Die Bindung von Zink durch Zellwände von Chlorella

Zusammenfassung Aus Chlorella pyrenoidosa präparierte Zellwände wurden durch Analyse und pH-Titration gekennzeichnet. Die Bindung von markiertem Zink durch die Zellwände, die reversibel ist, erfolgt an 2 Arten aktiver Stellen, die sich durch Affinität und Kapazität unterscheiden. Die Zahlenwerte dieser Größen wurden durch Aufnahme einer aus den beiden Komponenten zusammengesetztenLangmuir-Isotherme bestimmt. Die Verdrängung des Zinks von den Zellwänden durch mehrere Arten zweiwertiger Kationen wurde durch Gleichgewichtsdialyse gemessen und auf Grund der erhaltenen Affinitätsreihe die Natur der bindenden Gruppen diskutiert.

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Binding ofZn by cell walls of Chlorella

Cell wall material prepared from Chlorella pyrenoidosa was characterized by analysis and pH titration. Labelled zinc is found to be bound, reversibly, by 2 kinds of active sites. They differ in affinities and capacities, and these were determined from a 2-componentLangmuir isotherm. The displacement of zinc from the cell walls by several kinds of 2-valent cations was measured by equilibrium dialysis. The nature of the sites was discussed on the basis of the affinity series obtained.

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Mit 3 Abbildungen     

Comparison of laser ablation-inductively coupled plasma-mass spectrometry and micro-X-ray fluorescence spectrometry for elemental imaging in Daphnia magna

Visualization of elemental distributions in thin sections of biological tissue is gaining importance in many disciplines of biological and medical research. Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) and scanning micro-X-ray fluorescence spectrometry (micro-XRF) are two widely used microanalytical techniques for elemental mapping. This article compares the capabilities of the two techniques for imaging the distribution of selected elements in the model organism Daphnia magna in terms of detection power and spatial resolution. Sections with a thickness of 10 and 20 μm of the fresh water crustacean Daphnia magna were subjected to LA-ICP-MS and micro-XRF analysis. The elemental distributions obtained for Ca, P, S and Zn allow element-to-tissue correlation. LA-ICP-MS and micro-XRF offer similar limits of detection for the elements Ca and P and thus, allow a cross-validation of the imaging results. LA-ICP-MS was particularly sensitive for determining Zn (LOD 20 μg g⁻¹, 15 μm spot size) in Daphnia magna, while the detection power of micro-XRF was insufficient in this context. However, LA-ICP-MS was inadequate for the measurement of the S distributions, which could be better visualized with micro-XRF (LOD 160 μg g⁻¹, 5 s live time). Both techniques are thus complementary in providing an exhaustive chemical profiling of tissue samples.     

Protein expression dynamics during replicative senescence of endothelial cells studied by 2-D difference in-gel electrophoresis

Endothelial senescence contributes to endothelium dysfunctionality and is thereby linked to vascular aging. A dynamic proteomic study on human umbilical vein endothelial cells, isolated from three umbilical cords, was performed. The cells were cultured towards replicative senescence and whole cell lysates were subjected to 2-D difference gel electrophoresis (DIGE). Despite the biological variability of the three independent isolations, a set of proteins was found that showed senescence-dependent expression patterns in all isolations. We focused on those proteins that showed significant changes, with a paired analysis of variance (RM-ANOVA) p-value of < or =0.05. Thirty-five proteins were identified with LC-Fourier transform MS, and functional annotation revealed that endothelial replicative senescence is accompanied by increased cellular stress, protein biosynthesis and reduction in DNA repair and maintenance. Nuclear integrity becomes affected and cytoskeletal structure is also changed. Such important changes in the cell infrastructure might accelerate endothelium dysfunctionality. This study provides biological information that will initiate studies to further unravel endothelial senescence and gain more knowledge about the consequences of this process in the in vivo situation.     

Comparison of chromatographic ion-exchange resins V. Strong and weak cation-exchange resins

