Proteins macroion solutions

B) Rigid sphere model for Polyelectrolyies. — Nucleic acids, proteins and synthetic polypeptides exist in solutions as polyelectrolytes (macroions). The solutions of these ions naturally deviate from ideal character or behavior because of their sizes and charges. If we add a neutral salt such as NaCl to the solutions, the configurations of these polyelectrolytes are changed such that the dectrical neutrality is maintained. 

In this study we restrict our consideration by a class of ionic liquids that can be properly described based on the classical multicomponent models of charged and neutral particles. The simplest nontrivial example is a binary mixture of positive and negative particles disposed in a medium with dielectric constant e that is widely used for the description of molten salts [4-6], More complicated cases can be related to ionic solutions being neutral multicomponent systems formed by a solute of positive and negative ions immersed in a neutral solvent. This kind of systems widely varies in complexity [7], ranging from electrolyte solutions where cations and anions have a comparable size and charge, to highly asymmetric macromolecular ionic liquids in which macroions (polymers, micelles, proteins, etc) and microscopic counterions coexist. Thus, the importance of this system in many theoretical and applied fields is out of any doubt. 

When the molecular Interaction Is strong, as Is the case of ionomers in DMF, a virial expansion is not sufficient to describe the interference effect. We use a simple effective potential model with an effective diameter. This model, which treats the macroions (lonomers) as if they were neutral but have an effective size, was originally used by Doty and Steiner (231 to analyze light scattering data from protein solutions. The equation obtained is... 

Large polyelectrolytes, such as nucleic acids, and polyampholytes, such as proteins, are classified together as macroions. The electrostatic forces of attraction or repulsion between such charged particles play a major role in determining their behavior in solution. 

Debye-Huckel Theory - Polyampholytes like proteins or polyelectrolytes like DNA are called macroions because they are large and because, depending on the solution pH, they may carry a substantial net charge. 

In this context, attention is being given in our laboratory to the thermodynamics of macroion-counterlon interactions and of po-lyion-polylon interactions. Including (soluble) complex formation between polysaocharldic macroions and different polyampholites (e.g. proteins] in dilute aqueous solution. 

The dipole moments of protein and other gas-phase macroions differ from those of solution or solid state precursors because of (i) the change of z and consequent rearrangement of partial charges over the molecule and (ii) unavoidable geometry distortion upon ionization, even with the softest sources.At still higher z... 

Electrophoresis is generally applied in biochanistry and molecular biology laboratories to eharacterize and/or fractionate mixtures of macroions, such as proteins, DNA fragments, and so on. This may be performed in solutions (in a capillary), but more often a moist filter paper or a gel of, for example, polyacrylamide is used as the medium of migration. To improve separation, a pH gradient is applied to the stationary phase, that is, the paper or the gel. Then, each fraction stops migrating at the pH at whieh it is isoelectric. This technique is known as isoelectric focusing. Capillary electrophoresis may further be applied to position molecular species on (bio) analytical microchips. 

In Section 4 of Chapter 2, the strong ion-water interaction, in addition to the interionic interaction, was shown to be an influential factor in determining thermodynamic properties of polyelectrol3 e solutions. The hydration phenomenon of macroions is a typical example of the former type of interaction, but its quantitative aspect could not be discussed in terms of the mean activity coefficient. The measurement of the partial molal voliime of polyelectrol3 es is interesting because this volumetric quantity can furnish quantitative information on the hydration on one hand a because it is the pressure dernmtive of the mean activity coefficient on the other. In spite of its importance, however, only a few measurements have so far b n reported for synthetic polyelectrofytes (75, 79, 50). [For a review of the volumetric study of proteins, amino acids, and peptides, an earlier work by Cohn and Edsall should be consulted (5/)]. 

Small-angle X-ray scattering (SAXS) and neutron scattering (SANS) study show a distinct single broad peak for salt-free and low-salt solutions of ionic polymers such as synthetic polymers, proteins, polynucleotides and virus particles [For convenient reviews, see for example 1 and 2]. Based on our earlier work on thermodynamic activity of ionic polymers, the peak was taken as implying an ordered distribution of the macroions in solutions. The Bragg distance obtained from the peak (2D ) was much... 

Studying mixtrues of proteins. Information from these experiments was obtained on the role of charges in stabilizing macroions in solutions. Some selected results of mobilities and isoelectric points are given in Table I in order to gauge the magnitudes of the mobilities as well as illustrate the values of typical isoelectric points (where zero mobility would be observed) for these proteins. 

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