Fragmentation Reactions of Complexes of Alkali Metal Ions with Pentaserine, Pentaleucine and Pentalysine in Gas Phase†

doi:10.7503/cjcu20130721

Abstract

Abstract:

For exploring the effects of alkali metal ions on the dissociations of peptides with different side chains in the gas phase, the complexes of Li⁺, Na⁺, K⁺, Rb⁺ and Cs⁺ with pentapeptides, Ser-Ser-Ser-Ser-Ser(S5), Leu-Leu-Leu-Leu-Leu(L5) and Lys-Lys-Lys-Lys-Lys(K5), were chosen to investigate the fragmentation reaction pathways by mass spectrometry. The experimental results indicated that alkali metal ions and S5, L5, K5 can form 1∶1 and 2∶1 non-covalent complexes in the gas phase, and the binding strength between alkali metal ions and pentapeptides descend with the increasing of the radii of alkali metal ions. Quantitative analyses of mass spectra demonstrated that the binding constants for the complexes of K⁺ with S5, L5 and K5 are 8.94×10⁴, 2.83×10⁴ and 2.50×10³ L/mol, respectively, revealing that the binding strength of complexes decrease in order of S5, L5 and K5. The analyses of the fragment ions arising from the complexes of alkali metal ions with pentapeptides showed that the dissociations mainly occur in the backbones of the peptides. Among three pentapeptides, the complexes of pentaserines are the easiest to fragment, pentaleucines take second place, while pentalysines are the hardest. The dissociations also occur in the side chains, and there are significant differences among the three complexes. Moreover, the relationships among various fragment ions arising from the complex of Na⁺ with L5 were tested. Based on the theoretical model of Dunbar, it was proposed that in the fragmentation process, the alkali metal ion may shift to the N- or C-terminal of the pentapeptide. In 2∶1 complex, the first alkali metal ion may conjugate to the carbonyl groups of four amides, while the second one may conjugate to the oxygen atoms of carboxyl group of the pentapeptide.

Key words: Mass spectrometry, Collision induced dissociation, Alkali metal ion, Pentapeptide, Fragmentation reaction

CLC Number:

O657

TrendMD:

WEI Wanghui, WANG Qing, CHU Yanqiu, WANG Rizhi, DING Chuanfan. Fragmentation Reactions of Complexes of Alkali Metal Ions with Pentaserine, Pentaleucine and Pentalysine in Gas Phase^†[J]. Chem. J. Chinese Universities, 2014, 35(1): 37.

Figures/Tables 12

Scheme 1 Nomenclature used for the fragments of pentapeptideR1=R2=R3=R4=R5=—H, —CH2OH, —CH2CH(CH3)2, —(CH2)4NH2.

Fig.1 Mass spectra for competition reaction of pentapeptides with alkali metal ions in a molar ratio of 1∶1∶1∶1∶1∶1∶1(A) G5; (B) S5; (C) L5; (D) K5. c(Pentapeptide)=c(Alkali metal ion)=1.0×10-4 mol/L.

Table 1 Ka1 values of the complexes of G5 with K+

10⁵ [G5]₀/(mol·L^-1)	10⁵ [K⁺]₀/(mol·L^-1)	I_P	I_PM	I_PM2	a₁	a₂	10^-5 K_a1/(L·mol^-1)
5.00	10.00	7.54	100.00	97.94	0.487	0.477	4.84
5.00	15.00	3.17	100.00	98.03	0.497	0.487	4.06
5.00	20.00	1.92	100.00	98.35	0.499	0.491	3.96
5.00	25.00	1.68	100.00	98.42	0.499	0.492	3.15
5.00	30.00	1.32	100.00	99.31	0.498	0.495	3.15
Average							3.83
SD							0.70
RSD(%)							18.2

Table 2 Ka1 values of the complexes of S5 with K+

10⁵ [S5]₀/(mol·L^-1)	10⁵ [K⁺]₀/(mol·L^-1)	I_P	I_PM	I_PM2	a₁	a₂	10^-4 $K a 1$ /(L·mol^-1)
5.00	10.00	23.99	100.00	51.09	0.571	0.292	9.86
5.00	15.00	12.80	100.00	70.47	0.546	0.384	9.25
5.00	20.00	8.15	100.00	97.10	0.487	0.473	9.49
5.00	25.00	6.97	100.00	97.57	0.489	0.477	8.09
5.00	30.00	5.47	100.00	98.15	0.491	0.482	8.00
Average							8.94
SD							0.84
RSD(%)							9.4

