Observation of Ultrafast Vibrational Energy Transfer in Fibrinogen and Fibrin Fibers DuttaBiplab VosBart E. RezusYves L. A. KoenderinkGijsje H. BakkerHuib J. 2018 We study the secondary structure of the blood protein fibrinogen using two-dimensional infrared spectroscopy. With this technique, we identify the amide I′ vibrational modes of the antiparallel β-sheets and turns of fibrinogen. We observe ultrafast energy flow among these amide I′ vibrational modes with a time constant of ∼7 ps. This energy transfer time constant does not change significantly upon fibrin fiber formation, indicating that the secondary structure of the fibrinogen monomers remains largely unchanged in the polymerization process.