Supporting Information for
Sequence effects on peptide assembly characteristics observed by using scanning tunneling microscopy Xiaobo Maoa,‡, Yuanyuan Guoa,‡, Yin Luob‡, Lin Niua, Lei Liua, Xiaojing Maa, Huibin Wanga, Yanlian Yanga*, Guanghong Weib*, Chen Wanga* a
National Center for Nanoscience and Technology, 11 Beiyitiao Zhongguancun, Beijing 100190, China State Key Laboratory of Surface Physics, Key Laboratory for Computational Physical Sciences (Ministry of Education), and Department of Physics, Fudan University, 220 Handan Road, Shanghai, 200433, China b
Fourier Transform Infrared (FTIR) Spectroscopy Fourier Transform Infrared Spectroscopy analysis of R4G4H8 and F4G4H8 was performed on Nicolet Nexus 470 FTIR. To prepare samples, R4G4H8 and F4G4H8 were first dissolved in Milli-Q water into a concentration of 0.1mg/mL, respectively. Then a drop of solution containing peptides (R4G4H8 and F4G4H8) was deposited directly onto the surface of highly oriented pyrolytic graphite (HOPG) followed by air-drying. Then the samples were analyzed by using FTIR. The beta-sheet secondary structures of R4G4H8 and F4G4H8 are revealed by FTIR results shown in Fig. S1A and Fig. S1B, respectively. The presence of the band in FTIR spectra, namely the major band at 1633 cm-1 for R4G4H8 and at 1631 cm-1 for F4G4H8 are characteristic of beta-sheet of the peptide assembly. The absence of a band at >1680 cm-1 suggests the parallel stacking of beta-sheet.
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(A)
(B)
R4G4H8
F4G4H8
1633 cm‐1
1631 cm‐1
Figure S1. (A) FTIR spectrum of R4G4H8. (B) FTIR spectrum of F4G4H8.
(A)
(B)
F4
H8
G4
G4 R4
H8 (D)
(C)
R4
G4
H8
H8
F4 G4
Figure S2. The identification of the three different segments of R4G4H8 and F4G4H8 in STM images. (A) and (B) The STM images of R4G4H8 and F4G4H8 assemblies, respectively. The red and green lines mark the length measurements of R4G4H8 lamellae in (A). Tunneling conditions: I = 307.5 pA, V = 773.2 mV. The black line marks the length measurement of F4G4H8 lamellae in (B). Tunneling conditions: I = 521.7 pA, V = -450.0 mV. (C) and (D) Cross-sectional profiles corresponding to the lines in (A) and (B), respectively. The thick solid lines represent the averaged heights of the peptide strands, corresponding to three different segments.
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A
B
C
D
Figure S3. STM images of F4G4H8 at different bias voltages and polarities. (A) Large-scale STM image of F4G4H8 assembly. (B) Highresolution STM image of F4G4H8 assembly corresponding to the area highlighted by the white square in (A). Tunneling conditions: I = 300.5 pA, and bias change from -450 mV to -300 mV, and then back to -450 mV. (C) and (D) STM images of F4G4H8 assembly with negative and positive bias polarities. Tunneling conditions: (C) I = 347.3 pA, and V = -500.8.mV. (D) I = 382.8 pA, and V = 500.8 mV.
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Figure S4. (A) The normalized brightness contrasts of H and F at various bias voltages and polarities, in which the brightness of H is assigned to 100%. (B) The absolute value for brightness of R, G, H, F in STM images are presented as the apparent height measured by the SPM software .
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Figure S5. The probability density function (PDF) of end-to-end distance of F4G4H8 and R4G4H8 peptides on graphene surface. For each system, the data are averaged over the last 50-ns of two independent 100-ns MD runs.
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Table S1. Statistical length distribution of R4G4H8 at different ranges. aRange
of peptide chain length (nm) 4.225～4.550 4.550～4.875 4.875～5.200 5.200～5.525
bPossible
numbers of amino acid 14 15 16 17
cCounts
dPercent
8 51 60 8
6.3 40.2 47.2 6.3
(%)
a The range is defined by the minimum length and the maximum length measured from STM images using an increment of 0.325 nm (the separation between the two neighboring amino acids in the peptide chain structure). b The possible numbers of residues are calculated by dividing the chain lengths by 0.325 nm. c Counts indicate the total number of chains in the different measured length ranges. d The percentage of peptide chains in the ranges are shown in the fourth column.
Table S2. Statistical length distribution of F4G4H8 at different ranges. aRange
of peptide chain length (nm) 3.575～4.225 4.225～5.850 5.850～6.500
bPossible
numbers of amino acid 12-13 14-18 19-20
cCounts
46 221 25
dPercent
(%)
15.8 75.7 8.5
a The range is defined by the minimum length and the maximum length measured from STM images using an increment of 0.325 nm (the separation between the two neighboring amino acids in the peptide chain structure). b The possible numbers of residues are calculated by dividing the chain lengths by 0.325 nm. c Counts indicate the total number of chains in the different measured length ranges. d The percentage of peptide chains in the ranges are shown in the fourth column.
Table S3. Statistical length distribution of H5F5 at different ranges. aRange
of peptide chain length/nm 2.600-2.925 2.925-3.250 3.250-3.575 3.575-3.900 3.900-4.225 4.225-4.550 4.550-4.875
bPossible
numbers of amino acid 9 10 11 12 13 14 15
cCounts
dPercent(%)
6 19 41 69 28 2 6
3.5% 11.1% 24.0% 40.4% 16.4% 1.2% 3.5%
a The range is defined by the minimum length and the maximum length measured from STM images using an increment of 0.325 nm (the separation between the two neighboring amino acids in the peptide chain structure). b The possible numbers of residues are calculated by dividing the chain lengths by 0.325 nm. c Counts indicate the total number of chains in the different measured length ranges. d The percentage of peptide chains in the ranges are shown in the fourth column.
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Table S4. Statistical length distribution of F5H5 at different ranges. aRange
of peptide chain length/nm 4.225-4.550 4.550-4.875 4.875-5.200 5.200-5.525 5.525-5.850 5.850-6.175 6.175-6.500
bPossible
numbers of amino acid 14 15 16 17 18 19 20
cCounts
dPercent(%)
5 16 9 21 30 39 32
3.3% 10.5% 5.9% 13.8% 19.7% 25.7% 21.1%
a
The range is defined by the minimum length and the maximum length measured from STM images using an increment of 0.325 nm (the separation between the two neighboring amino acids in the peptide chain structure). b The possible numbers of residues are calculated by dividing the chain lengths by 0.325 nm. c Counts indicate the total number of chains in the different measured length ranges. d The percentage of peptide chains in the ranges are shown in the fourth column.
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