Negative charge stabilizing group

In addition to hydrogen bonding between the two polynucleotide chains the double helical arrangement is stabilized by having its negatively charged phosphate groups on the outside where they are m contact with water and various cations Na" Mg and ammonium ions for example Attractive van der Waals forces between the... 

Figure 16.18 Nucleophilic aromatic substitution on nitrochlorobenzenes. Only in the ortho and para intermediates is the negative charge stabilized by a resonance interaction with the nitro group, so only the ortho and para isomers undergo reaction.

Figure 2.1 Three types of fluorophenyl esters have been used for coupling to amine-containing molecules. The PFP and TFP esters are relatively hydrophobic and typically have better stability toward hydrolysis in aqueous solution than NHS esters. The STP ester is water-soluble due to the negatively charged sulfonate group, and it provides better solubility to associated crosslinkers or bioconjugation reagents similar to that of a sulfo-NHS ester group.

Overall, the effects of polycations on the helix-coil transition of DNA are similar to those exhibited by the small cations both of them induce thermal stabilization of DNA duplex and decrease the cooperativity of the helix-coil transition In both cases the reasons for the stabilization effects are the screening of the negatively charged phosphate groups of the DNA, which reduces their electrostatic repulsion (Schildkraut, 1965). However, the effective concentration of a simple salt at which the same stabilization effect is achieved is ca. 103 times higher than the effective concentrations of a polycation. Consequently, polycations provide for a much more efficient screening of the DNA phosphate groups than the small cations. 

A is correct. The carbonyl group withdraws negative charge, stabilizing the conjugate base of pyruvate,... 

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