Showing papers by "University of Marburg published in 1982"

Different Ks values for hydrogen of methanogenic bacteria and sulfate reducing bacteria: An explanation for the apparent inhibition of methanogenesis by sulfate

Abstract: Desulfovibrio vulgaris (Marburg) and Methanobrevibacter arboriphilus (AZ) are anaerobic sewage sludge bacteria which grow on H2 plus sulfate and H2 plus CO2 as sole energy sources, respectively. Their apparent Ks values for H2 were determined and found to be approximately 1 μM for the sulfate reducing bacterium and 6 μM for the methanogenic bacterium. In mixed cell suspensions of the two bacteria (adjusted to equal Vmax) the rate of H2 consumption by D. vulgaris was five times that of M. arboriphilus, when the hydrogen supply was rate limiting. The apparent inhibition of methanogenesis was of the same order as expected from the different Ks values for H2. Difference in substrate affinities can thus account for the inhibition of methanogenesis from H2 and CO2 in sulfate rich environments, where the H2 concentration is well below 5 μM.

Kinetic mechanism for the ability of sulfate reducers to out-compete methanogens for acetate

Abstract: Methanosarcina barkeri and Desulfobacter postgatei are ubiquitous anaerobic bacteria which grow on acetate or acetate plus sulfate, respectively, as sole energy sources. Their apparent K s values for acetate were determined and found to be approximately 0.2 mM for the sulfate-reducing bacterium and 3 mM for the methanogenic bacterium. In mixed cell suspensions of the two bacteria (adjusted to equal V max) the rate of acetate consumption by D. postgatei approached 15-fold the rate of M. barkeri at low acetate concentrations. The apparent inhibition of methanogenesis was of the same order as expected from the different K s value for acetate. Difference in substrate affinities can thus account for the inhibition of methanogenesis from acetate in sulfate-rich environments, where the acetate concentration is well below 1 mM.

Protease resistance and conformation of laminin.

Abstract: Laminin, obtained from a tumor basement membrane, was treated with neutral proteases (trypsin, chymotrypsin, elastase, subtilisin, Stuphylococcus aureus protease), which all produced similar fragment patterns upon prolonged digestion. The patterns were different from those obtained for fibronectin, which showed a much higher susceptibility to proteolysis by the same enzymes. Four large fragments could be purified which accounted together for more than half of the mass of laminin. They were found to differ in size, amino acid composition, spectral properties and antigenicity. The largest fragment 1 (Mr 260000-300000) was rich in half-cystine (120 residues/1000) and showed a circular dichroism spectrum indicating the absence of α helix and β structure. Fragment 3 (Mr= 50000) possessed beta; structure and was able to bind onto heparin-Sepharose. Fragments 2 (Mr= 50000) and 4 (Mr= 75000) were related structures and their relative yields depended on the protease used. They showed spectra similar to those of fragment 1. Electron microscopy revealed that fragment 1 consists of three rodlike elements (length 26 nm) connected to each other at one end. The other fragments appeared as globules (fragment 3), short rods (fragment 2) or globules connected to a short rod (fragment 4). Data obtained from limited proteolysis indicated that fragment 1 and 4 (or 2) are in close proximity to each other in the three short arms of laminin, which in its intact form has the shape of an asymmetric cross. The long arm appeared to be readily degraded by proteases. Circular dichroism studies of native laminin indicated about 55%, aperiodic structures, 15%β structure and 30%× helix. The α helix was readily destroyed by proteolysis and showed a sharp, reversible transition at 58° C. Stability of these structures was decreased by reduction of disulfide bonds or by increasing concentrations of guanidine. Heat denaturation rendered laminin susceptible to plasmin, which did not degrade the native protein. Cleavage occurred mainly within the 440000-Mrpolypeptide chain of laminin and was accompanied by a partial loss of the long arm.

