Showing papers by "ETH Zurich published in 1981"
824 citations
TL;DR: In this paper, it was shown that spin-spin couplings can lead to J cross-peak in analogy to cross-peaks in two-dimensional autocorrelated spectroscopy.
745 citations
TL;DR: In this article, a surface complexation model is used to describe the dependence of the extent of adsorption on pH and other solution variables, and a set of equilibrium constants has been determined which permits calculation of the amount bound to the surface and of the surface charge as a function of pH and total concentrations.
565 citations
TL;DR: 1H‐Nmr was used to measure the rate of cis–trans interconversion of X‐Pro bonds in linear and cyclic oligopeptides and found that replacement of Ala by Phe, Tyr, or Trp resulted in a 10‐fold slower interconverting rate, whereas after substitution of AlaBy His or Glu, the rate decreased only slightly.
Abstract: 1H-Nmr was used to measure the rate of cis–trans interconversion of X-Pro bonds in linear and cyclic oligopeptides. k(cis → trans) = 2.5 × 10−3 s−1 at 25°C was found for the zwitterionic form of H-Ala-Pro-OH, in good agreement with earlier measurements. Replacement of Ala by Phe, Tyr, or Trp resulted in a 10-fold slower interconversion rate, whereas after substitution of Ala by His or Glu, the rate decreased only slightly. Independent of the residues X, the interconversion rate was increased by a factor of ca. 20 when the peptide chain was elongated by addition of Ala to the C-terminal Pro. An additional increase by a factor of 6 was observed when going from the protected linear peptide CF3CO-Gly-Gly-Pro-Ala-OCH3 to the closely related cyclic compound c[-Gly-Gly-Pro-Gly-Ala-]. These data are evaluated with regard to their possible use in future studies on the role of X-Pro cis–trans isomerization in the kinetics of protein folding.
358 citations
TL;DR: In this paper, the Michael-additions of aliphatic, alicyclic, and arylsubstituted nitroolefins and enamines lead to γ-nitroketones 3 in good chemical and excellent (> 90%) diastereomeric yields.
Abstract: The Michael-additions of aliphatic, alicyclic, and arylsubstituted nitroolefins and enamines lead to γ-nitroketones 3 in good chemical and excellent (> 90%) diastereomeric yields (see Table 1).
The known threo-configuration of one type of adducts 3 (entries 8, 10, and 11 of Table 1) can be arrived at by assuming the approach 8 of the Michael-acceptor and -donor; the reaction follows a topological rule, which is formulated and which is applicable to such diverse reactions as the diene synthesis, cyclopropanations, carbonyl olefinations and methylenations, aldol- and nitroaldol-type additions, as well as additions of lithium, boron, and chromium derivatives to aldehydes (see 9, 10, 11, and Table 2).
339 citations
TL;DR: In a field study of 162 VDT and 133 control workplaces it was found that constrained postures of VDT workplaces and in full-time typists were sometimes associated with physical impairments in the hands, arms, shoulders and neck.
Abstract: In a field study of 162 VDT and 133 control workplaces it was found that constrained postures of VDT workplaces and in full-time typists were sometimes associated with physical impairments in the hands, arms, shoulders and neck. The reported complaints were confirmed by medical findings on muscles, tendons and joints. The incidence of impairments was increased when the distance from the surface of the keyboards to the desk surface was large; the height of the keyboard from the floor was low; there was insufficient space to rest the forearms and hands; the lateral deviation of the hands operating keyboards was great; and there Was a pronounced inclination or turning of the head. Several recommendations for the proper design of VDT workstations are deduced from the present study
304 citations
TL;DR: In this article, the authors were able to isolate and purify the large central vacuoles of barley mesophyll cells and found most of the accumulated nitrate in the vacuole.
