Showing 2161 - 2170 of 5708 Items
Investigating the Effect of Side Chains with Hydrogen Bonding Capabilities on Peptoid Catalysts for Enantioselective Trifluoromethylation of 4-Chlorobenzaldehyde Access to this record is restricted to members of the Bowdoin community. Log in here to view.
- Restriction End Date: 2025-06-01
Date: 2020-01-01
Creator: Rebecca Londoner
Access: Access restricted to the Bowdoin Community
A structural role for arginine in proteins: Multiple hydrogen bonds to backbone carbonyl oxygens
Date: 1994-01-01
Creator: C. L. Borders, John A. Broadwater, Paula A. Bekeny, Johanna E. Salmon, Ann S., Lee, Aimee M. Eldridge, Virginia B. Pett
Access: Open access
- We propose that arginine side chains often play a previously unappreciated general structural role in the maintenance of tertiary structure in proteins, wherein the positively charged guanidinium group forms multiple hydrogen bonds to backbone carbonyl oxygens. Using as a criterion for a “structural” arginine one that forms 4 or more hydrogen bonds to 3 or more backbone carbonyl oxygens, we have used molecular graphics to locate arginines of interest in 4 proteins: Arg 180 in Thermus thermophilus manganese superoxide dismutase, Arg 254 in human carbonic anhydrase II, Arg 31 in Streptomyces rubiginosus xylose isomerase, and Arg 313 in Rhodospirillum rubrum ribulose‐1,5‐bisphosphate carboxylase/oxygenase. Arg 180 helps to mold the active site channel of superoxide dismutase, whereas in each of the other enzymes the structural arginine is buried in the “mantle” (i.e., inside, but near the surface) of the protein interior well removed from the active site, where it makes 5 hydrogen bonds to 4 backbone carbonyl oxygens. Using a more relaxed criterion of 3 or more hydrogen bonds to 2 or more backbone carbonyl oxygens, arginines that play a potentially important structural role were found in yeast enolase, Bacillus stearothermophilus glyceraldehyde‐3‐phosphate dehydrogenase, bacteriophage T4 and human lysozymes, Enteromorpha prolifera plastocyanin, HIV‐1 protease, Trypanosoma brucei brucei and yeast triosephosphate isomerases, and Escherichia coli trp aporepressor (but not trp repressor or the trp repressor/operator complex). In addition to helping form the active site funnel in superoxide dismutase, the structural arginines found in this study play such diverse roles as stapling together 3 strands of backbone from different regions of the primary sequence, and tying α‐helix to α‐helix, βturn to β‐turn, and subunit to subunit. Copyright © 1994 The Protein Society
Characterization of O-Linked Glycosylated Neuropeptides in the American Lobster (Homarus americanus): The Use of Peptide Labeling Following Beta Elimination
Date: 2020-01-01
Creator: Edward Myron Bull
Access: Open access
- Neuropeptides are a class of small peptides that govern various neurological functions, and the American lobster (Homarus americanus) provides a model system for their characterization. Neuropeptides are commonly post-translationally modified (PTM), and one common PTM is glycosylation. Past research in the Stemmler lab has found glycosylated neuropeptides in H. americanus; however, the extent and biological role of this modification has not been well characterized. This study was undertaken to determine the number of glycosylated peptides in the sinus glands of H. americanus and to develop an approach to tag the site of glycosylation using beta-elimination chemistry. LC-MS paired with high pH reverse phase fractionation was used to survey for glycosylated neuropeptides and beta elimination with an amine tag was used as an approach to characterize the site of glycosylation. Our results indicate that high pH fractionation is a useful approach to simplify complex mixtures of neuropeptides and improve glycopeptide detection. Efforts to use beta elimination and tagging to characterize glycosylated neuropeptides have been less successful. Beta elimination of full length peptides resulted in peptide degradation. An approach utilizing chymotrypsin to reduce peptide size coupled with beta elimination and labeling with 2-dimethylaminoethanethiol showed less evidence for degradation, and this approach yielded data isolating two potential serine residues for the site of glycosylation; however, the data was not sufficient to distinguish the two sites. Work to optimize reaction conditions using a glycopeptide standard showed that multiple isomeric products were formed during beta elimination. With the goal of optimizing reaction conditions, future work will further examine reaction kinetics to eventually apply the approach to the entire sinus gland
