Biomedical subjects
Publications and source records attributed to Kwan Kim.
Two metastable calcium carbonate polymorphs, hemispherical vaterite and needle-like aragonite, are selectively formed at the air/water interface by the mediation of poly(ethyleneimine)(with molecular weights of 25000 and 2000, respectively) dissolved in supersaturated calcium bicarbonate solution.
The structure and thermal behavior of silver 16-hydroxyhexadecanoate (Ag-HHDA) have been investigated by using various analytical tools. The X-ray diffraction pattern was composed of a series of peaks that could be indexed to (0k0) reflections of a layered structure. Diffuse reflectance infrared Fourier transform spectroscopy revealed that the alkyl chains in Ag-HHDA as prepared were in an all-trans conformational state. Upon heating the sample, noticeable structural changes took place particularly in two temperature regions. The first structural change occurring at approximately 380 K was a partially irreversible one in which the binding state of carboxylate to silver converted from bridging into unidentate. A second dramatic structural change occurring at approximately 480 K was a totally irreversible process that could be associated with the decomposition of Ag-HHDA. All of these thermal characteristics of Ag-HHDA are comparable to those of silver stearate (Ag-STA). Separately, we have endeavored without success to intercalate polar molecules into the OH-group terminated layers in Ag-HHDA; the exfoliation of Ag-HHDA in various polar solvents was also unsuccessful. This is indicative of the presence of a rather stronger H-bond in Ag-HHDA, but the comparable thermal characteristics of Ag-HHDA and Ag-STA dictate that the thermal behavior of silver alkanoate is determined exclusively by the silver-to-carboxylate group interaction. This is in sharp contrast to the case of two-dimensional self-assembled monolayers for which the terminal functionalities play a crucial role in determining the structure and thermal stability of entire monolayers.
Silver nanoparticles capped with organoisocyanide and host or guest molecules are a very effective molecular sensing/recognition mediator via surface-enhanced Raman spectroscopy.
This work demonstrates that optically tunable, SERS-active Ag films can be reproducibly fabricated on glass by the thermal decomposition of layered silver alkanecarboxylates.
Perfluorocarboxylate-stabilized silver nanoparticles have been prepared uniformly via the thermal decomposition of layered silver perfluorocarboxylates (AgCO2(CF2)nCF3, n = 10, 12, 14 and 16).
The adsorption behavior of 1,4-benzenedithiol (1,4-BDT) on colloidal gold and silver surfaces has been investigated by means of surface-enhanced Raman scattering (SERS). 1,4-BDT chemisorbed dissociatively on both gold and silver surfaces but as mono- and dithiolate, respectively. Regardless of the bulk concentration of 1,4-BDT, only a monolayer was assembled on the silver surface with a flat orientation by forming two Ag-S bonds. On the gold surface, the monothiolate species,1,4-BDT(-1), appeared to assume a rather flat orientation at a very low surface coverage, but as the surface coverage was increased, the adsorbate took a perpendicular orientation. Furthermore, when the bulk concentration of 1,4-BDT was close to that required for a full-monolayer coverage limit, a band assignable to the S-S stretching vibration appeared at approximately 536 cm(-1) in the gold sol SERS spectra. A separate ellipsometry measurement performed with vacuum-evaporated gold substrates revealed that up to tetralayers could be assembled on gold in 1 mM n-hexane solution of 1,4-BDT while at best a bilayer formed in either methanol or ethanol solution. The different adsorbate structure of 1,4-BDT on gold and silver was overall quite comparable to that of p-xylene-alpha,alpha'-dithiol. Copyright 2001 Academic Press.
To understand the binding nature of organoselenium compounds on gold, we have examined the adsorption behavior of several representative organoselenium compounds, i.e., benzeneselenol (BSe), diphenyl diselenide, dibenzyl diselenide, dioctyl diselenide, and benzyl phenyl selenide (BPSe) on the Au surface by virtue of surface-enhanced Raman spectroscopy (SERS). BSe chemisorbs on gold as selenolate with a tilted orientation. Upon adsorption, the Se-Se bonds of diselenides are cleaved to form selenolates, analogous to the formation of thiolate monolayers from disulfides. BPSe adsorbs on gold without any C-Se bond scission. The benzyl moiety of BPSe assumes a rather vertical stance while the phenyl moiety is more tilted to the gold surface. Copyright 2001 Academic Press.
