Hydration Shell Water Structure and Aggregation of Small Amphiphilic Solutes

My research aims to address long-standing questions in physical chemistry about water-mediated hydrophobic and ionic interactions of biological relevance. For example, my research has provided some of the first experimental evidence of water driving hydrophobic groups apart rather than pushing them together in solution, thus damping rather than enhancing the contact free energy of oily molecules in water. I have also obtained some of the first experimental evidence concerning the structure of water structure around nonpolar groups in solution, thus demonstrating that hydrophobic hydration-shells have a clathrate hydrate-like structure. In addition, I am currently studying ionic interactions in water, which are important due to the ubiquity of solvated ions in living systems, along with three additional projects investigating solute polarity, charge, and substituent placement effects on solute aggregation and water structure. Finally, I have contributed to one project that probes aggregation of hydrophobic solutes in binary alcohol/water mixtures and to another, highly collaborative project that addresses the continued debate regarding the structure of hydrated protons in liquid water. Here, the combined application of Raman spectroscopy and multivariate curve resolution (Raman-MCR) to aqueous solutions has been used to reveal solute-correlated (SC) spectra, which contain vibrational spectral features arising from the hydration shell around a dissolved solute, as well as the solute itself. Such spectra are used to obtain information about changes in water structure, as a function of solute identity, size, shape, polarity, and charge. Moreover, Raman-MCR is used to probe water-mediated interactions between solute molecules, by detecting interaction-induced changes in the SC spectra of variable solution concentrations

Synthetically Guided Investigation of Lanthanide and Actinide Redox and Bonding Properties

