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TRANSCRIPT
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Christof WöllLehrstuhl Physikalische Chemie I
Ruhr-Universität Bochum
The Physics and Chemistry of Organic Surfaces: Fabrication of Model Systems
using the Selfassembly of Organothiols on Gold
Gold-Substrat
Bochum University
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Molecules and Surfaces
LCD Display
Sensor DevicesCell Membranes
Friction and LubricationP < 10mBar-9 P
(P < 10mBar)-9
HeterogenousCatalysis
Molecular Beam Epitaxy
Chemical Vapour Deposition
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Why Organic surfaces ?• Inorganic Surfaces
– Metals (Heterogeneous Catalysis, Electronics, Corrosion, Friction, Adhesion)
– Semiconductors (Electronics, Interfaces)– Insulators (Heterogeneous Catalysis, Corrosion inhibitions, Friction,
Adhesion)
• Organic Surfaces– Large Variety of Molecules– Relevance for Biology and Biochemistry– Friction, Corrosion, Adhesion, Sensor devices……– But…. application of standard Surface Science
techniques not straightforward (insulating, soft, sensitive to radiation,…)
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Organic molecule with liquid crystalline phase
Polymer substrate (Polyimide)
Liquid crystal displays
LCD
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5
Fabrication of organic surfaces
• Surfaces of polymers (plastics) prepared by cutting or casting– Disadvantage: Very difficult to obtain surfaces
exposing predefined chemical functionality– Quality of surfaces (cleanliness, structural
order) often not satisfying– Standard methods in Surface Science not
applicable
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• Adsorption of a simple (monofunctional) molecule not very efficient
• Either bonding is so strong that molecule is modified• Or bonding is so weak that system is unstable at
room-temperature
Grafting of interesting molecules to a metal substrate
~30°~30°
Better: Anchor – Chain - Function
Substrate
Example: benzene
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Required: Strong binding to substrate
Unspecific ionic coupling (LB films) not enough
Ideal: Formation of a covalent chemical bond
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Different anchor groups for different substrates
• Si, SiO2, Al2O3,…. (-OH groups available)– Trichlorsilane, Trimethoxysilane
e.g. (Cl3)-Si-(CH2) n-CH3 Anchoring by covalent bonds, formation of HCl(Trichlorsilane) or methanol CH3OH (Trimethoxysilane)
• Au, Cu, Ag– Organothiols
e.g. Alkanthiols HS-(CH2)n-CH3Anchoring by (weak) covalent bonds, Au-thiolates,
dihydrogen formation
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Most important system today:SAMs made from organothiols
Anchor
chain,backbone
Head group
Octanethiol, alkanethiols
H Gold substrate
Anchoring through Au-thiolate bond
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Most organic molecules are suited for incorporation into organothiols ….
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Characterisation of alkanethiolate adlayers
Pfennig (copper)coated uncoated
coated uncoated
Contact angleH2O
hydrophilichydrophobic
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Quantitative characterization of SAMsusing photoelectron spectroscopy
hν e--
X-ray photoelectronspectroscopy (XPS)
• Laboratory technique, no single crystals required, fast
binding energy of core electrons
EB=hν -Ekin
Clean Au (111) substrate
ca. 1 nm HeptanethiolateMonolayer
1000 800 600 400 200 00
500
1000
1500
2000
2500
3000
3500
Zähl
rate
Bindungsenergie [eV]
Au 4fAu 4f
Au 4dAu 4d
1000 800 600 400 200 00
500
1000
1500
2000
2500
3000
3500
Zähl
rate
Bindungsenergie [eV]
300 290 280 270400
600
800
1000
Zählr
a te
Bindungsenergie[eV]
C 1s
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Two principal ways to make SAMs …
Deposition in Ultrahigh Vacuum (UHV) Deposition from solution
10-10 mBar 1 Bar
Very difficult to determine preparation method for SAM after
formation!
All UHV-methods are applicable !
