Bond enthalpy of all involved bonds

When the magnetic force is applied to the magnetic marker, the force is applied to all bonds between the surface and the marker. Because the weakest bond will break first, only this bond can be examined in these experiments. Because we want to examine the ligand-receptor bonds, we have to make sure that these bonds (streptavidin-biotin or avidin-biotin) are the weakest.

Figure 4.6: Bond enthalpy of all bonds between the surface and the magnetic marker. The xDNA strand has a phosphor backbone with a bond enthalpy for the P-O bond of 407kJ/mol. Enthalpy values are from [108,92]

Figure 4.6 shows all involved bonds and their corresponding bond enthalpy. Except for the ligand-receptor bonds, all bonds are covalent bonds with a bond enthalpy of several hundred kJ/mol. The weakest covalent bond is O-N with a bond enthalpy of 181kJ/mol. But the non-covalent ligand-receptor bonds we want to examine are clearly weaker. For full binding capacity (i.e. all four binding sites occupied), streptavidin-biotin has a bond enthalpy of 96.2kJ/mol and avidin-biotin of 85kJ/mol [55]. Therefore, it is clear that only the ligand-receptor bonds will be ruptured in the experiments and nothing else.