Table 2 Ka1 values of the complexes of S5 with K+

10⁵ [S5]₀/(mol·L^-1)	10⁵ [K⁺]₀/(mol·L^-1)	I_P	I_PM	I_PM2	a₁	a₂	10^-4 $K a 1$ /(L·mol^-1)
5.00	10.00	23.99	100.00	51.09	0.571	0.292	9.86
5.00	15.00	12.80	100.00	70.47	0.546	0.384	9.25
5.00	20.00	8.15	100.00	97.10	0.487	0.473	9.49
5.00	25.00	6.97	100.00	97.57	0.489	0.477	8.09
5.00	30.00	5.47	100.00	98.15	0.491	0.482	8.00
Average							8.94
SD							0.84
RSD(%)							9.4

Table 3 Ka1 values of the complexes of L5 with K+

10⁵ [L5]₀/(mol·L^-1)	10⁵ [K⁺]₀/(mol·L^-1)	I_P	I_PM	I_PM2	a₁	a₂	10^-4 $K a 1$ /(L·mol^-1)
5.00	10.00	51.03	100.00	8.19	0.628	0.051	3.08
5.00	15.00	33.63	100.00	13.53	0.680	0.092	2.79
5.00	20.00	21.85	100.00	15.31	0.729	0.112	3.01
5.00	25.00	18.68	100.00	17.09	0.737	0.126	2.68
5.00	30.00	15.71	100.00	20.75	0.733	0.152	2.57
Average							2.83
SD							0.21
RSD(%)							7.4

Table 3 Ka1 values of the complexes of L5 with K+

10⁵ [L5]₀/(mol·L^-1)	10⁵ [K⁺]₀/(mol·L^-1)	I_P	I_PM	I_PM2	a₁	a₂	10^-4 $K a 1$ /(L·mol^-1)
5.00	10.00	51.03	100.00	8.19	0.628	0.051	3.08
5.00	15.00	33.63	100.00	13.53	0.680	0.092	2.79
5.00	20.00	21.85	100.00	15.31	0.729	0.112	3.01
5.00	25.00	18.68	100.00	17.09	0.737	0.126	2.68
5.00	30.00	15.71	100.00	20.75	0.733	0.152	2.57
Average							2.83
SD							0.21
RSD(%)							7.4

Table 4 Ka1 values of the complexes of K5 with K+

10⁵ [K5]₀/(mol·L^-1)	10⁵ [K⁺]₀/(mol·L^-1)	I_P	I_PM	I_PM2	a₁	a₂	10^-3 $K a 1$ /(L·mol^-1)
5.00	10.00	100.00	22.88	7.29	0.176	0.056	2.68
5.00	15.00	100.00	34.33	14.11	0.231	0.095	2.66
5.00	20.00	100.00	42.90	22.47	0.259	0.136	2.47
5.00	25.00	100.00	51.93	31.90	0.282	0.174	2.37
5.00	30.00	100.00	61.13	40.60	0.303	0.201	2.31
Average							2.50
SD							0.17
RSD(%)							6.8

Table 4 Ka1 values of the complexes of K5 with K+

10⁵ [K5]₀/(mol·L^-1)	10⁵ [K⁺]₀/(mol·L^-1)	I_P	I_PM	I_PM2	a₁	a₂	10^-3 $K a 1$ /(L·mol^-1)
5.00	10.00	100.00	22.88	7.29	0.176	0.056	2.68
5.00	15.00	100.00	34.33	14.11	0.231	0.095	2.66
5.00	20.00	100.00	42.90	22.47	0.259	0.136	2.47
5.00	25.00	100.00	51.93	31.90	0.282	0.174	2.37
5.00	30.00	100.00	61.13	40.60	0.303	0.201	2.31
Average							2.50
SD							0.17
RSD(%)							6.8

Fig.2 Relationship between intensity of mass spectrometric peak and normalized collision energy The precursors are the complexes of G5(■), S5(●), L5(▲) or K5(◆) with H+(A), Li+(B) and 2Li+(C).

Fig.3 CID spectra for the precursor of [K5+Na]+ at different collision energies

Fig.4 CID breakdown curves for the complexes of Na+ with pentaleucinea. Precursor ion [L5+Na]+; b. [b4+Na+OH]+; c. [b4+Na-H]+; d. [y3+Na+H]+; e. [b3+Na-H]+; f. [y2+Na+H]+.

