Browsing by Subject "Selectivity"
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Item Capturing the nature of issue publics : selectivity, deliberation, and activeness in the new media environment(2013-08) Chen, Hsuan-Ting, active 2013; Coleman, Renita; Stroud, Natalie JominiThis dissertation seeks to understand how issue publics contribute to citizen competence and the functioning of democracy. In the first part of the dissertation, a new measurement was constructed by theoretically and empirically analyzing the attributes of issue public members. Through the hypotheses testing, the new measure was more reliable in identifying issue public members compared to previous measurement strategies. Employing the new measure, results show that issue public members with concern about a specific issue, exercised their issue-specificity in seeking information (i.e., issue-based selectivity) with exposure to both attitude-consistent and counter-attitudinal perspectives. Issue public membership also had significant effects on issue-specific knowledge, and generating rationales for their own and other's oppositional viewpoints. These direct effects were mediated by issue-based selectivity. The relationships highlight the importance of issue publics in contributing to the deliberative democracy. In addition, issue publics play a significant role in contributing to the participatory democracy in that issue public members have greater intentions to participate in issue-related activities than nonmembers. However, while issue publics come close to solve the deliberative-participatory paradox, it was found that their information selectivity and argument generation were unbalanced in a way of favoring pro-attitudinal perspectives over counter-attitudinal perspectives. The second part of the dissertation examined conditional factors--accuracy and directional goals in affecting information selectivity and processing. The findings show that directional goals influenced participants to apply either the strategies of selective approach or selective avoidance to seek information depending on the issue. Accuracy goals exerted a main effect on the issue that is relatively less controversial and less obtrusive. They also interacted with issue public membership in influencing the less controversial and less obtrusive issue. Argument generation was not affected by accuracy or directional goals. Overall, through conceptualizing citizens as members of different issue publics, individuals are more competent then we thought. Their intrinsic interest in an issue serves as a strong factor affecting their information selectivity, information processing, and political actions. Despite finding an optimistic role for issue publics in the democratic process, their limitations also should be recognized. The implications for the deliberative and participatory democracy are discussed.Item Conformational dynamics plays a significant role in HIV reverse transcriptase resistance and substrate selection(2012-12) Nguyen, Virginia Myanh; Johnson, Kenneth A. (Kenneth Allen)Human immunodeficiency virus reverse transcriptase (HIV RT) is a virally encoded polymerase responsible for replicating the HIV genome. Most HIV treatments include nucleotide RT inhibitors (NRTIs) which inhibit HIV RT replication by serving as a substrate for the polymerase reaction but then blocks subsequent polymerization after incorporation. However, resistance to these NRTIs may occur through specific mutations in HIV RT that increase the discrimination of HIV RT for natural nucleotides over NRTIs. The role of enzyme conformational dynamics in specificity and substrate selection was studied using transient kinetic methods on HIV RT enzymes that have been site-specifically labeled with a conformationally sensitive fluorophore, to measure the rates of binding and catalysis. First, HIV RT with the mutation of lysine to arginine at the residue position 65 (K65R) was examined for its resistance against the NRTI tenofovir diphosphate (TFV), an acyclic deoxyadenosine triphosphate (dATP) analog. It was found that HIV RT K65R resistance to TFV was achieved through decreased rates of catalysis and increased rates of dissociation for TFV over dATP when compared with the kinetics of wild-type HIV RT. Moreover, global fitting analysis confirmed a mechanism where a large conformational change, after initial ground state binding of the substrate, contributed significantly to enzyme specificity. This led to our investigation of the molecular basis for enzyme specificity using HIV RT as a model system. Again, transient kinetic methods were applied with the addition of molecular dynamics simulations. The simulated results were substantiated by the corroborating experimental results. It was found that a substrate-induced conformational change in the transition of HIV RT from an open nucleotide-bound state to a closed nucleotide-bound state was the major determinant in enzyme specificity. The molecular basis for substrate selection resulted from the molecular alignments of the substrate in the active-site, which induced the conformational change. When the correct nucleotide was bound, optimal molecular interactions in the active-site yielded a stably closed complex, which promoted nucleotide incorporation. In contrast, when an incorrect nucleotide was bound, the molecular interactions at the active-site were not ideal, which yielded an unstable closed complex, which promoted substrate dissociation rather than incorporation.Item Selective anion exchange and anion-tuned gas sorption in a phosphine coordination material(2019-05-06) Riparetti, Ryan Douglas; Humphrey, Simon M.Herein we report a new ligand tris(4-(pyrid-4-yl)phenyl)phosphine sulfide (tppps) as a building block for the synthesis of a zeolite-like Phosphine Coordination Material (PCM). PCM-63 was made solvothermally with tppps and AgNO₃, producing off-white prisms. The material underwent selective anion exchange with PF₆ ̄ and ClO₄ ̄ over five other anions in a competition experiment. PCM-63 could remove 36.4% and 27.0% of 1 mM ReO₄ ̄ and ClO₄ ̄ in the presence of 100 mM Cl ̄, respectively. Four single-crystal to single-crystal studies were carried out with ReO₄ ̄, PF₆ ̄, ClO₄ ̄, and BF₄ ̄, each showing numerous CH···X (X = O, F) interactions between the framework and the anion. The anion-exchanged materials exhibited a large increase in surface areas for gases. Most notably, PCM-63-BF₄ and PCM-63-PF₆ exhibited a CO₂ surface area of 463 m²g⁻¹ and 466 m²g⁻¹, respectively. This is a large increase in surface area from PCM-63, which has a CO₂ surface area of 80 m²g⁻¹, suggesting that CH···F interactions stabilize the framework