Stoichiometric and catalytic reactivity of half-sandwich imido complexes of the group 5 metals

This thesis describes investigations into the chemistry of half-sandwich imido complexes of the Group 5 metals, with particular emphasis on the development of complexes which can be applied to catalytic processes. Chapter 1 provides an introduction to the imido ligand and highlights aspects of the reactivity of half-sandwich transition metal imido and related complexes. The isolobal analogy between Group 4 bent me'tallocene. Group 5 half-sandwich imido and Group 6 bis(imido) metal fragments is outlined. In Chapter 2, reactions of CpV(NR)Cl(_2) (R=2,6-(^i)Pr(_2)C(_6)H(_3), 2,6-Me(_2)C(_6)H(_3)) with alkylating agents are described, yielding a number of highly unusual products. The novel structures of [CpV(N-2,6-(^i)Pr(_2)C(_6)H(_3))(|i-Me)2]2(l^-Mg) and [CpV(fx-N-2,6-iPr2C6H3)]2(|i-Me), featuring bridging methyl and imido substituents, have been determined. The former also possesses the first crystallograghically characterised V-Mg bond and multiple agostic interactions. The aim of Chapter 3 was to evaluate the steric and electronic influence of the imido substituent in half-sandwich imido complexes of niobium. For the [CpNb(N-2-(^t)BuC(_6)H(_4))] system, the successful isolation of a number of previously unstable species has been reported. The orientations of the diphenylacetylene and the ethylene ligands in CpNb(N-2-(^t)BuC(_6)H(_4))(PhC=CPh)(PMe(_3)) and CpNb(N-2,6-Cl(_2)C(_6)H(_3))(C(_2)H(_4))(PMe(_3)) respectively have been established through crystal structures and lend support to the isolobal relationship between the [Cp(_2)Zr] and [CpNb(NR)] fragments. In Chapter 4, the tantalum dialkyl complexes Cp*Ta(N(^t)Bu)(CH(_2)R)(_2) R=Ph, CMe(_2)Ph, CMe(_3)] are described and the molecular structure of Cp*Ta(NtBu)(CH(_2)CMe(_3))') reveals multiple agostic interactions. Reactions of Cp*Ta(N(^t)Bu)(CH(_2)R)(_2) with excess C(_6)F(_5)OH yield a number of crystallographically characterised pentafluorophenoxide and oxo-bridged products, namely [Cp*Ta(CH(_2)Ph)(0C(_6)F(_5))(µ-O)](_2), Cp*Ta(OC(_6)F(_5))(_4) and [Cp*Ta(OC(_6)F(_5))(_2)(µ-0)](_2). Chapter 5 discusses attempts to develop and explore the oxidative coupling chemistry at the half-sandwich tantalum imido fragment. Hence, a number of new tantalacyclopentane complexes and related species have been prepared, including Cp*Ta(N-2,6-(^i)Pr(_2)C(_6)H(_3))(σ-l,4-(2-Et)C(_4)H(_7)) and Cp*Ta(N- 2,6-(^i)Pr(_2)C(_6)H(_3))[a-l,6-C(0)(3-Et)C(_4)H(_7)C(0)].Chapter 6 contains the experimental details for Chapter 2-5

LANDING WITH A SUPINATED ANKLE JOINT COULD INCITE AN INVERSION SPRAIN INJURY

Ankle sprain injury mechanism has been recently analysed quantitatively. This study further investigated if a supinated ankle joint at landing is an aetiology of the injury. One inversion ankle sprain case from a previous study was selected, and the video sequences of two similar play movements performed by the same athlete without injury were collected and analysed by a model-based image-matching motion analysis method. The ankle joint orientations at the moment of landing in these three cases were compared. Results showed that the ankle joint was in a supination orientation with a combined 14 degrees inversion and 16 degrees plantarflexion at landing, while it was neutral in the inversion/eversion plane and dorsiflexed to 10-21 degrees in the non-injury cases. The supination ankle joint at landing was suggested to be the inciting event of the injury

