Modification of rhenium carbonyls with thienyl nucleophiles

In the reaction between [Re(CO)5Br] and 2–lithiumthienyl, X–ligand substitution was expected. Li+{C4H3S}¯did not substitute Br¯, but an intermediate negatively charged complex was obtained (non–mobile on silica gel) and it was found that the thienyl had bonded to a carbonyl ligand, producing a dirhenium acylate complex. Such complexes are the precursors to neutral Fischer carbene complexes. After alkylation with Et3OBF4, [Re2 (CO) 9C(OEt)C4H3S] (1) was obtained, instead of a monorhenium monocarbene complex. Greater yields of 1 could be obtained, from reactions with [Re2(CO) 10] instead of [Re(CO) 5Br]. [Re2 (CO) 10] reacted with 5–lithium–2,2'–bithienyl and 2–lithium–3,6– dimethylthieno[3,2–b]thienyl and was then alkylated with Et3OBF4. The reactions proceeded smoothly and [Re2 (CO) 9C(OEt)C8H5S2] (2) and [Re2 (CO) 9C(OEt)C8H7S2] (3) were obtained. The substrates thiophene, 2,2'–bithiophene and 3,6–dimethylthieno[3,2–b]thiophene, can all be doubly lithiated under appropriate reaction conditions. These lithiated species were reacted with two equivalents of [Re2 (CO) 10]. In the case of bithiophene this produced, in good yield, the tetrametal biscarbene complex [Re2 (CO) 9C(OEt)C8H4S2C(OEt)Re2 (CO) 9] (8). In the thiophene and dimethylthieno[3,2–b]thiophene cases [Re2 (CO) 9C(OEt)C4H2SC(OEt)Re2 (CO) 9] (7) and [Re2 (CO) 9C(OEt)C8H6S2C(OEt)Re2 (CO) 9] (9) could be isolated in meagre quantities. This was ascribed to poor double lithiation (also steric hindrance in the case of 7). The carbene ligands reacted with water on the silica gel during column chromatography or in a control experiment with degassed water to produce aldehydes by reductive elimination from the metal. Protonation of the acylrhenate afforded rhenium hydrides which is also a potential precursor to aldehyde formation. This is believed to be a facile process for especially complex 9, isolated in very small quantity. Complexes 7–9 produced monocarbene aldehyde complexes [Re2(CO) 9C(OEt)C4H2SC(O)H] (12), [Re2 (CO) 9C(OEt)C8H4S2C(O)H] (13) and [Re2 (CO) 9C(OEt)C8H6S2C(O)H] (14), as well as dialdehyde compounds. Complexes 2 and 3 also produced aldehyde compounds. The formation of aldehydes from ethoxycarbene complexes is believed to involve hydroxycarbene intermediate species. Experiments were performed on [Re2 (CO) 10] and [Re(CO) 5Br]. They were reacted with 2–lithiumthienyl and then protonated. In the case of [Re2(CO) 10], hydride signals were observed on the 1H NMR spectrum, as well as aldehyde signals. In the case of [Re(CO) 5Br] there was strong NMR evidence indicating the formation of a hydroxycarbene complex. Complexes 1, 2, and 3 were reacted with Br2 (l). The metal–metal bonds were cleaved by the bromine to produce monorhenium carbene complexes [Re(CO) 4{C(OEt)C4H3S}Br] (4), [Re(CO) 4{C(OEt)C8H5S2}Br] (5), and [Re(CO) 4{C(OEt)C8H7S2}Br] 6) and [Re(CO) 5Br]. Complex 8 reacted with bromine to produce a monocleaved complex [Re2 (CO) 9C(OEt)C8H4S2C(OEt)Re(CO) 4Br] (11) and a biscleaved complex [Re(CO) 4Br{C(OEt)C8H4S2C(OEt)}Re2 (CO) 4Br] (10). Unique complexes [Re(CO) 4{C(OH)C4H3S}{μ–H}Re(CO) 4{C(O)C4H3S}] (15) and [Re(CO) 4{C(OH)C8H5S2}{μ–H}Re(CO) 4{C(O) C8H5S2}] (16) were obtained by starting with [Re(CO) 5Br] or [Re2 (CO) 10] and reacting them with 2–lithiumthienyl and 5–lithium–2,2'– bithienyl. These complexes were isolated from the column as very polar compounds after eluation of the aldehyde complexes. The dirhenium complex was obtained with a carbonyl– modified ligand (hydroxycarbene/acyl) on each of the metals. The complexes consist of two fragments held together by a hydrogen atom that bridges the two rhenium atoms (hydrido) and one that bridges the oxygen atoms of the carbene/acyl ligands (protonic).Thesis (PhD)--University of Pretoria, 2011.Chemistryunrestricte

