Table 1.

Properties of Y, 3,5-F₂Y, α₃Y and α₃(3,5)F₂Y

System	λmax (nm) / ε (M–1 cm–1)	pKa [pKapp]	Potential vs. NHE (mV)e	Ref.
Y(Ac/NH2)a	275/1400 (Y-OH) 293/2420 (Y-O-)	10	Epeak 830 (pH 7.0)	31
3,5-F2Y(Ac/NH2)a	263/560 (Y-OH) 275/1830 (Y-O-)	7.0 ± 0.2	Epeak 770 (pH 7.0)	31
α3Y	277/1500 (Y-OH, pH 5.4) 294/2430 (Y-O-, pH 13.4)	[11.3 ± 0.1]	E°' 1059 (pH 5.7) E°' 980 (pH 7.0)	10, 22, 23 this work
α3(3,5)F2Y	~264/n.d. (Y-OH)a ~277/n.d. (Y-O-)a	[8.0 ± 0.1]	E°' 1026 (pH 5.7) E°' 952 (pH 7.0)f	this work

System	[Θ]222 × 103 (deg cm2 dmol–1)	Helix (%)b	ΔG (kcal mol–1)g	Ref.
α3Y	−20.0 ± 0.8 (pH 5.6)	75 ± 3 (pH 5.6)c 74 ± 1 (4.5-10)d	−3.7 ± 0.1 (pH 5.0) −3.9 ± 0.1 (pH 5.5)	10, 22, this work
α3(3,5)F2Y	−20.9 ± 0.6 (pH 5.6)	79 ± 2 (pH 5.6)c	−3.7 ± 0.1 (pH 5.0) −3.7 ± 0.1 (pH 5.5)	this work

^aAcetyl-tyrosinamide (Ac/NH₂), ε was not determined (n.d.).

^bScaled relative to the [Θ]₂₂₂ of α₃W (76 ± 1% α-helical, pH 4-10; 10, 25).

^c[Protein] determined by the Bradford assay.

^d[Protein] determined by UV absorption (10, 22).

^eAnodic peak potentials from irreversible differential pulse voltammograms (E_peak; 10, 11, 31). The standard error in E°' is ± ± 4 mV.

^fExtrapolated from the pH 5.7 value and assuming the same pH dependence as observed for α₃Y E°'(pH 5.7) and E°'(pH 7.0)(23).

^gFrom Fig. S5.