Polyelectrolyte effect

Commercial grades of PVP, K-15, K-30, K-90, and K-120 and the quaternized copolymer of vinylpyrrolidone and dimthylaminoethylmethacrylate (poly-VP/ DMAEMA) made by International Specialty Products (ISP) were used in this study. PEO standard calibration kits were purchased from Polymer Laboratories Ltd. (PL), American Polymer Standards Corporation (APSC), Polymer Standards Service (PSS), and Tosoh Corporation (TSK). In addition, two narrow NIST standards, 1923 and 1924, were used to evaluate commercial PEO standards. Deionized, filtered water, and high-performance liquid chromatography grade methanol purchased from Aldrich or Fischer Scientific were used in this study. Lithium nitrate (LiN03) from Aldrich was the salt added to the mobile phases to control for polyelectrolyte effects. 

Although the electrostatic potential on the surface of the polyelectrolyte effectively prevents the diffusional back electron transfer, it is unable to retard the very fast charge recombination of a geminate ion pair formed in the primary process within the photochemical cage. Compartmentalization of a photoactive chromophore in the microphase structure of the amphiphilic polyelectrolyte provides a separated donor-acceptor system, in which the charge recombination is effectively suppressed. Thus, with a compartmentalized system, it is possible to achieve efficient charge separation. 

Fig. 15. Comparison of the experimental data for the polyelectrolyte effect on ki of NH4-OCN reaction at 50 °C with the theoretical curves obtained from eq. 16. O NaPAA added, [NH4OCN] = 0.0205 M, O DECS added, [NH4OCN] = 0.1025 M (Ref.15 ))...

The 5 and 520,w obtained from Eqs. 1-3 will be apparent values because of the effects of solution non-ideality, deriving from co-exclusion and—for charged polysaccharides—polyelectrolyte effects [30]. To eUminate the effects of non-ideality it is necessary to measure either s or S2o,w for a range of different cell loading concentrations c, and perform an extrapolation to zero concentration. For polysaccharides this has been conventionally achieved from a plot of I/5 (or 1/S20,w) versus c [30] ... 

Poly(starch-g-(l-amidoethylene)) copolymer is not a polyelectrolyte and will be a smaller molecule in water than an equal molecular weight, partially hydrolyzed poly(l-amidoethylene). Polyelectrolyte effect should, however, cause the graft copolymer to expand in solution in the same way it causes poly(l -amidoethylene) to expand, so a series of hydrolyzed graft copolymers were prepared from poly(starch-g-(l-amidoethylene))(41-43) and these derivatives were tested to determine the effect of hydrolysis on copolymer properties in solution. 

Fig. 3. Schematics of the influence of electrostatic interactions on adsorption isotherms of polyelectrolytes. Effect of charge contrast between the polyelectrolyte and the sorbent surface in media of (a) low and (b) high ionic strength.

The poly(vinylpyridine) and poly(tert-butyl methacrylate) copolymers can easily be converted to either cationic or anionic polyelectrolytes by protonation of the pyridine rings or by base hydrolysis of the tert-butyl ester units, respectively. The highly branched structure of the molecules, in combination with the polyelectrolyte effect, should confer useful properties to these materials in solution for applications such as pH-sensitive reversible gels. 

Viscosity Measurements. Viscosity measurements were made in filtered DMF and IN NaOH at 25 =t 0.05°C. The DMF was dried over molecular sieve. Flow times were measured in Cannon-Ubbelohde dilution viscometers, and intrinsic viscosities were obtained from the extrapolation of rjsp/c from the Huggins equation to zero concentration. When an apparent polyelectrolyte effect was found in DMF, the intrinsic viscosities were determined by adding CaCl2 to the DMF or by extrapolation from the higher concentration portion of the Huggins curve. Intrinsic viscosities are probably accurate to about 5%. 

The nature of the viscosity determinations is illustrated in Figure 2. The upper curve shows the typical polyelectrolyte effect found for many of the resins in DMF. Adding CaCl2 to the DMF causes a saturation of charge and induces a relaxation of the resin structure, resulting in normal viscosity behavior. In the NaOH solution the resins acted normally. The... 

