Jin Ku Cho

Direct transformation of cellulose into 5-hydroxymethyl-2-furfural using a combination of metal chlorides in imidazolium ionic liquid

Direct transformation of cellulose into HMF was carried out using a combination of metal chlorides in ionic liquid [EMIM]Cl. From high throughput screening of various metal chlorides, a combination of CrCl2 and RuCl3 was found as the most effective catalyst. HMF was directly afforded from cellulose in nearly 60% yield. Gram scale-up synthesis of HMF was successfully performed from cellulose using CrCl2 and RuCl3. Furthermore, lignocellulosic raw material reed could be directly converted into HMF and furfural in reasonable yields under these conditions.

Synthesis of carbohydrate biomass-based furanic compounds bearing epoxide end group(s) and evaluation of their feasibility as adhesives

Current issues of energy and environment prompt us to replace fossil-based resources with renewable and sustainable ones. In this regard, carbohydrate biomass photosynthesized from atmospheric carbon dioxide attracts much attention due to its abundance and availability. Recently, furanic compounds that can be derived from carbohydrate biomass are highlighted as promising substitutes for aromatic compounds that are totally dependent on petroleum reforming processes. In this article, we report on several carbohydrate biomass-based furanic compounds as alternatives to petroleum-based adhesives. Furanic compounds bearing epoxide end group(s) were synthesized from renewable and sustainable carbohydrate biomass-based compounds (>70% yields). Another bis-epoxy furanic compound with a mimetic structure of bisphenol A (BPA) was also synthesized from xylose-derived 2-furan carboxylic acid and acetone (39% overall yield). In particular, epoxy groups were efficiently introduced to the hydroxymethyl functionality attached by furanic cores under the bi-phasic solvent system using phase transfer catalysis. Cationic photo-curing kinetic profiles of synthetic compounds were investigated in terms of heat flow integrals using photo-DSC. It was found that their halftime values (t 1/2), representing curing rates, ranged from 0.54 to 1.15 min when irradiated with 40 mW/cm2 UV light. When synthetic furanic compounds functionalized by epoxide group(s) were used for bonding polycarbonate by cationic photo-curing, we noted that tensile-shear strength of PC joints bonded with biomass-based furan mono-epoxide having furan ring was greater (4.7 MPa) than that of joints bonded with petrochemical-based phenyl glycidyl ether having phenyl ring (2.6 MPa). When bonded with di-epoxide functionalized furan di-epoxide, tensile-shear strength of PC joint was 3.5 MPa after photo-curing for 3 min at 40 °C. However, bis-furan di-epoxide (bFdE), the mimetic compound of BPA showed lower tensile-shear strength (approximately 1 MPa) due to structural features of bFdE, such as rigidity and hydrophobic property.

Tuning Helical Twisting Power of Isosorbide-Based Chiral Dopants by Chemical Modifications

Isosorbide-based chiral dopants (ICD) with various substituent groups were newly synthesized to control their helical twisting powers (HTP). Phase transition behaviors of ICD molecules were first investigated by combined techniques of differential scanning calorimetry, wide-angle X-ray diffraction, and cross-polarized optical microscopy. ICD with n-hexyloxy end groups formed the multiple ordered phases, and those with methoxy or acetoxy end groups exhibited a simple crystal-to-isotropic transition. Energy-minimized chemical conformations of ICD molecules revealed that all the ICDs had twisted conformations and that the extension of the benzoyl ester moiety induced a higher twisted conformation. By varying substitution groups, HTPs of ICDs were controlled from 26.6 to 80.2 μm−1. Particularly, ICD with an acetoxy end group (ICD-2) showed the largest HTP. It was also realized that by controlling the content of ICD-2 from 3.0 to 4.5 mol%, the helical pitch length of cholesteric LC mixture was adjusted to reflect a specific visible light.

A biobased photocurable binder for composites with transparency and thermal stability from biomass-derived isosorbide

A biobased photocurable binder was synthesized from isosorbide in a high yield (91%) and used as a binder for transparent glass fabric composites. The photocurable isosorbide binder showed a lower refractive index (n = 1.489) than that of glass (n = 1.560) and low viscosity (48.6 cP at 25 °C) owing to the wedge-shaped fused ring structure of the isosorbide moiety. Transparent glass fabric composites were prepared by refractive index matching using a cardo-type fluorene based binder (n = 1.583) as a co-binder. A glass fabric composite photocured with equal wt% of the cardo- and isosorbide-based binder showed 85% of transmittance at 550 nm by UV-visible spectroscopy. It also showed a considerably good coefficient of thermal expansion (α1 = 16.3 ppm K−1) and glass transition temperature (142 °C by DMA). As the wt% of the isosorbide-based binder increased, the network structure of the binder mixture became tight to give a higher glass transition temperature but the composites transparency was decreased.

Folic acid-tethered poly(N-isopropylacrylamide)–phospholipid hybrid nanocarriers for targeted drug delivery

A series of temperature-responsive lipopolymers have been synthesized by bioconjugating poly(N-isopropylacrylamide)n (n = 25, 40, 60) onto three different phospholipids by the combination of reversible addition fragmentation chain transfer polymerization and azide-alkyne click reactions. To achieve the active targeting of cancer cells, folic acid (FA) has also been tethered to the resulting hybrid materials. The doxorubicin (Dox) encapsulated uniform nanocarriers (150 nm in diameter) fabricated by the self-assembly of the lipopolymers display temperature responsive controlled release. The FA receptor-mediated delivery of Dox was then assessed using KB cell lines, and the anti-cancer activity was assessed by the blocking of folic acid receptors. The FA-tethered lipopolymers showing temperature-responsiveness are advantageous for the cell-specific release of Dox, potentiating their anti-cancer activity.

Bio-based chiral dopants having an isohexide skeleton for cholesteric liquid crystal materials

Chiral dopants were synthesized from bio-based epimeric isohexides (glucose-derived isosorbide and mannose-derived isomannide) and their phase transition behaviors and abilities for developing cholesteric liquid crystal (CLC) films were examined with a consideration of the core structure. In spite of lower reactivity of the endo hydroxy group of isomannide caused by the steric hindrance and intermolecular hydrogen bonding, final synthetic yields of chiral dopants bearing an isomannide core (64.5% for IH-2 and 65.0% for IH-4) did not show conspicuous difference compared with chiral dopants bearing isosorbide (68.4% for IH-1 and 74.0% for IH-3). On the other hand, in phase transition behaviors, chiral dopants bearing an isomannide core showed lower crystalline and melting temperatures than IH-1, IH-3 despite of the same substituents. The helical twisting power (HTP) of chiral dopants bearing isosorbide (IH-1 and IH-3) was higher than that of chiral dopants bearing isomannide (IH-2 and IH-4). The calculated HTPs of IH-1 and IH-3 were 26.6 and 42.1 μm−1, respectively. In the case of IH-3, the helical pitch length of CLC could be adjusted to reflect visible light by controlling its amount and showed best performance in the range 5.0 to 7.0 mol%. In contrast to IH-1 and IH-3, it was found that IH-2 and IH-4 could not induce CLC films that reflect visible light.