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: gmhuang@ustc.edu.cn

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