Propagation of Scalar Fields in a Plane Symmetric Spacetime

The present article deals with solutions for a minimally coupled scalar field propagating in a static plane symmetric spacetime. The considered metric describes the curvature outside a massive infinity plate and exhibits an intrinsic naked singularity (a singular plane) that makes the accessible universe finite in extension. This solution can be interpreted as describing the spacetime of static domain walls. In this context, a first solution is given in terms of zero order Bessel functions of the first and second kind and presents a stationary pattern which is interpreted as a result of the reflection of the scalar waves at the singular plane. This is an evidence, at least for the massless scalar field, of an old interpretation given by Amundsen and Grøn regarding the behaviour of test particles near the singularity. A second solution is obtained in the limit of a weak gravitational field which is valid only far from the singularity. In this limit, it was possible to find out an analytic solution for the scalar field in terms of the Kummer and Tricomi confluent hypergeometric functions.     

Increasing the solubility of strong reducing agents containing Mo(2)(4+) units and alkyl-substituted guanidinate ligands

Six very soluble paddlewheel compounds containing Mo(2)(n+) units, n = 4, 5, 6, and two alkyl-substituted bicyclic guanidinate ligands have been synthesized. The quadruply bonded complexes with n = 4, Mo(2)(TMhpp)(4) and Mo(2)(TEhpp)(4), (TMhpp = the anion of 3,3,9,9-tetramethyl-1,5,7-triazabicyclo[4.4.0]dec-4-ene and TEhpp = the anion of 3,3,9,9-tetraethyl-1,5,7-triazabicyclo[4.4.0]dec-4-ene) are easily oxidized. The electrode potentials in THF are -1.08 and -1.17 V vs. Ag/AgCl, respectively, for the Mo(2)(5+/4+) couple. These potentials are in accord with the low ionization potentials for the quadruply bonded compounds. Because of the high solubility of the Mo(2)(4+) compounds in most common organic solvents they are attractive candidates for use as strong reducing agents in homogeneous systems.     

Electronic localization versus delocalization determined by the binding of the linker in an isomer pair

By using stoichiometric amounts of (C5H5)2FePF6, the isomeric neutral diamidate-bridged molecules, alpha- and beta-(DAniF)3Mo2(ArN(O)CC(O)NAr)Mo2(DAniF)3, with Ar = p-MeOC6H4, have been oxidized to give the PF6 salts of the four cations alpha1+, alpha2+, beta1+, and beta2+. All four structures have been accurately determined and, together with supporting evidence from near-IR, EPR, NMR and magnetic susceptibility measurements, it clearly establishes that in the mixed-valent alpha+ species the unpaired electron is localized over only one of the Mo2 units while the alpha2+ cation behaves as a diradical having two Mo25+ units that are essentially uncoupled. However, the beta+ species is fully delocalized, in the time scale of the experiments, with the unpaired electron being equally shared by the two Mo2 units. It displays a HOMO-1 --> SOMO transition at 4700 cm-1 (Deltanu1/2 = 2300 cm-1). Because of strong coupling, the beta2+ species is diamagnetic.     

Modulating Electronic Coupling Using O- and S-donor Linkers

Structures of compounds having two dimolybdenum units Mo2(DAniF)3+ (DAniF = N,N'-di-p-anisylformamidinate) connected by unsubstituted oxamidate (1) and dithiooxamidate (2) linkers are isomorphous, and the cores of the molecules are planar because of two intramolecular hydrogen bonds within the linkers. Molecular mechanics calculations show a barrier of rotation along the C-C bond of approximately 10 kcal x mol(-1), which suggests that planar conformations are also expected in solution. Changing the two oxygen atoms in the linker of 1 to sulfur atoms results in a significant enhancement of the electronic coupling between the dimetal units (Delta(E1/2) = 204 mV for 1 and 407 mV for 2). The electronic spectrum of 2 shows an intense low energy (600 nm) metal-to-ligand charge transfer (MLCT) band, whereas that for 1 shows only a weak absorption band at 460 nm. DFT calculations on models 1' and 2', in which the anisyl groups were replaced by hydrogen atoms, show that the energy of the pi* orbital of the linker is much lower for 2'. This allows dpi-ddelta interactions from the electrons in the delta orbitals of the Mo2 unit to the sulfur atom that in turn facilitates an electron hopping pathway.     

Controls over spatial and seasonal variations on isotopic composition of the precipitation along the central and eastern portion of Brazil

Based on Global Network Isotopes in Precipitation (GNIP) isotopic data set, a review of the spatial and temporal variability of δ¹⁸O and δ²H in precipitation was conducted throughout central and eastern Brazil, indicating that dynamic interactions between Intertropical and South Atlantic Convergence Zones, Amazon rainforest, and Atlantic Ocean determine the variations on the isotopic composition of precipitation over this area. Despite the seasonality and latitude effects observed, a fair correlation with precipitation amount was found. In addition, Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) air mass back trajectories were used to quantify the factors controlling daily variability in stable isotopes in precipitation. Through a linear multiple regression analysis, it was observed that temporal variations were consistent with the meteorological parameters derived from HYSPLIT, particularly precipitation amount along the trajectory and mix depth, but are not dependent on vapour residence time in the atmosphere. These findings also indicate the importance of convective systems to control the isotopic composition of precipitation in tropical and subtropical regions.     