Short-term effects of a gain-focused reappraisal intervention for dementia caregivers: A double-blind cluster-randomized controlled trial

Objectives To examine the effects of a benefit-finding intervention, the key feature being the use of gain-focused reappraisal strategies to find positive meanings and benefits in caring for someone with dementia. Design: Cluster-randomized double-blind controlled trial. Setting: Social centers and clinics. Participants: 129 caregivers. Inclusion criteria were (a) primary caregiver aged 18+ and without cognitive impairment, (b) providing ≥14 care hours per week to a relative with mild-to-moderate Alzheimer's disease, and (c) scoring ≥3 on the Hamilton Depression Rating Scale. Exclusion criterion was care-recipient having parkinsonism or other forms of dementia. Interventions: The benefit-finding intervention was evaluated against two treatment-as-usuals, namely, simplified psychoeducation (lectures only) and standard psychoeducation. Each intervention lasted eight weeks, with a 2-hour session per week. Randomization into these conditions was based on center/clinic membership. Measurements: Primary outcome was depressive symptom. Secondary outcomes were Zarit Burden Interview, role overload, and psychological well-being. Self-efficacy beliefs and positive gains were treated as mediators. Measures were collected at baseline and posttreatment. Results: Regression analyses showed BF treatment effects on all outcomes when compared with SIM-PE, and effects on depressive symptoms and Zarit burden when compared with STD-PE. Effect sizes were medium-to-large for depressive symptoms (d=-0.77– -0.96), and medium for the secondary outcomes (d=|0.42–0.65|). Furthermore, using the bootstrapping method, we found significant mediating effects by self-efficacy in controlling upsetting thoughts and positive gains, with the former being the primary mediator. Conclusions: Finding positive gains reduces depressive symptoms and burden and promotes psychological well-being primarily through enhancing self-efficacy in controlling upsetting thoughts

Scalar Synchrotron Radiation in the Schwarzschild-anti-de Sitter Geometry

We present a complete relativistic analysis for the scalar radiation emitted by a particle in circular orbit around a Schwarzschild-anti-de Sitter black hole. If the black hole is large, then the radiation is concentrated in narrow angles- high multipolar distribution- i.e., the radiation is synchrotronic. However, small black holes exhibit a totally different behavior: in the small black hole regime, the radiation is concentrated in low multipoles. There is a transition mass at $M=0.427 R$, where $R$ is the AdS radius. This behavior is new, it is not present in asymptotically flat spacetimes.Comment: 13 pages, 6 figures, published version. References adde

An Integrin-Contactin Complex Regulates CNS Myelination by Differential Fyn Phosphorylation

The understanding of how adhesion molecules mediate the axon-glial interactions in the CNS that ensure target-dependent survival of oligodendrocytes and initiate myelination remains incomplete. Here, we investigate how signals from adhesion molecules can be integrated to regulate these initial steps of myelination. We first demonstrate that the Ig superfamily molecule contactin is associated in oligodendrocytes with integrins, extracellular matrix receptors that regulate target-dependent survival by amplification of growth factor signaling. This amplification is inhibited by small interfering RNA-mediated knockdown of contactin in oligodendrocytes. In contrast, the presence of L1-Fc, the extracellular portion of a contactin ligand expressed on axons, enhanced survival and additionally promoted myelination in cocultures of neurons and oligodendrocytes. We further demonstrate that the signals from contactin and integrin are integrated by differential phosphorylation of the Src family kinase Fyn. Integrin induced dephosphorylation of the inhibitory Tyr-531, whereas contactin increased phosphorylation of both Tyr-531 and the activating Tyr-420. The combined effect is an enhanced activity of Fyn and also a dynamic regulation of the phosphorylation/dephosphorylation balance of Fyn, as required for normal cell adhesion and spreading. We conclude, therefore, that a novel integrin/contactin complex coordinates signals from extracellular matrix and the axonal surface to regulate both oligodendrocyte survival and myelination by controlling Fyn activity