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Solubility Problems (solubility + problem)
Selected AbstractsAnalysis of the Voltammetric Response of Electroactive Guests in the Presence of Non-Electroactive Hosts at Moderate ConcentrationsELECTROANALYSIS, Issue 18 2004Sandra Mendoza Abstract In this work, we present a method to analyze the voltammetric response of reversible redox systems involving molecules that, bearing m non-interactive electroactive sites, can undergo fast complexation equilibria with host molecules present at concentrations of the same order of magnitude as those of the electroactive guest. The approach focuses on systems for which the relative values of the binding constants for the oxidized and reduced forms of the guest result in the displacement of the voltammetric response of the electroactive molecule as the concentration of the host is increased in the electrolytic solution. This behavior is commonly known as "one wave shift behavior". Based on a series of assumptions, the method allows calculation of all the thermodynamic parameters that describe the electrochemical and complexation equilibria of a given host-guest system. The main strength of the suggested method, however, relies on the fact that it only requires cyclic voltammetry data and that it can be used for systems in which large concentrations of the host can not be employed either due to important changes of the ionic strength or to solubility problems. Although the accuracy of the obtained information is limited by the quality of the data provided by the technique, and by the assumptions employed, it certainly represents an excellent starting point for subsequent refinement either using digital simulations or an independent experimental technique. [source] Synthesis of fluorinated oligomers for supercritical carbon dioxide applicationsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 21 2005N. Bilgin Abstract Syntheses of various fluorine-based surfactants, namely fluorinated-segment-containing block co-oligomers, were achieved by the radical polymerization of mainly acrylate-based monomers. These types of surfactants serve as stabilizers for supercritical carbon dioxide (scCO2) media based applications, for which the effective solubilization of materials in the supercritical phase is generally not possible because of solubility problems faced when CO2 is involved. Initially, a difunctional fluorinated initiator was synthesized in two steps. First, 4,4,-azobis-4-cyanovaleric acid was chlorinated with SOCl2, and then the product, 4,4,-azobis-4-cyanovaleryl chloride, was reacted with a fluorinated alcohol to obtain the initiator for the polymerization reactions. The synthesized triblock co-oligomers consisted of fluorinated side blocks and a hydrocarbon intermediate block. Efficient solubilization of the materials in scCO2 was observed. It was experimentally shown that the solubility efficiency was affected by specific interactions between CO2 and the oligomers, and these were determined by the nature and size of the inner block and by the chain length of the fluorinated side blocks in comparison with the inner block. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5312,5322, 2005 [source] Novel Polyolefins Containing Crystallizable Isotactic Polystyrene Side ChainsMACROMOLECULAR RAPID COMMUNICATIONS, Issue 18 2008Barbara T. Gall Abstract Vinyl-terminated isotactic polystyrene macromonomers were copolymerized with ethylene and 1-octene to new polyolefin graft copolymers with crystallizable polystyrene side chains. The iPS content was varied from 4 to 78 wt.-% using different metallocene and halfsandwich catalysts. No solubility problems of the stereoregular macromonomer occured, because iPS does not crystallize during polymerization. In addition the polymers show nanophase separation of the polyolefin backbone and the iPS side chains. The crystallization of iPS, having a melting point of about 200,°C, can be achieved by annealing. This synthesis strategy allows the fabrication of a new class of thermoplastic elastomers with improved heat distortion temperatures. [source] Cell-free production of transducible transcription factors for nuclear reprogramming,BIOTECHNOLOGY & BIOENGINEERING, Issue 6 2009William C. Yang Abstract Ectopic expression of a defined set of transcription factors chosen from Oct3/4, Sox2, c-Myc, Klf4, Nanog, and Lin28 can directly reprogram somatic cells to pluripotency. These reprogrammed cells are referred to as induced pluripotent stem cells (iPSCs). To date, iPSCs have been successfully generated using lentiviruses, retroviruses, adenoviruses, plasmids, transposons, and recombinant proteins. Nucleic acid-based approaches raise concerns about genomic instability. In contrast, a protein-based approach for iPSC generation can avoid DNA integration concerns as well as provide greater control over the concentration, timing, and sequence of transcription factor stimulation. Researchers recently demonstrated that polyarginine peptide conjugation can deliver recombinant protein reprogramming factor (RF) cargoes into cells and reprogram somatic cells into iPSCs. However, the protein-based approach requires a significant amount of protein for the reprogramming process. Producing fusion RFs in the large amounts required for this approach using traditional heterologous in vivo production methods is difficult and cumbersome since toxicity, product aggregation, and proteolysis by endogenous proteases limit yields. In this work, we show that cell-free protein synthesis (CFPS) is a viable option for producing soluble and functional transducible transcription factors for nuclear reprogramming. We used an E. coli -based CFPS system to express the above set of six human RFs as fusion proteins, each with a nona-arginine (R9) protein transduction domain. Using the flexibility offered by the CFPS platform, we successfully addressed proteolysis and protein solubility problems to produce full-length and soluble R9-RF fusions. We subsequently showed that R9-Oct3/4, R9-Sox2, and R9-Nanog exhibit cognate DNA-binding activities, R9-Nanog translocates across the plasma and nuclear membranes, and R9-Sox2 exerts transcriptional activity on a known downstream gene target. Biotechnol. Bioeng. 2009; 104: 1047,1058. © 2009 Wiley Periodicals, Inc. [source] Oligomerization of BenM, a LysR-type transcriptional regulator: structural basis for the aggregation of proteins in this familyACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 5 2007Sandra Haddad LysR-type transcriptional regulators comprise the largest family of homologous regulatory DNA-binding proteins in bacteria. A problematic challenge in the crystallization of LysR-type regulators stems from the insolubility and precipitation difficulties encountered with high concentrations of the full-length versions of these proteins. A general oligomerization scheme is proposed for this protein family based on the structures of the effector-binding domain of BenM in two different space groups, P4322 and C2221. These structures used the same oligomerization scheme of dimer,dimer interactions as another LysR-type regulator, CbnR, the full-length structure of which is available [Muraoka et al. (2003), J. Mol. Biol.328, 555,566]. Evaluation of packing relationships and surface features suggests that BenM can form infinite oligomeric arrays in crystals through these dimer,dimer interactions. By extrapolation to the liquid phase, such dimer,dimer interactions may contribute to the significant difficulty in crystallizing full-length members of this family. The oligomerization of dimeric units to form biologically important tetramers appears to leave unsatisfied oligomerization sites. Under conditions that favor association, such as neutral pH and concentrations appropriate for crystallization, higher order oligomerization could cause solubility problems with purified proteins. A detailed model by which BenM and other LysR-type transcriptional regulators may form these arrays is proposed. [source] |