Supporting Information s37

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 [CH 3-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 [CH 3-PDMS + 2 2+ NH4] precursor ion at m/z 950.3 ……………………………………………………….. 4

Table S2. Accurate mass measurements of product ions formed upon CID of [CH3- 2+ PDMS24 + 2 NH4] 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 [CH3O- + DMS25 + NH4] at m/z 1914.6 …………………………………………………………… 8 2+ Additional product ion series formed during CID of [CH3O-PDMS + 2NH4] 9

Table S4. Accurate mass measurements of product ions formed during CID of [CH3O- 2+ PDMS25 + 2 NH4] at m/z 966.3 ………………………………………………………... 9 References ……………………………………………………………………………………… 10

1 + Scheme S1. a) Proposed two-step pathway to account for the major formation of small b i 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 D3 + neutral. b) Most stable structures calculated for the smallest b2-4 product ions.

Elemental Error (m/z)theo (m/z)exp Assignment composition (ppm) + + C52H160NO24Si25 1882.5557 I.S. - [CH3-PDMS24 + NH4] + + C13H39O5Si6 443.1408 443.1398 - 2.3 b5 + + C11H33O4Si5 369.1220 369.1210 - 2.7 b4 + + C9H27O3Si4 295.1032 295.1027 - 1.7 b3 + + C7H21O2Si3 221.0844 221.0850 + 2.7 b2 + + C5H15OSi2 147.0656 147.0689 + 22.4 b1 + + C11H33O6Si6 429.0887 429.0893 + 1.4 b6 - TMS + + C9H27O5Si5 355.0699 355.0716 + 4.8 b5 - TMS + + C7H21O4Si4 281.0511 281.0505 - 2.1 b4 - TMS + + C5H15O3Si3 207.0324 207.0340 + 7.7 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 b i 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]

2+ Scheme S2. Main product ions proposed to be formed upon CID of [CH3-PDMS + 2 NH4] precursor ion at m/z 950.3.

Me Two main pathways could be proposed to account for the depletion of zj product ion signal. Me As indicated by peaks annotated with stars in the expanded zone III of Figure 1b, each zj 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. Me H + The zj primary product ions are also suspected to generate bk 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, TMeS + + detection of quite large bi + 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 TMeS + + process required for these cyclic neutrals to be released. Alternatively, bi + NH4 product ions would eliminate ammonia and a silanol species to generate a second series of doubly 2+ charged products observed in the expanded zone I of Figure 1b, and named Jq (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).

Elemental Error (m/z)theo (m/z)exp Assignment composition (ppm)

