Supplementary Information
5-Methoxysalicylic Acid Matrix for Ganglioside Analysis with Matrix-Assisted
Laser Desorption/Ionization Mass Spectrometry
Running Title: MSA Matrix for MALDI MS of Gangliosides
Dongkun Lee and Sangwon Cha*
Department of Chemistry, Hankuk University of Foreign Studies, Yongin, 449-791, Korea.
Correspondence to: Sangwon Cha; e-mail: swcha@hufs.ac.kr
1
Supplementary Table S1. Detailed peak assignments and relative peak intensities (%) for mass
spectra presented in Figure 1.
Ions originated from GD1a (d18:1/18:0) (M1)
Species
(a) DHB
(b) sDHB
+
[M1 - 2Neu5Ac + Na]
484.4
32.7
+
[M1 - 2Neu5Ac + K]
43.1
10.0
[M1 - Neu5Ac - Gal - H2O + H]+
0.0
5.1
+
[M1 - Neu5Ac - Gal + Na]
0.0
6.8
[M1 - Neu5Ac - CO2 + Na]+
112.5
10.8
+
[M1 - Neu5Ac + Na]
64.4
32.1
+
[M1 - Neu5Ac - H + 2Na]
42.3
10.8
[M1 - H2O + H]+
0.0
9.7
+ a)
[M1 + Na]
100.0
100.0
+
[M1 + K]
28.5
69.4
+
[M1 - H + 2Na]
53.0
30.4
+
+
[M1 - 2H + 3Na] , [M2 + K]
77.5
68.3
+
[M1 - H + 2K]
23.1
21.6
[M1 - 2H + 3K]+
0.0
6.8
m/z
1277.77
1293.74
1366.82
1406.81
1524.88
1568.87
1590.85
1819.97
1859.97
1875.94
1881.94
1903.95b)
1913.89
1951.85
a)
Relative intensity for the ion [M1 + Na]+ was set to 100.0 %. b) Isobaric ions are present.
Ions originated from GD1a (d20:1/18:0) (M2)
Species
(a) DHB
(b) sDHB
+
[M2 - 2Neu5Ac + Na]
527.7
42.7
+
[M2 - 2Neu5Ac + K]
37.7
12.0
+
[M2 - Neu5Ac - Gal - H2O + H]
0.0
4.5
+
[M2 - Neu5Ac - Gal + Na]
0.0
6.8
+
[M2 - Neu5Ac - CO2 + Na]
121.0
19.1
[M2 - Neu5Ac + Na]+
44.6
31.9
+
[M2 - Neu5Ac - H + 2Na]
36.2
11.6
+
[M2 - H2O + H]
0.0
14.3
[M2 + Na]+ a)
100.0
100.0
+
+
[M2 + K] , [M1 - 2H + 3Na]
75.4
86.6
+
[M2 - H + 2Na]
47.5
30.0
+
[M2 - 2H + 3Na]
51.0
18.2
+
[M2 - H + 2K]
23.8
24.2
+
[M2 - 2H + 3K]
11.5
7.1
m/z
1305.80
1321.78
1394.85
1434.84
1552.91
1596.90
1618.88
1848.00
1887.99
1903.95b)
1909.98
1931.96
1941.92
1979.88
a)
(c) MSA
8.7
0.0
10.4
3.1
3.9
15.8
6.4
36.4
100.0
19.2
35.6
36.9
6.6
0.0
(c) MSA
11.2
0.0
8.1
3.3
7.2
18.1
8.4
30.0
100.0
34.6
39.1
20.0
0.0
0.0
Relative intensity for the ion [M2 + Na]+ was set to 100.0 %. b) Isobaric ions are present.
2
Supplementary Table S2. Chemical, physical, and thermodynamic properties of 2,5dihydroxybenzoic acid (DHB) and 5-methoxysalicylic acid (MSA).
2,5-Dihydroxybenzoic acid
(DHB)
5-Methoxysalicylic acid
(MSA)
CAS number
490-79-9
2612-02-4
Molecular formula
C7H6O4
C8H8O4
MW (g/mol)
154.12
168.15
Physical state
Whit to yellow powder
Beige fine crystalline powder
Melting point (K)
473-478
411-413
pKa
2.951
3.01
Proton affinity
(kJ/mol)
Vapor pressure
(mmHg at 298K)
859a)
850-856b)
2.10E-06
2.09E-05
λmax = 330 nm
λmax = 326 nm
3122
3460
1190
1002
UV absorption profile
with λmax
(in 80% MeOH)
ε337nm (M-1 ∙ cm-1)
ε355nm (M-1 ∙ cm-1)
a)
J. Am. Soc. Mass Spectrom.15, 431-435 (2004)
J. Am. Soc. Mass Spectrom. 22, 1070-1078 (2011)
Other data sources: www.sigmaaldrich.com, www.chemnetbase.com, and pubchem.ncbi.nlm.nih.gov.
UV absorption spectra were acquired by using a Shimadzu UV-1800 UV-Vis spectrophotometer (Kyoto, Japan).
b)
3
Supplementary Figure S1. Structures of major gangliosides found in a bovine brain GD1a
extract. Two major ganglioside species, GD1a (d18:1/18:0) and GD1a (d20:1/18:0) were
annotated as M1 and M2, respectively, in Figure 1.
4
Supplementary Figure S2. Positive-ion mode MALDI mass spectra of a porcine brain total
ganglioside extract (0.5 μg per spot) with (a) DHB and (b) MSA as a matrix. 20mM NaCl was
added to a matrix solution for spectral simplification.
5
Supplementary Figure S3. Negative-ion mode MALDI mass spectra of a bovine brain GD1a
extract (0.5 μg per spot) with (a) DHB and (b) MSA as a matrix. As defined in Supplementary
Figure S1, M1 and M2 are GD1a (d18:1/18:0) and GD1a (d20:1/18:0), respectively.
6
Supplementary Figure S4. Positive-ion mode MALDI mass spectrum of a bovine brain GD1a
extract (0.5 μg per spot) with MSA and 3mM ammonium sulfate. As defined in Supplementary
Figure S1, M1 and M2 are GD1a (d18:1/18:0) and GD1a (d20:1/18:0), respectively.
7
Supplementary Figure S5. MALDI mass spectra of a bovine brain GD1a extract (0.5 μg per
spot) with MSA and an alkali salt additive: (a) NaCl, (b) KCl, (c) RbCl, or (d) CsCl. “M’
represents major GD1a species in the extract, GD1a (d18:1/18:0) and GD1a (d20:1/18:0).
8
Supplementary Figure S5. (Continued)
9
Supplementary Figure S6. Positive-ion mode MALDI mass spectra of a porcine brain total
ganglioside extract (0.5 μg per spot) with MSA and 20mM KCl.
10