Geckeler K.E., Nishide H. (Eds.) Advanced Nanomaterials

References 739

References

1 Haddon , R.C. ( 2002 ) Carbon nanotubes .

Acc. Chem. Res. , 35 , 997 .

2 Nepal , D. ( 2006 ) PhD thesis. Dispersion,

Individualization and Novel

Supramolecular Adducts of Carbon

Nanotubes. Department of Materials

Science and Engineering 140, Gwangju

Institute of Science and Technology

(GIST), Gwangju.

3 Nepal , D. and Geckeler , K.E. ( 2006 )

Functional Nanomaterials. In:

Functionalization of Carbon Nanotubes ,

(eds K.E. Geckeler and E. Rosenberg ),

American Scientiﬁ c Publishers , Valencia ,

pp. 57 – 79 .

4 Li , S.S. , He , H. , Jiao , Q.C. and Chuong ,

P.H. ( 2008 ) Applications of carbon

nanotubes in drug and gene delivery .

Prog. Chem. , 20 , 1798 – 1803 .

5 Kim , S.N. , Rusling , J.F. and

Papadimitrakopoulos , F. ( 2007 ) Carbon

nanotubes for electronic and

electrochemical detection of biomolecules .

Adv. Mater. , 19 , 3214 – 3228 .

6 Prato , M. , Kostarelos , K. and Bianco , A.

( 2008 ) Functionalized carbon nanotubes

in drug design and discovery . Acc. Chem.

Res. , 41 , 60 – 68 .

7 Kovtyukhova , N.I. , Mallouk , T.E. , Pan , L.

and Dickey , E.C. ( 2003 ) Individual

single - walled nanotubes and hydrogels

made by oxidative exfoliation of carbon

nanotube ropes . J. Am. Chem. Soc. , 125 ,

9761 – 9769 .

8 Ajayan , P.M. , Schadler , L.S. , Giannaris , C.

and Rubio , A. ( 2000 ) Single - walled carbon

nanotube - polymer composites: strength

and weakness . Adv. Mater. , 12 , 750 – 753 .

9 O ’ Connell , M.J. , Bachilo , S.M. , Huffman ,

C.B. , Moore , V.C. , Strano , M.S. , Haroz ,

E.H. , Rialon , K.L. , Boul , P.J. , Noon , W.H. ,

Kittrell , C. , Ma , J. , Haugl , R.H. ,

Weisman , R.B. , and Smalley , R.E. ( 2002 )

Band gap ﬂ uorescence from individual

single - walled carbon nanotubes . Science ,

297 , 593 – 596 .

10 Huang , J.Y. , Chen , S. , Wang , Z.Q. et al .

( 2006 ) Superplastic carbon nanotubes .

Nature , 439 , 281 .

11 Yu , M. - F. , Files , B.S. , Arepalli , S. and

Ruoff , R.S. ( 2000 ) Tensile loading of

ropes of single wall carbon nanotubes and

their mechanical properties . Phys. Rev.

Lett. , 84 , 5552 – 5555 .

12 Yu , M. - F. , Lourie , O. , Dyer , M.J. , Moloni ,

K. , Kelly , T.F. and Ruoff , R.S. ( 2000 )

Strength and breaking mechanism of

multiwalled carbon nanotubes under

tensile load . Science , 287 , 637 – 640 .

13 Hudson , J.L. , Casavant , M.J. and Tour ,

J.M. ( 2004 ) Water - soluble, exfoliated,

nonroping single - wall carbon nanotubes .

J. Am. Chem. Soc. , 126 , 11158 – 11159 .

14 Nepal , D. and Geckeler , K.E. ( 2006 )

pH - sensitive dispersion and debundling

of single - walled carbon nanotubes:

lysozyme as a tool . Small , 2 , 406 – 412 .

15 Barone , P.W. , Baik , S. , Heller , D.A. and

Strano , M.S. ( 2005 ) Near - infrared optical

sensors based on single - walled carbon

nanotubes . Nat. Mater. , 4 , 86 – 92 .

16 Saito , R. , Dresselhaus , G. and

Dresselhaus , M.S. ( 2000 ) Trigonal

warping effect of carbon nanotubes .

