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Supporting Information
Unexpected Reduction of Iminoquinone and Quinone Derivatives in
Positive Electrospray Ionization Mass Spectrometry and Possible
Mechanism Exploration
Jiying Pei,a,b Cheng-Chih Hsu,c Ruijie Zhang,a Yinghui Wang,a Kefu Yu,a and
Guangming Huangb*
aSchool of Marine Sciences, Guangxi University, Nanning, 530004, P. R. China
bDepartment of Chemistry, School of Chemistry and Materials Science, University of
Science and Technology of China (USTC), Hefei, 230026, P. R. China
cDepartment of Chemistry, National Taiwan University, Taipei 10617, Taiwan
*Contact Information for Corresponding Author:
Department of Chemistry, University of Science and Technology of China, Hefei,
Anhui, 230026, P. R. China. Guangming Huang: Tel: (+) 86 551 63600706. Fax: (+)
86 551 63600706. E-mail: [email protected]
Key word:
Iminoquinone, Quinone, Reduction, Corona discharge, Electrospray ionization
1
220 260 300 340m/z
0
Rel
ativ
e A
bund
ance
100281
282
283
354
355
356
IQ - (CH3CH2)2NH
SIQ - (CH3CH2)2NH
AQ - (CH3CH2)2NH
Figure S1. MS/MS spectra of IQ (m/z, 354), SIQ (m/z, 355), AQ (m/z, 356).
2
349 351 353 355 357 359 361 363 365m/z
0
100
0
100
Rel
ativ
e A
bund
ance
0
100356
354
356
354
356
354
x20 NL: 5.52E5
NL: 5.43E5
NL: 5.37E5
0.0-0.5 min
0.5-1.0 min
1.0-1.5 min
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4Time (min)
0
1000
100
Rel
ativ
e A
bund
ance
0
100
m/z 354
m/z 356
TIC
3 kV 5 kV 3 kV
Figure S2. Effect of spray voltage on the signal intensity of AQ before the solution was electrochemically oxidized. Conditions: CAQ = 0.25 μg/mL, CNH4Ac = 5 mM, flow rate = 2 μL/min, solvent, H2O.
3
0.0 0.4 0.8 1.2 1.60.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
CH3OH
I 354
/(I35
4+I 3
55+I
356)
Time/min
CH3OH/H2O (v/v, 1:1)
3 kV 4 kV 5 kV 3 kV
Figure S3. IQ reduction with CH3OH/H2O (v/v, 1:1) and CH3OH as the spray solvents under different spray voltages. Conditions: CAQ = 0.25 μg/mL, CNH4Ac = 5 mM, flow rate = 2 μL/min.
4
0.8 1.0 1.2 1.4 1.6 1.8 2.0Time (min)
0
Rel
ativ
e Abu
ndan
ce
100(-) SF6
(+) SF6(-) SF6
352 354 356 358 360 362m/z0
Rel
ativ
e Abu
ndan
ce
100
354
356355
0.8-1.1 min
1.2-1.6 min
1.7-2.0 min
TIC
SIC: m/z 354
SIC: m/z 355
SIC: m/z 356
(a)
0.8 1.2 1.6 2.00.0
0.2
0.4
0.6
(-) SF6
(+) SF6
I 354
/(I35
4+I 3
55+I
356)
Time (min)
(-) SF6
(b)
Figure S4. Effect of sheath gas (SF6) on IQ reduction during ESI. Conditions: CAQ = 0.25 μg/mL, CNH4Ac = 5 mM, flow rate = 2 μL/min, high voltage = 5 kV, solvent, H2O.
5
4 8 12 16 20 24 280.0
0.1
0.2
0.3
0.4
0.5
0.6
I 354
/(I35
4+I 3
55+I
356)
Time/min
3 kV5 kV
5 mm
10 mm20 mm
25 mm15 mm30 mm 35 mm
40 mm
Figure 5. Effect of spray tip-to-mass spectrometer inlet distance on IQ reduction.
6
Figure S6. Oxidation pathway of BQH2-GSH and MBQH2-GSH.
