Site-Isolated molecular iridium complex catalyst supported in the 1-dimensional channels of zeolite hssz-53: Characterization by spectroscopy and aberration-corrected scanning transmission electron microscopy
Lu J.,One Shields Avenue |
Aydin C.,One Shields Avenue |
Liang A.J.,Chevron |
Chen C.-Y.,Chevron |
And 4 more authors.
ACS Catalysis | Year: 2012
Zeolite HSSZ-53, which has 1-dimensional channels with 14-ring extra-large pores, was used as a support for a molecular iridium complex synthesized from Ir(C 2H 4) 2(C 5H 7O 2) and characterized with infrared (IR) and extended X-ray absorption fine structure (EXAFS) spectroscopies and atomic-resolution aberration-corrected scanning transmission electron microscopy (STEM). The spectra show that Ir(C 2H 4) 2(C 5H 7O 2) reacted readily with the bridging OH groups of the zeolite, leading to the removal of C 5H 7O 2 ligands and the formation of mononuclear Ir(C 2H 4) 2 complexes bonded to the zeolite by Ir-O bonds at the framework aluminum sites. STEM images confirm the spectra, showing site-isolated iridium centers within the zeolite channels, with no evidence of iridium clusters. The samples constitute a highly uniform, well-defined array of essentially molecular catalytic species in a highly uniform, confined environment, allowing precise investigations of the chemistry of the iridium complex in the absence of solvents. IR spectra show that the supported Ir(C 2H 4) 2 complexes were converted to Ir(C 2H 5) 2, Ir(CO) 2, Ir(CO)(C 2H 4), and Ir(CO)(C 2H 4) 2 as various mixtures of H 2, CO, and C 2H 4 reacted with the sample. The sample was tested as a catalyst for ethylene hydrogenation and for H-D exchange in the reaction of H 2 + D 2. The data, combined with results reported for isostructural iridium complexes bonded to zeolite HY and to MgO, demonstrate how the catalytic activity can be tuned by choice of the support, with the support being characterized as a ligand with electron-donating or electron-withdrawing properties. The results demonstrate that the rate of ethylene hydrogenation catalyzed by the supported iridium complexes is limited by H 2 activation when the iridium is electron rich (on the MgO support), whereas the rate-limiting step is C 2H 4 adsorption when the iridium is electron deficient (on either zeolite support). © 2012 American Chemical Society.
Brennan J.C.,University of California at Davis |
Denison M.S.,University of California at Davis |
Holstege D.M.,University of California at Davis |
Magiatis P.,National and Kapodistrian University of Athens |
And 4 more authors.
BMC Complementary and Alternative Medicine | Year: 2013
Background: The plant genus Fallopia is well-known in Chinese traditional medicine and includes many species that contain bioactive compounds, namely phytoestrogens. Consumption of phytoestrogens may be linked to decreased incidence of breast and prostate cancers therefore discovery of novel phytoestrogens and novel sources of phytoestrogens is of interest. Although phytoestrogen content has been analyzed in the rhizomes of various Fallopia sp., seeds of a Fallopia sp. have never been examined for phytoestrogen presence.Methods: Analytical chemistry techniques were used with guidance from an in vitro estrogen receptor bioassay (a stably transfected human ovarian carcinoma cell line) to isolate and identify estrogenic components from seeds of Fallopia convolvulus. A transiently transfected human breast carcinoma cell line was used to characterize the biological activity of the isolated compounds on estrogen receptors (ER) α and β.Results: Two compounds, emodin and the novel flavan-3-ol, (-)-epiafzelechin-3-O-p-coumarate (rhodoeosein), were identified to be responsible for estrogenic activity of F. convolvulus seed extract. Absolute stereochemistry of rhodoeosein was determined by 1 and 2D NMR, optical rotation and circular dichroism. Emodin was identified by HPLC/DAD, LC/MS/MS, and FT/ICR-MS. When characterizing the ER specificity in biological activity of rhodoeosein and emodin, rhodoeosein was able to exhibit a four-fold greater relative estrogenic potency (REP) in breast cells transiently-transfected with ERβ as compared to those transfected with ERα, and emodin exhibited a six-fold greater REP in ERβ-transfected breast cells. Cell type-specific differences were observed with rhodoeosein but not emodin; rhodoeosein produced superinduction of reporter gene activity in the human ovarian cell line (> 400% of maximum estradiol [E2] induction) but not in the breast cell line.Conclusion: This study is the first to characterize the novel flavan-3-ol compound, rhodoeosein, and its ability to induce estrogenic activity in human cell lines. Rhodoeosein and emodin may have potential therapeutic applications as natural products activating ERβ, and further characterization of rhodoeosein is necessary to evaluate its selectivity as a cell type-specific ER agonist. © 2013 Brennan et al.; licensee BioMed Central Ltd.
