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Article Cite This: ACS Omega 2019, 4, 5601−5608
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Photoreaction of 9,10-Anthraquinone-2,6-disulfonic Acid and Ascorbic Acid Complexed at the Cationic Bilayer Interface and Consecutive Radical Dynamics Fumitoshi Ema,*,†,∥ Zhebin Fu,‡,⊥ and Hisao Murai*,†,§ †
Department of Chemistry, Faculty of Science, ‡Department of Chemistry, Graduate School of Science and Technology, and Department of Chemistry, Graduate School of Science, Shizuoka University, 836 Ohya, Suruga-ku, Shizuoka 422-8529, Japan
§
ACS Omega 2019.4:5601-5608. Downloaded from pubs.acs.org by 193.56.74.154 on 03/27/19. For personal use only.
S Supporting Information *
ABSTRACT: The antioxidant ability of substances such as vitamin C has attracted wide attention, and many antioxidant effects on our body are considered to act in the biomembrane interface region. However, the detailed dynamics of the radicals at the interface have not been deeply clarified. Here, we studied the reaction of photoexcited 9,10-anthraquinone2,6-disulfonic acid dianion (AQDS2−) and ascorbic acid in the cationic vesicle solution of didodecyldimethyl ammonium bromide using time-resolved electron paramagnetic resonance (TR-EPR) and UV−vis absorption methods. The results were compared with those of micellar and aqueous systems. Analysis of UV−vis spectra revealed the formation of an intermolecular charge-transfer complex of ascorbic acid monoanion (AscH−) and AQDS2− at the cationic bilayer interface. The TR-EPR spectra revealed a hydrogen atom abstraction reaction by the excited triplet state of AQDS2− from AscH− to form an ascorbic acid monoanion radical (Asc•−) and an anthrasemiquinone dianion radical (AQDSH•2−). The spin relaxation of these radicals demonstrates that Asc•− is weakly bound at the interface, whereas AQDSH•2− is strongly anchored. These results suggest that the strong oxidative ability of the photoexcited quinone is quenched by complexed AscH− and stabilized at the cationic bilayer interface.
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INTRODUCTION Ascorbic acid (AscH2) widely known as water-soluble vitamin C is one of the most essential nutrient and popular antioxidants. Ascorbic acid cannot be synthesized and stored in our body, so vitamin C needs to be obtained from foods. Thus, vitamin C has attracted attention in terms of health foods and supplement tablets to scavenge reactive oxygen species and to synthesize collagen by hydroxylation.1−4 On the other hand, quinones act as electron acceptors in the primary electron-transfer process in a photosynthetic system.5−7 In this system, quinone molecules such as ubiquinone are embedded in a protein-pigment complex that is called the reaction center. These functions and reactions include a redox process, which is considered to be related to the biomembrane interface and protein environments.5,8−10 Biomembrane is composed of proteins and lipids. Lipids mainly consist of phospholipids, glycolipids, and cholesterol, where the acyl chains are oriented to form a lipid domain.11,12 Phosphatidylcholine is one of the phospholipid molecules having a head group of positively charged ammonium nitrogen. In addition, a negatively charged phosphate group is attached to the cationic head group, so the head group region has both positively and negatively charged parts.11,12 Vesicle is a selfassembled bilayer system ordinarily consisting of phospholipid molecules, where the polar head groups having the amphiphilic nature of the lipids are facing the external aqueous phase.12,13 © 2019 American Chemical Society
The vesicle is widely used as an artificial biological membrane model instead of the biomembrane because of its simplified structure. 13−15 Didodecyldimethyl ammonium bromide (DDAB) is a surfactant with a double tail that constructs multilayers and vesicles with a cationic interface.13 Micelle is known as a more simplified model, which can trap hydrophobic agents in itself. Ionic micelles having positively or negatively charged interfaces are widely used to study charge effects of the membrane surface on the interaction with molecules and ions dissolved in the solution.16−18 Then, single-layered cationic dodecyltrimethyl ammonium bromide (DTAB) and anionic sodium dodecyl sulfate (SDS) micelles were used to investigate the charge effect at the micellar interface.16,17 Ohara and co-workers, Xu and co-workers, and other researchers previously reported the hydrogen atom abstraction reaction of the excited state of quinones from vitamin C around the water−oil interface region of the micelles by a timeresolved electron paramagnetic resonance (TR-EPR) technique.19−21 They suggested that the reaction is controlled by the transportation of the excited triplet state of the quinones and vitamin C in the surface or inside the micelle. The reaction Received: March 2, 2019 Accepted: March 8, 2019 Published: March 20, 2019 5601
