thiolate-protected ag clusters: mass spectral studies of composition … · 2013-07-30 · 8 1000...
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Electronic Supplementary Information (ESI) for:
Thiolate-protected Ag32 clusters: Mass spectral studies
of composition and insights into the Ag-thiolate
structure from NMR
T. Udayabhaskararao, M. S. Bootharaju, and T. Pradeep*
DST Unit of Nanoscience (DST UNS) and Thematic Unit of Excellence (TUE), Department of Chemistry,
Indian Institute of Technology Madras, Chennai-600 036, India
*E-mail: [email protected]
Contents
Number Description Page number
S1 Schematic of synthetic process 2
S2 UV-vis spectra 3
S3 Luminescence spectra 4
S4 CD spectrum of Ag32SG19 5
S5 Comparison of UV-vis data 6
S6 MS/MS spectrum of glutathione 7
S7 ESI MS of Ag32SG19 8
S8 ESI MS of Au25SG18 9
S9 Luminescence spectra of Ag@MPG 10
S10 ESI MS of Ag32MPG19 11
S11 XPS 12
S12 FTIR 13
S13 EDAX 14
S14 XRD 15
S15 TEM, effect of electron beam irradiation 16
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NaBH4(s)
25 mg
Ground Ground
10 mL H2O
AgNO3 (s) + GSH (s)
23 mg 200 mg
Ag(I)SG +
excess GSH
Reaction mixture
I) II) III)
IV)
Electronic Supplementary Information 1
Scheme S1. Photographs representing the changes at various stages during the synthesis of Ag32SG19 clusters.
Photograph I is the initial mixture of silver nitrate and glutathione (both are colorless solids). Grinding the above for
10 minutes leads to the formation of an Ag(I)SG thiolate (photograph II). This thiolate shows a featureless spectrum
in its UV-vis profile (measured in water, data not shown). To this mixture, NaBH4(s) was added and ground
(photograph III). A 10 mL of distilled water was added to the above mixture (photograph IV). This solution contains
mixture of clusters which shows distinct peaks as shown in Figure 1a.
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300 450 600 750 900
Ab
sorb
ance
(a.
u.)
Wavelength (nm)
b
a
Electronic Supplementary Information 2
Figure S2. UV-vis absorption spectra of (a) the as-synthesized crude cluster, CC and (b) the solution obtained after
keeping the crude cluster overnight at ambient conditions (giving aged crude, ACC). The spectrum of ACC is
comparable to cluster 3 (trace 3, shown in Figure 1), except for the feature at 420 nm.
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400 480 560 640 720
In
ten
sity
(a.
u.)
Wavelength (nm)
2 nd
3 rd
Aged crude
λemi680
λemi670
λexc 420λexc 500
λexc 420λexc 490
Electronic Supplementary Information 3
Figure S3. Photoluminescence spectra of clusters extracted from 2nd and 3rd bands of gel electrophoresis of CC.
ACC also shows luminescence similar to cluster 3.
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300 450 600 750-10
0
10
20
30
40
Ab
sorb
ance
(a.
u.)
Inte
nsi
ty (
md
eg)
Wavelength (nm)
a
bc
Electronic Supplementary Information 4
Figure S4. CD spectra of GSH (a) and Ag32SG19 (b) compared with the absorption of ACC solution (c).
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a) b) c) d)
a) b)
Wavelength (nm)
400 600 800 1000
A
/nm
Ab
sorb
ance
Wavelength (nm)
d)
Electronic Supplementary Information 5
Figure S5. Absorption spectra of -SG protected Ag clusters (marked in green ellipse) from various groups, Kitaev et
al.1 (a), Bigoni et al.2 (b) and Pradeep et al.3 (c), compared with the present cluster (d). Spectra a, b and c are
reprinted from references 1, 2 and 3, respectively.
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100 150 200 250 300
m/z
-H2O
-H2O
-NH
3
-H2O
-NH
3-H
2O
-H2O
-NH
3-C
O
-gly
cin
e
-C5H
8O3N
(SG–H)-
-C5H8O3N
176 178m/z
Electronic Supplementary Information 6
Figure S6. MS/MS spectrum of m/z 306 peak (anoin of glutathione) in the negative mode. Apart from the common
H2O and NH3 losses, one prominent loss is due to C5H8O3N.
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1000 2000 3000 4000
m/z
400 600 800 1000 1200
m/z[A
g3S
G2]
-
[Ag
2SG
2]-
[Ag
2SG
]-
[Ag
SG
]-
Electronic Supplementary Information 7
Figure S7. ESI MS of Ag32SG19 measured in the negative mode in the range of m/z 500-4000. The peaks of interest
given in main text are in the marked region. Inset shows the ESI MS at the low mass region (m/z 400-1200). Peaks
at m/z 936, 828, 522 and 414 are assigned to [Ag3SG2-H]-, [Ag2SG2-H]-, [Ag2SG-H]- and [AgSG-H]-, respectively.
