Narine, Suresh SN

The study examines the phytochemical and phytohormone profiles of two ecotypes of Doliocarpus dentatus (Capadulla) from Guyana with an emphasis on their potential therapeutic applications, particularly in the context of erectile dysfunction. The research concentrates on the red and white ecotypes, which are visibly differentiated by the colouration of their inner and outer bark; moreover, the red ecotype is widely regarded by traditional knowledge to be more efficacious in treating erectile dysfunction. The study seeks to provide much-needed scientific evidence to support the traditional medicinal uses of D. dentatus and aims to accomplish this by providing semi-targeted and targeted analysis of its bioactive compounds.The thesis employs a multi-faceted approach, commencing with Chapter 2, an examination of the international and national frameworks that govern natural product research in Guyana, thereby ensuring ethical and sustainable practices. Chapter 3, Liquid chromatography-mass spectrometry-based metabolomics was utilized to analyze the phytochemical profiles of the red and white ecotypes of D. dentatus. Approximately 847 compounds were identified, with 138 tentatively classified as potentially therapeutic, particularly polyphenols exhibiting antioxidant properties. Chapter 4 focus on the phytohormone profiling revealed that the red ecotype generally exhibited higher levels of active cytokinins, particularly trans-zeatin (tZ) and cis-zeatin (cZ), compared to the white ecotype. A strong correlation was identified between specific cytokinins and secondary metabolites such as flavonoids and alkaloids, suggesting complex interactions that may enhance the therapeutic potential of D. dentatus. Chapter 5 further analysis of total phenolic content, flavonoid content, and their antioxidant capacities demonstrated differences between the red and white ecotypes, with the red ecotype generally showing higher levels of these compounds. Both ecotypes demonstrated significant antioxidant activity, with the red ecotype showing enhanced radical scavenging capacity. The study also revealed a diverse range of bioactive compounds, including flavonoids, terpenoids, and alkaloids, which may contribute to the plant's reported medicinal properties. This semi-targeted and targeted analysis provides novel insights into the phytochemical and phytohormone profiles of D. dentatus ecotypes, offering a scientific basis for their traditional medicinal uses and potential therapeutic applications. The findings suggest that D. dentatus, particularly the red ecotype, may have significant potential for developing new drugs, especially in the context of erectile dysfunction therapy.

Author Keywords: antioxidant, Bioactive compounds, liquid chromatography-electrospray ionization tandem mass spectrometry, metabolomics, secondary metabolites, therapeutic properties

The seed oil of Carapa guianensis, known as Crabwood oil (CWO) and its fractionation was studied, focussing on chemical composition and physicochemical functionality. Compounds never reported before in CWO were identified, including limonoids such as Trichillin, ketostearic and hydroxyoleic acids. Yield of olein and stearin fractions correlated strongly with solvent polarity. Important bioactives were partitioned as a function of solvent polarity in the olein vs. stearin fractions. For example, up to 35% more of Gedunin were present in the liquid fractions. Solid fat content, crystallization and melting temperature and microstructure were significantly affected by fractionation and shown to be strongly correlated with solvent polarity. Fractionation was demonstrated to be a powerful tool to extend the physical functionality of CWO and concentrate its bioactives.

Author Keywords: Carapa guianensis, Chemical characteristics, Crabwood Oil, Dry and Solvent fractionation, Fractionation, Physical characteristics

The replacement of petroleum with renewable feedstock for energy and materials has become a priority because of concerns over the environment and finite nature of petroleum. The structures of the available natural biomass feedstocks fall short in delivering key functionality required in materials such as lubricants and phase change energy storage materials (PCMs). The approach taken in this thesis was to combine select functional groups with vegetable oil derivatives to create novel PCMs and lubricantswhich deliver desired functionality. One series of diester PCMs were prepared with terephthalic acid and fatty alcohols to address known shortcomings of esters. The second class of PCMs are sulfones prepared from oxidation of fatty sulfides to improve thermal energy storage. Overall, the new PCMs presented narrow phase change temperature ranges, high transition temperature (between 67 to 110℃), high transition enthalpy (210 to 266J/g), minimal supercooling and congruent phase transitions unaffected by cooling rates. They also demonstrated higher thermal degradation stability with onset of degradation from 290 to 310℃. The series of lubricants studied consists of sulfide and sulfonyl functional groups attached to the unsaturation sites of oleyl oleate as pendant groups to improve the thermal and flow properties. The new lubricants present subzero crystallization temperatures, very low crystallization enthalpy and dynamic viscosity as high as 180mPas.

Furthermore, they also presented high onset of degradation (up to 322℃) and oxidation (up to 298℃). The PCMs and lubricants of the present thesis demonstrate that select functional groups can be used with common structural elements of vegetable oil such as fatty acids, ester groups and unsaturation sites to make a variety of molecular structures capable of delivering desired properties

Author Keywords: Crystal Structure, Lubricant, Phase Change Material, Renewable, Structure-Property Relationships, Vegetable Oil