DEER in biological multispin-systems: A case study on the fatty acid binding to human serum albumin

► Human serum albumin (HSA) and spin-labeled fatty acids self assemble in solution. ► DEER measurements on HSA are strongly affected by multispin correlations. ► With flip angle dependent DEER measurements we quantify multispin correlations. ► Small distances are overestimated and large distances are suppressed. ► It is favorable to use spin-diluted systems for a quantitative analysis.