Table 1. RNA stabilization by divalent ions^a.

RNA	divalent ion	pKab	[2+]0, mM	ΔΔG°obs, max, kcal/mol	ΔΓ2+, ions/RNA
A-riboswitch	Mg2+		0.104 ± 0.006	−7.30 ± 0.15	3.31 ± 0.20
A-riboswitch	putrescine	9.36 (9.35)	0.87 ± 0.57	−6.36 ± 0.14	2.39 ± 0.11
TLR RNA	Mg2+		0.1.62 ± 0.31	−5.33 ± 0.43	2.06 ± 0.30
TLR RNA	putrescine		9.80 ± 3.21	−3.88 ± 0.99	1.66 ± 0.47
A-riboswitch	cadaverine	(10.05)	1.30 ±0.15	−5.83 ±0.26	2.16 ± 0.17
A-riboswitch	1,3 diaminopropane	(8.6)	0.42 ± 0.2	−6.99 ± 0.12	2.58 ± 0.13
A-riboswitch	cis-1,4 diaminobutene	8.78	0.65 ± 0.06	−7.19 ± 0.26	2.41 ± 0.21
A-riboswitch	trans-1,4 diaminobutene	8.93	0.89 ±0.04	−7.09 ± 0.10	2.36 ± 0.07

^aΔΔG°_{obs, max} and [2+]₀ are for fits of eq (4) to data shown in Figures 2 and 3A. ΔΓ₂₊ was calculated by eq (5). All diamino compounds shown have a +2 charge at the pH of the experiments (6.8).

^bpK_a values are the observed macroscopic first acid dissociation constants for the diamino compounds. Values in parentheses were taken from the literature (49-51); other values were determined as described in Materials and Methods.