Synthesis of nucleoside dimers bridged on ribose with a butadiynyl group

[reaction: see text] The nucleoside dimer linked by a butadiynediyl group at C-3'beta may serve as a building block for the preparation of backbone-modified oligonucleotides for DNA repair or mutation in functional genomics. We prepared this type of dimer by an Eglington or Sonogashira coupling reaction. The unsymmetrical dimer was synthesized by coupling the acetylene with the bromoacetylene. Only marginal cytotoxicity was detected for one of the dimers.     

Enhancement of the phosphorescence of organic luminophores upon interaction with a mercury trifunctional Lewis acid

The interaction of the trinuclear mercury(II) complex [(o-C(6)F(4)Hg)(3)] (1) and pyrene leads to the formation of the 1:1 adduct 1.pyrene. The crystal structure of this adduct reveals the existence of supramolecular stacks in which molecules of 1 and molecules of pyrene alternate along the infinite chains. Steady-state and time-resolved photoluminescence measurements indicate the occurrence of a heavy atom effect which results in red, green, and blue (RGB) phosphorescent emissions for 1.pyrene, 1.naphthalene, and 1.biphenyl, respectively.     

Ab initio study of the (5R)- and (5S)-TT pyrimidine h5(6-4) pyrimidone photoproducts. Implications on the design of new biologically relevant analogues

A computational study of a series of N(1)- and/or C(6)-alkyl-5,6-dihydrothymine diastereomers at theory levels up to MP4(SDTQ)/6-31G//HF/6-31G and MP2/6-311G//HF/6-31G has demonstrated the respective importance of the substituents at positions 1, 5, and 6 on the energetically favored conformation of each isomer. Results obtained both in the gas and condensed phase indicate that unsubstitution of the N(1)-position favors a half-chair conformation with the C(5) -and C(6)-substituents in the equatorial position. On the other hand, in the case of the (6S)-1,6-dimethyl-5,6-dihydrothymine, the C(6)-substituent adopts the axial position to minimize its van der Waals interactions with the N(1)-substituent. Furthermore, if the configuration at the C(5)-dihydrothymine position has no resultant influence on the total molecular free energy, when a pyrimidone substituent is introduced at the dihydrothymine C(6)-position, additional repulsive forces between the C(5)- and C(6)-substituents make the diaxially substituted half-chair conformation the most energetically favorable one. These results indicate that the observed C(6)-axially substituted conformation of the thymine-thymine pyrimidine h(5)(6-4) pyrimidone photoproducts is not necessarily induced by the macrocyclic structure. They also nicely explain the formation mechanism of these photoproduct derivatives, and allow the prediction of the conformation of new analogues.     

The preparation of carrier-free102Rh and102m Rh

Long-lived rhodium radionuclides were produced by the following reactions:¹⁰³Rh(n, 2n)^102(m)Rh;¹⁰³Rh(γ,xn)¹⁰⁰Rh,¹⁰¹Rh,^102(m)Rh;¹⁰⁴Pd(d, α)^102(m)Rh; Ru(d, n)⁹⁹Rh,^101(m)Rh,^102(m)Rh; and . The average cross-section of the¹⁰³Rh(n, 2n)¹⁰²Rh reaction in a fission neutron spectrum is about 0.75 mb. Irradiation of rhodium in the bremsstrahlung spectrum of 50 MeV electrons yielded a¹⁰²Rh activity of 0.11 μCi/g after 3 days at a power of 2 kW. The thick target yield of the reaction¹⁰⁴Pd(d, α)¹⁰²Rh was 0.002 μCi/μAh for 12 MeV deuterons. The thick target yield of the reaction Ru(d,xn)¹⁰²Rh was 0.05 μCi/μAh for 12 MeV deuterons and 4.8 μCi/μAh for 18 MeV deuterons. The best yield was obtained by deuteron bombardment of ruthenium. The chemical separation of carrier-free Rh radionuclides from deuteron-irradiated ruthenium is described, with a chemical yield better than 90%. The same procedure has also been applied for the isolation of¹⁰⁵Rh from neutron-irradiated ruthenium. γ-Ray spectra of⁹⁹Rh,^101(m)Rh and^102(m)Rh from deuteron-irradiated ruthenium and of¹⁰⁵Rh from neutron-irradiated ruthenium, taken with a Ge(Li) detector, are shown; a number of γ-rays, not reported in the literature, were observed. The γ-ray energies were determined with a precision of ca. 0.3–0.4 keV.     

Application of capillary electrophoresis for inorganic selenium speciation in the frame of high-level waste management

Capillary electrophoresis (CE) with direct UV detection is proposed for speciation of inorganic Se in high-level liquid waste. In this aim, the optimal conditions of measurements (pH, electrolyte buffer concentration) and the influence of nitrate excess on the quantitative determination of Se(IV) and Se(VI) were studied. Different electrolyte buffers were considered: carbonate, phosphate and citrate. It was found, that citrate buffer is the most suitable for the application under consideration. Under the chosen optimal conditions (20 mmol L(-1) citrate buffer, pH 2.5), calibration curves for Se(IV) and Se(VI) are linear in the concentration range 10(-4)-10(-3) mol L(-1). The detection limits are 4x10(-6 )for Se(IV) and 2x10(-5) for Se(VI). The accuracy of the procedure was checked by calculating the recovery by spiking simulation solutions. Relative standard deviation (S(r)) is less than 10%.     

