Table II.

Apparent First-Order Rate Constants (k _obs) for the Photolysis of Riboflavin (k _obs) in the Presence of Acetate Buffer (pH 3.8–5.6), for the Formation of Formylmethyflavin (k ₁) and Lumichrome (k ₂) and Second-Order Rate Constants for the Interaction of Riboflavin and Acetate Buffer (k′)

pH	Concentration (M)	k obs × 104 s−1 ± SD	k 0 × 104 s−1a ± SD	k 1 × 10−4 s−1 ± SD	k 2 × 104 s−1 ± SD	k′ × 104 (M−1 s−1) ± SD
3.8	0.1	0.60 ± 0.03	0.24 ± 0.01	0.44 ± 0.02	0.16 ± 0.01	4.10 ± 0.20
	0.2	1.01 ± 0.05		0.71 ± 0.03	0.17 ± 0.02
	0.3	1.42 ± 0.08		0.95 ± 0.05	0.23 ± 0.02
	0.4	1.85 ± 0.07		1.22 ± 0.06	0.30 ± 0.04
	0.6	2.40 ± 0.16		1.60 ± 0.08	0.40 ± 0.02
4.1	0.1	0.65 ± 0.03	0.25 ± 0.02	0.50 ± 0.03	0.22 ± 0.01	4.33 ± 0.22
	0.2	1.12 ± 0.06		0.76 ± 0.04	0.37 ± 0.02
	0.3	1.51 ± 0.08		1.05 ± 0.06	0.50 ± 0.03
	0.4	1.93 ± 0.08		1.33 ± 0.07	0.63 ± 0.04
	0.6	2.85 ± 0.10		1.98 ± 0.20	0.88 ± 0.06
4.3	0.1	0.66 ± 0.03	0.24 ± 0.01	0.51 ± 0.02	0.15 ± 0.01	4.31 ± 0.26
	0.2	1.14 ± 0.06		0.80 ± 0.04	0.35 ± 0.02
	0.3	1.70 ± 0.09		1.10 ± 0.05	0.47 ± 0.03
	0.4	2.23 ± 0.11		1.40 ± 0.06	0.63 ± 0.03
	0.6	2.88 ± 0.15		2.24 ± 0.20	0.98 ± 0.05
4.6	0.1	0.43 ± 0.02	0.22 ± 0.02	0.48 ± 0.02	0.15 ± 0.01	3.27 ± 0.18
	0.2	0.63 ± 0.03		0.76 ± 0.04	0.26 ± 0.02
	0.3	1.02 ± 0.05		1.00 ± 0.05	0.37 ± 0.02
	0.4	1.10 ± 0.06		1.20 ± 0.07	0.48 ± 0.03
	0.6	2.20 ± 0.11		1.87 ± 0.12	0.71 ± 0.03
4.9	0.1	0.39 ± 0.02	0.12 ± 0.01	0.37 ± 0.02	0.04 ± 0.03	3.10 ± 0.15
	0.2	0.44 ± 0.03		0.56 ± 0.03	0.14 ± 0.05
	0.3	0.97 ± 0.05		0.73 ± 0.04	0.32 ± 0.02
	0.4	0.83 ± 0.05		0.95 ± 0.05	0.35 ± 0.02
	0.6	1.62 ± 0.10		1.26 ± 0.08	0.59 ± 0.03
5.1	0.1	0.24 ± 0.02	0.10 ± 0.01	0.27 ± 0.01	0.17 ± 0.01	2.58 ± 0.13
	0.2	0.44 ± 0.03		0.41 ± 0.02	0.22 ± 0.02
	0.3	0.83 ± 0.05		0.54 ± 0.03	0.37 ± 0.02
	0.4	0.83 ± 0.05		0.66 ± 0.03	0.41 ± 0.03
	0.6	1.20 ± 0.07		0.89 ± 0.04	0.48 ± 0.03
5.3	0.1	0.20 ± 0.02	0.09 ± 0.04	0.14 ± 0.06	0.11 ± 0.05	2.04 ± 0.10
	0.2	0.38 ± 0.02		0.16 ± 0.07	0.14 ± 0.06
	0.3	0.67 ± 0.03		0.39 ± 0.02	0.27 ± 0.02
	0.4	0.78 ± 0.04		0.49 ± 0.04	0.45 ± 0.03
	0.6	0.95 ± 0.06		0.67 ± 0.06	0.79 ± 0.04
5.6	0.1	0.18 ± 0.01	0.08 ± 0.02	0.06 ± 0.03	0.03 ± 0.02	1.75 ± 0.08
	0.2	0.34 ± 0.02		0.16 ± 0.07	0.14 ± 0.01
	0.3	0.62 ± 0.03		0.34 ± 0.02	0.23 ± 0.02
	0.4	0.76 ± 0.04		0.42 ± 0.03	0.33 ± 0.02
	0.6	0.60 ± 0.04		0.64 ± 0.04	0.53 ± 0.03

^a k ₀ is the first-order rate constant for the photolysis of riboflavin in the absence of acetate buffer