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101.
Battaglia TM Dunn EE Lilley MD Holloway J Dable BK Marquardt BJ Booksh KS 《The Analyst》2004,129(7):602-606
The development of a field portable fiber optic Raman system modified from commercially available components that can operate remotely on battery power and withstand the corrosive environment of the hydrothermal vents is discussed. The Raman system is designed for continuous monitoring in the deep-sea environment. A 785 nm diode laser was used in conjunction with a sapphire ball fiber optic Raman probe, single board computer, and a CCD detector. Using the system at ambient conditions the detection limits of SO(4)(2-), CO(3)(2-) and NO(3)(-) were determined to be approximately 0.11, 0.36 and 0.12 g l(-1) respectively. Mimicking the cold conditions of the sea floor by placing the equipment in a refrigerator yielded slightly worse detection limits of approximately 0.16 g l(-1) for SO(4)(-2) and 0.20 g l(-1) for NO(3)(-). Addition of minerals commonly found in vent fluid plumes also decreased the detection limits to approximately 0.33 and 0.34 g l(-1) respectively for SO(4)(-2) and NO(3)(-). 相似文献
102.
Jörg Senn-Bilfinger John R. Ferguson Keith W. Lumbard Karl Zech Peter J. Zimmermann 《Tetrahedron letters》2006,47(19):3321-3323
Glucuronide conjugates of Soraprazan (BY359), a potent novel anti-secretory drug (currently in Phase II clinical trials), were not directly accessible synthetically. This was due to the relative instability of Soraprazan under the harsh Lewis acid conditions employed in popular glucuronidation methodologies and a lack of reactivity under alternative, Koenigs-Knorr, coupling conditions. We have now devised a successful synthesis using the novel N-acetylated Soraprazan to access the required glucuronide metabolites on gram scale. Coupling of this novel aglycone with methyl 1-O-trichloroacetimidoyl-2,3,5-tri-O-isobutyryl-α-d-glucopyran-uronate in the presence of trimethylsilyl trifluoromethanesulfonate (TMSOTf) gave the protected glucuronide intermediates. A one-pot two-step deprotection involving hydrolysis of the ester functionalities and removal of the N-acetyl group with alkaline hydrazine delivered the title compounds in satisfactory yield. 相似文献
103.
Petra Hoffman Siegfried Hünig Leonhard Walz Karl Peters Hans-Georg von Schnering 《Tetrahedron》1995,51(48):13197-13216
Azo compounds 1 and 3 containing a CC-double bond in a parallel but distant position are quatemized by Me3OBF4 to 1,MeBF4 and 3,MeBF4, whereas MeI produces the cage compounds 2,HX and 4,HX. These [3+2] cycloadducts also are quantitatively formed from 1,MeBF4 and 3,MeBF4 with catalytic amounts of azo compounds. Intermolecular [3+2] cycloadditions occur with a mixture of DBH (5) or DBO (8), MeI and a variety of alkenes (→ HI) salts of (6, 7, 9 — 12). The intermediate azomethineimines, if stabilized by a fluorenylidene group, can be isolated (20, 22,24), but not, however, in the presence of a close parallel CC-bond (25 → 26). 相似文献
104.
Zusammenfassung Zur Bestimmung von Coffein in Erfrischungsgetränken (Cola), Kaffee und Tee wird die Differential-Pulsvoltammetrie verwendet. Bei dieser Methode wird Coffein bei pH 1,2 an einer glasartigen Kohlenstoffelektrode oxydiert und quantitativ bestimmt. Die voltammetrisch ermittelten Analysenergebnisse werden mit den Resultaten der Flüssigkeistchromatographie verglichen. Um einen weiteren Einblick in den Reaktionsverlauf zu erhalten, wurde Coffein anodisch bei pH 1,2, 2,3 und pH 6 oxydiert. Die Reaktionsprodukte wurden kathodisch durch Differential-Pulspolarographie identifiziert.
Voltammetric determination of caffeine in coffee, tea, and soft drinks
Summary Differential pulse voltammetry is used for the determination of caffeine in soft drinks, coffee, and tea. In this method caffeine is oxidised at a glassy carbon electrode at pH 1.2 and determined quantitatively. The voltammetric results are compared with those found by HPLC. To elucidate the mechanism of the electrode processes the reaction products were produced by anodic oxidation of caffeine at pH 1.2, 2.3 und pH 6 and then identified by cathodic differential pulse polarography.相似文献
105.