The complex bonding and redox properties of actinide elements are much less understood compared to common main group and transition metal elements. This is likely the result of fewer chemical studies, due to the challenges of working with these radioactive elements. Nevertheless, understanding the chemical behavior of these elements, and how they differ from the lanthanide series, is crucial for nuclear materials processing and waste management. Along these lines, the first chapter discusses the interactions of an ONO-chelating redox-active ligand with uranium. Uranium derivatives of a dioxophenoxazine ligand, (DOPOq)2UO2, (DOPOsq)UI2(THF)2, (DOPOcat)UI(THF)2, and Cp*U(DOPOcat)(THF)2 (DOPO = 2,4,6,8-tetra-tert-butyl-1-oxo-1H-phenoxazin-9-olate), have been synthesized from U(VI) and U(III) starting materials. Full characterization of these species show uranium complexes bearing ligands in three different oxidation states. The electronic structures of these complexes have been explored using 1H NMR and electronic absorption spectroscopies, and where possible, X-ray crystallography and SQUID magnetometry. The second chapter describes the stability imparted by this dioxophenoxazine ligand in the formation of tris(DOPO) complexes. This chapter involves the discussion of the first non-aqueous isostructural series of coordination compounds for members across the f-block, including thorium uranium, plutonium, americium, berkelium, and californium, which is the broadest, most well-studied series of trivalent metals known. While californium would be expected to show purely electrostatic contributions to bonding due to its location in the series, spectroscopic, structural, and computational analyses shows higher degrees of covalent bonding compared to its neighbors to the left. This work provides a greater understanding of bonding between organic ligands and actinides, which can aid in the design of new ligands for encapsulation and separation of metals at the bottom of the periodic table. The third chapter addresses subtle electronic characteristics associated with redox-active ligand uranium complexes. Uranium complexes (MesDAE)2U(THF) (1-DAE) and Cp2U(MesDAE) (2-DAE), bearing redox-innocent α-diamine ligands, have been synthesized and characterized for a full comparison with previously published, redox-active α-diamine complexes, (MesDABMe)2U(THF) (1-DAB) and Cp2U(MesDABMe) (2-DAB). These redox-innocent analogues maintain a similar steric environment to their redox-active ligand counterparts to facilitate a study aimed at determining the differing electronic behavior around the uranium center. Structural analysis by X-ray crystallography showed 1-DAE and 2-DAE have a very similar structural environment to 1-DAB and 2-DAB, respectively. The main difference occurs with coordination of the ene-backbone to the uranium center in the latter species. Electronic absorption spectroscopy reveals these new DAE complexes are nearly identical to each other. X-ray absorption spectroscopy of all four species notes that there is a significant difference between the bis(diamide)-THF uranium complexes as opposed to those that only contain one diamide and two cyclopentadienyl rings, but there is little difference in valency between the two ligand systems. Finally, magnetic measurements reveal that all complexes display temperature dependent behavior consist with uranium(IV) ions that are not supported by ligand radicals. Overall, this study determines that there is no significant bonding difference between the redox-innocent and redox-active ligand frameworks on uranium. Furthermore, there is no data to suggest covalent bonding character using the latter ligand framework on uranium, despite what is known for transition metals. The fourth chapter describes the synthesis of redox-active pyridine(diimine) (PDI) lanthanide complexes with an aim to bring redox activity to the notoriously redox non active metal centers. A full reduction series of the MesPDIMe ligated to neodymium was accomplished using NdI3(THF)3.5 as a starting material. This series included the three electron reduced dimer, [MesPDIMeNd(THF)]2, which is an interesting structural analogue to known uranium compounds. Also, this dimer has demonstrated high reactivity towards a variety of substrates, making it an exciting platform with which to explore redox chemistry at a lanthanide center. The fifth chapter describes the synthesis and reactivity of new uranyl complexes containing novel alkyl amide ligands. New uranyl derivatives featuring the amide ligand, -N(SiHMe2)tBu, were synthesized and characterized by X-ray crystallography, multinuclear NMR spectroscopy, and absorption spectroscopies. Steric properties of these complexes were also quantified using the computational program Solid-G. The increased basicity of the free ligand -N(SiHMe2)tBu was demonstrated by direct comparison to -N(SiMe3)2, a popular supporting ligand for uranyl. Substitutional lability on a uranyl center was also demonstrated by exchange with the -N(SiMe3)2 ligand. Reactions of these complexes with substituted anilines promotes new reactivity, and sets the ground work for the isolation of a uranyl imido. Finally, the sixth chapter discusses the development of new molecular neptunium halide complexes that can be used as an entry into nonaqueous chemistry. Solvent exchange of NpCl4(DME)2 with THF yielded the THF adduct, NpCl4(THF)3, whereas PuCl4(DME)2 appears to be unstable in THF, partially decomposing through disproportionation to the mixed valent plutonium salt, [PuCl2(THF)5][PuCl5(THF)]. Reduction of NpCl4(THF)3 led to the isolation and structural and spectroscopic characterization of NpCl3(py)4, which is a rare example of a trivalent neptunium halide that was sourced from neptunium oxides rather than Np0

The Interplay of Structure and Dynamics in the Raman Spectrum of Liquid Water over the Full Frequency and Temperature Range

While many vibrational Raman spectroscopy studies of liquid water have investigated the temperature dependence of the high-frequency O-H stretching region, few have analyzed the changes in the Raman spectrum as a function of temperature over the entire spectral range. Here, we obtain the Raman spectra of water from its melting to boiling point, both experimentally and from simulations using an ab initio-trained machine learning potential. We use these to assign the Raman bands and show that the entire spectrum can be well described as a combination of two temperature-independent spectra. We then assess which spectral regions exhibit strong dependence on the local tetrahedral order in the liquid. Further, this work demonstrates that changes in this structural parameter can be used to elucidate the temperature dependence of the Raman spectrum of liquid water and provides a guide to the Raman features that signal water ordering in more complex aqueous systems

Inner-sphere vs. outer-sphere reduction of uranyl supported by a redox-active, donor-expanded dipyrrin

