UV-Visible and Inelastic Electron Tunneling Spectroscopies of Brevetoxins

We have studied the UV-vis and vibrational spectra of the brevetoxins PbTx-2, PbTx-3, PbTx-9, and 2, 3, 27, 28, 41, 43-hexahydro-(reduced) PbTx-3. The absorption at 194 nm (ε ≈ 18 000 L mol−1 cm−1) of PbTx-2 and PbTx-3 is assigned to the Π–Π* transition of the lactone conjugated double bonds. The n-Π* transition of the lactone is seen at 239 nm (∈ ≈ 2 800 L mol−1 cm−1). The absorption band at 208 nm for PbTx-2 is assigned to the conjugated double bonds of the aldehyde function located on the K-ring side chain. The inelastic electron tunneling spectra of PbTx-2, PbTx-3, PbTx-9, and fully reduced PbTx-3 are presented and the vibrational bands are assigned. We show that inelastic electron tunneling spectroscopy can be used to monitor and measure the vibrational fingerprint of the brevetoxins at a level as low as 1 ng.