The Electronic State of Flavoproteins: Investigations with Proton Electron–Nuclear Double Resonance

Electron–nuclear double resonance (ENDOR) spectroscopy provides useful information on hyperfine interactions between nuclear magnetic moments and the magnetic moment of an unpaired electron spin. Because the hyperfine coupling constant reacts quite sensitively to polarity changes in the direct vicinity of the nucleus under consideration, ENDOR spectroscopy can be favorably used for the detection of subtle protein–cofactor interactions. A number of pulsed ENDOR studies on flavoproteins have been published during the past few years; most of them were designed to characterize the flavin cofactor by means of its protonation state, or to detect individual protein–cofactor interactions. The aim of this study is to compare the pulsed ENDOR spectra from different flavoproteins in terms of variations of characteristic proton hyperfine values. The general concept is to observe limits of possible influences on the cofactor’s electronic state by surrounding amino acids. Furthermore, we compare ENDOR data obtained from in vivo experiments with in vitro data to emphasize the potential of the method for gaining molecular information in complex media.     

Eliciting and Developing Teachers' Conceptions of Random Processes in a Probability and Statistics Course

The purpose of this study is to examine prospective mathematics specialists' engagement in an instructional sequence designed to elicit and develop their understandings of random processes. The study was conducted with two different sections of a probability and statistics course for K-8 teachers. Thirty-two teachers participated. Video analyses within a collaborative course design were used to support a teaching experiment about teachers' conceptions of random processes. In particular, teachers were asked whether the outcomes of Rock-Paper-Scissors (RPS) are generated randomly or not, were presented with a definition for random selection, and were asked to come to a conclusion about RPS. Teachers struggled to reconcile the equality of winning outcomes for each player with the potential for human interference in the process of generating outcomes. Ultimately, teachers concluded the outcomes were not generated randomly, but encountered a variety of unexpected obstacles along the way.     

Synthesis of novel 1,4,7,10-tetraazacyclodecane-1,4,7,10-tetraacetic acid (DOTA) derivatives for chemoselective attachment to unprotected polyfunctionalized compounds

A convenient synthesis of novel bifunctional poly(amino carboxylate) chelating agents allowing chemoselective attachment to highly functionalized biomolecules is described. Based on the well known chelator 1,4,7,10-tetraazacyclodecane-1,4,7,10-tetraacetic acid (DOTA), we synthesized novel bifunctional chelating agents bearing additional functional groups by alkylating 1,4,7,10-tetraazacyclododecane (cyclen) with one equivalent of para-functionalized alkyl 2-bromophenyl-acetate and three equivalents of tert-butyl 2-bromoacetate. The resulting compounds, which contain an additional carbonyl or alkyne functionality, allow site specific labeling of appropriately functionalized unprotected biomolecules in a rapid manner via click reactions. This was demonstrated by the attachment of our new DOTA derivatives to the somatostatin analogue Tyr3-octreotate by chemoselective oxime ligation and CuI-catalyzed azide-alkyne cycloaddition. Initial biodistribution studies in mice with the radiometalated compound demonstrated the applicability of the described DOTA conjugation.     

Zur Kenntnis der Rheometrie organischer Gläser

Zusammenfassung Die vorliegende Abhandlung besch?ftigt sich mit der Erforschung der Zusammenh?nge zwischen Flie?eigenschaften und Temperatur. Nach eingehender Diskussion der verschiedenen Flie?kurventypen werden die Flie?kurvendiagramme von 4 Polyvinylazetaten besprochen und der Begriff der Verformungsleistung entwickelt. Die Abh?ngigkeit der Verformungsleistung von der Temperatur kann durch eine ?hnliche Gleichung dargestellt werden, wie sie von Andrade und Sheppard für die Temperaturabh?ngigkeit der Viskosit?t angegeben wurde. Dadurch wird eine allgemeinere Auswertung von Flie?kurvendiagrammen m?glich. Die Verfasser danken dem Direktor der Reichsforschungsanstalt für Kleintierzucht, Herrn Prof. Dr. A. Koch, für sein wohlwollendes und stets f?rderndes Interesse an der Aufdeckung der mitgeteilten Zusammenh?nge. Wir danken der Firma Dr. Alexander Wacker, München, für die überlassung der verschiedenen Polyvinylazetate sowie Herrn Generaldirektor Wilke, Mitteldeutsche Spinnhütte G. m. b. H., Celle, für die Bereitstellung eines Ultrathermostaten. Unser Dank gilt ferner der Deutschen Forschungsgemeinschaft, die ein Konsistometer zur Verfügung stellte.     

