Reversible Water Intercalation Accompanied by Coordination and Color Changes in a Layered Metal-Organic Framework

A new two-dimensional 3d-4f mixed-metal mixed dicarboxylate (homocyclic and heterocyclic) of the formula [Gd2(H2O)2Ni(H2O)2(1,2-bdc)2(2,5-pydc)2] 3 8H2O (1; 1,2-H2bdc = 1,2-benzenedicarboxylic acid and 2,5-H2pydc = 2,5- pyridinedicarboxylic acid) has been prepared by employing the hydrothermal method. The structure has infinite onedimensional-Gd-O-Gd- chains formed by the edge-shared GdO9 polyhedral units, resulting exclusively from the connectivity between the Gd3+ ions and the 1,2-bdc units. The chains are connected by the [Ni(H2O)2(2,5-pydc)2]2- metalloligand, forming the two-dimensional layer arrangements. The stacking of the layers creates hydrophilic and hydrophobic spaces in the interlamellar region. A one-dimensional water ladder structure, formed by the extraframework water molecules, occupies the hydrophilic region while the benzene ring of 1,2-bdc occupies the hydrophobic region. To the best of our knowledge, the present compound represents the first example of a 3d-4f mixed-metal carboxylate in which two different aromatic dicarboxylate anions act as the linkers. The stabilization energies of the water clusters have been evaluated using density functional theory calculations. The water molecules in 1 are fully reversible accompanied by a change in color (greenish blue to brown) and coordination around Ni2+ ions (octahedral to distorted tetrahedral).

Interaction of rat testis protein, TP, with nucleic acids in vitro. Fluorescence quenching, UV absorption, and thermal denaturation studies

The nucleic acid binding properties of the testis protein, TP, were studied with the help of physical techniques, namely, fluorescence quenching, UV difference absorption spectroscopy, and thermal melting. Results of quenching of tyrosine fluorescence of TP upon its binding to double-stranded and denatured rat liver nucleosome core DNA and poly(rA) suggest that the tyrosine residues of TP interact/intercalate with the bases of these nucleic acids. From the fluorescence quenching data, obtained at 50 mM NaCl concentration, the apparent association constants for binding of TP to native and denatured DNA and poly(rA) were calculated to be 4.4 X 10(3) M-1, 2.86 X 10(4) M-1, and 8.5 X 10(4) M-1, respectively. UV difference absorption spectra upon TP binding to poly(rA) and rat liver core DNA showed a TP-induced hyperchromicity at 260 nm which is suggestive of local melting of poly(rA) and DNA. The results from thermal melting studies of binding of TP to calf thymus DNA at 1 mM NaCl as well as 50 mM NaCl showed that although at 1 mM NaCl TP brings about a slight stabilization of the DNA against thermal melting, a destabilization of the DNA was observed at 50 mM NaCl. From these results it is concluded that TP, having a higher affinity for single-stranded nucleic acids, destabilizes double- stranded DNA, thus behaving like a DNA-melting protein.

Theoretical studies of lithium bonding in lithium chloride/aliphatic amine complexes

In the systematic study of amine … LiCl [amines = NH3, CH3NH2, (CH3)2NH] complexes the possibility of an ion-pair structure and the effect of methylation on the stabilization energy is investigated. ΔEis evaluated by the SCF/4-31G method and augmented by the approximate dispersion energy calculated perturbationally. The interaction energy decreases with the increasing number of methyl groups in the amine. The dispersion energy plays a negligible role in the stabilization of complexes. None of the systems studied are ion pairs; their Li bonds are of a so-called molecular type. Due to the divergence of the multipole expansion, the attempt to correct the 4-31G stabilization energies via the electrostatic energy fails. The relative order of the ΔE in the series of complexes is verified instead in the extended basis set calculation. The lithium bonds are compared with their H-bonded analogues.