DOI: 10.1021/acsomega.9b00591 ACS Omega 2019, 4, 5601−5608
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and 100 mM, respectively. Solutions of the DTAB surfactant, SDS surfactant, and aqueous solution without surfactant were prepared in a similar way with the same concentration mentioned above. For UV−vis absorption measurements, one-tenth of the concentration mentioned above was also used. UV−Vis Absorption Spectroscopy. UV−vis absorption spectra were measured by a UV−vis absorption spectrometer (SHIMADZU, UV-1650PC) at room temperature using a quartz cell with 1 cm optical path length. TR-EPR Spectroscopy. TR-EPR measurements were performed by using an X-band continuous wave EPR spectrometer (JEOL, JES-FE2XG) without magnetic-field modulation at room temperature. A nanosecond-pulsed Nd:YAG laser (Continuum, Minilite; λ = 355 nm, repetition: 10 Hz, energy: 2.2−2.5 mJ/pulse) was used as an excitation light source. Oxygen of the sample solution was purged with nitrogen gas bubbling before and during TR-EPR experiments. The solution flowed through a flat quartz cell with 0.3 mm optical path installed in the microwave resonator. The directly detected microwave signals were amplified and accumulated by a digital oscilloscope. Then three-dimensional data (time, magnetic field, and signal intensity) were obtained in a personal computer. Details about TR-EPR experimental procedures are available from previous papers.24,25
depends on the acid−base dissociation equilibrium of vitamin C because of pH. Water-soluble anthraquinone-disulfonic acid (AQDS) derivatives have been utilized for the TR-EPR measurement because of efficient trigger for photoinduced reactions.22,23 However, the detailed reaction mechanism and the spin dynamics of the radical species in the physiological environment in vivo have not been well understood.20 In this study, the photoreaction of AscH2 monoanion (AscH−) with 9,10-anthraquinone-2,6-disulfonic acid dianion (AQDS2−) in the DDAB vesicle solution was investigated. The reaction mechanism and the spin dynamics of the photoreduction at the bilayer membrane interface were characterized using X-band TR-EPR and UV−vis absorption methods. In the DDAB system, the precursor molecules, AQDS2− and AscH−, comprise a charge-transfer (CT) complex at the cationic interface. The hydrogen atom abstraction reaction of the excited triplet state of AQDS2− (3AQDS2−*) from AscH− was confirmed to take place in the CT complex and generate strongly bound AQDS semiquinone dianion radical (AQDSH•2−) and weakly restrained Asc•− at the cationic DDAB bilayer surface boundary. Detailed radical dynamics in the DDAB system is discussed compared with those in other systems such as cationic DTAB micellar, anionic SDS micellar, and aqueous solutions.
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EXPERIMENTAL SECTION Materials. The chemical structures of compounds used in this study are shown in Scheme 1. 9,10-Anthraquinone-2,6-
RESULTS AND DISCUSSION Characterization of the Molecular Interaction Studied by UV−Vis Spectroscopy. Figure 1 shows the steadystate UV−vis absorption spectra of AscHNa and AQDSNa2 in the aqueous solution and in the DDAB vesicle solution observed at room temperature. In Figure 1a, the red line (AscHNa and AQDSNa2) is almost identical to the sum of the blue line (AscHNa) and the green line (AQDSNa2) in the aqueous solution. This indicates that there is no obvious interaction between AscH− and AQDS2− dissolved in the homogeneous aqueous phase. Figure 1b shows the result obtained in the DDAB solution. The blue line (AscHNa) and the green line (AQDSNa2) show Rayleigh scattering in the longer wavelength region than 320 nm. The observation of Rayleigh scattering indicates the formation of aggregates of DDAB, in other words, apparent formation of vesicles. On the basis of pH values, namely, the proton concentration at the cationic DDAB bilayer membrane, the average local proton concentration is much lower than that in the bulk aqueous phase. This is because cationic surfactant head groups attract OH− and keep H+ away because of the electrostatic force.26−28 Most of the ascorbic acid exists as the monoanion form (AscH−) under the high pH at the cationic interface because of the acid dissociation constant of ascorbic acid (pKa1 < 4.2).29,30 As for the case of AQDSNa2, it also exists as the dianion form (AQDS2−) at the cationic interface. Thus, AscH− and AQDS2− exist at the DDAB bilayer interface. The green line (AQDSNa2) shows a slight increase of the absorbance around 400 nm, probably due to the result of the interaction between AQDS2− and the interface. The red line (AQDSNa2 and AscHNa) shows a new absorption band at the wavelength longer than 370 nm. This new absorption band demonstrates the possible formation of the intermolecular CT complex between AscH− and AQDS2− in the ground state interacting with the cationic DDAB bilayer interface because of electrostatic attraction force. In the case of 10 times higher concentration of all the compounds (Figure 1c), the