Clonal diversity in an expanding community of Arctic Salix spp. and a model for recruitment modes of arctic plants
Date: 2010-11-01
Creator: Vladimir Douhovnikoff, Gregory R. Goldsmith, Ken D. Tape, Cherrie Huang, Nadine, Sur, M. Syndonia Bret-Harte
Access: Open access
- Rapid climate change in arctic environments is leading to a widespread expansion in woody deciduous shrub populations. However, little is known about the reproductive, dispersal, and establishment mechanisms associated with shrub expansion. It is assumed that harsh environmental conditions impose limitations on plant sexual reproduction in the Arctic, such that population survival and expansion is predominately a function of clonal recruitment. We present contrary evidence from microsatellite genetic data suggesting the prevalence of recruitment by seed. Further, we present a conceptual model describing modes of recruitment in relation to the abiotic environment. Climate change may be alleviating abiotic stress so that resources are available for more frequent recruitment by seed. Such changes have widespread implications for ecosystem structure and functioning, including species composition, wildlife habitat, biogeochemical cycling, and surface energy balance. © 2010 Regents of the University of Colorado.
Two-photon production of charged pion and kaon pairs
Date: 1994-01-01
Creator: J. Dominick, M. Lambrecht, S. Sanghera, V. Shelkov, T., Skwarnicki, R. Stroynowski, I. Volobouev, G. Wei, P. Zadorozhny, M. Artuso, M. Goldberg, D. He, N. Horwitz, R. Kennett, R. Mountain, G. C. Moneti, F. Muheim, Y. Mukhin, S. Playfer, Y. Rozen, S. Stone, M. Thulasidas, G. Vasseur, G. Zhu, J. Bartelt, S. E. Csorna, Z. Egyed, V. Jain, K. Kinoshita, K. W. Edwards, M. Ogg
Access: Open access
- A measurement of the cross section for the combined two-photon production of charged pion and kaon pairs is performed using 1.2 fb-1 of data collected by the CLEO II detector at the Cornell Electron Storage Ring. The cross section is measured at invariant masses of the two-photon system between 1.5 and 5.0 GeV/c2, and at scattering angles more than 53° away from the γγ collision axis in the γγ center-of-mass frame. The large background of leptonic events is suppressed by utilizing the CsI calorimeter in conjunction with the muon chamber system. The reported cross section is compared with leading order QCD models as well as previous experiments. Although the functional dependence of the measured cross section disagrees with leading order QCD at small values of the two-photon invaraint mass, the data show qualitatively a transition to perturbative behavior at an invariant mass of approximately 2.5 GeV/c2. © 1994 The American Physical Society.
Bowdoin College Catalogue (1930-1931)
Date: 1931-01-01
Access: Open access
- Bowdoin College Bulletin no. 193
Classifying Flow-kick Equilibria: Reactivity and Transient Behavior in the Variational Equation
Date: 2020-01-01
Creator: Alanna Haslam
Access: Open access
- In light of concerns about climate change, there is interest in how sustainable management can maintain the resilience of ecosystems. We use flow-kick dynamical systems to model ecosystems subject to a constant kick occurring every τ time units. We classify the stability of flow-kick equilibria to determine which management strategies result in desirable long-term characteristics. To classify the stability of a flow-kick equilibrium, we classify the linearization of the time-τ map given by the time-τ map of the variational equation about the equilibrium trajectory. Since the variational equation is a non-autonomous linear differential equation, we conjecture that the asymptotic stability classification of each instantaneous local linearization along the equilibrium trajectory indicates the stability of the variational time-τ map. In Chapter 3, we prove this conjecture holds when all of the asymptotic and transient behavior of the instantaneous local linearizations is the same. To explore whether the conjecture holds in general, we ask: To what degree can transient behavior differ from asymptotic behavior? Under what conditions can this transient behavior accumulate asymptotically? In Chapter 4, we develop the radial and tangential velocity framework to characterize transient behavior in autonomous linear systems. In Chapter 5, we use this framework to construct an example of a non-autonomous linear system whose time-τ map has asymptotic behavior that differs from the asymptotic behavior of each instantaneous linear system that composes it. Future work seeks to determine whether this constructed example can arise as a variational equation, and thus provide a counterexample for our conjecture.
