Showing papers by "ETH Zurich published in 1979"
TL;DR: There are six principal methods of umpolung: 1 2n-oxidation, heteroatom exchange and modification, homologation and its reversal, the cyclopropane “trick”, use of acetylenes, and redox reactions; under certain circumstances none of these techniques is necessary in cases where direct umpoline is possible.
Abstract: The past decade of organic chemistry may be charcterized as a period of violent development of new synthetic methods. This was accompained by a systematization of the analysis of synthetic problems (synthetic strategy). The planning of the synthesis of an organic target molecule is greatly facilitated by distinguishing between reagents X(C)n … with normal reactivity (acceptor properties at C1,3,5…, donor properties at X, C2,4…) and with reactivity umpolung (acceptor properties at X, C2,4…, donor properties at C1,3,5…). In this context, reactivity umpolung turned out to be useful as a heuristic principle, as a classification scheme, and as an aid for locating so-called strategic bonds (synthon, transform, and antithesis according to E. J. Corey). There are six principal methods of umpolung: 1 2n-oxidation, heteroatom exchange and modification, homologation and its reversal, the cyclopropane “trick”, use of acetylenes, and redox reactions; under certain circumstances none of these techniques is necessary in cases where direct umpolung is possible. Throughout the article, normal reactivity is indicated by green print; reactivity umpolung by red print.
968 citations
TL;DR: In this article, the 1H-nmr chemical shifts and spin-spin coupling constants of the common amino acid residues were measured in solutions of the linear tetrapeptides H-GlyGly-X-L-Ala-OH in D2O and H2O.
Abstract: The 1H-nmr chemical shifts and the spin–spin coupling constants of the common amino acid residues were measured in solutions of the linear tetrapeptides H-Gly-Gly-X-L-Ala-OH in D2O and H2O, the influence of X on the nmr parameters of the neighboring residues Gly 2 and Ala 4 was investigated. The titration parameters for the side chains of Asp, Glu, Lys, Tyr, and His were determined. The pKa values obtained in D2O, with the use of pH-meter readings with a combination glass electrode uncorrected for istope effects, were 0.06 pH units higher in the acidic range and 0.10 pH units higher in the basic range than the corresponding pKa values in H2O. This suggests that the present data are suitable “random-coil” 1H-nmr parameters for conformational studies of polypeptide chains in D2O and H2O solutions.
752 citations
424 citations
TL;DR: In order to measure muscle thickness and to define the muscular architecture at the gastroesophageal function, both en bloc fixation and a new method of preparing dried fiber specimens were used.
320 citations
TL;DR: Evidence from fluorescence, circular dichroism and 1H nuclear magnetic resonance experiments indicates that the conformation of melittin bound to micelles of various detergents or of diheptanoyl phosphatidylcholine is largely independent of the type of lipid and furthermore appears to be quite closely related to the conformational studies of membrane proteins.
267 citations
TL;DR: In this article, a method for the preparation of pentasubstituted cyclopentanes from monosaccharides is presented, involving two crucial steps, viz. the reductive fragmentation of 5-bromo-5-deoxyglucosides (such as 10, 17 and 23, see Scheme 3) with Zn or butyl lithium yielding 5,6-dideoxy-hex-5enoses, and the subsequent cyclization of these hexenoses with N-methyl- or N-(alkoxyalkyl)hydroxylam
Abstract: Carbocyclic Compounds from Monosaccharides. 1. Transformations in the Glucose Series
A method for the preparation of pentasubstituted cyclopentanes from monosaccharides is presented, involving two crucial steps, viz. the reductive fragmentation of 5-bromo-5-deoxyglucosides (such as 10, 17 and 23, see Scheme 3) with Zn or butyl lithium yielding 5,6-dideoxy-hex-5-enoses (such as 11 and 24, see Schemes 3 and 4), and the subsequent cyclization of these hexenoses with N-methyl- or N-(alkoxyalkyl)hydroxylamines (via the corresponding nitrones) to form cyclopentano-isoxazolidines (see Scheme 2). Thus, the glucosides 17 and 23 were converted diastereoselectively and in good yields into the cyclopentano-isoxazolidines 27 and 45 (Schemes 5 and 7), which were characterized by their transformation into various derivatives. 27 and 45 were correlated through the common derivative 62. The configuration of the cyclization products were established by pyrolysis of the N-oxide 65 to the enol ether 67 (Scheme 10).