The uranyl(VI) complex UO2Cl(L) of the redox-active, acyclic diimino-dipyrrin anion, L− is reported and its reaction with inner- and outer-sphere reductants studied. Voltammetric, EPR-spectroscopic and X-ray crystallographic studies show that chemical reduction by the outer-sphere reagent CoCp2 initially reduces the ligand to a dipyrrin radical, and imply that a second equivalent of CoCp2 reduces the U(VI) centre to form U(V). Cyclic voltammetry indicates that further outer-sphere reduction to form the putative U(IV) trianion only occurs at strongly cathodic potentials. The initial reduction of the dipyrrin ligand is supported by emission spectra, X-ray crystallography, and DFT; the latter also shows that these outer-sphere reactions are exergonic and proceed through sequential, one-electron steps. Reduction by the inner-sphere reductant [TiCp2Cl]2 is also likely to result in ligand reduction in the first instance but, in contrast to the outer-sphere case, reduction of the uranium centre becomes much more favoured, allowing the formation of a crystallographically characterised, doubly-titanated U(IV) complex. In the case of inner-sphere reduction only, ligand-to-metal electron-transfer is thermodynamically driven by coordination of Lewis-acidic Ti(IV) to the uranyl oxo, and is energetically preferable over the disproportionation of U(V). Overall, the involvement of the redox-active dipyrrin ligand in the reduction chemistry of UO2Cl(L) is inherent to both inner- and outer-sphere reduction mechanisms, providing a new route to accessing a variety of U(VI), U(V), and U(IV) complexes

Synthesis and Electronic Structure Determination of Uranium(VI) Ligand Radical Complexes

   Pentagonal bipyramidal uranyl complexes of salen ligands, N,N’-bis(3-tert-butyl-(5R)-salicylidene)-1,2-phenylenediamine, in which R = tBu (1a), OMe (1b), and NMe2 (1c), were prepared and the electronic structure of the one-electron oxidized species [1a-c]+ were investigated in solution. The solid-state structures of 1a and 1b were solved by X-ray crystallography, and in the case of 1b an asymmetric UO22+ unit was found due to an intermolecular hydrogen bonding interaction. Electrochemical investigation of 1a-c by cyclic voltammetry showed that each complex exhibited at least one quasi-reversible redox process assigned to the oxidation of the phenolate moieties to phenoxyl radicals. The trend in redox potentials matches the electron-donating ability of the para-phenolate substituents. The electron paramagnetic resonance spectra of cations [1a-c]+ exhibited gav values of 1.997, 1.999, and 1.995, respectively, reflecting the ligand radical character of the oxidized forms, and in addition, spin-orbit coupling to the uranium centre. Chemical oxidation as monitored by ultraviolet-visible-near-infrared (UV-vis-NIR) spectroscopy afforded the one-electron oxidized species. Weak low energy intra-ligand charge transfer (CT) transitions were observed for [1a-c]+ indicating localization of the ligand radical to form a phenolate / phenoxyl radical species. Further analysis using density functional theory (DFT) calculations predicted a localized phenoxyl radical for [1a-c]+ with a small but significant contribution of the phenylenediamine unit to the spin density. Time-dependent DFT (TD-DFT) calculations provided further insight into the nature of the low energy transitions, predicting both phenolate to phenoxyl intervalence charge transfer (IVCT) and phenylenediamine to phenoxyl CT character. Overall, [1a-c]+ are determined to be relatively localized ligand radical complexes, in which localization is enhanced as the electron donating ability of the para-phenolate substituents is increased (NMe2 > OMe > tBu)

