1H- and 13C-NMR, DEPT-135 spectroscopy, TGA and single-crystal X-ray diffraction. As shown by X-ray crystallography, the coordination geometry around the uranium centre is distorted pentagonal bipyramidal with two imine nitrogen atoms, two phenolic oxygen atoms and one methanol O atom occupying equatorial sites, together with two axial oxo groups. To obtain insights into the structure and spectral properties of the studied complex, density functional theory (DFT) and time dependent density functional theory (TD-DFT) calculations have been carried out. The computed results show that LUMO of the complex is featured with uranium f orbital character. TD-DFT results indicate that the complex displays two intense bands and one weak charge transfer band. The charge transfer band is primarily due to HOMO LUMO (53%). Two intense bands have main contributions from HOMO-2 LUMO (81%) and HOMO-3 LUMO (77%) transitions, respectively. TD-DFT results indicate that the complex displays the charge transfer band primarily due to HOMO LUMO (53%) and other two charge transfer bands have main contributions from HOMO-2 LUMO (81%), HOMO-3 LUMO (77%) transitions, respectively. NBO analysis reveals that the ground state of the complex is mainly stabilized by n-n* interaction. EDA analysis reveals that the interaction existing between the ligand and other parts of the complex is mainly electrostatic in nature. [ABSTRACT FROM AUTHOR]

A new class of surfactant Co(III) complexes, cis-[Co(ip)2(C12H25NH2)2](ClO4)3 (1) and cis-[Co(dpq)2-(C12H25NH2)2](ClO4)3 (2) (ip = imidazo[4,5-f ][1,10]phenanthroline, dpq = dipyrido[3,2-d:2'-3'-f]quinoxaline), have been synthesized and characterized by various spectroscopic and physico-chemical techniques. The critical micelle concentration (CMC) values of these complexes in aqueous solution were obtained from conductance measurements. The specific conductivity data (at 303, 308, 313, 318 and 323 K) served for the evaluation of the temperature-dependent CMC and the thermodynamics of micellization (ΔGm0, ΔHm0 and ΔSm0). The trend in DNA-binding affinities and the spectral properties of a series of complexes, cis-[Co(ip)2(C12H25NH2)2](ClO4)3 (1) and cis-[Co(dpq)2(C12H25NH2)2](ClO4)3 (2), have been experimentally and theoretically investigated. The experimental results indicate that the size and shape of the intercalated ligand and hydrophobicity of the complexes have a marked effect on the binding affinity of the complexes to CT DNA in intercalation mode, and the order of their intrinsic DNA-binding constants Kb is Kb(1) < Kb(2). In addition, the influence of the extended aromatic ring and optical properties of the complexes can be reasonably explained by applying the DFT calculations. The energy gap between HOMO and LUMO indicates that these complexes are prone to interact with CT DNA. Further, molecular docking calculations have also been performed to understand the nature of binding of the complexes and the result confirms that the complexes interact with CT DNA through the alkyl chain. The cytotoxic activity of these complexes on human liver carcinoma cancer cells were determined adopting MTT assay and specific staining techniques, which revealed that the viability of the cells thus treated was significantly decreased and the cells succumbed to apoptosis as seen in the changes in the nuclear morphology and cytoplasmic features. [ABSTRACT FROM AUTHOR]

The electronic structure and spectroscopic properties of seven recently reported rhenium(i) phenanthroline complexes were investigated theoretically by density functional theory (DFT) and time dependent density functional theory (TD-DFT) methods. All the seven complexes are shown here to be better electron transport materials with high quantum efficiency in OLED devices due to their high electron transport mobility and low λelectron values. Particularly, among these seven chosen complexes the difference between λhole and λelectron for tricarbonyl Re(i) complexes is smaller, suggesting that these complexes have a better hole- and electron-transport balance in OLED devices. The absorption is associated with 1MLCT/1LLCT transitions while the emission transition has 3MLCT/3LLCT/3ILCT character as revealed by natural transition orbital (NTO) analysis. The calculated results show that the absorption and emission transitions and device efficiency can be changed by varying the nature and position of the axial ligands as revealed by the structural and bonding features of the complexes through natural bond orbital (NBO) and quantum theory of atoms in molecule (QTAIM) analysis. [ABSTRACT FROM AUTHOR]