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Determination of molecular orientation using IR -spectroscopy
1000 950 900 850 800 750
0,00
0,05
0,10
0,15
0,20
Terphenylthiol Pellet
Wavenumbers [cm-1]
-0,0002
0,0000
0,0002
0,0004
0,0006
0,0008
prepared in EtOH solution
1000 950 900 850 800 750
Terphenylthiol/Au(111)
Θ
Thiolat-Adlayer on Au
E
Surface selection rule
Metal
Terphenylthiol
KBr pellet
IRRAS
IR bulk
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Near Edge X-ray absorption fine structure NEXAFS
Spectroscopy of unoccupied valence states using synchrotron radiation
IP
Unoccupiedmolecular orbitals
Synchrotron Synchrotron requiredrequired
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NEXAFS: Hexadecanethiol/Au(111)
280 290 300 310 3200
1
2
3
4 90° 55° 20°
HS(CH2)15CH3/Au
Photonenenergie [eV]
Inte
nsitä
t [Ei
nhei
ten
des
Kant
ensp
rung
s]
Goldkristall
35°
Determination of orientationby varying angle of incidence andanalyzing linear dichroism
• requires synchrotron
• fast (< 5 min/spectrum)
• straightforward analysis
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SAMs as model system for a systematicinvestigation of organic surfaces
• High degree of molecular orientation
• What about lateral order? What is the structural quality?
Goldkristall
35°
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Formation of highly orderedmolecular adlayers
LEEDDiffraction of low energy electrons(27 eV)
Decane thiolate
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Formation of highly orderedmolecular adlayers
LEEDDiffraction of low energy electrons(27 eV)
Decane thiolate
Substrate spots
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Formation of highly orderedmolecular adlayers
LEEDDiffraction of low energy electrons(27 eV)
Decane thiolate
Substrate spots
Superstructure spots
(2√3*√3)R30°
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Adsorption of Decanethiols on Au(111)Adsorption of Decanethiols on Au(111)1mM 24h@60 C°
depression
Domain boundary
5 nm Domain boundary
A
A
B
A-A translatuional domain boundaryA-B orientational domain boundary
0 10 20 30 40-0,20-0,15-0,10-0,050,000,050,100,150,20
Hei
ght(
nm)
Length (nm)
Au(111) Depression
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(2√3×3)
C10 adsorp on different sites such as : top, bridge, and hcphollow sites.
Au(111) Depression
NN brighter spot= 8.68A°
NN
bri
ghte
rsp
ot=
10A
°
(2√3
×3)
c(4×2)
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Self-assembled monolayers fabricated by immersion of Au-substrates into solutions of organothiols
• SAMs are ultrathin organic films with extremely high structural quality (2D single crystal)
• exhibits organic surfaces mainly defined by ω-function of thiol
• Basically all traditional techniques form traditional surface science can be applied (including XPS,UPS and STM)
• Ideal model system (?)
Goldkristall
35°
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Modification of SAM-surfacesubstrate
solutionof
thiols
adsorption fromsolution
termination-CH3
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Modification of SAM-surfacesubstrate
solutionof
thiols
adsorption fromsolution
termination-OH
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Modification of SAM-surfacesubstrate
solutionof
thiols
adsorption fromsolution
termination-COOH
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Characterization of organic surfaces using IR-Spectroscopy
3000 2900 2800 1600 1400 1200
0
2
4
6
8
10
12
14
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RO
O
IRRAS: MHDA/Au
Wavenumbers [cm-1]
Ester-bands
Sample 5: 0.02 mM MHDA/EtOH, 1% HCl
Sample 3: 0.5 mM MHDA/EtOH
Sample 4: 0.5 mM MHDA/EtOH, 5% AA
Sample 2: 0.02 mM MHDA/EtOH, 0.5 % TFA
Sample 1: 0.02 mM MHDA/EtOH
Abs
orba
nce
[10-3
AU
]
RO
O1800 1700 1600 15000
1
MDHAPellets
Wavenumbers [cm-1]
D H20
C=Omono-mer
C=O azyclic dimerC=O zyclic dimer
Abso
rban
ce [n
orm
.] R. Arnold, W. Azzam, A. Terfort, Ch. WöllLangmuir 18, 3980, (2002)
Mercapto-hexadecanoicAcid
A B
concentratedconcentrated
diluteddiluted
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Importance of organothiol backbone
High High degreedegree of order of order observedobserved forfor moremore rigidrigid backbonebackbone
Flexible backbone Rigid backbone
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SH
SH
BP3
BP4
SAMs from Organothiols with oligopheny-backbone
Systematic studies by
varying alkyl chain length
Circular depressions arenot defects in film, corrosion of Au-substrate
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2.5nm
A
BP3
BP4
STM LEED
(2√3×√3)-StructureMolecular area 21.6 Å2
Left: LEED patterns recorded for a BP3 monolayer at 345 K. Right: Schematic diffraction pattern for the (2√3×√3)- structure.