Zur Kenntnis des Faktors F430 aus methanogenen Bakterien: Struktur des porphinoiden Ligandsystems

Abstract: Factor F430 from Methanogenic Bacteria: Structure of the Porphninoid Ligand System A structure is proposed for F430M, a non-cristalline methanolysis product of isolates of the nickel-containing, porphinoid factor F430 from Methanobacterium thermoautotrophicum. Crucial to the structure determination are five incorporation experiments with M. thermoautotrophicum (strain Marburg) in which the specifically mono-13C-labeled biosynthetic precursors (2-13C), (3-13C), (4-13C)-, (5-13C) ALA (ALA = δ-amino-levulinic acid) and L-(methyl-13C)methionine were incorporated into F430 with high efficiency. The 13C-NMR,-spectra of the specifically labeled F430M samples derived therefrom, together with the UV./VIS. spectral data of F430M, contain all the information necessary for the deduction of the constitution of the F430M chromophore, assuming the established pattern of porphinoid biosynthesis to be operative in F430 biosynthesis. 1H-NMR. spectroscopy and, in particular, 1H-NMR.-NOE-difference spectroscopy corroborates and completes the constitutional assignments and, furthermore, makes possible an almost complete derivation of the molecule's relative configuration. Schemes 3 and 4 summarize the results of 1H-NMR. spectroscopy, presenting them within the context of the proposed structure for F430M. The assignment of absolute configuration implied in the formula is given preference because of F430M's very close structural and (assumed) biosynthetic relationship to sirohydrochlorin and vitamin B12 (with respect to ring C, the assignment is based on degradative evidence). According to the proposed structure, the nickel complex F430M possesses an uroporphinoid (Type III) ligand skeleton with an additional carbocyclic ring and a chromophore system not previously encountered among natural porphinoids. It can be considered to be a (tetrahydro) derivative of the corphin system, combining structural elements of both porphyrins and corrins.

Filoviridae: a Taxonomic Home for Marburg and Ebola Viruses ?

Abstract: Filoviridae: a Taxonomic Home for Marburg and Ebola Viruses ? M.P. Kiley E.T.W. Bowen G.A. Eddy M. Isaäcson K.M. Johnson J.B. McCormick F.A. Murphy S.R. Pattyn D. Peters O.W. Prozesky R.L. Regnery D.I.H. Simpson W. Slenczka P. Sureau G. van der Groen P.A. Webb H. Wulff Center for Infectious Diseases, Centers for Disease Control, Atlanta, Ga., USA; PHLS Centre for Applied Microbiology and Research, Porton Down, Salisbury, Wiltshire, UK; US Army Medical Research Institute for Infectious Diseases, Ft. Detrick, Frederick, Md., USA; The South African Institute for Medical Research, Johannesburg, South Africa; Colorado State University, College of Veterinary Medicine and Biomedical Sciences, Ft. Collins, Col., USA;Prins Leopold Instituut voor Tropische Geneeskunde, Antwerpen, Belgium; Bernard-Nocht-Institut für Schiffsund Tropenkrankheiten, Abteilung für Virologie, Hamburg, FRG; National Institute for Virology, Sandringham, Transvaal, South Africa;Hygiene-Institut der Universität, Marburg, FRG; Institut Pasteur, Paris, France

Nonshivering thermogenesis and cold resistance during seasonal acclimatization in the Djungarian hamster

Abstract: Djungarian hamsters,Phodopus sungorus, improved their cold limit during seasonal acclimatization from −24°C in summer to −68°CTa in winter. This was primarily due to an increase in their capacity for nonshivering thermogenesis from 23.4 mW/g in summer to 59.4 mW/g in winter, assisted by an improved utilization of heat in smaller winter acclimatized hamsters. BMR and shivering thermogenesis had only minor effects on seasonal improvements of cold tolerance.

Alteration of membrane fusion as a cause of acute pancreatitis in the rat

Abstract: Infusion of supramaximal doses of cerulein induces acute edematous pancreatitis in the rat. Cannulation of the main pancreatic duct does not prevent the formation of the edema but reveals an almost complete reduction of pancreatic flow. Using freeze-fracture techniques and thin-section electron microscopy, earliest structural alterations were observed at membranes of zymogen granules and the plasma membrane. Fusion of zymogen granules among each other leads to formation of large membrane-bound vacuoles within the cytoplasm. These and individual zymogen granules fuse with the basolateral plasma membrane, discharging their content into the interstitial space. The findings indicate severe changes in the specificity of the intracellular membrane fusion process induced by supramaximal doses of a pancreatic secretagogue, which finally result in autodigestion of the pancreas.

