Chemical modification of single walled carbon nanotubes with tetrazine-tethered gold nanoparticles via a Diels-Alder reaction

Article abstract of DOI:10.1039/c3cc46325g

A versatile methodology for the modification of single walled carbon nanotubes (SWCNTs) through an inverse electron demand Diels-Alder reaction with tetrazine-AuNPs (1-AuNPs) under ambient conditions is described. A robust covalently bonded hybrid nanocomposite is formed.

Full text of DOI:10.1039/c3cc46325g

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ARTICLE TYPE
Chemical Modification of Single Wall Carbon Nanotubes with
Tetrazine-tethered Gold Nanoparticles via a Diels-Alder Reaction
a,b
b
*, b
*,a
Jun Zhu Jonathan Hiltz, R. Bruce Lennox, Ralf Schirrmacher
Received (in XXX, XXX) Xth XXXXXXXXX 20XX, Accepted Xth XXXXXXXXX 20XX
DOI: 10.1039/b000000x
5
A versatile methodology for the modification of single wall
carbon nanotubes (SWCNT) through an inverse electron
microwave heating, are required to facilitate the completion of
these reactions. An efficient covalent-bonding methodology for
demand Diels-Alder reaction with tetrazine-AuNP (1-AuNP) 50 the preparation of CNT-AuNP nanocomposites using catalyst-
free and room temperature is thus much desired. We note that
similar constraints arising in polymer-grafting–CNT synthesis
and Diels-Alder reactions have been effectively used in this
under ambient conditions is described. A robust covalently
bonded hybrid nanocomposite is formed.
1
0
1
3
Both single wall carbon nanotubes (SWCNTs) and multiwall
carbon nanotubes (MWCNTs) continue to be of great interest
because of their many applications in the fabrication of advanced
regard.
55
Tetrazines react with strained dieneophiles in a rapid, atom
efficient, and catalyst free-manner. The inverse electron demand
Diels-Alder reaction of highly electron-deficient tetrazines with
1
,2
nanomaterials. Carbon nanotubes surface-modified with metal
nanoparticles (NP; mainly gold or silver) are of particular interest
because of their application in catalysis, imaging contrasting
1
4,15,16,17
1
2
2
3
3
4
4
5
0
5
0
5
0
5
strained alkenes or acetylenes has been widely explored.
3,6-Diaminotetrazines, for example, have been applied to the
agents, and drug delivery.3,4 Metal nanoparticles can be 60 modification of MWCNT at elevated temperatures. The
18
incorporated onto CNT through physical adsorption or covalent
bonding. Physical adsorption of NP onto CNT can be achieved
either by in-situ reduction of the corresponding metal ion or
through electrostatic interactions, van der Waals interactions, or
resulting amino-tethered MWCNT can be used as a crosslinker to
1
9
improve the wear performance of an MWCNT/epoxy resin. The
application of the tetrazine click chemistry to nanoparticle
modifications has however received relatively little attention. Han
aromatic interactions of pre-formed gold nanoparticles (AuNPs) 65 et al. demonstrated the application of tetrazine-dienophile Diels-
with the CNT. However, these inherently weak interactions result
in poor stability of the resulting nanostructures. Covalent
modification of CNT with the ligand shell of the NP can however
significantly improve the stability of the nanocomposites. Most
Alder chemistry to functionalize nanoparticles by attaching
tetrazine-modified dyes/biomolecules to dienophile (norbornene)
2
0
containing ligand-protected quantum dots. Audebert et al.
prepared tetrazine-doped silica nanoparticles to study the
2
1
importantly, using pre-formed AuNPs enables control of the 70 fluorescence emission properties of these NP. Here we report
shape, size, and functionality of the NPs. One drawback of most
CNT chemical modification methods is that the process usually
involves an initial oxidation of the CNT with concentrated nitric
acid and sulfuric acid, leading to the formation of various oxygen
the facile synthesis of a tetrazine-terminated AuNP (tetrazine-
AuNP or 1-AuNP), and the development of an efficient and
reproducible methodology to modify SWCNTs via the reverse
electron demand Diels-Alder reaction with these tetrazine-AuNP.
75 The tetrazine-AuNP can react with SWCNTs in ambient
conditions (room temperature and catalyst-free) to form a AuNP-
SWCNT complex. Covalent bonding of AuNP to CNT not only
increases the chemical and physical stability of the
nanocomposites, but also provides a versatile methodology for
5
,6
containing groups (mainly carboxyl group) on the defect sites.
7
,8,9,10
Esters or amides are often prepared in follow-up reactions.
This activation process results in a series of derivative sites on
CNT with little or no regiospecificity, mainly occurring at defects
or edges. The result is a poorly-controlled modification.