Table 5 Main fragment ions of protonated and alkali metal cationized S5 complexes obtained with CID

Precursor ion(#)	a_n/a_n^/a_n^*	$b n$ / $b n $ / $b n *$	$y n$ / $y n $ / $y n *$	Other
[S5+H]⁺	a₄, a₃, a₂, a₁, a₄-H₂O, a₄-2H₂O, a₃-H₂O, a₃-2H₂O, a₂-H₂O	b₄, b₃, b₂, b₄-H₂O, b₃-H₂O, b₂-H₂O, b₃-2H₂O	y₃, y₂, y₁	[#-H₂O]⁺, [#-2H₂O]⁺, [#-3H₂O]⁺, [#-4H₂O]⁺
[S5+Li]⁺	a₄^, a₄^-CH₂O, a₄^-H₂O, a₃^, a₃^-CH₂O, a₃^-H₂O, a₂^, a₂^-CH₂O, a₂^-H₂O, a₁^	[b₄+Li+OH]⁺, [b₄+Li+OH- CH₂O]⁺, b₄^-H₂O, b₄^-CO₂, [b₃+Li+OH]⁺, b₄^-H₂O-CH₂O, b₃^-H₂O, b₄^, b₃^-CO₂, [b₃+ Li+OH-CH₂O]⁺, b₃^, b₂^, b₃^-H₂O-CH₂O, b₂^-H₂O, b₂^*-H₂O-CH₂O	y₂^, y₂^-H₂O, y₁^*	[#-H₂O]⁺, [#-CH₂O]⁺, [#-H₂O-CH₂O]⁺ , [#-H₂O-CO₂]⁺, [#-H₂O-2CH₂O]⁺, [#-2H₂O-CH₂O]⁺
[S5+Na]⁺	a₄^, a₄^-CH₂O, a₃^, a₁^	[b₄+Na+OH]⁺, [b₄+Na+OH- CH₂O]⁺, b₄^, b₄^-H₂O, [b₃+ Na+OH]⁺, b₃^, b₂^, [b₃+Na+ OH-CH₂O]⁺	y₂^*	[#-H₂O]⁺, [#-CH₂O]⁺, [#-H₂O-CH₂O]⁺, [#-H₂O-CO₂]⁺
[S5+K]⁺	a₄^, a₄^-CH₂O	[b₄+K+OH]⁺, [b₄+K+OH- CH₂O]⁺, b₄^, b₄^-H₂O, [b₃+ K+OH]⁺, [b₃+K+OH-CH₂O]⁺, b₃^*		K⁺, [#-H₂O]⁺, [#-CH₂O]⁺, [#-2CH₂O]⁺
[S5+Rb]⁺				Rb⁺
[S5+Cs]⁺				Cs⁺
[S5+2Li-H]⁺	a₄^, a₃^, a₄^, a₃^	b₃^, b₃^-CH₂O, b₂^, b₂^-CH₂O	y₄^, y₃^, y₂^, y₁^, y₄^-CH₂O, y₃^-CH₂O, y₂^-CH₂O, y₁^-CH₂O, y₄^-2CH₂O, y₃^-CH₂O	[#-H₂O]⁺, [#-CH₂O]⁺, [#-2CH₂O]⁺, [#-3CH₂O]⁺, [#-4CH₂O]⁺, [#-H₂O-CH₂O]⁺, [#-H₂O-2CH₂O]⁺, [#-H₂O-3CH₂O]⁺, [#-2H₂O-3CH₂O]⁺
[S5+2Na-H]⁺	a₄^-CH₂O, a₄^-2CH₂O, a₄^-3CH₂O, a₃^-CH₂O	b₂^*, b₄^, b₄^*-CH₂O	y₄^, y₃^, y₂^, y₁^, y₄^-CH₂O, y₃^-CH₂O, y₂^-CH₂O, y₁^-CH₂O, y₃^-2CH₂O, y₂^-2CH₂O	[#-H₂O]⁺, [#-CH₂O]⁺, [#-2CH₂O]⁺, [#- 3CH₂O]⁺, [#-4CH₂O]⁺, [#-5CH₂O]⁺, [#-H₂O- CH₂O]⁺, [#-H₂O- 2CH₂O]⁺, [#-H₂O- 3CH₂O]⁺, [#-H₂O- 4CH₂O]⁺
[S5+2K-H]⁺	a₄^**-H₂O	b₃^-CH₂O, b₃^-2CH₂O, b₂^**-CH₂O	y₄^, y₃^, y₂^, y₁^, y₃^-CH₂O, y₂^-CH₂O, y₁^-CH₂O, y₂^-2CH₂O	K⁺, [#-H₂O]⁺, [#-2H₂O]⁺, [#-CH₂O]⁺, [#-2CH₂O]⁺, [#-3CH₂O]⁺, [#-4CH₂O]⁺, [#-H₂O-CH₂O]⁺, [#-H₂O-2CH₂O]⁺, [#-2H₂O- 2CH₂O]⁺, [#-H₂O- 3CH₂O]⁺, [#-2H₂O- 3CH₂O]⁺, [#-H₂O- 4CH₂O]⁺
[S5+2Rb-H]⁺	a₄^, a₄^-H₂O	b₃^, b₁^, b₃^**-2H₂O	y₄^, y₃^, y₂^, y₁^	Rb⁺, [#-H₂O]⁺, [#-CH₂O]⁺, [#-2CH₂O]⁺, [#-3CH₂O]⁺, [#-H₂O- CH₂O]⁺, [#-H₂O-2CH₂O]⁺
[S5+2Cs-H]⁺	a₄^**-H₂O	b₃^**	y₄^, y₃^, y₁^, y₁^-CH₂O	Cs⁺, [#-H₂O]⁺, [#-CH₂O]⁺, [#-2CH₂O]⁺, [#-H₂O-CH₂O]⁺, [#-H₂O-2CH₂O]⁺, [#-3CH₂O]⁺