Hopping transport in prototypical organic glasses

Abstract: Recent computer simulations have shown that the temperature dependence of the charge-carrier mobility in an amorphous organic hopping system, where the profile of the energy distribution of the hopping sites is a Gaussian, should follow $\ensuremath{\mu}(T)={\ensuremath{\mu}}_{0}\mathrm{exp}[\ensuremath{-}{(\frac{{T}_{0}}{T})}^{2}]$. ${T}_{0}$ is proportional to the Gaussian width $\ensuremath{\sigma}$. Experimental data obtained for the hole mobility in a variety of organic glasses confirm this relationship and yield $\ensuremath{\sigma}$ values on the order 0.1 eV and ${\ensuremath{\mu}}_{0}$ values on the order ${10}^{\ensuremath{-}2}$ ${\mathrm{cm}}^{2}$/V s. Changes of the $\ensuremath{\mu}(T)$ dependence observed near the glass transition temperature are attributed to an increase of $\ensuremath{\sigma}$ above ${T}_{g}$ as a result of dynamic disorder superimposed on the static fluctuations of site energies. The model predicts a field dependence of $\ensuremath{\mu}$ of the form $\ensuremath{\mu}(E)=\ensuremath{\mu}(E=0)\mathrm{exp}(\frac{E}{{E}_{0}})$ which is observed. Agreement between simulation results and experiment is excellent. It demonstrates that the field dependence of $\ensuremath{\mu}$ is an inherent consequence of hopping transport in a system subject to a Gaussian type of diagonal disorder. No charged trap states have to be invoked.

Post-translational glycosylation of coronavirus glycoprotein E1: inhibition by monensin.

Abstract: The intracellular sites of biosynthesis of the structural proteins of murine hepatitis virus A59 have been analyzed using cell fractionation techniques. The nucleocapsid protein N is synthesized on free polysomes, whereas the envelope glycoproteins E1 and E2 are translated on the rough endoplasmic reticulum (RER). Glycoprotein E2 present in the RER contains N-glycosidically linked oligosaccharides of the mannose-rich type, supporting the concept that glycosylation of this protein is initiated at the co-translational level. In contrast, O-glycosylation of E1 occurs after transfer of the protein to smooth intracellular membranes. Monensin does not interfere with virus budding from the membranes of the endoplasmic reticulum, but it inhibits virus release and fusion of infected cells. The oligosaccharide side chains of E2 obtained under these conditions are resistant to endoglycosidase H and lack fucose suggesting that transport of this glycoprotein is inhibited between the trans Golgi cisternae and the cell surface. Glycoprotein E1 synthesized in the presence of monensin is completely carbohydrate-free. This observation suggests that the intracellular transport of this glycoprotein is also blocked by monensin.

Definition and Classification of the Histamine-Release Response to Drugs in Anaesthesia and Surgery: Studies in the Conscious Human Subject* **

Abstract: In 2 clinical studies in 40 conscious human volunteers and 164 orthopedic patients histamine-release responses were diagnosed, defined and classified. Polygeline (Haemaccel) in its now outdated formulation [40] was chosen as a clinical histamine releaser. The main interest was not concentrated on the extreme, the “classical” anaphylactic response, but on theaverage histamine-release response found in clinical experiments with so many drugs in the last 10 years. In human volunteers 600 ng/kg histamine was i. v. injected. Indicants for a systemic anaphylactoid reaction with the highest incidence ratio were tachycardia, plasma histamine levels >1 ng/ml, “metallic taste”, flush, congestion of head, “wet eyes” and tears, hypertension and headache. Following polygeline none of these subjects developed a life-threatening reaction, but 12 showed a systemic response, 11 a cutaneous reaction and 17 were non-responders. Indicants for a systemic anaphylactoid reaction with the highest incidence ratio were plasma histamine levels >1 ng/ml, tachycardia, wheals, sensation of heat, narrowness of throat, hypertension, headache and wet eyes or tears. In a prolective, cohort study in the orthopedic patients 3 subjects with life-threatening reactions, 27 with systemic response, 96 with cutaneous reaction and 38 non-responders were included. Indicants with the highest incidence ratio were tachycardia, plasma histamine levels >1 ng/ml, erythema and wheals, cough, flush, stuffy nose and facial oedema. With this trial the indicants for diagnosing a systemic histamine release response in volunteers were validated in patients to a large extent. Thus the average histamine-release response was defined by clinical signs such as tachycardia and mild hypertension, scattered hives such as spots of erythema and wheals, respiratory symptoms in the laryngeal and nasal region, such as cough, narrowness in the throat, stuffy nose and sneezingand by pathological plasma histamine levels (>1 ng/ml). In addition histamine-release responses were differentiated as cutaneous responses, systemic responses and life-threatening responses by clinical and operational criteria and by plasma histamine levels. Using clinical trials and medical decision making procedures the incidence of systemic histamine-release responses in patients higher by two orders of magnitude than in other studies reported hitherto.

