Theses and Dissertations from UMD
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New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM
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Item Elevated Temperature Effects on Carotenoid Biosynthesis in the Diploid Strawberry, Fragaria vesca(2015) Jackson, Melantha E.; Sintim, Herman; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Carotenoids, a subfamily of the isoprenoids, are one of the most diverse classes of secondary metabolites distributed throughout nature. They are lipophilic in nature, and include over 600 tetraterpenoid compounds synthesized by plants, bacteria, and fungi. Carotenoids, as the major pigment responsible for the red, yellow, and orange colors of fruits and vegetable, help promote human health and wellness by serving as antioxidants and precursors to vitamin A. Climate changes that threaten plant reproduction, negatively impact crop production worldwide. Little is understood about the chemistry of carotenoids in plant reproductive structures. Insight into the metabolic roles and functions of carotenoids in plant reproduction and, the effects of abiotic stresses on carotenoid biosynthesis in these structures would globally impact agriculture production by reducing yield loss. The potential for these metabolites to protect the reproductive structures under elevated temperature stress was assessed using biochemical analysis, genomics, and genetic studies. Fourteen candidate genes involved in carotenoid biosynthesis were identified, revealing three small gene families. Quantitative real-time polymerase chain reaction (qPCR) expression analysis of these genes and targeted metabolic profiling using liquid chromatography-high resolution mass spectrometry (LC-HRMS) throughout plant development under control and moderately elevated temperature stress showed that gene expression and metabolite accumulation are tissue specific and differentially responsive to elevated temperature stress. Three phytoene synthase genes were identified and characterized. Genomic analyses revealed that the PSY gene family exhibits functional diversity in plant tissues, both with respect to location and stage of development, as well as in response to abiotic stress.Item The Relationship between Dietary intake and Biomarkers of carotenoids and Physical Functioning among U.S. Older Adults(2015) Sheikomar, Olfat Bakur; Sahyoun, Nadine; Nutrition; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Decline of physical function [PF] in old age might be related to oxidative damage caused by free radicals, and antioxidants may play a role in reducing the risk of physical functional limitations [PFL]. Yet little is known about the role of carotenoids in PFL. The purpose of this study was to assess the association of total and daily dietary intakes of carotenoids, fruit and vegetables [FV] and their biomarkers with PF among U.S. older adults. Data were from 2,905 men and women [≥ 60 years] in the National Health and Nutrition Examination Survey [NHANES] 2003-2006. Using logistic regression, we found that serum concentration of carotenoids was associated with limitations in PF. In the fully adjusted model, the ORs [95% CI] of having limitation in activities of daily living [ADLs], instrumental activities of daily living [IADLs] and movement difficulties [MD] were 2.03 [1.16 - 3.53], 2.34 [1.61 - 3.42], and 2.15 [1.46 - 3.18], respectively, comparing the lowest quintile of serum carotenoids to the highest. Total intake and dietary intake of carotenoids were found to be associated with limitations in IADL. However, low FV consumptions were not significantly associated with PF domains. In conclusion, elevated levels of serum carotenoids are significantly associated with better physical functional performance and may play an important role in delaying the onset of physical decline.Item Total Synthesis of an Oxidation Product of gamma-Carotene - a ProVitamin A Food Carotenoid(2011) Crawford, Kristine Sheila; Khachik, Frederick; Kahn, Jason; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Human serum carotenoids and their metabolites are known to function as antioxidants and inflammation mediators. In 1992, two oxidative metabolites of lycopene were isolated from human serum and tomato-based food products. These substances were subsequently prepared by partial synthesis from lycopene and characterized as a diastereomeric mixture of 2,6-cyclolycopene-1,5-diols I and II. Results of in vitro studies have demonstrated that the diols were more effective at inhibiting the growth of solid human tumor cells than lycopene. While the metabolisms of prominent hydrocarbon carotenoids such as lycopene and beta-carotene have been extensively studied, the functional role of gamma-carotene remains unexplored. Because the chemical structure of gamma-carotene is a hybrid of lycopene and beta-carotene, the total synthesis of the analogous metabolite of gamma-carotene 2,6-cyclo-gamma-carotene-1,5-diol was undertaken. The total synthesis 2,6-cyclo-gamma-carotene-1,5-diol was accomplished using a C15+C10+C15 Wittig coupling strategy. The C15-dihydroxyaldehdye key synthon with a defined stereochemistry, a protected C10-Wittig salt, and the beta-ionylidene-ethyltriphenylphosphonium chloride C15-Wittig salt provided the three building blocks in this synthesis. To arrive at the C15-dihydroxyaldehyde, citral epoxide was elongated to a C15-epoxynitrile which underwent acid-catalyzed cyclization to afford a C15-dihydroxynitrile. After reduction with DIBAL-H, the key C15-dihydroxyaldehdye was produced in 16% yield in three steps from citral epoxide. The major drawback of this synthesis was the cyclization step. According to this approach, 2,6-cyclo-gamma-carotene-1,5-diol was prepared in high purity in 5 steps in 2.4% overall yield. In a semi-synthetic approach, 12'-apo-beta-carotene-12'-al was transformed into a C25-Wittig salt and coupled to the C15-dihydroxyaldehyde synthon to afford 2,6-cyclo-gamma-carotene-1,5-diol in 16.8% overall yield in 3 steps. A third strategy involved the epoxidation of 12'-apo-psi-carotene-12'-al followed by cyclization to a C25-dihydroxyaldehyde upon silica gel chromatography. Final coupling of C25-dihydroxyaldehyde with the beta-ionylideneethyltriphenylphosphonium chloride C15-Wittig salt produced 2,6-cyclo-gamma-carotene-1,5-diol in 6.0% overall yield in 2 steps. This strategy does not require access to large amounts of pure C15-dihydroxyaldehdye and takes advantage of the commercial availability of 12'-apo-psi-carotene-12'-al, and is by far the most practical route to 2,6-cyclo-gamma-carotene-1,5-diol. The present methodologies provide novel access to an oxidation product of gamma-carotene that could be potentially formed in humans or biological systems.