Study of Controlling Secondary Building Units of Metal-organic Frameworks

Department of ChemistryA class of metal-organic frameworks (MOFs) were constructed by polynuclear metal clusters (secondary building unitshereinafter, SBUs) and their coordination with organic linkers (i.e., ligands). Such MOFs have been widely used in the various applications fields such as gas storage and separation, chemical sensing, and catalysis due to their stable structures and possibility of having a diverse set of functions. To make such MOFs have specific functions applicable to the application fields, we need to synthesize MOFs with specific crystal structures by controlling the two determinants of the crystal structures ??? the SBUs per se and/or their coordination with ligands. In this thesis, we reported the two research on controlling SBUs of MOFs. One research deals with the transformation of SBUs in synthesizing a rarely reported ndc-based Zn MOF. The other research deals with the formation of SBUs in synthesizing bdc-based Zn MOFs. For each research, we identified the set of parameters that facilitate the synthesis of MOFs with specific SBUs. First, we conducted the transformation of SBUs in synthesizing a rarely reported ndc-based Zn MOF. We transformed specific MOFs ???Zn MOFs having four handed paddlewheel SBUs linked by N-donor pillars ??? into another MOF ??? MOF having 7-coordinated Zn4O(COO)7 SBUs. We found that the two parameters ??? the presence of Zn+-O- in solution and the basicity of ligands ??? affect the transformation of SBUs. First, the presence of Zn+-O- in solution facilitates the transformation of SBUs. We conducted the transformation of the two same Zn-MOFs in two different solutions ??? one solution contains Zn+-O- in solution and the other solution does not contain Zn+-O- in solution. We found that the Zn-MOF in a solution containing Zn+-O- were transformed into the MOF that we want to obtain (i.e., MOF having 7-coordinated Zn4O(COO)7 SBUs) but the Zn-MOF in the other solution did not. Second, low basicity of ligands facilitates the solid-state transformation. We synthesized three Zn-MOFs by making each of them have different basicity of ligands and found that a Zn-MOF with a low level of basicity of ligands was successfully transformed into the other MOF that we want to obtain (i.e., a MOF having 7-coordinated Zn4O(COO)7 SBUs). We also conducted the formation of diverse SBUs in synthesizing bdc-based Zn MOFs (bdc = benzene-1,4-dicarboxylate). We found that the two parameters ??? the reaction temperature and the molar ratio of precursors (i.e., metal precursors and ligand precursors)??? influence the determination of the SBUs of the bdc-based Zn-MOFs .We found that at lower temperature, a Zn-MOF having Zn3(COO)6 SBUs was successfully formed. Secondly, we found that molar ratio of metal precursors to ligand precursors affects the formation of bdc-based Zn-MOFs. At the molar ratio of Zn(NO3)2??6H2O : H2bdc = 1 : 2, a Zn-MOF having Zn3(COO)6 SBU, to which two terminal DMF solvents are coordinated, was obtained. At the molar ratio of Zn(NO3)2??6H2O : H2bdc = 1 : 4, the other Zn-MOF having Zn3(COO)6(COOH)2 SBU (Not surely determined), which is linked by bdc pillars, was obtained. After studying how to synthesize MOFs, we further explored the possibility of using the MOF that is synthesized by the above-mentioned transformation of SBUs (i.e., 7C-MOF) for CO2 cycloaddition. 7C-MOF has been rarely reported in the academic field, so exploring the characteristics of this MOF that can be applicable into the ???real??? world may contribute to expanding the usage of 7C-MOF. We analyzed 7C-MOF using CO2 sorption isotherm and found that 7C-MOF is capable of adsorbing CO2 molecules. This is because 7C-MOF is an anionic framework and has cation complex [Zn(DMF)6]2+ in its pores. Thus, we expected that 7C-MOF can act as a Lewis catalyst for CO2 cycloaddition. By analyzing product yields (100[mole of cyclic carbonate] / [mole of cyclic carbonate and epoxide]) using H-nuclear magnetic resonance spectroscopy, we found that 7C-MOF can act as a Lewis acid catalyst which facilitates CO2 cycloaddition.ope

Short-term efficacy of intravitreal triamcinolone acetonide for macular edema secondary to retinal vein occlusion that is refractory to intravitreal bevacizumab