Kinetic and structural differences between cytochrome c oxidases from beef liver and heart.

Abstract: 1. The cytochrome content of beef liver mitochondria differs from that of beef heart mitochondria by an eightfold lower cytochrome aa3 and a twofold lower cytochrome b and c + c1 content. 2. The kinetic properties of cytochrome c oxidases from beef liver and heart were measured with intact cytochrome c-depleted membranes, deoxycholate-dissolved membranes, and with the isolated enzymes at various cytochrome c concentrations with an oxygen electrode. Under all conditions a higher V was found for the liver enzyme, both for the low-affinity and for the high-affinity binding site for cytochrome c. Differences were also found for the Km of the two enzymes. 3. Isolated beef heart mitochondria contained about twice as much cardiolipin than beef liver mitochondria. The isolated enzymes contained one mole cardiolipin per mole of the heart enzyme, but 2 moles cardiolipin per mole of the liver enzyme. 4. By application of a high performance sodium dodecylsulfate gel electrophoretic system the two isolated enzymes could be separated into 13 different protein components, three of which (polypeptides VIa, VIIa and VIII) were found to differ in their apparent molecular weights. The functional meaning of cytochrome c oxidase isoenzymes in liver and heart is discussed.

Long-range intervalence electron tunneling through fully saturated systems

Abstract: The compounds (..mu..-2,8-dithiadispirol(3.1.3.1)decane)-decaamminediruthenium(II,II) hexafluorophosphate, ((NH/sub 3/)/sub 5/RuS/sub 2/C/sub 8/H/sub 12/Ru(NH/sub 3/)/sub 5/)(PF/sub 6/)/sub 4/, and (..mu..-2,10-dithiatrispiro(3.1.1.3.1.1)tridecane)-decaamminediruthenium(II,II) hexafluorophosphate, ((NH/sub 3/)/sub 5/RuS/sub 2/C/sub 11/H/sub 16/Ru(NH/sub 3/)/sub 5/)(PF/sub 6/)/sub 4/, were prepared, and upon oxidation, their intervalence properties were measured. The spiro binuclear with three rings had an IT band at 808 nm (epsilon 9 +/- 1 M/sup -1/ cm/sup -1/) and that with four rings had an IT band at 690 nm (epsilon 2.3 +/- 0.7 M/sup -1/ cm/sup -1/). This compares with a band at 910 nm (epsilon 43 +/- 2) measured earlier for the two-ring spiro binuclear. The through-bond distances between ruthenium centers range from 11.3 to 17.5 angstrom. The values of the electron tunneling matrix elements were calculated from Hopfield's theory and were found to be 1.7 X 10/sup -2/, 6.8 X 10/sup -3/, and 3.1 X 10/sup -3/ eV for the two-ring, three-ring, and four-ring binuclears, respectively. These correspond to rate constants of 8.0 X 10/sup -7/, 4.9 X 10/sup -6/, and 3.5 X 10/sup -4/ s/sup -1/, respectively, for the three binuclears. The results are discussed in terms of long-range tunneling and are compared to results obtained in solid matrices and biological systems.

Absence of myosin-like immunoreactivity in stereocilia of cochlear hair cells.

