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Making chemistry selectable by linking it to infectivity

Gao, Changshou; Lin, Chao-Hsiung; Lo, Chih-Hung L.; Mao, Shenlan; Wirsching, Peter; Lerner, Richard A.; Janda, Kim D.
Fonte: The National Academy of Sciences of the USA Publicador: The National Academy of Sciences of the USA
Tipo: Artigo de Revista Científica
Publicado em 28/10/1997 EN
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The link between recognition and replication is fundamental to the operation of the immune system. In recent years, modeling this process in a format of phage-display combinatorial libraries has afforded a powerful tool for obtaining valuable antibodies. However, the ability to readily select and isolate rare catalysts would expand the scope of library technology. A technique in which phage infection controlled the link between recognition and replication was applied to show that chemistry is a selectable process. An antibody that operated by covalent catalysis to form an acyl intermediate restored phage infectivity and allowed selection from a library in which the catalyst constituted 1 in 105 members. Three different selection approaches were examined for their convenience and generality. Incorporating these protocols together with well known affinity labels and mechanism-based inactivators should allow the procurement of a wide range of novel catalytic antibodies.

Effects of unique ion chemistry on thin-film growth by plasma–surface interactions

Wijesundara, Muthu B. J.; Hanley, Luke; Ni, Boris; Sinnott, Susan B.
Fonte: The National Academy of Sciences Publicador: The National Academy of Sciences
Tipo: Artigo de Revista Científica
Publicado em 04/01/2000 EN
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Plasma processing is a standard industrial method for the modification of material surfaces and the deposition of thin films. Polyatomic ions and neutrals larger than a triatomic play a critical role in plasma-induced surface chemistry, especially in the deposition of polymeric films from fluorocarbon plasmas. In this paper, low energy CF3+ and C3F5+ ions are used to modify a polystyrene surface. Experimental and computational studies are combined to quantify the effect of the unique chemistry and structure of the incident ions on the result of ion-polymer collisions. C3F5+ ions are more effective at growing films than CF3+, both at similar energy/atom of ≈6 eV/atom and similar total kinetic energies of 25 and 50 eV. The composition of the films grown experimentally also varies with both the structure and kinetic energy of the incident ion. Both C3F5+ and CF3+ should be thought of as covalently bound polyatomic precursors or fragments that can react and become incorporated within the polystyrene surface, rather than merely donating F atoms. The size and structure of the ions affect polymer film formation via differing chemical structure, reactivity, sticking probabilities, and energy transfer to the surface. The different reactivity of these two ions with the polymer surface supports the argument that larger species contribute to the deposition of polymeric films from fluorocarbon plasmas. These results indicate that complete understanding and accurate computer modeling of plasma–surface modification requires accurate measurement of the identities...

Chemistry for the analysis of protein–protein interactions: Rapid and efficient cross-linking triggered by long wavelength light

Fancy, David A.; Kodadek, Thomas
Fonte: The National Academy of Sciences Publicador: The National Academy of Sciences
Tipo: Artigo de Revista Científica
Publicado em 25/05/1999 EN
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Chemical cross-linking is a potentially useful technique for probing the architecture of multiprotein complexes. However, analyses using typical bifunctional cross-linkers often suffer from poor yields, and large-scale modification of nucleophilic side chains can result in artifactual results attributable to structural destabilization. We report here the de novo design and development of a type of protein cross-linking reaction that uses a photogenerated oxidant to mediate rapid and efficient cross-linking of associated proteins. The process involves brief photolysis of tris-bipyridylruthenium(II) dication with visible light in the presence of the electron acceptor ammonium persulfate and the proteins of interest. Very high yields of cross-linked products can be obtained with irradiation times of <1 second. This chemistry obviates many of the problems associated with standard cross-linking reagents.

