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  • Chemistry  (5)
  • Acetylcholine receptor  (1)
  • Polymer and Materials Science
  • 1975-1979  (6)
  • 1
    ISSN: 0044-2313
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Contributions to the Thermal Behaviour of Sulfates. III. The Behaviour of CdSO4 at High TemperatureThe behaviour of CdSO4 was studied by means of high temperature Guinier photographs in the temperature range of 20 to 960°C. Except N-CdSO4 which is the thermodynamically stable modification at STP, there are 3 high temperature modifications (M, H1 and H2-CdSO4) of which only metastable M-CdSO4 can be obtained kineticly stable at room temperature. The lattice constants and the structure type of H1- and H2-CdSO4 were determined. The structure of H1-CdSO4 is closely related with that of N-CuSO4 but in difference of N-CuSO4 it has a superlattice. H1-CdSO4 crystallizes orthorhombic with a325°C = 17.80 Å, b325°C = 7.35 Å, c325°C = 4.84 Å, Z = 8.H2-CdSO4 crystallizes hexagonal with a850°C = 5.01 Å, c850°C = 7.64 Å, Z = 2 in a modified NaKSO4 structure type (space group P 3m 1) with Cd2+ only in the Na+ positions. The temperatur and sequence of transitions as well as the thermal expansion of N- and M-CdSO4 was determined
    Notes: Mit Heizguinieraufnahmen wurde das Verhalten von CdSO4 im Temperaturbereich von 25-960°C untersucht. Außer der bei Raumtemperatur thermodynamisch stabilen Modifikation (N-CdSO4) existieren 3 Hochtemperaturmodifikationen (M, H1 und H2-CdSO4), von denen nur das metastabile M-CdSO4 bei Raumtemperatur kinetisch stabil zu erhalten ist. Metrik und Strukturtyp von H1- und H2-CdSO4 wurden bestimmt. H1-CdSO4 ist mit N-CuSO4 strukturverwandt, besitzt jedoch eine Überstruktur. Es kristallisiert orthorhombisch mit a325°C = 17,80 Å, b325°C = 7,35 Å, c325°C = 4,84 Å, Z = 8. H2-CdSO4 kristallisiert hexagonal mit a850°C = 5,01 Å, c850°C = 7,64 Å, Z = 2 in einem modifizierten NaKSO4-Typ (RG: P 3m 1); Cd2+ nur auf Na+-Punktlagen. Temperatur und Verlauf der Umwandlungen sowie die thermische Dilatation von N- und M-CdSO4 wurden bestimmt.
    Additional Material: 4 Ill.
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  • 2
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: 2D NMR spectra have been measured at variable temperatures between -100°C and +110°C in a sample of melt crystallized deuterated polyethylene (PE). The line shape could be decomposed into a central part originating from deuterons in the amorphous regions and outer parts from crystalline regions of PE. The “NMR crystallinity” determined from this separation was 72% in agreement with the X-ray crystallinity of 74%. Changes of the crystalline NMR line shape were interperted in terms of oscillations around the chain axis, the r.m.s. oscillation amplitude varying from 5° at 40°C to 12° at 110°C. The central part of the NMR line shape indicates the existence of a “narrow” and a “medium” component due to different motional processes in the amorphous regions.
    Additional Material: 7 Ill.