No ordered diffraction pattern could be observed for BP4 monolayers
(5√3×3)-StructureMolecular area 27.05 Å2
Pronounced differencebetween odd and evennumber of methylene units !
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Structural Models
BP3
BP4
Au(111)
S S S S S S
(2√3×√3)-Structure
(5√3×3)-Structure
Au(111)
S S S S S
W. Azzam, P. Cyganik, G. Witte, M. Buck, Ch. WöllLangmuir 19, 8262, (2003)
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Organic (or molecular) electronics: Conductivity of single molecules
SiO2
Au
Au
SSH H
S
S
S
S
S
S
S
S
Biphenyldithiol
H
Evaporation of metal onto SAM
HHH Goal: fabrication of a SH-terminated surface
Binding to metal-electrode
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Orientierungsbestimmung mittels IR-Spektroskopie
S
S
S
S
S
S
S
SSSH H
SSHH
W.Azzam, B.I.Wehner, R.A.Fischer, A.Terfort, Ch. WöllLangmuir 18, 7766, (2002)
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Orientierungsbestimmung mittels IR-Spektroskopie
S
S
S
S
S
S
S
SSSH H
SSHH
W.Azzam, B.I.Wehner, R.A.Fischer, A.Terfort, Ch. WöllLangmuir 18, 7766, (2002)
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Orientierungsbestimmung mittels IR-Spektroskopie
S
S
S
S
S
S
S
S
S
S
SS
S
S
S
S
SSH H
SSHH
W.Azzam, B.I.Wehner, R.A.Fischer, A.Terfort, Ch. WöllLangmuir 18, 7766, (2002)
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C=O
CH3C=O
CH3
C=O
CH3 C=O
CH3
C=O
CH3 C=O
CH3
C=O
CH3 C=O
CH3
C=O
CH3
=
S
S
R CS R’
O
R’SRC O
O -
O HR CO H
O SR-
+
R CS R’
O
R’SRC O
O -
O HR CO H
O SR-
+
RC
S S
H
S
R’ R’ R’
OR C
O
O
-OH -
R C OH
O -
Using protection group chemistry to fabricatedithiol SAMs of high structural quality
ThioesterThioester, , deprotectiondeprotection usingusingbasicbasic agentsagents
Post-synthesis modification
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b) The SAM spectrum of BPDMAc-1+EtOH+H2O+NaOH (2days).