7
0.0 0.2 0.4 0.6
0.3
0.4
0.5
0.6 3 kV
3 kV
6.5 kV
I 428/(I
428+I
430)
Time (min)
0.1 0.2 0.3 0.4 0.5 0.6Time (min)
0
100R
elat
ive
Abu
ndan
ce
TIC
m/z 428
m/z 430
3 kV 6.5 kV 3 kV
(a) spray voltage
422 430 438 446 454m/z
0
100
Rel
ativ
e A
bund
ance
428430
0.0-0.2 min
0.2-0.4 min
(b) sheath gas
1.0 1.5 2.00.2
0.3
0.4
0.5
0.6
(+) N2
(-) N2
I 428/(I
428+I
430)
Time (min)
(-) N2
0.8 1.2 1.6 2.0Time (min)
0
Rel
ativ
e A
bund
ance
100
TIC
m/z 428
m/z 430
(-) N2 (-) N2(+) N2
430 438 446 454m/z
0
100428
430
Rel
ativ
e A
bund
ance
422
0.9-1.2 min
1.3-1.7 min
Figure S7. Effect of (a) spray voltage and (b) sheath gas (N2) on MBQ-GSH reduction during ESI. Conditions: CMBQ = 2 μg/mL, CGSH = 2.5 μg/mL, CNH4Ac = 5 mM, flow rate = 2 μL/min, solvent, CH3OH/H2O (v/v, 1:1). No sheath gas was used in (a) and the spray voltage is 3 kV for (b).
8
160 240 320 400m/z
0
100267
285182
287
270130 184 341
414
416
3391
2
3
2-H2O
1
2
2-NH3
Rel
ativ
e Abu
ndan
ce
4
4
Figure S8. MS/MS spectra of BQ-GSH (m/z 414) and BQH2-GSH (m/z 416).
9
x5 x5
420 425 430 435 440 445 450 455 460 465 470 475 480m/z
0
100
0
100
Rel
ativ
e Abu
ndan
ce
430
428462 468
466452450
428430
466468450452
0.0-0.2 min
0.25-0.4 min
Time (min)0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40
100
100
100
100
100
Rel
ativ
e Abu
ndan
ce
100
100
100
0
0
0
0
0
0
0
0
m/z 452: [MBQH2-GSH + Na]+
m/z 450: [MBQ-GSH + Na]+
m/z 462: [MBQH2 -GSH+ 2O]
m/z 466: [MBQ-GSH + K]+
m/z 468: [MBQH2-GSH + K]+
m/z 428: [MBQ-GSH + H]+
m/z 430: [MBQH2-GSH + H]+
TIC6.5 kV 3 kV
Figure S9. TIC and SICs of MBQ-GSH solution with adjustment of spray voltages. Conditions: CBQ = 2 μg/mL, CGSH = 2.5 μg/mL, CNH4Ac = 5 mM, flow rate = 2 μL/min, solvent, CH3OH/H2O (v/v, 1:1).
The peaks with m/z 462 are the addition of two oxygen atoms of MBQH2-GSH.
With the spray voltage of 6.5 kV, dramatic CD induced the oxidation of MBQH2-
GSH.
10
100416
414
Rel
ativ
e Abu
ndan
ce
400 410 420 430 440m/z
0
H2O, 2.5 kV
H2O, 4.0 kV
CH3OH/H2O(v:v, 1:1), 2.5 kV
CH3OH/H2O(v:v, 1:1), 4.0 kV
Figure S10. Effect of solvent on BQ-GSH reduction during ESI. Conditions: CBQ = 2 μg/mL, CGSH = 2.5 μg/mL, CNH4Ac = 5 mM, flow rate = 2 μL/min.
11
450 460 470 480 490m/z
0
100
0
100
Rel
ativ
e Abu
ndan
ce
464
466
464
466
3 kV + N2
5 kV + N2
m/z510 518 526 534 542
0
100
0
100
Rel
ativ
e Abu
ndan
ce
536
519
514516
536
519
514516
2 kV + N2
3 kV + N2
(a)
(b)
Figure 11. Effect of spray voltage and sheath gas (N2) on 1,4-NQ-GSH (1,4-NQ-GSH, m/z 464; 1,4-NQH2-GSH, m/z 466) and 1,4-AQ-GSH (1,4-AQ-GSH, m/z 514; 1,4-AQH2-GSH, m/z 516) reduction during ESI. The peaks labelled with an asterisk are CD-induced signal.
By increasing the spray voltage from 3 to 5 kV with N2 as sheath gas, the ratios
of the signal intensities of 1,4-NQ-GSH to 1,4-NQH2-GSH barely changed. Since
severe CD suppressed the signal of AQ-GSH, low spray voltage of 2 or 3 kV was
used. The results show that CD hardly induced 1,4-NQ-GSH and 1,4-AQ-GSH
reduction during ESI MS.
12