Showing papers by "Ludwig Maximilian University of Munich published in 1976"
TL;DR: The H 2 /Pt(111) system has been studied with LEED, ELS, thermal desorption spectroscopy and contact potential measurements as mentioned in this paper, showing that adsorption is completely dissociative with an initial sticking coefficient of 0.1, yielding an atomic H:Pt ratio of about 0.8:1 at saturation.
581 citations
TL;DR: In this article, the role of structural imperfections as active sites in surface reactions was investigated on a step Pt(S)-9 (111) × (111)-surface and showed that the presence of steps increases the initial sticking coefficient by a factor of four to a value of 0.34 and the activity for the H2-d2 exchange reaction is enhanced by an order of magnitude whereby however the apparent activation energy remains constant.
295 citations
TL;DR: In this paper, a self-consistently calculated density, potentials, and work functions of thin metal films are calculated with the planar uniform-background model and density functional formalism.
273 citations
TL;DR: In this article, a probe molecule other than the reactant is preadsorbed as a poison and its effect on the catalytic activity studied, from the nature of interaction of this probe molecule with the surface sites one may obtain information regarding the chemical nature of these sites and from the number of poisoning molecules necessary to bring the activity to zero one may estimate an upper limit of the active site density.
Abstract: Publisher Summary This chapter discusses the specific poisoning of a catalyst surface. A probe molecule other than the reactant is preadsorbed as a poison and its effect on the catalytic activity studied. From the nature of interaction of this probe molecule with the surface sites one may obtain information regarding the chemical nature of these sites and from the number of poisoning molecules necessary to bring the activity to zero one may estimate an upper limit of the active site density. Besides the obvious difficulty to discriminate between surface sites that purely absorb the probe molecule and those that are involved in the catalytic process as active sites, there are a number of other limitations making it difficult to obtain clear-cut information on the nature of active sites. The chapter describes the proposals that are indispensable for a proper application of this method and the precautions that have to be kept in mind while drawing conclusions from specific poisoning experiments. The chapter illustrates two examples—namely, the dehydration of alcohols and the isomerization of olefins on alumina.
252 citations
TL;DR: The results suggest that illumination of intact chloroplasts causes an increase in the Mg2+ concentration of 1-3 mM in the stroma, which appears to be high enough to have a possible function in the light regulation of CO2 fixation.
243 citations
01 Jan 1976
TL;DR: The inner mitochondrial membrane is known to contain a number of membrane-bound enzymes which are linked to oxidation and phosphorylation reactions, but particularly prominent are the metabolites associated with the tricar-boxylic acid cycle, with transamination reactions, and with phosphate transfer reactions in oxidative and substrate-levelosphorylation.
Abstract: The inner mitochondrial membrane is known to contain a number of membrane-bound enzymes which are linked to oxidation and phosphorylation reactions. During the past ten years, it has been found that this membrane also facilitates the specific transport of a number of metabolites which function as intermediates in metabolic pathways of mitochondria. Particularly prominent are the metabolites associated with the tricar-boxylic acid cycle, with transamination reactions, and with phosphate transfer reactions in oxidative and substrate-level phosphorylation (for reviews, see Klingenberg, 1970; Meijer and van Dam, 1974; LaNoue and Schoolwerth, 1979; Scarpa, 1979).
188 citations
TL;DR: The magnitude of the feedback response during retrograde perfusion was not changed by lowering NaCl concentration from 140 to 60 mM, but fell whenNaCl concentration was further reduced, and was insensitive to changes in flow rate.