Table 5 Main fragment ions of protonated and alkali metal cationized S5 complexes obtained with CID

Precursor ion(#)	a_n/a_n^/a_n^*	$b n$ / $b n $ / $b n *$	$y n$ / $y n $ / $y n *$	Other
[S5+H]⁺	a₄, a₃, a₂, a₁, a₄-H₂O, a₄-2H₂O, a₃-H₂O, a₃-2H₂O, a₂-H₂O	b₄, b₃, b₂, b₄-H₂O, b₃-H₂O, b₂-H₂O, b₃-2H₂O	y₃, y₂, y₁	[#-H₂O]⁺, [#-2H₂O]⁺, [#-3H₂O]⁺, [#-4H₂O]⁺
[S5+Li]⁺	a₄^, a₄^-CH₂O, a₄^-H₂O, a₃^, a₃^-CH₂O, a₃^-H₂O, a₂^, a₂^-CH₂O, a₂^-H₂O, a₁^	[b₄+Li+OH]⁺, [b₄+Li+OH- CH₂O]⁺, b₄^-H₂O, b₄^-CO₂, [b₃+Li+OH]⁺, b₄^-H₂O-CH₂O, b₃^-H₂O, b₄^, b₃^-CO₂, [b₃+ Li+OH-CH₂O]⁺, b₃^, b₂^, b₃^-H₂O-CH₂O, b₂^-H₂O, b₂^*-H₂O-CH₂O	y₂^, y₂^-H₂O, y₁^*	[#-H₂O]⁺, [#-CH₂O]⁺, [#-H₂O-CH₂O]⁺ , [#-H₂O-CO₂]⁺, [#-H₂O-2CH₂O]⁺, [#-2H₂O-CH₂O]⁺
[S5+Na]⁺	a₄^, a₄^-CH₂O, a₃^, a₁^	[b₄+Na+OH]⁺, [b₄+Na+OH- CH₂O]⁺, b₄^, b₄^-H₂O, [b₃+ Na+OH]⁺, b₃^, b₂^, [b₃+Na+ OH-CH₂O]⁺	y₂^*	[#-H₂O]⁺, [#-CH₂O]⁺, [#-H₂O-CH₂O]⁺, [#-H₂O-CO₂]⁺
[S5+K]⁺	a₄^, a₄^-CH₂O	[b₄+K+OH]⁺, [b₄+K+OH- CH₂O]⁺, b₄^, b₄^-H₂O, [b₃+ K+OH]⁺, [b₃+K+OH-CH₂O]⁺, b₃^*		K⁺, [#-H₂O]⁺, [#-CH₂O]⁺, [#-2CH₂O]⁺
[S5+Rb]⁺				Rb⁺
[S5+Cs]⁺				Cs⁺
[S5+2Li-H]⁺	a₄^, a₃^, a₄^, a₃^	b₃^, b₃^-CH₂O, b₂^, b₂^-CH₂O	y₄^, y₃^, y₂^, y₁^, y₄^-CH₂O, y₃^-CH₂O, y₂^-CH₂O, y₁^-CH₂O, y₄^-2CH₂O, y₃^-CH₂O	[#-H₂O]⁺, [#-CH₂O]⁺, [#-2CH₂O]⁺, [#-3CH₂O]⁺, [#-4CH₂O]⁺, [#-H₂O-CH₂O]⁺, [#-H₂O-2CH₂O]⁺, [#-H₂O-3CH₂O]⁺, [#-2H₂O-3CH₂O]⁺
[S5+2Na-H]⁺	a₄^-CH₂O, a₄^-2CH₂O, a₄^-3CH₂O, a₃^-CH₂O	b₂^*, b₄^, b₄^*-CH₂O	y₄^, y₃^, y₂^, y₁^, y₄^-CH₂O, y₃^-CH₂O, y₂^-CH₂O, y₁^-CH₂O, y₃^-2CH₂O, y₂^-2CH₂O	[#-H₂O]⁺, [#-CH₂O]⁺, [#-2CH₂O]⁺, [#- 3CH₂O]⁺, [#-4CH₂O]⁺, [#-5CH₂O]⁺, [#-H₂O- CH₂O]⁺, [#-H₂O- 2CH₂O]⁺, [#-H₂O- 3CH₂O]⁺, [#-H₂O- 4CH₂O]⁺
[S5+2K-H]⁺	a₄^**-H₂O	b₃^-CH₂O, b₃^-2CH₂O, b₂^**-CH₂O	y₄^, y₃^, y₂^, y₁^, y₃^-CH₂O, y₂^-CH₂O, y₁^-CH₂O, y₂^-2CH₂O	K⁺, [#-H₂O]⁺, [#-2H₂O]⁺, [#-CH₂O]⁺, [#-2CH₂O]⁺, [#-3CH₂O]⁺, [#-4CH₂O]⁺, [#-H₂O-CH₂O]⁺, [#-H₂O-2CH₂O]⁺, [#-2H₂O- 2CH₂O]⁺, [#-H₂O- 3CH₂O]⁺, [#-2H₂O- 3CH₂O]⁺, [#-H₂O- 4CH₂O]⁺
[S5+2Rb-H]⁺	a₄^, a₄^-H₂O	b₃^, b₁^, b₃^**-2H₂O	y₄^, y₃^, y₂^, y₁^	Rb⁺, [#-H₂O]⁺, [#-CH₂O]⁺, [#-2CH₂O]⁺, [#-3CH₂O]⁺, [#-H₂O- CH₂O]⁺, [#-H₂O-2CH₂O]⁺
[S5+2Cs-H]⁺	a₄^**-H₂O	b₃^**	y₄^, y₃^, y₁^, y₁^-CH₂O	Cs⁺, [#-H₂O]⁺, [#-CH₂O]⁺, [#-2CH₂O]⁺, [#-H₂O-CH₂O]⁺, [#-H₂O-2CH₂O]⁺, [#-3CH₂O]⁺