Scheme 1. Chemical Structures of Compounds Used in This Study
disulfonic acid disodium salt (AQDSNa2), L-ascorbic acid sodium salt (AscHNa), and SDS were purchased from Wako Pure Chemical Industries. DDAB and DTAB were from Tokyo Chemical Industry. These guaranteed reagent compounds were used as received. Purified water was used as a solvent for all sample preparations. Preparation of Sample Solutions. AQDSNa2 and AscHNa were previously dissolved in purified water, and the solution was mixed with the DDAB surfactant. Then, the purified water was added to the mixture to adjust the concentration, and it was sonicated until complete dissolution. The final concentrations of AQDSNa2, AscHNa, and DDAB for TR-EPR experiments were 4 mM (M: mol dm−3), 25 mM, 5602
DOI: 10.1021/acsomega.9b00591 ACS Omega 2019, 4, 5601−5608
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First of all, we show the assignment of the radical species formed in these systems. In the DDAB system (Figure 2a), strong emissive (downward) two peaks (asterisk, g = 2.0052, hyperfine coupling constant (hfcc) = 0.196 mT) were assigned to the ascorbic acid monoanion radical (Asc•−; g = 2.0050− 2.0054, hfcc(1) = 0.18−0.199 mT).19,20 A spectrum with widely distributed many peaks with nearly equi-separation in the higher field (dark triangle, g = 2.0039, hfcc = 0.06 mT) was assigned to AQDSH•2− (g = 2.00389, hfcc(3,7) = 0.122 mT, hfcc(1,4,5,8) = 0.061 mT).31 In the DTAB system (Figure 2b), strong two peaks (g = 2.0051, hfcc = 0.184 mT) and widely distributed many peaks (dark triangle, g = 2.0039, hfcc = 0.06 mT) were assigned to Asc•− and AQDSH•2−, respectively, similar to those obtained in the DDAB system. At the late time (ca. 3 μs) after laser irradiation, however, the spectral line shape and peak separation in the higher field region changed (open triangle, separation of ca. 0.04 mT). This suggests the possible formation of the AQDS semiquinone trianion radical (AQDS•3−; g = 2.00412, hfcc(1,5) = 0.036 mT, hfcc(3,7) = 0.121 mT, hfcc(4,8) = 0.042 mT),31−33 which may be generated via deprotonation of AQDSH•2−. The possible reason for this may be fast micellar material exchange and high pH at the interface boundary. TR-EPR spectra obtained in the aqueous system (Figure 2c) are different from those obtained in the DDAB and DTAB systems. The emissive strong doublet peak (g = 2.0052, hfcc = 0.170 mT) was assigned to the ascorbic acid radical (AscH•; g = 2.005, hfcc(1) = 0.17−0.176 mT).34,35 A spectrum of AQDSH•2− expected to appear at the higher field region of AscH•, which were observed in the cationic DDAB and DTAB systems, was not definitely observed. In the SDS system (Figure S2), the doublet peak (g = 2.0052, hfcc = 0.171 mT) was assigned to AscH•; however, AQDSH•2− was not significantly observed. These results were similar to those in the aqueous system (Figure 2c). Second, we discuss the analysis of the spectral pattern observed in these systems. Generally, a TR-EPR spectrum in the liquid phase in the case of the triplet precursor shows the chemically induced dynamic electron polarization (CIDEP) of an emissive (E)/absorptive (A) pattern because of the radical pair mechanism (RPM) and a total E (or A) pattern by the triplet mechanism (TM). RPM is induced by the re-encounter of paired radicals and TM is induced by the conservation of the spin polarization of the precursor excited triplet state. TR-EPR spectra observed in the DDAB bilayer system (Figure 2a) are explained by predominant contribution of the total E polarization of TM (see the simulation given in Figure 2d). This means that 3AQDS2−* reacts fast enough with AscH− and the spin polarization of 3AQDS2−* is transferred to Asc•− and AQDSH•2−. In the DTAB system (Figure 2b), the result at 0.8 μs is similar to that of the DDAB system. In contrast to this, the spectrum observed at 3 μs is simulated in Figure 2e, where the trianion radical of AQDS•3− is assumed. The reproduced TR-EPR spectra by simulation are shown in Figure S3. In both systems, the contribution of RPM was not apparently confirmed, indicating that free diffusion and reencounter of the generated radical species are restricted at the cationic interface. These results suggest that the photoexcited CT complex at the interfaces induces the hydrogen atom abstraction reaction, and two radicals cannot diffuse easily. However, the CIDEP spectrum of the spin-correlated radical pair (SCRP), that is, direct observation of a radical pair, was
Figure 1. Steady-state UV−vis absorption spectra of AscHNa, AQDSNa2, and a mixture of AQDSNa2/AscHNa in (a) aqueous and (b,c) DDAB solutions at room temperature. The concentration was set to (a) AscHNa: 2.5 mM, AQDSNa2: 0.4 mM, (b) AscHNa: 2.5 mM, AQDSNa2: 0.4 mM, DDAB: 10 mM, and (c) AscHNa: 25 mM, AQDSNa2: 4.0 mM, DDAB: 100 mM.