Strong and weak cation-exchangers were compared for a number of chromatographic parameters, i.e. pH dependence, efficiency, binding strength, particle size distribution, static and dynamic capacity, and scanning electron microscopy (SEM) pictures. Chromatographic resins investigated were Fractogel EMD SO3- (M), Fractogel EMD SE Hicap (M), Fractogel EMD COO- (M), MacroPrep 25S, MacroPrep High S, MacroPrep CM, CM HyperZ, and Matrex Cellufine C-500. Testing was done with three proteins: Anti-FVII Mab (IgG), aprotinin, and lysozyme. For lysozyme and aprotinin with pI above experimental pH, dependence of pH on retention was generally low, though some pronounced decrease of retention with increasing pH was observed for CM HyperZ. For Anti-FVII Mab with pI<7.5, binding was observed on several resins at pH 7.5. Efficiency results present the expected trend of increasing dependence of plate height as a function of increasing flow rate, and the highest flow dependence was observed for Fractogel EMD COO-. Particle size distribution was determined by two independent methods, coulter counting and SEM pictures, with fair agreement. Binding strength data of cation-exchange resins as a function of ionic strength depends on the protein, but binding and elution at high salt concentration may in general be performed with MacroPrep resins. Comparison of dynamic capacity data at 10% break-through and static capacity measurements shows that a very diverse utilization of approximately 25-90% of the total available capacity is employed during chromatographic operation. The effect of competitive binding from yeast fermentation components on dynamic binding capacity of aprotinin was studied showing a significant decrease in binding capacity. Sepharose FF, Toyopearl 650 M, and Ceramic HyperD F strong and weak cation-exchange resins were included in this study. Resins with good pure aprotinin capacity also performed well for aprotinin in fermentation broth, but the highest relative capacity was obtained with MacroPrep High S having a fairly low pure component dynamic capacity. Results of this paper may be used in the selection of resins for further testing in biopharmaceutical protein purification process development.     

Syntheses and quadratic optical nonlinearities of ruthenium(II) complexes with ethynyl-connected N-methylpyridinium electron acceptors

We have prepared a number of new dipolar complexes containing ethynyl or buta-1,3-diynyl units linking electron-rich {Ru(II)(NH3)5}2+, trans-{Ru(II)(NH3)4L}+ (L = pyridine or N-methylimidazole), or trans-{Ru(II)Cl(pdma)2}+ [pdma = 1,2-phenylenebis(dimethylarsine)] centers to pyridinium electron acceptors. In acetonitrile solutions at 295 K, the new complexes display unusual blue-shifting of their metal-to-ligand charge-transfer (MLCT) bands as the conjugation is extended, in a fashion similar to that of the corresponding ethenyl systems. Hyper-Rayleigh scattering (HRS) and Stark spectroscopic measurements provide direct and indirect estimates of static first hyperpolarizabilities beta0, and both the linear and nonlinear optical (NLO) properties are temperature- and medium-dependent. Thus, at 77 K in butyronitrile glasses, the MLCT bands display more normal red shifts upon conjugation extension. While the Stark-derived beta0 values generally increase as n (the number of ethynyl units) increases from 0 to 2, the HRS data show maximization at n = 1 for two of the ammine series but an increase upon moving from n = 1 to 2 for the pdma complexes. Comparisons with the analogous ethenyl chromophores show that the latter generally display larger beta0 values, whether determined via HRS or Stark data, and the inferiority of the ethynyl systems in terms of NLO response is more pronounced when n = 2. This differing behavior is attributable primarily to larger increases in the transition dipole moment mu12 (and, hence, donor-acceptor pi-electronic coupling) on elongation in the ethenyl chromophores.     

Syntheses and properties of two-dimensional, dicationic nonlinear optical chromophores based on pyrazinyl cores

Six new dicationic 2D nonlinear optical (NLO) chromophores with pyrazinyl-pyridinium electron acceptors have been synthesized by nucleophilic substitutions of 2,6-dichloropyrazine with pyridyl derivatives. These compounds have been characterized as their PF(6)(-) salts by using various techniques including electronic absorption spectroscopy and cyclic voltammetry. Large red shifts in the intense, π → π* intramolecular charge-transfer (ICT) transitions on replacing -OMe with -NMe(2) substituents arise from the stronger π-electron donor ability of the latter. Each compound shows a number of redox processes which are largely irreversible. Single crystal X-ray structures have been determined for five salts, including two nitrates, all of which adopt centrosymmetric packing arrangements. Molecular first hyperpolarizabilities β have been determined by using femtosecond hyper-Rayleigh scattering at 880 and 800 nm, and depolarization studies show that the NLO responses of the symmetric species are strongly 2D, with dominant "off-diagonal" β(zyy) components. Stark (electroabsorption) spectroscopic measurements on the ICT bands afford estimated static first hyperpolarizabilities β(0). The directly and indirectly derived β values are large, and the Stark-derived β(0) response for one of the new salts is several times greater than that determined for (E)-4'-(dimethylamino)-N-methyl-4-stilbazolium hexafluorophosphate. These Stark spectroscopic studies also permit quantitative comparisons with related 2D, binuclear Ru(II) ammine complex salts.     

