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101.
Christer Albano William Dunn Ulf Edlund Erik Johansson Bo Nordén Michael Sjöström Svante Wold 《Analytica chimica acta》1978,103(4):429-443
Problems of pattern recognition in chemistry and other subjects can be divided conveniently into four different types depending on the level of scope of the problem.(1) Classification into one of a number of defined classes. As an example blood samples taken from persons known to be either controls or welders are considered. The problem is whether trace element concentrations in these samples contain information on whether or not a person is a welder.(2) Level 1 plus the possibility that an object is an outlier, i.e. does not belong to any of the defined classes. As an example, the üse of 13C-n.m.r. data to decide whether 2-substituted norbornanes have the exo or endo structure is discussed. (2A) Level 2, asymmetric. This situation occurs when one class does not have a systematic structure, but another class is homogeneous and can be described by a level 2 model. This occurs in the classification of materials or compounds as good or bad, active or inactive, and in binary classifications. As an example the use of trace element data to classify steel samples as having good or poor properties of strength is discussed.(3) Level 2 plus the ability to relate the variables measured to external properties of continuous character. As an example, the classification of a series of chemical compounds as β -receptor blockers, β -receptor stimulants, or neither, on the basis of their structural variables is discussed. In addition, relations between these structural variables and the measured biological activity are sought within each of the two classes.(4) Level 3 with the difference that several external property variables in the objects are measured. It may be desirable to use variables of the objects both for classification and for relations to several property variables: such examples are numerous in analytical chemistry. 相似文献
102.
E. Asmus 《Fresenius' Journal of Analytical Chemistry》1965,210(6):401-411
Zusammenfassung Die Methode der kontinuierlichen Variationen nach OstromisslensKy-JOB lÄ\t sich mit sehr gutem Erfolg zur Ermittlung der Zusammensetzung von Verbindungen heranziehen, die sich beim Zusammengie\en von Lösungen als Niederschlag bilden. Im Gegensatz zu Komplexen in Lösungen, bei denen in der Praxis nur einfache Zusammensetzungen vorkommen und daher für x
max in der Regel nur die Werte 0,50, 0,67 und eventuell 0,75 auftreten, können bei NiederschlÄgen für die Abszisse des Maximums der Job-Kurve auch zahlreiche von den genannten Zahlen abweichende Werte reell beobachtet werden.
Für die Durchführung dieser Arbeit wurden dankenswerterweise Forschungsmittel aus dem ERP-Sondervermögen bereitgestellt. — Dem Verbande der Chemischen Industrie und der Deutschen Forschungsgemeinschaft, die diese Arbeit unterstützt haben, danken wir bestens. 相似文献
Summary The method of continuous variations according to Ostromisslensky Job can be successfully employed for the determination of the composition of precipitates formed by mixing of solutions. With complexes in solutions only simple compositions are encountered and generally only the values 0.50, 0.67, and possibly 0.75 are found for the abscissa of the maximum of the Job curve. In contrast to that numerous deviations from these values are observed in case of precipitates.
Für die Durchführung dieser Arbeit wurden dankenswerterweise Forschungsmittel aus dem ERP-Sondervermögen bereitgestellt. — Dem Verbande der Chemischen Industrie und der Deutschen Forschungsgemeinschaft, die diese Arbeit unterstützt haben, danken wir bestens. 相似文献
103.
Zusammenfassung Es wird eine neue, sehr empfindliche optische Methode zur Bestimmung von Nicotin und Pyridin im Tabakrauch beschrieben.
Für die Durchführung dieser Arbeit wurden dankenswerterweise Forschungsmittel aus dem ERP-Sondervermögen bereitgestellt.Dem Verbande der chemischen Industrie und der Deutschen Forschungsgemeinschaft, die diese Arbeit unterstützt haben, danken wir bestens. 相似文献
Summary A new, very sensitive, optical method is described for the determination of nicotine and pyridine in tobacco smoke.
Für die Durchführung dieser Arbeit wurden dankenswerterweise Forschungsmittel aus dem ERP-Sondervermögen bereitgestellt.Dem Verbande der chemischen Industrie und der Deutschen Forschungsgemeinschaft, die diese Arbeit unterstützt haben, danken wir bestens. 相似文献
104.
105.
Edward Szlyk Stanislaw Biniak Erik Larsen 《Journal of Solid State Electrochemistry》2001,5(3):221-226
The electrochemical properties and catalytic activity of a Co(II) complex with the optically active Schiff base derived from
(1R,2R)-(–)-cyclohexanediamine and salicylaldehyde have been studied in non-aqueous solutions. When dissolved in deoxygenated non-aqueous
solutions, the complex exhibits reversible redox properties for the Co(II)/Co(III) couple. Electrochemical reduction of oxygen
and oxidation of cobalt(II) was observed on cyclic voltammograms of solutions containing both dioxygen and the Schiff base-cobalt(II)
complex. An anodically formed film on a platinum electrode, studied by means of X-ray photoelectron spectroscopy, revealed
the presence of the oxidized Co(III) species. Cyclic voltammetry of oxygenated solutions examined after a period of time indicates
an electrochemical activity of coordinated superoxo/peroxo species in the 0.7–1.1 V potential range. In the presence of 4-methyl-1-cyclohexene
the cyclic voltammetry curves reveal changes similar to those caused by the removal of oxygen. The GC-MS technique was used
to identify some of the products formed by the catalytic oxidation of cyclohexene and 4-methyl-1-cyclohexene.