Abstract: To define the luminal agent(s) responsible for the reduction of nephron filtration rate following increases of loop of Henle flow rate early proximal flow rate (EPFR) during loop perfusion with 17 different salt solutions were compared to the non-perfused fubules. During orthograde microperfusions a reduction of EPFR as indication of a feedback response was noted with a number of nonovalent Cl− and Br− salts (LiCl, KCl, NaCl, RbCl, CsCl, NH4Cl, choline Cl, NaBr, KBr), with Na+ salts except Na acetate (NaHCO3, NaNO3, NaF, NaI, NaSCN), and with CaCl2 and MgCl2. These latter 2 solutions where used in a concentration of 70 mM while all other solutions had a concentration of 140 mM. During retrograde perfusion from the distal to the proximal end of the loop of Henle EPFR fell significantly with Cl− and Br− salts with percentage changes of EPFR ranging from −8.0 to −44.3%. In contrast, Cl− free salts and Cl− salts of divalent cations were associated with percentage changes of EPFR ranging from +7.1 to −6.2%, significance being reached only during perfusion with NaSCN. When furosemide (5×10−4M) was added to NaBr or KBr a feedback response was not observed. During orthograde perfusion with NaNO3 distal Cl− concentrations were 44.2±5.08 mM (mean±S.E.) at a perfusion rate of 10nl/min and 59.1±3.93 mM at a rate of 40 nl/min. CaCl2 perfusion induced a marked elevation of distal Cl− concentrations to levels higher than 140 mM. Loop chloride handling was normal during RbCl perfusion. The magnitude of the feedback response during retrograde perfusion was not changed by lowering NaCl concentration from 140 to 60 mM, but fell when NaCl concentration was further reduced. In contrast to orthograde perfusions it was insensitive to changes in flow rate. Our results are compatible with the thesis that feedback responses depend critically upon the rate of Cl− transport probably across the macula densa cells. Br− ions can replace Cl− because they appear to share a common transport pathway which can be inhibited with furosemide. Unspecificity of feedback responses during orthograde microperfusions is due to presence of Cl− ions in the macula densa region even when solutions are initially Cl− free. Cl− salts of divalent cations do not elicit a feedback response because Cl− transport is severely curtailed.
173 citations
TL;DR: It is concluded that the pial arterial resting tone is not influenced under experimental conditions by adenosine formed and released by brain tissue, and the dilatations measured at high theophylline concentrations are apparently due to a mechanism different from theAdenosine antagonism.
Abstract: The effect of adenosine upon pial resistance vessels was studied using local microapplication from the perivascular side and measurement of vascular diameter. Concentration-response curves revealed a concentration-dependent dilatatory effect of adenosine between 10−7 and 10−3 M. The degree of dilatation was independent of initial vessel size (47–260 μ). The dilatations due to adenosine could be reduced by theophylline in a reversible competitive antagonism. Concentration-response curves for theophylline yielded no vascular reaction at concentrations of up to 10−5 M theophylline. From these data it is concluded that the pial arterial resting tone is not influenced under our experimental conditions by adenosine formed and released by brain tissue. The dilatations measured at high theophylline concentrations are apparently due to a mechanism different from the adenosine antagonism.
171 citations
TL;DR: An analysis of cell kinetic parameters as a function of intralobular localization of hepatocytes was performed using autoradiographic methods to obtain a basis for a quantitative description of cell cycle compartments after partial hepatectomy.
Abstract: An analysis of cell kinetic parameters as a function of intralobular localization of hepatocytes was performed using autoradiographic methods to obtain a basis for a quantitative description of cell cycle compartments after partial hepatectomy.
The influx into the S compartment revealed a maximum in a lobular zone not immediately adjacent to the portal tract, with a decrease towards the perivenous and periportal area of the lobule. The maximum influx was found in the intermediate zone at 34 hr and a lower one in the perivenous parts of the lobule at 40 hr. The influx pattern at 56 hr was similar to the situation at 18 hr.
The fraction of labelled mitoses in the whole liver and in subunits of the lobule disclosed a constant duration of S whereas the duration of G2+ M was prolonged from the periportal to the perivenous zone.
A graphical model of kinetic events after partial hepatectomy is proposed, which describes the sizes of the various cell cycle compartments; the model successfully predicted the results of a continuous labelling experiment.
159 citations
TL;DR: In this article, it was shown that trees store a record of atmospheric temperature in their rings, and that the ratios of the stable isotopes of hydrogen and oxygen vary with the air temperature prevailing when the ring was formed.