The molecular characterization of polyelectrolytes in general, and of DADMAC polymers in particular is complicated for several reasons. First, in aqueous solution the individual properties of the macromolecules are dominated by Coulom-bic interactions. Therefore, the resulting polyelectrolyte effects have to be suppressed through the addition of low molecular electrolyte, such as NaCl. The increase of the ionic strength results in a decrease of the chain stiffness of the polyelectrolyte molecules (see Sect. 5). The chains then revert to the coil dimensions of neutral macromolecules in dilute solutions. However, problems may still arise, particularly since the mode of action of these effects is quite different in various characterization methods [27]. 

The model of Tipping et al. (1988) is an example of an electrostatic discrete functional group model. The effects of variable solution ionic strength and pH on the apparent surface acidity constants (polyelectrolyte effects) are accounted for by the incorporation of an electrostatic term exp(—2wzZ) in the equilibrium constants. A brief description of the model is given below. 

Figure 21.1 has been drawn to suggest that F+ > r. This inequality is generally true for nucleic acids in low to moderate salt, a phenomenon sometimes called the polyelectrolyte effect (Draper, 2008 Record and Richey, 1988). Any RNA conformational change that increases the density of phosphate charges will also increase T+ at the expense of T (Record et al., 1998). Flowever, T + may be similar to T at high salt concentrations for instance, T+ = 0.46 and T = —0.54 ions/nucleotide for DNA in 0.98 MNaBr (Strauss et al., 1967). 

Record, M. T., Jr., Zhang, W., and Anderson, C. F. (1998). Analysis of effects of salts and uncharged solutes on protein and nucleic acid equilibria and processes A practical guide to recognizing and interpreting polyelectrolyte effects, Hofmeister effects, and osmotic effects of salts. A dp. Protein Chem. 51, 281—353. 

To improve and control cell-fiber interactions, the fiber meshes can be either composed of biomacromolecules or postfunctionalized with appropriate biomolecules. The question arises as to which materials can be electrospun. In principle, all polymers can be spun if they provide enough entanglements in solution and adequate interactions between the solvent and solute. Biopolymers, in particular, show dominant H-bonding and/or polyelectrolyte effects, which lead to a strong viscosity increase or poor solvent evaporation. In order to prevent such... 

To interpret the gel mobility experiments, a quantitative predictive model was developed that describes the compactness of the RNA constructs [115, 116]. The model takes into account polyelectrolyte effects, salt concentration, pH of the buffer, screening of the hydrodynamic interactions, flexibility of the molecule, and concentration of the gel. 

Biochemical processes are among the most challenging and interesting reaction systems. Due to the nature of the constituents involved, macromolecules such as nucleic acids or proteins, the processes to be analyzed do not follow a simple physicochemical model, and their mechanism cannot be easily predicted. For example, well-known reactions for simple molecules, e.g., protonation equilibria, increase in complexity for macromolecules due to the presence of polyelectrolytic effects or conformational transitions. Because the data analysis cannot be supported in a model-fitting procedure (hard-modeling methods), the analysis of these processes requires soft-modeling methods that can unravel the contributions of the process without the assumption of an a priori model. 

Calorimetric data on the protonation of PVA, and linear PEI at various temperatures and ionic strengths have been published by St. Pierre et al.10). The very important point of this study is, that AH0 data allow a better evaluation of the polyelectrolyte effect. The following results are worth to be mentioned (Fig. 1). 

Jayaram B, DiCapua FM, Beveridge DL (1991) A theoretical study of polyelectrolyte effects in protein-DNA interactions Monte Carlo free energy simulations on the ion atmosphere contribution to the thermodynamics of lambda repressor-operator complex formation. J Am Chem Soc 113 5211-5221... 

The design of superior polymer catalysts is alw -s related to substrate selectivity and efficient turnover of catalysts. Some selectivity was observed among substrates that was due to hydrophobic and electrostatic factors. Especially the cooperative action of these two factors was effective for rate enhanconents. The efficiency of acid and alkali hydrolyses was increased iq> to 100 times in the presence of prdymers, but the simple polyelectrolyte effect would not yield further rate enhaiK menL More elaborate systems that include efficient general add and base catalyses must be developed. 

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