Kinetic study of the quenching reaction of singlet oxygen by α-, β-, γ-, δ-tocotrienols, and palm oil and soybean extracts in solution

Figures & data

Fig. 1. Molecular structures of α-, β-, γ-, and δ-tocopherols (Tocs) and α-, β-, γ-, and δ-tocotrienols (Toc-3s), α- and γ-carboxyethyl-6-hydroxychromans (α- and γ-CEHCs), trolox, and 2-methyl-2-pentene.

Table 1. (A) Contents of 8 vitamin E homologues (4 Tocs and 4 Toc-3s) included in palm oil extracts 1–5 and soybean extract 6 and (B) contents of 7 carotenoids included in palm oil extracts 1–5.

(A) wt% of 8 vitamin E homologues Palm oil extracts 1–5	α-Toc	β-Toc	γ-Toc	δ-Toc	α-Toc-3	β-Toc-3	γ-Toc-3	δ-Toc-3	Total Tocs and Toc-3s
	wt%	wt%	wt%	wt%	wt%	wt%	wt%	wt%	wt%
Extract 1 (crude palm oil)	0.0116	0.0003	0.0002	0.00	0.0115	0.0015	0.0196	0.0067	0.0515
Extract 2 (esterified fraction)	0.35	0.01	0.01	0.00	0.39	0.04	0.43	0.10	1.33
Extract 3 (purified fraction)	12.5	0.4	1.0	0.3	10.7	1.8	14.7	4.3	45.7
Extract 4 (distilled fraction)	20.5	1.1	1.2	0.3	19.6	2.6	23.9	6.5	75.7
Extract 5 (mixed Tocs and Toc-3s)	20.5	0.7	1.0	0.5	21.4	3.5	36.5	8.6	92.7
Soybean extract 6
Extract 6 (d-α-tocopherol 1000)	67.9	nd^a	2.3	0.1	Nd	nd	nd	nd	70.3
(B) wt% of 7 carotenoids Palm oil extracts 1-5	α-carotene	β-carotene	Lycopene	Capsanthin	Lutein	Zeaxanthin	β-cryptoxanthin
	wt%	wt%	wt%	wt%	wt%	wt%	wt%
Extract 1 (CPO)	0.0135	0.0160	0.0014	nd	nd	nd	nd
Extract 2	0.0009	0.0011	nd	nd	nd	nd	nd
Extracts 3–5	nd^a	nd	nd	nd	nd	nd	nd

^a nd, not detected.

Fig. 2. Measurement of the second-order rate constant (k_Q) for the reaction of γ-Toc-3 with ¹O₂.

Notes: (A) Change in absorbance of DPBF at 413 nm during the reaction of DPBF with ¹O₂ in the absence and presence of AOs (α-Toc or γ-Toc-3) in ethanol/chloroform/D₂O at 35 °C. [DPBF]_t=0 = 6.76 × 10⁻⁵ M and [EP]_t=0 = 4.41 × 10⁻⁴ M. The values of [α-Toc]_t=0 and [γ-Toc-3]_t=0 are shown in Fig. 2(A). (B) Plot of ln (absorbance) vs. t. (C) Plot of S_Blank/S_γ-Toc-3 vs. [γ-Toc-3]. (D) Plot of t_1/2^γ-Toc-3/t_1/2^Blank vs. [γ-Toc-3].

Table 2. UV–vis absorption maxima (λ_max) and molar extinction coefficients (ε_max) of the antioxidants (tocopherols, tocotrienols, CEHCs, and Trolox) in ethanol/chloroform/D₂O and ethanol, and peak oxidation potentials (E_p).

	In EtOH		In mixed solvent		In acetonitrile
Antioxidant	λmax^a	εmax^b	λmax^a	εmax^b	Ep vs SCE^c
	nm	M^−1 cm^−1	nm	M^−1 cm^−1	mV
α-Toc	292.0	3120	292.5	3330	860
α-Toc-3	292.0	3130	292.5	3140
α-CEHC	291.5	3020	292.0	3150	870
Trolox	291.0	3020	291.0	3280	900
β-Toc	296.0	3340	297.0	3300	920
β-Toc-3	296.0	3570	296.0	3350
γ-Toc	297.5	3750	298.0	3730	930
γ-Toc-3	297.5	3630	298.0	3640
γ-CEHC	297.0	3730	297.5	3670	960
δ-Toc	298.0	3470	298.5	3580	990
δ-Toc-3	297.5	3570	298.5	3570

^a Experimental errors are ± 0.5 nm.

^b Experimental errors are less than ~6%.

^c Values reported in Refs. ²⁶⁾ and ³¹⁾.

Table 3. The k_Q^AO (S) and k_Q^AO (t_1/2) values for 8 vitamin E homologues, α- and γ-CEHCs, trolox, and 2-Methyl-2-pentene (AOs) in ethanol/chloroform/D₂O solution at 35.0 °C, relative rate constants (k_Q^AO (S)/k_Q^α-Toc (S)), relative SOAC values, and ratio of the rate constants (k_Q^Toc−3 (S)/k_Q^Toc (S)).

