Sinoj Abraham

Encapsulation of Single Small Gold Nanoparticles by Diblock Copolymers

There has been considerable interest in recent years in using metal, semiconductor, and magnetic nanoparticles in biological applications. A wide range of ligation and encapsulation methods have been developed to render the nanoparticles soluble in aqueous solution, to prevent aggregation, and to provide means by which functional molecules can be attached. Among these methods, encapsulation of nanoparticles by a polymer, 9] phospholipid, or inorganic 12] shell is of particular interest to us, since these stable shells prevent dissociation of surface ligands and provide anchor points where biomolecules are unlikely to be lost once attached. This is a significant advantage over direct conjugation through surface ligands, since even strong thiol ligands can dissociate from or undergo exchange on gold surfaces, let alone weaker ligands on the surfaces of quantum dots or magnetic nanoparticles. Stable attachment of biomolecules would be particularly important where only a few biomolecules are selectively attached to a nanoparticle, or when multiple types of singly functionalized nanoparticles are mixed. Stable functionalization of quantum dots remains a challenge. While biomolecules have been attached to quantum dots and used for biological studies, a nondissociable ligand shell would be required for attachment of biomolecules selectively and with controlled valency. Recently, Taton et al. reported encapsulation of gold nanoparticles (AuNPs) and magnetic nanoparticles (MagNPs) by amphiphilic diblock copolymers. The resulting nanoparticles have a stable, well-defined core/shell structure impermeable to ionic species in aqueous solution. Such a polymer shell would be ideal for functionalization of quantum dots if a similar encapsulation methodology could be adopted. However, it was found that in this system small (d<10 nm) AuNPs and MagNPs act as solutes in polymer micelles and are therefore prone to multiple inclusion on encapsulation. In contrast, large AuNPs act as surface templates on which polymer molecules assemble into micellar shells that each encapsulate a single AuNP. Since most nanoparticles used for biological studies, particularly quantum dots, have diameters in the range of 2–9 nm, it is necessary that we develop new methods that can encapsulate single nanoparticles of sizes similar to quantum dots. Herein we report the encapsulation of single small AuNPs, in preparation for future work on quantum dots, since AuNPs are easier to handle and characterize. Diblock copolymers such as PS108PGA108, PS132PAA72, and PS159PAA62 [PS: polystyrene, PGA: poly(glutamic acid), PAA: poly(acrylic acid)] were used to encapsulate AuNPs in “hairy” micelles (Figure 1B); the resulting

Copolymerizations of ethylene with 1-hexene overansa-metallocene diamide complexes

We have performed copolymerizations of ethylene with 1-hexene using variousansa-metallocene compounds in the presence of the non-coordinative [CPh3][B(C6F5)4] ion pair as a cocatalyst. The metallocenes chosen for this study are isospecific metallocene diamide compounds,rac-(EBI)Zr(NMe2)2 [1, EBI = ethylene-1,2-bis(1-indenyl)],rac-(EBI)Hf(NMe2)2 (2),rac-(EBI)Zr(NC4H8)2 (3), andrac-(CH3)2Si(1-C5H2-2-CH3-4-tC4H9)2 Zr(NMe2)2 (4), and syndiospecific metallocene dimethyl compounds, ethylidene(cyclopentadienyl)(9-fluorenyl) ZrMe2 [5, Et(Flu)(Cp)ZrMe2] and isopropylidene(cyclopentadienyl)(9-fluorenyl)ZrMe2 [6,iPr(Flu)(Cp)ZrMe2]. The copolymerization rate decreased in the order4 >1 ∼3 >2 >5 >6. The reactivity of 1-hexene decreased in the order2 >6 >1 ∼3 ∼5 >4. We characterized the microstructure of the resulting poly(ethylene-co-1-hexene) by13C NMR spectroscopy and investigated various other properties of the copolymers in detail.

Synthesis of star-like random copolymers from resorcinarene-based octa-functional alkoxyamine initiatorvia nitroxide mediated free radical polymerization

An octa-functional alkoxyamine initiator, with the 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) free radical, was synthesized based on resorcinarene, with its efficiency to initiate the nitroxide-mediated free radical copolymerization of styrene and methyl methacrylate (MMA) described. A difunctional analogue of this initiator was also synthesized, using resorcinol as the core molecule. The structures of the resulting initiators were confirmed by homolysis studies based on electron spin resonance spectroscopy and molecular modeling. The polymerization behavior and characteristics of the polymers obtained using these two initiators were also compared. Well-defined star-shaped and linear random copolymers, with low polydispersities and controlled molecular weights, were prepared. The efficiencies of these initiators towards copolymerization, as well as the parameters permitting the formation of well-defined polymers, were also investigated. The reactivity ratios werera = 0.42 (a = styrene) andrb = 0.33 (b = MMA) for the octa-functional initiator system andra = 0.45 andrb = 0.39 for the difunctional initiator system.

Continuous Production of Spherical Microcapsules with Nano-Pores and Use as a Potential Encapsulant

This paper presents the fabrication of nano-porous polymer microcapsules using self-assembly of the block copolymers in the microchannel. The spherical microcapsule with the diameter of about 25 mum was successfully fabricated with the thickness distribution of 0.5-1.5 mum and nano pores. Its potential as an encapsulant use was demonstrated by comparing the release performance under the various microenvironments.