Estudio de la almidón sintetasa de papa (UDP-glucosa-alfa-1-4 glucan-alfa-4-glucosiltransferasa)

Se estudió la enzima que cataliza la transferencia de 1a glucosa de los nucleótidos UDP-glucosa o ADP-glucosa alalmidón o malto-oligosacáridos. La nueva unión que se formaes α-1-4. Dicha enzima se preparó a partir de tubérculos de lapapa. La actividad aumenta con 1a cantidad de complejo enzima-almidón y con el tiempo, aunque no en forma netamentelineal. La Km de 1a enzima respecto del UDP-glucosa resultóser de 3,8x10^-2 y se incorpora 0,8 μ mol de UDP-glucosa pormiligramo de proteina por hora. En pH óptimo de actividad de le enzima a 37°C fue de 8,2 usando buffer glicilglicina 0,5 M; EDTA 0,025 M. y entre 7,5 y 8,2 con buffer fosfato 0,5 M, EDTA 0,025 M. Todos los intentos para separar 1a enzima del gránulode almidón fracasaron. Esta enzima se inactiva parcialmente por acción de 1aglucosa y la panosa, y totalmente por el p-cloro-mercuribenzoato. Los malto-oligosacáridos inhiben competitivamente 1a incorporaciónde 1a glucosa del UDP-glucosa o ADP-glucosa alalmidón, Estos oligosacáridoe también actuan como sustratos. Los isomalto-oligosacáridos en cambio no tienen ningún efectosobre la enzima ni pueden actuar como sustratos. Los glucócidos fenólicos, lo mismo que sus agluconasinhiben apreciablemente 1a acción enzimática. No ocurre lomismo con los metil-glucósidos. Ninguno de los glucósidos resultóser sustrato de la reacción. Los nucleótidos adenílicos inhiben apreciablemente lareacción de síntesis de almidón o malto-oligosacáridos a partirdel UDP-glucosa y bastante menos a partir de ADP-glucosa. También se prepararon y estudiaron almidón sintetasas deotros vegetales, especialmente de la arveja arrugada y delmaíz waxy. Se ha encontrado que en el caso de la enzima deeste último los malta-oligosacáridos son sustratos mucho másefectivos que el almidón. Se determinó que la incorporación de 1a glucosa del nucleótido-azúcar, se realiza tanto en la amilosa como en laamilopectína, aunque en mayor proporción en la primera.Fil: Bryks, Rajzla. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina

Anisotropic Nanocrystals from Supramolecular Templates

The study of nanocrystals has proven to be a rapidly burgeoning field in the last couple of decades. Advances in characterization techniques and a rapidly maturing electronics industry has spurned continued interest in the development of materials with unique electrical and optical properties. The phenomena encountered at the nanoscale, such as quantum confinement and localized surface plasmon resonances, represent powerful tools to be utilized in next-generation optoelectronic devices. Accordingly, there has been a significant push towards understanding fundamental processes at the nanoscale, such as self-assembly, crystalline nucleation and growth, and surface chemical interactions. This dissertation discusses a method of producing supramolecular assemblies for the purposes of obtaining highly anisotropic and shaped nanocrystals from confined nucleation and growth. This method is noteworthy in that it differs from “traditional” nanocrystal synthesis. Traditional nanocrystal growth is accomplished via solvothermal reaction of anions and cations, or reduction of cations in the case of a metal, in the presence of chelating ligands or polymer in methods broadly termed colloidal synthesis. In that case, the resulting shape of the nanocrystal generated is dictated by the chemisorption or physisorption of coordinating chemical groups to specific crystalline facets, according to their surface energy. Here, we react metal with thiol to form metal alkanethiolate complexes, which adopt a lamellar structure; moreover, this lamellar structure is subject to structural mesomorphism, where it may adopt pseudo-liquid crystalline phases with heating. Lastly, these complexes represent single-source precursors for metal or metal sulfide nanocrystals upon heating in a process termed solventless thermolysis. The scope of this work has several components. Firstly, to understand the self-assembly of metal alkanethiolate complexes, and the mechanism of solventless thermolysis to metal or metal sulfide nanocrystal. Next, we seek to understand the chemical interactions which give rise to the thermal properties such as thermolysis temperature and structural transition temperatures. By understanding the chemical interactions which determine thermal properties, we seek to attain chemical control over thermal properties such that there is some tunability of the decomposition temperature or structural phase during thermolysis. In doing so, we leverage control over nanocrystal nucleation and growth within specific structural phases which serve as molecular templates and thus dictate nanocrystal growth in a format quite different from colloidal synthesis. We show that these supramolecular templates can facilitate nucleation and growth of nanocrystals within ordered, pseudo-liquid crystalline melts which have the capacity to impart extreme anisotropy to the nanocrystal morphology. Herein, we report the synthesis and characterization of a host of metal alkanethiolates and some metal alkaneselenolates, detail their thermal properties, and utilize them as platforms to synthesize an array of shaped metal, metal sulfide, and metal selenide nanocrystals

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Metallomesogen Templates for Shape Control of Metal Selenide Nanocrystals