concentration employed for TR-EPR observation, these phenomena are more remarkable. To look into the effects of the interaction between AscH− and the interface and AQDS2− and the interface, UV−vis absorption spectra were studied in other surfactant systems to compare with the DDAB system. In a cationic DTAB micellar solution of the concentration higher than the critical micelle concentration (cmc) of 14−15 mM,16 the intermolecular CT complex formed between AscH− and AQDS2−as well as the DDAB system was observed. Here, the increase of the absorbance around 400 nm observed in the system of AQDS2− and DDAB was not confirmed. On the other hand, in an anionic SDS solution of the concentration higher than the cmc of 8−9 mM,16 an absorption band such as the CT complex between ascorbic acid and AQDS was weakly observed. Note that an increase of the absorbance around 400 nm in the DDAB and DTAB solutions was much more remarkable than that observed in the SDS system. These results suggest that the photoreaction takes place in the intermolecular CT complex in the cationic interface systems. The UV−vis absorption spectra observed in the DTAB and SDS micellar systems are shown in Figure S1 in the Supporting Information. Photoinduced Chemical Reaction Studied by TR-EPR Spectroscopy. Figure 2a−c shows the TR-EPR spectra observed in the system of AscHNa and AQDSNa2 in the DDAB bilayer, DTAB micellar, and aqueous solutions, respectively. 5603
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Figure 2. TR-EPR spectra observed after laser irradiation in (a) DDAB, (b) DTAB, and (c) aqueous solution at room temperature. Simulated TREPR spectra of (d) Asc•− and AQDSH•2− formed by the TM, (e) Asc•− and AQDS•3− by the TM, and (f) Asc•− and AQDSH•2− by the RPM. In these simulated spectra, the absolute values of the integrated area were assumed to be the same for the respective radicals. Magnetic parameters used for these simulations are as follows: Asc•−: g = 2.0052, hfcc = 0.196 mT, AQDSH•2−: g = 2.0039, hfcc(3,7) = 0.122 mT, hfcc(1,4,5,8) = 0.061 mT (here, hfcc(OH) = 0.020 mT is assumed), AQDS•3−: g = 2.0041, hfcc(1,5) = 0.036 mT, hfcc(3,7) = 0.121 mT, hfcc(4,8) = 0.042 mT. Here, the downward spectral pattern shows an emissive signal of microwave.
atom from AscH− complexed at the cationic DDAB bilayer interface, and then AQDSH•2− and Asc•− are formed. Note that in the DDAB system, a spectrum of the alkyl radical derived from the surfactant23,36 was not definitely observed. This suggests that the initial hydrogen atom abstraction reaction by 3AQDS2−* could occur predominantly from AscH− but not from the alkyl chain in the DDAB system. In the DTAB system, the initial reaction is the same as that in the DDAB system because of the similar observation results. Spin Dynamics of the Radical Species. To investigate the spin dynamics of the ascorbic acid radicals, we tried to analyze the electron spin relaxation times of two strong spectral lines; namely, spin−lattice relaxation (longitudinal relaxation) time (T1) and spin−spin relaxation (transverse relaxation) time (T2) of the ascorbic acid radicals. T1 can be approximately determined by the decay of the TR-EPR signal intensity under weak microwave power condition. T2 may be estimated from the line width of the spectrum. T1 and T2 are given by eqs 1 and 2, respectively. Here, only the anisotropic g-factor is considered.
not confirmed in these systems, indicating that the radical− radical distance is separated far enough at the observation time. The disappearance of the spectral lines in the higher field region in the aqueous solution (Figure 2c) may be due to slight cancellation of TM (Figure 2d) and RPM (Figure 2f) spin polarization and fast reaction with AscH2 in the solution. In the SDS micellar system (Figure S2), the spectral pattern is close to that of the aqueous solution. Accordingly, the chemical reaction and the spin dynamics in the SDS system are similar to that in the aqueous phase. This suggests that the reaction exclusively takes place in the homogeneous aqueous phase outside the SDS micelle. These results of the assignment and spin polarization of the intermediate radicals can be explained by the formation of a CT complex in the ground state, resulting in the reaction as shown in Scheme 2. Namely, 3AQDS2−* abstracts a hydrogen Scheme 2. Mechanism of the Photoinduced Chemical Reaction Involving Hydrogen Atom Abstraction between 3 AQDS2−* and AscH− at the Cationic DDAB Bilayer Membrane Interface
6τcΔ2 1 = T1 1 + ω0 2τc 2
(1)
1 1 = 4τcΔ2 + T2 2T1
(2)
where τc is the rotational correlation time and ω0 is the spin angular frequency under EPR conditions. Δ is related to the g tensor anisotropy and the resonance magnetic field B0 as shown by the following equation:37,38 5604
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(Δg )2 μB 2 B0 2 30ℏ2
(3)
Unfortunately, the line width of the spectra of ascorbic acid radicals is mainly governed by the many hyperfine lines with small hfcc (probably less than 0.02 mT) because there are five (Asc•−) or six (AscH•) protons at different sites of the molecular frame of the radicals along with one proton having relatively large hfcc (0.17−0.20 mT). The observed spectral line width of all the ascorbic acid radicals showed nearly the same width of about 0.05 mT (half width at half-maximum). Therefore, it is not possible to determine T2 of the radicals by this way. Approximate T1 values of ascorbic acid radicals estimated by the decay of the spectral intensity are given in Table 1. Table 1. Experimentally Estimated Spin−Lattice Relaxation Time (T1) of Asc•− in DDAB and DTAB Solutions and AscH• in SDS and Aqueous Solutions
