The [Ru(CN)5(pyS)](4-) complex, an efficient self-assembled monolayer for the cytochrome c heterogeneous electron transfer studies

The organothiol 4-mercaptopyridine (pyS) has been used extensively as facilitator for the assessment of heterogeneous electron transfer reaction of cytochrome c (cyt c). Its efficiency, however, is strongly affected by the instability of the adlayer due to the C-S bond cleavage. The K(4)[Ru(CN)(5)(pyS)].3H(2)O complex was synthesized and characterized aiming its utilization as an inorganic self-assembled monolayer (SAM) that would enhance the gold adlayer stability. The SAM formed by this complex onto gold (RupySAu) was characterized by spectroscopic (FTIRRAS and SERS) and electrochemical (LSV) techniques. The ex situ vibrational SERS and FTIRRAS spectra data of this SAM formed onto gold suggest a sigma interaction between the gold and sulfur atoms of the complex, inducing a perpendicular arrangement in relation to the surface normal. Additionally, SERS and FTIRRAS spectra performed for freshly prepared RupySAu adlayer and for large immersion times in the precursor solution have not shown any significant change that would reflect the degradation of the adlayer. The LSV desorption curves of this SAM indicate an enhancement in the C-S bond strength of the pyS ligand when coordinated to the [Ru(CN)(5)](3-) moiety. Comparatively to the data obtained for the desorption process of the pyS monolayer, the reductive desorption potential, E(rd), of the RupySAu presents a shift of -17 mV. This bond strength intensification leads to an increase in the stability of the monolayer. The voltammetric curves of cyt c carried out with the RupySAu electrode showed electrochemical parameters consistent with those reported for the native protein, as well as the maintenance of the electrochemical kinetic data after repetitive cycles. The results all together suggest that the pi back-bonding effect from the [Ru(CN)(5)](3-) metal center plays an important role in the stability of the RupySAu adlayer, improving the assessment of the cyt c heterogeneous electron transfer reaction.     

Tripyrrolylphosphine as a unique bridging ligand in the Rh6CO14(mu2-P(NC4H4)3) cluster: structure,bonding, fluxionality,thermodynamics, and kinetics studies

Tripyrrolylphosphine reacts with the cluster Rh6CO15(NCMe) to afford the disubstituted Rh6CO14(mu2)-P(NC4H4)3) derivative (2) via the Rh6CO15P(NC4H4)3 intermediate (1) with eta(1)-P coordination. In the solid state, 2 has the phosphine occupying a bridging position where it is bonded to two neighboring Rh atoms in the Rh(6) octahedron through the P-atom and an approximately tetrahedral alpha-carbon atom of one of the pyrrolyl rings. This can be described by the interaction of an electron pair, associated with a negative charge on one of the canonical forms of the NC(4)H(4) ring, with the adjacent Rh center. (1)H NMR spectra show that the solid-state structure is retained in solution, but the phosphine is not rigid, and three distinctive dynamic processes are observed. Each of these represents independent hindered rotation of inequivalent pyrrolyl rings about P-N bonds, the ring involved in the interaction with the Rh(6) skeleton displaying the highest activation barrier with deltaH = 15.8 +/- 0.1 kcal mol(-1) and deltaS = 1.4 +/- 0.3 cal K(-1) mol(-1). The assignment has been confirmed by 1H TOCSY and EXSY experiments, and a mechanism is proposed. The formation of 2 from 1 is reversible in the presence of CO, which is highly unusual for bridged clusters. The kinetics of the forward and reverse reactions have been studied, and the values of DeltaH degrees and DeltaS degrees for formation of 2 (+1.3 +/- 0.5 kcal mol(-1) and -9 +/- 2 cal K(-1) mol (-1), respectively) show that the Rh-C bond in the bridge is comparable in strength with the Rh-CO bond it replaces. The intrinsic entropy of 2 is exceptionally unfavorable, overcoming the favorable entropy caused by CO release, and this allows the reversibility of bridge formation. The reactions proceed via a reactive intermediate that may involve agostic bonding of the ring. The reverse reaction has an exceedingly unfavorable activation entropy that emphasizes the unique nature of 2.     

