Following previous studies, standard ionization states were assigned to all the residues with the only exception of Asp32, which was protonated at low pH and ionized at high pH.
The DPA ligand in 7, on the other hand, was protonated at low pH; complexation with the metal in 9′ and 9a′ retained the positive charge from the fac-[MI CO 3]+ core regardless ofac-[MI CO 3
The functional groups of Arg (α1), His (α1), Ser (L5) and Asp (L5) contribute to this specificity, producing a zwitterionic S1-binding pocket (see Figure 2D), the geometry of which suggests that Asp is protonated at low pH in order to accept an aspartate in P1 [ 9].
Therefore, a fraction of superoxide anions is expected to be protonated at the low pH values observed in the present work.
These results indicated that although PLA itself was not an effective gene carrier, however, when combined with CS, it probably helped provide the positive charge to the polyplexes at pH 7.4 where CS alone could be protonated at the low extent.
Finally, 2,4′-MDA may be protonated at all three sites.
Dithionite-reduced TPQ is likely to be protonated at physiological pH and therefore unable to coordinate the metal.
On the other hand, 2,2′-MDA can be protonated at either the o-NH2 or ring position.
It seems plausible that electrostatic interactions involving the ε-NH2 groups of the lysines, which are anticipated to be protonated at neutral pH, contribute to the thermal stability.
From our prediction we observed that both E171 and E36 are likely to be protonated at pH 5.5 but not in alkaline conditions.