Positioning protein molecules on surfaces: A nanoengineering approach to supramolecular chemistry

Liu, Gang-Yu; Amro, Nabil A.
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
Publicado em 16/04/2002 EN
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We discuss a nanoengineering approach for supramolecular chemistry and self assembly. The collective properties and biofunctionalities of molecular ensembles depend not only on individual molecular building blocks but also on organization at the molecular or nanoscopic level. Complementary to “bottom-up” approaches, which construct supramolecular ensembles by the design and synthesis of functionalized small molecular units or large molecular motifs, nanofabrication explores whether individual units, such as small molecular ligands, or large molecules, such as proteins, can be positioned with nanometer precision. The separation and local environment can be engineered to control subsequent intermolecular interactions. Feature sizes as small as 2 × 4 nm2 (32 alkanethiol molecules) are produced. Proteins may be aligned along a 10-nm-wide line or within two-dimensional islands of desired geometry. These high-resolution engineering and imaging studies provide new and molecular-level insight into supramolecular chemistry and self-assembly processes in bioscience that are otherwise unobtainable, e.g., the influence of size, separation, orientation, and local environment of reaction sites. This nanofabrication methodology also offers a new strategy in construction of two- and three-dimensional supramolecular structures for cell...

Peroxone chemistry: Formation of H2O3 and ring-(HO2)(HO3) from O3/H2O2

Xu, Xin; Goddard, William A.
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
EN
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The recent observation [Wentworth, P., Jones, L. H., Wentworth, A. D., Zhu, X. Y., Larsen, N. A., Wilson, I. A., Xu, X., Goddard, W. A., Janda, K. D., Eschenmoser, A. & Lerner, R. A. (2001) Science 293, 1806–1811] that antibodies form H2O2 from 1O2 plus H2O was explained in terms of the formation of the H2O3 species that in the antibody reacts with a second H2O3 to form H2O2. There have been few reports of the chemistry for forming H2O3, but recently Engdahl and Nelander [Engdahl, A. & Nelander, B. (2002) Science 295, 482–483] reported that photolysis of the ozone–hydrogen peroxide complex in argon matrices leads to significant concentrations of H2O3. We report here the chemical mechanism for this process, determined by using first-principles quantum mechanics. We show that in an argon matrix it is favorable (3.5 kcal/mol barrier) for H2O2 and O3 to form a [(HO2)(HO3)] hydrogen-bonded complex [head-to-tail seven-membered ring (7r)]. In this complex, the barrier for forming H2O3 plus 3O2 is only 4.8 kcal/mol, which should be observable by means of thermal processes (not yet reported). Irradiation of the [(HO2)(HO3)-7r] complex should break the HO–OO bond of the HO3 moiety, eliminating 3O2 and leading to [(HO2)(HO)]. This [(HO2)(HO)] confined in the matrix cage is expected to rearrange to also form H2O3 (observed experimentally). We show that these two processes can be distinguished isotopically. These results (including the predicted vibrational frequencies) suggest strategies for synthesizing H2O3 and characterizing its chemistry. We suggest that the [(HO2)(HO3)-7r] complex and H2O3 are involved in biological...

Photocleavable fluorescent nucleotides for DNA sequencing on a chip constructed by site-specific coupling chemistry

Seo, Tae Seok; Bai, Xiaopeng; Ruparel, Hameer; Li, Zengmin; Turro, Nicholas J.; Ju, Jingyue
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
EN
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DNA sequencing by synthesis on a solid surface offers new paradigms to overcome limitations of electrophoresis-based sequencing methods. Here we report DNA sequencing by synthesis using photocleavable (PC) fluorescent nucleotides [dUTP-PC-4,4-difluoro-4-bora-3α,4α-diaza-s-indacene (Bodipy)-FL-510, dCTP-PC-Bodipy-650, and dUTP-PC-6-carboxy-X-rhodamine (ROX)] on a glass chip constructed by 1,3-dipolar azide-alkyne cycloaddition coupling chemistry. Each nucleotide analogue consists of a different fluorophore attached to the base through a PC 2-nitrobenzyl linker. We constructed a DNA microarray by using the 1,3-dipolar cycloaddition chemistry to site-specifically attach azido-modified DNA onto an alkyne-functionalized glass chip at room temperature under aqueous conditions. After verifying that the polymerase reaction could be carried out successfully on the above-described DNA array, we then performed a sequencing reaction on the chip by using a self-primed DNA template. In the first step, we extended the primer using DNA polymerase and dUTP-PC-Bodipy-FL-510, detected the fluorescent signal from the fluorophore Bodipy-FL-510, and then cleaved the fluorophore using 340 nm UV irradiation. This process was followed by extension of the primer with dCTP-PC-Bodipy-650 and the subsequent detection of the fluorescent signal from Bodipy-650 and its photocleavage. The same procedure was also performed by using dUTP-PC-ROX. The entire process was repeated five times by using the three fluorescent nucleotides to identify 7 bases in the DNA template. These results demonstrate that the PC nucleotide analogues can be incorporated accurately into a growing DNA strand during polymerase reaction on a chip...