+ 1882.555 + C52H160NO24Si25 1882.5629 + 3.8 [CH -PDMS + NH4] 7 3 24 1662.478 C H NO Si + 1662.4802 + 1.0 Mez 45 140 22 22 6 22 1588.459 C H NO Si + 1588.4669 + 4.5 Mez 43 134 21 21 8 21 1514.441 C H NO Si + 1514.4302 - 7.1 Mez 41 128 20 20 0 20 1440.422 C H NO Si + 1440.4618 + 27.5 Mez 39 122 19 19 2 19 1366.403 C H NO Si + 1366.4301 + 19.5 Mez 37 116 18 18 4 18 1292.384 C H NO Si + 1292.4262 + 32.2 Mez 35 110 17 17 6 17 1646.447 C H NO Si + 1646.4849 + 22.9 Mez – CH 44 136 22 22 3 22 4 1572.428 C H NO Si + 1572.3842 - 28.1 Mez – CH 42 130 21 21 5 21 4 1498.409 C H NO Si + 1498.4135 + 2.5 Mez – CH 40 124 20 20 7 20 4 1424.390 C H NO Si + 1424.4211 + 21.2 Mez – CH 38 118 19 19 9 19 4 2+ 2+ C52H164N2O24Si25 950.2948 I.S - [CH3-PDMS24 + 2NH4] 2+ 2+ C52H161NO24Si25 941.7815 941.7789 - 2.8 [CH3-PDMS24 + H + NH4] 2+ TMeS + + C43H133NO20Si21 785.7282 785.7258 - 3.1 b20 + NH4 2+ TMeS + + C41H127NO19Si20 748.7189 748.7243 + 7.2 b19 + NH4 2+ TMeS + + C39H121NO18Si19 711.7095 711.7076 - 2.7 b18 + NH4 2+ TMeS + + C37H115NO17Si18 674.7001 674.7000 - 0.1 b17 + NH4 2+ TMeS + + C35H109NO16Si17 637.6907 637.6978 + 11.1 b16 + NH4 2+ TMeS + + C33H103NO15Si16 600.6813 600.6845 + 5.3 b15 + NH4 2+ TMeS + + C31H97NO14Si15 563.6719 563.6753 + 6.0 b14 + NH4 2+ TMeS + + C29H91NO13Si14 526.6625 526.6686 + 11.6 b13 + NH4 2+ TMeS + + C27H85NO12Si13 489.6531 489.6484 - 9.6 b12 + NH4 + TMeS + C15H45O6Si7 517.1596 517.1558 - 7.3 b6 + TMeS + C13H39O5Si6 443.1408 443.1382 - 5.9 b5 + TMeS + C11H33O4Si5 369.1220 369.1210 - 2.7 b4 + TMeS + C9H27O3Si4 295.1032 295.1005 - 9.1 b3 + TMeS + C7H21O2Si3 221.0844 221.0835 - 4.1 b2 + H + C18H55O9Si9 667.1764 667.1683 - 12.1 b9 + H + C16H49O8Si8 593.1576 593.1637 + 10.3 b8 + H + C14H43O7Si7 519.1388 519.1351 -7.1 b7 + H + C12H37O6Si6 445.1200 445.1167 - 7.4 b6 + H + C10H31O5Si5 371.1012 371.1037 + 6.7 b5 2+ 2+ C30H90O14Si15 547.1429 547.1444 + 2.7 J13 2+ 2+ C28H84O13Si14 510.1335 510.1218 - 22.9 J12 2+ 2+ C26H78O12Si13 473.1242 473.1329 + 18.4 J11 2+ 2+ C24H72O11Si12 436.1148 436.1155 + 1.6 J10 2+ 2+ C22H66O10Si11 399.1054 399.1032 - 5.5 J9 2+ 2+ C20H60O9Si10 362.0960 362.1013 + 14.6 J8 + TMeS + C11H33O6Si6 429.0887 429.0848 - 9.1 b6 – TMS + TMeS + C9H27O5Si5 355.0699 355.0670 - 8.2 b5 – TMS

5 + TMeS + C7H21O4Si4 281.0511 281.0500 - 3.9 b4 – TMS

Table S2. Accurate mass measurements of product ions formed upon CID of [CH3-PDMS24 + 2 2+ NH4] at m/z 950.3 (Figure 1b). I.S.: internal standard. TMS: tetramethylsilane.

+ 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/6- 31G(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.

3 Figure S2. a) ESI-MS/MS spectrum of the CH3O-PDMS 9-mer adducted with ammonium, and MS 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 Error (m/z) (m/z) Assignment composition theo exp (ppm) + + C52H160NO26Si25 1914.5455 I.S. - [CH3O-PDMS25 + NH4] + + C51H153O25Si25 1865.4927 1865.4980 + 2.8 b25 + + C47H141O23Si23 1717.4551 1717.4212 - 19.7 b23 + + C45H135O22Si22 1643.4363 1643.4374 + 0.6 b22 + + C43H129O21Si21 1569.4175 1569.3657 - 33.0 b21 + + C41H123O20Si20 1495.3988 1495.4110 + 8.2 b20 + + C39H117O19Si19 1421.3800 1421.3657 - 10.0 b19 + + C37H111O18Si18 1347.3612 1347.3615 + 0.2 b18 + + C35H105O17Si17 1273.3424 1273.2921 - 39.5 b17 + + C33H99O16Si16 1199.3236 1199.3130 - 8.8 b16 + + C31H93O15Si15 1125.3048 1125.3007 - 3.6 b15 + + C29H87O14Si14 1051.2860 1051.2786 - 7.0 b14 + + C27H81O13Si13 977.2672 977.3052 + 38.9 b13 + + C25H75O12Si12 903.2484 903.2446 - 4.2 b12 + + C23H69O11Si11 829.2296 829.2326 + 3.6 b11 + + C21H63O10Si10 755.2108 755.1817 - 38.6 b10 + + C19H57O9Si9 681.1920 681.1891 - 4.3 b9 + + C17H51O8Si8 607.1733 607.1687 - 7.5 b8 + + C15H45O7Si7 533.1545 533.1542 - 0.5 b7 + + C13H39O6Si6 459.1357 459.1272 - 18.5 b6 + + C11H33O5Si5 385.1169 385.1153 - 4.2 b5 + + C9H27O4Si4 311.0981 311.0976 - 1.6 b4 + + C7H21O3Si3 237.0793 237.0790 - 1.3 b3 + + C5H15O2Si2 163.0605 163.0624 + 11.7 b2 + + C13H39O7Si7 503.1075 503.1086 + 2.2 b8 - 104 (Δ) + + C11H33O6Si6 429.0887 429.0829 - 13.5 b7 - 104 (Δ) + + C9H27O5Si5 355.0699 355.0672 - 7.6 b6 - 104 (Δ) + + C7H21O4Si4 281.0511 281.0504 - 2.5 b5 - 104 (Δ) + + C14H43O7Si7 519.1388 519.1404 + 3.1 K7 (□) + + C12H37O6Si6 445.1200 445.1151 - 11.0 K6 (□) + + C10H31O5Si5 371.1012 371.1005 - 1.9 K5 (□) + + C8H25O4Si4 297.0824 297.0824 + 0.0 K4 (□) + + C6H19O3Si3 223.0643 223.0619 - 10.8 K3 (□)