The Fourier Formula for Discontinuous Functions of Several Variables

An analog of the classical Fourier formula for the characteristic function of a convex compact set is considered:

Phase equilibria,charge transport,and mass transport in Sr<Subscript>4</Subscript>Nb<Subscript>2</Subscript>O<Subscript>9</Subscript>-“M<Subscript>4</Subscript>Nb<Subscript>2</Subscript>O<Subscript>9</Subscript>” (M = Cd,Cu, Ni,and Zn) systems

Homogeneous fields of Sr_{4 − x} M _x Nb₂O₉ (M = Cd, Cu, Ni, or Zn) solid solutions were determined using powder X-ray diffraction. Phase fields were plotted proceeding from the tolerance factor t and electronegativity ratio $ \bar k_A /\bar k_B $ \bar k_A /\bar k_B with a satisfactory fit of experimental results. Thermogravimetry was used to establish the major kinetic laws of solid-phase synthesis (conversion, rate-controlling stage, and effective activation energy) in (4 − x)SrCO₃ + xMO + Nb₂O₅ powdery mixtures. Direct radiometry was used to determine ⁹⁰Sr, ⁶³Ni, and ⁶⁵Zn self-diffusion coefficients in solid solutions based on the Sr₄Nb₂O₉ phase. Electrical conductivity was measured as a function of temperature for all Sr₄Nb₂O₉-“M₄Nb₂O₉” samples. The conductivity of Sr_{4 − x} M _x Nb₂O₉ (M = Cd, Cu, Ni, or Zn) solid solutions has a mixed ion-electron character.     

On the Inversion Formula of the Fourier Transform of the Characteristic Function of Several Variables

An approach to the inversion formula for the Fourier transform is proposed in some special case of characteristic functions. Bibliography: 6 titles.     

On rhodium(III) chloride complexes with N,N-dimethylformamide

A prolonged storage of a solution of RhCl₃·nH₂O in N,N-dimethylformamide (DMF) at room temperature is attended by the consecutive formation of two precipitates, which mainly contain the [(CH₃)₂NH₂][RhCl₅(DMF)] complex (I) and the complex [RhCl₃(DMF)₃] (II) liberates. The addition of PPh₄Cl to an aqueous solution of complex I brings about the precipitation of [PPh₄][RhCl₄(H₂O)₂] (III). Complex II (a mixture of mer-and fac-isomers) can be obtained also by treatment of [RhCl₃(CH₃CN)₃] with DMF. In the course of the latter reaction, the formation of intermediate complex [RhCl₃(CH₃CN)₂(DMF)] (IV) is observed. Complexes I–IV are characterized by elemental analysis; complexes I, II, and IV are characterized by the IR and ¹H and ¹³C NMR spectra. The structures of III and IV are determined by X-ray diffraction analysis.     

Investigation of s, p, d-element Niobates and Their Solid Solution Formation Processes by Thermal Analysis

The binary and ternary systems M'O(M'CO₃)-Nb₂O₅ and M'O(M'CO₃)-MO-Nb₂O₅, where M'=Ca,Sr and Ba and M=Cu, Ni, Cd, Zn and Pb, were investigated by means of thermal analysis in the temperature range 20–1500°C. The boundaries of stability of the solid solutions Sr_2−xMe_xNb₂O₇,Sr_2−xM_xNb₂O₇, Sr_4−xM_xNb₂O₉ and Sr_6−xM_xNb₂O₁₁ were determined by means of X-ray diffraction, and IR and Raman spectroscopy. The possibility of prognostication of the phase fields of stable solid solutions by calculation from the diagrams of the ‘comparative electronegativity of atoms vs. tolerance factor’ was demonstrated. The kinetic parameters of the interactions in theSrCO₃+MO+Nb₂O₅ powder mixtures were established. This revised version was published online in August 2006 with corrections to the Cover Date.     

Investigations into beam monitors at the AEg ̄ IS experiment

Detailed diagnostic of antiproton beams at low energies is required for essentially all experiments at the Antiproton Decelerator (AD), but will be particularly important for the future Extra Low ENergy Antiproton ring (ELENA) and its keV beam lines to the different experiments. Many monitors have been successfully developed and operated at the AD, but in particular beam profile monitoring remains a challenge. A dedicated beam instrumentation and detector test stand has recently been setup at the AE \(\bar {g}\) IS experiment (Antimatter Experiment: Gravity, Interferometry, Spectroscopy). Located behind the actual experiment, it allows for parasitic use of the antiproton beam at different energies for testing and calibration. With the aim to explore and validate different candidate technologies for future low energy beam lines, as well as the downstream antihydrogen detector in AE \(\bar {g}\) IS, measurements have been carried out using Silicon strip and pixel detectors, a purpose-built secondary emission monitor and emulsions. Here, results from measurements and characterization of the different detector types with regard to their future use at the AD complex are presented.     

Asymptotic behavior of the dirichlet kernel of fourier sums with respect to a polygon

One investigates the behavior for R+ of the two-dimensional Dirichlet kernels, where W² is a fixed polygon. It is known that for any polygon, and , if the coordinates of all the vertices of W are rational numbers. It is shown that in the general case the second result is not true: there exists a triangle W such that.Translated from Zapiski Nauchnykh Seminarov Leningradskogo Otdeleniya Matematicheskogo Instituta im. V. A. Steklova AN SSSR, Vol. 149, pp. 142–149, 1986.The author is grateful to G. I. Natanson and V. P. Khavin for useful discussion.