Energy analysis of chemistry for correct insertion by DNA polymerase β

Lin, Ping; Pedersen, Lars C.; Batra, Vinod K.; Beard, William A.; Wilson, Samuel H.; Pedersen, Lee G.
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
EN
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X-ray crystallographic structures of human DNA polymerase β with nonhydrolyzable analogs containing all atoms in the active site required for catalysis provide a secure starting point for a theoretical analysis (quantum mechanics/molecular mechanics) of the mechanism of chemistry without biasing of modeling assumptions as required in previous studies. These structures provide the basis for a detailed quantum mechanics/molecular mechanics study of the path for the complete transfer of a monophosphate nucleoside donor to the sugar acceptor in the active site. The reaction is largely associative with the main energetic step preceded by proton transfer from the terminal primer deoxyribose O3′ to Asp-256. The key residues that provide electrostatic stabilization of the transition state are identified and compared with those identified by mutational studies.

Copper-free click chemistry for dynamic in vivo imaging

Baskin, Jeremy M.; Prescher, Jennifer A.; Laughlin, Scott T.; Agard, Nicholas J.; Chang, Pamela V.; Miller, Isaac A.; Lo, Anderson; Codelli, Julian A.; Bertozzi, Carolyn R.
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
EN
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574.49758%
Dynamic imaging of proteins in live cells is routinely performed by using genetically encoded reporters, an approach that cannot be extended to other classes of biomolecules such as glycans and lipids. Here, we report a Cu-free variant of click chemistry that can label these biomolecules rapidly and selectively in living systems, overcoming the intrinsic toxicity of the canonical Cu-catalyzed reaction. The critical reagent, a substituted cyclooctyne, possesses ring strain and electron-withdrawing fluorine substituents that together promote the [3 + 2] dipolar cycloaddition with azides installed metabolically into biomolecules. This Cu-free click reaction possesses comparable kinetics to the Cu-catalyzed reaction and proceeds within minutes on live cells with no apparent toxicity. With this technique, we studied the dynamics of glycan trafficking and identified a population of sialoglycoconjugates with unexpectedly rapid internalization kinetics.

Geographic, seasonal, and precipitation chemistry influence on the abundance and activity of biological ice nucleators in rain and snow

Christner, Brent C.; Cai, Rongman; Morris, Cindy E.; McCarter, Kevin S.; Foreman, Christine M.; Skidmore, Mark L.; Montross, Scott N.; Sands, David C.
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
EN
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Biological ice nucleators (IN) function as catalysts for freezing at relatively warm temperatures (warmer than −10 °C). We examined the concentration (per volume of liquid) and nature of IN in precipitation collected from Montana and Louisiana, the Alps and Pyrenees (France), Ross Island (Antarctica), and Yukon (Canada). The temperature of detectable ice-nucleating activity for more than half of the samples was ≥ −5 °C based on immersion freezing testing. Digestion of the samples with lysozyme (i.e., to hydrolyze bacterial cell walls) led to reductions in the frequency of freezing (0–100%); heat treatment greatly reduced (95% average) or completely eliminated ice nucleation at the measured conditions in every sample. These behaviors were consistent with the activity being bacterial and/or proteinaceous in origin. Statistical analysis revealed seasonal similarities between warm-temperature ice-nucleating activities in snow samples collected over 7 months in Montana. Multiple regression was used to construct models with biogeochemical data [major ions, total organic carbon (TOC), particle, and cell concentration] that were accurate in predicting the concentration of microbial cells and biological IN in precipitation based on the concentration of TOC...

Mechanisms of Auger-induced chemistry derived from wave packet dynamics

Su, Julius T.; Goddard, William A.
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
EN
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574.49758%
To understand how core ionization and subsequent Auger decay lead to bond breaking in large systems, we simulate the wave packet dynamics of electrons in the hydrogenated diamond nanoparticle C197H112. We find that surface core ionizations cause emission of carbon fragments and protons through a direct Auger mechanism, whereas deeper core ionizations cause hydrides to be emitted from the surface via remote heating, consistent with results from photon-stimulated desorption experiments [Hoffman A, Laikhtman A, (2006) J Phys Condens Mater 18:S1517–S1546]. This demonstrates that it is feasible to study the chemistry of highly excited large-scale systems using simulation and analysis tools comparable in simplicity to those used for classical molecular dynamics.

