Synthesis, Characterization, and Reactivity of Putative High-Valent Nickel-Oxo Species

Terminal metal-oxo species are important intermediates in many biological systems such as the mononuclear non-heme iron oxygenases that utilize Fe(IV)-oxo intermediates to initiate oxidative transformations. The formation of a stable high-valent metal-oxo complex for late-transition metals is challenging synthetically and terminal metal-oxo ligands for metals in groups nine through twelve are rare. In this work, we synthesized a mononuclear Nickel complex through different oxidation states of +2, +3, and +4 supported by a dianionic, tridentate ligand. We produced a putative Ni(IV) complex by a single sequence reaction between Ni(III)OH and an oxidant, ceric ammonium nitrate (CAN). The reactivity of this proposed Ni (IV) complex is still under investigation as we move to determine the structure and the characterization of the complex. Our ongoing efforts aim to determine the C-H bond functionalization of the Ni(IV) complex

Synthesis & Reactivity of Iron (II) Pyridinediimine Complexes For the Reduction of Nitrite

The activation of small molecules has been studied by the scientific field for many decades as it plays a key role in nature such as photosynthesis and respiration. Many of these reactions are catalyzed by metalloenzymes in nature where the transfer of electrons and protons are coupled for the reaction to move forward. Noncovalent interactions in the secondary coordination sphere of metalloenzymes play an important role in determining the activity and selectivity. Hydrogen bonds are the most common noncovalent interactions that metalloenzymes utilize to control the reactivity in the secondary coordination sphere. Therefore, it is important to develop compounds and catalysts that can move both protons and electrons. Recent studies have been done by several groups on the mechanism of nitrite reduction. Based on those findings, we developed a series of iron (II) pyridinediimine (PDI) complexes that contain pendant bases, with varying pKa values, located in the secondary coordination sphere. These ligands were synthesized, coordinated to iron (II) and reduced under carbon monoxide (CO) to store electrons within the ligand scaffold. These reduced complexes were then protonated to form hydrogen bonds and fine tune the reactivity. These PDI complexes that are capable of storing both electrons and protons were investigated to functionally mimic the metalloenzyme nitrite reductase. To date, the mechanism of nitrite reduction remains unknown. In an attempt to determine how nitrite binds to the metal of our PDI complex, we synthesized a dinitrosyl iron complex. The synthesis of this complex should help to determine the mechanism of nitrite reduction

Implementing Engineering Based STEM Programs in High School Classrooms in the Republic of Korea

In 2022, South Korea announced new national curriculum that implement it from 2023. High school curriculum is about to fully implement the high school credit system, which allows students to choose subjects that suit their needs and career paths. In South Korea, technology education in middle school is a common compulsory subject, but high school technology education is a selective subject and has the name of technology and home-economics. High school technology education experiences difficulties that are not selected in many schools due to the confusion of identity of subject names and social negative perception of technology. The purpose of this is to develop an engineering education program that can be used in high school technology education and to verify its effect on students. To achieve the purpose of this study, an engineering education program was developed and students’ changes through the program were measured. This study was based on a single-group pre-post test design and was conducted with 96 10th grade students. As a result of this study, students’ engineering interest, engineering self-efficacy, and engineering career awareness were statistically significantly improved through the developed engineering education program. This study provides great implications for actively including and utilizing engineering in technology education. In addition, it will give great implication for the direction and program development of high school technology education

GENERATION, CHARACTERIZATION, AND C-H BOND ACTIVATION REACTIVITY BY MONONUCLEAR HIGH-VALENT COBALT(IV) AND NICKEL(IV) NON-OXO COMPLEXES

