JMS thanks the NIH 1R01GM111412 for funding. NMR facilities at UW-Madison are funded by the National Science Foundation (NSF; CHE-9208463, CHE-9629688) and National Institutes of Health (NIH; RR08389-01). The Q-Exactive mass spectrometer was acquired from an NIH-S10 award (NIH-1S10OD020022-1). The Bruker Quazar APEX2 was purchased by UW-Madison Department of Chemistry with a portion of a gift from Paul J. and Margaret M. Bender.