Design of nickel chelates of tetradentate N-heterocyclic carbenes with subdued cytotoxicity

A series of nickel complexes, 1b-3b, exhibiting subdued cytotoxicity have been designed with the intent of their use as agents for developing resistance to nickel toxicity. Indeed, the nickel complexes, 1b-3b, display less cytotoxic activity towards two commonly occurring human cancer cell lines namely, HeLa cells (16-64%) and MCF-7 cells (70-90%) in culture as compared to the maximum inhibition by NiCl₂ · 6H₂O under analogous conditions at three different concentrations (1 μM, 5 μM and 20 μM). Similarly, the suppression of cytotoxicity through chelation of the metal ion can also be seen in normal cells as was evident from a significant reduction in cytotoxicity (9-41%) for a non-tumorigenic CHO cell line in case of a representative complex 3b. The reduction in carcinogenic activity in the complexes relative to nickel(II) ion from NiCl₂ · 6H₂O is brought about by successful chelation of the metal center by a class of specially designed new tetradentate N/O-functionalized N-heterocyclic carbene ligands. The two strongly σ-donating carbene moieties coupled with two negatively charged amido moieties present in the N-heterocyclic carbene ligands facilitate complete chelation of the metal center and thereby significantly reduce the cytotoxic effects of the metal.     

Spin-entanglement in a three electron system produced in double Auger decay

The simultaneous emission of two electrons in photoionization, or in the non-radiative spontaneous decay of an inner-shell vacancy, are two of the best known examples of the failure of the independent-particle model of atoms and molecules. The later of these provides also one of the two competitive processes, following inner-shell photoionization, for producing three flying electrons which can, for example, be used in implementing many protocols hitherto developed in quantum information. The correlation properties of the three-particle system consisting of these two electrons plus the photoelectron are analyzed using methods from quantum information theory. The entanglement of the consequent tripartite spin-state is shown to be completely independent of the mechanism(s) which may be responsible for the emission of these three electronic qubits in two different steps in the absence of spin-orbit interaction. Our analysis shows that the tripartite state formed in the present case is more like a  |W〉  class of states possessing pairwise entanglement. The experimental characterization of these states is fully achieved merely by the measurements of the energies of three flying electrons, without requiring any entanglement witness or other similar protocols hitherto developed in quantum information. Changes in these entanglement properties of a tripartite state of electronic qubits on the inclusion of the spin-orbit interaction have also been discussed.     

Ultrafast intermolecular hydrogen bond dynamics in the excited state of fluorenone

Steady-state fluorescence and time-resolved absorption measurements in pico- and femtosecond time domain have been used to investigate the dynamics of hydrogen bond in the excited singlet (S(1)) state of fluorenone in alcoholic solvents. A comparison of the features of the steady-state fluorescence spectra of fluorenone in various kinds of media demonstrates that two spectroscopically distinct forms of fluorenone in the S(1) state, namely the non-hydrogen-bonded (or free) molecule as well as the hydrogen-bonded complex, are responsible for the dual-fluorescence behavior of fluorenone in solutions of normal alcoholic solvents at room temperature (298 K). However, in 2,2,2-trifluoroethanol (TFE), a strong hydrogen bond donating solvent, emission from only the hydrogen-bonded complex is observed. Significant differences have also been observed in the temporal evolution of the absorption spectroscopic properties of the S(1) state of fluorenone in protic and aprotic solvents following photoexcitation using 400 nm laser pulses. An ultrafast component representing the solvent-induced vibrational energy relaxation (VER) process has been associated with the dynamics of the S(1) state of fluorenone in all kinds of solvents. However, in protic solvents, in addition to the VER process, further evolution of the spectroscopic and dynamical properties of the S(1) state have been observed because of repositioning of the hydrogen bonds around the carbonyl group. In normal alcohols, two different kinds of hydrogen-bonded complex of the fluorenone-alcohol system with different orientations of the hydrogen bond with respect to the carbonyl group and the molecular plane of fluorenone have been predicted. On the other hand, in TFE, formation of only one kind of hydrogen-bonded complex has been observed. These observations have been supported by theoretical calculations of the geometries of the hydrogen-bonded complexes in the ground and the excited states of fluorenone. Linear correlation between the lifetimes of the equilibration process occurring because of repositioning of the hydrogen bonds and Debye or longitudinal relaxation times of the normal alcoholic solvents establish the fact that, in weakly hydrogen bond donating solvents, the hydrogen bond dynamics can be described as merely a solvation process. Whereas, in TFE, hydrogen bond dynamics is better described by a process of conversion between two distinct excited states, namely, the non-hydrogen-bonded form and the hydrogen-bonded complex.     

Study of Fusion Dynamics Using Skyrme Energy Density Formalism with Different Surface Corrections

Within the framework of Skyrme energy density formalism, we investigate the role of surface corrections on the fusion of colliding nuclei. The coefficient of surface correction is varied between 1/36 and 4/36, and its impact is studied on about 180 reactions. The detailed investigations indicate a linear relationship between the fusion barrier heights and strength of the surface corrections. Our analysis of the fusion barriers advocate the strength of surface correction of 1/36.     

