Native counterion

It is important to realize that the addition of ions which differ from the original counterion of the surfactant molecules leads to competitive ion adsorption. This could result in an exchange of the native counterion of the surfactant. Generally, ion-specific effects on foam films can be investigated in two ways (i) due to the addition of salt as already discussed before and (ii) by variation of the counterion of the surfactant. The latter approach has the advantage of having only one type of counterion present in the solution. 

For 10-fold 13C labelled retinal, it has been shown that the differences between chemical shifts for polyene chain carbons of the chromophore in its native environment and detergent-solubilised system were small67 Analysis of the environment of the Schiff base has supported the model of stabilisation based on the protonation by a complex counterion. Three factors were responsible for the excessive positive charge in polyene (i) electronegative nitrogen, (ii) protonation and (iii) counterion strength. 

Coates and Jordan, 1960 Herskovits et cU., 1961) suggest that the phosphate groups of the DNA molecule are extensively paired to counterions in methanol solution, such that a /D (Section IV,B,1) is only roughly one-sixth of its value in water. This applies to the disrupted conformation of the DNA molecule as it exists in methanol solutions, but it may be assumed that a /D is not greatly different for the hypothetical native helical conformation in methanol. It can be concluded, therefore, that there is a net reduction in electrostatic repidsive interactions, and in electrostatic free energy, for the native conformation of DNA in methanol compared to water. Similar considerations apply in ethanol, whose dielectric constant is still smaller than that of methanol. Therefore, electrostatic factors alone would tend to stabilize the helical conformation in these nonaqueous solvents, and in spite of this, the structure is disrupted. 

For both cations and anions the crystal radius increases with the increase ui coordination number. As the coordination number increases, the repulsions among the coordinating counterions become greater and cause them to back ofT a bit. Mter-natively, one can view a lower coordination number as allowing the counter-ions to compress the central ion and reduce its crystal radius. 

Anionic Polymerization. Polymerization of olefins by metallic sodium, sodium ethoxide, and aqueous alkalies has been known for some time. The mechanism of this polymerization is still open to question though the present evi( ence indicates that the mechanism is similar to that of cationic polymerization, except that a polymeric anion is formed and the counterion is a cation. For example, potassium in liquid anunonia forms potassium amide, the amide ion attacks the monomer, forming a n ative ion. This native ion attacks another monomer, and so on, until termination occurs. 

The spectral density S co) is flat in the case of native and of thermally denatured DNA (see Figure 9). These results show that— within the 2%-3% precision of noise measurements—it is not possible to assign a permanent dipole moment to the DNA molecule (see Section 4.2). The variations of R —at the same temperature—observed before and after the helix -> coil transition of DNA are related to counterion ejection phenomena described above and later in Section 4.1.2b. 

B-DNA is the native form of DNA what this means is that the DNA in our cells is in this conformation. Outside the cell, we can obtain B-DNA wdien the humidity is 92% and the counterion is an alkali etal such as Na. This is a right handed helix with a diameter of 20A. The helical twist per baise pair is 36" and the pitch is 34". There are 10 bases per turn of the helix. CD spectrum of B-DNA is shown in Figure 9.10. Note the negative band centered around 240 nm and a positive band around 275 nm. The zero occurs at about 258 nm. 

Several important conclusions were reached in this study. Firstly, there is a deficit in the number of associated counterions for oligomeric DNA (in its native or denatured states) with respect to a polymer. This is due to electrostatic... 

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