Macroion adsorption on a mixed, fluid, lipid membrane containing oppositely charged lipids induces local changes in lipid composition at the interaction zones, and gradients at their boundaries. Including these effects in the free energy of the macroion-dressed membrane we derive its spinodal equation, and show that nonideal lipid mixing can lead to (lipid-mediated) attraction between macroions and lateral phase separation in the composite membrane. The critical nonideality for this transition is substantially smaller than that of the bare lipid membrane, decreasing with macroion size and charge. That is, the lipid membrane is destabilized by macroion adsorption.
Mesenchymal Stem Cells (MSCs) are adult stem cells that constitute a variety of adult tissues. MSCs maintain self-renewal ability with the ability to give rise to different mesenchymal cells, and are therefore responsible in part, for the regenerative capacity of mesenchymal tissues. MSCs throughout a variety of species were found to be able to differentiate to several mesenchymal tissues including: bone, cartilage, stroma, adipose, connective tissue, muscle and tendon. MSCs are relatively easily isolated from the bone marrow and expanded in vitro. It was found that MSCs play an important role in bone physiology and hematopoiesis, and in part participate in the pathophysiology related to bone diseases, mainly osteoporosis. MSCs were widely used in experimental studies in vivo, and were shown to form mesenchymal tissues. These discovered features have made MSCs good candidates for the development of various therapeutic modalities aimed to regenerate mesenchymal tissues, mainly bone. The more important approaches currently utilizing MSCs are gene therapy and tissue engineering. Both exploit the current knowledge in molecular biology and biomaterial science in order to direct MSCs to differentiate in vivo to desired lineages and tissues. Better understanding of the molecular mechanism directing the differentiation of MSCs, will eventually allow us to properly manipulate MSCs both in vivo and ex vivo to allow the regeneration of complex tissues and organs.
Computing on the (sub) nanoscale is discussed and illustrated by a specific example of charge transfer along a molecular frame. The general research program is to implement an entire finite state logic machine on a molecule. It is proposed to do so in stages. The first stage is to implement Boolean logic circuits on a single molecule. This has already been achieved up to the level of a full adder. Our current work seeks to implement even more elaborate circuits, to go beyond Boolean logic gates and to go beyond combinational logic circuits to the level of sequential machines. In the longer run it will be necessary to concatenate logical units so that a molecule-like assembly is needed. Here we show by a concrete experimental example that intramolecular concatenation is possible: The molecular backbone is used to move information between two ends of a short peptide. The experiment is a gas phase laser excitation of a molecule with an aromatic chromophore at one end. The absorption by the chromophore localizes the initial excitation. Different outcomes are possible depending on additional inputs. Specifically, charge can be made to migrate to the other end of the molecule. (C) 2002 Elsevier Science B.V. All rights reserved.
The behavior of gelatin chem. modified with N-hydroxysuccinimide ester of caprylic acid at the aq. (NH4)2SO4 soln.-air interface is studied. The compression isotherms of gelatin monolayers whose pattern is dependent on the degree of gelatin modification are obtained. It is established that the area corresponding to the beginning of isotherm rise, two-dimensional pressure of completely compressed monolayer, and the modulus of monolayer surface elasticity increase with the degree of gelatin hydrophobization. The surface ("adsorption") activity of gelatin with the modification degree of 85% is approx. threefold higher than for the initial gelatin. [on SciFinder(R)]
The activity of native and modified glucose oxidase (I) from Aspergillus niger in the system of reversed micelles of Aerosol OT (AOT) in octane was investigated. Two forms of modified I were studied: a hydrophobized form obtained by the attachment of palmitic chains to Lys NH2 groups by the reaction with the palmitic acid ester of N-hydroxysuccinimide and a glycosylated (hydrophilized) form obtained by the attachment of cellobiose moieties. Native I and its derivs., while incorporated into micelles in a surfactant concn. range of 0.05-0.3M, displayed enzyme activity which was comparable with the activity in aq. soln. The dependence of enzyme activity on the degree of hydration of the surfactant (the molar ratio of water to surfactant, w0) did not indicate the formation of qual. new assocd. forms of enzyme subunits inside the micelles. The apparent size of AOT micelles obtained by dynamic light scattering gradually increased from 10 nm at low w0 values up to 25 nm at high w0. Incorporation of native and hydrophobized I into the micelles did not affect their mean size. Kinetic anal. showed that enzyme specificity was about an order of magnitude greater in the system of reverse micelles as compared with aq. soln. [on SciFinder(R)]