Abstract: Evidence is summarised here that trees store a record of atmospheric temperature in their rings. In each ring, the ratios of the stable isotopes of hydrogen and oxygen vary with the air temperature prevailing when the ring was formed. We have shown that the temperature records in three modern trees seem to follow the local mercury thermometer records, and have found that a Japanese cedar indicates a temperature fall of ∼1.5°C in the past 1,800 yr.
155 citations
TL;DR: The purification of chloroplast fructose bisphosphatase from spinach leaves to apparent homogeneity and with 80% yield is developed and the number of freely available sulphydryl groups increased from four to twelve per molecule, considered in the context of the observed activation of this enzyme following illumination of chloroplasts.
Abstract: A relatively straightforward procedure has been developed for the purification of chloroplast fructose bisphosphatase from spinach leaves to apparent homogeneity and with 80% yield. The molecular weight of the enzyme was about 160 000. Chloroplast fructosebisphosphatase consists of four possibly identical subunits and, at pH 8.8, EASILY DISSOCIATES INTO EQUAL HALVES WITH LOWered activity. Sigmoid saturation curves with Hill coefficients between 3.0 and 3.7 were obtained for fructose 1,6-bisphosphate and Mg2+. Incubation of the enzyme with 20 mM dithiothreitol slowly altered the response to pH from no activity measured at pH 7.5 and full activity at pH 8.8 to equal activity at each of these pH values; at the same time the number of freely available sulphydryl groups increased from four to twelve per molecule. These properties are considered in the context of the observed activation of this enzyme following illumination of chloroplasts.
TL;DR: Li+ net transfer across cell membranes was studied on human erythrocytes and ghosts preloaded with 1-2 mM Li+ and incubated in saline media of varying composition at initial thermodynamic equilibrium for Li+.
Abstract: Li+ net-transfer across cell membranes was studied on human erythrocytes and ghosts preloaded with 1–2 mM Li+ and incubated in saline media of varying composition at initial thermodynamic equilibrium for Li+ The following results were obtained: From the results it is concluded that the Li+ uphill transport across human red cell membranes is mediated by a Na+-dependent Li+ counter-transport system This system is not inhibited by ouabain and does not appear to be identical to the Na+−Na+ exchange system described by Garrahan and Glynn [24]
TL;DR: In this article, the authors studied the adaption of CO on Ni(111) surfaces by means of LEED, UPS and thermal desorption spectroscopy, and showed that the photoemission spectrum exhibits not a simple superposition of the features arising from the single component adsorbates, but a more weakly bound phase characterized by a √7 2 × √ 7 2R19° LEED pattern, interpreted with a hexagonal close-packed arrangement.
TL;DR: This parameter may be a useful index of the water relations of these plants under natural conditions and may reflect the different δD value of available water in areas of increasing aridity.
Abstract: The ratio of deuterium to hydrogen (expressed as δD) in hydrogen released as water during the combustion of dried plant material was examined. The δD value (metabolic hydrogen) determined on plant materials grown under controlled conditions is correlated with pathways of photosynthetic carbon metabolism. C3 plants show mean δD values of-132‰ for shoots and -117‰ for roots; C4 plants show mean δD values of -91‰ for shoots and-77‰ for roots and CAM plants a δD value of-75‰ for roots and shoots. The difference between the δD value of shoot material from C3 and C4 plants was confirmed in species growing under a range of glasshouse conditions. This difference in δD value between C3 and C4 species does not appear to be due to differences in the δD value (tissue water) in the plants as a result of physical fractionation of hydrogen isotopes during transpiration. In C3 and C4 plants the hydrogen isotope discrimination is in the same direction as the carbon isotope discrimination and factors contributing to the difference in δD values are discussed. In CAM plants grown in the laboratory or collected from the field δD values range from-75‰ to +50‰ and are correlated with δ(13)C values. When deprived of water, the δD value (metabolic hydrogen) in both soluble and insoluble material in leaves of Kalanchoe daigremontiana Hamet et Perr., becomes less negative. These changes may reflect the deuterium enrichment of tissue water during transpiration, or in field conditions, may reflect the different δD value of available water in areas of increasing aridity. Whatever the origin of the variable δD value in CAM plants, this parameter may be a useful index of the water relations of these plants under natural conditions.
