Raman spectroscopic determination of inosine nucleoside in nucleotides

Raman spectroscopy has been applied to the analytical determination of inosine nucleoside in nucleotides. Spectral characteristics of aqueous solutions of lithium, potassium and magnesium salts of inosine 5'-monophosphoric acid are described. Two characteristic bands located at 1553 and 1593 cm(-1) whose frequencies are not sensitive either to the nucleotide concentration or to alkaline cations present in the medium, have been used for this purpose. The concentration ranges over which the method was applicable were 2.5-80 and 11.5-80 mg ml(-1) of inosine using the 1553 and 1593 cm(-1) bands, respectively, with relative standard deviations of 2.5 and 4.0% and detection limits of 0.25 and 1.16% (w/w). As the above bands are not generated by the standard nucleobases, this method can be applied to the quantitative determination of inosine in transfer ribonucleic acids.     

Chimie organométallique du niobium VIII. Etude détaillée de la réaction d'acétyléniques perfluorés avec (η5C5H5)2NbH3: Mise en evídence de la coupure de liaison C-F,de la formation de liaison Nb-F et de la reduction du niobium. Structure cristalline d'un dérivé niobiacyclopentadiène

Hexafluorobutyne (CF₃CCCF₃ = Hfb) reacts with Cp₂NbH₃ (Cp = η⁵-C₅H₅) affording five new complexes I–V, whose structures have been studied by mass,

Ir, ESR and NMR spectroscopy. The X-ray study of II shows the presence of a planar NbC₄ ring Nb—C(1): 2.25(5); C(1)—C(2): 1.31(7); C(2)—C(3): 1.53(8); C(3)—(4): 1.34(7); C(4)—Nb: 2.23(5) Å. With trifluoropropyne (CF₃CCH = tfp), only the analog of III, i.e. Cp₂NbFf(tfpH), has been isolated.     

The index of a plane curve and green’s formula

In this paper we compute the line integral of a complex function on a rectifiable cycle homologous to zero obtaining a Green’s formula with multiplicities that involves the of the function and the index of the cycle. We consider this formula in several settings and we obtain a sharp version in terms of the Lebesgue integrability properties of the partial derivatives of the function. This result depends on the proven fact that the index of a rectifiable cycle is square integrable with respect to the planar Lebesgue measure. The work of both authors is partially supported by grants 2000SGR-00059, 2001SGR 00172 of Generalitat de Catalunya and BFM 2002-04072-C02-02 of Ministerio de Ciencia y Tecnologia     

Direct EPR detection of transient and continuous wave signals at 2.5 GHz

Direct detection of free induction decays and electron spin echoes, and the recording of echo-detected EPR spectra and electron spin echo envelope modulation patterns at a microwave frequency of 2.5 GHz is demonstrated. This corresponds to the measurement of the transverse magnetization in the laboratory frame, rather than in the rotating frame as usually done by down-converting the signal (homodyne detection). An oscilloscope with a 6-GHz analog bandwidth, a sampling rate of 20 GigaSamples per second, and a trigger frequency of 5 GHz for the edge trigger and 750 MHz for the advanced trigger, is used in these experiments. For signal averaging a 3-GHz microwave clock divider has been developed to synchronize the oscilloscope with the frequency of the EPR signal. Moreover, direct detection of continuous wave EPR signals at 2.5 GHz is described.     

A theoretical study of the hydrogen bond donor capability and co-operative effects in the hydrogen bond complexes of the diaza-aromatic betacarbolines

In this work, we present a quantum mechanical investigation on the hydrogen bond interactions of N(9)-methyl-9H-pyrido[3,4-b]indole, MBC, and N(2)-methyl-9H-pyrido[3,4-b]indole, BCA, with different hydrogen bond donors. Thus, it has been analysed the influence that the hydrogen bond donor strength and the co-operative effect of the increasing number of donor molecules have on the shape of the potential energy surfaces versus the N···H distances, r(N–H). To rationalize the nature of the interactions, the Bader theory has been applied and the characteristics of the bond critical points analysed. The results show that two different hydrogen bond complexes can be formed depending on the donor capabilities or the number of donor molecules included in the calculations. The topological parameters from the Bader theory are used to justify the statement that the analysed interactions can be classified as weak or partially covalent hydrogen bond interactions, respectively. As experimentally observed, weak hydrogen bond donors form weak hydrogen bond complexes, called HBC. Upon the increase of the donor strength the N···H proton is shifted nearest to the nitrogen atom giving rise to the observation of a stronger hydrogen bond complex, the proton transfer complex, PTC. The most outstanding result of these studies is the fact that the formation of the PTC can also be managed just by changing the number of donor molecules, that is, by a co-operative effect of the hydrogen bonds.     

