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Protonation and Non-Innocent Ligand Behavior in Pyranopterin Dithiolene Molybdenum Complexes
Get PDFThe complex [TEA][Tp*MoIV(O)(S2BMOPP)] (1) [TEA = tetraethylammonium, Tp* = tris(3,5-dimethylpyrazolyl)hydroborate, and BMOPP = 6-(3-butynyl-2-methyl-2-ol)-2-pivaloyl pterin] is a structural analogue of the molybdenum cofactor common to all pyranopterin molybdenum enzymes because it possesses a pyranopterin-ene-1,2-dithiolate ligand (S2BMOPP) that exists primarily in the ring-closed pyrano structure as a resonance hybrid of ene-dithiolate and thione-thiolate forms. Compound 1, the protonated [Tp*MoIV(O)(S2BMOPP-H)] (1-H) and one-electron-oxidized [Tp*MoV(O)(S2BMOPP)] [1-Mo(5+)] species have been studied using a combination of electrochemistry, electronic absorption, and electron paramagnetic resonance (EPR) spectroscopy. Additional insight into the nature of these molecules has been derived from electronic structure computations. Differences in dithiolene C–S bond lengths correlate with relative contributions from both ene-dithiolate and thione-thiolate resonance structures. Upon protonation of 1 to form 1-H, large spectroscopic changes are observed with transitions assigned as Mo(xy) → pyranopterin metal-to-ligand charge transfer and dithiolene → pyranopterin intraligand charge transfer, respectively, and this underscores a dramatic change in electronic structure between 1 and 1-H. The changes in electronic structure that occur upon protonation of 1 are also reflected in a large \u3e300 mV increase in the Mo(V/IV) redox potential for 1-H, resulting from the greater thione-thiolate resonance contribution and decreased charge donation that stabilize the Mo(IV) state in 1-H with respect to one-electron oxidation. EPR spin Hamiltonian parameters for one-electron-oxidized 1-Mo(5+)and uncyclized [Tp*MoV(O)(S2BDMPP)] [3-Mo(5+)] [BDMPP = 6-(3-butynyl-2,2-dimethyl)-2-pivaloyl pterin] are very similar to each other and to those of [Tp*MoVO(bdt)] (bdt = 1,2-ene-dithiolate). This indicates that the dithiolate form of the ligand dominates at the Mo(V) level, consistent with the demand for greater S → Mo charge donation and a corresponding increase in Mo–S covalency as the oxidation state of the metal is increased. Protonation of 1 represents a simple reaction that models how the transfer of a proton from neighboring acidic amino acid residues to the Mo cofactor at a nitrogen atom within the pyranopterin dithiolene (PDT) ligand in pyranopterin molybdenum enzymes can impact the electronic structure of the Mo-PDT unit. This work also illustrates how pyran ring–chain tautomerization drives changes in resonance contributions to the dithiolene chelate and may adjust the reduction potential of the Mo ion
Fichte and Hegel on free time
Get PDFTo us today, it seems intuitive that an ideal society would secure for its citizens some time for leisure that is, some time to do “whatever they want” after having attended to their various responsibilities and natural needs. But, in this essay, I argue that—in 19th century social philosophy—the status of leisure (Muße) in an ideal society was actually surprisingly controversial: whereas J.G. Fichte makes a strong case for leisure as part of an ideal society (going even so far as considering it its central good), G.W.F. Hegel implicitly argues against this idea. For him, leisure is a crook that we only need as long as the social conditions are not sufficiently ideal—whereas a truly rational society would create a new type of work that subsumes the benefits of leisure into work itself. In this essay, I reconstruct this largely forgotten disagreement and argue that although both positions contain an important overstatement, each includes an important lesson for the contemporary debate on leisure and society
Goethe’s Faust and the philosophy of money
Get PDFPhilosophers today do not think of Goethe’s Faust as an important contribution to the philosophy of money. But to discount the work in this way is a mistake, I argue. Underneath Faust’s lyrical form, Goethe develops a comprehensive view of money that came to be an important influence on left-wing (Karl Marx) and right-wing (Oswald Spengler) discussions of money. Centrally, Goethe argues that modern economic practices have transformed money obsession (long conceived of primarily as an individual vice) into a structural problem: social structures are now set up to systematically require individuals to engage in quasi-obsessive behaviors towards money (e.g. persistently talking about/sacrificing for money) independently, to a significant degree, from their individual choices. This structural power, Goethe proposes, requires a rethinking of how behavior towards money should be morally evaluated – and, importantly, a critique of moral attitudes that individualize what is, in truth, a social problem
The Shifting Role of Climate Change in the 2021 Bundestag Election
Get PDFThe climate crisis unfolded in real time during the 2021 Bundestag campaign, as western Germany experienced sudden, catastrophic flooding. The climate issue presented a varying and at times unexpected array of challenges and opportunities to the German political parties. In this article I will analyze the shifting role of climate change as it played out during the campaign, in the coalition discussions that followed, and in the first nine months of the new traffic light coalition government
Understanding and Harnessing the Structural Features that Govern HMG-CoA Reductase Activity
Get PDFThe enzyme 3-hydroxy-3-methylglutaryl coenzyme-A reductase (HMGR), which catalyzes the reduction of HMG-CoA to mevalonate using two equivalents of the cofactor NAD(P)H, is part of the mevalonate pathway, found in all kingdoms of life. This pathway is at the heart of natural product biosynthesis constituting one of the obligate routes to producing the building blocks for isoprenoids, which represent the largest and most diverse class of natural products. Natural products and its derivatives continue to provide important compounds in the fields of drug development, biomedical engineering, and commercially-driven products. Therefore, HMGR, which performs the rate-limiting step of the mevalonate pathway garners significant attention in these fields. Understanding of the mechanism of HMGR remains incomplete, with gaps pertaining to the role of a putative C-terminal flap domain (CTD) responsible for helping to modulate the positioning of active site residues as well as the flux of substrates, intermediates, and products during the reaction. Moreover, investigation into structural determinants of cofactor specificity, which contribute towards varied cofactor preferences observed among HMGR homologs, point to a cofactor helix as being crucial, and warrants further analysis.
