The nature of the silicaphilic fluorescence of PDMPO

PDMPO (2-(4-pyridyl)-5-((4-(2-dimethylaminoethylaminocarbamoyl)methoxy)phenyl)oxazole), has unique silica specific fluorescence and is used in biology to understand biosilicification. This ‘silicaphilic’ fluorescence is not well understood nor is the response to local environmental variables like solvent and pH. We investigated PDMPO in a range of environments: using UV-vis and fluorescence spectroscopy supported by computational data, (SPARC, molecular dynamics simulations, density functional theory calculations), dynamic light scattering and zeta potential measurements to understand the PDMPO–silica interaction. From absorption data, PDMPO exhibited a pKa of 4.20 for PDMPOH22+ to PDMPOH+ . Fluorescence emission measurements revealed large shifts in excited state pKa* values with different behaviour when bound to silica (pKa* of 10.4). PDMPO bound to silica particles is located in the Stern layer with the dye exhibiting pH dependent depolarising motion. In aqueous solution, PDMPO showed strong chromaticity with correlation between the maximum emission wavelength for PDMPOH+* and dielectric constant (4.8–80). Additional chromatic effects were attributed to changes in solvent accessible surface area. Chromatic effects were also observed for silica bound dye which allow its use as a direct probe of bulk pH over a range far in excess of what is possible for the dye alone (3–5.2). The unique combination of chromaticity and excited state dynamics allows PDMPO to monitor pH from 3 to 13 while also reporting on surface environment opening a new frontier in the quantitative understanding of (bio)silicification

New Strategies in Modeling Electronic Structures and Properties with Applications to Actinides

This chapter discusses contemporary quantum chemical methods and provides general insights into modern electronic structure theory with a focus on heavy-element-containing compounds. We first give a short overview of relativistic Hamiltonians that are frequently applied to account for relativistic effects. Then, we scrutinize various quantum chemistry methods that approximate the $N$-electron wave function. In this respect, we will review the most popular single- and multi-reference approaches that have been developed to model the multi-reference nature of heavy element compounds and their ground- and excited-state electronic structures. Specifically, we introduce various flavors of post-Hartree--Fock methods and optimization schemes like the complete active space self-consistent field method, the configuration interaction approach, the Fock-space coupled cluster model, the pair-coupled cluster doubles ansatz, also known as the antisymmetric product of 1 reference orbital geminal, and the density matrix renormalization group algorithm. Furthermore, we will illustrate how concepts of quantum information theory provide us with a qualitative understanding of complex electronic structures using the picture of interacting orbitals. While modern quantum chemistry facilitates a quantitative description of atoms and molecules as well as their properties, concepts of quantum information theory offer new strategies for a qualitative interpretation that can shed new light onto the chemistry of complex molecular compounds.Comment: 43 pages, 3 figures, Version of Recor

Evaluating skills, knowledge and values of learners exposed to a dialogical argumentation instruction and the traditional lecture method on fermentation

Paper presented at the SAARMSTE 2012 Conference, Crossroads Hotel, Malawi, 16-19 JanuaryThis case study which is part of a larger project, the Science and Indigenous Knowledge Systems Project (SIKSP) at the University of the Western Cape reports on findings of two cohorts of grade 10 science learners whose conceptions of fermentation as well as their Skills, Knowledge, Attitudes and values (SKAVs) on fermentation processes was assessed. One group was taught using Dialogical Argumentation Instruction (DAI) while the other group was taught using the Traditional Lecture Method (TLM) on the same topic, but taught by another experienced teacher. After the interventions which lasted a period of six weeks, both groups were again evaluated using the same conceptions questionnaire as well as a science achievement test to evaluate their SKAVs on activities of various cognitive abilities. This study employed a pre and post-test quasi-experimental design augmented with a qualitative design. The findings showed that learners exposed to dialogical approach developed higher knowledge, process skills, reasoning skills and values as compared to their counterparts who were taught using the TLM approach

Realising a science and indigenous knowledge systems curriculum: a case study of a dialogical argumentation-based teaching approach

Paper presented at the 3rd International Conference on Science and IKS, University of the Western Cape, 25-29 Octobe

Magmatism and metallogeny associated with mantle upwelling: zircon U-Pb and Lu-Hf constraints from the gold-mineralized Jinchang granite, NE China

Abstract not availableHua-Feng Zhanga, Sheng-Rong Lia, M. Santosha, Jia-Jun Liua, Chun-Rong DiWub, Hong Zhan

New evidence for ~4.45Ga terrestrial crust from zircon xenocrysts in Ordovician ignimbrite in the North Qinling Orogenic Belt, China

Evidence for the earliest known terrestrial crust comes predominantly from Jack Hills in Western Australia, where hafnium isotopic results from >3.8. Ga detrital zircons indicate crustal precursors as old as ~4.4-4.5. Ga. We present evidence from magmatic cores in >3.9. Ga xenocrystic zircons from a felsic volcanic rock in the North Qinling Orogenic Belt, China, of similar Hf crustal model ages up to 4.45 Ga. These lie on the same Lu/Hf trajectory as the least disturbed Jack Hills and Apollo 14 zircons, therefore providing only the second example of the earliest known generation of continental crust on Earth. In addition, the rims of two zircon grains record later growth at 3.7. Ga and, when combined with the fact that the grains are incorporated in Paleozoic volcanic rocks, imply long-lived crustal residence within the basement of the North China Craton. These results therefore establish the wider distribution and survival of the most ancient crustal material on the Earth and highlight the possibility for the further discovery of ancient crustal remnants