Mass fragmentation and structure of siphonaxanthin,siphonein and derivatives

High resolution mass spectrometry has been employed to establish the structural formulae of the unique carotenoid pigment siphonaxanthin, its natural ester, siphonein and several derivatives. Siphonaxanthin exhibits a fragmentation reaction that is unusual among carotenoid pigments, namely, the elimination of carbon dioxide, observed as [M - CO₂] and [M - (CO₂ + H₂O)]. This reaction involves the migration of an oxygen atom. Siphonaxanthol, a partially hydrogenated siphonaxanthin, exhibits a similar reaction involving the elimination of carbon monoxide and formaldehyde. From the fragmentation of derivatives of siphonaxanthin, such as the triacetate, the dimethyl ether and siphonaxanthol, and also from the fragmentation of related pigments, such as loroxanthin and fucoxanthin, the unique structural units responsible for the elimination of the carbon dioxide and carbon monoxide have been identified.     

Synthesis of functionalized oxacalix[4]arenes

Tetranitrooxacalix[4]arenes are generated in high yield by the room-temperature S(N)Ar reaction of 1,3-dihydroxybenzenes with 1,5-difluoro-2,4-dinitrobenzene. The reaction is tolerant to a range of functionality on the nucleophilic component, including hydroxyl-substitution at the 2- and 5-positions, which yields previously unknown 26,28- and 5,17-dihydroxyoxacalix[4]arenes.     

Excess molar volumes and isothermal vapor-liquid equilibrium in the binary system 1,1,1-trichloroethane with 1-chlorobutane and with pyridine at 25°C

Densities and vapor-liquid equilibrium were determined for 1-chlorobutane and pyridine with 1,1,1-trichloroethane at 25°C. From the experimental results, excess molal volumes and excess molar Gibbs energies were calculated. Information could be obtained about the possible interactions between the components of both binary systems. The Prigogine-Flory-Patterson theory was applied to calculate excess molar volumes. Liquid activity coefficients were calculated and correlated with different expressions existing in the literature.     

Eine Methode zur Bestimmung der elektrophoretischen Wanderungsgeschwindigkeit sehr kleiner kolloider Teilchen

Summary The mass transfer of colloid particles in an electric field can be measured with high accuracy by the Hittorf-method with automatic force compensation.

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Zusammenfassung Es wird eine Apparatur beschrieben, mit der der Massentransport kolloider Teilchen unter Wirkung eines elektrischen Feldes durch elektronische Kraftkompensation registriert werden kann.

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Mit 3 Abbildungen     

A geometric computing method for nonlinear optimal regulator problems with singular arcs

A computing algorithm, based on the geometry of certain reachable sets, is presented for fixed terminal time optimal regular problems having differential equations \(\dot x = f(x ,u , t)\) . Admissible controls must be measurable and have values in a setU, which must be compact, but need not be convex. Functionsf(x, u, t) andf _x (x, u, t) must be continuous and Lipschitz inx andu, but existence off _u (x, u, t) or second derivatives is not required. The algorithm is based on taking a sequence of nonlinear steps, each of which linearizes \(\dot x = f(x ,u , t)\) in state only, about a current nominal control and trajectory. Small perturbations are assured by keeping the perturbed controlclose to the nominal control. In each nonlinear step, a regulator problem,linear in state, is solved by a convexity method of Barr and Gilbert (Refs. 1–2), which is undeterred by the possibility of singular arcs. The resulting control function is substituted into the original nonlinear differential equations, producing an improved trajectory. Convergence of the algorithm is not proved, but demonstrated by a computing example, known to be singular. In addition, procedures are described for choosing parameters in the algorithm and for testing for theplausibility of convergence.     

Au nanoparticle-enhanced surface plasmon resonance sensing of biocatalytic transformations

N-(3-Aminopropyl)-N'-methyl-4,4'-bipyridinium is coupled to tiopronin-capped Au nanoparticles (diameter ca. 2 nm) to yield methyl(aminopropyl)viologen-functionalized Au nanoparticles (MPAV(2+)-Au nanoparticles). In situ electrochemical surface plasmon resonance (SPR) measurements are used to follow the electrochemical deposition of the bipyridinium radical cation modified Au nanoparticles on an Au-coated glass surface and the reoxidation and dissolution of the bipyridinium radical cation film. The MPAV(2+)-functionalized Au nanoparticles are also employed for the amplified SPR detection of NAD(+) and NADH cofactors. By SPR monitoring the partial biocatalyzed dissolution of the bipyridinium radical cation film in the presence of diaphorase (DP) NAD(+) is detected in the concentration range of 1x10(-4) M to 2x10(-3) M. Similarly, the diaphorase-mediated formation of the bipyridinium radical cation film on the Au-coated glass surface by the reduction of the MPAV(2+)-functionalized Au nanoparticles by NADH is used for the amplified SPR detection of NADH in the concentration range of 1x10(-4) M to 1x10(-3) M.     

Magnetoswitchable controlled hydrophilicity/hydrophobicity of electrode surfaces using alkyl-chain-functionalized magnetic particles: application for switchable electrochemistry

Magnetic nanoparticles consisting of undecanoate-capped magnetite (average diameter approximately 4.5 nm; saturated magnetization, M(s), 38.5 emu g(-1)) are used to control and switch the hydrophobic or hydrophilic properties of the electrode surface. A two-phase system consisting of an aqueous buffer solution and a toluene phase that includes the suspended capped magnetic nanoparticles is used to control the interfacial properties of the electrode surface. The magnetic attraction of the functionalized particles to the electrode by means of an external magnet yields a hydrophobic interface that acts as an insulating layer, prohibiting interfacial electron transfer. The retraction of the magnetic particles from the electrode to the upper toluene phase by means of the external magnet generates a hydrophilic electrode that reveals effective interfacial electron transfer. The electron-transfer resistance and double-layer capacitance of the electrode surface upon the attraction and retraction of the functionalized magnetic particles to and from the electrode, respectively, by means of the external magnet were probed by Faradaic impedance spectroscopy (R(et) = 170 Omega and C(dl) = 40 microF sm(-2) in the hydrophilic state of the electrode and R(et) = 22 k Omega and C(dl) = 0.5 microF sm(-2) in the hydrophobic state of the interface). The magnetoswitchable control of the interface enables magnetic switching of the bioelectrocatalytic oxidation of glucose in the presence of glucose oxidase and ferrocene dicarboxylic acid to "ON" and "OFF" states.     

The role of spectral selectivity in fluorescence detection for liquid chromatography

The use of a cut-off filter has been compared with a monochromator for emission energy selection in the fluorescence detector used in the analysis of environmental samples for polycyclic aromatic hydrocarbons by liquid chromatography. The use of a cut-off filter can provide greater sensitivity for compounds that are well separated by the chromatography. However, samples that contain a large number of compounds often result in overlapping peaks, and for such samples, it has been found that the spectral selectivity of monochromatic emission selection reduces the interference due to compounds eluting near the compounds of analytical interest. This spectral selectivity results in greater sensitivity and a smaller quantitation error in the analysis of these complex samples.