Here, class II HMGRs from Delftia acidovorans (DaHMGR) and Streptococcus pneumoniae (SpHMGR) are used as case-studies in elucidating biophysical, kinetic, and X-ray crystallographic features that aid in our understanding of the three-dimensional characteristics of class II HMGR including its catalytic and oligomeric states in solution, the role of the CTD in the mechanism and features governing cofactor specificity. We provide the first crystal structures of
DaHMGR alongside complementary kinetic studies showing it to be an NAD-preferring HMGR. We observe that NAD-preferring HMGRs are able to form hexamers whereas NADP-preferring HMGRs predominate as dimers. Structures obtained with the CTD in novel locations expands our knowledge on this domain. We observe a flipped conformation of the CTD that appears to capture an intermediate state. The importance of the cofactor helix is manifest through protein engineering efforts that switch specificity by switching this motif between HMGRs. This work expands on the current class II HMGR paradigm as it relates to structural and functional dynamics, providing greater insight into this biologically important enzyme
The Rural Settlements of Hellenistic and post-Hellenistic Central Asia: an Archaeology of Indigenous Life under Colonial Rule
Get PDFHellenistic Central Asia is among the most exoticized areas of study for Classical and Near Eastern archaeological research due to the discovery of ancient Greek colonies in the modern nations of Afghanistan, Tajikistan, and Uzbekistan. Most notable is the excavations of the Hellenistic “new foundation” at Ai Khanoum in the Dasht-i Qala Plain of northeast Afghanistan. This dissertation approaches Greek rule in Central Asia from a post-colonial perspective in decentering scholarly emphases on Hellenism in the east in favor of a new paradigm that emphasizes the diversity of indigenous lifeways among ancient, colonized Bactrians and Sogdians. Drawing on a vast overlooked dataset of Soviet and post-Soviet archaeological literature, as well as my own excavations of a rural farmstead at Bashtepa in western Uzbekistan, I situate indigenous life under colonial rule within the context of rural, non-elite agriculturally based economies. Methodologically this involves: first, the systematic GIS mapping of nearly 1,250 known archaeological sites from the 4th c. BCE – 4th c. CE to determine where ancient indigenous populations lived; and second, a detailed appraisal of rural settlement architecture across these vast landscapes. This data is then compared to preliminary results of excavations of a rural farmstead a Bashtepa, the first scientifically excavated pit-house farmstead in Central Asia. It is shown that standing biases in Classical and Near Eastern approaches to Central Asian archaeology have confused our understanding of ancient life in this region, overemphasized the importance of Greek rule, and ignored evidence for non-Greek rural life
Who Does That?: Further Conversations on Drawing Down the Moon
Get PDFThis paper addresses responses to Drawing Down the Moon by Shannon Grimes, James Davila, Gregory Shaw, and Naomi Janowitz, using the cues of extraordinary efficacy, performance, social location, and ends to determine whether something is labeled magic and by whom. In each of the papers, the cue of social location appears as the most significant, even though the others each play a role as well
The effects of field history on magnetic skyrmion formation in [Pt/Co/ Ir]3 multilayers
Get PDFWe report on the formation of Néel-type magnetic bubble skyrmions at room temperature in [Pt/Co/Ir]3 multilayered thin films after an in-plane magnetic field treatment. Polar magneto-optical Kerr Effect (p-MOKE) microscopy images show that the dendritic magnetic configurations observed after AC demagnetization evolve into magnetic bubble skyrmions after the application and subsequent removal of an in-plane magnetic field. Micromagnetic simulations were used to systematically investigate the role of the in-plane magnetic field magnitude, misalignment of the sample, and the Dzyaloshinskii-Moriya interactions (DMI) in generating bubble skyrmions during the field treatment. The simulations show that in-plane fields slightly below the saturation field are the most effective at producing skyrmions, and, furthermore, a small field angle away from the sample plane not only leads to improved skyrmion formation but also provides a means to select the skyrmion polarity where the direction of the out-of-plane component of the field is opposite to the direction of the skyrmion cores. This field treatment scheme leads to a simple and reliable way to create magnetic bubble skyrmions in multilayered thin films with DMI
