Organic/Metallic Nanohybrids Based on Amphiphilic Dumbbell-Shaped Dendrimers
ABSTRACT In this study, we synthesized a series of amphiphilic dumbbell-shaped dendrimers through the addition reactions of a hydrophilic poly(oxyalkylene) with hydrophobic dendrons based on 4-isocyanate-4'-(3,3-dimethyl-2,4-dioxo-azetidine)diphenylmethane with different numbers of branching generations. The addition reaction of azetidine-2,4-diones of dendrons to amines of poly(oxyalkylene) was proceeded by stirring the reactants in dry tetrahydrofuran (THF) under nitrogen at 60 °C. In aqueous media, the dumbbell-shaped dendrimers self-assembled into micelles with their hydrophobic dendrons in the core and their hydrophilic poly(oxyalkylene) segments forming loops in the corona shell. Employing the unique self-assembled micelle structures as templates for subsequent chemical reduction of the Ag(+) ions, we generated new types of organic/metallic [silver nanoparticle (AgNP)] nanohybrid clusters. The long poly(oxyalkylene) loops that extended into the aqueous phase complexed with the Ag(+) ions, providing the suspension with steric stabilization to prevent the AgNPs from collision and flocculation. After reduction, the AgNPs were present in a homogeneous distribution in the round dendrimer micelle-stabilized nanoclusters. The diameter of each AgNP was less than 10 nm; the diameter of each round nanocluster was in the range of 50-200 nm. The encapsulation efficiency of the AgNPs in micelles was about 54-69% for the dumbbell-shaped dendrimer based organic/AgNP nanohybrid.
SourceAvailable from: lu Shihuan[Show abstract] [Hide abstract]
ABSTRACT: A novel amphiphilic Tb(3+) complex (TbL(3+)(I)) consisting of a +3 charged head and a hydrophobic alkyl chain is developed. It spontaneously self-assembles in water and forms stable vesicles at neutral pH. TbL(3+)(I) has no aromatic groups (functioning as an antenna), and its intrinsic luminescence is thus minimized. These features lead to the self-assembling TbL(3+)(I) receptor molecules demonstrating an increased luminescence intensity upon binding of nucleotides. Upon addition of GTP, the luminescence from Tb(3+) was notably promoted (127-fold), as the light energy absorbed by the guanine group of GTP was efficiently transferred to the Tb(3+) center. In the case of GDP and GMP, respectively 78-fold and 43-fold increases in luminescence intensity were observed. This enhancement was less significant than that observed for GTP, due to fewer negative charges on GDP and GMP. No other nucleotides or the tested non-phosphorylated nucleosides affected the luminescence intensity to any notable extent. In marked contrast, all tested nucleotides, including guanine nucleotides, barely promoted the luminescence of molecularly dispersed receptors, TbL(3+)(II), indicating that the confinement and organization of molecules in a nanointerface play vital roles in improving the performance of a sensing system. This Tb(3+) complex nanointerface is successfully used for monitoring the GTP-to-GDP conversion.ACS Applied Materials & Interfaces 08/2014; 6(16). DOI:10.1021/am5031424 · 5.90 Impact Factor
[Show abstract] [Hide abstract]
ABSTRACT: Self‐segregating hyperbranched polymer (HBP) additives have been utilized to concentrate silver nanoparticles (AgNPs) at the air interface of polyurethane films. The limited spontaneous surface migration of the AgNPs was enhanced through the addition of appropriately functionalized HBPs. Both amine and thiol terminated additives were employed to allow interaction of the HBP with the nanoparticles. Both types of additives increased surface concentration of silver modestly, though the thiol‐terminated HBPs demonstrated nearly a seven‐fold enhancement of surface migration. It was also found that wholly‐aliphatic HBPs demonstrated only slightly reduced ability to bias AgNP concentration as compared to HBPs functionalized with perfluorinated chains. In addition, films containing 1% total silver concentration were tested for antimicrobial activity using the ASTM‐E 2180 protocol. Significant reduction of the microorganisms was observed for all samples, 6‐log reduction was achieved for the gram‐negative bacteria P. aeruginosa, the gram‐positive bacteria S. aureus, and the fungi C. albicans. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013Journal of Applied Polymer Science 06/2013; 128(6). DOI:10.1002/app.38620 · 1.64 Impact Factor
[Show abstract] [Hide abstract]
ABSTRACT: In this study, we synthesized water-soluble hyperbranched poly(amido acid)s (HBPAAs) featuring multiple terminal CO2H units and internal tertiary amino and amido moieties and then used them in conjunction with an in situ Fe2+/Fe3+ co-precipitation process to prepare organic/magnetic nanocarriers comprising uniformly small magnetic iron oxide nanoparticles (NP) incorporated within the globular HBPAAs. Transmission electron microscopy revealed that the HBPAA-γ-Fe2O3 NPs had dimensions of 6-11 nm, significantly smaller than those of the pristine γ-Fe2O3 (20-30 nm). Subsequently, we covalently immobilized a bacterial γ-glutamyltranspeptidase (BlGGT) upon the HBPAA-γ-Fe2O3 nanocarriers through the formation of amide linkages in the presence of a coupling agent. Magnetization curves of the HBPAA-γ-Fe2O3/BlGGT composites measured at 300 K suggested superparamagnetic characteristics, with a saturation magnetization of 52 emu g-1. The loading capacity of BlGGT on the HBPAA-γ-Fe2O3 nanocarriers was 16 mg g-1 support; this sample provided a 48% recovery of the initial activity. The immobilized enzyme could be recycled 10 times with 32% retention of the initial activity; it had stability comparable with that of the free enzyme during a storage period of 63 days. The covalent immobilization and stability of the enzyme and the magnetization provided by the HBPAA-γ-Fe2O3 NPs suggests that this approach could be an economical means of depositing bioactive enzymes upon nanocarriers for BlGGT-mediated bio-catalysis.Molecules 04/2014; 19(4):4997-5012. DOI:10.3390/molecules19044997 · 2.10 Impact Factor