Quest for new materials: Inorganic chemistry plays a crucial role

There is an endless quest for new materials to meet the demands of advancing technology. Thus, we need new magnetic and metallic/semiconducting materials for spintronics, new low-loss dielectrics for telecommunication, new multi-ferroic materials that combine both ferroelectricity and ferromagnetism for memory devices, new piezoelectrics that do not contain lead, new lithium containing solids for application as cathode/anode/electrolyte in lithium batteries, hydrogen storage materials for mobile/transport applications and catalyst materials that can convert, for example, methane to higher hydrocarbons, and the list is endless! Fortunately for us, chemistry - inorganic chemistry in particular - plays a crucial role in this quest. Most of the functional materials mentioned above are inorganic non-molecular solids, while much of the conventional inorganic chemistry deals with isolated molecules or molecular solids. Even so, the basic concepts that we learn in inorganic chemistry, for example, acidity/basicity, oxidation/reduction (potentials), crystal field theory, low spin-high spin/inner sphere-outer sphere complexes, role of d-electrons in transition metal chemistry, electron-transfer reactions, coordination geometries around metal atoms, Jahn-Teller distortion, metal-metal bonds, cation-anion (metal-nonmetal) redox competition in the stabilization of oxidation states - all find crucial application in the design and synthesis of inorganic solids possessing technologically important properties. An attempt has been made here to illustrate the role of inorganic chemistry in this endeavour, drawing examples from the literature its well as from the research work of my group.

A comparative study of tbe regulation of cytochrome P-450 and glutathione transferase gene expression in rat liver

A cDNA clone for the Ya subunit of glutathione transferase from rat liver was constructed in E.coli. The clone hybridized to Ya and Yc subunit messenger RNAs. On the basis of experiments involving cell-free translation and hybridization to the cloned probe, it was shown that prototype inducers of cytochrome P-450 such as phenobarbitone and 3-methylcholanthrene as well as inhibitors such as CoCl2 and 3-amino-l,2,4-triazole enhanced the glutathione transferase (Ya+Yc) messenger RNA contents in rat liver. A comparative study with the induction of cytochrome P-450 (b+e) by phenobarbitone revealed that the drug manifested a striking increase in the nuclear pre-messenger RNAs for the cytochrome at 12 hr, but did not significantly affect the same in the case of glutathione transferase (Ya+Yc). 3-Amino-l, 2,4-tnazole and CoCl- blocked the phenobarbitone mediated increase in cytochrome P-450 (b+e) nuclear pre-messenger RNAs. These compounds did not significantly affect the glutathione transferase (Ya+Yc) nuclear pre-messenger RNA levels. The polysomal, poly (A)- containing messenger RNAs for cytochrome P-450 (b+e) increased by 12–15 fold after phenobarbitone administration, reached a maximum around 16hr and then decreased sharply. In comparison, the increase in the case of glutathione transferase (Ya+Yc) mesenger RNAs was sluggish and steady and a value of 3–4 fold was reached around 24 hr. Run-off transcription rates for cytochrome P-450 (b+e) increased by nearly 15 fold in 4 hr after phenobarbitone administration, whereas the increase for glutathione transferase (Ya+Yc) was only 2.0 fold. At 12 hr after the drug administration, the glutathione transferase (Ya+Yc) transcription rates were near normal. Administration of 3-amino-l,2,4-triazole and CoCl2 blocked the phenobarbitone-mediated increase in the transcription of cytochrome P-450 (b+e) messenger RNAs. These compounds at best had only marginal effects on the transcription of glutathione transferase (Ya+Yc) messenger RNAs. The half-life of cytochrome P-450 (b+e) messenger RNA was estimated to be 3–4 hr, whereas that for glutathione transferase (Ya+Yc) was found to be 8-9 hr. Administration of phenobarbitone enhanced the half-life of glutathione transferase (Ya+Yc) messenger RNA by nearly two fold. It is suggested that while transcription activation may play a primary role in the induction of cytochrome P-450 (b+e), the induction of glutathione transferase (Ya+Yc) may essentially involve stabilization of the messenger RNAs.