Lerno L.A.,One Shields Avenue |
German J.B.,Food Science and Technology |
Lebrilla C.B.,One Shields Avenue |
Lebrilla C.B.,University of California at Davis
Analytical Chemistry | Year: 2010
A rapid method for the determination of lipid classes with high sensitivity is described. The referenced Kendrick mass defect (RKMD) and RKMD plots are novel adaptations of the Kendrick mass defect analysis that allows for the rapid identification of members of a homologous series in addition to identifying the lipid class. Assignment of lipid classes by the RKMD method is accomplished by conversion of the lipid masses to the Kendrick mass scale and then referencing the converted masses to each lipid class. Referencing of the masses to a given lipid class is achieved by first subtracting the heteroatom and lipid backbone contributions to the mass defect, leaving behind the contribution to the mass by the fatty acid constituents. The final step in the referencing makes use of spacing differences in mass defects between members of the same Kendrick class to identify members of the lipid class being referenced. The end result of this is that a lipid belonging to the class being referenced will have an integer RKMD with the value of the integer being the degrees of unsaturation in the lipid. The RKMD method was able to successfully identify the lipids in an idealized data set consisting of 160 lipids drawn from the glyceride and phosphoglyceride classes. As a real world example the lipid extract from bovine milk was analyzed using both accurate mass measurements and the RKMD method. © 2010 American Chemical Society.
Dyer A.R.,University of South Carolina |
Hardison J.L.,One Shields Avenue |
Rice K.J.,University of California at Davis
Plant Ecology | Year: 2012
Seasonal resource availability may act as a constraint on plant phenology and thereby influence the range of growth responses observed among populations of annual species, especially those occupying a wide range of environments. We compared a mesic and a xeric population of the non-native, annual grass, Bromus tectorum, to examine phenology in response to interspecific competition and water availability. Using a target-neighborhood approach, we assessed how phenological patterns of the two populations affected morphological and growth responses to enhanced resource availability represented by late-season soil moisture. The xeric population exhibited a highly constrained phenology and was unable to extend the growing season despite available soil resources. Because of the low phenotypic variation, allocation to reproduction was similar across resource conditions. In contrast, the mesic population flowered later and showed a more opportunistic phenology in response to late-season water availability. The mesic population was not able to maintain consistent reproductive allocation at low resource levels. The responses of the two populations to late-season water availability were not affected by the density of neighboring plants. We suggest that post-introduction selection pressure on B. tectorum in the xeric habitat has resulted in a more fixed phenology which limits opportunistic response to unpredictable, particularly late-season resource availability. Opportunistic and fixed responses represent contrasting strategies for optimizing fitness in temporally varying environments and, while both play important roles for ensuring reproductive success, these results suggest that local adaptation to temporal resource variation may reflect a balance between flexible and inflexible phenology. © 2011 Springer Science+Business Media B.V.
Zhang R.,One Shields Avenue |
Fan Z.,One Shields Avenue |
Kasuga T.,University of California at Davis |
Kasuga T.,U.S. Department of Agriculture
Protein Expression and Purification | Year: 2011
A gene encoding cellobiose dehydrogenase (CDH) from Neurospora crassa strain FGSC 2489 has been cloned and expressed in the heterologous host Pichia pastoris, under the control of the AOX1 methanol inducible promoter. Recombinant CDH without the native signal sequence and fused with a His 6-tag (rNC-CDH1) was successfully expressed and secreted. rNC-CDH1 was produced at the level of 652 IU/L after 2 days of cultivation in the induction medium. The His 6-tagged rNC-CDH1 was purified through a one-step Ni-NTA affinity column under non-denaturing conditions. The purified rNC-CDH1 has a CDH activity of 7451 IU/L (0.89 mg protein/mL), with a specific CDH activity of 8.37 IU/mg. The purity of the enzyme was examined by SDS-PAGE, and a single band corresponding to a molecular weight of about 120 kDa was observed. Activity staining confirmed the CDH activity of the protein band. The purified rNC-CDH1 has maximum CDH activity at pH 4.5, and a rather broad temperature optimum of 25-70 °C. Kinetic analysis showed cellobiose and cellooligosaccharides are the best substrates for rNC-CDH1. The K m value of the rNC-CDH1 for cellooligosaccharide increases with the elongation of glucosyl units. k cat remains relatively constant when the chain length changes. © 2010 Elsevier Inc. All rights reserved.