T1/μs
DDAB (Asc•−)
DTAB (Asc•−)
SDS (AscH•)
Aqueous (AscH•)
1.4
1.5
0.72
0.93
Figure 3 shows time profiles of TR-EPR signal intensity observed in AscHNa and AQDSNa2 in the DDAB bilayer, DTAB micellar, SDS micellar, and aqueous solutions. In the DDAB system, the decay time of AQDSH•2− is thought to be much longer than 10 μs because of no observable decay in the time window as shown in Figure 3a. This means that T1 of AQDSH•2− is extremely longer than that of Asc•− because the long rotational correlation time of the vesicle controls the T1 as represented in eq 1. The long T1 is known to be observable in the low-temperature solution and also in confined environments, where τc is long.39,40 This indicates that two kinds of radicals interact with the bilayer interface differently, namely, there is no possibility that these radicals exist as a complexed radical pair after the photoreaction. This is consistent with no observation of SCRP. This result suggests that AQDSH•2− is anchored at the interface because of the strong electrostatic attraction between the cationic head group of DDAB and anionic AQDSH•2−. In contrast to this, Asc•− is not strongly bound and may be tumbling there as represented in Figure 4a. This may be explained by the smaller molecular size and the weaker electrostatic binding of Asc•− to the cationic head group compared to those of AQDSH•2−. In the DTAB system (Figure 3b), T1 of Asc•− is close to that obtained in the DDAB system. However, T1 of AQDSH•2− is estimated to be ca. 4 μs and longer than that of Asc•−. Here, the spectrum of AQDSH•2− is gradually converted to that of AQDS•3−. Therefore, these two spectra are superposed and not separated. Accordingly, AQDSH•2− (and AQDS•3−) and Asc•− are thought to be bound in the cationic DTAB micellar interface as well as in the case of the DDAB system, where Asc•− may tumble there as demonstrated in Figure 4b. Here, T1 of AQDSH•2− may be governed by the rotational motion originating from the micellar size. The difference of T1 between the DDAB and DTAB systems is clearly explained by the different diameter of a vesicle and micelle; that is, the differences of the DDAB vesicle and DTAB micelle are some 100 nanometers (ca. 200−700 nm) and some nanometers (ca. 4 nm), respectively.42−44
Figure 3. Time profiles of TR-EPR signal intensity observed after laser excitation: (a) Asc•− (black line) and AQDSH•2− (blue line) in DDAB solution; (b) Asc•− (black line), peak of AQDSH•2− (blue line), and peak of AQDS•3− (red line) in DTAB solution; and (c) ascorbic acid radical (AscH•; black line) in aqueous solution without surfactant, AscH• (blue line) in SDS solution, Asc•− (green line) in DTAB solution, and Asc•− (red line) in DDAB solution. Here, these time profiles were obtained at the lower field region of the emissive signal of two strong peaks of ascorbic acid radicals. The slight oscillation of (a,b) appearing outside of the resonant field of Asc•− is Torrey’s nutation.41
The significance of the smooth curves obtained by a monoexponential fit in the region of t > 0.8 μs is shown in Figure 3c. These curves gave us T1 values of Asc•− and AscH• as shown in Table 1. Note that the T1 values for Asc•− and AscH• were approximately determined because the decay rate is apparently faster in the alternating magnetic field of the microwave. T1 of AscH• in the SDS and aqueous systems is apparently shorter than that of Asc•− in the DDAB and DTAB systems (Figure 3c and Table 1). This suggests that AscH• is not bound in the anionic SDS micellar interface and it diffuses away in the homogeneous aqueous phase as illustrated in Figure 4c. T2 of Asc•− and AscH• should be shorter than T1 of respective radicals (eqs 1 and 2). However, T2 of Asc•− and AscH• cannot be determined in this way as mentioned before. As shown in Figure 2, the envelope of the spectral line of ascorbic acid radicals was not broader than that in the aqueous system. Therefore, T2 of Asc•− in DDAB and DTAB is close to that in the aqueous phase. This means that τc of these radicals 5605
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interface. The intermediate oxidative radical, here anthrasemiquinone radical, is anchored at the interface.
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CONCLUSIONS We studied the photoinduced chemical reaction of AQDS2− and AscH− in the cationic DDAB vesicle solution in real time, using a TR-EPR method. Analysis of UV−vis absorption spectra clarified the formation of an intermolecular CT complex between AscH− and AQDS2− at the cationic DDAB bilayer interface before photolysis. The TR-EPR spectra revealed a hydrogen atom abstraction reaction of 3AQDS2−* from AscH− and formation of weakly bound Asc•− and strongly anchored AQDSH•2− at the interface. These results suggest that the strong oxidative ability of the excited triplet state of the particular quinone is quenched by complexed ascorbic acid, and both radicals are stabilized at the cationic bilayer interface. These results provide us new insights into not only antioxidative ability at the interface but also control of the reaction at the surface in the inhomogeneous region in terms of surface chemistry.
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ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsomega.9b00591. UV−vis absorption spectra and detailed analysis of TREPR spectra (PDF)
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Figure 4. Schematic illustration of the proposed molecular dynamics of the generated radical species in the (a) cationic DDAB vesicle, (b) cationic DTAB micellar, and (c) anionic SDS micellar systems.