Abstract: Nitrate, the principal nitrogen source of most plants, can accumulate in large quantities in certain crop plants, notably members of the Chenopodiaceae (spinach and beet), Gramineae, Cruciferae (radish and kale) and Compositae (lettuce). Concentrations may exceed 2% fresh weight (17–24% dry weight) in extreme physiological conditions1. This is alarming because nitrate is readily reduced in organisms to the toxic nitrite, which may react with amines to form very potent carcinogenic nitrosamines2. Large stores of nitrate can be maintained in plant cells even in the presence of high nitrate reductase activity3–8. Incoming nitrate does not seem to mix with existing stores4–6,9 and a steady influx of nitrate into the cells was found to be necessary to keep nitrate reductase stably induced3,6. Such observations have been explained by postulating a small ‘metabolic’ pool of nitrate accessible to nitrate reductase4 and presumably also responsible for the induction of the enzyme3, and a large ‘storage’ pool separate from the sites of metabolism3–9,14. Repeated attempts to measure these pools by an indirect method4 have given equivocal results1,10, but storage pools of nitrate have been generally thought to be located in vacuoles, which are difficult to isolate and analyse. However, we were able to isolate and purify the large central vacuoles of barley mesophyll cells and found most of the accumulated nitrate in the vacuoles.
303 citations
TL;DR: There have been many treatments of the theoretical basis of molecular vibrational spectroscopy, and more recently a comprehensive discussion has been presented by Bellamy (1975), which accentuate the correlation of vibratory spectra with molecular structure from an essentially empirical point of view.
Abstract: Application of vibrational spectroscopy to the problem of structure determination of molecules of biological interest goes back to the early uses of raman and infrared spectroscopy in the study of organic molecules. For reviews of earlier work the reader is referred to compilations by Kohlrausch (1943) and by Jones and Sandorfy (1956), whereas more recently a comprehensive discussion has been presented by Bellamy (1975). These compilations accentuate the correlation of vibrational spectra with molecular structure from an essentially empirical point of view and culminate in the establishment of empirical correlation charts. For typical examples the reader is referred to Weast (1974) and Bellamy (1975). There have been many treatments of the theoretical basis of molecular vibrational spectroscopy. Among them the classical work by Herzberg (1945) and by Wilson et al. (1955) should be mentioned. Applications of infrared spectroscopy (IR) to structure problems of biological interest have been summarized by Susi (1969), Fraser and MacRae (1973), and Wallach and Winzler (1974). It was remarked quite eraly that relevant structural information about biological systems often requires study in aqueous solution, which forms the natural environment for most biologically important systems. Besides critical control of experimental conditions and samples the conventional methods of raman spectroscopy may be applied to aqueous solutions in a quite straightforward manner, cf. the contribution by Lord and Mendelson, Chapter 8.
300 citations
TL;DR: In a new approach for the determination of polypeptide conformation, experimental data on intramolecular distances between pairs of hydrogen atoms obtained from nuclear Overhauser enhancement studies are used as input for a distance geometry algorithm that determines the limits of the conformation space occupied by the polyPEptide chain.
247 citations
TL;DR: In this article, a new class of multipulse sequences specifically designed for low-power requirements is introduced, and it is found that of all sequences tested BR-24 leads to optimum performance.
236 citations
TL;DR: In this article, the authors present substantial evidence that the Al distribution in ZSM-5 crystals is non-uniform, showing that Al is invariably concentrated in the rim portion of the crystals.
Abstract: ZSM-5, a prominent member of the new generation of high silica zeolites, is a potential catalyst. The activity of ZSM-5 type synthetic zeolites with respect to acid-catalysed reactions is a linear function of the Al content1 which can assume extremely low values, but in catalytic applications is typically 1–3 Al per unit cell containing 96 Si+Al atoms. We now present substantial evidence that the Al distribution in ZSM-5 crystals is non-uniform. We first noted zoning of Al in ZSM-5 when examining scanning X-ray micrographs (Al Kα) of 50 µm crystals. The comparatively large crystals necessary for detailed measurements of Al concentration profiles using electron probe analysis suggest that Al is invariably concentrated in the rim portion of the crystals. No comparable zoning has been reported previously for zeolites.