Eleven human hair samples were taken from the Chinese residents of Hong Kong for the study of hair trace elemental level and
environmental exposures. Absolute neutron activation analysis and Ge(Li) gamma-ray spectrometry were applied in the determination
of the trace elemental level. All results are reported in parts per million except for sulfur and oxygen which are reported
in percent. The trace element content of hair from a drug addict was found to be considerably different from other sampled
people. Comparison of the normal concentrations of the trace elements of the Chinese residents of Hong Kong was made with
those from people of various other national, socio-cultural and environmental backgrounds. It was found that together with
a few other trace elements, Ni, Sr, Zr and Hg content of the Chinese Residents of Hong Kong show a higher level than those
of the other sampled people. 相似文献
106.
Pd(0) was generated at preselected sites on an electrochemically addressable chip and then utilized to effect a Heck reaction. The Pd(0) was confined to the preselected electrodes with the use of allylmethyl carbonate. Unlike most mediated electrochemical reactions, the electrolysis in this case was not used to convert a stoichiometric process into a catalytic one by recycling the metal. Instead, the unique environment of the chip was used to interfere with a catalytic process to make it stoichiometric. This was done to gain spatial control over the reaction. The development of a strategy for conducting Pd(0)-catalyzed reactions on the chips should greatly expand the synthetic chemistry available for building chip-based libraries. 相似文献
107.
A simple and inexpensive equipment for the optical resolution of enantiomers (and separation of diastereomers) on triacetylcellulose in ethanol at elevated pressure is described. It involves a closed circuit of solvent (pump—column—detector—pump) allowing a continuous chromatography up to 16 cycles without stopping the flow or handling fractions.This useful and versatile method permitting also the determination of enantiomeric purities is illustrated by several examples of centro-, axial- and planarchiral arenes and metallocenes.Herrn Prof. Dr.U. Schmidt, Stuttgart, zum 60. Geburtstag gewidmet. 相似文献
108.
Zusammenfassung Die Stammsubstanzen des Lignins gehören der Gruppe der p-Hydroxyzimtalkohole an. Sie werden durch wäßrige Mineralsäure polymerisiert. Um das Wesen dieser Reaktion kennenzulernen, wurde der Zimtalkohol selbst in verdünnter wäßriger Lösung der Wirkung von Säure ausgesetzt. Er bildet ein Dimeres der Konstitution VIII, die durch Abbau und Synthese bewiesen wurde. Es ist anzynehmen, daß die Polymerisation der p-Hydroxyzimtalkohole nacl, einem Schema verläuft, von dem die Dimerisation des Zimtalkohols die erste Stufe ist.Institut für die Chemie dei Holzes und der PolysaccharideKollegenA. Wacek in alter Freundschaft zum 60. Geburtstag gewidmet.K. Freudenberg. 相似文献
109.
Wolfgang Hnle Walter Schmettow Karl Peters Jen‐Hui Chang Hans Georg von Schnering 《无机化学与普通化学杂志》2004,630(12):1858-1862
The novel ternary polyphosphides M4P21I (M = K, Rb) have been synthesized from the elements in single crystalline form, representing further examples for the formation of mixed crystals between simple salts and binary phosphides. They form as ruby‐red platelets and dark‐red prisms, respectively, and are only slightly sensitive to moisture and oxygen. The compounds are isotypic (Ccmm (no 63); Z = 4; oP104; K4P21I: a = 12.853Å; b = 21.795Å; c = 9.748Å; 1168 hkl, R = 0.033; Rb4P21I: a = 13.281Å; b = 21.868Å; c = 9.771Å; 777 hkl, R = 0.053) and feature corrugated 2D networks formed from two different types of polymerized P7 units. The networks form large cavities filled by M+ and I‐ ions. Zigzag chains of condensed trigonal M6 prisms, centered by the I‐ anions, separate the polyphosphide nets. The mean homoatomic P‐P bond length (d = 2.216Å) corresponds to a P‐P single bond. However, the individual P‐P distances vary with position and function (2.126 ‐ 2.247Å) and these are compared with those of the isolated P21‐3 anion. 相似文献
110.
The effect of surfactants on surface instabilities of thin liquid film flow on a rotating disk was studied at different flow rates Q (0.5相似文献