Honggon Kim

Imidazolium zinc tetrahalide-catalyzed coupling reaction of CO2 and ethylene oxide or propylene oxide

Abstract Imidazolium zinc tetrahalides, (1-R-3-methylimidazolium) 2 ZnX 2 Y 2 ( R =CH 3 , C 2 H 5 , n -C 4 H 9 , CH 2 C 6 H 5 ; X=Cl, Br; Y=Cl, Br), prepared by reacting ZnX 2 with (1-R-3-methylimidazolium)Y, were found to have surprisingly high activities for the coupling reaction of CO 2 and ethylene oxide or propylene oxide to produce corresponding cyclic carbonate. The catalytic activity of imidazolium zinc tetrahalide was greatly influenced by the nature of halide groups bonded to the zinc center. The catalytic activity was found in the order of [ZnBr 4 ] 2− >[ZnBr 2 Cl 2 ] 2− ⪢[ZnCl 4 ] 2− . The turnover frequencies (TOF: h −1 ) increased with increasing temperature, but remained almost unchanged with the increase of pressure.

Electrodynamically sprayed thin films of aqueous dispersible graphene nanosheets: highly efficient cathodes for dye-sensitized solar cells.

Highly efficient cathodes for dye-sensitized solar cells (DSSCs) were developed using thin films of graphene nanosheets (GNS), which were fabricated by the electrospray method (e-spray) using aqueous dispersions of chemically driven GNS. The e-sprayed GNS films had the appropriate properties to be an efficient counter electrode (CE) for DSSCs; sufficient electrocatalytic activity for I(-)/I3(-) redox couples and low charge transfer resistance (RCT) at the CE/electrolyte interface as characterized by cyclic voltammetry and electrochemical impedance analysis. The performance of the GNS film based CEs was optimized by manipulating the density of surface chemical functional groups and plane conjugation of GNS via post thermal annealing (TA). Upon TA, the oxygen-containing surface functional groups, which have been shown to improve electrocatalytic activity of carbon based materials, were significantly reduced, while the electrical conductivity was enhanced by ∼40 times. The improvement of electrocatalytic activity and fill factor (FF) with reduced RCT of DSSCs after TA was primarily attributed to the increased charge transport within the GNS films, while the chemically prepared GNS typically contained sufficient defects, edges and surface functional groups for electrocatalysis. The performance of the DSSCs using our GNS-CEs was nearly identical (>95%) to the DSSCs using the state-of-the-art CE, thermolytically prepared Pt crystals. Our e-sprayed GNS-CE based DSSCs had a higher FF (69.7%) and cell efficiency (6.93%) when compared previously reported graphene based CEs for DSSCs, demonstrating the outstanding properties of graphene as the electrodes in electrochemical devices.

Use of a real time continuous glucose monitoring system as a motivational device for poorly controlled type 2 diabetes.

OBJECTIVE The use of a real time continuous glucose monitoring system (RT-CGM) was studied as a behavior modification tool and the effectiveness of a RT-CGM in glucose control for patients with type 2 diabetes was determined. METHODS We conducted a prospective, open-label, randomized, controlled clinical trial in 65 patients with poorly controlled type 2 diabetes (8.0</=HbA1c</=10%) over a 3-month period. The intervention group was monitored monthly with a RT-CGM (three days at a time for 3 months) and the control group continued self-monitoring blood glucose (SMBG) at least four times a week for 3 months. RESULTS The HbA1c of the RT-CGM group was significantly reduced after 12 weeks compared with the SMBG group (9.1+/-1.0% to 8.0+/-1.2% vs. 8.7+/-0.7% to 8.3+/-1.1%, respectively; P=0.004). In the RT-CGM group, there was a significant reduction in total daily calorie intake, weight, body mass index (BMI), and postprandial glucose level, and a significant increase in total exercise time per week after 3 months. CONCLUSIONS We demonstrated that the RT-CGM was useful in modifying a patients diet and exercise habits and could induce better glycemic control than SMBG for patients with type 2 diabetes.