Abstract: Movements of the stiff sensory hairs, the stereocilia, which extend outwards from the apical surface of the hair cells in the auditory organ, are thought to have a key role in the process of transduction of sound energy into electrical impulses. Each stereocilium is supported by a paracrystalline axial bundle of actin filaments, which have identical polarities and are extensively cross-linked1–4. Recent immunohistochemical observations on whole mounts of the guinea pig organ of Corti indicated myosin-like immunoreactivity in association with hair cell stereocilia5. Considering the steric situation, it is, however, difficult to imagine any functional interaction between the bundled actin filaments and the assumed myosin molecules. Here we report that in semi-thin, transverse sections of quick-frozen, freeze-dried and plastic-embedded guinea pig organ of Corti, myosin-like immunostaining was restricted to the apical cytoplasm of hair cells and was not detected along the stereocilia. With respect to the immunohistochemical distribution of actin, myosin and the muscular Z-line protein, α-actinin, the apex of hair cells strongly resembles the intestinal epithelial brush border6–7.

Solvent effects on chemical reactivity

Abstract: Typical examples for different types of solvent effects on chemical reactivity are given, e. g. solvent effects on reaction rates, on the position of chemical equilibria, on competitive reaction mechanisms, on dichotomic reaction paths, on chemoselectivity, and on stereoselectivity. According to their solvent sensitivity, most organic reactions can be classified into dipolar transition-state reactions, isopolar transition-state reactions, and free-radical transition-state reactions, typical examples of which are given. Attempts to describe the solvation capability by virtue of empirical parameters of solvent polarity are mentioned. Particular attention is merited by the ET(30)-parameter, an empirical parameter derived from a negatively solvatochromic pyridinium-N-phenolate betaine dye as reference compound. Some examples of the application of this ET(30)-scale to solventsensitive chemical reactions are given.

Diffusion in discrete nonlinear dynamical systems

Abstract: Diffusive processes in one-dimensional discrete chaotic systems are considered. Drift and diffusion coefficients are calculated, which show critical behavior including logarithmic corrections. A Kubo formula for the diffusion coefficient in terms of the time-correlation function is given. Nondiffusive states may exist in certain parameter windows showing drift with broken symmetry or strict localization. Period-doubling bifurcations and states of periodic chaos describing chaotic but nondiffusive drift occur.

Time decay of excitations in the one-dimensional trapping problem

Abstract: An exact solution is obtained for the survival fraction in the one-dimensional diffusion problem with randomly distributed deep traps. The time decay is studied both with and without a bias field. The small concentration (x) long time (t) decay behaves as exp[-(x 2 t/t 0)1/3]. The exact results are compared with the coherent potential approximation (CPA) and the first passage time approach (FPT). We find that in most cases of practical interest the FPT is superior to the CPA.

Clinical results and pharmacokinetics of high‐dose cytosine arabinoside (HD ARA‐C)

Abstract: Four patients with acute nonlymphoblastic leukemia and one malignant teratoma refractory to conventional chemotherapy were treated with high doses of cytosine arabinoside (HD ARA-C). They received up to 12 cycles of 1.8 to 3 g/m2 every 12 hours applied by 2-hour infusions. A total of 55 HD ARA-C infusions was performed. All leukemic patients responded. A complete clearance of blasts from the bone marrow was observed in two patients following 8-12 cycles of 3 g/m2. However, relapses occurred after three and seven weeks, in one case with resistance to HD ARA-C. The patient with malignant teratoma did not respond. No severe toxicity emerged even after repeated applications. Adverse reactions included moderate nausea and vomiting (4 patients), diarrhea (2 patients), hepatic dysfunction (1 patient), bone pain (1 patient), blurred vision (1 patient), conjunctivitis (1 patient), and exanthema with partial epidermiolysis (1 patient). Granulocytopenia occurring between 3-8 days after having started the therapy, subsided within 4-25 days. Plasma levels of ARA-C and the metabolite uracil arabinoside (ARA-U) were monitored. At steady state plasma concentrations of ARA-C were 32-97 microM (8-24 micrograms/ml). ARA-C disappeared from the plasma mono- or biphasic with a terminal half-life (t50%) of 7.8-12.6 minutes. The total clearance (Cl) of ARA-C varied between 1.7 and 2.9 liters/kg . h, and the distribution volume (Vss) between 0.44 and 0.86 liters/kg. Cerebrospinal fluid (CSF) levels of ARA-C reached 10-15% of steady state concentrations in plasma.