Direct electrochemistry of cytochrome c on nanotextured diamond surface

Nanotextured diamond surfaces with geometrical properties close to protein dimensions were used for the realization of direct electron transfer of cytochrome c (cyt c) without any covalent bonding. The peroxidase activity of native and denatured cyt c was also investigated. Cyclic voltammograms of native cyt c show quasi-reversible electron transfer reactions, while no heme redox activity is detected for denatured cyt c. Unfolding (denaturation) of cyt c can be achieved in the presence of hydrogen peroxide. Partially or fully denatured cyt c showed higher peroxidase activity than native cyt c. This is because denatured cyt c loses its tertiary structure and hydrogen peroxide is easier to access the heme redox center. The apparent Michaelis–Menten constant K_m for native and denatured cyt c has been determined to be 0.23 mM and 0.08 mM.     

Systemic Risk and Stochastic Games with Delay

We propose a model of inter-bank lending and borrowing which takes into account clearing debt obligations. The evolution of log-monetary reserves of banks is described by coupled diffusions driven by controls with delay in their drifts. Banks are minimizing their finite-horizon objective functions which take into account a quadratic cost for lending or borrowing and a linear incentive to borrow if the reserve is low or lend if the reserve is high relative to the average capitalization of the system. As such, our problem is a finite-player linear–quadratic stochastic differential game with delay. An open-loop Nash equilibrium is obtained using a system of fully coupled forward and advanced-backward stochastic differential equations. We then describe how the delay affects liquidity and systemic risk characterized by a large number of defaults. We also derive a closed-loop Nash equilibrium using a Hamilton–Jacobi–Bellman partial differential equation approach.     

Reversible Double C?H Bond Activation of Linear and Cyclic Ethers To Form Iridium Carbenes

The double C? H bond activation of a series of linear and cyclic ethers by the iridium complex [Tp^tol′Ir(C₆H₅)(N₂)] ( 2? N₂), which features a cyclometalated hydrotris(3‐p‐tolylpyrazol‐1‐yl)borate ligand (Tp^tol′) coordinated in a κ⁴‐N,N′,N′′,C manner, has been studied. Two methyl ethers, namely, Me₂O and MeOtBu, along with diethyl ether and the cyclic ethers tetrahydrofuran, tetrahydropyran (THP), and 1,4‐dioxane have been investigated with formation in every case of the corresponding hydride carbene complexes 3 – 8 , which are stabilized by κ⁴‐coordination of the ancillary Tp^tol′ ligand. Five of the compounds have been structurally authenticated by X‐ray crystallography. A remarkable feature of these rearrangements is the reversibility of the double C? H bond activation of Me₂O, MeOtBu, Et₂O, and THP. This has permitted catalytic deuterium incorporation into the methyl groups of the two methyl ethers, although in a rather inefficient manner (for synthetic purposes). Although possible in all cases, C? C coupling by migratory insertion of the carbene into the Ir? C σ bond of the metalated linkage has only been observed for complex 8 that contains a cyclic carbene that results from α,α‐C? H activation of 1,4‐dioxane. Computational studies on the formation of iridium carbenes are also reported, which show a role for metalated Tp ligands in the double C? H activation and account for the reversibility of the reaction in terms of the relative stability of the reagents and the products of the reaction.     

Synthesis, solid-state structure, and bonding analysis of the beryllocenes [Be(C5Me4H)2], [Be(C5Me5)2], and [Be(C5Me5)(C5Me4H)

The beryllocenes [Be(C(5)Me(4)H)(2)] (1), [Be(C(5)Me(5))(2)] (2), and [Be(C(5)Me(5))(C(5)Me(4)H)] (3) have been prepared from BeCl(2) and the appropriate KCp' reagent in toluene/diethyl ether solvent mixtures. The synthesis of 1 is facile (20 degrees C, overnight), but generation of decamethylberyllocene 2 demands high temperatures (ca. 115 degrees C) and extended reaction times (3-4 days). The mixed-ring beryllocene 3 is obtained when the known [(eta(5)-C(5)Me(5))BeCl] is allowed to react with K[C(5)Me(4)H], once more under somewhat forcing conditions (115 degrees C, 36 h). The structures of the three metallocenes have been determined by low-temperature X-ray studies. Both 1 and 3 present eta5/eta1 geometries of the slip-sandwich type, whereas 2 exhibits an almost regular, ferrocene-like, sandwich structure. In the mixed-ring compound 3, C(5)Me(5) is centrally bound to beryllium and the eta(1)-C(5)Me(4)H ring bonds to the metal through the unique CH carbon atom. This is also the binding mode of the eta(1)-ring of 1. To analyze the nature of the bonding in these molecules, theoretical calculations at different levels of theory have been performed on compounds 2 and 3, and a comparison with the bonding in [Be(C(5)H(5))(2)] has been made. As for the latter molecule, energy differences between the eta5/eta5 and the eta5/eta1 structures of 2 are very small, being of the order of a few kcal mol(-1). Constrained space orbital variations (CSOV) calculations show that the covalent character in the bonding is larger for [Be(C(5)Me(5))(2)] than for [Be(C(5)H(5))(2)] due to larger charge delocalization and to increased polarizability of the C(5)Me(5) fragment.