Absorptionsspektrographische Studien an l-Ascorbinsäure I

Ohne ZusammenfassungMit 9 Abbildungen.Vgl. hierzuE. Schauenstein, Chemie56, 156 (1943) bzw.R. Czmiel, W. Halden undE. Schauenstein, Naturwiss.30, 586 (1942). — Eine Zusammenfassung der vorliegenden Arbeit erschien bereits in dieser Zeitschrift [Mh. Chem.78, 415 (1948)] als vorläufige Mitteilung.     

Detection of Copper Deposition on Anodes of Over-Discharged Lithium Ion Cells by GD-OES Depth Profiling

A method based on glow discharge optical emission spectroscopy (GD-OES) depth profiling is developed to detect copper deposition on graphite electrodes for the first time. Commercial 18650 cells with graphite anodes were subject to Cu dissolution by over-discharge to 0 V. On a first approach, the depth profiles for Cu show significant differences for over-discharged cells compared to a baseline graphite electrode from cells discharged to the end-of-discharge voltage. An accumulation of Cu is found on the anode surface by GD-OES, which is consistent with SEM and EDX. The trend of the total Cu amount is compared with ICP-OES measurements.     

Non-bonded sulphur-sulphur interactions in 3,5-dithiaheptane and 3,6-dithiaoctane

Enthalpies of combustion and vaporization at 298.15 K have been measured for 3,5-dithiaheptane and 3,6-dithiaoctane. Enthalpies of formation at 298.15 K have been derived for the compounds in the liquid and gaseous states. The results are:

     

18.

Structure property relationships in the ATi₂O₄ (A=Na, Ca) family of reduced titanates     

Margret J. Geselbracht  Ann S. Erickson  John E. Greedan  Matthew W. Stoltzfus  Patrick M. Woodward 《Journal of solid state chemistry》2006,179(11):3489-3499

Reduced titanates in the ATi₂O₄ (A=Li, Mg) spinel family exhibit a variety of interesting electronic and magnetic properties, most notably superconductivity in the mixed-valence spinel, Li_1+xTi_2−xO₄. The sodium and calcium analogs, NaTi₂O₄ and CaTi₂O₄, each differ in structure, the main features of which are double rutile-type chains composed of edge-sharing TiO₆ octahedra. We report for the first time, the properties and band structures of these two materials. XANES spectroscopy at the Ti K-edge was used to probe the titanium valence. The absorption edge position and the pre-edge spectral features observed in the XANES data confirm the assignment of Ti³⁺ in CaTi₂O₄ and mixed-valence Ti³⁺/Ti⁴⁺ in NaTi₂O₄. Temperature-dependent resistivity and magnetic susceptibility studies are consistent with the classification of both NaTi₂O₄ and CaTi₂O₄ as small band-gap semiconductors, although changes in the high-temperature magnetic susceptibility of CaTi₂O₄ suggest a possible insulator-metal transition near 700 K. Band structure calculations agree with the observed electronic properties of these materials and indicate that while Ti-Ti bonding is of minimal importance in NaTi₂O₄, the titanium atoms in CaTi₂O₄ are weakly dimerized at room temperature.     

19.