Moreover, reactions involving the most common AuNPs, 80 further modification of CNTs through the thiol exchange
thiolate-protected AuNPs, only tolerate mild ambient conditions
because of the relative lability of the Au-S bond. Harsh
conditions, such as heating at high temperature (>100 ºC for
prolonged periods) or photo-irradiation can cause severe
reaction.
The synthesis of the gold nanoparticle grafted single wall
carbon nanotubes is shown in Scheme 1. To prepare the
tetrazine-AuNP (1-AuNP), the undecanolthiolate-terminated gold
degradation of the ligand shell and ultimately, the NP. Obvious 85 nanoparticles (MUD-AuNP) were prepared by following a
entries to chemical derivatization that do not require oxidative
activation, such as Diels-Alder reactions, unfortunately often
involve reaction conditions that are incompatible with the thiolate
AuNP, although CNT can serve as a dienophile in possible Diels-
standard place-exchange procedure involving mixing 11-
mecaptoundecanol (MUD) with dodecanethiolate protected
AuNP, at a ligand ratio of 1:1, for 1h. The MUD-AuNP were
purified by washing with ethanol and acetonitrile.
Alder reactions.8,11,12 Harsh conditions, including reflux or 90 Characterization by H-NMR spectroscopy reveals the absence of
1
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sharp ligand peaks, indicating the purity of the product AuNP.
The pure MUD-AuNP are soluble in THF, chloroform, DCM,
and toluene. 3,6-Dichlorotetrazine (1) was then prepared
HR-TEM images of SWCNT before (Figure 1a) and after
(Figure 1 c,d) the Diels-Alder reaction with tetrazine-AuNP for
2h demonstrate the association between CNT and AuNP. An
increase in the reactants ratio of tetrazine-AuNP to SWCNT leads
following a previous reported procedure with an overall yield of
4,22,23
5
0
5
0
80%.1
Triaminoguanidine (3) was first synthesized by 120 to a greater density of AuNP attached onto the SWCNT surface.
refluxing guanidine hydrochloride (2) and hydrazine
monohydrate in dioxin for 2 hour, followed by treatment with
Interestingly, the AuNP remain quite evenly distributed along the
CNT. Covalent bonding of AuNP to SWCNT is confirmed by a
control experiment. MUD-AuNP and SWCNT were mixed under
the same reaction conditions. As expected, the MUD-AuNP
2
,4-pentanedione to form the dihydrotetrazine precursor (4). The
precursor 4 was then oxidized by sodium nitrite to yield 3,6-
1
1
2
bis(3,5-dimethyl-1H-pyrazol-1-yl)-s-tetrazine (5). The 3,6- 125 without tetrazines do not react with SWCNT and only
dichlorotetrazine (1) was subsequently generated by treatment of
with hydrazine and trichloroisocyanuric acid. 3,6-
underivatized SWCNT were isolated after purification
(Supporting information, Figure S10.d). Energy dispersive X-ray
(EDX) spectrum analysis confirms the presence of Au, S, Cl, and
N in the AuNP-SWCNT sample (Figure S11).
5
dichlorotetrazine (1) is a very hygroscopic compound and is
readily hydrolyzed when exposed to moisture. To protect the
integrity of the tetrazine moieties and maintain their high
reactivity toward the dienophile, the chlorotetrazine was
introduced onto the hydroxyl-terminated MUD-AuNP in the last
step, under anhydrous conditions. The tetrazine-capped AuNP (1-
AuNP, 1.9±0.3 nm, Fig.1b) are synthesized by mixing the MUD-
AuNP with excess of tetrazine 1 at room temperature for 2 h.
O
O
NH
2
NHNH
2
HN NH
N
Hydrazine
HN
N
N
N
o
N
N N
Dioxane, reflux, 2h
H
2
O, 70 C
NH
2
H
2
N
NHNH
2
4
2
3
2
NaNO ,
CH COOH
3
O
Cl
Cl
O
N
N
N
N
N
N
NH
NH
2
Hydrazine, dioxane
CH3CN, reflux
N
N
N
N
N
O
N
Cl
N
N
N
HN
2
N
N
N
Cl
Cl
N
CN, 0 oC
H
CH
3
N
1
6
5
HS
OH
S
S
S
OH
5
5
5
5
Au
Cl
S
Au
5
MUD-AuNP
5
5
S
S
Au
65
N
N
O
Fig. 1. HR‐TEM of (a) SWCNT, (b) 1‐AuNP, (c) low 1‐AuNP loading AuNP‐
SWCNT sample and (d) high 1‐AuNP loading AuNP‐SWCNT sample.
N
N
S
O
5
Au
S
N
Cl
N
5
- N
2
AuNP-SWCNT
Raman spectroscopy provides evidence for the chemical
1
-AuNP
2
4
modification of carbon nanotubes. The HeNe laser line at 633
Scheme 1. Synthesis of tetrazine‐AuNP (1‐AuNP) and the Diels‐Alder
reaction between tetrazine‐AuNP and SWCNT to prepare AuNP‐SWCNT.
