Table 2.

Predicted, simulated, and experimental K⁺ /Na⁺ ion selectivities for various structures

Structure	ΔG Predicted	ΔG Simulated/ (Ref.)	ΔG Experimental/ (Ref.)	ΔG Predicted ɛ > 1	% χn	% χq	% χr
1. K+ channel model	6.6	5.6 (13)	5–6 (6–9)	5.5	60	40	0
2. Na+ channel model	−2.6	−5.3	∼−3 (40)	−3.5	−30	−70	0
3. LeuT Na1	−1.8	−6.1 (36)	<−5 (41)	−3.2	−20	−10	−70
4. LeuT Na2	−0.7	−3.2 (36)		−2.7	−10	−30	−60
5. GltPh Na1	−2.2	−1.3	<−3 (42)	−3.6	−20	−5	−75
6. GltPh Na2	1.0	−0.6		−0.3	−10	45	−45
7. DNA quadruplex	6.7	4.0	1.7 (43)	5.5	60	40	0
8. ARK	0.8	1.3	>0 (44)	−0.4	−45	−25	30
9. Valinomycin	3.0	7.2	5–7 (45,46)	1.1	−35	65	0∗
10. 18-crown-6	3.1	2.6	0–2 (47)	3.1	0	100	0
11. NaK channel	∼0	−1.0–1.0 (35)	∼0 (48)	—	—	—	—
12. Nonactin	0.2	0.7	0.7–1.0 (47)	—	—	—	—

Predicted selectivities determined with the binding site surrounded by vacuum and by bulk solvent (ɛ > 1) are shown. A percentage breakdown of contributions toward selectivity from coordination number restriction, χ_n; ligand dipole moment, χ_q; and cavity size/ligand thermal motion, χ_r, is included. A positive value indicates a contribution toward K⁺ preference whereas a negative value indicates a contribution toward Na⁺ preference. Dashes indicate that the coordination number is different for Na⁺ and K⁺, making an estimate of contribution to selectivity difficult.

^∗In contrast to other studies (as discussed in the text), nonlocal effects that are important in valinomycin are not included in this number.