Supporting Information
Use of doubly charged precursors to validate dissociation mechanisms of singly charged
poly(dimethylsiloxane) oligomers
Thierry Fouquet, Valérie Toniazzo, David Ruch and Laurence Charles
Table of contents
Page
Scheme S1. a) Major formation of small bi+ product ions from singly charged ammonium
adduct of CH3-PDMS. b) Most stable structures calculated for the smallest b2-4+ product ions ...
2
Table S1. Accurate mass measurements of product ions formed upon CID of [CH3-PDMS24 +
NH4]+ at m/z 1882.5 ……………………………………………………………………………..
2
Figure S1. Electrospray mass spectra of a) CH3-PDMS and b) CH3O-PDMS in methanolic
solution of ammonium acetate (3 mM) ………………………………………………………….
3
Additional product ion series formed during CID of [CH3-PDMS + 2 NH4]+
4
Scheme S2. Main product ions proposed to be formed upon CID of [CH3-PDMS + 2
NH4]2+ precursor ion at m/z 950.3 ………………………………………………………..
4
Table S2. Accurate mass measurements of product ions formed upon CID of [CH3PDMS24 + 2 NH4]2+ at m/z 950.3 ………………………………………………………...
5
Scheme S3. Structure proposed for the b3+ product ion generated upon CID of singly charged
adduct of CH3O-PDMS oligomers ………………………………………………………………
6
Scheme S4. Partial charge distribution for a CH3O-PDMS3 model computed from the
B3LYP/6-31G(d) energy calculation, using the atomic Polar Tensor (APT) method …………..
6
Additional product ion series formed during CID of [CH3O-PDMS + NH4]+
7
Figure S2. a) ESI-MS/MS spectrum of the CH3O-PDMS 9-mer adducted with
ammonium, and MS3 spectra using product ions at b) m/z 459 and c) m/z 371 as
secondary precursor ions …………………………………………………………………
7
Table S3. Accurate mass measurements of product ions generated upon CID of [CH3ODMS25 + NH4]+ at m/z 1914.6 ……………………………………………………………
8
Additional product ion series formed during CID of [CH3O-PDMS + 2NH4]2+
9
Table S4. Accurate mass measurements of product ions formed during CID of [CH3OPDMS25 + 2 NH4]2+ at m/z 966.3 ………………………………………………………...
9
References ………………………………………………………………………………………
10
1
Scheme S1. a) Proposed two-step pathway to account for the major formation of small bi+ product ions
from singly charged ammonium adduct of CH3-PDMS: the smallest bi+ congeners would be formed
upon dissociation of the largest ones, which would undergo multiple releases of the very stable D 3
neutral. b) Most stable structures calculated for the smallest b2-4+ product ions.
Elemental
composition
C52H160NO24Si25+
C13H39O5Si6+
C11H33O4Si5+
C9H27O3Si4+
C7H21O2Si3+
C5H15OSi2+
C11H33O6Si6+
C9H27O5Si5+
C7H21O4Si4+
C5H15O3Si3+
(m/z)theo
(m/z)exp
Error (ppm)
Assignment
1882.5557
443.1408
369.1220
295.1032
221.0844
147.0656
429.0887
355.0699
281.0511
207.0324
I.S.
443.1398
369.1210
295.1027
221.0850
147.0689
429.0893
355.0716
281.0505
207.0340
- 2.3
- 2.7
- 1.7
+ 2.7
+ 22.4
+ 1.4
+ 4.8
- 2.1
+ 7.7
[CH3-PDMS24 + NH4]+
b5+
b4+
b3+
b2+
b1+
b6+ - TMS
b5+ - TMS
b4+ - TMS
b3+ - TMS
Table S1. Accurate mass measurements of product ions formed upon CID of [CH3-PDMS24 + NH4]+
at m/z 1882.5 (Figure 1a). I.S.: internal standard. The secondary product ion series, detected in the low
m/z range of the MS/MS spectrum of Figure 1a, was formed after bi+ fragments have release
tetramethylsilane TMS).