Phys. Rev. B , 61 , 2981 .

17 Moore , V.C. , Strano , M.S. , Haroz , E.H. ,

Hauge , R.H. and Smalley , R.E. ( 2003 )

Individually suspended single - walled

carbon nanotubes in various surfactants .

Nano Lett. , 3 , 1379 – 1382 .

18 Zhang , Z.H. , Yang , X.Y. , Zhang , Y. ,

Zeng , B. , Wang , Z.J. , Zhu , T.H. , Roden ,

R.B.S. , Chen , Y.S. and Yang , R.C. ( 2006 )

Delivery of telomerase reverse

transcriptase small interfering RNA in

complex with positively charged

single - walled carbon nanotubes

suppresses tumor growth . Clin. Cancer

Res. , 12 , 4933 – 4939 .

19 Hillebrenner , H. , Buyukserin , F. , Stewart ,

J.D. and Martin , C.R. ( 2006 ) Template

synthesized nanotubes for biomedical

delivery applications . Nanomedicine , 1 ,

39 – 50 .

20 Nepal , D. , Balasubramanian , S. ,

Simonian , A.L. and Davis , V.A. ( 2008 )

Strong antimicrobial coatings: single -

walled carbon nanotubes armored with

biopolymers . Nano Lett. , 8 , 1896 – 1901 .

21 Dubin , R.A. , Callegari , G.C. , Kohn , J. and

Neimark , A.V. ( 2008 ) Carbon nanotube

ﬁ bers are compatible with mammalian

740 23 Interactions of Carbon Nanotubes with Biomolecules: Advances and Challenges

cells and neurons . IEEE Trans.

Nanobioscience , 7 , 11 – 14 .

22 Hu , H. , Ni , Y. , Mandal , S.K. , Montana ,

V. , Zhao , B. , Haddon , R.C. and Parpura ,

V. ( 2005 ) Polyethyleneimine

functionalized single - walled carbon

nanotubes as a substrate for neuronal

growth . J. Phys. Chem. B , 109 , 4285 – 4289 .

23 Usui , Y. , Aoki , K. , Narita , N. , Murakami ,

N. , Nakamura , I. , Nakamura , K. , Ishigaki ,

N. , Yamazaki , H. , Horiuchi , H. , Kato , H. ,

Taruta , S. , Kim , Y.A. , Endo , M. and Saito ,

N. ( 2008 ) Carbon nanotubes with high

bone - tissue compatibility and bone -

formation acceleration effects . Small , 4 ,

240 – 246 .

24 Harrison , B.S. and Atala , A. ( 2007 )

Carbon nanotube applications for tissue

engineering . Biomaterials , 28 , 344 – 353 .

25 Bandyopadhyaya , R. , Nativ - Roth , E. ,

Regev , O. and Yerushalmi - Rozen , R.

( 2002 ) Stabilization of individual carbon

nanotubes in aqueous solutions . Nano

Lett. , 2 , 25 – 28 .

26 Wenseleers , W. , Vlasov , I.I. , Goovaerts ,

E. , Obraztsova , E.D. , Lobach , A.S. and

Bouwen , A. ( 2004 ) Efﬁ cient isolation and

solubilization of pristine single - walled

nanotubes in bile salt micelles . Adv.

Funct. Mater. , 14 , 1105 – 1112 .

27 Zhang , M. , Smith , A. and Gorski , W.

( 2004 ) Carbon nanotube - chitosan system

for electrochemical sensing based on

dehydrogenase enzymes . Anal. Chem. , 76 ,

5045 – 5050 .

28 Hasegawa , T. , Fujisawa , T. , Numata , M. ,

Umeda , M. , Matsumoto , T. , Kimura , T. ,

Okumura , S. , Sakurai , K. , and Shinkai , S.

( 2004 ) Single - walled carbon nanotubes

acquire a speciﬁ c lectin - afﬁ nity through

supramolecular wrapping with lactose -

appended schizophyllan . Chem. Commun. ,

2150 – 2151 .

29 Star , A. , Steuerman , D.W. , Heath , J.R.

and Stoddart , J.F. ( 2002 ) Starched carbon

nanotubes . Angew. Chem. Int. Ed. Engl. ,

41 , 2508 – 2512 .