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1000 1200 1400 1600 1800
Inte
nsi
ty
m/z
[Au25SG18-nH]q-
6-7-8-9- =q
Electronic Supplementary Information 8
Figure S8. ESI MS of Au25SG18, measured under the same conditions as in the case of Ag32SG19. Spectrum shows
the multiply charged species of [Au25SG18-nH]q- (where q= 6, 7, 8 and 9), which are labeled. The optimized conditions
for this measurement are reported in the instrumentation section.
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Electronic Supplementary Information 9
Figure S9. Photoluminescence spectra of Ag@MPG clusters in water at room temperature.
400 500 600 700 800 900
Inte
nsi
ty
Wavelength (nm)
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900 950 1000 2000 2500 3000
m/z
[Ag
27(M
PG
-H) 1
6Na x
H16
-x]3-
[Ag
32(M
PG
-H) 1
9Na x
H16
-x]3-
+
[Ag
5(M
PG
) 3-H
]-
[Ag
4(M
PG
) 3-H
]-
[Ag
4(M
PG
) 3-2
H+
Na]
-
× 5
i
ii
iii
a)
1020 1024 1028 1032
m/z912 915 918 921 924
m/z
i iiiii
933 936 939 942 945
m/z
Electronic Supplementary Information 10
Figure S10. a) ESI MS of Au32MPG19, measured in the negative mode in the range of m/z 900-3200. All the peaks
are marked with their respective ions. Sodium adduct of Ag27MPG16 is obtained due to the loss of Ag5MPG3 species
(iii) from [Ag32(MPG-H)19NaxH16-x]3-. Mass spectrum in the range m/z 1000-3200 is enhanced for 5 times in the
vertical axis. Labels i, ii and iii are [Ag4MPG3-H]-, [Ag4MPG3-H+Na]- and [Ag5MPG3-H]-, respectively. Simulated
spectra for i, ii and iii, depicted with lines match well with the experiment.
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366 369 372 375
Co
un
ts
Binding energy (eV)
3d3/2
3d5/2
Ag 3d
160 162 164 166
2p1/2
2p3/2 S 2p
Co
un
ts
Binding energy (eV)
0 300 600 900
Co
un
ts
Binding energy (eV)
Ag
3pO
1s
Na
KL
L
N 1
sA
g 3
d
S 2
s
S 2
p
C 1
s
A
b
a
b
a
b
a
B C
Electronic Supplementary Information 11
Figure S11. XPS survey spectra, Ag 3d and S 2p regions (A, B and C, respectively) of the crude and Ag32SG19
clusters (traces a and b, respectively). The Ag:S atomic ratio is 1:0.57±0.03 for Ag32SG19 which matches with the
expected value 1:0.59.
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3500 3000 2500 2000 1500 1000 500
Tra
nsm
itta
nce
%
Wavenumber (cm-1)
GSH
Ag32
SG19
Electronic Supplementary Information 12
Figure S12. FTIR spectra of GSH and Ag32SG19. The S−H stretching feature at 2572 cm-1 in GSH is absent in cluster
which is in agreement with the XPS data. GSH features in the region 2000-500 cm-1 confirm the presence of SG
protection of the cluster.
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Ag L
C KO K
S KSEM
N K
Ag L
C KO K
S KSEM
N K
a) b) c)
d) e) f)
Electronic Supplementary Information 13
Figure S13. SEM-EDAX spectrum of Ag32SG19. (a) SEM image of the Ag32SG19 cluster aggregate from which the
EDAX spectrum is taken. Elemental maps of (b) Ag Lα, (c) S Kα, (d) O Kα, (e) C Kα and (f) N Kα are shown. Si Kα is
due to the substrate used. Ag:S atomic ratio measured is 1:0.56±0.03 which matches with the expected value of
1:0.59 for Ag32SG19.
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20 40 60 80
(222)(311)(220)
(200)
(111)
Inte
nsi
ty (
a. u
.)
2 (degree)
b
a
Electronic Supplementary Information 14
Figure S14. Comparison of the X-ray diffraction patterns of glutathione protected silver nanoparticles (Ag@SG NPs)
and Ag32SG19 clusters (traces a and b, respectively). Nanoparticles show peaks corresponding to Ag planes (111),
(200) (220), (311) and (222) whereas Ag32SG19 shows a broad peak around 2θ ≈ 38o.
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10 nm 10 nm
A) B)
Electronic Supplementary Information 15
Figure S15. TEM images of the Ag32SG19 before (A) and after electron beam irradiation for 5 min (B). Both are from
the same regions of the grid. QCs are strongly sensitive to electron beam exposure and they convert gradually to
larger aggregates or nanoparticles during TEM examination.
References
(1) N. Cathcart and V. Kitaev, J. Phys. Chem. C 2010, 114, 16010.
(2) S. Kumar, M. D. Bolan and T. P. Bigioni, J. Am. Chem. Soc. 2010, 132, 13141.
(3) T. Udayabhaskararao, B. Nataraju and T. Pradeep, J. Am. Chem. Soc. 2010, 132, 16304.
Electronic Supplementary Material (ESI) for NanoscaleThis journal is © The Royal Society of Chemistry 2013