TL;DR: An electron density map at 5 A resolution of the human myeloma protein Kol shows 'a quaternary structure different from previously reported Fab fragments and provides evidence for flexibility in the switch peptides between variable and constant domains on heavy and light chains.
TL;DR: Evidence is provided that at least two different adenine nucleotide compartments of the heart serve as precursors for the formation of adenosine and cAMP, one characterized by a high SA, the other by a lower SA.
Abstract: After prelabeling the adenine nucleotides (ATP, ADP, AMP) of isolated perfused guinea pig hearts with either14C-adenine or14C-adenosine for 35 min, labeled adenosine, inosine, hypoxanthine and cyclic 3′5′-AMP (cAMP) were continuously released into the cardiac perfusate. Determination of the specific activities (SA) of the adenine nucleotides, cAMP, and their breakdown products (adenosine, inosine, hypoxanthine) in tissue and perfusate revealed: Under steady state conditions the SA of adenosine and cAMP in the perfusate were of the same order of magnitude and proved to be many times higher than the SA of the respective precursor adenine nucleotides. This difference was observed regardless whether adenine or adenosine was used as prelabeling substance. The SA of inosine and hypoxanthine in the perfusate were constantly lower than the SA of adenosine. Cardiac ischemia of 6 min, which resulted in a markedly increased formation of adenosine, led to a pronounced decrease in the SA of adenosine released from the heart. Our findings provide evidence that at least two different adenine nucleotide compartments of the heart serve as precursors for the formation of adenosine and cAMP, one characterized by a high, the other by a lower SA. Under normoxic conditions adenosine and cAMP released into the cardiac perfusate are derived mainly from a nucleotide fraction of high SA, which appears to be rather small. During ischemia a second compartment of much lower SA in addition contributes to the formation of adenosine.
TL;DR: Chromosomes were analysed in peripheral lymphocytes of 24 workers in a zinc smelting plant who had increased blood levels of lead and cadmium and the number of cells with structural chromosome aberrations was significantly increased as compared with 15 controls.
Abstract: Chromosomes were analysed in peripheral lymphocytes of 24 workers in a zinc smelting plant who had increased blood levels of lead and cadmium. The number of cells with structural chromosome aberrations was significantly increased as compared with 15 controls. The observed chromosome damage was mainly of the chromatid type (single breaks and exchanges) accompanied by acentric fragments. The observed chromosome aberrations cannot be causally related to cadmium because the workers were additionally exposed to lead and zinc. However, from existing cytogenetic data on heavy metals an effect of cadmium could be well deduced, although possible synergistic effects of several metal compounds, especially under conditions, in vivo, cannot be excluded.
TL;DR: The distribution of ganglion cells was measured in whole mounts of the retina from pig, sheep, ox, horse, and dog to determine shape and location of the central area, typical for the particular species.
Abstract: In order to ascertain shape and location of the central area, the distribution of ganglion cells was measured in whole mounts of the retina from pig, sheep, ox, horse, and dog. Although exact comparison of corresponding points of measurement in different animals was not possible, the measurements allowed the mapping of retinal ganglion cell density, typical for the particular species. In all ungulates a streak of high cell density extends along a straight horizontal line, dorsal to the optic disc. As a rule a maximum of ganglion cell density is found close to the temporal end of the visual streak. In the dog a well demarcated oval portion of the streak continues into a short temporal (variable) and a long nasal linear arm. The functional significance of these findings is discussed.
TL;DR: In this article, the elastic constants of V, Nb, and Ta were determined at room temperature after loading with hydrogen and deuterium by ultrasonic methods in cubic α-phases.