263 citations
TL;DR: The principle and the experimental realization of spin echo correlated spectroscopy (SECSY) are described and its use for studies of proteins is illustrated with 1H n.m.r. spectra of the basic pancreatic trypsin inhibitor.
229 citations
TL;DR: In this paper, the Hall coefficient has been measured between 2 and 300 K for small crystals of Sm${\mathrm{B}}_{6}$ in which the resistivity at 4 K is nearly ${10}^{4}$ times greater than its 300-K value of 290 \ensuremath{\mu}\ensuredmath{\Omega} cm.
Abstract: The Hall coefficient ${R}_{H}$ has been measured between 2 and 300 K for small crystals of Sm${\mathrm{B}}_{6}$ in which the resistivity $\ensuremath{\rho}$ at 4 K is nearly ${10}^{4}$ times greater than its 300-K value of 290 \ensuremath{\mu}\ensuremath{\Omega} cm. Significant differences from previous results reported for samples with a much smaller low-temperature resistivity rise have been found. It is shown that the size of the resistivity increase precludes its being ascribed to a scattering mechanism for a metallic number of carriers, and that the size of ${R}_{H}$ implies numbers of holes and electrons less than \ensuremath{\sim}5 \ifmmode\times\else\texttimes\fi{} ${10}^{17}$/${\mathrm{cm}}^{3}$ at 4 K. The origin of the low-temperature residual conductivity is discussed.
217 citations
TL;DR: The rare Phanerozoic rock type boninite petrographically resembles Archaean basaltic komatiites and the range of boninite compositions overlaps that of base-komatiite as discussed by the authors.
Abstract: The rare Phanerozoic rock type boninite petrographically resembles Archaean basaltic komatiites and the range of boninite compositions overlaps that of basaltic komatiites. Quench amphibole and hydrous glass in the groundmass of boninites confirm earlier ideas that they may be the products of partial melting of peridotite in hydrous conditions, whereas basaltic komatiites have been assumed to result from fractionation of dry melts. Where field relationships are known, boninites are found either in ophiolites or a fore-arc tectonic environment.
212 citations
TL;DR: The results indicate that the following enzyme activities are mostly, if not exclusively, located in the vacuome, probably all in the typical large vacuoles present in the protoplasts: exo-and endopolyphosphatase, proteases A and B, carboxypeptidase Y, an aminopeptidases, RNase, α-mannosidase, and phosphatases which hydrolyze a number of different substrates.
Abstract: Almost all the vacuoles (about 95%) remained intact after “polybase-induced lysis” of the yeast protoplasts. These vacuoles could be sedimentated together with other cell organelles which were equally well preserved, leaving as a supernatant a cytosol fraction which was essentially uncontaminated by the contents of disrupted vacuoles. After density gradient centrifugation more than half of the vacuoles were recovered in a fraction which was highly purified as judged from the measurement of several marker enzymes and from light and electron microscopic observations. Polyphosphate, which has been shown to be located exclusively in the vacuolar sap of protoplasts, was used as a vacuolar marker to determine the yields of vacuoles in the different fractions obtained from the density gradients. It was also used to assess the overall distribution of lytic enzymes in the cytosol and in the vacuome. The results indicate that the following enzyme activities are mostly, if not exclusively (>90%), located in the vacuome, probably all in the typical large vacuoles present in the protoplasts: exo-and endopolyphosphatase, proteases A and B, carboxypeptidase Y, an aminopeptidase, RNase, α-mannosidase, and phosphatases which hydrolyze a number of different substrates. The polyphosphatases are thus in the same compartment as the polyphosphate. The activities of some other hydrolases, notably of a Mg2+ dependent, Oligomycin and NaN3 insensitive ATPase and alkaline phosphatase, were partially associated with the vacuoles. The activities of pyrophosphatase, tripolyphosphatase, α-glucosidase, and aminopeptidase active in the presence of EDTA, were located almost exclusively in the soluble, cytosolic fraction.
190 citations
TL;DR: The reflectivity of magnetite (Fe3O4) has been measured in the spectral energy range between 003 and 12 eV by means of a Kramers-Kronig analysis.