Frey S.D.,University of New Hampshire |
Lee J.,One Shields Avenue |
Melillo J.M.,Ecosystem Center |
Six J.,One Shields Avenue |
Six J.,ETH Zurich
Nature Climate Change | Year: 2013
Soils are the largest repository of organic carbon (C) in the terrestrial biosphere and represent an important source of carbon dioxide (CO2) to the atmosphere, releasing 60-75 Pg C annually through microbial decomposition of organic materials. A primary control on soil CO2 flux is the efficiency with which the microbial community uses C. Despite its critical importance to soil-atmosphere CO2 exchange, relatively few studies have examined the factors controlling soil microbial efficiency. Here, we measured the temperature response of microbial efficiency in soils amended with substrates varying in lability. We also examined the temperature sensitivity of microbial efficiency in response to chronic soil warming in situ. We find that the efficiency with which soil microorganisms use organic matter is dependent on both temperature and substrate quality, with efficiency declining with increasing temperatures for more recalcitrant substrates. However, the utilization efficiency of a more recalcitrant substrate increased at higher temperatures in soils exposed to almost two decades of warming 5°C above ambient. Our work suggests that climate warming could alter the decay dynamics of more stable organic matter compounds, thereby having a positive feedback to climate that is attenuated by a shift towards a more efficient microbial community in the longer term. © 2013 Macmillan Publishers Limited. All rights reserved.
Greco B.J.,One Shields Avenue |
Brown T.K.,California State University, San Marcos |
Andrews J.R.M.,San Diego Zoo Global |
Swaisgood R.R.,San Diego Zoo Global |
Caine N.G.,California State University, San Marcos
Animal Cognition | Year: 2013
Social learning is a more efficient method of information acquisition and application than trial and error learning and is prevalent across a variety of animal taxa. Social learning is assumed to be important for elephants, but evidence in support of that claim is mostly anecdotal. Using a herd of six adult female African bush elephants (Loxodonta africana africana) at the San Diego Zoo's Safari Park, we evaluated whether viewing a conspecific's interactions facilitated learning of a novel task. The tasks used feeding apparatus that could be solved in one of two distinct ways. Contrary to our hypothesis, the method the demonstrating animal used did not predict the method used by the observer. However, we did find evidence of social learning: After watching the model, subjects spent a greater percentage of their time interacting with the apparatus than they did in unmodeled trials. These results suggest that the demonstrations of a model may increase the motivation of elephants to explore novel foraging tasks. © 2012 Springer-Verlag Berlin Heidelberg.
Kesich A.,One Shields Avenue
Journal of Physics: Conference Series | Year: 2012
Thermal suppression of quarkonium production in heavy-ion collisions, due to Debye screening of the quark-antiquark potential, has been proposed as a clear signature of quark-gluon plasma (QGP) formation. At RHIC energies, the γ meson is a clean probe of the early system thanks to negligible levels of enhancement from bb̄ recombination and non-thermal suppression from co-mover absorption. We report on our measurement of the γ → e +e- cross section in Au+Au collisions at √s NN=200 GeV. We compute the Nuclear Modification Factor by comparing these results to p+p collisions. In order to have a complete assessment of both hot and cold nuclear matter effects on Upsilon production we also report on results from d+Au collisions.
Medina V.,One Shields Avenue |
Gilbert M.E.,One Shields Avenue
Functional Plant Biology | Year: 2016
Limited rainfall is the main constraint to agriculture, making agricultural research to understand plant behaviour that leads to avoidance of soil water deficit a matter of priority. One focus has screened for crop varieties that decrease stomatal conductance under high vapour pressure deficit (VPD), a proxy for the leaf evaporative gradient. However, the link between stomatal closure and physiological consequences in field environments is not yet clear. A field experiment on soybeans demonstrated that considerable variation in leaf temperature relative to air temperature occurred, leading to evaporative gradients differing substantially from VPD. Thus, transpiration is decreased by stomatal closure at high VPD, but to compensate, transpiration is somewhat increased due to higher leaf temperatures. Soil water deficit led to lower stomatal conductance, particularly under low evaporative conditions, not just under hot conditions. Non-stomatal photosynthetic limitations were observed due to combined occurrence of stomatal closure and high temperature under high VPD. Although leaves reached temperatures higher than the threshold for a decrease in maximum photochemical efficiency, and displayed non-stomatal photosynthetic limitations, no photoinhibition or damage was observed by night-time. The results demonstrate that more understanding of physiological strategies for achieving altered water use is needed to avoid trade-offs and heat stress. © CSIRO 2016.
PubMed | One Shields Avenue
Type: Journal Article | Journal: Animal cognition | Year: 2013
Social learning is a more efficient method of information acquisition and application than trial and error learning and is prevalent across a variety of animal taxa. Social learning is assumed to be important for elephants, but evidence in support of that claim is mostly anecdotal. Using a herd of six adult female African bush elephants (Loxodonta africana africana) at the San Diego Zoos Safari Park, we evaluated whether viewing a conspecifics interactions facilitated learning of a novel task. The tasks used feeding apparatus that could be solved in one of two distinct ways. Contrary to our hypothesis, the method the demonstrating animal used did not predict the method used by the observer. However, we did find evidence of social learning: After watching the model, subjects spent a greater percentage of their time interacting with the apparatus than they did in unmodeled trials. These results suggest that the demonstrations of a model may increase the motivation of elephants to explore novel foraging tasks.