TL;DR: In this paper, the ages of two or more calibration points in a composite marine magnetic-anomaly profile and interpolating between or extrapolating beyond these points, assuming constant spreading rates in each interval, were assigned to the Late Cretaceous-Cenozoic geomagnetic reversal time scale.
Abstract: Since 1968, absolute ages have been assigned to the Late Cretaceous–Cenozoic geomagnetic reversal time scale by fixing the ages of two or more calibration points in a composite marine magnetic-anomaly profile and interpolating between or extrapolating beyond these points, assuming constant spreading rates in each interval. Previously, no more than 4 calibration points were used, but it is now possible to specify 11 calibration points, in addition to the 0 m.y. datum. This improvement is based on magnetostratigraphic studies in Italian pelagic limestones; these studies closely tie the geomagnetic reversal sequence to the foraminiferal and coccolith zonations. Absolute ages of calibration points are provided by the best available dates on stage boundaries, which are located from the biostratigraphic zonation. The greatest changes from previous scales come in the late Paleocene–early Eocene, where the new ages are as much as 3 m.y. younger than in the 1977 scale of LaBrecque and others, and as much as 1.8 m.y. younger than in the 1980 scale of Ness and others.
TL;DR: In this paper, the relationship between magnetic susceptibility anisotropy, finite strain, and progressive deformation has been studied in Permian red shales and slates of the Maritime Alps (southeastern France).
TL;DR: A test procedure for capillary gas chromatographic columns, first published three years ago, is described in further detail, giving practical guidelines based on accumulated experience as discussed by the authors. But this procedure is not suitable for column-based analysis.
TL;DR: Rec A protein, which is essential for the recombination process in Escherichia coli, was incubated in the presence of 5′-γ-thiotriphosphate with circular plasmid pBR β G containing small single-stranded gaps forming stable complexes.
TL;DR: In this paper, the diffraction efficiency and energy transfer in photorefractive Bi12SiO20 (BSO) crystals were investigated and the optimum crystallographic orientation for each effect was determined for vertical polarization of the recording beams.
Abstract: The diffraction efficiency and energy transfer are investigated in photorefractive Bi12SiO20 crystals (BSO). Dependence on fringe spacing, electric fields, light intensity and rise-time constants are reported. The optimum crystallographic orientation for each effect is determined for vertical polarization of the recording beams. It is shown that beam coupling is a very sensitive phenomenon in BSO crystals where charge transport lengths are equivalent to usual fringe spacings. Experimental results are interpreted on the basis of the nonlinear theory of self-diffraction developed by Kukhtarev et al. [10].
TL;DR: In this article, the authors proposed a novel expt. is referred to as accordion spectroscopy, in which the dimension is reduced from 3 to 2 by synchronous incrementation of evolution period t, and the mixing time tm parameters: tm = Kt1.
TL;DR: A simple and rapid method discriminating between covalently closed circular (CCC), open circular (OC), and linear (L) forms of plasmid DNA is presented.
TL;DR: It has been found that each organelle has its own peculiar composition in fatty acids, which may be profoundly influenced by the diet, but to different degrees in different organelles.
Abstract: The influence of diets having different fatty acids composition on the fatty acid content of (the phospholipids) of rat liver mitochondria and microsomes, heart mitochondria, brain mitochondria and microsonies has been analyzed. It has been found that each organelle has its own peculiar composition in fatty acids. This composition may be profoundly influenced by the diet, but to different degrees in different organelles. Those of brain are most resistant.
The changes observed are rather rapid, being generally already maximal after three weeks of treatment. The parallel between fatty acid composition of diets, and the changes observed in the organelles, is not strict, and is probably influenced by the metabolic competition among oleic acid, linoleic acid, linolenic acid. Unusual fatty acids like crucic acid. trans-oleic acid. and trans-linoleic acid can also become incorporated into the membranes of cell organelles.
TL;DR: A facultatively methylotrophic bacterium isolated from enrichment cultures containing dichloromethane as the sole carbon source, identified as a Hyphomicrobium species, grew exponentially in batch cultures with 10 mM dichlorometrichane and was stricly dependent on glutathione.