2
Figure S1. Electrospray mass spectra of a) CH3-PDMS and b) CH3O-PDMS in methanolic solution of
ammonium acetate (3 mM). Insets emphasize the relative abundance of oligomers adducted with
multiple ammonium cations as compared to their singly charged counterparts.
3
Additional product ion series formed during CID of [CH3-PDMS + 2 NH4]+
Scheme S2. Main product ions proposed to be formed upon CID of [CH3-PDMS + 2 NH4]2+ precursor
ion at m/z 950.3.
Two main pathways could be proposed to account for the depletion of Mezj product ion signal.
As indicated by peaks annotated with stars in the expanded zone III of Figure 1b, each Mezj
product ion was observed to release methane, via transfer of their labile H α end-group to a
methyl hold by any in-chain silicon [1], leading to cyclic moiety in the so-formed product ion.
The Mezj primary product ions are also suspected to generate Hbk+ fragments (with k = 5-9),
observed in the expanded zone I of Figure 1b, upon release of ammonia and of a silanol
neutral formed after protonation of an oxygen atom in a DMS unit (central secondary pathway
in Scheme S2). Consecutive dissociation of the (no longer detected) highest congeners in the
TMeS +
bi product ion series via the fast release of stable cyclic Dx (left-hand-side of Scheme S2)
would also contribute to increase the abundance of the lowest congeners. In contrast,
detection of quite large TMeSbi+ + NH4+ product ions, although with a low abundance, indicates
that their signal has not been completely depleted by the commonly fast process consisting of
the release of cyclic Dx neutrals. This could be due to the presence of the adducted
ammonium which would, depending on its location on the oligomeric backbone, prevent the
backbiting process required for these cyclic neutrals to be released. Alternatively, TMeSbi+ +
NH4+ product ions would eliminate ammonia and a silanol species to generate a second series
of doubly charged products observed in the expanded zone I of Figure 1b, and named Jq2+
(with q = 8-14) since they do no longer contain any of the original end-group of the ions they
arise from (as shown in the right hand-side of Scheme S2). All assignments were supported
by accurate mass measurements (Table S2).
4
Elemental
composition
C52H160NO24Si25+
C45H140NO22Si22+
C43H134NO21Si21+
C41H128NO20Si20+
C39H122NO19Si19+
C37H116NO18Si18+
C35H110NO17Si17+
C44H136NO22Si22+
C42H130NO21Si21+
C40H124NO20Si20+
C38H118NO19Si19+
C52H164N2O24Si252+
C52H161NO24Si252+
C43H133NO20Si212+
C41H127NO19Si202+
C39H121NO18Si192+
C37H115NO17Si182+
C35H109NO16Si172+
C33H103NO15Si162+
C31H97NO14Si152+
C29H91NO13Si142+
C27H85NO12Si132+
C15H45O6Si7+
C13H39O5Si6+
C11H33O4Si5+
C9H27O3Si4+
C7H21O2Si3+
C18H55O9Si9+
C16H49O8Si8+
C14H43O7Si7+
C12H37O6Si6+
C10H31O5Si5+
C30H90O14Si152+
C28H84O13Si142+
C26H78O12Si132+
C24H72O11Si122+
C22H66O10Si112+
C20H60O9Si102+
C11H33O6Si6+
C9H27O5Si5+
C7H21O4Si4+
(m/z)theo
(m/z)exp
Error (ppm)
1882.5557
1662.4786
1588.4598
1514.4410
1440.4222
1366.4034
1292.3846
1646.4473
1572.4285
1498.4097
1424.3909
950.2948
941.7815
785.7282
748.7189
711.7095
674.7001
637.6907
600.6813
563.6719
526.6625
489.6531
517.1596
443.1408