30 Zheng , M. , Jagota , A. , Strano , M.S. ,

Santos , A.P. , Barone , P. , Chou , S.G. ,

Diner , B.A. , Dresselhaus , M.S. , McLean ,

R.S. , Onoa , G.B. , Samsonidze , G.G. ,

Semke , E.D. , Usrey , M. , and Walls , D.J.

( 2003 ) Structure - based carbon nanotube

sorting by sequence - dependent DNA

assembly . Science , 302 , 1545 – 1548 .

31 Cathcart , H. , Quinn , S. , Nicolosi , V. , Kelly ,

J.M. , Blau , W.J. and Coleman , J.N. ( 2007 )

Spontaneous debundling of single - walled

carbon nanotubes in DNA - based

dispersions . J. Phys. Chem. C , 111 , 66 – 74 .

32 Liu , Y. , Chen , J. , Anh , N.T. , Too , C.O. ,

Misoska , V. and Wallace , G.G. ( 2008 )

Nanoﬁ ber mats from DNA, SWNTs, and

poly(ethylene oxide) and their application

in glucose biosensors . J. Electrochem. Soc. ,

155 , K100 – K103 .

33 Jonganurakkun , B. , Liu , X.D. , Nodasaka ,

Y. , Nomizu , M. and Nishi , N. ( 2003 )

Survival of lactic acid bacteria in

simulated gastrointestinal juice protected

by a DNA - based complex gel . J. Biomater.

Sci., Polym. Ed. , 14 , 1269 – 1281 .

34 Fink , H. - W. and Schonenberger , C. ( 1999 )

Electrical conduction through DNA

molecules . Nature , 398 , 407 – 410 .

35 Yan , H. , Zhang , X. , Shen , Z. and

Seeman , N.C. ( 2002 ) A robust DNA

mechanical device controlled by

hybridization topology . Nature , 415 ,

62 – 65 .

36 Turberﬁ eld , A. ( 2003 ) Phys. World , 16 ( 3 ),

43 – 46 .

37 Steckl , A.J. ( 2007 ) DNA – a new material

for photonics? Nat. Photonics , 1 , 3 – 5 .

38 Zheng , M. , Jagota , A. , Semke , E.D. ,

Diner , B.A. , Mclean , R.S. , Lustig , S.R. ,

Richardson , R.E. and Tassi , N.G. ( 2003 )

DNA - assisted dispersion and separation

of carbon nanotubes . Nat. Mater. , 2 ,

338 – 342 .

39 Nepal , D. , Sohn , J. - I. , Aicher , W.K. , Lee ,

S. and Geckeler , K.E. ( 2005 )

Supramolecular conjugates of carbon

nanotubes and DNA by a solid - state

reaction . Biomacromolecules , 6 ,

2919 – 2922 .

40 Tsang , S.C. , Guo , Z. , Chen , Y.K. , Green ,

M.L.H. , Hill , H.A.O. , Hambley , T.W. and

Sadler , P.J. ( 1997 ) Immobilization of

platinated and iodinated oligonucleotides

on carbon nanotubes . Angew. Chem. Int.

Ed. Engl. , 36 , 2198 – 2200 .

41 Nakashima , N. , Okuzono , S. , Murakami ,

H. , Nakai , T. and Yoshikawa , K. ( 2003 )

DNA dissolves single - walled carbon

nanotubes in water . Chem. Lett. , 32 ,

456 – 457 .

42 Baker , S.E. , Cai , W. , Lasseter , T.L. ,

Weidkamp , K.P. and Hamers , R.J. ( 2002 )

Covalently bonded adducts of

References 741

deoxyribonucleic acid (DNA)

oligonucleotides with single - wall carbon

nanotubes: synthesis and hybridization .

Nano. Lett. , 2 , 1413 – 1417 .

43 Keren , K. , Berman , R.S. , Buchstab , E. ,

Sivan , U. and Braun , E. ( 2003 ) DNA -

templated carbon nanotube ﬁ eld - effect

transistor . Science , 302 , 1380 – 1382 .

44 Drexler , K. ( 1992 ) Nanosystems: Molecular

Machinery, Manufacturing, and

Computation , John Wiley & Sons, Inc. ,

New York .