Abstract: The reflectivity of magnetite (Fe3O4) has been measured in the spectral energy range between 003 and 12 eV The optical constants have been determined by means of a Kramers-Kronig analysis The interband transition spectrum can be interpreted by O 2p to Fe4s transitions and be Fe3dn to 3dn-14s orbital promotion processes including final-state effects of the atom-like 3dn-1 configurations
TL;DR: Studies of proton-proton nuclear Overhauser effects were used to obtain individual assignments of 17 amide proton resonances in the 360 MHz proton nuclear magnetic resonance spectrum of the basic pancreatic trypsin inhibitor and it is suggested that these techniques could serve quite generally to obtaining individual resonance assignments in beta-sheet secondary structures of proteins.
TL;DR: In this paper, a deactivation procedure based on a published method using hexamethyldisilazane in the gas phase is described, which produces truly neutral columns which allow simultaneous analysis of moderately strong free acids and bases.
Abstract: A deactivation procedure is described based on a published method using hexamethyldisilazane in the gas phase. In addition to unusually high inertia and thermostability, the method produces truly neutral columns which allow simultaneous analysis of moderately strong free acids and bases. The silylated columns show their full potential only with on-column injection. Preliminary experimental directions are given; more elaborate directions will become available after extended optimization work.
TL;DR: Theorie der „gummiartigen“ Flussigkeit stellt bei kleinen Deformationen eine korrekte Beschreibung des rheologischen Verhaltens polymerer Losungen and Schmelzen dar as mentioned in this paper.
Abstract: Die vonLodge vorgeschlagene Theorie der „gummiartigen“ Flussigkeit stellt bei kleinen Deformationen eine korrekte Beschreibung des rheologischen Verhaltens polymerer Losungen und Schmelzen dar. Bei groseren Deformationen versagt sie jedoch zunehmend, da sie nicht in der Lage ist, strukturviskoses Verhalten, d. h. die Abnahme der Scherviskositat und der 1. Normalspannungsfunktion mit zunehmender Schergeschwindigkeit, zu erklaren. Auch bei uniaxialer Dehnung verhalten sich Polymer-Schmelzen vom Standpunkt der Lodgeschen Gleichung aus betrachtetstrukturviskos. Aus dem Vergleich des experimentell ermittelten und des fur eine gummiartige Flussigkeit vorausgesagten Spannungsverlaufs bei Relaxationsversuchen und bei Spannversuchen kann der Schlus gezogen werden, das die Struktur des temporaren Netzwerkes einer Polymer-Schmelze bei groseren Deformationen zunehmend zerstort wird. Die Zahl der das Netzwerk aufbauenden Haftstellen nimmt mit zunehmender Deformation ab. Fur den Fall der einfachen Scherung und der uniaxialen Dehnung einer wohldefinierten Polyathylen-Schmelze wird die Deformationsabhangigkeit der Haftstellenzahl angegeben und verglichen.
TL;DR: In this paper, a numerical comparison of the relative sensitivity and minimum performance time for various techniques including projection-reconstruction methods, Fourier imaging, selective excitation, and sensitive point techniques is presented.
TL;DR: In this paper, it was shown that backbone amide proton titration shifts in polypeptide chains are a very sensitive manifestation of intramolecular hydrogen bonding between carboxylate groups and backbone amides.
Abstract: This paper shows that backbone amide proton titration shifts in polypeptide chains are a very sensitive manifestation of intramolecular hydrogen bonding between carboxylate groups and backbone amide protons. The population of specific hydrogen-bonded structures in the ensemble of species that constitutes the conformation of a flexible nonglobular linear peptide can be determined from the extent of the titration shifts. As an illustration, an investigation of the molecular conformation of the linear peptide H-Gly-Gly-L-Glu-L-Ala-OH is described. The proposed use of amide proton titration shifts for investigating polypeptide conformation is based on 360-MHz 1H-nmr studies of selected linear oligopeptides in H2O solutions. It was found that only a very limited number of amide protons in a polypeptide chain show sizable intrinsic intration shifts arising from through-bond interactions with ionizable groups. These are the amide proton of the C-terminal amino acid residue, the amide protons of Asp and the residues following Asp, and possibly the amide proton of the residue next to the N-terminus. Since the intrinsic titration shifts are upfield, the downfield titration shifts arising from conformation-dependent through-space interactions, in particular hydrogen bonding between the amide protons and carboxylate groups, can readily be identified.
TL;DR: The quaternary ammonium salt methyl-trioctylammonium chloride enables the transfer of α-chymotrypsin, tryps in, pepsin and glucagone from water to cyclohexane and the possible relevance of this ‘double transfer’ as a model for the vectorial transport of biopolymers or a separation technique is discussed.
