covalent and non-covalent functionalization of single walled carbon nanotubes (swnts) paul s. engel,...
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Covalent and non-Covalent Functionalization of Single Walled Carbon Nanotubes
(SWNTs)
Paul S. Engel, Vittal B. Gudimetla, David W. Abmayr, Runtang Wang,
W.E. Billups, Ravi Singh, and Suzy Torti
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As discovered by W. E. Billups and coworkers, SWNT radical anions can react with a variety of organic compounds to functionalize the SWNT sidewalls. We find that sulfides react as well and can be used to introduce thiol groups onto SWNTs.
SWNTLi
NH3-33 oC
SWNT•- Li+S
S
SWNTS
SH
1.
2. workup
Thiol groups are potentially useful for covalent bonding topolymers, and attaching fluorescent labels and biologicallyactive compounds under mild conditions.
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The evidence for SWNT functionalization is a large increase in the Raman D:G ratio, a sizeable weight loss on TGA and the appearance of “worms” of 1.5 to 4.3 nm height in AFM.
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• In contrast to forming chemical bonds to SWNTs, noncovalent functionalization has been used to render SWNTs soluble in water and has the advantage that the fluorescence properties of SWNTs are preserved.
• However, SWNTs can easily become detached from surfactants like SDBS and poloxomers like pluronic.
• A possible solution is to encapsulate SWNTs in a water-soluble polymer from which escape is difficult.
• This might be achieved by first complexing SWNTs with an appropriate polymer and then crosslinking the backbone.
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The crosslinking concept is illustrated here. A triblock copolymer is selected consisting of an inner hydrophobic core (gray), a center crosslinkable block (red) and an outer,water-soluble segment (blue).
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• The very hydrophobic SWNT is surrounded by a polystyrene (PS) inner block.
• The outer block is a hydrophilic polyethylene glycol (PEG or PEO).
• The central block is polyacrylic acid (PAA), which is crosslinked by addition of a carbodiimide (EDC) and a water soluble diamine.
• The resulting species was termed a “PEG-egg” by Richard Smalley.
PEO(17)-PAA(35)-PS(14) suspending SWNT in water
EDC
Diamine crosslinker
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• The black suspension of PEG-eggs (right hand vial above) fluoresces as intensely as SWNTs suspended in SDBS and remains unchanged for years.
• PEG-eggs can be isolated, lyophilized, and readily re-suspended in water.
• The aqueous suspension is stable to bovine serum albumin and shows no acute toxicity at 33 ug/mL towards macrophage and kidney cells.
• 1064 nm NIR irradiation of aqueous PEG-eggs produces a large temperature rise potentially useful for killing cancer cells.
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concentration (ug/mL)
0 200 400 600 800 1000 1200
Te
mp
era
ture
incr
ea
se (
oC
)
0
5
10
15
20
25
30
35
Temperature of aqueous PEG-eggs after 30 s exposure to a 3W/cm2 YAG laser. Starting temp. was 22 oC.
A higher concentration produces a greater temperature rise but multi-walled carbon nanotubes (MWNTs) are very likely to give an even greater response if MWNT PEG-eggs can be made. Control experiments are required to verify that the observed heating is notdue merely to the blackness of the suspension.
Eggs only
SWNT PEG-egg,1 mg/mL