45 Wang , G. - W. , Komatsu , K. , Murata , Y.

and Shiro , M. ( 1997 ) Synthesis and X - ray

structure of dumb - bell - shaped C120 .

Nature , 387 , 583 – 586 .

46 Pan , H. , Guo , Z. - X. , Dai , L. , Zhang , F. ,

Zhu , D. , Czerw , R. and Carroll , D.L.

( 2003 ) Carbon nanotubols from

mechanochemical reaction . Nano Lett. ,

3 , 29 – 32 .

47 Tu , X. and Zheng , M. ( 2008 ) A DNA -

based approach to the carbon nanotube

sorting problem . Nano Res. , 1 , 185 – 194 .

48 Kane , R.S. and Stroock , A.D. ( 2007 )

Nanobiotechnology: protein - nanomaterial

interactions . Biotechnol. Prog. , 23 ,

316 – 319 .

49 Huang , W.J. , Taylor , S. , Fu , K.F. , Lin , Y. ,

Zhang , D.H. , Hanks , T.W. , Rao , A.M.

and Sun , Y.P. ( 2002 ) Attaching proteins

to carbon nanotubes via diimide - activated

amidation . Nano Lett. , 2 , 311 – 314 .

50 Zorbas , V. , Ortiz - Acevedo , A. , Dalton ,

A.B. , Yoshida , M.M. , Dieckmann , G.R. ,

Draper , R.K. , Baughman , R.H. , Jose -

Yacaman , M. , and Musselman , I.H.

( 2004 ) Preparation and characterization of

individual peptide - wrapped single - walled

carbon nanotubes . J. Am. Chem. Soc. , 126 ,

7222 – 7227 .

51 Zorbas , V. , Smith , A.L. , Xie , H. ,

Ortiz - Acevedo , A. , Dalton , A.B. ,

Dieckmann , G.R. , Draper , R.K. ,

Baughman , R.H. , and Musselman , I.H.

( 2005 ) Importance of aromatic content for

peptide/single - walled carbon nanotube

interactions . J. Am. Chem. Soc. , 127 ,

12323 – 12328 .

52 Xie , H. , Becraft , E.J. , Baughman , R.H. ,

Dalton , A.B. and Dieckmann , G.R. ( 2008 )

Ranking the afﬁ nity of aromatic residues

for carbon nanotubes by using designed

surfactant peptides . J. Peptide Sci. , 14 ,

139 – 151 .

53 Karajanagi , S.S. , Yang , H. , Asuri , P. ,

Sellitto , E. , Dordick , J.S. and Kane , R.S.

( 2006 ) Protein - assisted solubilization of

single - walled carbon nanotubes .

Langmuir , 22 , 1392 – 1395 .

54 Ma , Y. , Chiu , P.L. , Serrano , A. , Ali , S.R. ,

Chen , A.M. and He , H. ( 2008 ) The

electronic role of DNA - functionalized

carbon nanotubes: efﬁ cacy for in situ

polymerization of conducting polymer

nanocomposites . J. Am. Chem. Soc. , 130 ,

7921 – 7928 .

55 Han , X. , Li , Y. and Deng , Z. ( 2007 )

DNA - wrapped single walled carbon

nanotubes as rigid templates for

assembling linear gold nanoparticle

arrays . Adv. Mater. , 19 , 1518 – 1522 .

56 Badaire , S. , Zakri , C. , Maugey , M. , Derre ,

A. , Barisci , J.N. , Wallace , G. and Poulin ,

P. ( 2005 ) Liquid crystals of DNA -

stabilized carbon nanotubes . Adv. Mater. ,

17 , 1673 – 1676 .

57 Barisci , J.N. , Tahhan , M. , Wallace , G.G. ,

Badaire , S. , Vaugien , T. , Maugey , M. and

Poulin , P. ( 2004 ) Properties of carbon

nanotube ﬁ bers spun from DNA -

stabilized dispersions . Adv. Funct. Mater. ,

14 , 133 – 138 .

58 Lynam , C. , Moulton , S.E. and Wallace ,

G.G. ( 2007 ) Carbon - nanotube bioﬁ bers .

