Symmetrical and Asymmetrical Bisphosphonate Esters. Synthesis, Selective Hydrolysis, and Isomerization

Two simple and efficient one-pot procedures for the synthesis of a series of α-branched N-heterocycle-substituted methane-1,1-bisphosphonates are outlined. In the first method, the parent halosubstrates were reacted with cyanomethylphosphonate followed by reaction with dialkyl phosphonates to give asymmetrical or symmetrical bisphosphonates (BPs). In the second approach, the same halocompounds were reacted with tetraethyl methyl-1,1-bisphosphonate to give the requisite BPs. Partial and complete hydrolysis of the prepared BPs were also investigated. The products contain functional groups advantageous for further synthetic modification as structural units for coupling with the drug.     

Coexistence of multiple conformations in cysteamine monolayers on Au(111)

The structural organization, catalytic function, and electronic properties of cysteamine monolayers on Au(111) have been addressed comprehensively by voltammetry, in situ scanning tunneling microscopy (STM) in anaerobic environment, and a priori molecular dynamics (MD) simulation and STM image simulation. Two sets of voltammetric signals are observed. One peak at -(0.65-0.70) V (SCE) is caused by reductive desorption of cysteamine. The other signal, at -(0.25-0.40) V consists of a peak doublet. The pH dependence of the latter suggests that the origin is catalytic dihydrogen evolution. The doublet feature is indicative of two distinct cysteamine configurations. Cysteamine monolayer formation from initial nucleation to a highly ordered phase has been successfully observed in real time using oxygen-free in situ STM. Random cellular patterns, disordered adlayer formation accompanied by high step edge mobility, and ultimately a highly ordered (square root 3 x 4) R30 degrees lattice are observed sequentially. Pits are formed due to enclosure of the mobile edges during the adsorption process. In the highly ordered cysteamine layer, each unit has two spots with apparent 0.6 A height difference in STM images. The coverage 5.7 +/- 0.1 x 10(-10) mol cm(-2) determined by voltammetry supports that the spots represent two individual cysteamine molecules. A priori MD and density functional simulations hold other clues to the image interpretation and indicate that the NH(3)(+) groups dominate the tunneling contrast. A wide range of interface structures, showing variations in the sulfur binding site and orientation, gauche and trans conformers, and especially hydrogen-bonding interactions, are examined, from which it is concluded that the adsorbate structure is controlled by interactions with the solvent rather than with the substrate.     

Qualitative interpretation of physico-chemical and isotopic parameters in the Krka River (Croatia) assessed by multivariate statistical analysis

Multivariate statistical analyses were applied on the measured physico-chemical (Cd, Pb, Cu, Zn, Mg, Ca, O₂, alkalinity, temperature, pH, SAS, DOC and DIC) and isotopic parameters (δ¹³C and δ¹⁸O) to estimate and distinguish anthropogenic from natural influences to the water system of the Krka River. Analyses were conducted on the data collected during six years from twelve sampling sites. On the basis of orientation, positioning and grouping of parameters arranged by biplots, four main hypotheses were defined and finally statistically confirmed. Thereof, two main and distinct processes occurring in the Krka River could be highlighted: (i) upstream pollution, caused by the inflow of untreated waste-waters of city of Knin and (ii) downstream self-purification, caused by the sedimentation and/or co-precipitation of pollutants coupled by the inflow of clean subterranean water (groundwater recharge). Grouping of (i) hydrological and carbon cycle connected parameters, and (ii) anthropogenically influenced correlated parameters were proposed as a result of statistical analysis. Regarding the pH, it is shown that a stream section influenced by the subterranean inflow of Zrmanja River is statistically significantly different for all sampling campaigns during six years, being lower for about 0.5 pH unit.     

Wittig reaction of 1-dicyanomethyleneacenaphthen-2-one

The Wittig reaction of the titled compound 2 with alkoxycarbonylmethylenetriphenylphosphoranes ( 1a,b ) has been investigated and the reaction products 6, 10 , and 11 isolated and identified. On the other hand, reaction of 2 with benzoylmethylenetriphenyl-phosphorane ( 1c ) proceeded only at high temperature, yielding 7c and 10 . Mechanisms accounting for the formation of the adducts are discussed, and the synthetic utility of the products were tested.     

Pseudo-schwarzschild spherical accretion as a classical black hole analogue

We demonstrate that a spherical accretion onto astrophysical black holes, under the influence of Newtonian or various post-Newtonian pseudo-Schwarzschild gravitational potentials, may constitute a concrete example of classical analogue gravity naturally found in the Universe. We analytically calculate the corresponding analogue Hawking temperature as a function of the minimum number of physical parameters governing the accretion flow. We study both the polytropic and the isothermal accretion. We show that unlike in a general relativistic spherical accretion, analogue white hole solutions can never be obtained in such post-Newtonian systems. We also show that an isothermal spherical accretion is a remarkably simple example in which the only one information–the temperature of the fluid, is sufficient to completely describe an analogue gravity system. For both types of accretion, the analogue Hawking temperature may become higher than the usual Hawking temperature. However, the analogue Hawking temperature for accreting astrophysical black holes is considerably lower compared with the temperature of the accreting fluid.     

Bis­(tetra­methyl­ammonium) hexa­molyb­date hydrate, [(CH3)4N]2[Mo6O19]·H2O

The crystal and molecular structure of the title compound, (C₄H₁₂N)₂[Mo₆O₁₉]·H₂O, has been determined from X‐ray diffraction data. The poly­oxo­anion [Mo₆O₁₉]^2? is built up from six distorted MoO₆ octa­hedra sharing common edges and one common vertex at the central O atom, and has crystallographic m3m (O_h) symmetry. The cation has crystallographic 3m symmetry.     

On the thermodynamics of an ideal fermi gas on the lattice at finite density

We study the ideal gas of fermions on a lattice at finite density for both naive and Wilson fermions. Comparing the thermodynamical quantities thus calculated with the known results in the continuum theory, we are led to propose a modification of the naive form of the lattice action, which is same for both the naive and the Wilson fermions. The thermodynamical quantities, calculated by using this form, are shown to have the correct continuum limit.     

The nature of the adsorption of nucleobases on the gold [111] surface

Biochip technology is based on the immobilization of biological macromolecules on the surface of electronic devices. The biochemical properties of the immobilized molecules can be influenced to a large extent by the interaction with the inorganic surface. The interaction of DNA with the surface of gold, a metal commonly used in biochip technologies, is sequence dependent as the four nucleobases, adenine, thymine, cytosine, and guanine, interact to a different extent with the gold surface. The nature of nucleobase adsorption on the gold [111] surface has been investigated by performing density functional theory and post-Hartree-Fock calculations. It turns out that the interaction is dominated by dispersion forces and an appreciable degree of chemisorption is observed for adenine only. A set of Lennard-Jones parameters that describe the interaction was derived from the post-Hartree-Fock calculations. Classical molecular dynamics simulations of nucleobase monolayers based on these parameters are in remarkable agreement with the experiment and show that the interaction of the nucleobases with the gold surface is strongly modulated by base-base interactions and reaches a maximum when a full monolayer is formed.