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  • 3
    ISSN: 0044-2313
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Contributions to the Thermal Behaviour of Sulfates. II. On the Thermal Dehydration of ZnSO4 · 7 H2O and the Effect of High Temperature upon Anhydrous ZnSO4The dehydration of ZnSO4 · 7 H2O and effect of high temperature upon unhydrous ZnSO4 was examined by means of continous high temperature Guinier photographs. On heating in air ZnSO4 · 7 H2O decomposes stepwise to ZnSO4 · 6 H2O, to an unknown hydrate, to the monohydrate and finally to N—ZnSO4, which is the thermodynamically stable modification at S.T.P. At about 700°C a reversible transformation to H-ZnSO4 can be observed which can start from N—ZnSO4 or H-ZnSO4, proceeds to the oxide sulfate Zn3O(SO4)2 and finally to ZnO.ZnSO4 · 6 H2O crystallizes monoclinically in the hexahydrite structure with a25°C = 9.981 Å, b25°C = 7.250 Å, c25°C = 24.280 Å, β25°C = 98.45°, Z = 8, space group: C 2/c. Cubic H-ZnSO4 is the first A2+B6+O4 compound of H-Cristobalit structure; probable space group F 43 m with a700°C = 7.18 Å, Z =4, N-Zn3O(SO4)2 is monoclinic probable space group B 2 with a25°c=13.987 Å, b25°c=6.706 Å, c25°c =7.379 Å β25°c=90.69°, Z=4, Above 420°C N-Zn3(SO4)2 becomes orthorhombic where at first of all H′-Zn3O(SO4)2 which has a reversible transformation point to H-Zn3O(SO4)2 at 655°C is formed. The probable space group of H-Zn2O(SO4)2 is C 2221 with a 850°C = 7.36 Å, b350°C = 13.96 Å, c850°C = 6.79 Å Z = 4, The solid solution N—Cu1,5Zn1,5O(SO4)2 is isotypic with N—Zn3O(SO4)2 and has the lattice constants a25°C = 14.03 Å, b25°C = 6.62 Å, c25°C = 7.33 Å, β25°C = 90.58°, Transoformations into the non quenchable high temperature modifications H-ZnSO4, H′-Zn3O(SO4)2 and H-Zn3O(SO4)2 are displacive. The thermal expansion of N-ZnSO4 and H-ZnSO4 and H-ZnSO4 has been exa-mined.
    Notes: Mit kontinuierlichen Heizguinieraufnahmen wurde die Dehydratisierung von ZnSO4 · 7 H2O und das Hochtemperaturverhalten von wasserfreiem ZnSO4 untersucht. Der Abbau von ZnSO4 · 7 H2O verläuft an der Luft über das 6-Hydrat, eine unbekannte Hydratphase und das 1-Hydrat zum N-ZnSO4, der Normaltemperaturform; bei etwa 700°C wird die reversible Umwandlung in H-ZnSO4 beobachtet. Die Thermolyse, die von N-ZnSO4 oder H-ZnSO4 ausgehen kann, verläuft über das Oxidsulfat Zn3O(SO4)2 weiter zum ZnO.ZnSO4 · 6 H2O kristallisiert monoklin im Hexahydrit (MgSO4 · 6 H2O)-Typ mit a25°C = 9,981 Å b25°c = 7,250 Å, c25°C = 24,280 Å, β25°C = 98,45°, Z = 8, RG: C 2/c. Das kubische H-ZnSO4 ist die erste A2+B6+O4-Verbindung mit H-Cristobalit-Struktur; wahrscheinliche RG: F 43 m mit a700°C = 7,18 Å, Z = 4. N—Zn3O(SO4)2 ist monoklin mit der wahrscheinlichen RG: B 2 mit a25°C = 13,987 Å b25°C = 6,706 Å, c25°C = 7,379 Å, β25°C = 90,69°, Z = 4. Oberhalb 420°C wird das Oxidsulfat orthorhombisch, wobei zunächst H′-Zn3O(SO4)2 entsteht, das bei 655°C reversibel in H-Zn3O(SO4) übergeht. Für H-Zn2O(SO4)2 ist die wahrscheinliche RG: C 2221 mit a850°C = 7,36 Å, b 850°C = 13,96 Å, c850°C = 6,79 Å, Z = 4. Der Mischkristall N—Cu1,5 Zn1,5O(SO4)2 ist isotyp mit N-Zn3O(SO4)2 und besitzt die Gitterkonstanten a25°C = 14,03 Å, b25°C = 6,62 Å, c25°C = 7,33 Å, β25°C = 90,58°, Z = 4. Die Umwandlungen in die nicht abschreckbaren Hochtemperaturformen (H-ZnSO4 H'-Zn3O(SO1)2 und H-Zn3O(SO4)2) erfolgen displaziv. Die thermische Dilatation von N-ZnSO4 und H-ZnSO4 wurde ermittelt.