Serum osteoprotegerin levels are associated with inflammation and pulse wave velocity

Objective  We examined the association between serum osteoprotegerin (OPG) levels, systemic inflammation and arterial stiffness in normal and diabetic patients.

Serum retinol-binding protein 4 levels are elevated in non-alcoholic fatty liver disease

Objective  Retinol‐binding protein 4 (RBP4) is a recently identified adipokine that is elevated in the serum in several insulin‐resistant states. We investigated the relationship between non‐alcoholic fatty liver disease (NAFLD) and serum RBP4 in nondiabetic adults.

Highly efficient copper-zinc-tin-selenide (CZTSe) solar cells by electrodeposition.

Highly efficient copper-zinc-tin-selenide (Cu2ZnSnSe4 ; CZTSe) thin-film solar cells are prepared via the electrodepostion technique. A metallic alloy precursor (CZT) film with a Cu-poor, Zn-rich composition is directly deposited from a single aqueous bath under a constant current, and the precursor film is converted to CZTSe by annealing under a Se atmosphere at temperatures ranging from 400 °C to 600 °C. The crystallization of CZTSe starts at 400 °C and is completed at 500 °C, while crystal growth continues at higher temperatures. Owing to compromises between enhanced crystallinity and poor physical properties, CZTSe thin films annealed at 550 °C exhibit the best and most-stable device performances, reaching up to 8.0 % active efficiency; among the highest efficiencies for CZTSe thin-film solar cells prepared by electrodeposition. Further analysis of the electronic properties and a comparison with another state-of-the-art device prepared from a hydrazine-based solution, suggests that the conversion efficiency can be further improved by optimizing parameters such as film thickness, antireflection coating, MoSe2 formation, and p-n junction properties.

Water-Based Thixotropic Polymer Gel Electrolyte for Dye-Sensitized Solar Cells

For the practical application of dye-sensitized solar cells (DSSCs), it is important to replace the conventional organic solvents based electrolyte with environmentally friendly and stable ones, due to the toxicity and leakage problems. Here we report a noble water-based thixotropic polymer gel electrolyte containing xanthan gum, which satisfies both the environmentally friendliness and stability against leakage and water intrusion. For application in DSSCs, it was possible to infiltrate the prepared electrolyte into the mesoporous TiO2 electrode at the fluidic state, resulting in sufficient penetration. As a result, this electrolyte exhibited similar conversion efficiency (4.78% at 100 mW cm(-2)) and an enhanced long-term stability compared to a water-based liquid electrolyte. The effects of water on the photovoltaic properties were examined elaborately from the cyclic voltammetry curves and impedance spectra. Despite the positive shift in the conduction band potential of the TiO2 electrode, the open-circuit voltage was enhanced by addition of water in the electrolyte due to the greater positive shift in the I(-)/I3(-) redox potential. However, due to the dye desorption and decreased diffusion coefficient caused by the water content, the short-circuit photocurrent density was reduced. These results will provide great insight into the development of efficient and stable water-based electrolytes.

Completely Transparent Conducting Oxide-Free and Flexible Dye-Sensitized Solar Cells Fabricated on Plastic Substrates

To achieve commercialization and widespread application of next-generation photovoltaics, it is important to develop flexible and cost-effective devices. Given this, the elimination of expensive transparent conducting oxides (TCO) and replacement of conventional glass substrates with flexible plastic substrates presents a viable strategy to realize extremely low-cost photovoltaics with a potentially wide applicability. To this end, we report a completely TCO-free and flexible dye-sensitized solar cell (DSSC) fabricated on a plastic substrate using a unique transfer method and back-contact architecture. By adopting unique transfer techniques, the working and counter electrodes were fabricated by transferring high-temperature-annealed TiO2 and Pt/carbon films, respectively, onto flexible plastic substrates without any exfoliation. The fabricated working electrode with the conventional counter electrode exhibited a record efficiency for flexible DSSCs of 8.10%, despite its TCO-free structure. In addition, the completely TCO-free and flexible DSSC exhibited a remarkable efficiency of 7.27%. Furthermore, by using an organic hole-transporting material (spiro-MeOTAD) with the same transfer method, solid-state flexible TCO-free DSSCs were also successfully fabricated, yielding a promising efficiency of 3.36%.

