Mixed-valence bimetallic dithiolates of iron, cobalt, and nickel and their relevance to the hydrogenases

The world's energy economy is driven by petroleum, but this resource is limited and its consumption drives global climate change. As a result, it is crucial for the ongoing prosperity of humans to find an alternative means of energy production and storage. One alternative is hydrogen. Nature utilizes metalloproteins called hydrogenases (H2ases) to efficiently interconvert protons and electrons with dihydrogen. Though this is one of the simplest possible reactions, it is of utmost importance for countless microorganisms. The performance of these enzymes exceeds that of the leading artificial catalyst used by humans: platinum. Though platinum based catalysts are currently the best, the scarcity of this metal makes widespread utilization unfeasible. Nature, by necessity, must utilize earth abundant metals. Indeed, the premier enzymes that facilitate this reaction utilize the abundant metals nickel and iron. The active sites the [NiFe]- and [FeFe]-H2ases possess bimetallic cores bridged by thiolates. The iron centers are ligated by species that are peculiar in biological systems: carbon monoxide and cyanide. Due to the effectiveness of H2ases as H2 oxidation proton reduction catalysts, there is a strong drive to synthesize small molecule models of these active sites. Chapter 1 introduces hydrogen in the context of energy storage and microbiology and continues on to describe the details of the hydrogenases. The second half of this chapter discuses model compounds of the hydrogenases and various strategies, challenges, and successes in this area. Though more is known about the [NiFe]-H2ase, model compounds to date have largely failed to replicate any of the extensive mixed-valent states of this active site. This thesis advances this area specifically through the synthesis and examination of mixed-valent bimetallic dithiolate complexes. Chapter 2 focuses on the NiRu dithiolate compound (dppe)Ni(pdt)Ru(pcymene)(dppe = 1,2-bis(diphenylphosphino)ethane; pdt = 1,3-propanedithiolate, p-cymene =p-isopropyltoluene). The protonation and oxidation chemistry of this system are described. The principal finding this work is that the mixed-valent cation [(dppe)Ni(pdt)Ru(p-cymene)]+ both structurally and spectroscopically mimics the [NiFe]-H2ase active site in the Ni-L state and is the first such reported example. A disadvantage of these compounds is that they contain the platinum-group metal ruthenium. All other chapters in this thesis utilize only first row transition metals. Chapter 3 discusses the synthesis and properties of the cyclopentadienyl NiFe compound [CpNi(pdt)Fe(dppe)CO]BF4 (Cp = cyclopentadienide). These cyclopentadienyl complexes are the first reported examples of model compounds to accurately replicate theredox inactive iron center of [NiFe]-H2ase. Additionally, this system is shown to stabilize nickel in the first, second, and third oxidation states. Treatment of the Ni(II)Fe(II) compound [CpNi(pdt)Fe(dppe)CO]BF4 affords the neutral, mixed-valent compound CpNi(pdt)Fe(dppe)CO, which has been extensively characterized through numerous spectroscopic techniques and DFT calculations to be a bona fide Ni(I)Fe(II) complex. When this compound is treated with acid, the Ni(II)Fe(II) cation [CpNi(pdt)Fe(dppe)CO]+ is regenerated with the concomitant production of 0.5 equiv. of H2 making this system a proton reduction catalyst. The catalytic cycle was analyzed using DFT. The mixed-valence hydride [CpNi(pdt)(μ-H)Fe(dppe)CO]BF4 is not observed directly but is unambiguously Ni(III)Fe(II), akin to the mixed-valent Ni-C state of [NiFe]-H2ase, by DFT analysis. Chapter 4 describes the synthesis and characterization of mixed-valent di- and tri-nickel cyclopentadienyl dithiolates. The reaction between nickelocene and monothiols has long been known to yield dimers of the form [CpNi(SR)]2 with loss of CpH. The reaction of nickelocene with dithiols is investigated in chapter 4 and is found to be quite complex: dinickel, trinickel, and pentanickel species are formed. In contrast to the known monothiolate dimers, the dithiolate compounds feature a pyramidalized Ni2S2 core by virtue of the dithiolate linker. This distortion of the Ni2S2 core forces the two nickel centers together. As a consequence, the dinickel compounds Cp2Ni2(pdt) and Cp2Ni2(edt) (edt = 1,2-ethanedithiolate) have a thermally accessible triplet state, a feature which has been proposed in some DFT analyses of the [NiFe]-H2ase active site. Another consequence of the close proximity of these metal centers is a facile one electron oxidation to generate Ni(2.5)2 compounds. This chapter includes DFT analysis of the monothiolate dimer Cp2Ni2(SEt)2 in which the Ni2S2 core is distorted computationally. This study shows the drastic effects of bending the Ni2S2 core. Chapter 5 investigates the properties of the mixed-valent cation [Cp2Co2(pdt)]+ and the mixed-valent bridging hydride complexes Cp2Co2(xdt)H (xdt = edt, pdt). The CpCo fragment is isoelectronic with the Fe(CO)3 fragment that frequently appears in model complexes. The cation [Cp2Co2(pdt)]+ generates the bridging hydroxide cation[Cp2Co2(pdt)OH]+ upon treatment with aqueous THF. Similarly, the bridging thiolates compounds are generated upon treatment of [Cp2Co2(pdt)]+ with thiols. Both the mixed-valent bridging hydride compounds and the mixed-valent cation are discrete Co(III)Co(II) species, in contrast to the Ni(2.5)2 species in the analogous nickel systems

