Isolation of a new member of the ecdysteroid glycoside family: 2-deoxy-20-hydroxyecdysone 22-O-beta-D-glucopyranoside

A new ecdysteroid glycoside, 2-deoxy-20-hydroxyecdysone 22-O-beta-D-glucopyranoside, is isolated from the herb Silene italica ssp. nemoralis (Waldst. and Kit.) Nyman. The compound is purified with multistep chromatography, such as classical column chromatography on alumina and droplet countercurrent distribution. Also, it is expanded using twice low-pressure reversed-phase liquid column chromatography. Chromatography in four steps results in the purified 2-deoxy-20-hydroxyecdysone 22-O-beta-D-glucopyranoside. Two other ecdysteroids have also been separated, including the formerly identified integristerone A and 24(28)-dehydromakisterone A.     

Charge-transfer phenomena in novel,dual-component,sugar-based organogels

The synthesis of a new saccharide-based gelator (2) containing a donor moiety has been described. Gelation experiments of a dual-component gel consisting of a saccharide-based gelator bearing an acceptor group (1) and of 2 have been performed in a variety of organic solvents and water. Moreover, gelation tests at different molar ratios of 1 and 2 have been performed in water, octanol, and diphenyl ether. In these last two solvents a gel color change was observed, from colorless to yellow, upon cooling of the sample to room temperature. This phenomenon was further investigated by UV-visible spectroscopy, which revealed the presence of charge-transfer interactions in the gel, in octanol. Temperature-dependence UV spectroscopy confirmed that such interactions occur in the gel but not in the corresponding solution sample. Furthermore, T(gel) measurements show that dual-component gels of 1 and 2 present increased thermal stability at a 50:50 ratio of the two gelators, in dependence of the solvent. Transmission electron microscopy (TEM) images of the single-component gels in diphenyl ether revealed that they consist of a fibrous network, while the dual-component gel presents a novel, helical, fibrous-bundle structure.     

Flow injection chemiluminescence determination of hydrazine by oxidation with chlorinated isocyanurates

A rapid and sensitive flow injection chemiluminescence (CL) method is described for the determination of hydrazine based on the CL generated during its reaction with either sodium dichloroisocyanurate (SDCC) or trichloroisocyanuric acid (TCCA) in alkaline medium. The emission intensity is greatly enhanced if dichlorofluorescein (DCF) as sensitizer is present in the reaction medium. The presence of citrate prevents the precipitation of some cations in the reaction medium and also causes an enhancement in emission intensity. The effect of analytical and flow injection variables on these CL systems and determination of hydrazine are discussed. The optimum parameters for the determination of hydrazine were studied and were found to be the following: SDCC and TCCA both 1x10(-3) M; NaOH, 2x10(-1) M; DCF, 5x10(-6) M; citrate, 1x10(-3) M and flow rate, 3.8 ml min(-1). The optimized method yielded 3sigma detection limits of 2x10(-7) and 3x10(-7) M for hydrazine with SDCC and TCCA oxidants, respectively. The method is simple, fast, sensitive, and precise and was applied to the determination of hydrazine in water samples.     

A high precision spectrophotometric method for on-line shipboard seawater pH measurements: the automated marine pH sensor (AMpS)

Measurement strategies for understanding the oceanic CO(2) (carbon dioxide) system are moving towards in situ and ship of opportunity sampling techniques. Automated instrumentation with high accuracy and sampling frequencies will enable a greater understanding of the fluxes of marine carbon and lead to a more reliable constrain on the calculated uptake of anthropogenic CO(2) by the oceans. This paper describes the automated marine pH sensor (AMpS); new instrumentation and methodology for the determination of seawater pH using dual spectrophotometric measurements of sulfonephthalein indicator in a semi-continuous seawater stream. The pH values measured during a recent study in the Weddell Sea are used to illustrate the excellent properties of the AMpS. The method has an on-line precision of better than 0.001 pH units and an estimated accuracy of better than 0.004 pH units. The instrument is compact, portable and has a measurement frequency of 20 samples per hour. The instrument is ideally suitable for operation on ships of opportunity.     

Design and development of cyclohexane-based P,N-ligands for transition metal catalysis

[reaction: see text] A new class of cyclohexane-based P,N-ligands is readily obtained through aziridine ring opening with suitable phosphorus nucleophiles under acidic conditions. trans-1-Amino-2-diphenylphosphinocyclohexane is resolved with tartaric acid to give the final product in >99% ee. The new ligands show high stability toward oxidation at the phosphorus atom.     