Abstract: A facultatively methylotrophic bacterium was isolated from enrichment cultures containing dichloromethane as the sole carbon source. It was identified as a Hyphomicrobium species. The organism grew exponentially in batch cultures with 10 mM dichloromethane at a specific growth rate of 0.07 h-1. The release of Cl- from dichloromethane and the disapperance of substrate paralleled growth. Resting dichloromethane-grown cells, in the presence of potassium sulphite as a trapping agent, converted cichloromethane methane quantitatively to formaldehyde. The conversion of dichloromethane to formaldehyde by cell extracts was stricly dependent on glutathione. Other thiols were inactive. Glutathione was not consumed in the course of the reaction. The specific activity of the enzymic dehalogenation of dichloromethane amounted to 3.8 mkat/kg protein in extracts of dichloromethane-grown cells and to less than 0.1 mkat/kg protein in extracts from cells grown on methanol.
TL;DR: The EPR spectral parameters for the different spin labels and the 1H- and 13C-NMR relaxation rates for nuclei of the detergent molecules indicated that inclusion of up to one spin label molecule per micelle had little influence on the spatial organization of the micelles, and glucagon backbone runs roughly parallel to the micelle surface.
TL;DR: In this article, the cross-linking reaction which produces an immobilized stationary phase is strongly dependent on the structure of the stationary phase and the selection of a suitable peroxide for the crosslink reaction is discussed.
TL;DR: A new mathematical model is developed for the prediction of the pressure and flow pulses propagating in the arterial system that permits a more realistic simulation of bifurcation and stenoses than was possible previously.
Abstract: Based on earlier theoretical studies, a new mathematical model is developed for the prediction of the pressure and flow pulses propagating in the arterial system. This model permits a more realistic simulation of bifurcation and stenoses than was possible previously. By making use of a computer, it allows us to calculate the pulse shapes along branching arteries. It is based on the assumption that each arterial conduit can be represented by a suitable combination of three basic segments, namely segments with no or only small-calibre side branches, short segments with big side branches, and short segments with pathological changes of the conduit. Along segments of the first type, the pulse propagation is calculated with the aid of the method of characteristics and a first order integration. For the other two types, the linearized mass balance and momentum equations are utilized together with the boundary conditions to determine the pressure and flow values at the ends of the segment. A standard case for the human arterial conduit extending from the heart to the foot, with eight major branches, is defined using published data and prescribing the ejection pattern from the heart. The computed pulse shapes and their changes with propagation exhibit the characteristic features observed in man under normal conditions.
TL;DR: Partition coefficients in n-octanol-water have been determined for the naturally occurring and some synthetic α-amino acids using thin-layer chromatography in different solvent systems as discussed by the authors.
TL;DR: In this article, core level binding energy shifts for the element A of a large number of dilute alloys AB have been measured, where the concentration of the dilute component A is 10% or less.
TL;DR: In this article, the potential function to internal rotation of 1,2-difluoroethane was derived from the far i.r.Ar matrix i.i.d. gas spectrum.
TL;DR: The astroglial character of pituicytes was apparently retained in the implantation conditions, whereas neurosecretory axons had already disappeared.
TL;DR: In this article, large-scale experiments on non-channelized turbidity currents show that a wide flow opening angle forms and a rapid dilution of the current with distance takes place, resulting in tongue-shaped isopachs.
TL;DR: The solubility properties and the number of disulfide groups per molecule of the crystal protein of Bacillus thuringiensis were shown to be similar to that of wool keratin this paper.
Abstract: The solubility properties and the number of disulfide groups per molecule of the crystal protein of Bacillus thuringiensis were shown to be similar to that of wool keratin. Dissolution of the crystals required scission of S-S bonds. This could be achieved at neutral pH without loss of toxicity. Molecular weight determinations with gel electrophoresis and ultracentrifugation indicated that the crystal subunit is a dimer. With the exception of the variety israelensis, all strains belonging to ten different subspecies revealed crystal subunits of the same molecular weight.