Thermodynamic energies for the interaction of PF4 with UFH, LMWH, HO16, HO08, HO06, and fondaparinux at 25°C, calculated per mole of PF4 tetramers
| Complexes . | Enthalpy, ∆H (cal/mol) . | Comparison* . | Required enthalpy, ∆Hreq (cal/mol)† . |
|---|---|---|---|
| PF4/UFH | −6682 ± 1150 | > | −4673 ± 1238 |
| PF4/HO16 | −7260 ± 1365 | > | −3415 ± 1865 |
| PF4/LMWH | −6663 ± 906 | > | −3450 ± 1140 |
| PF4/HO08 | −4240 ± 1467 | ≈ | −3840 ± 717‡ |
| PF4/HO06 | −2071 ± 35 | < | −3840 ± 717‡ |
| PF4/fondaparinux | −1333 ± 57 | < | −3840 ± 717‡ |
| Complexes . | Enthalpy, ∆H (cal/mol) . | Comparison* . | Required enthalpy, ∆Hreq (cal/mol)† . |
|---|---|---|---|
| PF4/UFH | −6682 ± 1150 | > | −4673 ± 1238 |
| PF4/HO16 | −7260 ± 1365 | > | −3415 ± 1865 |
| PF4/LMWH | −6663 ± 906 | > | −3450 ± 1140 |
| PF4/HO08 | −4240 ± 1467 | ≈ | −3840 ± 717‡ |
| PF4/HO06 | −2071 ± 35 | < | −3840 ± 717‡ |
| PF4/fondaparinux | −1333 ± 57 | < | −3840 ± 717‡ |
A comparison of the minimum required enthalpy with the measured enthalphy indicates if an antigenicity inducing conformational change (similar to UFH, LMWH, and HO16) is thermodynamically allowed (ΔH > ΔHreq), unlikely (ΔH ≈ ΔHreq), or forbidden (ΔH < ΔHreq).
The lower limit for the enthalpy required to drive antigenicity inducing conformational changes was estimated using TΔS by taking either the measured ΔS values (UFH, LMWH, HO16) or assuming ΔS = −12.8 cal/mol/K (for heparins labeled with ‡), which is the average of the entropy changes for UFH and HO16.