Biomedical subjects

Choong-Do Park

Publications and source records attributed to Choong-Do Park.

3 recordsLinked to original sources

PubMed2007

Photo-, thermally, and pH-responsive microgels.

Microgels with photo-, thermally, and pH-responsive properties in aqueous suspension have been synthesized and characterized using dynamic light scattering and UV-visible spectroscopy. The new route involved first preparing poly(N-isopropylacrylamide) (PNIPAM)-allylamine copolymer microgels and a spiropyran photochrome (SP) bearing a carboxylic acid group. Then the functionalized spiropyran was coupled to the microgel via an amide bond. The dark-equilibrated gel particles feature spiropyran molecules in the polar, merocyanine form. After irradiation of visible light, the particle size becomes smaller because spiropyran changes to the relatively nonpolar, closed spiro form. The PNIPAM-SP microgels undergo a volume phase transition in water from a swollen state to a collapsed state with increasing temperature under all light conditions. However, the transition temperature range of the PNIPAM-SP is much broader than that for the PNIPAM without SP. The PNIPAM-SP microgels are monodisperse and self-assemble into a crystalline lattice while in suspension. The UV-visible spectra of an aqueous suspension of PNIPAM-SP microgel in the dark-adapted, merocyanine form showed both an absorption peak around 512 nm due to the merocyanine (giving a reddish color to the suspension) and two sharp peaks from Bragg diffraction of colloidal crystallites. Upon visible irradiation, the 512-nm band bleached significantly due to spiropyran photoisomerization. The spiropyran photoisomerization and accompanying color changes of the suspension were reversible upon alternating dark, UV, and visible light irradiation. Due to the residues of amine groups, the swelling capability of PNIPAM-SP microgels reduces as the pH value is changed from 7 to 10.

Acrylic Resins↗

PubMed2006

All-photonic molecular half-adder.

One molecule acts as both an AND and an XOR Boolean logic gate that share the same two photonic inputs. The molecule comprises a half-adder, adding two binary digits with only light as inputs and outputs, and consists of three covalently linked photochromic moieties, a spiropyran and two quinoline-derived dihydroindolizines. The AND function is based on the absorption properties of the molecule, whereas the XOR function is based on an off-on-off response of the fluorescence to the inputs that results from interchromophore excited-state quenching interactions. The half-adder is simple to operate and can be cycled many times.

Journal Article↗

PubMed2006

Control of nanopore wetting by a photochromic spiropyran: a light-controlled valve and electrical switch.

By modifying the surface of nanoporous alumina membranes using mixtures of a photochromic spiropyran and hydrophobic molecules, it is possible to control the admission of water into the membrane using light. When the spiropyran is in the thermally stable, relatively hydrophobic closed form, the membrane is not wet by an aqueous solution. Upon exposure to UV light, the spiropyran photoisomerizes to the more polar merocyanine form, allowing water to enter the pores and cross the membrane. Thus, the photosensitive membrane acts as a burst valve, allowing the transport of water and ions across the membrane. If the aqueous solution contains ions, then the membrane acts as an electrical switch; photoisomerization leads to a two-order-of-magnitude increase in ionic conductance, allowing a current to flow across the membrane. Exposure to visible light causes photoisomerization of the merocyanine back to the closed, spiro form, but dewetting of the membrane does not occur spontaneously, due to a high activation barrier.

Benzopyrans↗