Jong Man Kim

Molecularly imprinted polymers having amidine and imidazole functional groups as an enzyme-mimetic catalyst for ester hydrolysis

A molecularly imprinted polymer (MIP) having both amidine and imidazole functional groups in the active site has been prepared usingp-nitrophenyl phosphate as a transition state analogue (TSA). The imprinted polymer MIP with amidine and imidazole found to have the highest hydrolysis activity compared with other MIPs with either amidine or imidazole groups only. It is postulated a cooperative effect between amidine and imidazole in the hydrolysis ofp-nitrophenyl methyl carbonate (NPMC) as a substrate when both groups were arranged in proximity by molecular imprinting. The rate enhancement of the hydrolysis by MIP was 60 folds over the uncatalyzed solution reaction and two folds compared with the control non-imprinted polymer CP1 having both functional groups. The enzyme-mimetic catalytic hydrolysis ofp-nitrophenyl acetate by MIP was evaluated in buffer at pH 7.0 withKm of 1.06 mM andkcat of 0.137 h−1.

Patterned polydiacetylene-embedded polystyrene nanofibers based on electrohydrodynamic jet printing

AbstractElectrohydrodynamic (EHD) jet printing is a direct-writing technique which ejects ink through a fine nozzle using an electric field, which has the advantages of high-resolution, rapid printing speed and a wide range of ink selectivity. In this article, the EHD jet printing system is utilized to print patterns of polystyrene (PS) nanofibers. The effect of parameters such as ink concentration, working distance, applied voltage, and stage speed on the diameter of the printed nanofibers was investigated. The EHD jet printing technology is further utilized to print various patterns of polydiacetylene (PDA)-embedded PS nanofibers. The EHD jet printing based nanofiber printing is advantageous over conventional electrospining based approaches in terms of patterned PDA images. In addition, an advanced EHD jet printing system which is adopted for aligned nanofiber printing will expand the application of nanofibers from bio and chemical sensors to tissue engineering and electronics.

Fluorogenic Conjugated Polymer Fibers from Amphiphilic Diacetylene Supramolecules

ConclusionsWe have developed a simple strategy for the preparation of fluorogenic polydiacetylene fibers. The diacetylenic isophthalic acid PCDA-IPA was found to form microfibers when warm aqueous ethanolic solutions are cooled to room temperature. Irradiation of the self-assembled diacetylene wires with 254 nm UV light afforded blue-colored polydiacetylene wires, as evidenced by optical, fluorescence and scanning electron microscopic analyses. Relatively long polymer ribbons (ca. 100 μm) were obtained when 30–50% H2O-EtOH solvent systems are used while much shorter wires (< 10 μm) form in 60% H2O-EtOH. Thus, wire lengths can be varied by changing solvents. Importantly, the nonfluorescent polymerized ribbons were transformed to fluorescent PDAs upon heating. The observations made in this effort should be useful in the development of new and interesting PDA-based materials.

Conjugated polymer-embedded thermochromic strip sensors with a tunable colorimetric Response

ConclusionsIn this effort, we have prepared various types of PDAembedded PVA films and investigated their colorimetric responses to thermal stimulation. Depending on the DA monomers employed, the PDA-embedded PVA films displayed different initial color changing temperatures. In general, DA monomers capable of providing stronger headgroup interactions result in the generation of colorimetrically more stable PDA supramolecules. The observations made in the current investigation should be assist the design of colorimetrically tunable conjugated polymer-embedded polymer films.

Layer-by-layer deposition of polydiacetylene vesicles and linear poly(sulfonates)

ConclusionsWe have prepared a multi-layered polydiacetylene vesicles on a glass substrate employing a layer-by-layer deposition method. A cationic bisdiacetylene monomer was readily prepared and the molecularly assembled monomers in an aqueous solution were photopolymerized to generate polymer vesicles. Layered polydiacetylenes were prepared by alternative deposition of positively charged polydiacetylene vesicles and negatively charged linear polymers such as PSS and PVS. The method described in current investigation should be useful when increase of signal intensity of polydiacetylene-based sensor system is necessary.

Thermochromic Polydiacetylene Supramolecules with Oligo(ethylene oxide) Headgroups for Tunable Colorimetric Response

ConclusionsIn this effort, we have prepared PDA suspensions derived from oligoethylene oxide-containing DA monomers and investigated their colorimetric responses to thermal stimulation. Depending on the DA monomers employed, the PDA supramolecules displayed different initial color changing temperatures. In general, DA monomers having larger headgroups result in the generation of colorimetrically less stable PDA supramolecules. The results described in the current investigation should provide useful information about the design of colorimetrically tunable PDA supramolecules.

Patterned Fluorescence Images with a t-Boc-Protected Coumarin Derivative

We have developed an efficient method for the generation of patterned fluorescence images using a protected precursor molecule. Thet-Boc-protecting group of a coumarin derivative was readily removed from a polymer film upon irradiation with UV light in the presence of a photoacid generator to provide the original properties of the coumarin. Fine fluorescence patterns were obtained when using this photolithographic method.

Unusual photopolymerization behavior of amino Acid-derived polydiacetylene supramolecules.

UV-irradiation of aqueous suspensions of amino acid-derived amphiphilic diacetylene supramolecules promotes a process that involves initial formation of species that absorb at 640 nm followed by the generation of polymers that have longer wavelength (686 nm) absorbance. The initially formed intermediate polydiacetylenes display substantial colorimetric reversibility while the long wavelength absorbing polymers show irreversible thermochromism during heating and cooling cycles. The long wavelength absorbing polydiacetylenes, formed from amino acid-derived amphiphilic diacetylene supramolecules, are suggested to have more planer backbone structures that allow more efficient overlap of the conjugated p-orbitals.

Fluorescence Quenching of a Partially Conjugated Polymer by Hemoglobin

ConclusionsWe have prepared a partially-conjugated water-soluble polymer by simply heating a solution of PPV precursor polymer. The partially conjugated polymer2 obtained by this method was strongly fluorescent and the fluorescence was quenched by proteins such as bovine serum albumin, α-chymotrypsin, and hemoglobin. Hemoglobin was found to be superior to other proteins investigated in terms of quenching ability. The fluorescence quenching of the conjugated polymer2 by hemoglobin is presumably due to the electron transfer from the polymer to heme moieties in the protein. Patterned fluorescence images were readily obtained by spotting hemoglobin on a PPV film by employing a modern array technology.

The solid-phase synthesis of amino acid-derived diacetylene lipids

We prepared amino acid-derived diacetylene monomers using solid-phase organic synthesis. The solidphase synthetic method allowed for the rapid and efficient preparation of functional diacetylenes. Amino acids having hydrophobic sidechains such as alanine, leucine, and phenylalanine, as well as hydrophilic sidechains such as aspartic acid and lysine, were successfully coupled to the diacetylene lipid. The diacetylene monomers prepared in this way were subjected to routine procedures for the generation of polydiacetylene vesicles. Depending on the nature of the side-chains, pink to blue colored polydiacetylenes were generated.