Table S3. Accurate mass measurements of product ions generated upon CID of [CH 3O-DMS25 + + NH4] at m/z 1914.6 (Figure 2a).

8 2+ Additional product ion series formed during CID of [CH3O-PDMS + 2NH4]

A series of peaks observed at m/z = 74i + 1 (with i=3-7) in the low m/z range of the MS/MS 2+ + spectrum of [CH3O-PDMS25 + 2 NH4] (Figure 2b) could be assigned to a H-(DMS)i H + structure based on accurate mass measurements (Table S4). These are typically bi product MeO ions expected to be generated upon dissociation of zi primary fragments holding an H α MeO + end-group [1]. Lack of the complementary zi ions would again indicate that, in the MeO dissociating zi product ion, the adducted ammonium is strongly bound to the methoxy ω H + termination. Due to the labile H of their α end-group, the bi 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 Error (m/z) (m/z) Assignment composition theo exp (ppm) 1678.480 C H NO Si + 1678.4735 + 3.9 MeOz 45 140 23 22 0 22 1604.409 C H NO Si + 1604.4547 - 28.4 MeOz 43 134 22 21 1 21 2+ 2+ C52H164N2O26Si25 966.2897 I.S. - [Me-DMS25-OMe + 2 NH4] 1629.425 C H O Si + 1629.4207 + 2.9 Hb + 44 133 22 22 4 22 + H + C14H43O7Si7 519.1388 519.1397 + 1.7 b7 + H + C12H37O6Si6 445.1200 445.1213 + 2.9 b6 + H + C10H31O5Si5 371.1012 371.0969 - 11.6 b5 + H + C8H25O4Si4 297.0824 297.0790 - 11.4 b4 + H + C6H19O3Si3 223.0637 223.0660 + 10.3 b3 + Me + C13H39O6Si6 459.1357 459.1488 + 28.5 b6 + Me + C11H33O5Si5 385.1169 385.1107 - 16.1 b5 + Me + C9H27O4Si4 311.0981 311.0977 - 1.3 b4 + Me + C7H21O3Si3 237.0793 237.0790 - 1.3 b3 + H + C17H51O9Si9 651.1451 651.1306 - 22.3 b9 – CH4 (*) + H + C15H45O8Si8 577.1263 577.1298 + 6.1 b8 – CH4 (*) + H + C13H39O7Si7 503.1075 503.1043 - 6.4 b7 – CH4 (*) + H + C11H33O6Si6 429.0887 429.0852 - 8.2 b6 – CH4 (*) + H + C9H27O5Si5 355.0699 355.0698 - 0.3 b5 – CH4 (*) + H + C7H21O4Si4 281.0511 281.0478 - 11.7 b4 – CH4 (*) + C9H27O7Si6 415.0367 415.0327 - 9.6 H + b7 – CH4 – TMS ( ) + C7H21O6Si5 341.0179 341.0146 - 9.7 H + b6 – CH4 – TMS ( ) + C5H15O5Si4 266.9991 266.9990 - 0.4 H + b5 – CH4 – TMS ( )

Table S4. Accurate mass measurements of product ions formed during CID of [CH3O-PDMS25 + 2 2+ NH4] at m/z 966.3 (Figure 2b). I.S.: internal standard. TMS: tetramethylsilane.

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