Adv. Mater. , 19 , 1244 – 1248 .

59 Razal , J.M. , Gilmore , K.J. and Wallace ,

G.G. ( 2008 ) Carbon nanotube bioﬁ ber

formation in a polymer - free coagulation

bath . Adv. Funct. Mater. , 18 , 61 – 66 .

60 Shin , S.R. , Lee , C.K. , So , I.S. et al . ( 2008 )

DNA - wrapped single - walled carbon

nanotube hybrid ﬁ bers for supercapacitors

and artiﬁ cial muscles . Adv. Mater. , 20 ,

466 – 470 .

61 Mu ñ oz , E. , Suh , D. - S. , Collins , S. ,

Selvidge , M. , Dalton , A.B. , Kim , B.G. ,

Razal , J.M. , Ussery , G. , Rinzler , A.G. ,

Mart í nez , M.T. and Baughman , R.H.

( 2005 ) Highly conducting carbon

nanotube/polyethyleneimine composite

ﬁ bers . Adv. Mater. , 17 , 1064 – 1067 .

62 Kozlov , M.E. , Capps , R.C. , Sampson ,

W.M. , Ebron , V.H. , Ferraris , J.P. and

Baughman , R.H. ( 2005 ) Spinning solid

and hollow polymer - free carbon nanotube

ﬁ bers . Adv. Mater. , 17 , 614 – 617 .

63 Yogeswaran , U. , Thiagarajan , S. and

Chen , S.M. ( 2008 ) Recent updates of

DNA incorporated in carbon nanotubes

742 23 Interactions of Carbon Nanotubes with Biomolecules: Advances and Challenges

and nanoparticles for electrochemical

sensors and biosensors . Sensors , 8 ,

7191 – 7212 .

64 Cherukuri , P. , Gannon , C.J. , Leeuw , T.K. ,

Schmidt , H.K. , Smalley , R.E. , Curley , S.A.

and Weisman , R.B. ( 2006 ) Mammalian

pharmacokinetics of carbon nanotubes

using intrinsic near - infrared ﬂ uorescence .

Proc. Natl Acad. Sci. USA , 103 ,

18882 – 18886 .

65 Chakravarty , P. , Marches , R. ,

Zimmerman , N.S. , Swafford , A.D.E. ,

Bajaj , P. , Musselman , I.H. , Pantano , P. ,

Draper , R.K. , and Vitetta , E.S. ( 2008 )

Thermal ablation of tumor cells with anti

body - functionalized single - walled carbon

nanotubes . Proc. Natl Acad. Sci. USA ,

105 , 8697 – 8702 .

Nanoparticle - Cored Dendrimers and Hyperbranched Polymers:

Synthesis, Properties, and Applications

Young - Seok Shon

743

Advanced Nanomaterials. Edited by Kurt E. Geckeler and Hiroyuki Nishide

ISBN: 978-3-527-31794-3

24

24.1

Introduction

Functionalized nanoparticles have attracted remarkable academic and industrial

interest due to their unique chemical, biological, catalytic, optical, and electronic

properties, as well as their potential applications in electronic devices, sensors,

molecular reagents, and catalysis [1 – 3] . Nanoparticles protected by a polymeric

ligand have been employed to prepare nanoscale building blocks for functional

materials. Polymeric stabilizers such as thiolated polymers [4 – 6] and electrostatic

polymer multilayers [7 – 9] have been used for the stabilization of metal nanopar-

ticles. Nanoparticles have also been modiﬁ ed with polymer chains covalently

bound to the surface using “ grafting from ” reactions, such as atom transfer radical

( ATR ) polymerization, living cationic ring - opening polymerization, and surface -

immobilized ring - opening metathesis polymerization ( ROMP ) [10 – 12] .

Dendrimers have attracted an intense interest because of their well - deﬁ ned

structures with interior cavities and chemical versatility [13 – 15] . Dendrimers also

often have provided some of the most versatile tools to building blocks used in

the construction of three - dimensional ( 3 - D ) organic/inorganic nanostructures [16] .

The current research on dendrimers is mostly focused on the development of

functionalized dendrimers with an active core or external surface groups [17 – 19] .