c) BPDMAc-1 SAM (afterone day of immersion into dichloromethanesolution of BPDMAc-1 [100 µM] at RT )
Theory
Monitoring the de-protection of BPDMAC by IR spectroscopy
Bulk pellet
BPDMAC SAM
C=O
CH3C=O
CH3
C=O
CH3 C=O
CH3
C=O
CH3 C=O
CH3
C=O
CH3 C=O
CH3
C=O
CH3
0
2x10-3
0
2x10-30
2x10-3
1800 1600 1400 1200 1000 8000
1x102
2x1020
5x100
b)
e)
d)
c)
a)
Ab
sorb
ance
[AU
]
Wavenumber (cm-1)
=
S
S
Deprotected film
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XPSNEXAFS
292 290 288 286 284 282 280
284.4
287.6*
BPDMAc-1Deprotected BPDMAc-1
Inte
nsity
(Cps
)
Binding Energy (eV)
285,
2
287,
428
9,1
293,
8
285 290 295 300 305
Dep. BPDMAc-1 30° Dep. BPDMAc-1 90°
*
Norm
aliz
ed P
artia
l Ele
ctro
n Yi
eld
Photon Energy (eV)
BPDMAc-1 30° BPDMAc-1 90°
1800 1650 1500 1350 1200 1050 900
Dep. BPDMAc-1
Wavenumber (cm-1)
Abso
rban
ce
* BPDMAc-1
IR
Disappearance of C=O stretching vibration of the acetate group of BPDMAc-1 at 1695 cm-1 in IR, π* resonance of C=O of BPDMAc-1 at 287.4 eV in NEXAFS and the peak at 287.6 eV corresponding to the C=O of BPDMAc-1 in XPS indicates the deacylation
process.
The NEXAFS spectra of both BPDMAc1 and the deprotected BPDMAc1 show a pronounced dichroism, which suggests good orientational order in these SAMs.
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Deprotection: Problems with reproducibility
• Some samples: Deprotection done in a few hours, complete conversion after a day
• Other samples are not converted even after 2 days
R CS R’
O
R’S HR C
O
O
-
OH -
R C
OH
O
SR’
-
+
RC
S S
H
S
R’ R’ R’
OR C
O
O
-OH -
R C OH
O -
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How fast is the deprotection ?
1800 1700 1600 1500 1400 1300 1200 1100 1000
1604
.7
958.
610
05.0
1142
.8
1357
.0
1496
.7
1695
.4
-45x
10-3
10
DeprotectedBPDMAc-1
Wavenumber /cm−1
0 12 24 36 48 60 72 84
Sample -1Sample -2Sample -3
BPDMAc-1
Abs
orba
nce
900
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Deprotection speeds depends on sample conditions
• Reaction very fast in solution (minutes at most)
• At organic surfaces significantly delayed
• Influence of defects ?
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OH-
Thioacetate Thiol
Base
S
S
Au (111) Au (111)
S
S
HS
S
Au (111)
COO
+ R
OHR
-ORO
OH-
DeprotectedBPDMAc-1
BPDMAc-1
S
S SS S S S S
S S S S S SS S
S S
S S
S S S SS S
S S S SS S S S
In solution the deprotection reaction is fairly fast (<10 minutes).The attack of the basic agent requires nucleation centers
This makes the process very slow (3.5 days) for samples withlow defect density
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Before deprotection 3 h 5 h 25 h
SEM micrographs of deprotection process (0.01 M NaOH)
OH-
DeprotectedBPDMAc-1
BPDMAc-1
S
S SS S S S S
S S S S S SS S
S S
S S
S S S SS S
S S S SS S S S
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Self-assembled organic layers (monolayers) on metal substrates
• Why organic surfaces?• Fabricaton of organic surfaces• Why self-assembly?• Particular advantages of organothioles
• Characterisation of ultrathin organic adlayers
• Adressing topics in biology and biochemistry usingSAMs as model biomolecular surfacesAppying in-situ methods
• Generate lateral structures using μ-contact printing
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SPR - Surface Plasmon Resonance
Total reflection of light at the base plane of a prism
Excitation of surface plasmonson top of Au surface
Totalreflexion
Prisma
θ
θ
Gold-Schicht
Totalreflexion
Prisma
θ
ReflectedIntensity
θ
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SPR: Monitoring adsorption of octadecanethiol
15 20 25 30 35 40 45 50 55 60 65 70 750,2
0,3
0,4
0,5
0,6
0,7
0,8
0,9
42°
44.5°
SPR : Octadecanthiol-Layer on 50 nm gold film
clean gold film octadecanthiol adsorption (0.5 h)
46.1°
43.3°
Inte
nsity
[AU
]
θprism [deg]