Abstract: The quaternary ammonium salt methyl-trioctylammonium chloride enables the transfer of α-chymotrypsin, trypsin, pepsin and glucagone from water to cyclohexane. Reversed micelles, whose polar core solubilizes both protein and water, are probably formed in the apolar phase. The influence of various parameters on the phase transfer (concentration, pH, solvent, temperature, etc.) has been investigated.
Absorption, fluorescence and circular dichroism studies of the biopolymers in the cyclohexane system have been carried out. For trypsin and chymotrypsin, the CD. signal in the 200 nm region is very similar in water and in cyclohexane, which suggests that the polypeptide folding is not substantially different in the two phases. The fluorescence quantum yield is always much larger in the cyclohexane phase than in water. The longer wavelength region of the UV. absorption spectrum is slightly red-shifted relative to water, and a band at 225 nm, probably arising from the aromatic chromophore, is apparent in the organic phase. Reasons for these spectral perturbations are discussed. The enzymes transferred from water into cyclohexane phases can be continuously retransferred into a second water phase. The possible relevance of this ‘double transfer’ as a model for the vectorial transport of biopolymers or a separation technique is discussed.
TL;DR: Techniques for improving the gain of MOS amplifiers are discussed and an experimental single stage amplifier was realized using CMOS transistor arrays which achieved gain of 3200.
Abstract: Techniques for improving the gain of MOS amplifiers are discussed. These techniques depend on technology used. An experimental single stage amplifier was realized using CMOS transistor arrays which achieved gain of 3200.
TL;DR: Analysis of nuclear magnetic resonance observations of the exchange with deuterium of the solvent of numerous individually assigned interior amide protons in the basic pancreatic trypsin inhibitor and related proteins implies that exchange of interior amid protons must be governed by global fluctuations of the spatial protein structure.
TL;DR: In this paper, the deuterium atoms occupy tetrahedral interstices formed by two Zr and two Mn atoms and represent a 3-dimensional infinite network of diffusion paths for the D atoms.
TL;DR: Coordination sequences as discussed by the authors provide a practical numerical scale for expressing the degree of similarity of three-dimensional 4-connected nets found in zeolite structures when weighted mean values are used for topologically heterogeneous nets.
TL;DR: The most complete stratigraphic section from Hole 380, at 2107 m water depth on the western edge of the abyssal plain, is 1074 m thick, and provides the most complete and complete dating of the sediments.
TL;DR: It is shown that enzymatic activity with cytidine-2′:3′-phosphate and RNA is maintained in the hydrocarbon phase, and that under certain conditions it is even higher than in water solution.
TL;DR: Study of the contributions from the local ring current fields of the aromatic rings to the overall conformation dependent chemical shifts in the basic pancreatic trypsin inhibitor indicates that ring current shifts are the dominant contribution to the observed conformationdependent chemical shifts of the peripheral aliphatic side chain protons.
TL;DR: It is shown, mainly by equilibrium dialysis, on vacuolar extracts, that the retention of arginine in the vacuoles is due to binding by polyphosphate, and this confirms the observation that under conditions provoking “polyphosphates overcompensation” the accumulation of enormous quantities of polyph phosphate is associated with that of corresponding quantities ofArginine.
Abstract: Isolated and purified vacuoles from yeast protoplasts contain the bulk of the cellular pool of arginine. The arginine is firmly retained in the isolated vacuoles despite of the presence of a permease which mediates arginine diffusion through the vacuolar membrane (Boller et al., 1975). It is shown, mainly by equilibrium dialysis, on vacuolar extracts, that the retention of arginine in the vacuoles is due to binding by polyphosphate. The polyphosphate appears to be located exclusively in the vacuoles. Enzymes hydrolysing polyphosphate are also located in the vacuoles. Isolated vacuoles from arginine grown cells contain about three times as much polyphosphate as vacuoles from ammonium grown cells; the vacuolar pool of arginine is correspondingly greater. Thus there seems to be a close correlation between the storage of arginine and polyphosphate. This confirms the observation that under conditions provoking “polyphosphate overcompensation” (Liss and Langen, 1962) the accumulation of enormous quantities of polyphosphate is associated with that of corresponding quantities of arginine, provided this amino acid is supplied in the medium. Yet, under certain growth conditions the cells are able to store, and to mobilize, both arginine and polyphosphate independently.
TL;DR: In this article, it is shown that SC networks are time-variant sampled-data networks, which can be viewed as tandem connected four-ports in the z-domain.