These functional dendrimers have shown a variety of applications in the ﬁ elds of

medicinal chemistry (e.g., magnetic resonance imaging and drug delivery), host –

guest chemistry, and catalysis [17 – 19] . Signiﬁ cant research progress has also been

made in the use of dendritic frameworks to surround functional core molecules

such as rotaxane, porphyrin, and fullerene [20 – 23] .

Due to the interesting properties of metal nanoparticles [1] , the incorporation

of nanoparticles into the dendrimer templates has been attempted [24 – 33] . For

example, monometallic nanoparticles of gold, palladium, platinum, copper, and

silver were incorporated into the dendrimers by reduction of their metal salts with

NaBH

4

in the presence of “ Tomalia - type ” poly(amidoamine) dendrimers [24 – 26] .

These materials were synthesized using a template approach in which metal ions

744 24 Nanoparticle-Cored Dendrimers and Hyperbranched Polymers: Synthesis, Properties, and Applications

were ﬁ rst extracted into the interior of dendrimers and then subsequently reduced

by chemical reactants to yield quite monodisperse particles having dimensions of

less than 5 nm. Both, bimetallic and semiconductor nanoparticles have also been

incorporated into the dendrimers by similar routes [28, 29] . These materials have

a number of applications, but are especially useful in catalysis (e.g., hydrogena-

tions, Heck coupling, Stille, and Suzuki reactions) [30 – 33] . Several reviews have

been prepared detailing the synthesis, characterization, and application of den-

drimer - encapsulated nanoparticles [23 – 25] .

Structurally well - deﬁ ned, inorganic, cluster - cored dendrimers have also

attracted interest. Dendrimers supported by the [Re

6

Se

8

]

2+

metal cluster were

synthesized by Zheng and coworkers [34] , this being the ﬁ rst example of utiliz-

ing metal clusters to construct cluster - cored metallodendrimers. These dendrim-

ers exhibited dramatic color changes with only slight variations in the structure

of dendrons, which suggested their interesting – and potentially impor-

tant – optical tunability. Gorman et al. reported the synthesis and characteriza-

tion of iron – sulfur [Fe

4

S

4

] cluster - cored dendrimers [35, 36] . Here, it was

recognized that the iron – sulfur cluster employed as the core unit in these den-

drimers displayed redox potentials that were very sensitive to environments

such as the generation of dendrons and the solvent media. Dendrimers based

on polyhedral oligomeric silsesquioxane ( POSS ) cores were also prepared, and

provided an increased selectivity in hydroformylation reactions due to a positive

dendrimer effect [37] .

Nanoparticle - cored dendrimers represent an organic – inorganic hybrid nanos-

tructure with a nanoparticle core and well - deﬁ ned dendritic wedges (Figure 24.1 )

[38 – 58] . The preparation of nanoparticle - cored dendrimers represents an impor-

tant advance in the control and preparation of new organized nanostructures.

Dendritic scaffolds offer an enhanced stability and well - deﬁ ned property to the

materials, and can provide some segregation of external groups and internal nano-

particle core. While the external functionality mainly controls the overall solubility

and reactivity of nanoparticle - cored dendrimer s ( NCD s), internal functionality

provides a completely different environment for the nanoparticle core from that

of the bulk solution and the exterior. Another important structural feature of NCDs

Figure 24.1 General structure of nanoparticle - cored dendrimer s ( NCD s).

is the large void spaces present inside; these may act as guest cavities and also

function as “ reaction vessels ” for catalytic reactions.

In this chapter we present a concise review of synthetic strategies for nanopar-

ticle - cored dendrimers, along with their properties and applications. The most

popular synthetic approach – the direct method – uses a modiﬁ ed Schiffrin reaction

with dendrons containing thiols or disulﬁ des [38 – 49] . In contrast, the indirect

method involves two - step reactions, namely the synthesis of monolayer - stabilized

nanoparticles followed by the ligand - place exchange of thiolated dendrons [47,

50 – 54] . A third synthetic strategy is also described, in which single or multistep

organic reactions are employed to build dendritic architectures around a monol-

ayer - protected metal nanoparticle [55 – 58] . Finally, the synthesis of nanoparticle -

cored hyperbranched polymers is introduced as the convenient alternate for

nanoparticle - cored dendrimers. In this approach, well - deﬁ ned hyperbranched

polymers are grafted onto a nanoparticle by self - organization [59 – 61] . The chemi-

cal and physical properties, and also the technological applications, of nanoparti-

cle - cored dendrimers and hyperbranched polymers are described with regards to

the synthetic methods for these nanostructures.