Crystallographic/experimental electron density characterizations and reactions with nucleophiles of beta-enaminonitriles possessing a pyrrolobenzazepine core

In connection with a total synthesis of cephalotaxine (1a), we have examined the addition of various nucleophilic reagents to [ABC] subunits 2 and 7 possessing a pyrrolobenzazepine core. In fact, this reaction implicates invariably the carbonyl group of 2. Regarding the reaction of 7 with nucleophiles, the most striking aspect is the complete lack of reactivity of the enaminonitrile moiety. For instance, the condensation of 7 with methylmagnesium bromide involves exclusively the cleavage of the dioxole ring, yielding regioisomers 9 and 10. With the aim of understanding the unexpected reactivity of 2 and 7 toward nucleophiles, crystallographic studies of 2 and 7 and an experimental electron density determination of 7 were carried out. The marked reactivity of the carbonyl group of 2 was interpreted by invoking the weakness of the amide resonance, due to a pronounced delocalization of the N(9) lone pair over the enaminonitrile moiety. The electron density study of 7 reveals this electron delocalization along the enaminonitrile fragment, highlighted and quantified through the bond geometries, topological indicators, and atomic charges, a phenomenon that is responsible for the failure of the addition of nucleophilic species.     

Copper/Zinc Oxide Catalysts. Part XII. Solid Solution Formation in the CuO/ZnO System. X-Ray Powder Diffraction Study

Coordination compounds Zn(mal)(H₂O)₂ (ZMH) (mal=maleate anion (C₂H₂(CO₂)₂^2-)), Cu_0.06Zn_0.94(mal)(H₂O)₂ (ZCMH), Cu(mal)(H₂O) (CMH), and physical mixtures of CMH and ZMH were used as precursors for calcination experiments in air at 500 and 1000°C lasting 18 hours. The obtained oxides were investigated by X-ray powder diffraction technique. Calcination at 500°C yielded pure zincite phase (ZnO), tenorite phase (CuO), or their mixtures. The calcination of the Zn-rich sample ZCMH at 1000°C lead to zincite phase displaying a slightly lower cell volume than the pure zincite phase obtained from Zn-only containing precursor (ZMH). These results suggest that the assumed solid solution Cu_xZn_1–xO (x=0.01–0.02) exhibits a solubility limit lower than the copper content in the ZCMH precursor (6mol-%). On the other hand, the calcination of the Cu-rich samples at 1000°C, in the presence of Zn(II), yielded tenorite phase exhibiting cell parameters significantly different from those reported for the pure tenorite phase, due to the formation of Zn_0.03Cu_0.97O solid solutions. All these results are corroborated by intensity analysis of the diffraction peaks.     

Lipase-catalyzed production of short-chain acids terpenyl esters of interest to the food industry

The production of low molecular weight esters as flavor compounds by biotechnological processes has a potential interest for the food industry. The use of natural available substrates and enzymes is an essential part of the process design, because the products may obtain natural label. In this study, direct esterification of citronellol and geraniol with short-chain fatty acids catalyzed by free lipase from Mucor miehei was performed with high yields in n-hexane. The effects of the acid:alcohol ratio on the bioconversion rate of increasing chain length esters was investigated. To reach the optimum yield, substrates and enzyme concentration were determined. The inhibiting effects of acid are strongly attenuated by reducing the quantity of acid and increasing the amount of enzyme in media following the optimum values. Improvements have been made to increase the ester purity. The consumption of excess substrate by adding calculated amounts of acid gives a 10% yield enhancement, and leads to 100% pure terpenyl esters. The first steps to a scale-up application were attempted using a reactor that allowed us to produce ester quantities up to 100 cm³. Separation and purification of the products were treated with success, underlining the lipase stability and efficiency under the conditions of this study. The ability to recover the enzyme, and reusing it in bioconversions, plays a major role in reducing the cost of the overall process.     

The radical trap in atom transfer radical polymerization need not be thermodynamically stable. A study of the MoX(3)(PMe(3))(3) catalysts

The molybdenum(III) coordination complexes MoX(3)(PMe(3))(3) (X = Cl, Br, and I) are capable of controlling styrene polymerization under typical atom transfer radical polymerization (ATRP) conditions, in conjunction with 2-bromoethylbenzene (BEB) as an initiator. The process is accelerated by the presence of Al(OPr(i))(3) as a cocatalyst. Electrochemical and synthetic studies aimed at identifying the nature of the spin trap have been carried out. The cyclic voltammogram of MoX(3)(PMe(3))(3) (X = Cl, Br, I) shows partial reversibility (increasing in the order Cl < Br < I) for the one-electron oxidation wave. Addition of X(-) changes the voltammogram, indicating the formation of MoX(4)(PMe(3))(3) for X = Cl and Br. On the other hand, I(-) is more easily oxidized than the MoI(3)(PMe(3))(3) complex; thus, the putative MoI(4)(PMe(3))(3) complex is redox unstable. Electrochemical studies of MoI(3)(PMe(3))(3) in the presence of X(-) (X = Cl or Br) reveal the occurrence of facile halide-exchange processes, leading to the conclusion that the MoI(3)X(PMe(3))(3) products are also redox unstable. The oxidation of MoX(3)(PMe(3))(3) with (1)/(2)Br(2) yields MoX(3)Br(PMe(3))(3) (X = Cl, Br), whose molecular nature is confirmed by single-crystal X-ray analyses. On the other hand, the oxidation of MoI(3)(PMe(3))(3) by I(2) slowly yields a tetraiodomolybdate(III) salt of iodotrimethylphosphonium, [Me(3)PI][MoI(4)(PMe(3))(3)], as confirmed by an X-ray study. This product has no controlling ability in radical polymerization. The redox instability of MoI(3)X(PMe(3))(3) can be reconciled with its involvement as a radical trapping species in the MoI(3)(PMe(3))(3)-catalyzed ATRP, given the second-order nature of its decomposition rate.