Abstract: By ultrasonic methods the elastic constants of V, Nb, and Ta are determined at room temperature after loading with hydrogen and deuterium. For Nb and Ta also the change of the temperature dependence of the elastic constants on alloying are determined up to 300°C. All measurements are performed in the cubic α-phases. The three alloy systems show qualitatively the same behaviour: The bulk moduli are nearly unaffected whereas the shear constants C44 increase. These changes are independent of the hydrogen isotope. The shear constants (C11–C12)/2 decrease as a function of alloy concentration and these decreases are isotope-dependent, being stronger for hydrogen than for deuterium.
Durch Ultraschallmessungen werden die elastischen Konstanten von V-, Nb- und Ta-Wasserstoff bzw. Deuterium-Legierungen bei Raumtemperatur bestimmt. Fur Nb und Ta wird auch die Anderung der Temperaturabhangigkeit der elastischen Konstanten durch Legieren bis 300°C gemessen. Alle Messungen werden in den kubischen α-Phasen durchgefuhrt. Die drei Legierungssysteme zeigen qualitativ das gleiche Verhalten. Der Kompressionsmodul bleibt nahezu konstant, wahrend der Schermodul C44 zunimmt. Die Anderungen in diesen zwei Moduln sind unabhangig vom Wasserstoffisotop. Im Gegensatz hierzu nimmt die Scherkonstante (C11–C12)/2 mit zunehmender Beladung ab. Die Abnahme ist fur Wasserstoff jeweils starker als fur Deuterium.
TL;DR: In this article, eine new Methode for quantitativen bestimmung der Creatinkinase MB-Aktivitat im Serum berichtet.
Abstract: Es wird uber eine neue Methode zur quantitativen Bestimmung der Creatinkinase MB-Aktivitat im Serum berichtet. Die Methode beruht auf einer direkten Messung der Aktivitat der Creatin-kinase-Untereinheit B nach Hemmung der Aktivitat der Creatinkinase-Untereinheit M durch inhibierende Antikorper und benotigt zur Durchfuhrung 15 min. Bei allen 83 untersuchten Patienten mit klinisch gesichertem Myokardinfarkt konnten zwischen der 6. und 28. Stunde nach Infarkteintritt Creatinkinase MB-Aktivitat gemessen werden. Der Creatinkinase MB-Anteil zum Zeitpunkt der hochsten Creatinkinase-Gesamtaktivitat betrug 6–17%, im Mittel 8%. Diese Methode ermoglicht daher in der Notfalldiagnostik eine Differentialdiagnose unklarer Creatinkinase-Gesamtaktivitats-Erhohungen.
TL;DR: The potential profile of the frog skin epithelium incubated in Cl-Ringer was reinvestigated with improved technique and was demonstrated to be trough like in contrast to the stair-step like potential profile reported by previous investigators.
Abstract: The potential profile of the frog skin epithelium incubated in Cl-Ringer was reinvestigated with improved technique. Under open circuit conditions (PDtr up to 120 mV) the potential profile was demonstrated to be trough like in contrast to the stair-step like potential profile reported by previous investigators which has probably been recorded after injuring of the punctured cells. In 67 successful impalements the potential difference across the basolateral membranes was 108 +/- 2 mV. The potential across the outer, epithelial-facing membrane was inversely related to the transepithelial PD, but was found to be negative (with respect to the epithelial bathing solution) in all punctures. Electrogenic sodium transport might be responsible for part of the potential difference across the basolateral membranes which correlatee directly with the short circuited state was -73 +/- i mV and decreased with increasing short cirucit current. It is suggested that these changes result from variations of the outer membrane sodium conductance.
TL;DR: The amount of creatine kinase MB with respect to total CK activity after reinfarction is higher than the amount after initial infarction, and the percentage of creatine Kinase MB of peak CK-total is 6-25%, with a mean of 11.1%.