1
95 nm was used in the characterization of AuNP-SWCNT in order to
avoid the strong extinctions of AuNP at 488 nm and 514 nm,
which are otherwise common excitation wavelengths for Raman
spectroscopy. The Raman spectrum of pristine SWCNTs
(Supporting information Figure S12a) is consistent with data
Whereas most (the exception being the aforementioned
polymer CNT conjugates ) published chemical modification
methods of SWCNTs require pre-treatment and relatively harsh
1
3
2
3
3
4
4
5
0
5
0
5
conditions, SWCNTs react with tetrazine-AuNP under ambient 200 reported in literature, with two prominent features: a weak D
-
1
-1
conditions, without any pre-treatment. A stock suspension of
SWCNT in dry THF was first prepared by sonication of 5 mg of
SWCNT in 5 mL of anhydrous THF. A tetrazine-AuNP/THF
solution was immediately prepared before use by dissolving 1 mg
band and a strong G band around 1325 cm and 1580 cm ,
2
4
respectively. The spectrum of AuNP-SWCNT nanocomposites
(Figure S12.b,c) shows significant changes compared to that of
SWCNT alone. The decrease in the G/D ratio from 20/1 for the
of 1-AuNP in 5 mL of dry THF. 1mL of a SWCNT suspension 205 pristine SWCNT (Figure S12.a) to 8/1 for the low AuNP loading
and different volumes of the tetrazine-AuNP solution (50 µL and
AuNP-SWCNT sample (Figure S12.b) is consistent with sidewall
,
25
5
00 µL for this study) were mixed for 2 h at room temperature to
modification of the SWCNT.5 The D and G bands almost
disappear in the case of the high AuNP loading sample
(Supporting information Figure S12.c). At the same time, new
allow for the completion of the Diels-Alder reaction. The reaction
mixture was then centrifuged (5 min, 12,000 rpm); the upper
black supernatant was then removed. The resulting AuNP- 210 bands associated with the AuNP-SWCNT were observed (Table
-1
-1
SWCNT pellet was re-suspended in THF, bath sonicated for 5
min and centrifuged again, discar0064ing the supernatant. This
purification procedure was repeated with THF, DCM, toluene,
and acetonitrile, 10 times per solvent until the supernatant was
1). New peaks at 429 cm (ring deformation), 705 cm (C-S
-1
stretching mode), 810 cm (C-Cl stretch mode, broad) and a
-1
broad peak around 1090cm (C-C-C stretching mode) are
observed. The characteristic features of a C-N stretch mode, a
clear and colorless. The pure AuNP-SWCNT sample was then 215 tetrazine ring stretch mode, and the C=N stretch mode were also
-1
-1
-1
suspended in THF for further characterization. The reaction
between the tetrazine-AuNP and SWCNT was confirmed by
TEM, EDX, Raman spectroscopy, and XPS.
observed around 1270 cm , 1390 cm and 1660 cm ,
respectively. These new Raman bands in the functionalized
SWCNT sample confirm the presence of the AuNP on the surface
2
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H3A 2K6, Canada. Fax: +1 514-398-3797; Tel: +1-514-398-5244; E-
mail: bruce.lennox@mcgill.ca
of the SWCNTs.
4
4
0
5
Table 1. Summary of the raman bands of the AuNP-SWCNT
† Electronic Supplementary Information (ESI) available: [details of any
supplementary information available should be included here]. See
DOI: 10.1039/b000000x/
Raman Shift (cm-1)
Vibrational mode
ring deformation
C-S stretch
4
7
8
29
05
10
This work was supported by grants from CHIR (RS), NSERC (RS,
RBL) and FQRNT (RBL).
C-Cl stretch
1
1
1
1
090
270
390
660
C-C-C stretch
C-N stretch
1
2
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2
2
3
0
5
0
SWCNT are shown to be efficiently functionalized with
tetrazine-AuNP through a versatile reverse electron demand
Diels-Alder reaction under ambient conditions, e.g. room
temperature, no irradiation, and catalyst-free. The loading of
tetrzaine-AuNP on the SWCNT sidewall could be readily
controlled by varying the ratio of these two reactants. The
tetrazine-AuNP can react directly with the sidewalls of SWCNTs
and no pre-treatment of the nanotubes is required. More
importantly, the high reactivity of tetrazine-AuNP with SWCNT
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5
University Street, Montreal, QC H3A 2B4, Canada . Fax: +1 514-340-
7
502; Tel: +1-514-398-1857; E-mail: ralf.schirrmacher@mcgill.ca
Department of Chemistry and Centre for Self-Assembled Chemical
b
Structures, McGill University, 801 Sherbrooke St. West, Montreal, QC
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