Antioxidant	kQ^AO (S)	kQ^AO (t1/2)	kQ^AO (S) /kQ^α-Toc (S)	Relative SOAC value	kQ^Toc−3 (S) /kQ^Toc (S)
	M^−1s^−1	M^−1s^−1		Based on mol L^−1 unit
α-Toc	1.31 × 10^8	1.29 × 10^8	1.00	1.00
β-Toc	9.45 × 10^7	8.72 × 10^7	0.721	0.880
γ-Toc	8.15 × 10^7	7.52 × 10^7	0.622	0.695
δ-Toc	4.79 × 10^7	4.36 × 10^7	0.365	0.429
α-Toc-3	1.22 × 10^8	1.11 × 10^8	0.931	0.902	0.931
β-Toc-3	1.05 × 10^8	8.78 × 10^7	0.801	0.839	1.11
γ-Toc-3	8.14 × 10^7	6.89 × 10^7	0.621	0.701	0.998
δ-Toc-3	4.97 × 10^7	4.14 × 10^7	0.379	0.400	1.04
α-CEHC	1.09 × 10^8	8.09 × 10^7	0.832	0.820	0.832
γ-CEHC	7.46 × 10^7	5.86 × 10^7	0.569	0.613	0.915
Trolox	4.20 × 10^7	3.66 × 10^6	0.321	0.349	0.321
2-Methyl-2-pentene	5.98 × 10^5	4.41 × 10^5	0.00456	0.00450

Fig. 3. Measurement of the second-order rate constant (k_Q) for the reaction of palm oil extract 1 with ¹O₂.

Notes: (A) Change in absorbance of DPBF at 413 nm during the reaction of DPBF with ¹O₂ in the absence and presence of AOs (α-tocopherol and palm oil extract 1) in ethanol/chloroform/D₂O at 35 °C. [DPBF] = 6.29 × 10⁻⁵ M and [EP] = 4.20 × 10⁻⁴ M. The values of [α-Toc] and [Extract 1] are shown in Fig. 3(B). (B) Change in absorbance of DPBF, where the correction of baseline due to palm oil extract 1 was performed (see text). (C) Plot of ln (absorbance) vs. t. (D) Plot of S_Blank/S_{Extract 1} vs. [Extract 1]. (E) Plot of t_1/2^{Extract 1}/t_1/2^Blank vs. [Extract 1].

Table 4. The k_Q^Extract (S) and k_Q^Extract (t_1/2) values for palm oil extracts 1–5 and soybean extract 6 in ethanol/chloroform/D₂O solution at 35.0 °C, relative rate constants (k_Q^Extract (S)/k_Q^α-Toc (S)), and relative SOAC values.

Antioxidant	kQ^Extract (S)	kQ^Extract (t1/2)	kQ^Extract (S) /kQ^α-Toc (S)	Relative SOAC value
	L g^−1s^−1	L g^−1s^−1		Based on g L^−1 unit
α-Toc	3.04 × 10^5	3.00 × 10^5	1.00	1.00
Palm oil extracts 1–5
Extract 1 (crude palm oil)	7.32 × 10^3	6.48 × 10^3	0.0241	0.0271
Extract 2 (esterified fraction)	5.09 × 10^3	4.83 × 10^5	0.0167	0.0174
Extract 3 (purified fraction)	1.84 × 10^5	1.87 × 10^5	0.605	0.721
Extract 4 (distilled fraction)	2.08 × 10^5	1.72 × 10^5	0.684	0.769
Extract 5 (mixed Tocs and Toc-3s)	2.37 × 10^5	2.15 × 10^5	0.780	0.802
Soybean extract 6
Extract 6 (d-α-tocopherol 1000)	2.30 × 10^5	2.02 × 10^5	0.757	0.812

Table 5. Comparison between observed and calculated ¹O₂-quenching rates (k_Q^{Extract 5} (S) (Obsd.) and Σ k_Q^AO-i (S) × ([AO-i]/100) (Calcd.)) for palm oil extract 5 in ethanol/chloroform/D₂O solution.