Biosynthetic pathways of Vibrio succinogenes growing with fumarate as terminal electron acceptor and sole carbon source

Abstract: 1. With fumarate as the terminal electron acceptor and either H2 or formate as donor, Vibrio succinogenes could grow anaerobically in a mineral medium using fumarate as the sole carbon source. Both the growth rate and the cell yield were increased when glutamate was also present in the medium. 2. Glutamate was incorporated only into the amino acids of the glutamate family (glutamate, glutamine, proline and arginine) of the protein. The residual cell constituents were synthesized from fumarate. 3. Pyruvate and phosphoenolpyruvate, as the central intermediates of most of the cell constituents, were formed through the action of malic enzyme and phosphoenolpyruvate synthetase. Fructose-1,6-bisphosphate aldolase was present in the bacterium suggesting that this enzyme is involved in carbohydrate synthesis. 4. In the absence of added glutamate the amino acids of the glutamate family were synthesized from fumarate via citrate. The enzymes involved in glutamate synthesis were present. 5. During growth in the presence of glutamate, net reducing equivalents were needed for cell synthesis. Glutamate and not H2 or formate was used as the source of these reducing equivalents. For this purpose part of the glutamate was oxidized to yield succinate and CO2. 6. The α-ketoglutarate dehydrogenase involved in this reaction was found to use ferredoxin as the electron acceptor. The ferredoxin of the bacterium was reoxidized by means of a NADP-ferredoxin oxidoreductase. Enzymes catalyzing the reduction of NAD, NADP or ferredoxin by H2 or formate were not detected in the bacterium.

Element‐Element‐Bindungen. I. Synthese und Struktur des Tetra(tert‐butyl)tetrarsetans und des Tetra(tert‐butyl)tetrastibetans

Abstract: Dilithium-(tert-butyl)arsenid reagiert mit (tert-Butyl)dichlorarsan zum Tetra(tert-butyl)tetrarsetan 1; das homologe Tetrastibetan 2 bildet sich bei der Reduktion von (tert-Butyl)dichlorstiban mit Magnesium. Die isotypen Verbindungen kristallisieren monoklin in der Raumgruppe P21/c mit Z = 4. Die bei der Mestemperatur von −45 ± 5°C bestimmten Gitterkonstanten von 1/2 sind: a = 957,4(8)/1 000,2(3); b = 1 399,1(14)/1 423,9(4); c = 1 697,4(9)/1 749,8(7) pm; β = 96,02(6)/96,77(3)°. Nach den Ergebnissen der Rontgenstrukturanalysen (3 531/3 232 symmetrieunabhangige Reflexe, Rg = 4,0/4,6%) sind die E4-Ringe (E = As, Sb) gefaltet; die voluminosen organischen Substituenten stehen pseudo-aquatorial in der all-trans-Konfiguration. Charakteristische mittlere Bindungslangen und -winkel sind: EE 244/282; EC 202/221 pm; ∢ EEE 86/85° ∢ EEC 101/99°. Die Diederwinkel der von den Ringatomen aufgespannten Bisphenoide betragen 139/133°. Element-Element Bonds. I. Syntheses and Structure of Tetra(tert-butyl)tetrarsetane and of Tetra(tert-butyl)tetrastibetane Dilithium (tert-butyl)arsenide reacts with (tert-butyl)dichloroarsine to give tetra-(tert-butyl)tetrarsetane 1; homologous tetra(tert-butyl)tetrastibetane 2 is formed by reduction of (tert-butyl)dichlorostibane with magnesium. The isotypic compounds 1/2 crystallize in the monoclinic space group P21/c with Z = 4. The dimensions of the unit cells determined at −45 ± 5°C are: a = 957.4(8)/1 000.2(3); b = 1 399.1(14)/1 423.9(4); c = 1 697.4(9)/1 749.8(7) pm; β = 96.02(6)/96.77(3)°. As shown by low temperature X-ray structure determinations (3 531/3 232 symmetry independent reflections; Rg = 4.0/4.6%) the four membered rings E4 (E = As or Sb) are folded; in all-trans configuration the bulky organic substituents occupy pseudo-equatorial positions. Characteristic averaged bond distances and angles are: EE 244/282; EC 202/221 pm; ∢ EEE 86/85° ∢ EEC 101/99°. The dihedral angels of the bisphenoides built up by the atoms of the rings are found to be 139/133°.

