Observation of Ultrafast Vibrational Energy Transfer in Fibrinogen and Fibrin Fibers

[Image: see text] 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.