Solvolysis Reaction Kinetics, Rates and Mechanism for Phenyl N-Phenyl Phosphoramidochloridate

Choi, Hojune,Yang, Kiyull,Koh, Han Joong,Koo, In Sun Korean Chemical Society 2014 Bulletin of the Korean Chemical Society Vol.35 No.8

The rate constants of solvolysis of phenyl N-phenyl phosphoramidochloridate (PhNHPO(Cl)OPh, Target Compound-TC1) have been determined by a conductivity method. The solvolysis rate constants of TC1 are well correlated with the extended Grunwald-Winstein equation, using the $N_T$ solvent nucleophilicity scale and YCl solvent ionizing scale, and sensitivity values of $0.85{\pm}0.14$ and $0.53{\pm}0.04$ for l and m, respectively. These l and m values were similar to those obtained previously for the complex chemical substances dimethyl thiophosphorochloridate; N,N,N',N'-tetramethyldiamidophosphorochloridate; 2-phenyl-2-ketoethyl tosylate; diphenyl thiophosphinyl chloride; and 9-fluorenyl chloroformate. As with the five previously studied solvolyses, an $S_N2$ pathway is proposed for the solvolyses of TC1. For four representative solvents, the rate constants were measured at several temperatures, and activation parameters (${\Delta}H^{\neq}$ and ${\Delta}S^{\neq}$) were estimated. These activation parameters are also in line with the values expected for an $S_N2$ reaction.

Improved Performance of Flexible Cu₂ZnSn(S,Se)₄ Thin Film Solar Cells by Ge Doping

Hojun Choi,Jinhyeok Kim 한국신재생에너지학회 2022 AFORE Vol.2022 No.9

Design and Synthesis of Hollow Mesoporous Zirconia by Tannic Acid/Formaldehyde Resin

Hojun Choi,Jeonghun Kim 한국신재생에너지학회 2022 AFORE Vol.2022 No.9

Biodistribution of Exosomes and Engineering Strategies for Targeted Delivery of Therapeutic Exosomes

Choi Hojun,Choi Yoorim,임화영,Mirzaaghasi Amin,Yoo Jae-Kwang,최철희 한국조직공학과 재생의학회 2021 조직공학과 재생의학 Vol.18 No.4

Exosomes are cell-secreted nano-sized vesicles which deliver diverse biological molecules for intercellular communication. Due to their therapeutic potential, exosomes have been engineered in numerous ways for efficient delivery of active pharmaceutical ingredients to various target organs, tissues, and cells. In vivo administered exosomes are normally delivered to the liver, spleen, kidney, lung, and gastrointestinal tract and show rapid clearance from the blood circulation after systemic injection. The biodistribution and pharmacokinetics (PK) of exosomes can be modulated by engineering various factors such as cellular origin and membrane protein composition of exosomes. Recent advances accentuate the potential of targeted delivery of engineered exosomes even to the most challenging organs including the central nervous system. Major breakthroughs have been made related to various imaging techniques for monitoring in vivo biodistribution and PK of exosomes, as well as exosomal surface engineering technologies for inducing targetability. For inducing targeted delivery, therapeutic exosomes can be engineered to express various targeting moieties via direct modification methods such as chemically modifying exosomal surfaces with covalent/non-covalent bonds, or via indirect modification methods by genetically engineering exosome-producing cells. In this review, we describe the current knowledge of biodistribution and PK of exosomes, factors determining the targetability and organotropism of exosomes, and imaging technologies to monitor in vivo administered exosomes. In addition, we highlight recent advances in strategies for inducing targeted delivery of exosomes to specific organs and cells.

Correlation of the Rates of Solvolyses of 4-Methylthiophene-2-carbonyl Chloride Using the Extended Grunwald-Winstein Equation

Hojune Choi,구인선 대한화학회 2012 Bulletin of the Korean Chemical Society Vol.33 No.2

The specific rates of sovolysis of 4-methylthiophene-2-carbonyl chloride (1) have been determined in 26 pure and binary solvents at 25.0 oC. Product selectivities are reported for solvolyses of 1 in aqueous ethanol and methanol binary mixtures. Comparison of the specific rates of solvolyses of 1 with those for p-methoxybenzoyl chloride (2) in terms of linear free energy relationships (LFER) are helpful in mechanistic considerations, as is also treatment in terms of the extended Grunwald-Winstein equation. It is proposed that the solvolyses of 1 in binary aqueous solvent mixtures proceed through an SN1 and/or ionization (I) pathway rather than through an associative SN2 and/or addition-elimination (A-E) pathway.

31P NMR and ESI-MS Study of Fenitrothion-Copper Ion Complex: Experimental and Theoretical Study

Hojune Choi,양기열,박종근,구인선 대한화학회 2010 Bulletin of the Korean Chemical Society Vol.31 No.5

31P NMR and ESI-MS studies of Cu2+ binding to Fenitrothion (FN) were performed by experimentally and theoretically. The calculated 31P NMR chemical shifts for FN-Cu2+ complexes are in good agreement with experimental chemical shifts in order, and the results present an important information for organophosphorus pesticide metal complexes. ESI-MS and low energy CID MS/MS experiments of FN-Cu2+ complexes combined with accurate mass measurements give insight into the metal localization and allow unambiguous identification of fragments and hydrolysis products.

