Organic structure determination using atomic-resolution scanning probe microscopy.

Nature offers a huge and only partially explored variety of small molecules with potential pharmaceutical applications. Commonly used characterization methods for natural products include spectroscopic techniques such as nuclear magnetic resonance spectroscopy and mass spectrometry. In some cases, however, these techniques do not succeed in the unambiguous determination of the chemical structure of unknown compounds. To validate the usefulness of scanning probe microscopy as an adjunct to the other tools available for organic structure analysis, we used the natural product cephalandole A, which had previously been misassigned, and later corrected. Our results, corroborated by density functional theory, demonstrate that direct imaging of an organic compound with atomic-resolution force microscopy facilitates the accurate determination of its chemical structure. We anticipate that our method may be developed further towards molecular imaging with chemical sensitivity, and will become generally useful in solving certain classes of natural product structures.