ALBERT

Notes: Abstract Accumulation rates of Cd have been studied in the common mussel Mytilus edulis L. under different laboratory conditions. Semi-static and through-flow experiments were carried out at Cd concentrations of 200 ppb and 50/100 ppb in the water, respectively. A linear uptake of Cd throughout the experimental periods of 36 or 124 d was found in all experiments. The accumulation rate was 3.10 ppm d-1 at 50 ppb in the through-flow water experiment, 4.1 ppm d-1 in starved and 6.6 ppm d-1 in fed mussels in the semi-static experiments with 200 ppb Cd in the water. The Cd-accumulation rate in various fractions of soft parts decreased in the order: body〉mantle〉muscles. Elution patterns obtained from gel-filtrations showed an increasing amount of Cd-binding proteins (metallothioneins) when the body burden of Cd increased. The Cd content in the body fraction of mussels transferred to clean water for 42 d after first being exposed to Cd during 124 d decreased from 564 ppm on a dry weight basis to 417 ppm while the fraction of Cd bound to metallothioneins rose from 22 to 78% during the same period.

Notes: Abstract The electrophysiological membrane parameters of the unicellular green alga Eremosphaera viridis were determined using an improved computer-supported single-microelectrode technique. These cells developed an average membrane potential of-150 mV in the light and a specific resistance of 1 Ω m2 with an external potassium concentration of 1.1 mM and pH 5.5. In the dark, many cells showed a less polarized potential of 30–40 mV and a smaller membrane resistance. At potassium concentrations in the external medium higher than 1 mM, the membrane potential strongly depends on the external potassium content apart from a small electrogenic component. At concentrations lower than 1 mM K+, a dependence of the membrane potential upon external potassium concentrations could not be verified. Inserting the internal ion activities in the Goldmann equation shows that, in this range, the proton conductance seems to be predominant over the potassium conductance. Transient changes in the membrane potential and in the membrane resistance were observed after switching off the light, after addition of 3-(3′,4′-dichlorophenyl)-1,1-dimethylurea or N,N′-dicyclohexylcarbodiimide, after a sudden decrease in temperature, and after current pulses. These changes resemble the action potentials (AP) found in other plant cells (Chara, Acetabularia). On average, the AP has a delay period of 5.1 s and a duration of 43.8 s showing a sudden decrease and a slower regeneration. The voltage peak during an AP followed exactly the Nernst potential of potassium over a range of external potassium concentrations from 5 μM to 0.2 M. This is true for depolarization or hyperpolarization, depending on the external K+-concentration. Tetraethylammonium-hydrogensulphate, a rather specific inhibitor of K+ channels in nervous cells, suppressed the AP. The correlation of the appearance of the AP with a short-term opening of potassium channels in the membrane of Eremosphaera is discussed.

Notes: Abstract In the present report we summarize recent results concerning our studies on messenger ribonucleoprotein particles and RNA-binding proteins from the cytoplasm of mouse erythroblasts and mouse Krebs II ascites cells.