The possibility of simultaneous addition of η2-H2 to both the metals (Ni and Fe) in the active site of the as isolated state of the enzyme (Ni-SI) is examined here by an atom-by-atom electronic energy partitioning based on the QTAIM method. Results show that the 4LS state prefers H2 removal than addition. Destabilization of the atomic basins of the thiolate bridges and decrease of the electrophilicity of the Fe and Ni, resulting in poor back donation to the CO ligand, are the bottlenecks that hamper dihydrogen activation simultaneously. The study helps to understand why such states are seldom accessed in the activation of dihydrogen. Moreover, Ni has been found to be the natural choice for the dihydrogen binding. [ABSTRACT FROM AUTHOR]

The halogen bond is relatively a less characterized intermolecular interaction compared to the hydrogen bond and the structure, stability and electronic structures of halogenated base pairs, particularly at the wobble junction have been investigated using DFT. Three halogens, namely Cl, Br and I, have been tested for their role in such situations with uracil as the anticodon base. Computed results reveal that when halogen atoms replace protons in the hydrogen bonding positions they induce lot of geometric changes that flip some of the observed base pairs into unobserved base pairs and vice versa. NCI, NBO and AIM analyses explain these changes at the electronic level. The new codons will have lot of impact in future applications, particularly in self assembly of biomaterials and t-RNA synthetic strategies. [ABSTRACT FROM AUTHOR]

A series of 2-quinolinone-based molecular systems with three different acceptor groups and N/ O-alkylated quinolinone compounds have been synthesised in an attempt to understand their optical properties. All the compounds were characterised by 1H NMR, 13C NMR and mass analysis. Absorption measurements revealed that charge-transfer transition was observed by introducing electron-withdrawing acceptor groups. Alkylation of 2-quinolinone at the O-position thwarts the charge-transfer transitions, whereas N-alkylation retains the charge-transfer property. The presence of resonance zwitterionic forms in the unalkylated and N-alkylated quinolinone compounds play an important role in charge-transfer transition. The effects of solvents on the absorption and emission properties of these compounds were probed through Lippert Mataga and ET(30) correlation. The Stokes shifts of O-alkylated compounds were larger than those of the unalkylated and N-alkylated quinolinone compounds. The observed higher quantum yield and Stokes shift for these compounds will make them ideal fluorescent probes. Incorporation of acceptor groups and alkylation in the quinolinone moiety alters their energy levels. Good thermal stability was observed for both unalkylated and alkylated quinolinone compounds. The trends observed in the photophysical and electrochemical properties were supported by theoretical studies. The observed tunable optical properties, which were achieved through simple N- vs. O-alkylation, results in large Stokes shifts and thermal stability, which means that the 2-quinolinone-based molecular systems are expected to emerge as potential candidates for photovoltaic and biological applications. [ABSTRACT FROM AUTHOR]

A search for novel organic luminogens led us to design and synthesize some N-fused imidazole derivatives based on imidazo[1,2- a]pyridine as the core and arylamine and imidazole as the peripheral groups. The fluorophores were synthesized through a multicomponent cascade reaction (A3 coupling) of a heterocyclic azine with an aldehyde and alkyne, followed by Suzuki coupling and a multicomponent cyclization reaction. All of the compounds exhibited interesting photophysical responses, especially arylamine-containing derivatives, which displayed strong positive solvatochromism in the emission spectra that indicated a more polar excited state owing to an efficient charge migration from the donor arylamine to the imidazo[1,2- a]pyridine acceptor. The quantum yields ranged from 0.2 to 0.7 and depended on the substitution pattern, most notably that based on the donor group at the C2 position. Moreover, the influence of general and specific solvent effects on the photophysical properties of the fluorophores was discussed with four-parameter Catalán and Kamlet-Taft solvent scales. The excellent thermal, electrochemical, and morphological stability of the compounds was explored by cyclic voltammetry, thermogravimetric analysis, and AFM methods. Furthermore, to understand the structure, bonding, and band gap of the molecules, DFT calculations were performed. The performance of the electroluminescence behavior of the imidazo[1,2- a]pyridine derivative was investigated by fabricating a multilayer organic light-emitting diode with a configuration of ITO/NPB (60 nm)/EML (40 nm)/BCP (15 nm)/Alq3 (20 nm)/LiF (0.5 nm)/Al(100 nm) (ITO=indium tin oxide, EML=emissive layer, BCP=2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline, Alq3=tris(8-hydroxyquinolinato)aluminum), which exhibited white emission with a turn-on voltage of 8 V and a brightness of 22 cd m−2. [ABSTRACT FROM AUTHOR]