DNA fingerprinting in zoology: past, present, future

In 1962, Thomas Kuhn famously argued that the progress of scientific knowledge results from periodic 'paradigm shifts' during a period of crisis in which new ideas dramatically change the status quo. Although this is generally true, Alec Jeffreys' identification of hypervariable repeat motifs in the human beta-globin gene, and the subsequent development of a technology known now as 'DNA fingerprinting', also resulted in a dramatic shift in the life sciences, particularly in ecology, evolutionary biology, and forensics. The variation Jeffreys recognized has been used to identify individuals from tissue samples of not just humans, but also of many animal species. In addition, the technology has been used to determine the sex of individuals, as well as paternity/maternity and close kinship. We review a broad range of such studies involving a wide diversity of animal species. For individual researchers, Jeffreys' invention resulted in many ecologists and evolutionary biologists being given the opportunity to develop skills in molecular biology to augment their whole organism focus. Few developments in science, even among the subsequent genome discoveries of the 21st century, have the same wide-reaching significance. Even the later development of PCR-based genotyping of individuals using microsatellite repeats sequences, and their use in determining multiple paternity, is conceptually rooted in Alec Jeffreys' pioneering work

High-resolution sequencing of DNA G-quadruplex secondary structures in the human genome

This is the author accepted manuscript. The final version is available from NPG via http://dx.doi.org/10.1038/nbt.3295During active transcription and replication chromatin architecture is altered, allowing formation of DNA secondary structures. G-quadruplexes (G4s) have emerged as important regulatory DNA structures and have been associated with genomic instability, genetic diseases and cancer progression. Experimental evidence for G4 prevalence in the entire human genome is still lacking. We present a high-resolution sequencing-based method that detected 716,310 distinct G4s in the human genome, more than predicted by computational methods, including structural variants previously uncharacterised in a genomic context. We observed high G4-density in functional regions, such as 5’ UTRs and splicing sites, and in genes not predicted to have such structures (BRCA1 and BRCA2). We found a significant association of G4 formation with oncogenes and tumor suppressors, and with Somatic Copy-Number Alterations (SCNAs) that act as cancer drivers. Our results support that G4s are promising targets for cancer intervention and suggest novel candidates for further biological and mechanistic studies.We are grateful to the Biotechnology and Biological Sciences Research Council (BBSRC) and Illumina® for the studentship supporting V.C (BB/I015477/1). The S.B. research group is supported by programme funding from Cancer Research UK and from the European Research Council and project funding from BBSRC

The Ursinus Weekly, October 20, 1972

Frats select queens for 1972 Homecoming • Ursinus graduate awarded Nobel Prize for medicine • Homecoming, dedication and Founder\u27s Day scheduled Saturday • Bailey named to Bowl Committee • Elliott Pool makes splash for Ursinus community • Editorial: Thank you • S.F.A.R.C. Committee gets three new faces • Myrin Library opens new listening room • Fidler on the wax: Foghat • Churches near Collegeville area welcome Ursinus students • Ursinus admits 308 freshmen; Campus rumors unfounded • Butterflies are free in review • The State of our prisons: The Case at Graterford • Judo class on campus, Judoka anyone? • Harriers roll over Kings and Scranton; Big tests still ahead • Ursinus soccer; Fans love it? • Oh, that astro turf! • Bears tame Mules • The Olympic idea and ideal • Sports buffs\u27 cornerhttps://digitalcommons.ursinus.edu/weekly/1088/thumbnail.jp

Mechanistic definition of the cardiovascular mPGES-1/COX-2/ADMA axis

Aims: Cardiovascular side effects caused by non-steroidal anti-inflammatory drugs (NSAIDs), which all inhibit cyclooxygenase (COX)-2, have prevented development of new drugs that target prostaglandins to treat inflammation and cancer. Microsomal prostaglandin E synthase-1 (mPGES-1) inhibitors have efficacy in the NSAID arena but their cardiovascular safety is not known. Our previous work identified asymmetric dimethylarginine (ADMA), an inhibitor of eNOS, as a potential biomarker of cardiovascular toxicity associated with blockade of COX-2. Here we have used pharmacological tools and genetically modified mice to delineate mPGES-1 and COX-2 in the regulation of ADMA. Methods and Results: Inhibition of COX-2 but not mPGES-1 deletion resulted in increased plasma ADMA levels. mPGES-1 deletion but not COX-2 inhibition resulted in increased plasma prostacyclin levels. These differences were explained by distinct compartmentalisation of COX-2 and mPGES-1 in the kidney. Data from prostanoid synthase/receptor knockout mice showed that the COX-2/ADMA axis is controlled by prostacyclin receptors (IP and PPARβ/δ) and the inhibitory PGE2 receptor EP4, but not other PGE2 receptors. Conclusions: These data demonstrate that inhibition of mPGES-1 spares the renal COX-2/ADMA pathway and define mechanistically how COX-2 regulates ADMA