Notes: Einkristalle von α-ZnAl2S4 mit Spinellstruktur (a = 10,0093 Å) lassen sich durch chemische Transportreaktion bei 740°C erhalten. Beim Erhitzen der Verbindung auf 800-900°C tritt Zerfall in eine ZnS-arme defekte Spinellphase und in eine ZnS-reiche Phase mit defekter Wurtzitstruktur ein. Bei 830-860°C liegen die Grenzen des zweiphasigen Bereichs etwa bei Zn0,98Al2,01S4 (kubische α-Phase, a = 10,0072 Å (25°C)) und Zn1,80Al1,47S4 (hexagonale Wurtzitphase, a = 3,760, c = 6,15 Å (25°C)). Mischungen von ZnS, Al und S entsprechend der Zusammensetzung ZnxAl8/3-2x/3S4 mit 0,33 ≤ x ≤ 0,98, die auf 830-860°C (70-140 h) erhitzt worden sind, liefern nach Abkühlung auf Raumtemperatur homogene Produkte mit defekter Spinellstruktur. Die bei der Zusammensetzung Al2S3 · ZnS beobachtete Mischungslücke setzt sich bei höherer Temperatur unter Verschiebung der Phasengrenzen und Ausbildung von Hochtemperatur-Phasen fort. Eine Hochtemperaturmodifikation des ZnAl2S4 existiert bis 1080°C nicht. Mischungen von ZnS, Al und S mit 0,44 ≤ x ≤ 0,85, die auf 1060-1080°C (72-96 h) erhitzt worden sind, zeigen nach Abkühlung auf Raumtemperatur eine bisher nicht beschriebene rhomboedrische Hochtemperaturphase (γ-Phase), deren Struktur als eine Defektstruktur des ZnIn2S4-Typs aufgefaßt werden kann. Bei x = 1,00 erhält man nach thermischer Behandlung bei 1060-1080°C ein zweiphasiges Produkt, das neben der γ-Phase eine orthorhombische Phase (β-Phase, Überstruktur des Wurtzit-Typs) enthält. Die β-Phase tritt als einzige Phase auf, wenn für die Ausgangsmischung gilt: 1,40 ≤ x ≤ 1,70. Die Löslichkeit von Al2S3 in ZnS (Wurtzit) unter Bildung einer statistischen Defektstruktur des Wurtzit-Typs reicht bei 1060-1080°C bis Zn1,70-1,80Al1,53-1,47S4(Al2S3 · (2,2-2,5) ZnS).Preparative and X-Ray Investigations on the System Al2S3—ZnS (Temperature Region 800-1080°C)Single crystals of α-ZnAl2S4 with spinel structure (a = 10.0093 Å) have been obtained by chemical transport reaction at 740°C. Heating of the compound to 800-900°C leads to decomposition and formation of a ZnSαpoor defect spinel phase and a ZnS-rich phase with a defect wurtzite structure. The boundaries of the two-phase region at 830-860°C are approximately Zn0,98Al2.01S4 (cubic α-phase, a α 10.0072 Å (25°C)) and Zn1.80Al1.47S4 (hexagonal wurtzite-phase, a = 3.760, c = 6.15 Å (25°C)). Mixtures of ZnS, Al and S with the composition ZnxAl8/3-2x/3S4 and 0.33 ≤ x ≤ 0.98, which are heat treated at 830-860°C (70-140 h), yield after cooling to room temperature homogeneous products with a defect spinel structure. The miscibility gap at the composition Al2S3 · ZnS continues at higher temperatures with a shift of the phase boundaries and formation of high-temperature phases. A high-temperature modification of ZnAl2S4 does not exist up to 1080°C. When mixtures of ZnS, Al and S with 0.44 ≤ x ≤ 0.85 are heat treated at 1060-1080°C(72-96 h), a rhombohedra1 high-temperature phase (γ-phase) is obtained after cooling to room temperature, which has not previously been observed. I t s structure can be described as a defect structure of the ZnIn, S, type. With x = 1.00, after thermal treatment a t 1060-1080°C, a two-phase product is obtained, containing γ-phase in addition to an orthorhombic phase (β-phase, super-lattice of the wnrtzite type). The β-phase is the only phase occuring in products with 1.40 ≤ x ≤ 1.70. The solubility of Al, S, in ZnS (wurtzite) at 1060-1080°C with formation of a defect wurtzite structure, in which the cations are disordered, reaches as far as Znl.70-1.80All.53-1.47S4[Al2S3·(2.2-2.5)ZnS].

Notes: Die Kristallstruktur des ZnAl2S4 wird unter Verwendung dreidimensionaler Einkristall-Röntgendaten verfeinert. Die Gitterkonstante der durch Transportreaktion bei 740°C erhaltenen Einkristalle beträgt 1000,9(1) pm. In Anbetracht der Beobachtung zahlreicher schwacher Reflexe vom Typ h k 0 mit h + k = 4n + 2, die in der üblicherweise für die Spinellstruktur angenommenen Raumgruppe Fd3m verboten sind, werden Verfeinerungsrechnungen in den Raumgruppen Fd3m und F43m durchgeführt. Die Ergebnisse zeigen, daß es keinen Grund gibt, von der Raumgruppe Fd3m abzugehen. Die verbotenen Reflexe lassen sich auf Umweganregung zurückführen. Der Ortsparameter des S-Atoms beträgt x = 0,38463(2). Die Verteilung der Kationen entspricht der normalen Spinellstruktur, der Inversionsparameter i (Bruchteil der durch Al besetzten Tetraederlücken) ist kleiner als 0,02.