Gold dendrimer-encapsulated

The possibility of using electrostatic charge attraction has been exploited in the preparation of gold dendrimer encapsulated nanoparticles (DENs), which under appropriate conditions can be fully distributed along the surface of monodispersed MWCNTs (Fig. 3.21) [103]. 

R.W.J. Scott, O.M. Wilson, S.K. Oh, E.A. Kenik, R.M. Crooks, Bimetallic Palladium-Gold Dendrimer-Encapsulated Catalysts, Journal of the American Chemical Society 126, 15583, 2004. 

Scott RWJ, Wilson OM, Oh SK, Kenik EA, Crooks RM (2004) Bimetallic palladium-gold dendrimer-encapsulated catalysts. J Am Chem Soc 126 15583... 

However, for the dendrimer nanocomposite metallic systems this change in shape was not observed. Again, due to the high stability to intense laser pulses, the anisotropy value of the gold dendrimer nanocomposite, which can be viewed as a measure of the symmetry of the particle, did not change after several repeated cycles of measurements. It is possible that the initial optical pumping of the electron-phonon modes of the metal particles is partially absorbed by the encapsulating PAMAM dendrimer. 

The emission of the metal particles may thus originate from a band-to-band transition in the metal particle, which occurs at about 516 nm for gold [60, 119]. As stated above, the nature of the interaction of the dendrimer (PAMAM) host is still uncertain, there could be very strong electrostatic interactions that may play a part in the enhancement of the metal particles quantum efficiency for emission. However, one would expect that this enhancement would result in slightly distorted emission spectra, different from what was observed for the gold dendrimer nanocomposite. Further work is necessary to completely characterize the manner in which the dendrimer encapsulation enhances the emission of the metal nanoparticles. With further synthetic work in preparation of different size nanoparticles (in other words elongated and nonspherical shape particles, including nanorods) it may be possible to develop the accurate description of a... 

Other much less detailed results concerning gold-catalysed hydrogenation have been reported. Norbornene was hydrogenated on Au/MgO above 353 K,33 and propenol (allyl alcohol) was reduced by very small dendrimer-encapsulated gold particles PdAu particles worked better.34 Diethyl-itaconate has been reduced by means of supported Au3+ ions, reinforcing... 

Y.G. Kim, S.K. Oh, R.M. Crooks, Preparation and Characterization of 1-2 nm Dendrimer-Encapsulated Gold Nanoparticles Having Very Narrow Size Distributions, Chemistry of Materials 16, 167, 2004. 

Y. Haba, C. Kojima, A. Harada, T. Ura, H. Horinaka and K. Kono, Preparation of poly(ethylene glycol)-modified poly(amido amine) dendrimers encapsulating gold nanoparticles and their heat-generating ability. Langmuir, 23,5243-5246 (2007). 

Kim, Y.-G., Oh, S.-K. and Crooks, R.M. (2004) Preparation and characterization of l-2nm dendrimer-encapsulated gold nanoparticles having very narrow size distributions. Chemistry (f Materials, 16, 167 72. 

Dendrimers can be used as templates for synthesis of monodisperse gold particles, which can then be deposited onto oxide supports metal particles are encapsulated within dendrimers, and the size of the particles can be tuned by varying the metal-to-dendrimer ratio prior to reduction. 

Another type of dendrimer, that has been used to encapsulate Au32 particles is hydroxyl-terminated fifth-generation dendrimers (G5-PAMAM). The particles were adsorbed on silica (0.3wt.% Au),108 and after washing and removal of the dendrimer under oxygen at 573 K, followed by reduction under hydrogen at 573 K, the supported gold particles were even larger than above (14.5 nm), probably because silica is not a support that easily leads to small particles. 

While they are not strictly redox-containing dendrimers. Crooks and Zhao have encapsulated platinum and other metallic nanoparticles inside PAMAM dendrimers. The catalytic properties of these materials have been examined using cyclic voltammetry, and it was found that a gold electrode, modified with large hydroxyl-terminated PAMAM dendrimers containing clusters of 60 platinum atoms, was readily able to catalyze O2 reduction [98]. Similar results have been reported for palladium clusters encapsulated in the same hydroxyl-terminated PAMAM dendrimers [99]. 

Although many of the surface dendrimer amines are occluded by the gold or quantum dot nanoparhcles, silica condensahon still occurs. In fact, the CdSe/ZnS core shell quantum dots with negahvely charged surface carboxylates were encapsulated with 99% efficiency, which suggests that the electrostatic attraction between the quantum dots and the templates was sufficient for encapsulation of these materials [69]. 

Photothermal ablation therapy with metal nanoparticles is further enhanced with these particles being encapsulated inside dendrimers that improve biocompatibility and retention and facihtate surface modifications. For example, gold nanoparticles have been entrapped in G5 PAMAM dendrimers with fohc acid on the surface for targeting malignant tumors (Shi et al. 2007). 

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