369.1220
295.1032
221.0844
667.1764
593.1576
519.1388
445.1200
371.1012
547.1429
510.1335
473.1242
436.1148
399.1054
362.0960
429.0887
355.0699
281.0511
1882.5629
1662.4802
1588.4669
1514.4302
1440.4618
1366.4301
1292.4262
1646.4849
1572.3842
1498.4135
1424.4211
I.S
941.7789
785.7258
748.7243
711.7076
674.7000
637.6978
600.6845
563.6753
526.6686
489.6484
517.1558
443.1382
369.1210
295.1005
221.0835
667.1683
593.1637
519.1351
445.1167
371.1037
547.1444
510.1218
473.1329
436.1155
399.1032
362.1013
429.0848
355.0670
281.0500
+ 3.8
+ 1.0
+ 4.5
- 7.1
+ 27.5
+ 19.5
+ 32.2
+ 22.9
- 28.1
+ 2.5
+ 21.2
- 2.8
- 3.1
+ 7.2
- 2.7
- 0.1
+ 11.1
+ 5.3
+ 6.0
+ 11.6
- 9.6
- 7.3
- 5.9
- 2.7
- 9.1
- 4.1
- 12.1
+ 10.3
-7.1
- 7.4
+ 6.7
+ 2.7
- 22.9
+ 18.4
+ 1.6
- 5.5
+ 14.6
- 9.1
- 8.2
- 3.9
Assignment
[CH3-PDMS24 + NH4]+
Me
z22
Me
z21
Me
z20
Me
z19
Me
z18
Me
z17
Me
z22 – CH4
Me
z21 – CH4
Me
z20 – CH4
Me
z19 – CH4
[CH3-PDMS24 + 2NH4]2+
[CH3-PDMS24 + H + NH4]2+
TMeS
b20+ + NH4+
TMeS
b19+ + NH4+
TMeS
b18+ + NH4+
TMeS
b17+ + NH4+
TMeS
b16+ + NH4+
TMeS
b15+ + NH4+
TMeS
b14+ + NH4+
TMeS
b13+ + NH4+
TMeS
b12+ + NH4+
TMeS +
b6
TMeS +
b5
TMeS +
b4
TMeS +
b3
TMeS +
b2
H +
b9
H +
b8
H +
b7
H +
b6
H +
b5
J132+
J122+
J112+
J102+
J92+
J82+
TMeS +
b6 – TMS
TMeS +
b5 – TMS
TMeS +
b4 – TMS
Table S2. Accurate mass measurements of product ions formed upon CID of [CH3-PDMS24 + 2
NH4]2+ at m/z 950.3 (Figure 1b). I.S.: internal standard. TMS: tetramethylsilane.
5
Scheme S3. Structure proposed for the b3+ product ion generated upon CID of singly charged adduct
of CH3O-PDMS oligomers. The high stability of this ion would be due to its cyclic trimeric structure
holding a methyl substituent, that is, an electron donor group, on the positively charged oxygen atom.
Scheme S4. Partial charge distribution for a CH3O-PDMS3 model computed from the B3LYP/631G(d) energy calculation, using the atomic Polar Tensor (APT) method. * refers to the partial charge
of the methyl group (addition of the partial charges of the hydrogen and the carbon atoms). Geometry
optimizations were performed using the hybrid B3LYP density functional theory (DFT) approach as
implemented in Gaussian 03 [2]. The functional includes the three parameter Becke exchange
functional [3] and the LYP correlation functional [4]. This type of approach is reputedly robust against
the choice of the basis set, [5] although in some instances differences have been documented. [6] We
used here a moderate-size basis set, the standard 6-31G(d), [7] which usually gives relevant
geometries and energies in such closed shell systems for geometrical optimizations of neutrals and
ammonium adducts. Electronic charge distribution for neutral was computed using the Atomic Polar
Tensors (APT) method provided by Gaussian.
6
Additional product ion series formed during CID of [CH3O-PDMS + NH4]+
Two other product ion series of low abundance were observed in the low m/z range of the
MS/MS spectrum of [CH3O-PDMS25 + NH4]+ (Figure 2a). Focusing on the most intense
congeners, one series is composed of fragments detected at m/z 355, m/z 429 and m/z 503,
while the other one comprises m/z 371, m/z 445 and m/z 519 product ions.
