Dependence between change in enthalpy and heparin chain length. The change in enthalpy (circles, values taken from Table 2) increases with chain length and reaches the values of HO16 and UFH at a heparin chain length around 11 monosaccharides, which is close to the critical heparin chain length (=12) that has to be exceeded to form antigenic PF4/heparin complexes. The error bars for HO05 and HO06 are so small that they are hidden by the circles.