Quadratic and cubic nonlinear optical properties of salts of diquat-based chromophores with diphenylamino substituents

A series of chromophoric salts has been prepared in which 4-(diphenylamino)phenyl (Dpap) electron donor groups are connected to electron-accepting diquaternized 2,2'-bipyridyl (diquat) units. The main aim is to combine large quadratic and cubic nonlinear optical (NLO) effects in potentially redox-switchable molecules with 2D structures. The chromophores have been characterized as their PF(6)(-) salts by using various techniques including electronic absorption spectroscopy and cyclic voltammetry. The visible absorption spectra are dominated by intense π → π* intramolecular charge-transfer (ICT) bands, and all of the compounds show two reversible or quasireversible diquat-based reductions and partially reversible Dpap oxidations. Single crystal X-ray structures have been obtained for one salt and for the precursor compound (E)-4-(diphenylamino)cinnamaldehyde, both of which adopt centrosymmetric space groups. First hyperpolarizabilities β have been measured by using hyper-Rayleigh scattering (HRS) with a 800 nm laser, and Stark (electroabsorption) spectroscopy of the ICT bands affords estimated static first hyperpolarizabilities β(0). The directly and indirectly derived β values are large and generally increased substantially for the bis-Dpap derivatives when compared with their monosubstituted analogues. Polarized HRS studies show that the NLO responses of the disubstituted species are dominated by "off-diagonal" β(zyy) components. Lengthening the diquaternizing alkyl unit lowers the electron-acceptor strength and therefore increases the ICT energies and decreases the E(1/2) values for diquat reduction. However, compensating increases in the ICT intensity prevent significant decreases in the Stark-based β(0) responses. Cubic NLO properties have been measured by using the Z-scan technique over a wavelength range of 520-1600 nm, revealing relatively high two-photon absorption cross-sections of up to 730 GM at 620 nm for one of the disubstituted chromophores.     

Quantum Mechanics from Symmetry and Statistical Modeling

Quantum theory is derived from a set ofplausible assumptions related to the following generalsetting: For a given system there is a set ofexperiments that can be performed, and for each suchexperiment an ordinary statistical model is defined. Theparameters of the single experiments are functions of ahyperparameter which defines the state of the system.There is a symmetry group acting on the hyperparameters, and for the induced action on the parameters ofthe single experiment a simple consistency property isassumed, called permissibility of the parametricfunction. The other assumptions needed are rather weak. The derivation relies partly on quantumlogic, partly on a group representation of thehyperparameter group, where the invariant spaces areshown to be in 1-1 correspondence with the equivalenceclasses of permissible parametric functions. Planck'sconstant only plays a role connected to generators ofunitary group representations.     

Synthesis and debenzoylation products of two perbenzoylated 2-substituted 5-D-galactosyl-1,3,4-oxadiazoles

The synthesis of 2-(p-chlorophenyl)-5-[1′,2′,3′,4′,5′-penta-O-benzoyl-D-galactopentitol-1-yl]-1,3,4-oxadiazole is described. Its debenzoylation gave an equilibrium mixture of the 1,3,4-oxadiazole derivative without protection of the hydroxyl group and the N-benzoyl-D-galactono-1,4-lactonehydrazone. A similar equilibrium was observed by debenzoylation of 2-phenyl-5-[1′,2′,3′,4′,5′-penta-O-benzoyl-D-galactopentitol-1-yl]-1,3,4-oxadiazole. The ¹H, ¹³C nmr and ms spectra of these compounds are presented.     

Temperature‐Programmed Packed Capillary Liquid Chromatography Coupled to Fourier‐Transform Infrared Spectroscopy

Temperature‐programmed packed capillary liquid chromatography has been coupled off‐line to Fourier‐transform infrared spectroscopy, utilizing a commercially available interface with a pneumatic nebulizer rebuilt to handle low flow rates at elevated temperatures. The modified interface showed excellent performance with regard to non‐aqueous reversed phase separations of polymer additives, resulting in constructed Gram‐Schmidt chromatograms comparable to chromatograms obtained using UV detection. The spray of the in‐house constructed nebulizer was not influenced by temperature changes of the column effluent, and hence temperature‐programmed gradient separations could be used successfully. The relative standard deviation of peak height was 4.4% (n = 5) and the mass limit of detection was determined to be about 40 ng, using a polymer antioxidant as model compound. The present instrumental coupling has been used for characterization of the antioxidant Irgafos P‐EPQ.