Abstract: Switched-capacitor (SC) networks comprise capacitors interconnected by an array of periodically operated switches. Such networks are particularly attractive in light of the high circuit density possible with MOS integrated circuit technology and hybrid integrated circuits using thin-film and silicon technology. The paper describes the analysis of SC networks by using nodal charge equations. It is shown that SC networks are time-variant sampled-data networks, which can be viewed as tandem connected four-ports in the z -domain. One pair of ports is viewed as a signal path corresponding to the even time slots, the other pair of ports as a path corresponding to the odd time slots of the periodically operated switches. In a subsequent publication the authors will show how four-port equivalent circuits in the z-domain of six basic building blocks can be used for the description of any SC network. This method allows the direct use of traditional network analysis tools like the transmission matrix for deriving transfer functions. The method ultimately leads to a two-port analysis of SC networks in which conventional two-port theory can be applied.
TL;DR: In this paper, the carbon-13 values of the calcareous nannofossils serve as indicators of paleocirculation in the Lower Cretaceous Maiolica Formation of the southern Alps.
Abstract: Cyclic black shale and nannofossil limestone units of the Lower Cretaceous Maiolica Formation of the southern Alps have been studied. From sedimentological data, the black shale units appear to have been formed in an euxinic basin that experienced periodic overturn and basinal aeration. The carbon-13 values of the calcareous nannofossils serve as indicators of paleocirculation. In the Barremian, the palynological spectra of the black shale units reveal a drastic alteration from a warm, dry to a cooler, humid climate. As a result, thermohaline circulation in the western Tethys Ocean was replaced by density stratification, and stagnation of the deeper basins followed.
TL;DR: The pelagic limestones exposed in the valley of the Cismon river (near Feltre) appear to represent continuous deposition from Valanginian to Campanian, apart from a short hiatus in the Early Albian as mentioned in this paper.
TL;DR: In this paper, the authors measured thermal, magnetic, and transport properties of single-phase (Tm) and single-dimensional (Se) crystals and found that the valence state of the Tm ions is influenced by the chemical composition and the divalent character increases from 0.87 to 1.05.
Abstract: Various thermal, magnetic, and transport properties of single-phase ${\mathrm{Tm}}_{x}\mathrm{Se}$ crystals have been measured, partly as a function of temperature ($0.04\ensuremath{\le}T\ensuremath{\le}300$ K), and/or magnetic field ($H\ensuremath{\le}20$ kOe), and/or hydrostatic pressure ($p\ensuremath{\le}20$ kbar). The Tm to Se ratio of the samples has been varied between 0.87 and 1.05. The valence state of the Tm ions is influenced by the chemical composition and the divalent character increases from \ensuremath{\sim}0% for ${\mathrm{Tm}}_{0.87}$Se to \ensuremath{\sim}28% for ${\mathrm{Tm}}_{1.05}$Se. The low-temperature magnetic susceptibility and the anomalously high compressibility are consistent with the model that the ground state of each Tm ion contains both divalent and trivalent character. In all crystals with this homogeneously mixed-valent character, the localized $4f$ electrons and the itinerant $5d$ electrons strongly interact below \ensuremath{\sim}35 K. Magnetic ordering occurs in all compounds investigated, but the type of ordering and the critical parameters of the magnetic phase diagram are again strongly influenced by the chemical composition.
TL;DR: A simple method based on the dependence of bilayer capacitance on transmembrane voltage and the integrated Nernst-Planck equation gave consistent results for the surface potentials of phosphatidyl serine membranes asymmetrically shielded with calcium.
Abstract: A simple method for the determination of asymmetric surface potentials in lipid bilayers is described. The method is based on the dependence of bilayer capacitance on transmembrane voltage. The capacitance is measured by rectifying the 90° component of an applied alternating current signal. A superimposed slow triangular wave results in a hysteresis-like time course of capacitance. The center of the hysteresis figure is shifted along the voltage axis by an amount equal to the difference of the dipole plus surfacecharge potentials on the two sides of the bilayer (capacitance minimization potential). Alternatively, such bilayer asymmetry was studied by using the current-voltage characteristics in the presence of nonactin as a carrier. This analysis was based on the integrated Nernst-Planck equation, assuming a trapezoidal energy barrier and equilibrium of the surface reactions. The two methods gave consistent results for the surface potentials of phosphatidyl serine membranes asymmetrically shielded with calcium. In addition, the current analysis yields the positions of the corners of the barrier, found to be set in 13% for this lipid.