In 2007, Ludwig Bartels, a German-born American physical chemist, at the University of California, Riverside, expanding on his earlier 2004 walking “DTA molecule” experiments, wherein he used scanning tunneling microscopy (STM) techniques to investigate the diffusion of small molecules upon a CU(111) surface, began investigating so-called "molecular carriers", specifically by doing STM studies on AnthraQuinone (AQ) (Ѻ), a DTA-like molecule, formula , with two oxygen feet. The following shows an "AQ molecule" attaching to or carrying a molecule (or two molecules) during diffusion along the high-symmetry direction by means of individual steps: 
The following is a schematic representation of the attachment of a molecule during the diffusion of an AQ molecule along the high-symmetry direction by means of individual steps taken by sequentially moving either one of the two oxygen feet:
The following are related quotes:
- “The migration of anthraquinone (AQ) (following a mechanism analogous to ) along a high symmetry direction upon a surface was also investi-gated using STM. AQ was shown to attach reversibly and carry a CO2 molecule which exhibits surface-mediated attractive interactions with the walker's oxygen atoms (see: figure [above]). Upon binding of the first cargo, the diffusion velocity decreases by more than half (the diffusion barrier increases from 23 to 57 meV) while the second cargo attachment process slows the walking only by an additional 20% (diffusion barrier rises to 73 meV).”
- — David Leigh (2014), “Synthetic Small Molecular Walkers” 
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- AQ (subdomain) – Hmolpedia 2020.