24.2

Synthesis of Nanoparticle - Cored Dendrimers via the Direct Method, and their

Properties and Application

When, in 1994, Schiffrin et al. reported the convenient two - phase synthesis of

isolable and soluble alkanethiolate - protected gold nanoparticles, this had a major

impact on nanoparticle research and development [1] . In this reaction, AuCl

4

−

was

transferred to toluene, using tetraoctylammonium bromide as the phase - transfer

reagent. The addition of alkanethiol to organic - phase AuCl

4

−

, followed by reduc-

tion with NaBH

4

, generated alkanethiolate - protected gold nanoparticles. The ﬁ rst

examples of nanoparticle - cored dendrimers were synthesized using a modiﬁ ed,

two - phase Schiffrin protocol (Scheme 24.1 ).

Shultz, Linderman, Feldheim, and their coworkers reported that the alkene -

terminated tripodal ligand ( 1 ; Figure 24.2 ), which contained a branched structure

with a single thiolate group on one end and three alkene - terminated hydrocarbon

chains on the other end, could be used for the stabilization of gold nanoparticles

that were approximately 5 nm in diameter [38] . The alkene - terminated tripodal

ligand was used in order to maximize polymeric crosslinking, which led to the

formation of structurally rigid hollow capsules following removal of the gold nano-

particle. The dimensions of the capsules ( ∼ 10 ± 2.5 nm) agreed well with the

diameter expected based on the size of the template gold nanoparticle and

the length of the alkylthiol spacer. Crosslinking was carried out by oleﬁ n metath-

esis of the thiol - derivatized nanoparticles using a catalytic quantity of Grubbs cata-

lyst [62] .

Similarly, poly(oxymethyl) dendrons with a single thiol group ( 2 ; Figure 24.2 ) at

the focal point were used as the stabilizer, and produced dendron - stabilized gold

24.2 Synthesis of Nanoparticle-Cored Dendrimers via the Direct Method, and their Properties 745

746 24 Nanoparticle-Cored Dendrimers and Hyperbranched Polymers: Synthesis, Properties, and Applications

nanoparticles [39] . This approach afforded highly stable gold nanoparticles with

average diameters of 2.4 to 3.1 nm. Generation - one [G - 1], two [G - 2], and three [G - 3]

dendron - stabilized gold nanoparticles were highly stable, both in solution and in

the solid state. These NCDs remained unchanged after standing overnight at

elevated temperatures (at 50 ° C in solution, and at 160 ° C in the solid state). The

high stability of NCDs protected by dendrons with a thiol group was a clear

improvement over that of dendrimer - encapsulated nanoparticles. The core size

and size distribution of the nanoparticle - cored dendrimers, when examined with

high - resolution transmission electron microscopy ( HR - TEM ), were not signiﬁ -

cantly affected by the use of different molar ratios of dendrons/HAuCl

4

in this

study [39] .

Torigoe et al. also used poly(oxymethylphenylene) dendron s ( PPD s) ( 3 ; Figure

24.2 ) of generations 1 – 4 functionalized with a thiol group at the focal point as

capping ligands for gold nanoparticle - cored dendrimers [40] . The average particle

size was 1.5 and 1.4 nm for [G - 1] and [G - 2], respectively with a relatively small

standard deviation. The particle size was increased for higher - generation dendrons

(2.2 nm for [G - 3] and 3.8 nm for [G - 4]), with a much broader size distribution. The

spontaneous formation of one - dimensional ( 1 - D ) arrays of [G - 1] and [G - 2] NCDs

was observed over a larger area. This suggested that the dendron ligands had a

strong tendency to crystallize due to an intermolecular π – π stacking interaction of

thiol - terminated PPDs, as in the case of the pyridine derivative system in which

two - dimensional ( 2 - D ) superlattices have been observed [63] . The formation of 1 - D

arrays over a larger area would provide more elaborate nanoelectronic systems.

