Electronic structure of the 4d transition metal carbides: dispersed fluorescence spectroscopy of MoC, RuC, and PdC

Journal ArticleDispersed fluorescence studies of the diatomic molecules MoC, RuC, and PdC are reported. New states identified in MoC and RuC are the [...]2?112?1, 3,1?2 states and the [...]2? 312?1, 1?2 state, respectively. Five states re observed by dispersed fluorescence in PdC. The ground state is found to be [ ...]2? 412?2, 1?+, with the [ ...]2? 412?16rr1, 3II? manifold of states lying about 2500 cm-1 above the ground state. The [17.9]?=1 state of PdC is also identified as [...]2? 412?113?1, ?+(?=1), corroborating recent results of resonant two photon ionization spectroscopy studies. The spin-orbit interactions of these molecules are analyzed to deduce the composition of the molecular orbitals, and comparisons are made to ab initio theory when possible. An examination of the trends in bond energy, bond length, and vibrational frequency among the 4d transition metal carbides is also provided

Electronic structure of the 4 d transition metal carbides: dispersed fluorsecence spectroscopy of MoC, RuC, and PdC

Journal ArticleDispersed fluorescence studies of the diatomic molecules MoC, RuC, and PdC are reported. New states identified in MoC and RuC are the [...]2??12??, ?,??? states and the [...]2??12??, ??? state, respectively. Five states are observed by dispersed fluorescence in PdC. The ground state is found to be [...]2??12??, ??+, with the [...]2?? 12??6rr?, ?II? manifold of states lying about 2500 cm-? above the ground state. The [17.9]?=1 state of PdC is also identified as [...]??12??13??, ??+(?=1), corroborating recent results of resonant two photon ionization spectroscopy studies. The spin-orbit interactions of these molecules are analyzed to deduce the composition of the molecular orbitals, and comparisons are made to ab initio theory when possible. An examination of the trends in bond energy, bond length, and vibrational frequency among the 4d transition metal carbides is also provided

Development of sustainable catalytic methods for organic synthesis

This thesis covers two separate projects, but both of which can be linked by the overall aim to develop sustainable catalytic methodology for use in organic synthesis. A concerted effort has been made to move away from procedures within organic chemistry that use non-renewable expensive and toxic materials as reagents and catalysts, particularly those containing second and third row transition metals, and instead to develop processes that utilise sustainable, abundant and inexpensive reagents, such as base-metals and main group elements. The first project was the attempted development of an oxidative ring contraction of aromatic compounds, with the goal of applying it in the biomimetic total synthesis of fatouapilosin. The second project concerned the development of the borane-catalysed enantioselective hydroboration and reduction of propargylic ketones. Chapter 1 is an introduction to the first project, giving details regarding the isolation and proposed biosynthetic route to fatouapilosin, as well as giving an overview of the area of biomimetic total synthesis. The oxidative ring contraction reaction, the use of iron and copper for oxidation of organic compounds, and the potential of phenols as a renewable source of carbon are also discussed. Chapter 2 describes the first total synthesis of the coumarin natural product brosiparin, an important precursor in the proposed synthesis of fatouapilosin, which was the planned substrate on which to develop a method of oxidative ring contraction. Brosiparin was successfully prepared in a three-step procedure from pyrogallol, with an initial double demethylation followed by an O-prenylation, then a tandem Wittig olefination/para- Claisen rearrangement/lactonisation sequence. Chapter 3 focuses on the oxidation chemistry of brosiparin, and the efforts to develop a reliable method of oxidative ring contraction. Unfortunately trials with a wide variety of oxidising agents, including iron and copper catalysts, did not result in the desired transformation. The use of phenyliododiacetate (PIDA) enabled us to access a masked ortho-quinone compound, from which further reactions were attempted, including an interesting aryl-aryl coupling reaction, but the unprotected ortho-quinone proved very unstable and difficult to work with. Chapter 4 covers the second project, and starts with a broad introduction to the area of hydroboration, followed by a more focused look at enantioselective hydroboration and reduction of ketones. The successful development of an enantioselective reduction of propargylic ketones using substoichiometric myrtanyl borane with stoichiometric HBpin is then described. The reaction was shown by 1H and 11B NMR studies to proceed via a transborylation mechanism, and was applied to other propargylic ketone substrates

Dating Thach Lac: cryptic CaCO3 diagenesis in archaeological food shells and implications for C-14

In many locations around the world, shell radiocarbon dates underpin archaeological research. The dating of shell brings the chronological relationship between the sample and target event (e.g., hunting and food preparation) into congruence, while shells are valuable geochemical proxies for understanding past climate dynamics and environments. However, this information can be lost as the shell, composites of biopolymers and carbonate minerals (mostly calcite and or aragonite), undergo diagenetic alteration. While studies into Pleistocene-age carbonates are common in the radiocarbon literature, there has been little research into the impact of alteration on Holocene-age shells used to interpret recent societal developments. The limits of our understanding of these diagenetic changes became evident when dating Placuna placenta (naturally calcitic) and Tegillarca granosa (naturally aragonitic) shells from the site of Thach Lac in Vietnam. These shells returned ages significantly younger than associated charcoal and terrestrial bone at the site, but standard tests for secondary recrystallization (XRD and staining techniques) did not indicate any alteration. Further investigation revealed that cryptic recrystallization (i.e., of the same crystal structure) had occurred in both the calcite and aragonite shells. This finding suggests recrystallization may have an undetected impact on some shell radiocarbon dates