Rapid and high-yield solution-phase synthesis of DOTA-Tyr-octreotide and DOTA-Tyr-octreotate using unprotected DOTA     

Margret Schottelius  Markus SchwaigerHans-Jürgen Wester 《Tetrahedron letters》2003,44(11):2393-2396

An improved method for the solution-phase derivatization of Tyr³-Lys⁵(Dde)-octreotide (TOC(Dde)) and Tyr³-Lys⁵(Dde)-octreotate (TATE(Dde)) with the macrocyclic chelator DOTA (1,4,7,10-tetraazacyclododecane-N′,N″,N?,N?-tetraacetic acid) has been developed. The fully protected parent peptides were assembled via solid-phase peptide synthesis (SPPS) using Fmoc-strategy. After cleavage from the solid support, disulfide bond formation was carried out using H₂O₂. Both TOC(Dde) and TATE(Dde) were successfully coupled with DOTA in the presence of NHS, EDCI and DIPEA in a water/DMF solvent system. Yields of the coupling reaction were >98% within only 2 h with no detectable formation of sideproducts. This method for the preparation of DOTATOC, DOTATATE and other DOTA-peptide conjugates is therefore a rapid and economic alternative to the currently used methods.     

20.

Superconductivity and Phase Separation in NaxNbO2 (x < 1)     

Maria A. Rzeznik  Margret J. Geselbracht  Mark S. Thompson  Angelica M. Stacy 《Angewandte Chemie (International ed. in English)》1993,32(2):254-255

     

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	$\text{ΔH}{}_{\mathrm{f}}{}^{\mathrm{o}}\text{(l)/kJ mol}{}^{\mathrm{?1}}$	$\text{ΔH}{}_{\mathrm{f}}{}^{\mathrm{o}}\text{(g)/kJ mol}{}^{\mathrm{?1}}$
3,5-Dithiaheptane	?116.0 ± 1.5	?65.2 ± 1.5
3,6-Dithiaoctane	?142.5 ± 1.5	?83.0 ± 1.5

Structure property relationships in the ATi2O4 (A=Na, Ca) family of reduced titanates

Reduced titanates in the ATi₂O₄ (A=Li, Mg) spinel family exhibit a variety of interesting electronic and magnetic properties, most notably superconductivity in the mixed-valence spinel, Li_1+xTi_2−xO₄. The sodium and calcium analogs, NaTi₂O₄ and CaTi₂O₄, each differ in structure, the main features of which are double rutile-type chains composed of edge-sharing TiO₆ octahedra. We report for the first time, the properties and band structures of these two materials. XANES spectroscopy at the Ti K-edge was used to probe the titanium valence. The absorption edge position and the pre-edge spectral features observed in the XANES data confirm the assignment of Ti³⁺ in CaTi₂O₄ and mixed-valence Ti³⁺/Ti⁴⁺ in NaTi₂O₄. Temperature-dependent resistivity and magnetic susceptibility studies are consistent with the classification of both NaTi₂O₄ and CaTi₂O₄ as small band-gap semiconductors, although changes in the high-temperature magnetic susceptibility of CaTi₂O₄ suggest a possible insulator-metal transition near 700 K. Band structure calculations agree with the observed electronic properties of these materials and indicate that while Ti-Ti bonding is of minimal importance in NaTi₂O₄, the titanium atoms in CaTi₂O₄ are weakly dimerized at room temperature.     

Rapid and high-yield solution-phase synthesis of DOTA-Tyr-octreotide and DOTA-Tyr-octreotate using unprotected DOTA

An improved method for the solution-phase derivatization of Tyr³-Lys⁵(Dde)-octreotide (TOC(Dde)) and Tyr³-Lys⁵(Dde)-octreotate (TATE(Dde)) with the macrocyclic chelator DOTA (1,4,7,10-tetraazacyclododecane-N′,N″,N?,N?-tetraacetic acid) has been developed. The fully protected parent peptides were assembled via solid-phase peptide synthesis (SPPS) using Fmoc-strategy. After cleavage from the solid support, disulfide bond formation was carried out using H₂O₂. Both TOC(Dde) and TATE(Dde) were successfully coupled with DOTA in the presence of NHS, EDCI and DIPEA in a water/DMF solvent system. Yields of the coupling reaction were >98% within only 2 h with no detectable formation of sideproducts. This method for the preparation of DOTATOC, DOTATATE and other DOTA-peptide conjugates is therefore a rapid and economic alternative to the currently used methods.