Trimethylsilylverbindungen der Vb-Elemente. VI. Synthese, Molekül- und Kristallstruktur des Tetrakis(trimethylsilyl)distibans im Vergleich mit Tetraphenyldistiban

Abstract: Das erstmals bei Spaltungsreaktionen am Tris(trimethylsilyl)stiban von Breunig und Mitarb. [9] isolierte Tetrakis(trimethylsilyl)distiban 1 ist mit hoher Ausbeute auch aus Lithium-bis(trimethylsilyl)antimonid · 2THF und 1,2-Dibromathan in n-Pentan zuganglich. Die im festen Zustand intensiv rote, in Losung oder in der Schmelze aber nur noch schwach gelbe Verbindung kristallisiert monoklin in der Raumgruppe P21/c mit a = 680,6(1); b = 1672,8(2); c = 1190,0(1) pm; β = 119,01(5)°; Z = 2 bei + 20°C. Nach den Ergebnissen einer Rontgenstrukturanalyse (R = 0,017) stehen beide Bis(trimethylsilyl)stibano-Gruppen transoid zueinander; charakteristische Bindungslangen und -winkel sind: SbSb 286,7(1); SbSi 259,4 pm; SiSbSi 94,46(3); SbSbSi 98,68(3) und 94,43(3)°. Wie im ahnlichen, kurzlich von Ashe III und Mitarb. [8] publizierten 2,2′,5,5′-Tetramethyldistibolyl wird auch diese Kristallstruktur durch eine nahezu lineare Abfolge von SbSb Hanteln charakterisiert. Der intermolekulare SbSb-Kontakt innerhalb einer solchen Kette ist mit 399 pm gegenuber der mit 440 pm angegebenen Summe der van-der-Waals Radien verkurzt und durfte elektronische Wechselwirkungen unbekannter Art ermoglichen, die fur die Farbigkeit verantwortlich sein konnten. In ubereinstimmung mit dieser Annahme wird eine analoge Kettenbildung bei dem im festen Zustand nur gelben, von Rehder und Mitarb. [44] strukturell bereits untersuchten Tetraphenyldistiban 5 nicht beobachtet. Trimethylsilyl Derivatives of Vb-Elements. VI. Synthesis, Molecular and Crystal Structure of Tetrakis(trimethylsilyl)distibine Compared with Tetraphenyldistibine Tetrakis(trimethylsilyl)distibine already isolated by Breunig et al. [9] from cleavage reactions of tris(trimethylsilyl)stibine may also be obtained in high yields from lithium bis(trimethylsilyl)antimonide · 2THF and 1,2-dibromoethane in n-pentane. This compound intensely red in the solid state, but only slightly yellow in solution or in the melt crystallizes in the monoclinic space group P21/c with a = 680.6(1); b = 1672.8(2); c = 1190.0(1) pm; β = 119.01(5)°; Z = 2 at +20°C. An X-ray structure determination (R = 0.017) shows the bis(trimethylsilyl)-stibino groups to be arranged in a transoid position. Characteristic bond lengths and angles are: SbSb 286.7(1); SbSi 259.4 pm; SiSbSi 94.46(3); SbSbSi 98.68(3) and 94.43(3)°. As in similiar 2,2′,5,5′-tetramethyldistibolyl published recently by Ashe III et al. [8] this crystal structure, too, is characterized by a nearly linear sequence of SbSb groups. Compared with the sum of van-der-Waals radii the intermolecular Sb-Sb contact in such a chain is shortened from 440 to 399 pm. This probably allows electronic interactions of unknown type responsible for the colour of the crystals. In keeping with this assumption an analogous formation of chains is not found in solid, only yellow tetraphenyldistibine 5 the structure of which has already been studied by Rehder et al. [44].

Abstands- und Koordinations-Verhältnisse in den Schichtstrukturen der ternären Fluoride K2MF4 und K3M2F7(MII Mg, Mn, CoZn)

