Conceptual profile of chemistry: a framework for enriching thinking and action in chemistry education
AffiliationUniv Arizona, Dept Chem & Biochem
MetadataShow full item record
PublisherROUTLEDGE JOURNALS, TAYLOR & FRANCIS LTD
CitationMelquesedeque Freire, Vicente Talanquer & Edenia Amaral (2019) Conceptual profile of chemistry: a framework for enriching thinking and action in chemistry education, International Journal of Science Education, 41:5, 674-692, DOI: 10.1080/09500693.2019.1578001
Rights© 2019 Informa UK Limited, trading as Taylor & Francis Group
Collection InformationThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at email@example.com.
AbstractUnderstanding the nature of chemical thinking and action, as well as their application and impact on our world should be central goals of chemistry education at all educational levels. However, traditional school chemistry is still mostly focused on having students learn the body of declarative knowledge built over the years in the discipline. Achieving changes in curriculum and teaching practices in this context remains a challenging task. Studies in the history and philosophy of the discipline suggest that chemistry has unique characteristics that need to be recognised and considered in chemistry education. Many of these studies point to a pluralism in the discipline, and in the understanding of and about chemistry, that should be characterised and incorporated into our educational models. In this essay, we have attempted to build such a characterisation using conceptual profiles theory to propose a framework that can be used to enrich and support the thinking and action of chemistry teachers at all educational levels.
Note18 month embargo; published online: 18 February 2019
VersionFinal accepted manuscript
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Structure-activity relationship analysis: Developing glucagon agonists and antagonists for studies of glucagon action in normal and diabetic statesHruby, Victor J.; Azizeh, Bassem Yousef (The University of Arizona., 1996)Several glucagon analogues containing substitutions in the N-terminal region, in particular residues 1, 5, 6, 9 and 10 (histidine, threonine, phenylalanine, aspartic acid and tyrosine, respectively), were synthesized. In addition four β-methylphenylalanine isomers were introduced at position ten to assess the role of these topographical modifications on hormone activity, and to study the effect of constraint and biased conformational preferences of the side chain moieties on biological activity. All the analogues were synthesized by solid-phase methodology, purified to homogeneity by reverse-phase high-performance liquid chromatography, and characterized by electrospray mass spectroscopy, amino acid analysis and thin layer chromatography. Following characterization they were analyzed using rat liver plasma membranes for receptor-binding affinity as well as their ability to stimulate adenylate cyclase. Structure-activity relationship analysis provided critical information about the conformational, chemical and structural properties of amino acid residues required for receptor recognition and signal transduction in the glucagon sequence. His¹ was confirmed to operate along with Asp⁹ for the activation and binding to the glucagon receptor. These new findings should permit the design of more pure and potent glucagon receptor antagonists by focusing on the role of Phe⁶ and other residues in the N-terminal region. A newly developed assay for examining low levels of cAMP accumulation in response to glucagon antagonists, agonists and partial agonists was developed. Previously reported glucagon receptor antagonists had partial agonist activity in rat hepatocytes. This assay system, in conjunction with binding and adenylate cyclase studies in both hepatocytes and liver plasma membranes, redefines the major characteristics of pure glucagon antagonists. The most potent glucagon receptor antagonist [des-His¹, des-Phe⁶, Glu⁹]glucagon-NH₂ was studied using conformational analysis and 2D NMR techniques to analyze the secondary structure of the analogue. Proton resonance assignments using COSY, NOESY and TOCSY in d₆-DMSO were made.
Synthesis and characterization of heme models and spectroelectrochemical studies of heme proteinsWalker, F. Ann; Ding, Xiao Dong (The University of Arizona., 1997)To better understand the relationship between the structure and electronic properties of the iron center and the functions of heme proteins, both naturally occurring heme proteins and synthetically prepared heme models have been studied. The reduction potential (E°') and the pH dependence of E°' of nitrophorin 1 (NP1) and myoglobin (Mb) were determined by spectroelectrochemical techniques. The difference in the electrostatic interaction of the Fe(III) center with buried charged groups in the heme pocket of Mb and NP1 is the major factor that causes the 300 mV difference in E°. The pH dependence of the E°' determined between pH 5.5 and 7.5 is small for both Mb and NP1 because they have the same axial ligands. Three meso-ortho-phenyl substituted porphyrins, (o-F), (o-CF₃) and (2,6-Cl₂)(p-OCH₃)₃TPP and one meso-para-phenyl substituted porphyrin, (p-OCH₃)₄TPP, were synthesized as models of cytochrome b₅ . Cyclic voltammetry was used to measure their reduction potentials. The overall formation constants, logβ₂III and logβ₂II, have been calculated based on the reduction potentials of the iron(III)/(II) couple as a function of N-methylimidazole concentration. The values of logβ₂III are in the order of o-F > o-CF₃ > p-OCH₃ ≈ 2,6-Cl₂, indicating that the electron-donating ability is in the order of o-F < o-CF₃ < p-OCH₃ ≈ 2,6-Cl₂. The overlap and direct transfer of electron density from the halogen to the iron in the product reduces the Lewis acidity of iron(III), resulting in decreased logβ₂III. The order of logβ₂II for N-methylimidazole complexed Fe(II) porphyrinates is similar to that of the Fe(III) complexes, indicating no major difference in the Lewis acidity of Fe(II) as compared to Fe(III). Basket handle porphyrinates with covalently bound methionine and aliphatic amine model ligands (RCH₂SCH₃, RCH₂SCH₃ and RNH₂, RNH₂) were chosen as precusor of cytochrome c and f. The Fe(III) complexes were to be prepared and investigated by electrochemical and spectroscopic techniques. The precursor porphyrin was synthesized. Several schemes were investigated for the synthesis of the handles having methylthioether and aliphatic amine without success, and it was decided not to continue this project. Therefore, no final basket handle porphyrin was available for further characterization.
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