Study of the structure of poly(methyl methacrylate) obtained in the presence of potassium hydride

Electrospray ionization mass spectrometry (ESI-MS) in positive- and negative-ion mode and multi-step tandem mass spectrometry (ESI-MS ( n) ) were selected for the determination of the structure of poly(methyl methacrylate) obtained using potassium hydride as initiator. Macromolecules with methoxy and methyl starting groups, i. e. those situated at the beginning of the polymer backbone, were observed in this case. No other differences in the chain structure were found in the polymer.     

Water in carbon nanotubes: adsorption isotherms and thermodynamic properties from molecular simulation

Grand canonical Monte Carlo simulations are performed to study the adsorption of water in single-walled (6:6), (8:8), (10:10), (12:12), and (20:20) carbon nanotubes in the 248-548 K temperature range. At room temperature the resulting adsorption isotherms in (10:10) and wider single-walled carbon nanotubes (SWCNs) are characterized by negligible water uptake at low pressures, sudden and complete pore filling once a threshold pressure is reached, and wide adsorption/desorption hysteresis loops. The width of the hysteresis loops decreases as pore diameter narrows and it becomes negligible for water adsorption in (8:8) and (6:6) SWCNs. Results for the isosteric heat of adsorption, density profiles along the pore axis and across the pore radii, order parameter across the pore radii, and x-ray diffraction patterns are presented. Layered structures are observed when the internal diameter of the nanotubes is commensurate to the establishment of a hydrogen-bonded network. The structure of water in (8:8) and (10:10) SWCNs is ordered when the temperature is 298 and 248 K, respectively. By simulating adsorption isotherms at various temperatures, the hysteresis critical temperature, e.g., the lowest temperature at which no hysteresis can be detected, is determined for water adsorbed in (20:20), (12:12), and (10:10) SWCNs. The hysteresis critical temperature is lower than the vapor-liquid critical temperature for bulk Simple Point Charge-Extended (SPCE) water model.     

Cell-permeable GPNA with appropriate backbone stereochemistry and spacing binds sequence-specifically to RNA

Guanidine-based peptide nucleic acid (GPNA) with a d-backbone configuration and alternate spacing binds sequence-specifically to RNA and is readily taken up by both human somatic and embryonic stem (ES) cells.     

PFGSE-NMR study of the self-diffusion of sucrose fatty acid monoesters in water

The micellization of pure monosubstituted sucrose fatty acid esters in water, namely sucrose octanoate, sucrose decanoate, sucrose laurate, sucrose dodec-5-cis-enoate, sucrose myristate, and sucrose palmitate, has been investigated by means of two NMR methods, pulsed field gradient spin-echo NMR (PFGSE-NMR), giving access to the self-diffusion coefficients of free molecules and micelles in solution, and the ERETIC method (electronic reference to access in vivo concentrations) for the measurement of concentrations by external calibration of a synthetic NMR signal. The early micellar regions and, when possible, the premicellar regions were investigated. By this method, we obtained the hydrodynamic radii of micelles, displaying a linear progression in relation to the chain length and an accurate determination of critical micellar concentration (CMC) for each sucrose ester. The effect of the regiochemistry of fatty chain grafting has been investigated, showing special behavior for 1'-O-sucrose palmitate.     

Numerical treatment discussion and ab initio computational reinvestigation of physisorption of molecular hydrogen on graphene

A numerical treatment suitable for the computational investigation of physisorption of molecular hydrogen on carbon nanostructures has not been sufficiently discussed. In this paper it is shown that results used as a reference are actually a product of poorly solved interactions and contaminated estimates with errors which would be of the order of 60%. Moreover, using ab initio molecular orbital theory, under the rigid monomer supermolecular approach, the physisorption energy of molecular hydrogen on graphene was reinvestigated. The graphene surface was modeled as a coronenelike (C(24)H(12)) graphene sheet. The basis set superposition error was corrected by means of the counterpoise method. The H(2)-H(2) and H(2)-benzene interactions were examined, under systematic combinations of basis sets and correlation methods, including the aug-cc-pVQZ basis set and the coupled cluster correlation method with single, double, and noniterative triple excitations, searching for a numerical treatment with a reasonable trade-off between efficiency and accuracy. Asymmetrical modeling strategies, using diffusion augmented basis sets with preference for the adsorbate, were found to be effective. Also local modeling strategies, using more complete basis sets for the nearest atoms to the adsorbate than for the rest of the substrate, were considered. The aug-cc-pVTZ basis set for the adsorbate and for the nearest atoms to the adsorbate and the cc-pVTZ basis set for the rest of the cluster-modeled graphene, at the second-order Moller-Plesset perturbation theory correlation level, was selected as reference treatment. It was found that the physisorption energy of molecular hydrogen on graphene would be of the order of 0.06 eV, which would be 25% less than what has been previously published, though it would be sufficient to permit the storage of hydrogen physisorbed on carbon. To our knowledge this would be the most realistic theoretical estimate of the mentioned energy to date.