Supporting Information for
Formation and dissociation of the interstrand i-motif by the
sequences d(XnC4Ym) monitored with electrospray ionization
mass spectrometry
Yanwei Cao1, Yujiao Qin1,3, Michael Bruist2,*, Shang Gao1, Bing Wang1, Huixin Wang1 and
Xinhua Guo1,*
1
College of Chemistry, Jilin University, 2699 Qianjin Street, Changchun 130012, P. R. China
2
Department of Chemistry & Biochemistry, University of the Sciences, Philadelphia, PA 19104,
USA
3
Changchun Gold Research Institute, 6760 Nanhu Road, Changchun, 130012, P. R. China
Corresponding authors:
Dr. Xinhua Guo
Phone: 86-431-85166389
Fax: 86-431-85166389
Email: guoxh@jlu.edu.cn
Dr. Michael F. Bruist
Phone: 215-596-8530
Fax: 215-596-8543
Email: m.bruist@usciences.edu
Figure S1. The mass spectrum of 150 μM DNA strands d(G4T4G4) incubated in 40 mM NH4+
solution (pH=6.7) for 36 hours and detected in a solution diluted with an equal volume of 60 %
methanol before mass spectrometric analysis
Figure S2. CD spectra of the nine different oligonucleotides studied that follow the sequence
d(XmC4Yn) at 200 μM in 50 mM ammonium acetate buffer [(a) pH 4.5 and (b) pH 9.0] after 36
hours equilibrium time at 4 °C; UV melting curves of [d(XnC4Ym)]4 measured (c) at 295 nm
and (d) at 265 nm. The oligonucleotides are at 60 µM in a 50 mM ammonium acetate buffer
(pH 4.5) with the thermal gradient of 0.5 °C/min.
Figure S3. CD spectra d(TC4): samples were diluted with equal volume of water after slowly
cooled to room temperature (blank solid) or equal volume of 60 % methanol after slowly cooled
to room temperature(dot) and before data recording (gray solid).
Figure S4. Mass spectra of the sequences (a) d(C4A), (b) d(AC4), (c) d(C4G), (d) d(GC4), (e)
d(T2C4) and (f) d(A2C4); the percentage of [M - H]- and [4M - 4H]4- is 9.11 % , and 10.60 % for
multiple ions in Figure S3a inset; the percentage of [M - H]- and [4M - 4H]4- is 7.58 % , and
10.23 % for multiple ions in Figure S3c inset; both of the [2M - 2H]2- contributions are negligible
in the insets.
Figure S5. (a) UV spectra of the strand d(TC4) annealed at different strand concentrations
from 10 to 80 µM in a 50 mM ammonium acetate buffer (pH 4.5) and measured at 10 °C;
(b) Tm values of annealed d(TC4) determined at various strand concentration.
Figure S6. Mass spectra show the gradual increase of i-motif formed by the sequence
d(T2C4) in 50 mM NH4+ acetate-acetic acid buffer solution at pH 4.5. Samples were heated
to 90 °C for 15min (a) and allowed to cool to 4 °C at the rate of -1 °C/min, and then stored
in 4 °C for further incubation; aliquots were taken out after incubating at indicated time: (b)
1.5 hours；(c) 6 hours；and (d) 24 hours.
Figure S7. Mass spectra of annealed d(T 2C4) that were slowly heated to (a) 35 °C, (b) 45 °C,
(c) 55 °C and (d) 60 °C at the rate of 1 °C/min, respectively and then were immediately
subjected to ESI-MS analysis. The annealing was performed by heating the samples to 90 °C
for 15 min in 50 mM NH4+ acetate-acetic acid buffer solution at pH 4.5 and then cooling to 4 °C
and stored for 36 h.
Figure S8. product-ion spectra of the d(T2C4) [4M - 5 H]5- ion collided at energies of (a) 5
eV, (b) 10 eV, (c) 15 eV and (d) 25 eV. The percentages of [M - H]-, [2M - 2H]2- and [3M 3H]3- are 17.60 % , 9.95 % and 13.48 % for multiple ions in d.
Figure S9. Melting and cooling profiles of i-motif formed by (a) d(C4) and (b) d(C4T) at 265
nm with the thermal gradient of ±1 °C/min