Metal alkanethiolates are organometallic single-source precursors that have been used to synthesize metal sulfide nanocrystals (NCs) from thermal decomposition reactions. Ag and Cu alkanethiolates are remarkable because they adopt lamellar bilayer nanostructures that give rise to mesogenic behavior akin to that of thermotropic liquid crystals. Such metallomesogen precursors have been demonstrated to template the nucleation and growth of highly anisotropic NC morphologies. In this work, we synthesize novel metallomesogen compounds, namely, CuSeC₁₂H₂₅ and AgSeC₁₂H₂₅, to target shaped metal selenide NCs. We show that these compounds adopt lamellar bilayer structures and undergo mesogenic transitions at elevated temperatures. We find that structural disparities between the CuSeC₁₂H₂₅ and AgSeC₁₂H₂₅ mesophases lead to the formation of distinct two- and one-dimensional NC morphologies, respectively. Moreover, both compounds exhibit an isotropic phase that produces either nanospheres or irregularly shaped particles. By exploiting the morphology-directing capability of the mesogenic regime, we detail the synthesis of ultrathin Cu₂Se nanoribbons, Ag₂Se nanorods, and AgCuSe nanospheres. This work demonstrates that metallomesogens can serve as a novel class of NC precursors with the ability to access highly anisotropic morphologies and tailored compositions

Effects of Carrier Density and Shape on the Localized Surface Plasmon Resonances of Cu_2–<i>x</i>S Nanodisks

A major challenge in the synthesis of plasmonic semiconductor nanocrystals is the ability to control localized surface plasmon resonance (LSPR) properties by varying the size, shape, and carrier density of the nanocrystal. For example, copper sulfide (Cu_2–<i>x</i>S) nanodisks possess two distinct LSPR modes that occur in the infrared range. Here, we demonstrate that the wavelengths of these LSPR modes can be modulated by independently varying the aspect ratio of the disk and the overall carrier density of Cu_2–<i>x</i>S. These variables can be controlled during nanocrystal growth by carrying out thermolysis of a copper-thiolate precursor under a specific gas environment. Our results show that during thermolysis, the presence of oxygen enhances the growth rate of crystalline Cu_2–<i>x</i>S nanodisks and the formation of Cu vacancies that contribute to free carrier concentration. By carrying out thermolysis under a nitrogen environment, we are able to tune the aspect ratio of nanodisks independent of Cu vacancy formation. Using these methods to carefully control nanodisk size and carrier density, we demonstrate that nanodisks achieve a critical carrier density beyond which the nanocrystals undergo an irreversible phase change, placing a limit on LSPR wavelength tuning in these doped semiconductor nanocrystals

Preparing Your School Integrated Pest Management (IPM) Plan

12 pp.This document is intended to help you develop an implementable IPM Plan for your school or school district. We have provided a modifiable template which can be downloaded at: http://cals.arizona.edu/apmc/westernschoolIPM.html#pubs

Preparing Your School Integrated Pest Management (IPM) Plan

12 pp.This document is intended to help you develop an implementable IPM Plan for your school or school district. We have provided a modifiable template which can be downloaded at: http://cals.arizona.edu/apmc/westernschoolIPM.html#pubs

Supramolecular Precursors for the Synthesis of Anisotropic Cu₂S Nanocrystals

Copper alkanethiolates are organometallic precursors that have been used to form Cu₂S nanodisks upon thermal decomposition. Here, we demonstrate that molecular assembly of Cu alkanethiolates into an ordered liquid crystalline mesophase plays an essential role in templating the disk morphology of the solid-state product. To examine this templating effect, we synthesize Cu alkanethiolate precursors with alkane tails of varying chain length and sterics. We demonstrate that short chain precursors produce two-dimensional (2D) nanosheets of Cu₂S, while longer-chained variants produce Cu₂S nanodisks exclusively. This work provides new insights into the use of liquid crystalline phases as templates for nanocrystal synthesis and as a potential route for achieving highly anisotropic inorganic nanostructures

Influence of pipelines and environmental factors on the endangered plant, Halimolobos virgata (Nutt.) O.E. Schultz over a 10 year period

We investigated the effects of pipeline construction and environmental factors on the occurrence and characteristics of the endangered plant Halimolobos virgata (Nutt.) O.E. Schultz. The plants were surveyed from 2007 to 2016 at three sites along the Keystone Pipeline in southern Alberta, Canada. Plant height, number of flowers and siliques, as well as microhabitat and climate data were collected up to 300 m away from the pipeline. Pipeline construction and distance had no effect on plant numbers or physical characteristics, with occurrences increasing markedly over time. Greater litter cover and depth and spring precipitation were associated with plant height and number of flowers and siliques. Vegetation cover was negatively correlated with H. virgata cover; however, plant height and number of flowers and seed pods were positively influenced by graminoid cover. The highest occurrences of H. virgata coincided with the driest and wettest years, and higher winter and spring temperatures. Some of this pattern can be attributed to the plant’s annual, biennial, and short perennial life forms, which may overlap and create a temporary exponential growth rate for an annual plant under ideal conditions. This research highlights the importance of understanding a species’ life history for the development of effective conservation and recovery strategies.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author