Effects of Teaching Model for Hot Conceptual Change on Students’ Chemistry Conceptions

For decades, conceptual change teaching models have been continually developed to promote students conception of science. The recent Teaching Model for Hot Conceptual Change (TMHCC) proposed by Kural and Kocakulah (2016) used the support of motivational and metacognitive strategies to support change in student physics conception. Although the model worked well in Physics, its effects on students’ chemistry concept had never been studied. This study was a one group pretest-posttest design which aimed to study the percentage of students who developed chemistry conception after having learned chemistry through TMHCC. Participants were 42 eleventh-grade students who were studying in science program of a public secondary school in Phrae, Thailand. This implementation spent2 months. The research instrument was a two- tier multiple choice test, consisting of 12 items that covered 12 chemistry conceptions. The findings revealed that before and after implementation, students’ average scores in chemistry conception test were 24.07% and 38.12% respectively. The three highest frequencies of chemistry conception that students developed their chemistry conceptions were the concepts of “Nomenclature of terminal triple bond” (76.19%), “Nomenclature of alkene” (69.05%), and “Isomer” (69.05%). The frequencies of students who had no change in some chemistry concepts were founded in the concepts of “Boiling and melting point of alcohol ether and phenol” (61.90%), “Definition of hydrocarbon” (57.14%), and “Bond-line structure” (54.76%). However, there was a declined in the students’ chemistry concepts partially in the concepts of “Amide formation” (30.95%),“Esterification reaction” (16.67%), and “Boiling and melting points of alcohol, ether, and phenol” (11.90%)

Electrochemical Detection of Ammonia in Aqueous Solution using Fluorescamine: A Comparison of Fluorometric Versus Voltammetric Analysis

荧光胺是一种非荧光剂，其易与伯胺反应形成荧光产物，被普遍用于伯胺的荧光光谱定量分析. 本文利用荧光胺与伯胺反应发展了一种新型灵敏的伏安法用于检测水溶液中的伯胺. 首先，在有、无伯胺的0.1 mol L-1 PBS (pH 9.0)缓冲液中，研究了玻碳电极表面荧光胺的循环伏安电化学行为. 荧光胺的不可逆氧化峰出现在0.70 V (vs. SCE)，当加入伯胺时，在0.46 V (vs. SCE)出现另一不可逆的氧化峰，为荧光胺与伯胺反应的产物. 继续加入氨水，荧光胺的氧化峰变弱，反应产物的氧化峰则由于荧光胺按反应化学计量比随氨消耗增多而随之增大. 上述两个阳极峰分别对应于荧光胺及其反应产物，采用方波伏安和荧光光谱技术可实现水溶液中伯胺的定量检测. 在0 ~ 60 μmol L-1氨浓度范围内，该反应产物方波伏安检测成线性响应. S/N = 3或3σ时检测下限分别为0.71 μmol L-1和3.17 μmol L-1，与荧光法检测的结果相近.Fluorescamine is a non-fluorescent reagent widely used for the quantitative determination of primary amines by fluorescence spectroscopy as it reacts readily with primary amines to form a fluorescent product. In this work, a new sensitive voltammetric method for the detection of ammonia in aqueous solution by the reaction with fluorescamine has been developed. First, the electrochemical behaviour of fluorescamine in the absence and presence of ammonia was investigated in 0.1 mol L-1 borate buffer solution (pH 9.0) by cyclic voltammetry using a glassy carbon (GC) electrode. As for fluorescamine itself, a well-defined irreversible oxidation peak could be observed at ca. 0.70 V vs. SCE. When ammonia was added to the fluorescamine solution, another irreversible oxditaion peak corresponding to the oxidation of the reaction product formed between fluorescamine and ammonia could be observed at ca. 0.46 V vs. SCE. Upon the addition of ammonia, the oxidation peak of fluorescamine became smaller while the oxidation peak of the reaction product formed increased in height, due to the stoichiometric chemical consumption of fluorescamine by ammonia and the formation of the product during the reaction, respectively. These two anodic peaks corresponding to the oxidation of fluorescamine and its fluorescent product formed were then used for the quantitative detection of ammonia, explored by square wave voltammetry and by fluorescence spectroscopy. The square wave voltammetric response of the reaction product formed showed a linear response over ammonia concentration range of 0 to 60 μmol L-1. The limits of detection (LOD) was found to be 0.71 μmol L-1 and 3.17 μmol L-1 determined based upon Signal/Noise (S/N) = 3 and 3σ, respectively. These limits of detection are similar to those obtained with the fluorometric method.Syngenta are acknowledged for partial funding of this work.Syngenta are acknowledged for partial funding of this work.作者联系地址：牛津大学化学系，物理化学与理论化学实验室，英国 牛津OX1 3QZAuthor's Address: Department of Chemistry, Physical and Theoretical Chemistry Laboratory, University of Oxford, South Parks Road, Oxford OX1 3QZ, United Kingdom通讯作者E-mail：[email protected]

Phenazine virulence factor binding to extracellular DNA is important for Pseudomonas aeruginosa biofilm formation

Bacterial resistance to conventional antibiotics necessitates the identification of novel leads for infection control. Interference with extracellular phenomena, such as quorum sensing, extracellular DNA integrity and redox active metabolite release, represents a new frontier to control human pathogens such as Pseudomonas aeruginosa and hence reduce mortality. Here we reveal that the extracellular redox active virulence factor pyocyanin produced by P. aeruginosa binds directly to the deoxyribose-phosphate backbone of DNA and intercalates with DNA nitrogenous base pair regions. Binding results in local perturbations of the DNA double helix structure and enhanced electron transfer along the nucleic acid polymer. Pyocyanin binding to DNA also increases DNA solution viscosity. In contrast, antioxidants interacting with DNA and pyocyanin decrease DNA solution viscosity. Biofilms deficient in pyocyanin production and biofilms lacking extracellular DNA show similar architecture indicating the interaction is important in P. aeruginosa biofilm formation

A green approach to Fenton chemistry: mono-hydroxylation of salicylic acid in aqueous medium by the electrogeneration of Fenton's reagent

First, the electrochemical characteristics of Fenton's reagent (Fe(iii), Fe(ii) and hydrogen peroxide), including its catalytic (EC′) behaviour were investigated. Second, the electrogeneration of hydrogen peroxide by a two-electron reduction of dissolved oxygen was conducted at a carbon electrode in a divided electrolysis cell and the concentration of hydrogen peroxide obtained was determined by the titration. The two approaches were then combined to give a one-pot, relatively green approach to aromatic hydroxylation reactions, with the electro-Fenton method allowing the iron to be used catalytically and the oxygen/water employed as the hydroxylation reagent by the in situ production of hydrogen peroxide. In particular, the preparative-scale hydroxylation of salicylic acid has been studied in an oxygen-saturated 0.1 M Na 2SO 4 pH 3.0 solution containing 5 mM Fe(ii) and 5 mM salicylic acid at the controlled potential of -1.0 V vs. SCE. The study showed that after the attack of the hydroxyl radical produced in situ by the electro-Fenton process on salicylic acid, 2,3- and 2,5-dihydroxybenzoic acids were detected as primary monohydroxylated products with the highest yield of ca. 21.6 ± 2.5%. © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2012