Gold-Substrat
Gold-Substrat
Strong shift of surface plasmon frequency
Change in optical densityclose to Au-surface
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Adhesion of proteins to surfaces
Ophiopteris papillosa (Seestern)Zucht von Jakobsmuscheln Patella (Seeschnecken) auf Fels
Scallops Brittlestar
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Adsorption of RNaseon a CH3-terminated organic surface
M. Mrksich, G.B. Sigal, G. M. Whitesides
Langmuir 11, 4383, (1995)
Surface Plasmon Resonance (SPR)
Unspecific adsorptionof proteins
Reference
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Making surfaces protein resistantusing polyethyleneglycol
M. Mrksich, G.B. Sigal, G. M. Whitesides
Langmuir 11, 4383, (1995)
Au
HS-(CH2)11 (OCH2CH2) 6OH)
Organic surfaceexhibiting protein resistance
SPR
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Specific binding: Biotin/Streptavidin
StreptavidinBiotin
Au
Thiol with biotin attached
Protein-resistant thiol
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Biotin/Streptavidin: SPR-Measurements
No specificAdsorption
SpecificAdsorption
J.Spinke, M. Liley, F.-J. Schmitt, H.-J. Guder, L. Angermaier and W.Knoll,J. Chem. Phys. 99, 7012, (1993)
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Self-assembled organic layers (monolayers) on metal substrates
• Why organic surfaces?• Fabricaton of organic surfaces• Why self-assembly?• Particular advantages of organothioles
• Characterisation of ultrathin organic adlayers
• Adressing topics in biology and biochemistry usingSAMs as model biomolecular surfaces
• Generate lateral structures using μ-contact printing
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μ-contact printing
Poly-Dimethylsiloxane(PDMS) stamp Ink with Organothiol 1
Stamp, imprint
Immersion in Thiol 2
Thiol 2
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RememberRuhr University Bochum Department of Physical Chemistry I
adsorption of streptavidin on biotynilated surfaces
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Crystal structure data for streptavidin
results:
height of protein
40-43 Å
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OEG(6)-Thiol
OH-Thiol/Biotinthiol+
Streptavidin
result:
height of streptavidin
(19,8±2)Å
height-measurement of streptavidin by AFM (air)
Not consistent !
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height-determination of streptavidin by AFM (liquid)
result:
height of streptavidin
(42,2±3)Å
Measurements in liquid
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Conclusions on specific binding of streptavidin
- high specific adsorption of
the streptavidin on the
patterned surface
- no unspecific adsorption on
the proteinresistant parts
of the surface
- good consistence in height of literature and experiments only when imaged in liquid
no proteinprotein
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5959
BiomolecularBiomolecular MultilayersMultilayers
10%-Biotinthiol 200nM Streptavdin 150nM bHRP
6060
AFM in Wasser:
Höhe des Proteinlayers
(76,5±4)Å
folglich für die Höhe der bHRP:
(34,3±3,5)Å
gute Übereinstimmung mit Literatur
Ruhr Universität Bochum Lehrstuhl für Physikalische Chemie I Proteinchemie an OberflächenR. Chelmowski
AFM in Wasser:
Höhe der SA-Lage:
(42,2±3)Å
„Phasen“-bild der strukturierten Thiolbereiche
Biomolekulare MehrfachschichtenBiomolekulare Mehrfachschichten
3 µm 3 µm 3 µm
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Fabrication of highly ordered molecular adlayers using organothiols
Some applicationsSPR
Topics
Characterization of organic surfacs
Tailoring properties of Organic Surfaces
Gold-Substrat
The Physics and Chemistry of Organic Surfaces: Fabrication of Model Systems
using the Selfassembly of Organothiols on Gold
Au80 µm 80 µm
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