Novel carbene complexes with pyrrole ligands

Please read the abstract in the section 00front of this documentDissertation (MSc (Chemistry))--University of Pretoria, 2006.Chemistryunrestricte

Invisible design: exploring insights and ideas through ambiguous film scenarios

Invisible Design is a technique for generating insights and ideas with workshop participants in the early stages of concept development. It involves the creation of ambiguous films in which characters discuss a technology that is not directly shown. The technique builds on previous work in HCI on scenarios, persona, theatre, film and ambiguity. The Invisible Design approach is illustrated with three examples from unrelated projects; Biometric Daemon, Panini and Smart Money. The paper presents a qualitative analysis of data from a series of workshops where these Invisible Designs were discussed. The analysis outlines responses to the films in terms of; existing problems, concerns with imagined technologies and design speculation. It is argued that Invisible Design can help to create a space for critical and creative dialogue during participatory concept development

Performance analysis of GA and PBIL variants for real-world location-allocation problems.

The Uncapacitated Location-Allocation problem (ULAP) is a major optimisation problem concerning the determination of the optimal location of facilities and the allocation of demand to them. In this paper, we present two novel problem variants of Non-Linear ULAP motivated by a real-world problem from the telecommunication industry: Uncapacitated Location-Allocation Resilience problem (ULARP) and Uncapacitated Location-Allocation Resilience problem with Restrictions (ULARPR). Problem sizes ranging from 16 to 100 facilities by 50 to 10000 demand points are considered. To solve the problems, we explore the components and configurations of four Genetic Algorithms [1], [2], [3] and [4] selected from the ULAP literature. We aim to understand the contribution each choice makes to the GA performance and so hope to design an Optimal GA configuration for the novel problems.We also conduct comparative experiments with Population-Based Incremental Learning (PBIL) Algorithm on ULAP. We show the effectiveness of PBIL and GA with parameter set: random and heuristic initialisation, tournament and fined grained tournament selection, uniform crossover and bitflip mutation in solving the proposed problems

Glacial influence on the geochemistry of riverine iron fluxes to the Gulf of Alaska and effects of deglaciation

This paper is not subject to U.S. copyright. The definitive version was published in Geophysical Research Letters 38 (2011): L16605, doi:10.1029/2011GL048367.Riverine iron (Fe) derived from glacial weathering is a critical micronutrient source to ecosystems of the Gulf of Alaska (GoA). Here we demonstrate that the source and chemical nature of riverine Fe input to the GoA could change dramatically due to the widespread watershed deglaciation that is underway. We examine Fe size partitioning, speciation, and isotopic composition in tributaries of the Copper River which exemplify a long-term GoA watershed evolution from one strongly influenced by glacial weathering to a boreal-forested watershed. Iron fluxes from glacierized tributaries bear high suspended sediment and colloidal Fe loads of mixed valence silicate species, with low concentrations of dissolved Fe and dissolved organic carbon (DOC). Iron isotopic composition is indicative of mechanical weathering as the Fe source. Conversely, Fe fluxes from boreal-forested systems have higher dissolved Fe concentrations corresponding to higher DOC concentrations. Iron colloids and suspended sediment consist of Fe (hydr)oxides and organic complexes. These watersheds have an iron isotopic composition indicative of an internal chemical processing source. We predict that as the GoA watershed evolves due to deglaciation, so will the source, flux, and chemical nature of riverine Fe loads, which could have significant ramifications for Alaskan marine and freshwater ecosystems.We appreciate support from the USGS CMGP, NCCWSC, and the Mendenhall Postdoctoral Program

Neuronal Calcium Imaging, Excitability, and Plasticity Changes in the \u3cem\u3eAldh2\u3c/em\u3e\u3csup\u3e-/-\u3c/sup\u3e Mouse Model of Sporadic Alzheimer\u27s Disease