Single Electron Transfer (SET) Pathway: Nucleophilic Substitution Reaction of 4-Chloro-7-nitrobenzofurazan with Anilines in MeOH-MeCN Mixtures

Hojune Choi,양기열,이상경,이종팔,구인선 대한화학회 2010 Bulletin of the Korean Chemical Society Vol.31 No.10

A nucleophilic substitution reaction of 4-chloro-7-nitrobenzofurazan (NBF-Cl) with anilines in MeOH-MeCN mixtures was conducted at 25, 35, and 45 oC. Based on the higher βnuc values (1.0 - 1.6) of the reaction and a good correlation of the rate constants with the reduction potentials of the aniline nucleophiles, the present reaction was initiated by a single electron transfer (SET). After this step, the reaction proceeds through a transition state similar to the normal SNAr-Ad.E pathway.

Hyper-inflammatory responses in COVID-19 and anti-inflammatory therapeutic approaches

( Hojun Choi ),( Eui-cheol Shin ) 생화학분자생물학회 2022 BMB Reports Vol.55 No.1

The coronavirus disease 2019 (COVID-19) is an ongoing global pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Patients with severe COVID-19 exhibit hyper-inflammatory responses characterized by excessive activation of myeloid cells, including monocytes, macrophages, and neutrophils, and a plethora of pro-inflammatory cytokines and chemokines. Accumulating evidence also indicates that hyper-inflammation is a driving factor for severe progression of the disease, which has prompted the development of anti-inflammatory therapies for the treatment of patients with COVID-19. Corticosteroids, IL-6R inhibitors, and JAK inhibitors have demonstrated promising results in treating patients with severe disease. In addition, diverse forms of exosomes that exert anti-inflammatory functions have been tested experimentally for the treatment of COVID-19. Here, we briefly describe the immunological mechanisms of the hyper-inflammatory responses in patients with severe COVID-19. We also summarize current anti-inflammatory therapies for the treatment of severe COVID-19 and novel exosome-based therapeutics that are in experimental stages. [BMB Reports 2022; 55(1): 11-19]

Solvolysis Reaction Kinetics, Rates and Mechanism for Phenyl N-Phenyl Phosphoramidochloridate

Hojune Choi,양기열,Han Joong Koh,구인선 대한화학회 2014 Bulletin of the Korean Chemical Society Vol.35 No.8

The rate constants of solvolysis of phenyl N-phenyl phosphoramidochloridate (PhNHPO(Cl)OPh, Target Compound-TC1) have been determined by a conductivity method. The solvolysis rate constants of TC1 are well correlated with the extended Grunwald-Winstein equation, using the NT solvent nucleophilicity scale and YCl solvent ionizing scale, and sensitivity values of 0.85 ± 0.14 and 0.53 ± 0.04 for l and m, respectively. These l and m values were similar to those obtained previously for the complex chemical substances dimethyl thiophosphorochloridate; N,N,N',N'-tetramethyldiamidophosphorochloridate; 2-phenyl-2-ketoethyl tosylate; diphenyl thiophosphinyl chloride; and 9-fluorenyl chloroformate. As with the five previously studied solvolyses, an SN2 pathway is proposed for the solvolyses of TC1. For four representative solvents, the rate constants were measured at several temperatures, and activation parameters (ΔH≠ and ΔS≠) were estimated. These activation parameters are also in line with the values expected for an SN2 reaction.

예비 화학교사들의 유기화학 학업성취도와 Kolb 학습양식과의 상관관계

최호준(Choi Hojune),김봉곤(Kim Bong-Gon) 학습자중심교과교육학회 2021 학습자중심교과교육연구 Vol.21 No.17

목적 본 연구는 예비 화학교사들의 유기화학 학업성취도와 Kolb의 학습양식을 확인하고 이들 간의 상관관계를 확인하기 위한 목적으로 수행되었다. 방법 자료 수집은 경남 소재 예비화학교사 70명을 대상으로 개인차 변인을 분석하기 위해 Kolb의 학습양식 진단 검사지를 통해 시행하였다. 유기화학 학업성취도는 대상 학생들의 유기화학 1, 2 학기 GPA 점수를 수치화하여 사용하였고, 추가적으로 유기화학에 대한 개념 이해도와 학습양식과 상관성을 분석하기 위해서 할로젠화 알킬 단원을 선정하고 문제 해결과정에서 학생들의 사고과정을 알아보기 위해 심층면담을 진행하였다. 결과 연구 대상자들의 Kolb 학습양식 분포는 융합자와 수렴자가 23명(32.9%)으로 가장 많았으며, 적응자 15명(21.4%), 분산자 9명(12.9%) 순 이었다. 유기화학 학업성취도와 Kolb 학습양식과의 상관성을 살펴본 연구 결과 정보를 처리하는 것과는 상관성이 적은 것으로 나타났으며, 정보를 인식하는 것과는 상관성을 보였다. 결론 정보를 인식하는데 있어 감각적으로 인식하는 감각적 학습자 보다는 사고적으로 인식하는 사고적 학습자가 유기화학의 학업성취도가 높게 나타났다. Objectives This study investigates the differences between the Kolb learning styles and the achievements of pre-service chemistry teachers’ who received the organic chemistry course from the same instructor. Methods The study was conducted with 70 students from Department of Chemistry Education in Gyeongnam. Individual differences surveys were classified using the Kolb learning style inventory. In addition, alkyl halide unit was selected to analyze the relationship between the conceptual understanding of organic chemistry and learning style. Results As a result of this study, the distributions of Kolb learning styles of pre-service chemistry teachers were in order of assimilator(32.9%) & convergent, accomodator(21.4%), and diverger (12.9%). The following conclusions were obtained from the relationships analysis between academic achievement of oraganic chemistry and Kolb learning style. Conclusions First, the learning achievement of organic chemistry depends on the information perceiving preference index rather than the type of information processing. Second, the academic achievement of organic chemistry was higher in the thinking learners who perceived thinking rather than the sensory learners who perceived sensibly.