To validate the origin of these two series, MS3 experiments were mandatory and for
sensitivity issues, this study was performed on a lower mass precursor, e.g. the 9-mer at m/z
730 in Figure S2.
Figure S2. a) ESI-MS/MS spectrum of the CH3O-PDMS 9-mer adducted with ammonium, and MS3
spectra using product ions at b) m/z 459 and c) m/z 371 as secondary precursor ions.
Based on accurate mass data (Table S3), product ions of the first series (annotated with open
triangles in Figure S2a) would be formed after bi+ product ions have eliminated
trimethylmethoxysilane (104 Da), according to the same mechanism as proposed for loss of
tetramethylsilane from bi+ fragments generated from CH3-PDMS ammonium adducts. For
example, as illustrated in Figure S2b, the m/z 355 product ion was generated upon activation
of the b6+ primary fragment at m/z 459. Alternatively, they could be generated after product
ions of the second series (annotated with open squares in Figure S2a) have eliminated
methane, as shown by the intense peak observed at m/z 355 when activating the m/z 371
product ion (Figure S2c). Interestingly, MS3 experiments also indicate that the product ion
series annotated with open squares does not arise from consecutive dissociation of bi+
fragments (Figure S2b). As a result, this second series would be directly formed from the
precursor ion. Again, the particular conformation adopted by PDMS oligomers due to
7
complexation of ammonium by both chain ends (as depicted in Scheme 2) would allow a
dimethylether neutral to be released upon transfer of the α methyl moiety to the ω methoxy
group. This 46 Da loss, occurring in a concerted manner with elimination of ammonia, could
be detected with low abundance from ammonium adducts of very small CH3O-PDMS. The
so-formed cyclic product ion does no longer contain any of the original end-groups (hence
named Ki+) and would rapidly further dissociate (via the release of stable D3 neutral, for
example), accounting for the main detection of lowest congeners of the series when the size of
the dissociating precursor increases.
Elemental composition
C52H160NO26Si25+
C51H153O25Si25+
C47H141O23Si23+
C45H135O22Si22+
C43H129O21Si21+
C41H123O20Si20+
C39H117O19Si19+
C37H111O18Si18+
C35H105O17Si17+
C33H99O16Si16+
C31H93O15Si15+
C29H87O14Si14+
C27H81O13Si13+
C25H75O12Si12+
C23H69O11Si11+
C21H63O10Si10+
C19H57O9Si9+
C17H51O8Si8+
C15H45O7Si7+
C13H39O6Si6+
C11H33O5Si5+
C9H27O4Si4+
C7H21O3Si3+
C5H15O2Si2+
C13H39O7Si7+
C11H33O6Si6+
C9H27O5Si5+
C7H21O4Si4+
C14H43O7Si7+
C12H37O6Si6+
C10H31O5Si5+
C8H25O4Si4+
C6H19O3Si3+
(m/z)theo
(m/z)exp
1914.5455
1865.4927
1717.4551
1643.4363
1569.4175
1495.3988
1421.3800
1347.3612
1273.3424
1199.3236
1125.3048
1051.2860
977.2672
903.2484
829.2296
755.2108
681.1920
607.1733
533.1545
459.1357
385.1169
311.0981
237.0793
163.0605
503.1075
429.0887
355.0699
281.0511
519.1388
445.1200
371.1012
297.0824
223.0643
I.S.