Antioxidant	kQ^AO-i (S)	Mw	kQ^AO-i (S)	[AO-i]	kQ^AO-i (S) × ([AO-i]/100)
	M^−1s^−1		L g^−1s^−1	wt％	L g^−1s^−1
α-Toc	1.31 × 10^8	430.71	3.04 × 10^5	20.5	6.23 × 10^4
α-Toc-3	1.22 × 10^8	424.66	2.87 × 10^5	21.4	6.14 × 10^4
β-Toc	9.45 × 10^7	416.69	2.27 × 10^5	0.7	1.58 × 10^3
β-Toc-3	1.05 × 10^8	410.64	2.56 × 10^5	3.5	8.92 × 10^3
γ-Toc	8.15 × 10^7	416.69	1.96 × 10^5	1.0	1.95 × 10^3
γ-Toc-3	8.14 × 10^7	410.64	1.98 × 10^5	36.5	7.23 × 10^4
δ-Toc	4.79 × 10^7	402.67	1.19 × 10^5	0.5	5.95 × 10^2
δ-Toc-3	4.97 × 10^7	396.62	1.25 × 10^5	8.6	1.07 × 10^4
				Total 92.7
Σ kQ^AO-i (S) × ([AO-i]/100)(Calcd.)					2.20 × 10^5
kQ^Extract 5 (S)(Obsd.)					2.37 × 10^5

Table 6. Comparison between observed and calculated ¹O₂-quenching rates (k_Q^Extract (S) (Obsd.) and k_Q^Extract (S) (Calcd.)) for palm oil extracts 1–5 and soybean extract 6 in ethanol/chloroform/D₂O solution, ratio of the rate constants (k_Q^Extract (S) (Obsd.)/k_Q^Extract (S) (Calcd.)), and total wt% of Tocs and Toc-3s.

Antioxidant	kQ^Extract (S) (Obsd.)	kQ^Extract (S) (Calcd.)	kQ^Extract (S) (Obsd.) /kQ^Extract (S) (Calcd.)	Total Tocs and Toc-3s
	L g^−1s^−1	L g^−1s^−1		wt%
Palm oil extracts 1–5
Extract 1 (CPO)	7.32 × 10^3	Tocs = 1.20 × 10^2 ^a	Tocs = 61.0	0.0515
		Cars = 6.09 × 10^3 ^b
		Total = 6.21 × 10^3 ^c	Total = 1.18
Extract 2	5.09 × 10^3	Tocs = 3.30 × 10^3 ^a	Tocs = 1.54	1.33
		Cars = 3.88 × 10^2 ^b
		Total = 3.69 × 10^3 ^c	Total = 1.38
Extract 3	1.84 × 10^5	1.11 × 10^5 ^a	1.66	45.7
Extract 4	2.08 × 10^5	1.86 × 10^5 ^a	1.12	75.7
Extract 5	2.37 × 10^5	2.20 × 10^5 ^a	1.08	92.7
Soybean extract 6
Extract 6	2.30 × 10^5	2.11 × 10^5 ^a	1.09	70.3

^a The k_Q^Extract (S) (Calcd.) value calculated for total Tocs and Toc-3s.

^b The k_Q^Extract (S) (Calcd.) value calculated for total carotenoids (abbreviated as “cards”).

^c The k_Q^Extract (S) (Calcd.) value calculated for total Tocs, Toc-3s, and carotenoids.

Table 7. The k_Q^AO (S) and relative SOAC values for 11 tocopherol derivatives in ethanol/chloroform/D₂O and ethanol solutions at 35.0 °C.

	In mixed solv		In EtOH
Antioxidant	kQ^AO (S)	Relative SOAC value	kQ^AO (S)	Relative SOAC value
	L g^−1s^−1	Based on g L^−1 unit	L g^−1s^−1	Based on g L^−1 unit
α-Toc	3.04 × 10^5	1.00	4.76 × 10^5	1.00
β-Toc	2.27 × 10^5	0.910	4.46 × 10^5	0.856
γ-Toc	1.96 × 10^5	0.718	3.79 × 10^5	0.676
δ-Toc	1.19 × 10^5	0.459	1.65 × 10^5	0.336
α-Toc-3	2.87 × 10^5	0.915	5.27 × 10^5	1.045
β-Toc-3	2.56 × 10^5	0.880	4.55 × 10^5	0.886
γ-Toc-3	1.98 × 10^5	0.735	3.75 × 10^5	0.729
δ-Toc-3	1.25 × 10^5	0.434	1.76 × 10^5	0.313
α-CEHC	3.92 × 10^5	1.269	6.90 × 10^5	1.271
γ-CEHC	2.82 × 10^1	0.999	4.84 × 10^1	0.916
Trolox	1.68 × 10^5	0.601	3.22 × 10^5	0.576

Fig. 4. Plot of k_Q (S) (EtOH) vs. k_Q (S) (mixed solvent) for (A) four Tocs (○), four Toc-3s (□), two CEHCs (Δ), and trolox (●); (B) α-Toc (○), palm oil extracts 1–5 (□), and soybean extract 6 (Δ); and (C) four Tocs (○), four Toc-3s (□), two CEHCs (Δ), trolox (●), extracts 1–5 (■), and extract 6 (▲).

Fig. 5. Relative SOAC value (EtOH) vs. relative SOAC value (mixed solvent) for four Tocs (○), four Toc-3s (□), two CEHCs (Δ), trolox (●), extracts 1–5 (■), and extract 6 (▲).

short-legendScheme 1.

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