Undisciplined: Reading Affects in Late Medieval England

This dissertation analyzes scenes of “undisciplined reading” in late medieval texts: that is, scenes in which characters read without formal training and with the “wrong” emotions. As audiences for vernacular literature continued to expand in the fifteenth and sixteenth centuries, the undisciplined reader emerged as an important fiction for imagining their role in literary culture. I focus on genres of early literacy training such as fable, liturgy, and complaint because these forms were handled by novice, non-professional readers and, thus, were readily assumed to be vulnerable to misinterpretation. I argue that these generic forms enabled premodern authors to anticipate the multiple affects (or emotions) of developing reading audiences. In this way, the undisciplined reader comes to figure an English readership that would be defined by its affect as both collective and individual, educated and illiterate. My chapters examine undisciplined readers in Geoffrey Chaucer's Nun’s Priest Tale, Robert Henryson's fables, John Lydgate's Disguising at Hertford, and John Skelton's Phyllyp Sparowe and Speke Parot. My case studies include a layman (mis)interpreting a fable, a young girl (mis)performing a mass, and a company of peasants (mis)appropriating a complaint. In different ways, these representations illustrate how undisciplined reading is a mechanism in the late medieval period for negotiating––and sometimes challenging––the relation between reading, affect, gender, and class norms. A major implication of this project is that the undisciplined reader is not just a comic stereotype but a complex site of historical inquiry. In each chapter, the ambivalent affects of undisciplined readers––pleasure, anger, grief––shed light on late medieval literate activity that is absent from the historical archive. We have little archival evidence of the literate practices of medieval people who did not have regular access to books or who did not know how to write. In addition, this dissertation follows a sustained effort in the field of medieval studies to move beyond the domain of affective piety when we talk about the relationship between affect and reading. Fifteenth-century literature demonstrates the work of minor or lesser feelings in a period during which readers were imagined to engage with books by affectively irregular and irrational means. Altogether, I argue that the undisciplined reader illuminates the phenomenon of late medieval reading not only as a question of understanding or competence but also of feeling.PHDEnglish Language & LiteratureUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/174220/1/annikaj_1.pd

Leading for Social Justice A Principal's Utilization of a Rigorous College-Prep Curriculum to Challenge Injustice and Inequity in an Urban, High-Poverty High School

Nowhere is the nation’s commitment to equity of opportunity and outcomes more tested than in urban, high-poverty high schools. In considering efforts to address the persistent issues plaguing these schools, one distinct body of literature suggests that externally developed, academically rigorous college-prep programs can positively impact student outcomes. A second body purports that principal leadership, especially principals leading for social justice, is critical to achieving both academic and equity outcomes. Despite the existence of these bodies of literature, there remains a gap in the research linking the two in order to understand how principals leading for social justice can use an externally developed, academically rigorous college-prep program to improve equity for the historically marginalized students attending urban, high-poverty high schools. To fill this gap, this qualitative case study examined the following questions: 1) In what ways does an urban, high-poverty high school principal leading for social justice leverage an externally developed, academically rigorous college-prep program to increase access to core learning and academically rigorous content, improve core teaching, and create a climate of belonging? 2) What barriers does an urban, high-poverty high school principal leading for social justice encounter when endeavoring to implement and sustain an externally developed, academically rigorous college-prep program in a manner focused on justice and equity? 3) What strategies does an urban, high-poverty high school principal leading for social justice employ to counteract the barriers and resistance faced when attempting to implement and sustain an externally developed, academically rigorous college-prep program in a manner focused on justice and equity?Theoharis’ Framework for Social Justice Leadership (2009) served as the conceptual framework for this study. Descriptions of the principal, school, community, and the selected externally developed, academically rigorous college-prep program were shared to provide context. In answering the research questions, this study’s findings led to the conceptualization of frameworks regarding the social justice principal’s cycle of school improvement and system of student support. Implications for practitioners and future research are provided at the end of the study

Influence of Cononsolvency on the Aggregation of Tertiary Butyl Alcohol in Methanol–Water Mixtures

The term cononsolvency has been used to describe a situation in which a polymer is less soluble (and so is more likely to collapse and aggregate) in a mixture of two cosolvents than it is in either one of the pure solvents. Thus, cononsolvency is closely related to the suppression of protein denaturation by stabilizing osmolytes. Here, we show that cononsolvency behavior can also influence the aggregation of tertiary butyl alcohol in mixtures of water and methanol, as demonstrated using both Raman multivariate curve resolution spectroscopy and molecular dynamics simulations. Our results imply that cononsolvency results from the cosolvent-mediated enhancement of the attractive (solvophobic) mean force between nonpolar groups, driven by preferential solvation of the aggregates, in keeping with Wyman–Tanford theory