Table 6 Main product ions of protonated and alkali metal cationized L5 complexes obtained with CID

Precursor ion(#)	a_n/ $a n $ / $a n *$	$b n$ / $b n $ / $b n *$	$y n$ / $y n $ / $y n *$	Other
[L5+H]⁺	a₄, a₂, a₁, a₄-NH₃, a₃-NH₃, a₄-CH₂-CH-(CH₃)₂	b₃, b₂	y₄, y₃, y₂	[#-H₂O]⁺
[L5+Li]⁺	a₄^, a₃^, a₃^-(CH₃)₂, a₄^- CH₂-CH-(CH₃)₂, a₂^, a₂^-(CH₃)₂	[b₄+Li+OH]⁺, b₄^-NH₃, [b₃+Li+OH]⁺, b₃^-NH₃, b₄^, b₃^, b₂^*	y₃^, y₂^, y₁^*	[#-H₂O-NH₃]⁺
[L5+Na]⁺	a₄^, a₃^, a₁^, a₃^-CH₂-CH- (CH₃)₂, a₂^*-CH₂-CH-(CH₃)₂	[b₄+Na+OH]⁺, b₃^, [b₃+Na+OH]⁺, b₂^	y₂^, y₁^
[L5+K]⁺	a₄^, a₃^	[b₄+K+OH]⁺, b₄^*, [b₃+K+OH]⁺	y₂^, y₂^-NH₃, y₄^*-CO	K⁺, [#-CO]⁺, [#-CO₂]⁺
[L5+Rb]⁺		[b₄+Rb+OH]⁺		Rb⁺
[L5+Cs]⁺				Cs⁺
[L5+2Li-H]⁺	a₄^, a₃^, a₄^, a₃^, a₁^, a₃^-CO₂, a₂^*-CO₂	b₂^, b₄^-H₂O-NH₃, b₃^*-H₂O-NH₃	y₄^, y₂^, y₁^*, y₃^, y₁^*	[#-CO₂]⁺, [#-H₂O-NH₃]⁺
[L5+2Na-H]⁺	a₄^*, a₄^, a₃^, a₂^, a₁^, a₃^-H₂O-NH₃, a₂^-H₂O-NH₃, a₂^-CH₂-CH-(CH₃)₂	b₃^, b₃^-NH₃	y₄^, y₃^, y₂^, y₁^, y₂^**-CO₂	[#-CO₂]⁺
[L5+2K-H]⁺	a₄^, a₃^, a₂^, a₁^-(CH₃)₂		y₄^, y₃^, y₂^, y₁^, y₁^**-H₂O-NH₃	K⁺
[L5+2Rb-H]⁺	a₃^-CH₂-CH-(CH₃)₂, a₂^-CH₂-CH-(CH₃)₂		y₃^, y₂^, y₁^, y₃^-NH₃	Rb⁺
[L5+2Cs-H]⁺	a₂^**-CH₂-CH-(CH₃)₂		y₃^, y₂^, y₁^, y₄^-CH₂-CH-(CH₃)₂	Cs⁺