High-pressure photodissociation of water as a tool for hydrogen synthesis and fundamental chemistry

Ceppatelli, Matteo; Bini, Roberto; Schettino, Vincenzo
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
EN
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579.3283%
High-pressure methods have been demonstrated to be efficient in providing new routes for the synthesis of materials of technological interest. In several molecular compounds, the drastic pressure conditions required for spontaneous transformations have been lowered to the kilobar range by photoactivation of the reactions. At these pressures, the syntheses are accessible to large-volume applications and are of interest to bioscience, space, and environmental chemistry. Here, we show that the short-lived hydroxyl radicals, produced in the photodissociation of water molecules by near-UV radiation at room temperature and pressures of a few tenths of a gigapascal (GPa), can be successfully used to trigger chemical reactions in mixtures of water with carbon monoxide or nitrogen. The detection of molecular hydrogen among the reaction products is of particular relevance. Besides the implications in fundamental chemistry, the mild pressure and irradiation conditions, the efficiency of the process, and the nature of the reactant and product molecules suggest applications in synthesis.

Copper-free click chemistry in living animals

Chang, Pamela V.; Prescher, Jennifer A.; Sletten, Ellen M.; Baskin, Jeremy M.; Miller, Isaac A.; Agard, Nicholas J.; Lo, Anderson; Bertozzi, Carolyn R.
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
EN
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579.3283%
Chemical reactions that enable selective biomolecule labeling in living organisms offer a means to probe biological processes in vivo. Very few reactions possess the requisite bioorthogonality, and, among these, only the Staudinger ligation between azides and triarylphosphines has been employed for direct covalent modification of biomolecules with probes in the mouse, an important model organism for studies of human disease. Here we explore an alternative bioorthogonal reaction, the 1,3-dipolar cycloaddition of azides and cyclooctynes, also known as “Cu-free click chemistry,” for labeling biomolecules in live mice. Mice were administered peracetylated N-azidoacetylmannosamine (Ac4ManNAz) to metabolically label cell-surface sialic acids with azides. After subsequent injection with cyclooctyne reagents, glycoconjugate labeling was observed on isolated splenocytes and in a variety of tissues including the intestines, heart, and liver, with no apparent toxicity. The cyclooctynes tested displayed various labeling efficiencies that likely reflect the combined influence of intrinsic reactivity and bioavailability. These studies establish Cu-free click chemistry as a bioorthogonal reaction that can be executed in the physiologically relevant context of a mouse.

Archaeopteryx feathers and bone chemistry fully revealed via synchrotron imaging

Bergmann, U.; Morton, R. W.; Manning, P. L.; Sellers, W. I.; Farrar, S.; Huntley, K. G.; Wogelius, R. A.; Larson, P.
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
EN
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585.72477%
Evolution of flight in maniraptoran dinosaurs is marked by the acquisition of distinct avian characters, such as feathers, as seen in Archaeopteryx from the Solnhofen limestone. These rare fossils were pivotal in confirming the dinosauria-avian lineage. One of the key derived avian characters is the possession of feathers, details of which were remarkably preserved in the Lagerstätte environment. These structures were previously simply assumed to be impressions; however, a detailed chemical analysis has, until now, never been completed on any Archaeopteryx specimen. Here we present chemical imaging via synchrotron rapid scanning X-ray fluorescence (SRS-XRF) of the Thermopolis Archaeopteryx, which shows that portions of the feathers are not impressions but are in fact remnant body fossil structures, maintaining elemental compositions that are completely different from the embedding geological matrix. Our results indicate phosphorous and sulfur retention in soft tissue as well as trace metal (Zn and Cu) retention in bone. Other previously unknown chemical details of Archaeopteryx are also revealed in this study including: bone chemistry, taphonomy (fossilization process), and curation artifacts. SRS-XRF represents a major advancement in the study of the life chemistry and fossilization processes of Archaeopteryx and other extinct organisms because it is now practical to image the chemistry of large specimens rapidly at concentration levels of parts per million. This technique has wider application to the archaeological...

