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Table I.

K+/Na+ selectivity by experiment and calculation

Method Solvent ΔΔG (kcal/mol) Selective for 
 Formamidea −0.9 Na+ 
Experiment Formamidebc −0.7 Na+ 
 NMAbd −1.1 Na+ 
 Formamidec (CHARMM27) 0.9 K+ 
 Formamidec (OPLS-AA) 1.3 K+ 
Pairwise Additive NMAe (CHARMM22) 1.6 K+ 
 NMAcd (CHARMM27) 2.8 K+ 
 NMAcd (CHARMM27/NBFIX) 4.7 K+ 
 Formamidec (AMOEBA) −1.3 Na+ 
Polarizable Formamidef (QM/MM) −2.2 Na+ 
 NMAd (Drude) −0.3 Na+ 
Method Solvent ΔΔG (kcal/mol) Selective for 
 Formamidea −0.9 Na+ 
Experiment Formamidebc −0.7 Na+ 
 NMAbd −1.1 Na+ 
 Formamidec (CHARMM27) 0.9 K+ 
 Formamidec (OPLS-AA) 1.3 K+ 
Pairwise Additive NMAe (CHARMM22) 1.6 K+ 
 NMAcd (CHARMM27) 2.8 K+ 
 NMAcd (CHARMM27/NBFIX) 4.7 K+ 
 Formamidec (AMOEBA) −1.3 Na+ 
Polarizable Formamidef (QM/MM) −2.2 Na+ 
 NMAd (Drude) −0.3 Na+ 

K+/Na+ selectivity of bulk liquid formamide and NMA as determined by experimental work, pairwise-additive (nonpolarizable) force field calculations, polarizable force field (AMOEBA and Drude) calculations, and QM/MM (hybrid quantum mechanical and molecular mechanical) calculations. Note that the pairwise-additive force field calculations display positive (K+) selectivity, whereas all other determinations display negative (Na+) selectivity.

a

Marcus, 1983.

b

Cox and Parker, 1973, and Schmid et al., 2000.

c

Grossfield et al., 2003.

d

Yu et al., 2010a.

e

Noskov et al., 2004.

f

Varma and Rempe, 2008.

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