Metallaheteroborane clusters of group 5 transition metals derived from dichalcogenide ligands

Treatment of group 5 metal polychlorides such as, [Cp_nMCl_4-x] (M = V: n, x = 2; M = Nb: n = 1, x = 0), or [Cp∗TaCl₄] (Cp = η⁵-C₅H₅, Cp∗ = η⁵-C₅Me₅), with [LiBH₄·THF] followed by thermolysis in the presence of diphenyl diselenide yielded metallaheteroborane clusters [{CpV(μ-SePh)}₂(μ-Se)], 1 [(CpNb)₂B₄H₉(μ-SePh)], 2 and [(Cp∗Ta)₂B₄H₁₁(SePh)], 3 in modest yields. Compound 1 is an organovanadium selenolato cluster in which two (CpV) moieties bridged by (μ-Se) and two (μ-SePh) ligands. Compound 2 exhibits a bicapped tetrahedral core with one (μ-SePh) ligand. 3 is a tantalahexaborane cluster in which one of the terminal BH protons is substituted by SePh. Compounds 1-3 have been characterized by mass spectrometry, ¹H, ¹¹B, ¹³C NMR spectroscopy, and the geometric structures were unequivocally established by crystallographic analysis of 1-3.     

Thermal Non-equilibrium Heat Transfer and Entropy Generation due to Natural Convection in a Cylindrical Enclosure with a Truncated Conical,Heat-Generating Porous Bed

Natural convection in enclosures driven by heat-generating porous media has diverse applications in fields like geothermal, chemical, thermal and nuclear energy. The present article focuses on heat transfer and entropy generation characteristics of a heat-generating porous bed, placed centrally within a fluid-filled cylindrical enclosure. Pressure drop and heat transfer in the porous bed are modelled using the Darcy–Brinkmann–Forchheimer approximation and the local thermal non-equilibrium model, respectively. Energy flux vectors have been utilised for visualising convective energy transfer within the enclosure. The study of a wide range of Rayleigh number (\(10^{7}\)–\(10^{11}\)) and Darcy number (\(10^{-6}\)–\(10^{-10}\)) reveals that heat transfer in the porous region can be classified into conduction-dominated and convection-dominated regimes. This is supplemented with an entropy generation analysis in order to identify and characterise the irreversibilities associated with the phenomenon. It is observed that entropy generation characteristics of the enclosure closely follow the above-mentioned regime demarcation. Numerical computations for the present study have been conducted using ANSYS FLUENT 14.5. The solid energy equation is solved as a user-defined scalar equation, while data related to energy flux vectors and entropy generation are obtained using user-defined functions.     

Synthesis, Crystal Structures, Magnetic Properties and Catecholase Activity of Double Phenoxido-Bridged Penta-Coordinated Dinuclear Nickel(II) Complexes Derived from Reduced Schiff-Base Ligands: Mechanistic Inference of Catecholase Activity

Three double phenoxido-bridged dinuclear nickel(II) complexes, namely [Ni(2)(L(1))(2)(NCS)(2)] (1), [Ni(2)(L(2))(2)(NCS)(2)] (2), and [Ni(2)(L(3))(2)(NCS)(2)] (3) have been synthesized using the reduced tridentate Schiff-base ligands 2-[1-(3-methylamino-propylamino)-ethyl]-phenol (HL(1)), 2-[1-(2-dimethylamino-ethylamino)-ethyl]-phenol (HL(2)), and 2-[1-(3-dimethylamino-propylamino)-ethyl]-phenol (HL(3)), respectively. The coordination compounds have been characterized by X-ray structural analyses, magnetic-susceptibility measurements, and various spectroscopic methods. In all complexes, the nickel(II) ions are penta-coordinated in a square-pyramidal environment, which is severely distorted in the case of 1 (Addison parameter τ = 0.47) and 3 (τ = 0.29), while it is almost perfect for 2 (τ = 0.03). This arrangement leads to relatively strong antiferromagnetic interactions between the Ni(II) (S = 1) metal centers as mediated by double phenoxido bridges (with J values of -23.32 (1), -35.45 (2), and -34.02 (3) cm(3) K mol(-1), in the convention H = -2JS(1)S(2)). The catalytic activity of these Ni compounds has been investigated for the aerial oxidation of 3,5-di-tert-butylcatechol. Kinetic data analysis following Michaelis-Menten treatment reveals that the catecholase activity of the complexes is influenced by the flexibility of the ligand and also by the geometry around the metal ion. Electrospray ionization mass spectroscopy (ESI-MS) studies (in the positive mode) have been performed for all the coordination compounds in the presence of 3,5-DTBC to characterize potential complex-substrate intermediates. The mass-spectrometry data, corroborated by electron paramagnetic resonance (EPR) measurements, suggest that the metal centers are involved in the catecholase activity exhibited by the complexes.