Reactive polymer enables efficient in vivo bioorthogonal chemistry

Devaraj, Neal K.; Thurber, Greg M.; Keliher, Edmund J.; Marinelli, Brett; Weissleder, Ralph
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
EN
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There has been intense interest in the development of selective bioorthogonal reactions or “click” chemistry that can proceed in live animals. Until now however, most reactions still require vast surpluses of reactants because of steep temporal and spatial concentration gradients. Using computational modeling and design of pharmacokinetically optimized reactants, we have developed a predictable method for efficient in vivo click reactions. Specifically, we show that polymer modified tetrazines (PMT) are a key enabler for in vivo bioorthogonal chemistry based on the very fast and catalyst-free [4 + 2] tetrazine/trans-cyclooctene cycloaddition. Using fluorescent PMT for cellular resolution and 18F labeled PMT for whole animal imaging, we show that cancer cell epitopes can be easily reacted in vivo. This generic strategy should help guide the design of future chemistries and find widespread use for different in vivo bioorthogonal applications, particularly in the biomedical sciences.

Size distribution dynamics reveal particle-phase chemistry in organic aerosol formation

Shiraiwa, Manabu; Yee, Lindsay D.; Schilling, Katherine A.; Loza, Christine L.; Craven, Jill S.; Zuend, Andreas; Ziemann, Paul J.; Seinfeld, John H.
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
EN
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Organic aerosols are ubiquitous in the atmosphere and play a central role in climate, air quality, and public health. The aerosol size distribution is key in determining its optical properties and cloud condensation nucleus activity. The dominant portion of organic aerosol is formed through gas-phase oxidation of volatile organic compounds, so-called secondary organic aerosols (SOAs). Typical experimental measurements of SOA formation include total SOA mass and atomic oxygen-to-carbon ratio. These measurements, alone, are generally insufficient to reveal the extent to which condensed-phase reactions occur in conjunction with the multigeneration gas-phase photooxidation. Combining laboratory chamber experiments and kinetic gas-particle modeling for the dodecane SOA system, here we show that the presence of particle-phase chemistry is reflected in the evolution of the SOA size distribution as well as its mass concentration. Particle-phase reactions are predicted to occur mainly at the particle surface, and the reaction products contribute more than half of the SOA mass. Chamber photooxidation with a midexperiment aldehyde injection confirms that heterogeneous reaction of aldehydes with organic hydroperoxides forming peroxyhemiacetals can lead to a large increase in SOA mass. Although experiments need to be conducted with other SOA precursor hydrocarbons...

Observation of the controlled assembly of preclick components in the in situ click chemistry generation of a chitinase inhibitor

Hirose, Tomoyasu; Maita, Nobuo; Gouda, Hiroaki; Koseki, Jun; Yamamoto, Tsuyoshi; Sugawara, Akihiro; Nakano, Hirofumi; Hirono, Shuichi; Shiomi, Kazuro; Watanabe, Takeshi; Taniguchi, Hisaaki; Sharpless, K. Barry; Ōmura, Satoshi; Sunazuka, Toshiaki
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
EN
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582.301%
Several in situ click chemistry studies have been reported. To date, there is evidence to indicate that proteins act as mold between azide and alkyne fragments by X-ray analysis of protein–ligand complexes. However, only “postclick” structural evidence has been available. We succeeded in obtaining crystal structures of a chitinase complexed with an azide inhibitor and an O-allyl oxime fragment as a mimic of a click partner, revealing a mechanism for accelerating triazole formation in chitinase. This is an example to express the “preclick” state of in situ click chemistry and a demonstration to show that the in situ click chemistry approach will benefit from this analysis for future plans. We also performed density functional theory calculations to explore the chitinase-contributed Huisgen cycloaddition.