The Ursinus Weekly, October 5, 1972

Jerrold Schecter speaks on China: Mao in control • Ursinus administration appoints twelve new faculty members for coming year • Voting deadline nears; Have you registered? • News editors hope for expansion and diversity • Editorial: A falling star? • Focus: Andrea Turner • Ursinus receives a big fat government grant • Coordinating the freshmen, or Thank God for the relay races • Tired of classes? • Harriers upset by DelVal; Win streak ends • Soccer team impressive in Villanova victory • New coach takes over • Gridders drop first two to F&M, Lebanon Valley • Sports buffs\u27 corner • Sports scoreboardhttps://digitalcommons.ursinus.edu/weekly/1086/thumbnail.jp

Efficacy and safety of oral methazolamide in patients with type 2 diabetes: A 24-week, placebo-controlled, double-blind study

OBJECTIVE To evaluate the safety and efficacy of methazolamide as a potential therapy for type 2 diabetes. RESEARCH DESIGN AND METHODS This double-blind, placebo-controlled study randomized 76 patients to oral methazolamide (40 mg b.i.d.) or placebo for 24 weeks. The primary efficacy end point for methazolamide treatment was a placebo-corrected reduction in HbA1c from baseline after 24 weeks (ΔHbA1c). RESULTS Mean ± SD baseline HbA1c was 7.1 ± 0.7% (54 ± 5 mmol/mol; n = 37) and 7.4 ± 0.6% (57 ± 5 mmol/mol; n = 39) in the methazolamide and placebo groups, respectively. Methazolamide treatment was associated with a ΔHbA1c of –0.39% (95% CI –0.82, 0.04; P < 0.05) (–4.3 mmol/mol [–9.0, 0.4]), an increase in the proportion of patients achieving HbA1c ≤6.5% (48 mmol/mol) from 8 to 33%, a rapid reduction in alanine aminotransferase (∼10 units/L), and weight loss (2%) in metformin-cotreated patients. CONCLUSIONS Methazolamide is the archetype for a new intervention in type 2 diabetes with clinical benefits beyond glucose control

Prospecting for Energy-Rich Renewable Raw Materials: \u3cem\u3eAgave\u3c/em\u3e Leaf Case Study

Plant biomass from different species is heterogeneous, and this diversity in composition can be mined to identify materials of value to fuel and chemical industries. Agave produces high yields of energy-rich biomass, and the sugar-rich stem tissue has traditionally been used to make alcoholic beverages. Here, the compositions of Agave americana and Agave tequilana leaves are determined, particularly in the context of bioethanol production. Agave leaf cell wall polysaccharide content was characterized by linkage analysis, non-cellulosic polysaccharides such as pectins were observed by immuno-microscopy, and leaf juice composition was determined by liquid chromatography. Agave leaves are fruit-like--rich in moisture, soluble sugars and pectin. The dry leaf fiber was composed of crystalline cellulose (47-50% w/w) and non-cellulosic polysaccharides (16-22% w/w), and whole leaves were low in lignin (9-13% w/w). Of the dry mass of whole Agave leaves, 85-95% consisted of soluble sugars, cellulose, non-cellulosic polysaccharides, lignin, acetate, protein and minerals. Juice pressed from the Agave leaves accounted for 69% of the fresh weight and was rich in glucose and fructose. Hydrolysis of the fructan oligosaccharides doubled the amount of fermentable fructose in A. tequilana leaf juice samples and the concentration of fermentable hexose sugars was 41-48 g/L. In agricultural production systems such as the tequila making, Agave leaves are discarded as waste. Theoretically, up to 4000 L/ha/yr of bioethanol could be produced from juice extracted from waste Agave leaves. Using standard Saccharomyces cerevisiae strains to ferment Agave juice, we observed ethanol yields that were 66% of the theoretical yields. These data indicate that Agave could rival currently used bioethanol feedstocks, particularly if the fermentation organisms and conditions were adapted to suit Agave leaf composition

Ethnic Variation in Inflammatory Profile in Tuberculosis

PMCID: PMC3701709This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited

An Overview of Research and Evaluation Designs for Dissemination and Implementation

The wide variety of dissemination and implementation designs now being used to evaluate and improve health systems and outcomes warrants review of the scope, features, and limitations of these designs