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.     

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.     

Induction of chirality in an achiral monolayer at the liquid/solid interface by a supramolecular chiral auxiliary

An achiral oligo(p-phenylene vinylene) derivative with a ureido-triazine hydrogen bonding unit self-assembles into rows of hydrogen bonded dimers at the liquid/solid interface. Scanning tunneling microscopy reveals the formation of chiral domains, but overall, the surface remains racemic. Addition of a chiral auxiliary which is able to interact with the dimers through hydrogen bonding, showed that global organizational chirality could be achieved since a majority of the domains show the same handedness. After removing the chiral auxiliary with a volatile solvent, the global organizational chirality could be trapped, revealing a memory effect. With this straightforward supramolecular approach, we were able to create a chiral surface with preferred handedness composed of achiral molecules at the air/solid interface.     

Elastic recovery of immiscible blends Part 2: Transient flow histories

Immiscible polymer blends are known to display an unusual elastic recovery after stress release. Recoil after steady-state shearing is well understood and obeys specific scaling relations. Releasing the stress before the steady-state morphology has been reached results in a more complex elastic recovery, including very large final values. This behaviour is investigated systematically. Model blends are used, consisting of nearly inelastic components; hence the measured recoil can be attributed totally to contributions from the interface. The instantaneous structure at the onset of the recoil can vary greatly in transient experiments, ranging from slightly deformed droplets to highly elongated filaments. The effects of this initial structure on the ultimate recoil and time scale of the recovery are studied. The morphological changes during recovery are considered as well. It is demonstrated that they can be computed from the normal stresses during stress relaxation with comparable initial morphologies. This indicates that the same morphological changes occur during stress relaxation and constrained recoil. A scaling relation for the recoil curves has been derived from the Doi-Ohta theory, which is confirmed by the experiments. Received: 9 December 1998 Accepted: 5 April 1999     

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.     

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     

Controlling the position of functional groups at the liquid/solid interface: impact of molecular symmetry and chirality

With the aim of controlling the position of functional groups in a substrate-supported monolayer, a new family of functionalized linear alkyl chains was designed and synthesized, aided by molecular mechanics and dynamics simulations of its two-dimensional self-assembly on graphite. The self-assembly of these amino functionalized diamides at the liquid/solid interface was investigated with scanning tunneling microscopy. Intermolecular hydrogen-bonding interactions involving amides, combined with the effect of molecular symmetry and chirality, were found to guide the self-assembly. Control of the relative position and orientation of the amine groups was achieved, in the case of enantiopure compounds. Interestingly, racemates led to both racemic conglomerate and solid solution formation, with a concomitant loss of positional and orientational control of the amino groups as a result.