48,955 research outputs found
Mechanistic Investigation of Intermolecular Reductive C–H PCET via Isotopic Fractionation
No full textIn this thesis, preliminary experimental evidence in support of a possible concerted intermolecular C–H Multi-site Proton-Coupled Electron Transfer (MS-PCET) elementary step is described. While oxidative C–H MS-PCET reactions have been investigated recently in various contexts for homolytic cleavage of strong C–H bonds, many limitations still exist for the application of such an underutilized elementary step. Previous work by the Knowles lab featured a photoredox C–H alkylation reaction featuring an oxidative C–H MS-PCET step between the substrate and a noncovalent complex between the Ir photocatalyst and the phosphate base. However, reductive C–H MS-PCET as an elementary step has been uncommon especially in an intermolecular context, as a result of the precise orientation of the proton required for efficient C–H bond formation. In this thesis, the mechanism of photocatalyzed decarboxylation of potassium triphenyl acetates is investigated, with the emphasis on distinguishing between stepwise electron transfer/proton transfer (ET/PT) and intermolecular MS-PCET for C–H bond formation via isotopic fractionation. Isotopic fractionation is a highly sensitive method to distinguish between concerted MS-PCET and stepwise ET/PT, as the fractionation slope of ET/PT is independent of the redox potential of the photocatalyst. Previous research in the Knowles group identified that in decarboxylation of triphenyl acetate anions, the H/D isotopic fractionation slope was dependent on the identity of the Ir photocatalyst. In this thesis, the dependence is further explored with a range of photoredox catalysts covering a wide range of E°Red (PC/PC-), where a transition between a slope of 1.7 ± 0.1 and 2.64 ± 0.07 with decrease in magnitude of E°Red (PC/PC-) providing support for a transition from ET/PT to a concerted MS-PCET mechanism. Thus, this thesis provides preliminary mechanistic evidence in support of the viability of intermolecular reductive C–H MS-PCET as a novel elementary step
Acute colonic pseudo-obstruction
No full textBackground: Acute colonic pseudo-obstruction is characterized by clinical and radiological evidence of acute large bowel obstruction in the absence of a mechanical cause. The condition usually affects elderly people with underlying co-morbidities, and early recognition and appropriate management are essential to reduce the occurrence of life-threatening complications. Methods: A part-systematic review was conducted. This was based on key publications focusing on advances in management. Results and conclusions: Although acute colonic dilatation has been suggested to result from a functional imbalance in autonomic nerve supply, there is little direct evidence for this. Other aetiologies derived from the evolving field of neurogastroenterology remain underexplored. The rationale of treatment is to achieve prompt and effective colonic decompression. Initial management includes supportive interventions that may be followed by pharmacological therapy. Controlled clinical trials have shown that the acetylcholinesterase inhibitor neostigmine is an effective treatment with initial response rates of 60-90 per cent; other drugs for use in this area are in evolution. Colonoscopic decompression is successful in approximately 80 per cent of patients, with other minimally invasive strategies continuing to be developed. Surgery has thus become largely limited to those in whom complications occur. A contemporary management algorithm is provided on this basi
Molecular analysis of type 1 duck hepatitis virus indicated that it should be assigned to a new genus
No full textLetter from C. H. Gensler, Havasupai Agency to Carl Hayden
No full textLetter from C. H. Gensler expressing concern on behalf of the Havasupai Tribe regarding the proposed park boundaries
Citations of the author H C Rajpoot
No full textThe list of the articles, research papers, theses, and book chapters globally citing the author H. C. Rajpoot</p
Letter from Carl Hayden to C. H. Gensler
No full textLetter from Carl Hayden to C. H. Gensler informing him of the proposed Grand Canyon National Park bill
Letter from C. H. Gensler, Havasupai Agency to Carl Hayden
No full textLetter from C. H. Gensler to Carl Hayden asking for a meeting in regards to the Havasupai pasture land in light of the national park bill
Silver-Mediated Direct sp(3) C-H Bond Functionalization
No full textDirect sp(3) C-H bond functionalization is an efficient, straightforward, and powerful method to construct new C-X (X = C, N, F, S) bonds from nonfunctionalized aliphatic motif of organic molecules, which has been used in late-stage modification of complex molecules. In this chapter, the recent developments of silver-mediated direct sp(3) C-H functionalizations are reviewed, categorized by C-C bond formation (C-H insertion), C-N bond formation (intramolecular and intermolecular amination/amidation), C-F bond formation, and C-S bond formation.SCI(E)[email protected]
Student Captures First Knowles Science Teaching Foundation Fellowship
No full textIncluding Jenkins, only four fellows have been selected out of South Carolina. The foundation was established by Janet H. and C. Harry Knowles with the goal of both developing and supporting exemplary science and mathematics high school teachers
Letter from Carl T. Hayden to C. H. Gensler, Havasupai Reservation
No full textLetter from Carl T. Hayden to C. H. Gensler, Havasupai Indian Reservation, regarding Hualapai and Cataract Canyons geography
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