. 2018 Mar 15;115(14):E3126–E3134. doi: 10.1073/pnas.1722042115

Table 1.

Ratio of carboxylate/amide I ground-state bleach signal amplitudes (arbitrary units) at different t₂ values and calculated time constants for the amide I and carboxylate vibrations

Sample	(S_COO−/S_AmI) 150 fs	(S_COO−/S_AmI) 500 fs	Ratio	τ_AmI, fs	τ_COO−, fs
apo	0.17	0.069	0.41	590	230
Ca²⁺	0.15	0.095	0.63	670	360
La³⁺	0.19	0.079	0.42	670	250
Tb³⁺	0.25	0.13	0.52	670	300

S_COO− is the peak spectroscopic amplitude of the carboxylate ground-state bleach, normalized to the strongest feature in the 2D IR spectrum. S_AmI is the peak spectroscopic amplitude of the normalized amide I ground-state bleach. Ratio is the quotient of the amplitude ratios at 150 fs and 500 fs. Ratios were calculated using the maximum value for each peak at each t₂ delay; τ_AmI is the time constant for decay of the amide I vibration; τ_COO− is the time constant for decay of the carboxylate vibration. These metrics were not calculated for Lu³⁺-bound forms of the protein because the side-chain absorptions could not be separated from the amide I band in spectra of the Lu³⁺-bound samples. Additional parameters are available in Table S2.