A new approach to micropatterning is demonstrated. The approach is based on driving an electrochemical process at the solid-liquid interface through the formation of a flux of ions from a micropipet that is held in close proximity to the surface. The flux of ions is generated by the so-called potential assisted ion transfer at the interface between two immiscible electrolyte solutions (ITIES). As a model system, the local deposition of silver was examined. Specifically, a constant potential, which was applied to a micropipet filled with an aqueous solution of silver ions, caused the transfer of Ag(+) into the outer nitrobenzene (NB) solution that consisted of an electrolyte, tetrabutylammonium tetrakis[4-chlorophenyl]borate (TBATPBCl). To facilitate the transfer of silver ions a macrocyclic ligand, that is, dibenzo-24-crown-8 (DB24C8), was added to the organic phase. The Faradaic current of this micro-ITIES was used as a means of controlling the tip-surface distance in scanning electrochemical microscopy (SECM) and depositing silver microstructures on a gold substrate.[on SciFinder (R)]
A new approach to micropatterning is demonstrated. The approach is based on driving an electrochem. process at the solid-liq. interface through the formation of a flux of ions from a micropipet that is held in close proximity to the surface. The flux of ions is generated by the so-called potential assisted ion transfer at the interface between two immiscible electrolyte solns. (ITIES). As a model system, the local deposition of silver was examd. Specifically, a const. potential, which was applied to a micropipet filled with an aq. soln. of silver ions, caused the transfer of Ag+ into the outer nitrobenzene (NB) soln. that contained an electrolyte, tetrabutylammonium tetrakis[4-chlorophenyl]borate (TBATPBCl). To facilitate the transfer of silver ions a macrocyclic ligand, i.e., dibenzo-24-crown-8 (DB24C8), was added to the org. phase. The faradaic current of this micro-ITIES was used as a means of controlling the tip-surface distance in scanning electrochem. microscopy (SECM) and depositing silver microstructures on a gold substrate. [on SciFinder(R)]
A new characteristic timescale of a catchment is presented, the response timescale (RTS). It is a range of averaging time intervals which, when applied to catchment rainfall, yield smoothed time series that best approximate that of the resultant runoff. In determining the RTS, nothing is assumed about the nature of the rainfall-runoff transformation. In addition, this new measure is shown to be robust against measurement errors. An objective, automatic, observations-based algorithm is described that introduces the concept of peaks density for the estimation of RTS. Estimation is exemplified for single and multiple rainfall-runoff events through application to small catchments in Panama and Israel. In all cases, relatively stable values of response timescale are obtained. It is concluded that at least for the case studies, the response timescale is an intrinsic characteristic of the catchment and it is generally expected to be different from the catchment lag time and time of concentration. INDEX
A new characteristic timescale of a catchment is presented, the response timescale (RTS). It is a range of averaging time intervals which, when applied to catchment rainfall, yield smoothed time series that best approximate that of the resultant runoff. In determining the RTS, nothing is assumed about the nature of the rainfall-runoff transformation. In addition, this new measure is shown to be robust against measurement errors. An objective, automatic, observations-based algorithm is described that introduces the concept of peaks density for the estimation of RTS. Estimation is exemplified for single and multiple rainfall-runoff events through application to small catchments in Panama and Israel. In all cases, relatively stable values of response timescale are obtained. It is concluded that at least for the case studies, the response timescale is an intrinsic characteristic of the catchment and it is generally expected to be different from the catchment lag time and time of concentration. INDEX