AUTHOR INFORMATION
Corresponding Authors
*E-mail:
[email protected] (F.E.). *E-mail:
[email protected] (H.M.). Present Addresses ∥
Department of Chemistry, Graduate School of Science, Kobe University, 1-1 Rokkodai-cho, Nada-ku, Kobe 657-8501, Japan. ⊥ Department of Chemistry, Graduate School of Science and Engineering, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8550, Japan.
does not strongly depend on the system employed in the present cases. This suggests that even though Asc•− is bound in DDAB and DTAB systems, this radical tumbles quickly at the interface because of its small molecular size and mononegative charge as mentioned before. Photoinduced Initial Reaction. To acquire further insights into the molecular dynamics of the radical species initially generated in the photoinduced reaction between AscH− and 3AQDS2−* in the bilayer membrane interface region, the line shape of the TR-EPR spectra observed immediately after laser irradiation is carefully analyzed. In all the systems, emissive broadened spectra with multiple peaks were observed at 0.2 μs after laser irradiation (Figure S4 in the Supporting Information). These spectra showing an average hfcc of 0.060 mT exhibit the generation of AQDSH•2− before appearance of emissive spectra of the ascorbic acid radical. All the TR-EPR spectra in the early time were explained mainly by the emissive TM. The spectra at 0.3 μs after laser excitation exhibit gradual appearance of the ascorbic acid radical as shown in Figure 2. However, in the SDS micellar and the aqueous solutions, the spectrum of AQDSH•2− rapidly disappeared and that of the ascorbic acid radical appeared. The data of this report indicate that the photoexcited paraquinones at the biological membrane interface may exclusively react with ascorbic acid complexed; in other words, the excited molecule is efficiently quenched by ascorbic acid before formation of oxidative radical species at the
Author Contributions
The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS We thank Prof. Yasuhiro Kobori (Kobe University) for many supports and useful discussions. We also thank Dr. Tomoaki Miura (Niigata University) for fruitful discussions. We are grateful to the center of Instrumental Analysis of Shizuoka University for using TR-EPR instruments. We also thank Shizuoka University for the continuous financial support.
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ABBREVIATIONS AscH2, ascorbic acid; AQDS2−, 9,10-anthraquinone-2,6-disulfonic acid dianion; DDAB, didodecyldimethyl ammonium bromide; DTAB, dodecyltrimethyl ammonium bromide; SDS, sodium dodecyl sulfate; TR-EPR, time-resolved electron paramagnetic resonance; TM, triplet mechanism; RPM, radical pair mechanism 5606
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with Xanthone in Aqueous Sodium Lauryl Sulfate, Hexadecyltrimethylammonium Chloride, and Triton X-100 Micelle Solutions. J. Phys. Chem. B 2003, 107, 11527−11533. (20) Xu, X.-S; Shi, L.; Liu, Y.; Ji, X.-H.; Cui, Z.-F. TR-ESR Investigation on Reaction of Vitamin C with Excited Triplet of 9,10phenanthrenequinone in Reversed Micelle Solutions. Chin. J. Chem. Phys. 2011, 24, 150−154. (21) Wen, X.-L.; Zhang, J.; Liu, Z.-L.; Han, Z.-X.; Rieker, A. Micellar Effects on the Oxidative Electrochemistry of Lipophilic Vitamin C Derivatives. J. Chem. Soc., Perkin Trans. 2 1998, 905−910. (22) Görner, H. Photoreduction of 9, 10-Anthraquinone Derivatives: Transient Spectroscopy and Effects of Alcohols and Amines on Reactivity in Solution. Photochem. Photobiol. 