1865.4980
1717.4212
1643.4374
1569.3657
1495.4110
1421.3657
1347.3615
1273.2921
1199.3130
1125.3007
1051.2786
977.3052
903.2446
829.2326
755.1817
681.1891
607.1687
533.1542
459.1272
385.1153
311.0976
237.0790
163.0624
503.1086
429.0829
355.0672
281.0504
519.1404
445.1151
371.1005
297.0824
223.0619
Error (ppm)
+ 2.8
- 19.7
+ 0.6
- 33.0
+ 8.2
- 10.0
+ 0.2
- 39.5
- 8.8
- 3.6
- 7.0
+ 38.9
- 4.2
+ 3.6
- 38.6
- 4.3
- 7.5
- 0.5
- 18.5
- 4.2
- 1.6
- 1.3
+ 11.7
+ 2.2
- 13.5
- 7.6
- 2.5
+ 3.1
- 11.0
- 1.9
+ 0.0
- 10.8
Assignment
[CH3O-PDMS25 + NH4]+
b25+
b23+
b22+
b21+
b20+
b19+
b18+
b17+
b16+
b15+
b14+
b13+
b12+
b11+
b10+
b9+
b8+
b7+
b6+
b5+
b4+
b3+
b2+
b8+ - 104 (Δ)
b7+ - 104 (Δ)
b6+ - 104 (Δ)
b5+ - 104 (Δ)
K7+ (□)
K6+ (□)
K5+ (□)
K4+ (□)
K3+ (□)
Table S3. Accurate mass measurements of product ions generated upon CID of [CH3O-DMS25 +
NH4]+ at m/z 1914.6 (Figure 2a).
8
Additional product ion series formed during CID of [CH3O-PDMS + 2NH4]2+
A series of peaks observed at m/z = 74i + 1 (with i=3-7) in the low m/z range of the MS/MS
spectrum of [CH3O-PDMS25 + 2 NH4]2+ (Figure 2b) could be assigned to a H-(DMS)i+
structure based on accurate mass measurements (Table S4). These are typically Hbi+ product
ions expected to be generated upon dissociation of MeOzi primary fragments holding an H α
end-group [1]. Lack of the complementary MeOzi+ ions would again indicate that, in the
dissociating MeOzi product ion, the adducted ammonium is strongly bound to the methoxy ω
termination. Due to the labile H of their α end-group, the Hbi+ fragments were observed to
eliminate methane, accounting for product ions annotated with an asterisk in Figure 2b,
followed by the release of tetramethylsilane to generate fragments designated by filled stars.
These two dissociation pathways were typically observed during MS2 experiments performed
on HO-PDMS standards adducted with ammonium [1].
Elemental
composition
(m/z)theo
(m/z)exp
Error (ppm)
C45H140NO23Si22+
C43H134NO22Si21+
C52H164N2O26Si252+
C44H133O22Si22+
C14H43O7Si7+
C12H37O6Si6+
C10H31O5Si5+
C8H25O4Si4+
C6H19O3Si3+
C13H39O6Si6+
C11H33O5Si5+
C9H27O4Si4+
C7H21O3Si3+
C17H51O9Si9+
C15H45O8Si8+
C13H39O7Si7+
C11H33O6Si6+
C9H27O5Si5+
C7H21O4Si4+
C9H27O7Si6+
C7H21O6Si5+
C5H15O5Si4+
1678.4735
1604.4547
966.2897
1629.4207
519.1388
445.1200
371.1012
297.0824
223.0637
459.1357
385.1169
311.0981
237.0793
651.1451
577.1263
503.1075
429.0887
355.0699
281.0511
415.0367
341.0179
266.9991
1678.4800
1604.4091
I.S.