BACKGROUND: Dysregulated signaling in neurons and astrocytes participates in pathophysiological alterations seen in the Alzheimer\u27s disease brain, including increases in amyloid-β, hyperphosphorylated tau, inflammation, calcium dysregulation, and oxidative stress. These are often noted prior to the development of behavioral, cognitive, and non-cognitive deficits. However, the extent to which these pathological changes function together or independently is unclear. OBJECTIVE: Little is known about the temporal relationship between calcium dysregulation and oxidative stress, as some reports suggest that dysregulated calcium promotes increased formation of reactive oxygen species, while others support the opposite. Prior work has quantified several key outcome measures associated with oxidative stress in aldehyde dehydrogenase 2 knockout (Aldh2-/-) mice, a non-transgenic model of sporadic Alzheimer\u27s disease. METHODS: Here, we tested the hypothesis that early oxidative stress can promote calcium dysregulation across aging by measuring calcium-dependent processes using electrophysiological and imaging methods and focusing on the afterhyperpolarization (AHP), synaptic activation, somatic calcium, and long-term potentiation in the Aldh2-/- mouse. RESULTS: Our results show a significant age-related decrease in the AHP along with an increase in the slow AHP amplitude in Aldh2-/- animals. Measures of synaptic excitability were unaltered, although significant reductions in long-term potentiation maintenance were noted in the Aldh2-/- animals compared to wild-type. CONCLUSION: With so few changes in calcium and calcium-dependent processes in an animal model that shows significant increases in HNE adducts, Aβ, p-tau, and activated caspases across age, the current findings do not support a direct link between neuronal calcium dysregulation and uncontrolled oxidative stress

Viewing ambiguous social interactions increases functional connectivity between frontal and temporal nodes of the social brain.

Social behaviour is coordinated by a network of brain regions, including those involved in the perception of social stimuli and those involved in complex functions like inferring perceptual and mental states and controlling social interactions. The properties and function of many of these regions in isolation is relatively well-understood, but less is known about how these regions interact whilst processing dynamic social interactions. To investigate whether the functional connectivity between brain regions is modulated by social context, we collected functional MRI (fMRI) data from male monkeys (Macaca mulatta) viewing videos of social interactions labelled as "affiliative", "aggressive", or "ambiguous". We show activation related to the perception of social interactions along both banks of the superior temporal sulcus, parietal cortex, medial and lateral frontal cortex, and the caudate nucleus. Within this network, we show that fronto-temporal functional connectivity is significantly modulated by social context. Crucially, we link the observation of specific behaviours to changes in functional connectivity within our network. Viewing aggressive behaviour was associated with a limited increase in temporo-temporal and a weak increase in cingulate-temporal connectivity. By contrast, viewing interactions where the outcome was uncertain was associated with a pronounced increase in temporo-temporal, and cingulate-temporal functional connectivity. We hypothesise that this widespread network synchronisation occurs when cingulate and temporal areas coordinate their activity when more difficult social inferences are being made.SIGNIFICANCE STATEMENT:Processing social information from our environment requires the activation of several brain regions, which are concentrated within the frontal and temporal lobes. However, little is known about how these areas interact to facilitate the processing of different social interactions. Here we show that functional connectivity within and between the frontal and temporal lobes is modulated by social context. Specifically, we demonstrate that viewing social interactions where the outcome was unclear is associated with increased synchrony within and between the cingulate cortex and temporal cortices. These findings suggest that the coordination between the cingulate and temporal cortices is enhanced when more difficult social inferences are being made

Rhenium ethoxy- and hydroxycarbene complexes with thiophene substituents

Please read abstract in article.This work was supported financially by the University of Pretoria and by the National Research Foundation (NRF) of South Africa under Grant number: 73679 (SL).http://www.rsc.org/dalto

How well do global ocean biogeochemistry models simulate dissolved iron distributions?

Numerical models of ocean biogeochemistry are relied upon to make projections about the impact of climate change on marine resources and test hypotheses regarding the drivers of past changes in climate and ecosystems. In large areas of the ocean, iron availability regulates the functioning of marine ecosystems and hence the ocean carbon cycle. Accordingly, our ability to quantify the drivers and impacts of fluctuations in ocean ecosystems and carbon cycling in space and time relies on first achieving an appropriate representation of the modern marine iron cycle in models. When the iron distributions from 13 global ocean biogeochemistry models are compared against the latest oceanic sections from the GEOTRACES program, we find that all models struggle to reproduce many aspects of the observed spatial patterns. Models that reflect the emerging evidence for multiple iron sources or subtleties of its internal cycling perform much better in capturing observed features than their simpler contemporaries, particularly in the ocean interior. We show that the substantial uncertainty in the input fluxes of iron results in a very wide range of residence times across models, which has implications for the response of ecosystems and global carbon cycling to perturbations. Given this large uncertainty, iron fertilization experiments based on any single current generation model should be interpreted with caution. Improvements to how such models represent iron scavenging and also biological cycling are needed to raise confidence in their projections of global biogeochemical change in the ocean