Rhodium-Catalyzed Enantioselective Synthesis,Structures, and Properties of Single and Double Azahelicene-Like Molecules

The enantioselective synthesis of aza[6] and [7]helicene-like molecules have been achieved by the cationic rhodium(I)/axially chiral biaryl bisphosphine complex-catalyzed intramolecular [2+2+2] cycloaddition of cyanodiynes. This protocol was successfully applied to the diastereo- and enantioselective synthesis of an S-shaped double aza[6]helicene-like molecule with a high ee value of 89 %. Although no epimerization and racemization were observed in the double carbo[6]helicene-like molecule at 80 °C, epimerization and racemization of the double aza[6]helicene-like molecule proceeded at 80 °C. This double aza[6]helicene-like molecule showed good fluorescent quantum yields and chiroptical responses under both neutral and acidic conditions.     

Improvement of chemical analysis of antibiotics. IX. A simple method for residual tetracyclines analysis in honey using a tandem cartridge clean-up system

A simple, rapid and precise analytical method for the residual tetracyclines in honey has been established using a tandem cartridge clean-up system (prepacked reversed-phase and ion-exchange cartridges) followed by high-performance liquid chromatography. The recoveries of oxytetracycline (OTC), tetracycline (TC), chlortetracycline (CTC) and doxycycline (DC) from honey spiked at a level of 1.0 ppm are 87.1, 85.3, 98.0 and 99.0%, respectively, with coefficients of variation of 1.1-3.9%. The detection limits in honey are 0.02 ppm for OTC and TC, and 0.05 ppm for CTC and DC, respectively. The time required for the analysis of four samples is only 1 h.     

Improvement of chemical analysis of antibiotics. X. Determination of eight tetracyclines using thin-layer and high-performance liquid chromatography

Analytical methods for eight tetracyclines (TCs) were established using silica gel high-performance thin-layer chromatography (HPTLC), reversed-phase thin-layer chromatography (RP-TLC) and high-performance liquid chromatography (HPLC). Good separations of eight TCs were obtained using chloroform-methanol-5% disodium ethylenediaminetetraacetate solution (65:20:5) (lower layer) and methanol acetonitrile 0.5 M oxalic acid solution (1:1:4) (pH 3.0) on silica gel HPTLC and C8 TLC plates, respectively. A combination of HPTLC and RP-TLC made possible the identification of the eight TCs. Each calibration graph was linear between 0.1 and 1.0 microgram using UV densitometry except for rolitetracycline. For detection reagents, the diazonium salts including Fast Violet B gave variously coloured spots with the eight TCs and good sensitivities were obtained except with minocycline. In HPLC, the simultaneous analysis of the eight TCs on a C8 column was possible using methanol-acetonitrile-0.01 M oxalic acid solution (1:1.5:7) adjusted to pH 3.0 as the mobile phase. A linear relationship was obtained between 1.0 and 10 ng using the usual sample preparation except for rolitetracycline. The direct determination of rolitetracycline was possible using tetrahydrofuran, dimethyl sulphoxide and the mobile phase as solvents for preparation of the sample. For the determination of residual rolitetracycline, it was effective to measure the amount of rolitetracycline as tetracycline by HPLC, HPTLC and RP-TLC after conversion of rolitetracycline to tetracycline by incubating for 5 min in methanol at 50 degrees C.     

On the interpretation of solubilization results obtained from semi-equilibrium dialysis experiments

The interpretation of intramicellar solubilization data obtained from semi-equilibrium dialysis (SED) experiments is described, and methods are presented for determining equilibrium constants for the solubilization of organic species by aqueous surfactant solutions as well as activity coefficients of both the organic solute and the surfactant within the micelle. The solubilization equilibrium constant of an organic solute in an aqueous micellar solution (K) is defined as the ratio of the mole fraction of organic solute in the micellar pseudophase (X) to the concentration of the unsolubilized monomeric organic solute in the aqueous phase (c ₀). Expressions compatible with the Gibbs-Duhem equation are used to represent the concentration dependence of activity coefficients of both the solubilizate and surfactant in the micellar pseudophase; the analysis leads to calculated values of the concentrations of free and intramicellar surfactant and organic solute in both compartments of the equilibrium dialysis cell. Solubilization equilibrium constants for many amphiphiles are well correlated by the simple expressionK=K ₀(1-BX)², whereB is an empirical constant andK ₀ is the limiting value ofK asX approaches 0.     

