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1.
Starch belongs to the polyglucan group. This type of polysaccharide shows a broad β-relaxation process in dielectric spectra at low temperatures, which has its molecular origin in orientational motions of sugar rings via glucosidic linkages. This chain dynamic was investigated for α(1,4)-linked starch oligomers with well-defined chain lengths of 2, 3, 4, 6, and 7 anhydroglucose units (AGUs) and for α(1,4)-polyglucans with average degrees of polymerization of 5, 10, 56, 70, and so forth (up to 3000; calculated from the mean molecular weight). The activation energy (Ea) of the segmental chain motion was lowest for dimeric maltose (Ea = 49.4 ± 1.3 kJ/mol), and this was followed by passage through a maximum at a degree of polymerization of 6 (Ea = 60.8 ± 1.8 kJ/mol). Subsequently, Ea leveled off at a value of about 52 ± 1.5 kJ/mol for chains containing more than 100 repeating units. The results were compared with the values of cellulose-like oligomers and polymers bearing a β(1,4)-linkage. Interestingly, the shape of the Ea dependency on the chain length of the molecules was qualitatively the same for both systems, whereas quantitatively the starch-like substances generally showed higher Ea values. Additionally, and for comparison, three cyclodextrins were measured by dielectric relaxation spectroscopy. The ringlike molecules, with 6, 7, and 8 α(1,4)-linked AGUs, showed moderately different types of dielectric spectra. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 188–197, 2004 相似文献
2.
A. Schaufuß P. Roßbach I. Uhlig R. Szargan 《Analytical and bioanalytical chemistry》1997,358(1-2):262-265
The systems galena/2-mercaptobenzothiazole (MBT) and pyrite/MBT have been studied using synchrotron radiation excited photoelectron spectroscopy (SRXPS). The chemisorption of MBT and the multilayer formation of 2,2′-dithiobis(benzothiazole) (BBTD) are evidenced by additional structures, observed beside the substrate signals, in the S2p-spectra of cleaved mineral surfaces after adsorption of MBT. The amount of the complex remains constant at concentrations as high as 10–5 mol/L whereas the amount of BBTD increases. From the dependence of the adsorbate intensities on the excitation energy the conclusion can be drawn that an overlayer of BBTD on a chemisorbed layer of MBT is formed. The very weak adsorption of MBT on pyrite in alkaline solutions may explain the selective flotation of galena from pyrite in alkaline media. 相似文献
3.
Semi-insulating electrical properties of undoped inp after heat treatment in a phosphorus atmosphere 总被引:1,自引:0,他引:1
D. Hofmann G. Müller N. Streckfuß 《Applied Physics A: Materials Science & Processing》1989,48(4):315-319
Nominally undoped InP wafers have been annealed in a phosphorus atmosphere under a pressure of about 5 bar at temperatures of 900 °C for about 80 h. It was found that the electrical properties of the samples changed considerably after this treatment. A room temperature resistivity of up to 2×107cm (semi-insulating behaviour) was obtained in the bulk of the samples. The resistivity finally obtained depends on the starting carrier concentration of the untreated samples. The Hall coefficient and Hall mobility have been measured up to 600 °C. The results can be interpreted in terms of a deep electronic level (E
A=0.63 ... 0.65 eV below the conduction band). The Hall coefficient was always found to be negative resulting in a Hall mobility of 1.4 to 4.9×103 cm2/Vs. The highest resistivity in nominally undoped bulk InP so far reported in the literature [1] was =3.6 × 105cm. Therefore, this paper demonstrates for the first time that a really semi-insulating behaviour of >107 cm can be achieved for bulk InP with the purity of nominally undoped material (1015 to 1016cm–3). 相似文献
4.
Dr. H. Demel Dipl.-Ing H. J. Grießer Prof. Dr. K. Hummel 《Colloid and polymer science》1977,255(11):1131-1132
Ohne ZusammenfassungMit 1 Abbildung und 1 Tabelle 相似文献
5.
Let Z be a centrally symmetric polygon with integer side lengths. We answer the following two questions:
- When is the associated discriminantal hyperplane arrangementfree in the sense of Saito and Terao?
- When areall of the tilings of Z by unit rhombicoherent in the sense of Billera and Sturmfels?
6.
7.
The "epimerisation" of UDP-GlcNAc to ManNAc, the first step in the biosynthesis of sialic acids, is catalyzed by UDP-GlcNAc 2-epimerase. In this paper we report the synthesis of transition state based inhibitors of this enzyme. To mimic the assumed first transition state of this reaction (TS 1), we designed and synthesized the novel UDP-exo-glycal derivatives 1-4. We also report herein the synthesis of 5 and 6, the first C-glycosidic derivatives of 2-acetamidoglucal, and the synthesis of the ketosides 7 and 8, which were designed as bis-substrate analogue and bis- product analogue, respectively, to mimic the second step of the reaction via the assumed second transition state TS 2. 相似文献
8.
K. Greßmann 《Mikrochimica acta》1963,51(4):782-783
Zusammenfassung Durch Tüpfeln auf Chromatographiepapier, das mit Brucin, Benzidin und Phosphorsäure imprägniert wurde, läßt sich Nitrit empfindlieh und spezifisch nachweisen. 20 ng Nitrit können neben Nitrat und anderen Anionen festgestellt werden.
Summary Nitrite can be detected sensitively and specifically by spotting on Chromatograph paper impregnated with brucine, benzidine and phosphoric acid. It is possible to detect 20g nitrite in the presence of nitrate and other anions.
Résumé On peut rechercher les nitrites d'une manière sensible et spécifique sur les taches du papier chromatographique et qui a été imprégné de brucine, de benzidine et d'acide phosphorique. On peut déceler 20g de nitrite en présence de nitrates et d'autres ions A-.相似文献
9.
Zusammenfassung Die Herstellung eines Reagenspapiers wird beschrieben, mit dessen Hilfe die Identifizierung oxydierender Anionen [Nitrit, Hypochlorit, Chromat, Bromat, Hexacyanoferrat(III), Peroxydisulfat, Jodat, Chlorat und Nitrat ] durch einen einfachen Tüpfeltest möglich ist.
Summary The preparation of a reagent is described with whose aid it is possible to identify oxidant anions through a simple spot test. The anions are: nitrite, hypochlorite, chromate, bromate, hexacyanoferrate (III), peroxodisulfate, iodate, chlorate, nitrate.
Résumé On décrit la préparation d'un papier-réactif permettant l'identification des anions oxydants (nitrite, hypochlorite, chromate, bromate, ferricyanure, peroxydisulfurique, iodate, chlorate et nitrate) par une réaction à la touche simple.相似文献
10.
Dr.-Ing. K. P. Großkurth 《Colloid and polymer science》1981,259(2):163-170
Zusammenfassung Im vorfibrillaren Stadium besitzt die Crazematerie eine in Verformungsrichtung deformierte Netzwerkstruktur, die sich bei Polystyrol und Styrol-Acrylnitril-Copolymerisat elektronenoptisch an Oberflächenabdrücken sauerstoffionengeätzter Proben nachweisen läßt. Während die durchschnittlichen Globulitverformungen zumeist deutlich unterhalb von 50% liegen, werden partiell Spitzenwerte von bis zu 300% erreicht. Am Beispiel des Polystyrols verdeutlichen quantitative Strukturvergleiche mit warmgerecktem Material, daß die molekulare Beweglichkeit während des Crazewachstums und der Schulter-Hals-Verstreckung derjenigen entspricht, die für thermisch aktiviertes Material oberhalb der Glastemperatur charakteristisch ist.Mit 7 Abbildungen und 2 Tabellen 相似文献