Kinetic estimation of hydrogen isotope exchange reaction between tritiated-water (HTO) vapor and each amino acid in a heterogeneous system

Figures & data

Figure 1. Activity of l-aminobutyric acid vs. mass of the material for the reaction. Gas sample material: HTO vapor; Reaction temp: 70°C; Reaction time: 1.0 h.

Figure 2. T specific activity vs. time for the reaction between l-aminobutyric acid and HTO vapor. Reaction temp: 25°C.

Figure 3. A″-McKay plots for l-aminobutyric acid in the reaction at 25°C. ▴: COOH group, •: NH₂ group.

Table 1. Rate constants (k) for COOH and NH₂ groups in each sample material and activation energy (E _a).

Material	Structural formula		k/10^−2 h^−1					E a
			25°C	36°C	50°C	60°C	70°C	kJ · mol^−1
l-glycine [15]		k NH2	3.3	3.9	5.9	7.2	8.2	18
		k COOH	3.9	5.4	10	11	13	24
l-α-alanine [15]		k NH2	3.1	3.7	5.3	8.4	12.5	26
		k COOH	3.8	5.3	14	20	37	44
l-aminobutyric acid		k NH2	2.7	3.5	5.6	7.3	8.5	23
		k COOH	3.7	5.1	12	17	21	35
l-norvaline [17]		k NH2	2.5	3.3	5.5	7.3	7.9	23
		k COOH	3.6	4.8	11	16	20	35
l-valine		k NH2	2.3	3.0	5.3	6.7	7.5	24
		k COOH	3.3	4.2	10	15	17	34
l-leucine		k NH2	2.4	3.2	5.4	6.9	7.7	24
		k COOH	3.5	4.5	11	16	19	35
l-2-phenylglycine [18]		k NH2	3.5	4.0	6.0	7.6	8.7	18
		k COOH	3.7	5.6	14	17	18	33
l-2-phenylalanine [18]		k NH2	3.4	4.0	5.8	7.6	8.2	18
		k COOH	3.9	5.6	14	16	18	33

Figure 4. Arrhenius plots for the COOH and NH₂ groups in l-aminobutyric acid. ▵: COOH group, ○: NH₂ group.

Figure 5. A plot (based on Taft's equation) of COOH group for each amino acid. Reaction temp: 25°C. ×: l-aminobutyric acid (obtained in this work), *: l-valine (obtained in this work), □: l-2-phenylglycine, ⋄: l-phenylalanine, ▵: l-α-alanine, ○: l-norvaline.

Figure 6. A plot (based on Taft's equation) of NH₂ group for each amino acid. Reaction temp: 25°C. ×: l-aminobutyric acid, *: l-valine, ▪: l-2-phenylglycine, ♦: l-phenylalanine, ▴: l-α-alanine, •: l-norvaline.

Table 2. The ratio of the reaction constant (ρ*) to the steric effect (δ).

Temperature	Functional group	ρ*	δ
25°C	COOH	2	8
	NH2	9	1
36°C	COOH	4	6
	NH2	8	2
50°C	COOH	3	7
	NH2	10	0
60°C	COOH	3	7
	NH2	10	0
70°C	COOH	3	7
	NH2	10	0

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