On the kinetic and thermodynamic reactivity of lithium di(alkyl)amidozincate bases in directed ortho metalation

Sequential reaction of HTMP (= 2,2,6,6-tetramethylpiperidine) with nBuLi and Et2Zn affords unsolvated polymer chains of EtZn(micro-Et)(micro-TMP)Li 6. The scope of this reagent in directed ortho metalation (DoM) chemistry has been tested by its reaction with N,N-diisopropylnaphthamide in THF to give EtZn(micro-C10H6C(O)NiPr2-2)2Li.2THF 7. Data reveal that 6 has undergone reaction with 2 equiv of aromatic tertiary amide and imply that it exhibits dual alkyl/amido basicity. DFT calculations reveal that direct alkyl basicity is kinetically disfavored and instead point to a stepwise mechanism whereby 6 acts as an amido base, liberating HTMP during the first DoM event. Re-coordination of the amine at lithium then incurs the elimination of EtH. Reaction of the resulting alkyl(amido)(arylamido)zincate with a second equivalent of N,N-diisopropylnaphthamide eliminates HTMP and affords 7. Both DoM steps involve the exhibition of amido basicity and each reveals a low kinetic barrier to reaction. Understanding of this reaction sequence is tested by treating 6 with N,N-diisopropylbenzamide in THF. On the basis of theory and experiment, the presence of THF solvent (in place of stronger Lewis bases) combined with the use of a sterically less congested aromatic amide is expected to encourage threefold, stepwise reaction. Isolation and characterization of the resulting tripodal zincate Zn(micro-C6H4C(O)NiPr2-2)3Li.THF 8 bears this out and suggests a significant new level of control in zincate-induced DoM chemistry through the combination of experiment and DFT studies.     

Solubilization of oleyl alcohol by pure and mixtures of surfactants

The solubilization behavior of oleyl alcohol by pure and mixtures of surfactants systems have been studied in terms of the maximum additive concentration (MAC), the solubilizing power, and the particle sizes of micelles with or without oleyl alcohol. The surfactants used are amphoteric (N,N-dimethyl-N-lauroyl lysine, DMLL; N,N,N-trimethyl-N-lauroyl lysine, TMLL; N,N-dimethyl-N-(carboxymethyl)-lauryl ammonium, DMCL), anionic (sodium dodecyl sulfate, SDS) and nonionic (alkyl polyoxyethylene ethers).The maximum additive concentration of oleyl alcohol by pure surfactants is larger by nonionic surfactants than by others.For a nonionic surfactant system mixed with DMLL, the mixing effect of surfactant on the increase in the MAC is not recognized. While, for DMLL mixed with SDS, the MAC becomes larger than that by pure surfactants. This may be attributed to the fact that the large micellar size will result in increasing the maximum additive concentration.     

Facile Insertion of Carbon Dioxide into Cu2(μ‐H) Dinuclear Units Supported by Tetraphosphine Ligands

Reactions of meso‐bis[(diphenylphosphinomethyl)phenylphosphino]methane (dpmppm) with Cu^I species in the presence of NaBH₄ afforded di‐ and tetranuclear copper hydride complexes, [Cu₂(μ‐H)(μ‐dpmppm)₂]X ( 1 ) and [Cu₄(μ‐H)₂(μ₄‐H)(μ‐dpmppm)₂]X ( 2 ) (X=BF₄, PF₆). Complex 1 undergoes facile insertion of CO₂ (1 atm) at room temperature, leading to a formate‐bridged dicopper complex [Cu₂(μ‐HCOO)(dpmppm)₂]X ( 3 ). The experimental and DFT theoretical studies clearly demonstrate that CO₂ insertion into the Cu₂(μ‐H) unit occurred with the flexible dicopper platform. Complex 2 also undergoes CO₂ insertion to give a formate‐bridged complex, [Cu₄(μ‐HCOO)₃(dpmppm)₂]X, during which the square Cu₄ framework opened up to a linear tetranuclear chain.     

Transcendence of Certain Reciprocal Sums of Linear Recurrences

 Suppose that {R _n } _n ⩾ 0 is a sequence of integers satisfying a binary linear recurrence relation with suitable conditions. We prove the transcendency of the numbers

Trypanocidal terpenoids from Laurus nobilis L

Trypanocidal constituents of dried leaves of Laurus nobilis L. (Lauraceae) were examined. Activity-guided fractionation of the methanol extract resulted in the isolation of two guaianolides, dehydrocostus lactone (1) and zaluzanin D (2), and a new p-menthane hydroperoxide, (1R,4S)-1-hydroperoxy-p-menth-2-en-8-ol acetate (3). The minimum lethal concentrations of these compounds against epimastigotes of Trypanosoma cruzi were 6.3, 2.5, and 1.4 microM, respectively.