Production and decay of D1 (2420)0 and D2* (2460)0
Date: 1994-06-30
Creator: P. Avery, A. Freyberger, J. Rodriguez, R. Stephens, S., Yang, J. Yelton, D. Cinabro, S. Henderson, T. Liu, M. Saulnier, R. Wilson, H. Yamamoto, T. Bergfeld, B. I. Eisenstein, G. Gollin, B. Ong, M. Palmer, M. Selen, J. J. Thaler, K. W. Edwards, M. Ogg, B. Spaan, A. Bellerive, D. I. Britton, E. R.F. Hyatt, D. B. MacFarlane, P. M. Patel, A. J. Sadoff, R. Ammar, S. Ball, P. Baringer
Access: Open access
- We have investigated D+ π- and D*+ π- final states and observed the two established L = 1 charmed mesons, the D1 (2420)0 with mass 2421-2-2+1+2 MeV/c2 and width 20-5-3+6+3 MeV/c2 and the D2* (2460)0 with mass 2465 ± 3 ± 3 MeV/c2 and width 28-7-6+8+6 MeV/c2. Properties of these final states, including their decay angular distributions and spin-parity assignments, have been studied. We identify these two mesons as the jlight = 3 2 doublet predicted by HQET. We also obtain constraints on Γs/ (Γs + ΓD) as a function of the cosine of the relative phase of the two amplitudes in the D1 (2420)0 decay. © 1994.
Reading & Teaching Chaucer: the "Good Wif"?
Date: 2020-01-01
Creator: Sophie Friedman
Access: Open access
- This two-chapter project applies formalist and feminist thinking to the thirty-line description of the Wife of Bath in Geoffrey Chaucer’s medieval, British work The Canterbury Tales. It is an interdisciplinary project; it studies how to read and teach Chaucer at the secondary level based off of these two approaches. In this formalist chapter, I study narrative voice, rhyme, irony, and ekphrasis, writing about the history and function of each of those tools and their role in the passage. I argue that the formalist close reading approach is an excellent teaching tool that generates thorough, rigorous, and joyful reading. In this feminist chapter, I compile a critical literary history of scholarly feminist and pre-feminist engagement with the passage over time. I read into an underlying genotype text, arguing that the Wife of Bath was a female entrepreneur who used textiles as a means of social, professional, and aesthetic expression and empowerment. Then I advocate for a feminist ethical teaching approach—one where we use the text as a non-ethical space in which to explore ethical questions surrounding gender. Ultimately, I argue that feminist and formalist approaches are interdependent and complementary; for both reading and teaching Chaucer, they stand stronger together.
Measurement of the branching fraction scrB(τ-→h- →π0ντ)
Date: 1994-01-01
Creator: M. Artuso, M. Goldberg, D. He, N. Horwitz, R., Kennett, R. Mountain, G. C. Moneti, F. Muheim, Y. Mukhin, S. Playfer, Y. Rozen, S. Stone, M. Thulasidas, G. Vasseur, X. Xing, G. Zhu, J. Bartelt, S. E. Csorna, Z. Egyed, V. Jain, K. Kinoshita, B. Barish, M. Chadha, S. Chan, D. F. Cowen, G. Eigen, J. S. Miller, C. O'Grady, J. Urheim, A. J. Weinstein, D. Acosta
Access: Open access
- Using data from the CLEO II detector at the Cornell Electron Storage Ring, we measure scrB(τ-→h-π0ντ) where h- refers to either π- or K-. We use three different methods to measure this branching fraction. The combined result is scrB(τ-→h-π0ντ)=0.2587±0. 0012±0.0042, in good agreement with standard model predictions. © 1994 The American Physical Society.