2003, 77, 171−179. (23) Moribe, S.; Ikoma, T.; Akiyama, K.; Tero-kubota, S. TimeResolved EPR Study on Photoreduction of Sodium Anthraquinone-2Sulfate in Liposomes. Chem. Phys. Lett. 2008, 457, 66−68. (24) Miura, T.; Kageyama, A.; Torii, S.; Murai, H. Photoreactions and Molecular Dynamics of Radical Pairs in a Reversed Micelle Studied by Time-Resolved Measurements of EPR and Magnetic Field Effect. J. Phys. Chem. B 2010, 114, 14550−14558. (25) Ishigaki, A.; Murai, H. Time-Resolved ESR Study on a LongLived Radical-Ion Pair Formed in the Photoinduced ElectronTransfer Reaction of Xanthone and N,N-Diethylaniline in 2-Propanol. Chem. Phys. Lett. 2006, 426, 81−84. (26) Rodrigues, R.; Vautier-Giongo, C.; Silva, P. F.; Fernandes, A. C.; Cruz, R.; Maçanita, A. L.; Quina, F. H. Geminate Proton Recombination at the Surface of SDS and CTAC Micelles Probed with a Micelle-Anchored Anthocyanin. Langmuir 2006, 22, 933−940. (27) Bunton, C. A.; Faruk, N.; Frank, H. Q.; Laurence, S. R. Ion Binding and Reactivity at Charged Aqueous Interfaces. Acc. Chem. Res. 1991, 24, 357−364. (28) Sabatino, P.; Szczygiel, A.; Sinnaeve, D.; Hakimhashemi, M.; Saveyn, H.; Martins, J. C.; Van der Meeren, P. NMR Study of the Influence of Ph on Phenol Sorption in Cationic CTAB Micellar Solutions. Colloids Surf., A 2010, 370, 42−48. (29) Cabral, J.; Haake, P. Ascorbic acid. 2. Structural determination and synthesis of 2- and 3-acyl derivatives of 5,6-O-isopropylidene-Lascorbic acid. J. Org. Chem. 1988, 53, 5742−5750. (30) Capuzzi, G.; Nostro, P. L.; Kulkarni, K.; Fernandez, J. E. Mixtures of Stearoyl-6-O-Ascorbic Acid and r-Tocopherol : A Monolayer Study at the Gas/Water Interface. Langmuir 1996, 11, 3957−3963. (31) Geimer, J.; Beckert, D. Study of Radical Pairs Generated by Photoreduction of Anthraquinone-2,6-Disulfonic Acid with Thymine by Fourier Transform Electron Paramagnetic Resonance. Chem. Phys. Lett. 1998, 288, 449−458. (32) Säuberlich, J.; Brede, O.; Beckert, D. Investigation of the Photoreduction of Anthraquinonedisulfonic Acid by Triethylamine with Fourier Transform Electron Spin Resonance. J. Phys. Chem. A 1997, 101, 5659−5665. (33) White, R. C.; Gorelik, V.; Bagryanskaya, E. G.; Forbes, M. D. E. Photoredox Chemistry of AOT: Electron Transfer and Hydrogen Abstraction in Microemulsions Involving the Surfactant. Langmuir 2007, 23, 4183−4191. (34) Togashi, H.; Shinzawa, H.; Yong, H.; Takahashi, T.; Noda, H.; Oikawa, K.; Kamada, H. Ascorbic Acid Radical, Superoxide, and Hydroxyl Radical Are Detected in Reperfusion Injury of Rat Liver Using Electron Spin Resonance Spectroscopy. Arch. Biochem. Biophys. 1994, 308, 1−7. (35) Laroff, G. P.; Fessenden, R. W.; Schuler, R. H. Electron Spin Resonance Spectra of Radical Intermediates in the Oxidation of Ascorbic Acid and Related Substances. J. Am. Chem. Soc. 1972, 94, 9062−9073. (36) Caregnato, P.; Jarocha, L. E.; Esinhart, H. S.; Lebedeva, N. V.; Tarasov, V. F.; Forbes, M. D. E. Electrostatic Control of Spin Exchange Between Mobile Spin-Correlated Radical Pairs Created in Micellar Solutions. Langmuir 2011, 27, 5304−5309.
REFERENCES
(1) Stone, N.; Meister, A. Function of Ascorbic Acid in the Conversion of Proline to Colagen Hydroxyproline. Nature 1962, 194, 555−557. (2) Lee, I.-M. Antioxidant Vitamins in the Prevention of Cancer. Proc. Assoc. Am. Phys. 1999, 111, 10−15. (3) Arrigoni, O.; De Tullio, M. C. Ascorbic Acid: Much More than just an Antioxidant. Biochim. Biophys. Acta 2002, 1569, 1−9. (4) Vertuani, S.; Angusti, A.; Manfredini, S. The Antioxidants and Pro-Antioxidants Network: An Overview. Curr. Pharm. Des. 2004, 10, 1677−1694. (5) van den Brink, J. S.; Spoyalov, A. P.; Gast, P.; van Liemt, W. B. S.; Raap, J.; Lugtenburg, J.; Hoff, A. J. Asymmetric Binding of the Primary Acceptor Quinone in Reaction Centers of the Photosynthetic Bacterium Rhodobacter Sphaeroides R26, Probed with Q-Band (35 GHz) EPR Spectroscopy. FEBS Lett. 1994, 353, 273−276. (6) Gardiner, A. T.; Zech, S. G.; MacMillan, F.; Käss, H.; Bittl, R.; Schlodder, E.; Lendzian, F.; Lubitz, W.; Kass, H.; Bittl, R.; et al. Electron Paramagnetic Resonance Studies of Zinc-Substituted Reaction Centers from Rhodopseudomonasviridis. Biochemistry 1999, 38, 11773−11787. (7) Heinen, U.; Utschig, L. M.; Poluektov, O. G.; Link, G.; Ohmes, E.; Kothe, G. Structure of the Charge Separated State in the Photosynthetic Reaction Centers of Rhodobactersphaeroides by Quantum Beat Oscillations and High-Field Electron Paramagnetic Resonance: Evidence for Light-Induced Reorientation. J. Am. Chem. Soc. 2007, 129, 15935−15946. (8) Nagaoka, S.