Table 6 Main product ions of protonated and alkali metal cationized L5 complexes obtained with CID

Precursor ion(#)	a_n/ $a n $ / $a n *$	$b n$ / $b n $ / $b n *$	$y n$ / $y n $ / $y n *$	Other
[L5+H]⁺	a₄, a₂, a₁, a₄-NH₃, a₃-NH₃, a₄-CH₂-CH-(CH₃)₂	b₃, b₂	y₄, y₃, y₂	[#-H₂O]⁺
[L5+Li]⁺	a₄^, a₃^, a₃^-(CH₃)₂, a₄^- CH₂-CH-(CH₃)₂, a₂^, a₂^-(CH₃)₂	[b₄+Li+OH]⁺, b₄^-NH₃, [b₃+Li+OH]⁺, b₃^-NH₃, b₄^, b₃^, b₂^*	y₃^, y₂^, y₁^*	[#-H₂O-NH₃]⁺
[L5+Na]⁺	a₄^, a₃^, a₁^, a₃^-CH₂-CH- (CH₃)₂, a₂^*-CH₂-CH-(CH₃)₂	[b₄+Na+OH]⁺, b₃^, [b₃+Na+OH]⁺, b₂^	y₂^, y₁^
[L5+K]⁺	a₄^, a₃^	[b₄+K+OH]⁺, b₄^*, [b₃+K+OH]⁺	y₂^, y₂^-NH₃, y₄^*-CO	K⁺, [#-CO]⁺, [#-CO₂]⁺
[L5+Rb]⁺		[b₄+Rb+OH]⁺		Rb⁺
[L5+Cs]⁺				Cs⁺
[L5+2Li-H]⁺	a₄^, a₃^, a₄^, a₃^, a₁^, a₃^-CO₂, a₂^*-CO₂	b₂^, b₄^-H₂O-NH₃, b₃^*-H₂O-NH₃	y₄^, y₂^, y₁^*, y₃^, y₁^*	[#-CO₂]⁺, [#-H₂O-NH₃]⁺
[L5+2Na-H]⁺	a₄^*, a₄^, a₃^, a₂^, a₁^, a₃^-H₂O-NH₃, a₂^-H₂O-NH₃, a₂^-CH₂-CH-(CH₃)₂	b₃^, b₃^-NH₃	y₄^, y₃^, y₂^, y₁^, y₂^**-CO₂	[#-CO₂]⁺
[L5+2K-H]⁺	a₄^, a₃^, a₂^, a₁^-(CH₃)₂		y₄^, y₃^, y₂^, y₁^, y₁^**-H₂O-NH₃	K⁺
[L5+2Rb-H]⁺	a₃^-CH₂-CH-(CH₃)₂, a₂^-CH₂-CH-(CH₃)₂		y₃^, y₂^, y₁^, y₃^-NH₃	Rb⁺
[L5+2Cs-H]⁺	a₂^**-CH₂-CH-(CH₃)₂		y₃^, y₂^, y₁^, y₄^-CH₂-CH-(CH₃)₂	Cs⁺

Table 7 Main product ions of protonated and alkali metal cationized K5 complexes obtained with CID

Precursor ion(#)	a_n/ $a n $ / $a n *$	$b n$ / $b n $ / $b n *$	$y n$ / $y n $ / $y n *$	Other
[K5+H]⁺	a₄-(CH₂)₄-NH₂, a₃-(CH₂)₄-NH₂, a₁, a₁-NH₃	b₄, b₃, b₂, b₁, b₄-H₂O, b₃-H₂O, b₂-H₂O, b₄-H₂O-NH₃, b₄-H₂O-2NH₃, b₃-H₂O-NH₃, b₃-H₂O-2NH₃, b₂-H₂O-NH₃, b₂-H₂O-2NH₃	y₄, y₃, y₂, y₁	[#-H₂O]⁺
[K5+Li]⁺	a₁^, a₂^- (CH₂)₄-NH₂	[b₄+Li+OH]⁺, b₄^, b₃^, b₂^, b₁^, b₄^-H₂O, b₄^-H₂O-NH₃, [b₃+Li+OH]⁺, b₃^-H₂O, b₃^-H₂O-NH₃, b₂^-H₂O, b₂^-H₂O-NH₃	y₂^, y₁^	[#-H₂O]⁺
[K5+Na]⁺	a₁^, a₃^- (CH₂)₄-NH₂	[b₄+Na+OH]⁺, b₄^, b₃^, b₂^, b₁^, b₄^-H₂O, b₂^-H₂O-NH₃, [b₃+Na+OH]⁺, b₃^*-H₂O	y₄^-CO₂, y₂^, y₁^*	[#-H₂O]⁺
[K5+K]⁺	a₂^*	[b₄+K+OH]⁺, b₄^, b₃^, b₂^, b₁^, b₃^-H₂O, b₂^-H₂O, [b₃+K+OH]⁺	y₂^, y₁^, y₁^*-(CH₂)₄	K⁺, [#-H₂O]⁺, [#-CO₂]⁺
[K5+Rb]⁺		[b₄+Rb+OH]⁺		Rb⁺
[K5+Cs]⁺		[b₄+Cs+OH]⁺		Cs⁺
[K5+2Li-H]⁺	a₄^, a₃^, a₂^, a₂^-H₂O-NH₃, a₁^*	b₃^, b₂^, b₄^, b₃^, b₁^*	y₄^, y₃^, y₂^, y₁^, y₄^, y₁^	[#-CO₂]⁺, [#-CO₂-CH₂-NH₂]⁺
[K5+2Na-H]⁺	a₄^, a₄^-4CH₂	b₄^, b₄^-CO₂, b₄^, b₃^, b₂^*	y₄^, y₃^, y₂^, y₁^, y₃^-CO₂, y₂^-CO₂, y₄^, y₃^, y₂^, y₁^, y₁^**-4CH₂	[#-CO₂]⁺
[K5+2K-H]⁺	a₂^, a₂^- (CH₂)₄-NH₂	b₄^*	y₄^, y₃^, y₂^, y₁^, y₄^, y₃^	K⁺, [#-CO₂]⁺
[K5+2Rb-H]⁺		b₄^*	y₃^, y₂^, y₁^*, y₃^	Rb⁺
[K5+2Cs-H]⁺		b₄^*	y₃^, y₂^, y₁^**	Cs⁺