Degenerate rhombohedral and orthorhombic states in Ca-substituted Na0.5Bi0.5TiO3

Neutron powder diffraction and temperature dependent dielectric studies were carried out on Ca-substituted Na0.5Bi0.5TiO3, i.e., (Na0.5Bi0.5)(1-x)CaxTiO3. Stabilization of an orthorhombic phase even at a low Ca concentration (0.05 < x < 0.10) suggests that Na0.5Bi0.5TiO3 (NBT) is susceptible to orthorhombic distortion. The orthorhombic and rhombohedral phases coexist for x=0.10, suggesting these phases to be nearly degenerate. The orthorhombic distortion favoring tendency of Ca assists in promoting the inherent instability with regard to this structure in pure NBT, which was reported recently.

Boundary layer transition observations on a body of revolution with surface heating and cooling in water

Boundary layer flow visualization in water with surface heat transfer was carried out on a body of revolution which had the predicted possibility of laminar separation under isothermal conditions. Flow visualization was by in-line holographic technique. Boundary layer stabilization, including elimination of laminar separation, was observed to take place on surface heating. Conversely, boundary layer destabilization was observed on surface cooling. These findings are consistent with the theoretical predictions of Wazzan et al. in The stability and transition of heated and cooled incompressible laminar boundary layers, in Proceedings of the Fourth International Heat Transfer Conference, Vol. 2, FCI 4. Elsevier, Amsterdam (1970).

Amide-based Room Temperature Molten Salt as Solvent cum Stabilizer for Metallic Nanochains

A simple and efficient method for spontaneous organization of long assemblies of gold nanoparticles is described. This is achieved in a molten solvent containing acetamide, urea and ammonium nitrate that acts as a solvent cum stabilizer. There is no external aggregating agent or stabilizing agent added to the system. Depending on the concentration of the metal salt in the ternary melt, either chain-like assemblies or individual nanoparticles could be obtained. The amine groups present in the components of the melt (acetamide and urea) help in the stabilization of nanoparticles. Ammonium ions present in the eutectic mixture are likely to assist in the organization of the particles. The method is simple, highly reproducible and does not require any templating agent for the formation of chain-like assemblies.

A Modified Heffron-Phillip's Model for The Design of Power System Stabilizers

In this paper a modified Heffron-Phillip's (K-constant) model is derived for the design of power system stabilizers. A knowledge of external system parameters, such as equivalent infinite bus voltage and external impedances or their equivalent estimated values is required for designing a conventional power system stabilizer. In the proposed method, information available at the secondary bus of the step-up transformer is used to set up a modified Heffron-Phillip's (ModHP) model. The PSS design based on this model utilizes signals available within the generating station. The efficacy of the proposed design technique and the performance of the stabilizer has been evaluated over a range of operating and system conditions. The simulation results have shown that the performance of the proposed stabilizer is comparable to that could be obtained by conventional design but without the need for the estimation and computation of external system parameters. The proposed design is thus well suited for practical applications to power system stabilization, including possibly the multi-machine applications where accurate system information is not readily available.

Inhibition of cortisol-mediated induction of hepatic tryptophan-2,3-dioxygenase by norepinephrine

Norepinephrine inhibits cortisol-mediated induction of hepatic tryptophan pyrrolase in rats. During cold exposure the stabilization of this enzyme appears to occur by an interaction of corticoids and norepinephrine on the induction process.

Unusual effects of anisotropic bonding in Cu(II) and Ni(II) oxides with K2NiF4 structure