The systematic characterization of stable gold nanoparticle - cored dendrimers

with different generations ([G - 1] to [G - 5]) prepared by the Schiffrin reaction using

polyaryl ether dendritic disulﬁ de as a capping reagent, was reported by Whitesell

and Fox in 2003 ( 4 ; Figure 24.2 ) [41] . Results obtained with transmission electron

microscopy ( TEM ) suggested that the nanoparticle core of NCDs exhibited a rela-

tively high polydispersity. The average core sizes were increased from [G - 1] NCDs

to [G - 4] NCDs, and then showed a decrease as the dendron wedge sizes increased

to [G - 5]. The structure and composition of NCDs were more carefully studied

Scheme 24.1 Synthesis and structure of nanoparticle - cored

dendrimers (NCDs), where Gn represents a dendritic wedge

of variable generation number. Reproduced with permission

using ultraviolet ( UV ), Fourier transform infrared ( FT - IR ) and nuclear magnetic

resonance ( NMR ) spectrosocopies in this study. The surface plasmon bands

( ∼ 520 nm) of these NCDs were similar to those for arenethiolate - protected clusters

reported elsewhere [1, 3] . The IR spectra of NCDs and their dendritic disulﬁ de

precursors were almost identical. In the

1

H NMR spectra, the peaks appeared very

similar for dendrons and NCDs, except for broadened peaks in the bases. The

Figure 24.2 Dendron thiols and disulﬁ des used for the

synthesis of nanoparticle - cored dendrimers.

24.2 Synthesis of Nanoparticle-Cored Dendrimers via the Direct Method, and their Properties 747

748 24 Nanoparticle-Cored Dendrimers and Hyperbranched Polymers: Synthesis, Properties, and Applications

number of dendron units on a nanoparticle core, which was obtained via TEM

and thermogravimetric analysis ( TGA ), decreased with the increased generation

of the dendrons, with values falling from 2.18 nm

− 2

for [G - 2] NCDs to 0.27 nm

− 2

for [G - 5] NCDs. Therefore, for the higher - generation NCDs a large fraction of the

surface area of the metal nanoparticle was not passivated and thus available for

the catalytic reaction. Based on these characteristics, transition metal - based NCDs

were recognized as being good catalysts for many organic reactions.

Whitesell and Fox prepared [G - 3] Pd NCDs (as shown in Scheme 24.2 ) and

investigated their catalytic properties [42] . A combination of data acquired using

TEM and TGA showed that, for the Pd NCDs, more than 90% of the nanoparticle

surface was unpassivated. If most of the unpassivated surface atoms were to be

available for catalysis, and the required reagents could penetrate the dendritic

exterior to reach the metal surface, then these NCDs might serve as excellent cata-

lysts for many organic reactions. The Heck and Suzuki reactions (Scheme 24.3 ),

both of which are normally carried out on Pd - phosphine catalysts, were tested on

these Pd NCDs. The turnover number ( TON ; calculated as moles of product per

mole catalyst) and turnover frequency ( TOF ; calculated as moles of product per

mole catalyst per hour) for both the Heck and Suzuki reactions were very high.

In addition, the absence of any side product other than the starting compound,

products, and solvent for both reactions indicated the high efﬁ ciency of Pd NCDs

as a new catalytic system.

Whitesell and Fox also reported the synthesis of NCDs stabilized by polyaryl

ether dendrons with ester groups on the periphery, using the Schiffrin reaction

[43] . The ester - terminated NCDs were converted to the corresponding carboxylate -

functionalized NCDs by treatment with sodium hydroxide (Scheme 24.4 ). The

sodium salts of carboxylate - terminated NCDs were soluble in water and exhibited

micelle - like properties in solution; this was an important point because dendritic

micelles can be used as catalysts in water and as drug - delivery agents. The micellar

properties of NCDs were probed by the spectral shifts of dye molecules (Figure

Scheme 24.2 Synthesis of Pd - G - 3 NCDs. Reproduced with

Society.

Geckeler K.E., Nishide H. (Eds.) Advanced Nanomaterials

Подождите немного. Документ загружается.