The study of terminal high-valent transition metal-oxo complexes has increased significantly over the years as it is believed that they are key reactive intermediates for a wide range of biological and industrial catalytic processes. These complexes are powerful oxidants for the activation of strong C-H bonds. The chemical and physical properties of these complexes remain elusive. It is therefore desirable to study the properties and function of these complexes through synthetic models. There have been many efforts and reports of synthetic high-valent metal-oxo complexes of early and middle transition metals (up to group 8 on the Periodic Table of Elements), but as we go beyond group 9, the generation of stable high-valent metal oxo complexes for these transition metals is challenging synthetically. This phenomenon is referred to as the “oxo-wall.” There have been many efforts to break this “oxo-wall” and remains intact to this date. The focus of this research is to study a series of mononuclear cobalt and nickel complexes with oxidation states of +2, +3, and +4. These complexes are supported by a di-anionic, tridentate ligand system and were characterized using various spectroscopic methods such as X-ray crystallography, NMR, EPR, UV-Vis, and DFT computational methods. The generated complexes with an oxidation state of +4 can cleave strong sp3 C-H bonds. This work will inspire to generate more reactive high-valent late transition metal-oxo and non-oxo complexes and understand C-H bond activation in high-valent metal chemistry. Chapter 1 provides a background of synthetic chemistry, generation of high-valent metal-oxo complexes, and the “oxo-wall” theory. Chapter 2 describes the work of the early stages and development of this project leading to how we got to the point in our research currently. Chapter 3 examines and describes the generation, characterization, and reactivity studies of a novel Co(IV)-dinitrate complex. As well as providing preliminary data of a more reactive Co(IV) species. Chapter 4 introduces going beyond cobalt and conducting the similar chemistry with nickel resulting in a high-valent Ni(IV)-nitrate complex. Chapter 5 provides an overall summary and future perspective of the project

Meta-analysis on Students’ Effects of Technology Education Classes under the South Korean National Curriculum

In South Korea, Technology education is one of the national curriculum compulsory subjects, and despite the importance and value, public awareness toward technology and technology education is very low. Whenever the curriculum is revised, the value and place of technology education have been challenged. The purpose of this study is to analyse effects on students of technology education classes. Meta-analysis is conducted to calculate the effect size of technology education classes in the Republic of Korea. Data are collected through an integrated searching engine of Korean academic database. From 2000 to 2022, 61 studies are analysed by Comprehensive Meta Analysis 4.0. The result shows an intermediate effect size in technology education classes. A total of 148 effect sizes are analysed by dividing the subcategories into publishing type, teaching method, school level, experimental type, and dependent variable. For the publishing type, academic journals and thesis papers show the intermediate effect size. Particularly, studies for elementary school level indicate a high effect size, followed by middle school and high school. The dependent variables show intermediate effect sizes of the order of affective variables (e.g., attitude, motivation), psychomotor variable, and cognitive variables (e.g., academic achievement). Based on the findings, this study can make the following recommendations. More studies for proving the value and importance of technology education classes should be conducted. Key Word : Technology Classes, Effect Size, Meta-analysis, Students, South Kore

In vitro modeling of urological diseases by three-dimensional printed miniature bladder

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Quantifying the effects of non-pharmaceutical and pharmaceutical interventions against COVID-19 epidemic in the Republic of Korea: Mathematical model-based approach considering age groups and the Delta variant

Early vaccination efforts and non-pharmaceutical interventions (NPIs) were insufficient to prevent a surge of COVID-19 cases triggered by the Delta variant.  A compartment model that includes age, vaccination, and variants was developed. We estimated the transmission rates using maximum likelihood estimation, and phase-dependent NPIs according to government policies from 26 February to 8 October 2021. Simulations were done to examine the effects of varying  dates of initiation and intensity of eased NPIs, arrival timing of Delta, and speed of vaccine administration. The estimated transmission rate matrices show distinct patterns, with transmission rates of younger groups (0-39 years) much larger with Delta. Social distancing (SD) level 2 and SD4 in Korea were associated with transmission reduction factors of 0.63 to 0.70 and 0.70 to 0.78, respectively. The easing of NPIs to a level comparable to SD2 should be initiated not earlier than 16 October to keep the number of severe cases below Korea's healthcare capacity. Simulations showed that a surge prompted by Delta can be prevented if the number of people vaccinated daily or SD level when Delta arrived was higher. The timing of easing, intensity of NPIs, vaccination speed, and screening measures are key factors in preventing another epidemic wave