1629.4254
519.1397
445.1213
371.0969
297.0790
223.0660
459.1488
385.1107
311.0977
237.0790
651.1306
577.1298
503.1043
429.0852
355.0698
281.0478
415.0327
341.0146
266.9990
+ 3.9
- 28.4
+ 2.9
+ 1.7
+ 2.9
- 11.6
- 11.4
+ 10.3
+ 28.5
- 16.1
- 1.3
- 1.3
- 22.3
+ 6.1
- 6.4
- 8.2
- 0.3
- 11.7
- 9.6
- 9.7
- 0.4
Assignment
MeO
z22
z21
[Me-DMS25-OMe + 2 NH4]2+
H
b22+
H +
b7
H +
b6
H +
b5
H +
b4
H +
b3
Me +
b6
Me +
b5
Me +
b4
Me +
b3
H +
b9 – CH4 (*)
H +
b8 – CH4 (*)
H +
b7 – CH4 (*)
H +
b6 – CH4 (*)
H +
b5 – CH4 (*)
H +
b4 – CH4 (*)
H +
b7 – CH4 – TMS ( )
H +
b6 – CH4 – TMS ( )
H +
b5 – CH4 – TMS ( )
MeO
Table S4. Accurate mass measurements of product ions formed during CID of [CH3O-PDMS25 + 2
NH4]2+ at m/z 966.3 (Figure 2b). I.S.: internal standard. TMS: tetramethylsilane.
9
References
[1] Fouquet, T., Bour, J., Toniazzo, V., Ruch, D., Charles, L.: Characterization of ethanolysis products
of poly(dimethylsiloxane) species by electrospray ionization tandem mass spectrometry. Rapid
Commun. Mass Spectrom. 26, 2057-2067 (2012)
[2] Frisch, M.J., Trucks, G.W., Schlegel, H.B., Scuseria, G.E., Robb, M.A., Cheeseman, J.R.,
Montgomery Jr, J.A., Vreven, T., Kudin, K.N., Burant, J.C., Millam, J.M., Iyengar, S.S., Tomasi, J.,
Barone, V., Mennucci, B., Cossi, M., Scalmani, G., Rega, N., Petersson, G.A., Nakatsuji, H., Hada,
M., Ehara, M., Toyota, K., Fukuda, R., Hasegawa, J., Ishida, M., Nakajima, T., Honda, Y., Kitao, O.,
Nakai, H., Klene, M., Li, X., Knox, J.E., Hratchian, H.P., Cross, J.B., Adamo, C., Jaramillo, J.,
Gomperts, R., Stratmann, R.E., Yazyev, O., Austin, A.J., Cammi, R., Pomelli, C., Ochterski, J.W.,
Ayala, P.Y., Morokuma, K., Voth, G.A., Salvador, P., Dannenberg, J.J., Zakrzewski, V.G., Dapprich,
S., Daniels, A.D., Strain, M.C., Farkas, O., Malick, D.K., Rabuck, A.D., Raghavachari, K., Foresman,
J.B., Ortiz, J.V., Cui, Q., Baboul, A.G., Clifford, S., Ciolowski, J., Stefanov, B.B., Liu, G., Liashenko,
A., Piskorz, P., Komaromi, I., Martin, R.L., Fox, D.J., Keith, T., Al-Laham, M.A., Peng, C.Y.,
Nanayakkara, A., Challacombe, M., Gill, P.M.W., Johnson, B., Chen, W., Wong, M.W., Gonzalez, C.,
Pople, J.A. Gaussian 03, C.02; Wallingford, 2004.
[3] Becke, A.D.: Density-functional thermochemistry. 3. The role of exact exchange. J. Chem. Phys.
98, 5648–5652 (1993)
[4] Lee, C.T., Yang, W.T., Parr, R.G.: Development of the Colle-Salvetti correlation-energy formula
into a functional of the electron density. Phys. Rev. B: Condens. Matter 37, 785–789 (1988)
[5] De Proft, F., Tielens, F., Geerlings, P.: Performance and basis set dependence of density functional
theory dipole and quadrupole moments J. Mol. Struct.THEOCHEM 506, 1–8 (2000)
[6] De Jong, G.T., Geerke, D.P., Diefenbach, A., Bickelhaupt, F.M.: DFT benchmark study for the
oxidative addition of CH4 to Pd. Performance of various density functional. Chem. Phys. 313, 261–
270 (2005)
[7] Hariharan, P.C., Pople, J.A.: The influence of polarization functions on molecular orbital
hydrogenation energies. Theor. Chim. Acta 28, 213-222 (1973)
10