What physical forces are at work in anion-pi interactions such that the residue (i.e. Tyrosine) with an aromatic ring when interacting with negatively charged Aspartate will have a positive dipole. In the research paper that I will reference the authors mention that the arene is electron deficient. I don't get how that works.
If you would be so kind, please see paragraph 2 of the introduction to this research paper and please explain to me what the authors are communicating.
Source: http://onlinelibrary.wiley.com/doi/10.1002/chem.201304995/full
Thank you very much!