Geometric constraints present in A2BO4 compounds with the tetragonal-T structure of K2NiF4 impose a strong pressure on the B---OII---B bonds and a stretching of the A---OI---A bonds in the basal planes if the tolerance factor is t congruent with RAO/√2 RBO < 1, where RAO and RBO are the sums of the A---O and B---O ionic radii. The tetragonal-T phase of La2NiO4 becomes monoclinic for Pr2NiO4, orthorhombic for La2CuO4, and tetragonal-T′ for Pr2CuO4. The atomic displacements in these distorted phases are discussed and rationalized in terms of the chemistry of the various compounds. The strong pressure on the B---OII---B bonds produces itinerant σ*x2−y2 bands and a relative stabilization of localized dz2 orbitals. Magnetic susceptibility and transport data reveal an intersection of the Fermi energy with the d2z2 levels for half the copper ions in La2CuO4; this intersection is responsible for an intrinsic localized moment associated with a configuration fluctuation; below 200 K the localized moment smoothly vanishes with decreasing temperature as the d2z2 level becomes filled. In La2NiO4, the localized moments for half-filled dz2 orbitals induce strong correlations among the σ*x2−y2 electrons above Td reverse similar, equals 200 K; at lower temperatures the σ*x2−y2 electrons appear to contribute nothing to the magnetic susceptibility, which obeys a Curie-Weiss law giving a μeff corresponding to S = 1/2, but shows no magnetic order to lowest temperatures. These surprising results are verified by comparison with the mixed systems La2Ni1−xCuxO4 and La2−2xSr2xNi1−xTixO4. The onset of a charge-density wave below 200 K is proposed for both La2CuO4 and La2NiO4, but the atomic displacements would be short-range cooperative in mixed systems. The semiconductor-metallic transitions observed in several systems are found in many cases to obey the relation Ea reverse similar, equals kTmin, where varrho = varrho0exp(−Ea/kT) and Tmin is the temperature of minimum resistivity varrho. This relation is interpreted in terms of a diffusive charge-carrier mobility with Ea reverse similar, equals ΔHm reverse similar, equals kT at T = Tmin.

Charge transfer complexes of crown ethers with neutral organic gyama-acceptor, 2-dicyanoethylene 1,3-indane dione

The interaction of benzo-15-crown-5, dibenzo-18-crown-6 and dibenzo-24-crown-8 with 2-dicyanoethylene 1,3-indane dione in CH2Cl2 has been described in terms of the formation of 1 : 1 molecular complexes. The magnitude of association constants and thermodynamic parameters indicate cooperative interactions of oxygens with the acceptors. The 1H and 13C NMR spectra of the complexes show that gyama-gyama interactions are a major source of ground state stabilization in these complexes.

Stability of large flexible damped spacecraft modeled as elastic continua

Vibrational stability of a large flexible, structurally damped spacecraft subject to large rigid body rotations is analysed modelling the system as an elastic continuum. Using solution of rigid body attitude motion under torque free conditions and modal analysis, the vibrational equations are reduced to ordinary differential equations with time-varying coefficients. Stability analysis is carried out using Floquet theory and Sonin-Polya theorem. The cases of spinning and non-spinning spacecraft idealized as a flexible beam plate undergoing simple structural vibration are analysed in detail. The critical damping required for stabilization is shown to be a function of the spacecraft's inertia ratio and the level of disturbance.

Electron Spectroscopic Studies of Oxygen and Carbon Dioxide Adsorbed on Metal Surfaces

Adsorption of oxygen on Ni, Cu, Pd, Ag, and Au surfaces has been investigated by employing UV and X-ray photoelectron spectrscopy as well as electron energy loss spectroscopy (EELS). Molecularly chemisorbed (singlet) oxygen is found on Ni, Cu, Ag, and Au surfaces showing features such as stabilization of the rB* orbital, destabilization of the .nu orbital, higher O(1s) binding energy than the atomic species, and a band 2-3 eV below the Fermi level due to metal d-O(2p)u* interaction. 0-0 and metal-oxygen stretching frequencies have been observed in EELS. Physical adsorption of O2 is found to occur on Pd and Ni surfaces, only at high exposures in the latter case. Physical adsorption and multilayer condensation of CO, on metal surfaces are distinguished by characteristic relaxation shifts in UPS as well as O(1s) binding energies. Adsorption of CO on a Ni surface covered with presorbed atomic oxygen gives rise to C02.

Non-linear response of a gyrostabilized platform to transient input

In this paper the response of a gyrostabilized platform subjected to a transient torque has been analyzed by deliberately introducing non-linearity into the command of the servomotor. The resulting third-order non-linear differential equation has been solved by using a transformation technique involving the displacement variable. The condition under which platform oscillations may grow with time or die with time are important from the point of view of platform stabilization. The effect of deliberate addition of non-linearity with a view to achieving the ideal response—that is, to bring the platform back to its equilibrium position with as few oscillations as possible—has been investigated. The conditions under which instability may set in on account of the small transient input and small non-linearity has also been discussed. The analysis is illustrated by means of a numerical example. The results of analysis are compared with numerical solutions obtained on a digital computer.