TL;DR: In this paper, the Anderung der Selektivitat is described as a Funktion der Aenerung der polaritat of ambifunktionelle Anionen, i.e., the relative Ladungsdichte P = lX/lY-X and Y are the potentiellen reaktiven Zentren.
Abstract: Die Chemie der ambifunktionellen Anionen ist fur die praparative organische Chemie von groser Bedeutung. Um Synthesen planen zu konnen, benotigt man Regeln, die einen Zusammenhang zwischen Struktur und Selektivitat herstellen. Nach dem „Allopolarisierungs-Prinzip” last sich der Einflus von Substituenten auf kinetisch kontrollierte Reaktionen beschreiben: die Anderung der Selektivitat ist eine Funktion der Anderung der „Polaritat” der ambifunktionellen Anionen. Als „Polaritatsindex” dient die relative Ladungsdichte P = lX/lY- X und Y sind die potentiellen reaktiven Zentren. Anhand von Beispielen aus verschiedenen Verbindungsklassen wird versucht, die Brauchbarkeit dieses Prinzips zu demonstrieren.
15 Oct 1976
TL;DR: In this article, the magnetic field modulation of the pyrene triplet and pyrene anion concentrations formed through quenching of singlet excited pyrene molecules by N,N -diethylaniline in methanol at room temperature was investigated.
Abstract: Measuring transient absorptions on the nanosecond time range, we observed the magnetic field ( H = 40 Oe) modulation of the pyrene triplet and pyrene anion concentrations formed through quenching of singlet excited pyrene molecules by N,N -diethylaniline in methanol at room temperature. We interpret this effect as being due to a magnetic field dependent triplet production in the geminate radical ion pair, induced by hyperfine interaction of the unpaired electrons. The discussion is based on a simple model related to the radical pair model in CIDNP theory. Moreover, the sign of the magnetic field modulation of triplets and radical ions allows to infer on the relative probability for the formation of excited and ground state molecules in ion recombination processes.
TL;DR: In this article, the authors give a sufficient condition for a completely positive dynamical semigroup of a N-level system to have a unique (invariant) equilibrium state and for every initial state to approach this equilibrium state as t → ∞.
TL;DR: The concept of allopolarization permits a description of substituent effects on kinetically controlled reactions: the change in selectivity is a function of change in polarity of the ambifunctional anions.
Abstract: The chemistry of ambifunctional anions is of great importance in organic preparations. Planning of syntheses requires a set of rules correlating structure and selectivity. The concept of allopolarization permits a description of substituent effects on kinetically controlled reactions: the change in selectivity is a function of the change in polarity of the ambifunctional anions. The relative charge density P = lx/ly serves as “polarity index”; X and Y are the potential sites of reaction. An attempt is made to illustrate the utility of this principle by means of examples taken from various classes of compounds.
TL;DR: In this article, first and second order Raman scattering was observed in NbC and ZrN and the position of the Raman peaks showed satisfactory agreement with high values of the phonon density obtained from neutron scattering data.
TL;DR: The pH in the cytoplasmic and thylakoid spaces of the blue-green alga, Anacystis nidulans, has been determined in the light and in the dark by uptake of 5,5-dimethyloxazolidine-2,4-dione and methylamine into the sucrose-impermeable (3)H-H(2)O space, as measured by silicon layer filtering centrifugation.
Abstract: The pH in the cytoplasmic and thylakoid spaces of the blue-green alga, Anacystis nidulans , has been determined in the light and in the dark by uptake of 5,5-dimethyloxazolidine-2,4-dione and methylamine into the sucrose-impermeable 3 H-H 2 O space, as measured by silicon layer filtering centrifugation. Illumination causes an alkalinization in the cytoplasm which is accompanied by an acidification in the thylakoid space, reflecting light-dependent proton transport across the thylakoid membrane. Under light conditions, a pH gradient of approximately 2.8 between the cytoplasmic and thylakoid spaces has been measured that can be abolished almost completely by addition of the uncoupler, 3-chlorocarbonyl cyanide phenylhydrazone. The pH in the cytoplasm is independent of the pH in the medium.