Table 7 Main product ions of protonated and alkali metal cationized K5 complexes obtained with CID

Precursor ion(#)	a_n/ $a n $ / $a n *$	$b n$ / $b n $ / $b n *$	$y n$ / $y n $ / $y n *$	Other
[K5+H]⁺	a₄-(CH₂)₄-NH₂, a₃-(CH₂)₄-NH₂, a₁, a₁-NH₃	b₄, b₃, b₂, b₁, b₄-H₂O, b₃-H₂O, b₂-H₂O, b₄-H₂O-NH₃, b₄-H₂O-2NH₃, b₃-H₂O-NH₃, b₃-H₂O-2NH₃, b₂-H₂O-NH₃, b₂-H₂O-2NH₃	y₄, y₃, y₂, y₁	[#-H₂O]⁺
[K5+Li]⁺	a₁^, a₂^- (CH₂)₄-NH₂	[b₄+Li+OH]⁺, b₄^, b₃^, b₂^, b₁^, b₄^-H₂O, b₄^-H₂O-NH₃, [b₃+Li+OH]⁺, b₃^-H₂O, b₃^-H₂O-NH₃, b₂^-H₂O, b₂^-H₂O-NH₃	y₂^, y₁^	[#-H₂O]⁺
[K5+Na]⁺	a₁^, a₃^- (CH₂)₄-NH₂	[b₄+Na+OH]⁺, b₄^, b₃^, b₂^, b₁^, b₄^-H₂O, b₂^-H₂O-NH₃, [b₃+Na+OH]⁺, b₃^*-H₂O	y₄^-CO₂, y₂^, y₁^*	[#-H₂O]⁺
[K5+K]⁺	a₂^*	[b₄+K+OH]⁺, b₄^, b₃^, b₂^, b₁^, b₃^-H₂O, b₂^-H₂O, [b₃+K+OH]⁺	y₂^, y₁^, y₁^*-(CH₂)₄	K⁺, [#-H₂O]⁺, [#-CO₂]⁺
[K5+Rb]⁺		[b₄+Rb+OH]⁺		Rb⁺
[K5+Cs]⁺		[b₄+Cs+OH]⁺		Cs⁺
[K5+2Li-H]⁺	a₄^, a₃^, a₂^, a₂^-H₂O-NH₃, a₁^*	b₃^, b₂^, b₄^, b₃^, b₁^*	y₄^, y₃^, y₂^, y₁^, y₄^, y₁^	[#-CO₂]⁺, [#-CO₂-CH₂-NH₂]⁺
[K5+2Na-H]⁺	a₄^, a₄^-4CH₂	b₄^, b₄^-CO₂, b₄^, b₃^, b₂^*	y₄^, y₃^, y₂^, y₁^, y₃^-CO₂, y₂^-CO₂, y₄^, y₃^, y₂^, y₁^, y₁^**-4CH₂	[#-CO₂]⁺
[K5+2K-H]⁺	a₂^, a₂^- (CH₂)₄-NH₂	b₄^*	y₄^, y₃^, y₂^, y₁^, y₄^, y₃^	K⁺, [#-CO₂]⁺
[K5+2Rb-H]⁺		b₄^*	y₃^, y₂^, y₁^*, y₃^	Rb⁺
[K5+2Cs-H]⁺		b₄^*	y₃^, y₂^, y₁^**	Cs⁺

