Studies of multicomponent assemblies

textThis dissertation is divided into three major sections (one on dendrimers, one on tripodal metal ligands and one on a research oriented chemistry curricula) with a primary focus on different types of multicomponent assemblies. In the first chapter, a system is described that used a multicomponent assembly of AT-PAMAM dendrimers and an indicator, carboxyfluorescein, to detect and identify various polyanions at a low micromolar concentration. The system was able to successfully differentiate twelve anions, many of biological interest, including three tricarboxylates. The tricarboxylates were differentiated based primarily on the regiochemistry of the anionic groups. In the second chapter, further studies with AT-PAMAM dendrimers were carried out to provide some understanding of the thermodynamic origins of binding. Utilizing isothermal titration calorimetry, the binding of the dendrimers to large polyanionic dendrons with increasing numbers of charges was studied. Through these studies, the thermodynamic values of the binding events were obtained allowing us to explore the properties of the dendrimers. The cooperativity of the system was measured, and primarily negative cooperativity determined by the entropic contributions was uncovered. As the dendrimers increased in size, the thermodynamic origins of binding were determined to a greater extent by the entropy of binding. In the third chapter, a novel dynamic ligand system for metal binding is described. In the presence of a metal salt, a heterocyclic aldehyde and a secondary amine with two heterocyclic arms reversibly condense to form a hemiaminal with a tripodal metal binding site. This chapter describes studies on the metal binding ability, the variety of metals that will lead to this formation, the effects of anions and the range of aldehydes that can be used are described. Furthermore, the system’s reversibility was explored. Finally, the use of a bistriazole secondary amine was explored. The modular nature of triazole formation could lead to the introduction of additional functionalities. The fourth chapter discusses how the novel ligand system could be used to study the enantiomeric excess (ee) of chiral thiols. Based upon the system’s ability to form a stable hemiaminal thioether, a CD signal could be generated that is proportional to the amount of a particular enantiomer in solution. Using this system, a calibration curve relating CD signal and ee can be generated giving the ee of an unknown solution. In the final chapter, a look at the Freshman Research Initiative will be carried out with a focus on the ability to teach basic skills in an introductory laboratory through research. Four different skills or techniques will be explored through three different FRI streams,x and how they teach the four skills. Finally, analysis of the success of the program, particularly students’ success in the next laboratory course in the sequence, is discussed, and a model for adopting this type of teaching at other universities is given.Chemistr

Zeroing in on more photons and gluons

We discuss radiation zeros that are found in gauge tree amplitudes for processes involving multi-photon emission. Previous results are clarified by examples and by further elaboration. The conditions under which such amplitude zeros occur are identical in form to those for the single-photon zeros, and all radiated photons must travel parallel to each other. Any other neutral particle likewise must be massless (e.g. gluon) and travel in that common direction. The relevance to questions like gluon jet identification and computational checks is considered. We use examples to show how certain multi-photon amplitudes evade the zeros, and to demonstrate the connection to a more general result, the decoupling of an external electromagnetic plane wave in the ``null zone". Brief comments are made about zeros associated with other gauge-boson emission.Comment: 26 page

An Introduction: Adapting to a Rapidly Changing World

The 2015 American Society of International Law (ASIL) Annual Meeting aimed to assess how international law is and should be adapting to the profound global changes that are now underway. The Meeting took place against a dramatic backdrop of events: the rapid expansion of the so-called Islamic State in Syria and Iraq; a security and refugee crisis in the Middle East; escalating conflict in Eastern Ukraine and Crimea; an Ebola crisis in West Africa; and the build-up to a widely anticipated round of negotiations on climate change. These and similar geopolitical developments raise serious questions about the continued relevance and adequacy of existing international legal arrangements and institutions. For example, are the traditional processes for making international law capable of effectively and legitimately addressing these challenges? Can existing international institutions maintain their relevance in an increasingly multi-polar system? And how should the world tackle complex problems such as the proliferation of violence among non-state actors, degradation of the global environment, and persistent levels of severe poverty

Navigational Efficiency of Nocturnal Myrmecia Ants Suffers at Low Light Levels

Insects face the challenge of navigating to specific goals in both bright sun-lit and dim-lit environments. Both diurnal and nocturnal insects use quite similar navigation strategies. This is despite the signal-to-noise ratio of the navigational cues being poor at low light conditions. To better understand the evolution of nocturnal life, we investigated the navigational efficiency of a nocturnal ant, Myrmecia pyriformis, at different light levels. Workers of M. pyriformis leave the nest individually in a narrow light-window in the evening twilight to forage on nest-specific Eucalyptus trees. The majority of foragers return to the nest in the morning twilight, while few attempt to return to the nest throughout the night. We found that as light levels dropped, ants paused for longer, walked more slowly, the success in finding the nest reduced and their paths became less straight. We found that in both bright and dark conditions ants relied predominantly on visual landmark information for navigation and that landmark guidance became less reliable at low light conditions. It is perhaps due to the poor navigational efficiency at low light levels that the majority of foragers restrict navigational tasks to the twilight periods, where sufficient navigational information is still available.AN acknowledges funding support from the Australian Research Council’s (ARC) Centres of Excellence Scheme, ARC Discovery Project and Australian Postdoctoral Fellowship (DP0986606), ARC Discovery Early Career Award (DE120100019), Hermon Slade Foundation and The Defence Science and Technology Organization. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript