Добірка наукової літератури з теми "ZnCe6"

Photosystem II (PSII) is the chlorophyll/protein complex in green plants that catalyzes the oxidation of water to molecular oxygen. We have utilized bacterioferritin (BFR), an iron storage protein found in Escherichia coli, as a protein scaffold to build in PSII cofactors in a simpler in vitro model system. Previously, we have shown that the native heme in BFR can be replaced with the chlorophyll analog zinc-chlorin (ZnCe6) and that the intrinsic di-iron site can bind two manganese ions. Upon flash excitation of the ZnCe6 modified BFR, not only is the dinuclear manganese complex oxidized but also a tyrosine residue. There are seven tyrosine residues in each BFR monomeric subunit. We mutated the three tyrosine residues within electron tunnelling distance of the ZnCe6. Here we present evidence based on electron paramagnetic resonance and fluorescence spectroscopy that one is not oxidized while the other two seem to be oxidized in parallel. Localization of this photoactive tyrosine is the first step in creating a linear electron flow in BFR like in PSII.

Abstract ZnC6(NO2)2O4 · 2 H2O was grown in aqueous silicagel. It crystallizes monoclinically (space group I2/c). Zn2+ has CN 6 . It is surrounded in a distorted octahedral fashion by 2 water molecules in cis -position and 4 oxygen atoms of the bis-chelating [C6(NO2)2O4]2- ions. Thereby infinite corrugated chains are formed consisting of Zn2+ and the nitranilate dianions. These chains are interlinked by hydrogen bonds between H2O and the NO2 groups. The NO2 groups are twisted against the ring plane. The bond lengths in the dianion are typical of completely delocalized π-electrons.

The M against H loops and single peaks in dM/dH vs. H curves were noticed in SrFe₁₂O₁₉/MnCe_0.04Fe_1.96O₄, SrFe₁₂O₁₉/CuCe_0.04Fe_1.96O₄ and SrFe₁₂O₁₉/ZnCe_0.04Fe_1.96O₄ hard/soft nanocomposites that indicated the manifestation of well exchange-coupled effect among hard and soft phases in these composites.

The photosynthetic reaction centre (RC) is central to conversion of solar energy into chemical energy. In this thesis, in order to introduce the redox-active cofactors similar to that of the Photosystem II RC, a non-photosynthetic protein scaffold was used as an in vitro model. The protein tasked for this purpose was the heme containing bacterioferritin (BFR) protein found in E. coli. The BFR protein naturally expresses as a homodimer based on a 4-helix bundle monomer. Desirable properties included: (i) a promiscuos di-nuclear metal binding site which provides ligands for class II metals such as Mn (ii) a hydrophobic pocket at the dimer interface which can bind a photosensitive porphyrin, in this case a chlorin (Ce6), and (iii) presence of tyrosine residues proximal to the bound cofactors, which can be utilised as efficient electron-tunnelling intermediates. The work in this thesis extends earlier work in the group by refining and improving the BFR system. Several mutants were made and an improved protein expression system was developed. For these samples experiments demonstrated ligation of weakly coupled equivalent Mn2II,II at the di-nuclear binding site of apo-BFR, and binding of the photo-active pigment ZnCe6 in hydrophobic pocket of the protein. Light-induced electron transfer from proximal tyrosine residue(s) to the photo-oxidised ZnCe6+, in the modified BFR reconsitituted with both ZnCe6 and MnII is presented. Three site-specific tyrosine mutants (Y25F, Y58F and Y45F) were made to localise the redox-active tyrosine in this engineered system. The results indicate that: (i) presence of bound MnII is necessary to observe tyrosine oxidation in all BFR variants, (ii) Y45 (within van Der Waals network of ZnCe6) is singly the most important tyrosine as the immediate electron donor to the oxidised ZnCe6+, and (iii) Y25 and Y58 are both redox-active in this system, but appear to be interchangebale. A high-resolution (~1.5 Ã…) crystal structure of the three tyrosine mutants was obtained and these structures showed there to be no mutation-induced effects on the overall 3-D structure of the protein. Minimal effects observed in the Y45F mutant are reported. The molecular design of a "second generation" of the BFR series is also presented where the symmetry of the BFR homodimer is broken to generate a BFR heterodimer to contain genetically distinct electron donor and acceptor subunits. The BFR heterodimer was made by introducing a small (20 aa) peptide linker between the two subunits. The ultimate goal will be to demonstrate light-induced directional electron flow in the BFR heterodimer.

Housing approximately half a million residents, the New York City Housing Authority (NYCHA) has long been cast as the exception to the rule of ‘demolish and replace’ models of public housing in the United States. Yet as NYCHA faces a dire fiscal and administrative crisis, it has proposed a suite of privatization efforts that threaten its successful reputation. With a focus on NYCHA’s effort to allow private developers to construct mixed-income ‘infill’ projects on existing ‘underutilized’ public housing land through the NextGeneration NYCHA and NYCHA 2.0 plans, in this dissertation, I ask: how do various stakeholders, including residents, the housing authority, private developers, elected officials, and non-profit and advocacy stakeholders justify, react to, and resist NYCHA’s plans for redevelopment? While most studies consider the impacts of mixed-income housing on residents after lease up of a development, interpreting it as either a de facto beneficial policy or as a tool for state-led gentrification, this work differs in its focus on the range of viewpoints about the plan prior to construction. In so doing, it straddles the literature on mixed-income housing and urban planning processes through the lens of pragmatism. A pragmatic approach centers those most impacted in planmaking and considers how diverse stakeholder experiences co-exist and contrast in public deliberation processes. In other words, this dissertation considers how the housing authority’s various publics have reacted differently to the plans for its transformation with the goal of informing how to craft more restorative, equitable, and deliberative planning processes. Using data from over a year and a half of participant observation, interviews, and media and policy sources, I craft a qualitative narrative case of the deliberations surrounding NYCHA’s first five years of redevelopment from a variety of stakeholder perspectives. Using narrative and framework analysis, I organize this dissertation around three empirical chapters: 1) an anatomy of the formal and dialogical channels of engagement between speakers and NYCHA officials at 10 public meetings following the NextGeneration NYCHA plan’s release; 2) an account of the housing authority’s stop-and-start approach to pursuing infill set amidst its various crises, including an analysis of the viewpoints of public officials and a private developer selected for a pilot infill site; and 3) a description of residents’ opposition to the plan, which includes descriptions of spaces of contestation citywide and at a specific pilot infill development on the Upper East Side of Manhattan. I find that while multiple stakeholders agree on the end goal of repairing existing public housing, actors promote a series of contradictions in their means to fix it, shaping a hotly contested landscape that has eroded public trust and further delayed action. Despite critiquing the housing authority for their management practices, residents launched a campaign to keep their homes publicly-operated that extended beyond the walls of their developments to citywide and even national progressive issues. This dissertation contributes to the housing policy and urban planning literature in three ways. First, it proposes an understanding of mixed-income housing that eschews past binary approaches and shows its perceived benefits and risks as highly dependent on the values and goals of the stakeholder. Second, it looks at conflicting attitudes to planmaking outside of a traditional consensus-based models, inviting a contextual understanding of power dynamics while also placing value on the experiences and actions of the majority Black and Latinx public housing residents who are the most impacted by the infill plans. Lastly, this dissertation also serves to profile pragmatism’s power–and limits– for theorizing more equitable redevelopment processes in planning.