Active and widespread halogen chemistry in the tropical and subtropical free troposphere

Wang, Siyuan; Schmidt, Johan A.; Baidar, Sunil; Coburn, Sean; Dix, Barbara; Koenig, Theodore K.; Apel, Eric; Bowdalo, Dene; Campos, Teresa L.; Eloranta, Ed; Evans, Mathew J.; DiGangi, Joshua P.; Zondlo, Mark A.; Gao, Ru-Shan; Haggerty, Julie A.; Hall, Sam
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
EN
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Our measurements show that tropospheric halogen chemistry has a larger capacity to destroy O3 and oxidize atmospheric mercury than previously recognized. Halogen chemistry is currently missing in most global and climate models, and is effective at removing O3 at altitudes where intercontinental O3 transport occurs. It further helps explain the low O3 levels in preindustrial times. Public health concerns arise from bioaccumulation of the neurotoxin mercury in fish. Our results emphasize that bromine chemistry in the free troposphere oxidizes mercury at a faster rate, and makes water-soluble mercury available for scavenging by thunderstorms. Naturally occurring bromine in air aloft illustrates global interconnectedness between energy choices affecting mercury emissions in developing nations and mercury deposition in, e.g., Nevada, or the southeastern United States.

Where is physical organic chemistry going?

Roberts, John D.
Fonte: International Union of Pure and Applied Chemistry Publicador: International Union of Pure and Applied Chemistry
Tipo: Article; PeerReviewed Formato: application/pdf
Publicado em /02/1997
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John D. Roberts graduated from the University of California at Los Angeles with an A. B. (hons) degree in 1941 and the Ph. D. degree in 1944. His academic career began in 1945, as Instructor at UCLA. In 1945-1946 he was National Research Council Fellow and Instructor at Harvard. He went to MIT in 1946 as an Instructor, was Assistant Professor in 1947 and Associate Professor in 1950. In 1953 he became Professor of Organic Chemistry at Caltech and in 1972 Institute Professor of Chemistry. He is now Institute Professor of Chemistry, Emeritus and Lecturer. He is a member of the National Academy of Sciences (1956) and the American Philosophical Society (1974). He received the Welch Award (1990, with W. E. Doering), the National Medal of Science (1990), and the ACS Arthur C. Cope Award (1994). Since 1939 his research has been concerned with the mechanisms of organic reactions and the chemistry of small-ring compounds. His current work involves applications of nuclear magnetic resonance spectroscopy to physical organic chemistry.

An analysis of the alignment of the grade 12 physical sciences examination and the core curriculum in South Africa

Edwards,Nazeem
Fonte: South African Journal of Education Publicador: South African Journal of Education
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2010 EN
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I report on an analysis of the alignment between the South African Grade 12 Physical Sciences core curriculum content and the exemplar papers of 2008, and the final examination papers of 2008 and 2009. A two-dimensional table was used for both the curriculum and the examination in order to calculate the Porter alignment index, which indicates the degree of match between the two. Alignment indices of 0.8 and 0.6 for Physics and Chemistry, respectively, were computed and remained constant for Physics, but fluctuated initially for Chemistry before levelling off. Using the revised Bloom's taxonomy, discrepancies were found in terms of cognitive levels as well as content areas in both Physics and Chemistry. The cognitive level Remember is under-represented in the Chemistry and Physics examinations, whereas the cognitive levels Understand and Apply were over-represented in Chemistry. It is argued that the shift to higher cognitive levels is in line with the reported increase in cognitive complexity of the Physical Sciences curriculum. The significance of the study for Physical Science teachers is highlighted, and the potential for further research is also indicated.

High school Physical Sciences teachers' competence in some basic cognitive skills

Selvaratnam,Mailoo
Fonte: South African Journal of Chemistry Publicador: South African Journal of Chemistry
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2011 EN
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The successful implementation of the national high school Physical Sciences curriculum in South Africa, which places strong emphasis on critical thinking and reasoning abilities of students, would need teachers who are competent in cognitive skills and strategies. The main objectives of this study were to test South African high school Physical Sciences teachers' competence in the cognitive skills and strategies needed for studying Physical Sciences effectively and also to identify possible reasons for their difficulties and suggest methods for overcoming them. The study method used was the analysis of teachers' answers to questions that were carefully designed to test competence in explanation skills, mathematical skills, graphical skills, three-dimensional visualization skills, information-processing skills and reasoning skills. Seventy-three teachers from about 50 Dinaledi schools in the North West and Kwazulu-Natal provinces were tested. Teachers' competence was found to be poor in most of the skills tested. About 40 % (average performance in all 14 test questions) of them had difficulty in answering the questions. Teachers' lack of competence in cognitive skills and strategies would be an important limiting factor in the successful implementation of the Physical Sciences curriculum. An urgent need therefore exists for training teachers to increase their competence in the cognitive skills and strategies that are needed for studying science effectively.