-I.; Inoue, M.; Nishioka, C.; Nishioku, Y.; Tsunoda, S.; Ohguchi, C.; Ohara, K.; Mukai, K.; Nagashima, U. Tunneling Effect in Antioxidant, Prooxidant, and Regeneration Reactions of Vitamin E. J. Phys. Chem. B 2000, 104, 856−862. (9) Sonnen, A. F.-P.; Bakirci, H.; Netscher, T.; Nau, W. M. Effect of Temperature , Cholesterol Content , and Antioxidant Structure on the Mobility of Vitamin E Constituents in Biomembrane Models Studied by Laterally Diffusion-Controlled Fluorescence Quenching. J. Am. Chem. Soc. 2005, 127, 15575−15584. (10) Ouchi, A.; Nagaoka, S.-I.; Mukai, K. Tunneling Effect in Regeneration Reaction of Vitamin E by Ubiquinol. J. Phys. Chem. B 2010, 114, 6601−6607. (11) Singer, S. J.; Nicolson, G. L. The Fluid Mosaic Model of the Structure of Cell Membranes. Science 1972, 175, 720−731. (12) Bruce, A.; Dennis, B.; Karen, H.; Alexander, D. J.; Julian, L.; Martin, R.; Keith, R.; Peter, W. Essential Cell Biology, 4th ed.; Garland Science: New York, U. S. A., 2013. (13) Walde, P.; Umakoshi, H.; Stano, P.; Mavelli, F. Emergent Properties Arising from the Assembly of Amphiphiles. Artificial Vesicle Membranes as Reaction Promoters and Regulators. Chem. Commun. 2014, 50, 10177−10197. (14) Liu, W.; Wang, Z.; Fu, L.; Leblanc, R. M.; Yan, E. C. Y. Lipid Compositions Modulate Fluidity and Stability of Bilayers: Characterization by Surface Pressure and Sum Frequency Generation Spectroscopy. Langmuir 2013, 29, 15022−15031. (15) Tsuchiya, K.; Nakanishi, H.; Sakai, H.; Abe, M. TemperatureDependent Vesicle Formation of Aqueous Solutions of Mixed Cationic and Anionic Surfactants. Langmuir 2004, 20, 2117−2122. (16) Bahri, M. A.; Hoebeke, M.; Grammenos, A.; Delanaye, L.; Vandewalle, N.; Seret, A. Investigation of SDS, DTAB and CTAB Micelle Microviscosities by Electron Spin Resonance. Colloids Surf., A 2006, 290, 206−212. (17) Pellosi, D. S.; Estevão, B. M.; Freitas, C. F.; Tsubone, T. M.; Caetano, W.; Hioka, N. Photophysical Properties of Erythrosin Ester Derivatives in Ionic and Non-Ionic Micelles. Dyes Pigm. 2013, 99, 705−712. (18) de Souza, M.; Perpétua, M.; de Morais, F.; Lama, D.; Siuiti, A.; Mary, R.; Georgetto, Z. Binding of Chloroquine to Ionic Micelles: Effect of Ph and Micellar Surface Charge. J. Lumin. 2014, 147, 49−58. (19) Ohara, K.; Watanabe, R.; Mizuta, Y.; Nagaoka, S.-I.; Mukai, K. Time-Resolved Electron Paramagnetic Resonance Investigation of Photoinitiated Antioxidant Reaction of Vitamin C (Ascorbic Acid) 5607
DOI: 10.1021/acsomega.9b00591 ACS Omega 2019, 4, 5601−5608
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(37) Alan, C.; Andrew, D. M. Introduction to Magnetic Resonance with Applications to Chemistry and Chemical Physics; Harper Int.; Harper &Row: New York, Evanston, London, 1967. (38) Charles, P. P.; Horacio, A. F. Relaxation in Magnetic Resonance; Academic Press: New York and London, 1971. (39) Prisner, T.; Dobbert, O.; Dinse, K. P.; Van Willigen, H. FT ESR Study of Photoinduced Electron Transfer. J. Am. Chem. Soc. 1988, 110, 1622−1623. (40) Miura, T.; Maeda, K.; Oka, Y.; Ikoma, T. Gigantic Magnetic Field Effect on the Long-Lived Intermolecular Charge-Separated State Created at the Nonionic Bilayer Membrane. J. Phys. Chem. B 2018, 122, 12173−12183. (41) Torrey, H. C. Transient Nutations in Nuclear Magnetic Resonance. Phys. Rev. 1949, 76, 1059−1068. (42) Lu, X.; Nan, M.; Zhang, H.; Liu, X.; Yuan, H.; Yang, J. Investigation of the Antioxidant Property of Ascorbic Acid. J. Phys. Chem. C 2007, 111, 14998−15002. (43) Ge, L.; Ji, J. Fabrication and Stability Study of Multilayer Liposome. Asian J. Chem. 2010, 22, 66−78. (44) Dey, S.; Mandal, U.; Sen Mojumdar, S.; Mandal, A. K.; Bhattacharyya, K. Diffusion of Organic Dyes in Immobilized and Free Catanionic Vesicles. J. Phys. Chem. B 2010, 114, 15506−15511.
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DOI: 10.1021/acsomega.9b00591 ACS Omega 2019, 4, 5601−5608