    Additional Material: 3 Ill.
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  • 4
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Stability in aqueous solution of some complexes of heavy metals with diaza-polyoxamacrocyclic ligandsStability of metal complexes (Mn+ = Cu2+, Ni2+, Co2+, Zn2+, Pb2+, Ag+ and Cd2+) with five diaza-polyoxamacrocycles (L = [2.1.1], [2.2.1], [2.2.2], [2.1] and [2.2] ) have been determined at 25°, in 0.1 M Et4N+ClO4- aqueous solutions, by means of potentiometric titrations. All cations form MLn+ complexes; Cu2+ also forms the MHL(n+1)+ protonated species with both [2.2.1] and [2.1.1] ligands. The stability of these complexes has been discussed in terms of structure and by considering the ionic radii of the cations together with the radii of the macrocyclic cavities. Different behaviour is observed between some of these complexes and the well known alkali and alkaline-earth cryptates, partly due to the more covalent nature of bonds formed by the investigated cations and the donor sites of the ligands. The effect of the substitution of two oxygen by two sulfur atoms in the pentadentate ligand [2.1] on the stability of the complexes is reported.
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  • 5
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Complexation in anhydrous methanol of Cu (II) and Zn (II) with diaza-polyoxamacrocyclic ligandsProtonation of five diaza-polyoxamacrocyclic ligands, (L = [2.1], [2.2], [2.1.1.], [2.2.1], [2.2.2]), and their complexing properties towards Cu2+ and Zn2+ cations have been studied in anhydrous methanolic solutions.Potentiometric measurements have been carried out at 25°, using 5 · 10-2MEt4N+ClO4- as support-electrolyte, in order to determine the nature of the species formed upon complexation and their stability constants. The results were confirmed by spectrophotometry, for the cupric complexes of [2.1] and [2.2.2], and the electronic spectra of the different complexes were calculated.Comparison between complexation in aqueous and methanolic solutions have been made: as in water, ML2+ species and sometimes protonated MHL3+ species, with higher stability constants, are present in methanol; but the main difference is the formation of dinuclear complexes M2L4+, between Cu2+ and all ligands except [2.1]. In these complexes the Cu2+ cations cannot be both ‘encaged’ in the ligand cavity because of its small size. The different possible structures are discussed in terms of the stability constants values. The protonation constants values and the existence of the binuclear complexes may indicate a possible conformational change in the complexing ligand on changing the solvent from water to methanol.
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  • 6
    ISSN: 1432-1912
    Keywords: p-Nitrophenyl diazonium fluoroborate ; Cholinergic neurons ; Acetylcholine receptor ; Acetylcholinesterase ; Affinity labelling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Electrophysiological experiments were done to investigate the effect of p-nitrophenyl diazonium fluoroborate (p-NPD) on motor endplates of the frog's m. cutaneus pectoris. The compound has no direct depolarizing effect on the postsynaptic membrane and stabilizes it irreversibly when added to the bath. Longtime iontophoretical applications of p-NPD produce a biphasic effect: initially a potentiation of the depolarizations due to acetylcholine (ACh) (both iontophoretically applied and presynaptically liberated), and subsequently an inhibition of the response to ACh. When the acetylcholinesterase (AChE) is inactivated previously, only the inhibiting effect of the compound is demonstrable. The association constant of p-NPD to purified AChE and to membrane fragments of electroplax was determined by biochemical methods. The compound's affinity to the AChE was found to be about 20 times greater than to the acetylcholine receptor (AChR). Iontophoretical application of p-NPD to cholinergic neurons in the hippocampal cortex of the cat also produced the characteristic biphasic effect on ACh-induced activity of these investigated neurons. The results suggest that the biphasic effect depends on the capacity of p-NPD to combine with both the AChE and the AChR. The AChE is first inhibited with low concentrations thereby potentiating the ACh response. At higher concentrations the AChR's are progressively inhibited too, thereby diminishing the excitability of the postsynaptic membrane up to a complete block.
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