Association between endogenous secretory RAGE, inflammatory markers and arterial stiffness

BACKGROUND Advanced glycation end products (AGEs) and its receptor (RAGE) were known to play a pivotal role in the development of cardiovascular complications of diabetes. We investigated the association between circulating endogenous secretory RAGE (esRAGE) levels, inflammatory markers and arterial stiffness measured using brachial-ankle pulse wave velocity (baPWV). METHODS The study subjects were composed of 76 type 2 diabetic patients and 78 age- and sex-matched non-diabetic subjects. RESULTS Circulating esRAGE levels were significantly lower in subjects with type 2 diabetes (0.237+/-0.123 ng/ml vs. 0.307+/-0.177 ng/ml, p=0.005), and those levels were inversely correlated with body mass index (BMI), waist circumference, blood pressure, triglyceride, fasting glucose level and insulin resistance. Furthermore, esRAGE levels were significantly associated with adiponectin (r=0.164, p=0.044), interleukin-6 (IL-6) (r=-0.242, p=0.009) levels and baPWV (r=-0.296, p<0.001). Multiple regression analysis showed that fasting insulin, IL-6, glucose level and insulin resistance are major factor determining esRAGE (R(2)=0.186). Moreover, baPWV was found to be associated with age, systolic blood pressure, triglyceride, sex, BMI, fasting insulin and esRAGE level (R(2)=0.583). CONCLUSIONS Circulating esRAGE levels were significantly lower in type 2 diabetic patients, and were associated with inflammation and arterial stiffness. These results suggest that esRAGE may play an important role on ligand-RAGE interaction propagated inflammation and atherosclerosis.

Nanoscopic Management of Molecular Packing and Orientation of Small Molecules by a Combination of Linear and Branched Alkyl Side Chains

We synthesized a series of acceptor-donor-acceptor-type small molecules (SIDPP-EE, SIDPP-EO, SIDPP-OE, and SIDPP-OO) consisting of a dithienosilole (SI) electron-donating moiety and two diketopyrrolopyrrole (DPP) electron-withdrawing moieties each bearing linear n-octyl (O) and/or branched 2-ethylhexyl (E) alkyl side chains. X-ray diffraction patterns revealed that SIDPP-EE and SIDPP-EO films were highly crystalline with pronounced edge-on orientation, whereas SIDPP-OE and SIDPP-OO films were less crystalline with a radial distribution of molecular orientations. Near-edge X-ray absorption fine structure spectroscopy disclosed an edge-on orientation with a molecular backbone tilt angle of ∼22° for both SIDPP-EE and SIDPP-EO. Our analysis of the molecular packing and orientation indicated that the shorter 2-ethylhexyl groups on the SI core promote tight π-π stacking of the molecular backbone, whereas n-octyl groups on the SI core hinder close π-π stacking to some degree. Conversely, the longer linear n-octyl groups on the DPP arms facilitate close intermolecular packing via octyl-octyl interdigitation. Quantum mechanics/molecular mechanics molecular dynamics simulations determined the optimal three-dimensional positions of the flexible alkyl side chains of the SI and DPP units, which elucidates the structural cause of the molecular packing and orientation explicitly. The alkyl-chain-dependent molecular stacking significantly affected the electrical properties of the molecular films. The edge-on oriented molecules showed high hole mobilities in organic field-effect transistors, while the radially oriented molecules exhibited high photovoltaic properties in organic photovoltaic cells. These results demonstrate that appropriate positioning of alkyl side chains can modulate crystallinity and molecular orientation in SIDPP films, which ultimately have a profound impact on carrier transport and photovoltaic performance.