Forgotten news: shellfish isotopic insight into changing sea-level and associated impact on the first settlers of the Mariana Archipelago

The colonisation of the Pacific is an important chapter in human dispersal for which chronological control is primarily provided by radiocarbon (14C) dates. In this context, the ability to reliably date shellfish is important because alternative dating materials, such as charcoal and bone, are typically highly degraded. However, the interpretation of shell 14C results is not always black and white because 14C is not evenly distributed throughout the marine environment, with estuarine taxa more likely to incorporate terrestrial sources of carbon. Regions where water has percolated through limestone bedrock provide an additional problem since ancient carbon is introduced into the estuarine waters. This “hardwater” has been put forward to explain old 3500 cal. BP results from culturally significant shells recovered from the site of Unai Bapot (Bapot-1) on the island of Saipan (Petchey et al. 2017). While arguments for (Carson and Hung 2017) and against (Rieth and Athens 2017) early settlement dates remain polarised, little attention has been given to the idea of change in the marine 14C reservoir over time, or to possible species-specific offsets in shell 14C. In this paper, we further develop a tri-isotope approach using 14C, δ13C, δ18O to identify carbon source. To investigate which shellfish are more prone to erroneous ages we have selected shell taxa that cover a range of nearshore environments commonly found in Pacific archaeological sites; including Anadara antiquata, Gafrarium pectinatum (both estuarine) and Tridacna (marine/reef). To test the possibility of change over time we extend the dating of the site beyond the earliest occupation layers to deposits considered to post-date the end of the mid-Holocene drawdown in sea-level

A boron-oxygen transborylation strategy for a catalytic Midland reduction

The enantioselective hydroboration of ketones is a textbook reaction requiring stoichiometric amounts of an enantioenriched borane, with the Midland reduction being a seminal example. Here, a turnover strategy for asymmetric catalysis, boron.oxygen transborylation, has been developed and used to transform the stoichiometric borane reagents of the Midland reduction into catalysts. This turnover strategy was demonstrated by the enantioselective reduction of ketones, including derivatives of biologically active molecules and those containing reducible groups. The enantioenriched borane catalyst was generated in situ from commercially available reagents, 9-borabicyclo[3.3.1]nonane (H-B-9-BBN) and β-pinene, and B.O transborylation with pinacolborane (HBpin) was used for catalytic turnover. Mechanistic studies indicated that B.O transborylation proceeded by B.O/B.H boron exchange through a stereoretentive, concerted transition state, resembling σ-bond metathesis

Dating Thach Lac: cryptic CaCO3 diagenesis in archaeological food shells and implications for 14c

In many locations around the world, shell radiocarbon dates underpin archaeological research. The dating of shell brings the chronological relationship between the sample and target event (e.g., hunting and food preparation) into congruence, while shells are valuable geochemical proxies for understanding past climate dynamics and environments. However, this information can be lost as the shell, composites of biopolymers and carbonate minerals (mostly calcite and or aragonite), undergo diagenetic alteration. While studies into Pleistocene-age carbonates are common in the radiocarbon literature, there has been little research into the impact of alteration on Holocene-age shells used to interpret recent societal developments. The limits of our understanding of these diagenetic changes became evident when dating Placuna placenta (naturally calcitic) and Tegillarca granosa (naturally aragonitic) shells from the site of Thach Lac in Vietnam. These shells returned ages significantly younger than associated charcoal and terrestrial bone at the site, but standard tests for secondary recrystallization (XRD and staining techniques) did not indicate any alteration. Further investigation revealed that cryptic recrystallization (i.e., of the same crystal structure) had occurred in both the calcite and aragonite shells. This finding suggests recrystallization may have an undetected impact on some shell radiocarbon dates

Investigation of NRXN1 deletions: Clinical and molecular characterization

Deletions at 2p16.3 involving exons of NRXN1 are associated with susceptibility for autism and schizophrenia, and similar deletions have been identified in individuals with developmental delay and dysmorphic features. We have identified 34 probands with exonic NRXN1 deletions following referral for clinical microarray‐based comparative genomic hybridization. To more firmly establish the full phenotypic spectrum associated with exonic NRXN1 deletions, we report the clinical features of 27 individuals with NRXN1 deletions, who represent 23 of these 34 families. The frequency of exonic NRXN1 deletions among our postnatally diagnosed patients (0.11%) is significantly higher than the frequency among reported controls (0.02%; P  = 6.08 × 10 −7 ), supporting a role for these deletions in the development of abnormal phenotypes. Generally, most individuals with NRXN1 exonic deletions have developmental delay (particularly speech), abnormal behaviors, and mild dysmorphic features. In our cohort, autism spectrum disorders were diagnosed in 43% (10/23), and 16% (4/25) had epilepsy. The presence of NRXN1 deletions in normal parents and siblings suggests reduced penetrance and/or variable expressivity, which may be influenced by genetic, environmental, and/or stochastic factors. The pathogenicity of these deletions may also be affected by the location of the deletion within the gene. Counseling should appropriately represent this spectrum of possibilities when discussing recurrence risks or expectations for a child found to have a deletion in NRXN1 . © 2013 Wiley Periodicals, Inc.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/97220/1/35780_ftp.pd