The interactions of hemoglobin with glutamic acid-based gemini surfactants (L(2)G(2)C(n)) and with n-dodecylammonium alpha-glutamate (GDA) have been studied with isothermal titration microcalorimetry, fluorescence spectroscopy, UV-vis spectroscopy, and circular dichroism. The results indicate that GDA monomer can make the hemoglobin denatured, and that when the concentration of GDA is higher than cmc, heme monomer is released from the hydrophobic cavity of hemoglobin. On the other hand, L(2)G(2)C(n) surfactants can also interact with hemoglobin. Compared with GDA. L(2)G(2)C(n) have a much smaller binding ability with hemoglobin, and the circular dichroism spectra results show that the secondary structure of hemoglobin is possibly stabilized by a small amount of L(2)G(2)C(n), which may generate hydrophobic linkages between the nonpolar residues of hemoglobin. However, with further addition of L(2)G(2)C(n), the secondary structure of hemoglobin is unfolded, and the percentage of alpha helix in hemoglobin molecule is decreased. In addition, the L(2)G(2)C(n), surfactant with a longer spacer can reduce the denaturing degree of hemoglobin. (C) 2008 Elsevier Inc. All rights reserved.