The effect of poly(ethylenimine) (PEI) dissolved in water on the surface pressure-area isotherm of oleic acid (OA) at the air/water interface was investigated. On a concentrated PEI solution, the isotherm of the OA monolayers exhibited a noticeable difference as a function of subphase pH. PEI caused the collapse pressure of the OA monolayer to increase up to 45 mN/m, due to a stronger acid-base-type interaction occurring between the amine group of the PEI and the carboxyl group of OA; on a pure water subphase, the collapse pressure was;28 mN/m. On the other hand, owing to a stronger OA-PEI interaction, the OA monolayers favored a liquid-expanded state more on the PEI-containing water subphase than on the pure water. From the QCM measurement, each OA molecule appeared to interact, on average, with 4.3-5.8 ethylenimine repeating units at basic pHs. We also found that OA multilayers could be assembled on a hydrophilic substrate by a Z-type Langmuir-Blodgett (LB) deposition in a PEI-containing subphase at basic pHs. The ATR-IR spectral data revealed that, in a Z-type LB film, the headgroup of OA was mostly present as carboxylate, interacting in an ionic state with the protonated amine groups of PEI. In acidic conditions, neither a Y-type nor a Z-type deposition was really accomplished. Nonetheless, the ATR-IR spectral data suggested that OA molecules should exist in a monomeric state in a LB film assembled at acidic pHs without PEI while they would form intermolecular hydrogen bridges and/or dimers in the presence of PEI. Copyright 2000 Academic Press.
Interior tertiary amine groups of PAMAM-OH dendrimers (hydroxyl-terminated polyamidoamine, PAMAM) were modified by methylation to make these polymers have a more cationic character, which enabled electrostatic interaction between PAMAM-OH and plasmid DNA. A methylation reaction was dose-dependent, producing internally quaternized PAMAM-OH (QPAMAM-OH), thereby making tertiary amine/quaternary amine ratio adjustment possible. More highly condensed particles of plasmid DNA were formed as the degree of quaternization increased, whereas unmodified polymer (PAMAM-OH) could not. The location of positive charges in the internal position of QPAMAM-OH resulted in the formation of neutral polyplexes in which zeta potential leveled off near the zero value even at high charge ratios (+/-) of 10. A light scattering experiment showed that the polyplex formed by QPAMAM-OH was very small with the size of 53.3 nm at the optimum condition. QPAMAM-OH/DNA polyplexes were round-shaped with the more compact and small particles formed as the charge ratio increased. QPAMAM-OH showed much reduced cytotoxicity compared with starburst PAMAM and branched polyethyleneimine (PEI) in which shielding of interior positive charges by surface hydroxyls might be the reason for this favorable result. These results suggest that QPAMAM-OH could be a promising tool as a nonviral vector both by itself and in conjugated form with targeting ligands.
Biodegradable cross-linked poly(beta-amino ester) (CLPAE) was synthesized by Michael addition of pentaerythritol triacrylate and N,N-dimethylethylenediamine and modified with aminohexanoic acid and lysine to CLPAE-Ahx and CLPAE-Lys, respectively, for a gene delivery system. They could self-assemble with plasmid DNA, forming nanosized polyplexes, and CLPAE-Ahx polyplex released plasmid DNA slowly during a week through stepwise degradation. The polymers showed minimal cytotoxicity on 293 cells due to their biodegradability and biocompatibility. Transfection efficiencies of CLPAE-Ahx and CLPAE-Lys were comparable to that of PEI in 293 cells and C2C12 cells. Additionally, high transfection of CLPAE-Ahx on primary rat aorta vascular smooth muscle cells (SMC) and primary mouse embryonic fibroblast cells (MEF) shows a potential for a gene delivery system on primary cells, restenosis treatment of human SMC, and MEF cell function research. In conclusion, CLPAE-Ahx could be used as a nontoxic and highly efficient gene delivery system.
A novel triblock copolymer, PAMAM-block-PEG-block-PAMAM was synthesized and applied as a gene carrier. PAMAM dendrimer is proven to be an efficient gene carrier itself, but it is associated with certain problems such as low water solubility and considerable cytotoxicity. Therefore, we introduced PEG to engineer a nontoxic and highly transfection efficient polymeric gene carrier because PEG is known to convey water-solubility and biocompatibility to the conjugated copolymer. This copolymer could achieve self-assembly with plasmid DNA, forming compact nanosized particles with a narrow size distribution. Fulfilling our expectations, the copolymer was found to form highly water-soluble polyplexes with plasmid DNA, showed little cytotoxicity despite its poor degradability, and finally achieved high transfection efficiency comparable to PEI in 293 cells. Consequently, these data show that an approach involving the introduction of PEG to create a tree-like cationic copolymer possesses a great potential for use in gene delivery systems.