Tetra‐μ‐acetato‐κ8O:O′‐bis[(N1,N2‐di‐p‐anisylformamidine‐κN2)ruthenium(II)](Ru—Ru): an example of an axial bis‐adduct of {Ru2}4+ tetracarboxyl­ate with N‐donor ligands

The title compound, [Ru₂(C₂H₃O₂)₄(C₁₅H₁₆N₂O₂)₂], lies on a crystallographic inversion center and exhibits an Ru—Ru bond length of 2.2847 (8) Å. There are weak intramolecular hydrogen‐bonding interactions between the N¹,N²‐di‐p‐anisylformamidine (HDAniF) ligands and the bridging acetate ligands. The molecule is one of the few examples of a crystallographically characterized axial bis‐adduct of a {Ru₂}⁴⁺ complex with two N‐donor ligands.     

Separation and Immobilization of Lipase from Penicillium simplicissimum by Selective Adsorption on Hydrophobic Supports

Lipases are an enzyme class of a great importance as biocatalysts applied to organic chemistry. However, it is still necessary to search for new enzymes with special characteristics such as good stability towards high temperatures, organic solvents, and high stereoselectivity presence. The present work’s aim was to immobilize the lipases pool produced by Penicillium simplissicimum, a filamentous fungi strain isolated from Brazilian babassu cake residue. P. simplissicimum lipases were separated into three different fractions using selective adsorption method on different hydrophobic supports (butyl-, phenyl-, and octyl-agarose) at low ionic strength. After immobilization, it was observed that these fractions’ hyperactivation is in the range of 131% to 1133%. This phenomenon probably occurs due to enzyme open form stabilization when immobilized onto hydrophobic supports. Those fractions showed different thermal stability, specificity, and enantioselectivity towards some substrates. Enantiomeric ratio for the hydrolysis of (R,S) 2-O-butyryl-2-phenylacetic acid ranged from 1 to 7.9 for different immobilized P. simplissicimum lipase fractions. Asymmetry factor for diethyl 2-phenylmalonate hydrolysis ranged from 11.8 to 16.4 according to the immobilized P. simplissicimum lipase fractions. Those results showed that sequential adsorption methodology was an efficient strategy to obtain new biocatalysts with different enantioselectivity degrees, thermostability, and specificity prepared with a crude extract produced by a simple and low-cost technology.     

Time-course expression of DNA repair-related genes in hepatocytes of zebrafish (Danio rerio) after UV-B exposure

The objective of this study was to evaluate the time-course effects of UV-B exposure on expression of genes involved in the DNA repair system of zebrafish ( Danio rerio ) hepatocytes, a highly competent species in terms of damage repair induced by UV radiation. For gene expression analysis (RT-PCR), cells were exposed to 23.3 mJ cm⁻² UV-B, which was the dose that affected viable cell number (reduction of 30% when compared with the control group) and produced no visual alteration on cell morphology. The early response observed (6 h) showed induction in the expression of the CDKI gene (cyclin-dependent kinase inhibitor) and genes related to DNA damage repair (mainly XPC and DDB2 ), while the late response observed (24 h) was more related to up-regulation of p53 and genes involved in cell cycle arrest ( gadd45a , cyclinG1 ). In all times analyzed, the anti-apoptotic gene Bcl-2 was down-regulated. Another interesting result observed was the up-regulation of the Apex- 1 gene after UV-B exposure, which could indicate the induction of oxidative lesions in the DNA molecule. In conclusion, these results demonstrate an activation of the DNA repair system in hepatocytes of zebrafish exposed to UV-B radiation, mainly involving the participation of p53.     

An Iron Complex with an Unsupported Fe–Fe Bond

Full metal bonding : The reduction of a six‐coordinate, mononuclear Werner‐type iron(II) complex (see scheme) resulted in the isolation of a compound with an extraordinarily rare, unsupported Fe–Fe bond having an experimental Fe–Fe distance of 2.6869(6) Å and a calculated bond order of 0.5.

     

Facilitating access to the most easily ionized molecule: an improved synthesis of the key intermediate, W2(hpp)4Cl2, and related compounds

A far superior synthesis is reported for W(2)(hpp)(4)Cl(2), a key intermediate in the synthesis of the most easily ionized closed-shell molecule W(2)(hpp)(4) (hpp = the anion of the bicyclic guanidine compound 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine). At 200 degrees C, the one-pot reaction of the air-stable and commercially available compounds W(CO)(6) and Hhpp in o-dichlorobenzene produces W(2)(hpp)(4)Cl(2) in multigram quantities with isolated yields of over 90%. At lower temperatures, the reaction can lead to other compounds such as W(Hhpp)(2)(CO)(4) or W(2)(mu-CO)(2)(mu-hpp)(2)(eta(2)-hpp)(2), which are isolable in good purity depending upon the specific conditions employed. These compounds provide insight into the reaction pathway to W(2)(hpp)(4)Cl(2) and W(2)(hpp)(4). Two additional derivatives, W(2)(hpp)(4)X(2) where X is PF(6)(-) or the anion tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (TFPB), have also been synthesized and structurally characterized. A comparison of the electrode potentials of W(2)(mu-CO)(2)(mu-hpp)(2)(eta(2)-hpp)(2) and the di-p-anisylformamidinate analogue shows that oxidation of the hpp compound is significantly displaced (1.12 V) and shows that the bicyclic guanidinate ligand is considerably better than the formamidinate anion at stabilizing high oxidation states. A differential pulse voltammogram of W(2)(hpp)(4)(TFPB)(2) in THF shows two reduction processes with an E(1/2) of -0.97 V for the first and -1.81 V (vs Ag/AgCl) for the second. DFT calculations on the W(2)(hpp)(4)(2+) units in W(2)(hpp)(4)X(2) compounds show that the metal-metal bonding orbitals are destabilized by the axial ligands, which accounts for significant variations in the W-W distances. The low-energy gas-phase ionizations of W(2)(hpp)(4) are also reported and discussed.