References 30

[1]	Li Y., Lin H. Q., Deng C. H., Yang P. Y., Zhang X. M., Proteomics, 2008, 8(2), 238—345
[2]	Xu Y. W., Zhang L. J., Lu H. J., Yang P. Y., Anal. Chem., 2008, 80(21), 8324—8328
[3]	Zhou M., McDonald J. F., Fernandez F. M., J. Am. Soc. Mass Spectrom., 2010, 21(1), 68—75
[4]	Chen C., Chu Y. Q., Dai X. H., Fang X., Ding C. F., Acta Phys. Chim. Sin., 2013, 29(6), 1336—1343
	(陈琛, 储艳秋, 戴新华, 方向, 丁传凡.物理化学学报, 2013,29(6), 1336—1343)
[5]	Halim V. A., Muck A., Hartl M., Ibanez A. Z., Giri A., Proteomics, 2009 , 9(1) , 171—181
[6]	Wilson J.J., Brodbelt J. S., Anal.Chem.,2007, 79,2067—2077
[7]	Biemann K., Methods Enzymol., 1990, 193, 455—460
[8]	Good D. M., Wenger C. D., Coon J. J., Proteomics, 2010, 10(1), 164—167
[9]	Spengler B., J. Mass. Spectrom., 1997, 32, 1019—1036
[10]	Qin Y. J., Wei S. G., Wang X. L., Yang F., Wang B., Guo X. H., Chem. J. Chinese Universities, 2011, 32(8), 2748—2756
	(秦玉娇, 魏士刚, 王晓录, 杨帆, 汪兵, 国新华.高等学校化学学报, 2011,32(8), 2748—2756)
[11]	Wysocki V. H., Smith L. L., Breci L. A., J. Mass Spectrom., 2000, 35, 1399—1406
[12]	Harrison A. G., Mass Spectrom. Rev., 2009, 28(4), 640—654
[13]	Knapp-Mohammady M., Young A. B., Paizs B., Harrison A.G., J. Am. Soc. Mass Spectrom., 2009, 20(11), 2135—2143
[14]	Paizs B., Suhai S., Mass Spectrom. Rev., 2005, 24(4), 508—548
[15]	Bythell B. J., Somogyi A., Paizs B., J. Am. Soc. Mass Spectrom., 2009, 20(4), 618—624
[16]	Cydzik M., Rudowska M., Stefanowicz P., Szewczuk Z., J. Am. Soc. Mass Spectrom., 2011, 22(12), 2013—2107
[17]	Shields S. L., Bluhm B. K., Russell D. H., J. Am. Soc. Mass Spectrom., 2000, 11, 626—633
[18]	Pingitore F., Wesdemiotis C., Anal. Chem., 2005, 77, 1796—1803
[19]	Russell D. H., Mass Spectrom. Rev., 1986, 5, 167—189
[20]	Tang X., Ens W., Standing K. G., Westmore J. B., Anal. Chem., 1988, 60, 1791—1799
[21]	Teesch L. M., Adams J., J. Am. Chem. Soc., 1990, 112, 4110—4120
[22]	Teesch L. M., Orlando R. C., Adams J., J. Am. Chem. Soc., 1991, 113, 3668—3675
[23]	Crizer D. M., Xia Y., McLuckey S. A., J. Am. Soc. Mass Spectrom., 2009, 20(9), 1718—1722
[24]	Zhang H. R., Chen G., Wang L., Ding L., Tian Y., Jin W. J., Zhang H. Q., Int. J. Mass Spectrom., 2006, 252(1), 1—10
[25]	Chu Y. Q., Dai X. H., Jiang D., Fang X., Ding C. F., Rapid Commun. Mass Spectrom., 2010, 24, 2255—2262
[26]	Guo C., Hu N., Jiang K. Z., Chen W. X., Wang X. X., Pan Y. J., Rapid Commun. Mass Spectrom., 2010, 24, 409—414
[27]	Dunbar R. C., Polfer N. C., Berden G., Oomens J. , Int. J. Mass Spectrom., 2012, 330, 71—77
[28]	Dunbar R. C., Steill J. D., Polfer N. C., Oomens J., J. Phys. Chem. A, 2013, 117(6), 1094—1101
[29]	Pu D., Vincent J. B., Cassady C. J., J. Mass Spectrom., 2008, 43, 773—781
[30]	Wang Q., Chu Y. Q., Zhang K., Dai X. H., Fang X., Ding C. F., Acta Phys. Chim. Sin., 2012, 28, 971—978
	(王青, 储艳秋, 张开, 戴新华, 方向, 丁传凡.物理化学学报, 2012, 28, 971—978)