Aims: To evaluate the 1-month efficacy of intravitreal triamcinolone acetonide (TA) in treating macular edema secondary to retinal vein occlusion (RVO) that was refractory to intravitreal bevacizumab. Materials and Methods: This retrospective, observational study included 23 eyes from 23 patients with macular edema secondary to RVO. Macular edema that did not respond to two or more consecutive intravitreal bevacizumab injections was treated with intravitreal TA. Central foveal thickness (CFT) and best-corrected visual acuity (BCVA) were compared before and one month after TA injection. Results: Fifteen eyes were diagnosed with central RVO, and eight eyes were diagnosed with branch RVO. All patients were previously treated with 2.4 ± 0.6 intravitreal bevacizumab injections. The TA injection was performed, on average, 5.8 ± 1.4 weeks after the last bevacizumab injection. The CFT before TA injection was 516.6 ± 112.4 μm and significantly decreased to 402.3 ± 159.7 μm after TA therapy (P < 0.001). The logarithm of the minimal angle of resolution BCVA was 0.72 ± 0.34 before TA therapy and was not significantly improved by the treatment (0.67 ± 0.35, P = 0.119), despite a decrease in CFT. However, seven eyes (30.4%) had a BCVA gain of one or more lines. Conclusions: Intravitreal TA therapy was beneficial in some patients with macular edema secondary to RVO that was refractory to intravitreal bevacizumab therapy. This study suggests that intravitreal TA should be considered as a treatment option for refractory macular edema

Characterization and Cu Electroless Plating of Laser-drilled Through-Wafer via-holes in GaN/Al2O3

GaN on Al2O3 was drilled with a high power Nd:YAG laser. Micro-Raman spectroscopy showed that the induced damage was nominal at about 15 μm from the edge of the drilled through-wafer via-holes. Cu plating was accomplished using an electroless plating technique. FIB was employed to expose the interface between electrolessly plated Cu and GaN on the sidewall of the drilled holes, followed by SEM/EDX to confirm that the sidewall of the drilled holes was successfully covered with Cu. Cu electroless plating after laser drilling has the potential to simplify device layout and improve device integration.The research at Korea University was supported by the Korea Research Foundation Grant funded by the Korean Government (KRF- 2006-331-D00126) and by BK21 program

Short-Term Efficacy of Pulsed Radiofrequency Thermal Stimulation on Acupoints for Chronic Low Back Pain: A Preliminary Study of a Randomized, Single-Blinded, Placebo-Controlled Trial

Background. The objective of this study was to evaluate the pain-relief efficacy of thermal stimulation induced by a pulsed radiofrequency (PRF) thermal stimulation applied to acupoints (APs) in patients with low back pain (LBP). The study was designed as a randomized, single-blinded, placebo-controlled trial. Methods. Fifty-six LBP patients whose minimum pain intensity score on a visual analogue scale (VAS, 0-100 mm) was more than 30 mm were randomly allocated to either the placebo-controlled or the treatment group at a 1:1 ratio. The treatment and placebo-controlled groups received PRF thermal stimulation plus cupping therapy and cupping therapy only, respectively. Each patient was scheduled to receive a total of three treatment sessions over one week with allowing a window up to 4 days. Six of the 13 predefined APs were selected differently for each session depending on the change in patient’s symptoms and intensity of pain. The primary outcome was the mean difference between the placebo-controlled and treatment group of VAS changes from the baseline to the end of the follow-up period. Results. The patients’ reported VAS scores from baseline to the end of follow-up (average: 9.8 days) were significantly decreased by 8.036 points (two-sided 95% CI, -11.841 to -4.231) and 13.393 points (two-sided 95% CI: 17.198 to -9.588) in the treatment and the placebo-controlled groups, respectively. However, the change in VAS scores between the treatment group and the placebo-controlled group was not significantly different (2.015 mm, two-sided 95% CI: -5.288 to 9.317). Conclusion. The trial results indicated that treatment with either PRF thermal stimulation with cupping therapy or cupping therapy alone effectively relieved LBP. The efficacy of PRF thermal stimulation combined with cupping therapy was not superior to that of cupping therapy alone. Trial registration number: Clinical Research Information Service (KCT0002137). The trial was registered retrospectively on 10 November, 2016

Ethanol-based green-solution processing of alpha-formamidinium lead triiodide perovskite layers

Manufacturing of perovskite solar cells would benefit from the avoidance of hazardous solvents and multistep processing. Now, Yun et al. report an ethanol-based perovskite precursor solution that does not need an antisolvent step, enabling devices with 25% efficiency. The use of non-toxic or less-toxic solvents in the mass production of solution-processed perovskite solar cells is essential. However, halide perovskites are generally not completely soluble in most non-toxic solvents. Here we report the deposition of dense and uniform alpha-formamidinium lead triiodide (alpha-FAPbI(3)) films using perovskite precursor solutions dissolved in ethanol-based solvent. The process does not require an antisolvent dripping step. The combination of a Lewis base, such as dimethylacetamide (or dimethylsulfoxide), and an alkylammonium chloride (RNH3Cl) in ethanol results in the stable solvation of FAPbI(3). The RNH3Cl added to the FAPbI(3) precursor solution is removed during spin-coating and high-temperature annealing via iodoplumbate complexes, such as PbI2 center dot RNH2 and PbI2 center dot HCl, coordinated with dimethylacetamide (or dimethylsulfoxide). It is possible to form very dense and uniform alpha-FAPbI(3) perovskite films with high crystallinity by combining several types of RNH3Cl. We obtain power conversion efficiencies of 24.3% using a TiO2 electrode, and of 25.1% with a SnO2 electrode