Phosphates protonation

An additional opportunity that arises from applying polymer-based materials is the preparation of water-dispersible composites, which is an essential feature for biomedical purposes, as it is possible to attach bio-active molecules to the poly-mer/CNTs systems and specifically deliver them to cells. In this manner, plasmid DNA, siRNA (Fig. 3.11) and several anticancer agents have been successfully bound and delivered [61]. The stratagem to generate materials with good solubility in aqueous media usually involves the presence of water-soluble polar groups (e.g. phosphates, protonated amines etc.) embedded in the polymer chain. 

The shifts of the lamellar-hexagonal transition during titration are greater and in the opposite direction relative to changes of Tm- Thus, for didodecyl PE, the lamellar-hexagonal transition decreases by 41°C during phosphate protonation (pK 1.9) and by 50°C during amine protonation (pK 9.3), whereas for Tm these shifts are 6°C and 15° C, respectively, in the opposite direction (Fig. 3f) (54). 

Another approach being used to enhance the ionization process is the chemical modification of the nucleic acid molecule in order to improve ionic volatility. For example, the replacement of phosphate protons from native DNA backbones by alkyl groups,25 or the replacement of phosphate groups by phosphorothioate groups followed by alkylation26 have been reported. 

Fig. 1 Important phosphoiylated species. On phosphate protonation state in figures all phosphate groups, for the sake of simplicity, are shown as fully protonated. We recognize that the piotonation state of phosphates and phosphate monoesters is highly dependent upon enviromnent...

Fig. 12 In situ FTIR spectra of the changes in phosphate protonation in solution for different applied potential step between -0.25 V and the potentials indicated on a platinum electrode in a phosphate buffer pH = 7.4 ionic strength 0.2.

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