Electronic Publication 相似文献
106.
Clarissa C. Forneris Seyma Ozturk Erik J. Sorensen Mohammad R. Seyedsayamdost 《Tetrahedron》2018,74(26):3231-3237
The biosynthesis of glycopeptide antibiotics (GPAs) has been an active area of research for decades. But, insights into the activity of the cytochrome P450 enzymes required for installing the aromatic crosslinks, which form their cup-shaped topologies and render GPAs bioactive, have only recently emerged. Presently, little is known about the substrate scope and promiscuity of the P450 enzymes. Herein, we report that OxyBvan, the P450 enzyme that installs the first crosslink in vancomycin biosynthesis, is capable of catalyzing the formation of its conventional C-O-D bis-aryl ether bond in non-natural substrates and, furthermore, the formation of a second, novel linkage when D-Trp is incorporated at position 6. HR-MS/MS and isotope labeling studies indicate the second crosslink is formed between rings A and B, resulting in a novel GPA-type scaffold. OxyB is also capable of installing two crosslinks in kistamicin- and complestatin-like substrate peptides. These findings highlight the utility of OxyBvan in creating crosslinked GPA derivatives and provide clues regarding the unusual biosynthesis of kistamicin. 相似文献
107.
Alejandro R. Engelmann Mario A. Natiello Mikael Hghede Erik Engdahl Erkki Brndas 《International journal of quantum chemistry》1987,31(5):841-845
In the present article we show how the bound states of the Coulomb potential may be associated with resonances that occur when this potential is perturbed by a barrier potential. The main idea is to trace the bound states on successive switching on of the barrier perturbation. It is found that those bound states that are localized inside the barrier are highly sensitive to variation with respect to the barrier height, whereas those that are localized outside are less sensitive. However, there are certain intervals for the barrier height when the role of being “a state localized inside the barrier” is shifted from one bound state to another. The result can be pictured as a “relay race,” where the “deliveries of the baton” are carried out over corresponding avoided crossings. The baton is ultimately handed over to a shape-type resonance state. 相似文献
108.
109.
Simplest Monodentate Imidazole Stabilization of the oxy‐Tyrosinase Cu2O2 Core: Phenolate Hydroxylation through a CuIII Intermediate 下载免费PDF全文
Dr. Linus Chiang William Keown Dr. Cooper Citek Dr. Erik C. Wasinger Prof. T. Daniel P. Stack 《Angewandte Chemie (International ed. in English)》2016,55(35):10453-10457
Tyrosinases are ubiquitous binuclear copper enzymes that oxygenate to CuII2O2 cores bonded by three histidine Nτ‐imidazoles per Cu center. Synthetic monodentate imidazole‐bonded CuII2O2 species self‐assemble in a near quantitative manner at ?125 °C, but Nπ‐ligation has been required. Herein, we disclose the syntheses and reactivity of three Nτ‐imidazole bonded CuII2O2 species at solution temperatures of ?145 °C, which was achieved using a eutectic mixture of THF and 2‐MeTHF. The addition of anionic phenolates affords a CuIII2O2 species, where the bonded phenolates hydroxylate to catecholates in high yields. Similar CuIII2O2 intermediates are not observed using Nπ‐bonded CuII2O2 species, hinting that Nτ‐imidazole ligation, conserved in all characterized Ty, has functional advantage beyond active‐site flexibility. Substrate accessibility to the oxygenated Cu2O2 core and stabilization of a high oxidation state of the copper centers are suggested from these minimalistic models. 相似文献
110.
Brauer CS Craddock MB Kilian J Grumstrup EM Orilall MC Mo Y Gao J Leopold KR 《The journal of physical chemistry. A》2006,110(33):10025-10034
The Stark effect has been observed in the rotational spectra of several gas-phase amine-hydrogen halide complexes and the following electric dipole moments have been determined: H(3)(15)N-H(35)Cl (4.05865 +/- 0.00095 D), (CH(3))(3)(15)N-H(35)Cl (7.128 +/- 0.012 D), H(3)(15)N-H(79)Br (4.2577 +/- 0.0022 D), and (CH(3))(3)(15)N-H(79)Br (8.397 +/- 0.014 D). Calculations of the binding energies and electric dipole moments for the full set of complexes R(n)()(CH(3))(3)(-)(n)()N-HX (n = 0-3; X = F, Cl, Br) at the MP2/aug-cc-pVDZ level are also reported. The block localized wave function (BLW) energy decomposition method has been used to partition the binding energies into contributions from electrostatic, exchange, distortion, polarization, and charge-transfer terms. Similarly, the calculated dipole moments have been decomposed into distortion, polarization, and charge-transfer components. The complexes studied range from hydrogen-bonded systems to proton-transferred ion pairs, and the total interaction energies vary from 7 to 17 kcal/mol across the series. The individual energy components show a much wider variation than this, but cancellation of terms accounts for the relatively narrow range of net binding energies. For both the hydrogen-bonded complexes and the proton-transferred ion pairs, the electrostatic and exchange terms have magnitudes that increase with the degree of proton transfer but are of opposite sign, leaving most of the net stabilization to arise from polarization and charge transfer. In all of the systems studied, the polarization terms contribute the most to the induced dipole moment, followed by smaller but still significant contributions from charge transfer. A significant contribution to the induced moment of the ion pairs also arises from distortion of the HX monomer. 相似文献