Abstract: Ergebnisse rontgenographischer Einkristallstrukturverfeinerungen an den im K2NiF4− bzw. Sr3Ti2O7−Typ kristallisierenden Verbindungen K2MF4 (M Mg, Mn, Co, Ni) und K3M2F7 (M = Mn, Co, Ni), die alle der tetragonalen Raumgruppe I4/mmm angehoren, werden mitgeteilt. Die resultierenden Abstandsdaten werden unter Einbeziehung der Verbindungen mit M Cu, Zn diskutiert. Die weitgehend den zugehorigen Perowskiten KMF3 entsprechenden Abstandsverhaltnisse in den MF6−Oktaedern werden dem Einflus der KF9−Koordination zugeschrieben, deren kurzester Abstand KF in beiden Schichtstrukturtypen entgegen der Gitteraufweitung von 263,4 pm (K2MgF4) auf 258,0 pm (K2MnF4) abnimmt. Das aus der KF9−Koordination berechnete Ladungsverhaltnis der ungleich gebundenen Anionen fuhrt zu einer ausgeglicheneren Ladungsbilanz fur den K2MF4−Typ, als die Anwendung der Paulingschen Regeln. Relations of Distances and Coordination in the Layer Structures of the Ternary Fluorides K2MF4 and K3M2F7 (MII Mg, Mn, CoZn) Results of X-ray single crystal structure refinements of the compounds K2MF4 (M Mg, Mn, Co, Ni) and K3M2F7 (M Mn, Co, Ni), all crystallizing in the tetragonal space group I4/mmm of the K2NiF4 and Sr3Ti2O7 type, resp., are reported. The distances obtained are discussed, including data of the compounds with M Cu, Zn. The influence of the KF9 coordination is made responsible for the fact, that the octahedral MF6 dimensions are much the same as in the corresponding perovskites KMF3. The shortest KF distance of this KF9 group, occuring in both layer structure types, decreases against lattice widening from 263.4 pm (K2MgF4) to 258.0 pm (K2MnF4). The charge ratio calculated from the KF9 coordination for the unlike bonded anions leads to a better balanced charge distribution in the K2MF4 type, as is obtained by applying Pauling's rules.

Thermosensitivity and its possible fine-structural basis in mechanoreceptors in the beak skin of geese

Abstract: An electrophysiological study on single afferent nerve fibers in the ophthalmic nerve of the goose revealed two kinds of temperature-sensitive mechanoreceptors in the beak, which are innervated by large-diameter myelinated axons. Some Herbst corpuscles, which display rapidly adapting responses to mechanical stimulation, discharge tonically to cooling the receptive field. A static response maximum occurs at temperatures between 15 and 25°C. The vibration sensitivity of Herbst corpuscles decreases with temperature. Many slowly adapting Ruffini endings also respond with sustained discharges to cooling but behave like rapidly adapting mechanoreceptors on warming the receptive field. The temperature at which the maximal static response occurs in different slowly adapting units varies between 10 and 30°C. The fine structure of Herbst corpuscles and Ruffini endings was investigated electron microscopically in order to elucidate possible morphological substrates for the specific functional properties of the two receptor types. Both Herbst corpuscles and Ruffini endings are characterized by a distinct but different combination of nervous and nonnervous (auxiliary) tissue elements and by the occurrence of special structural units at the sensory nerve endings. Such “transducer sites” presumably correspond to those areas of the receptor membrane where the mechanoelectric transduction process takes place. The most prominent constituent of a transducer site is a spurlike axon process, which in the Herbst corpuscle projects between the lamellae of the inner core, and in the Ruffini endings comes into contact with collagenous microfibrils, either directly or indirectly through the mediation of Schwann cell processes. Two morphological variants of Ruffini endings were recognized and were found to occur at different locations in the dermis underlying the horny covering of the bill tip. One type is distinguished by the presence of a specialized terminal cell making contact with the initial branches of the arborizing receptor axon. The other type of Ruffini ending lacks the terminal cell. The structure-function relations in Herbst corpuscles and Ruffini endings are discussed on the basis of the electrophysiological and ultrastructural observations. It is argued that the different response characteristics of both receptor types to mechanical stimuli result from the specific kind and arrangements of the auxiliary receptor structures and from the mechanical properties of the latter. On this basis the thermosensitivity of Herbst corpuscles and Ruffini endings can be explained as a consequence of the differential effects which temperature changes have on one hand on the auxillary receptor structures and on the other hand on the mechanically elicited receptor potential. It is concluded that the temperature sensitivity of some types of mechanoreceptors may be a secondary result of that differentiation of the auxiliary receptor structures which makes the discriminative function of the different types of mechanoreceptors possible and, therefore, does not necessarily conflict with the principle of modality specificity in sensory receptors.