Picosecond time resolved spectroscopy used as a tool to probe excited state photophysics of biologically and environmentally relevant systems

• Main Author: Chowdhury, Pramit Kumar
• Format: Text
• Language: English
• Published: Iowa State University Digital Repository 2004
• Subjects: Chemistry; Physical chemistry; Analytical Chemistry; Sperm whale
• Online Access: https://lib.dr.iastate.edu/rtd/766; https://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=1765&context=rtd

This dissertation focuses on the applicability of a variety of time-resolved spectroscopic techniques to probe the excited state photophysics of a range of biologically and environmentally relevant systems.;Hypericin, a biologically active perylene quinone and an efficient photosensitizing agent has a wide spectrum of light induced biological activities. However, it is highly insoluble in water. Insertion of hypericin in the well-characterized AOT reverse micelles gives us the opportunity to study its excited-state photophysics as a function of varying pH. Hypomycin B, another biologically active perylene quinone is unique in the sense that it has only one hydroxyl group peri to a carbonyl group as opposed to four in hypericin. Transient absorption data failed to reveal any stimulated emission for hypomycin B. This result has been discussed in the context of the number of H-atoms that may be transferred in the excited state for hypericin and whether the transfer is stepwise or concerted.;Geminate recombination of ligands in heme proteins is mainly affected either by the proximal pocket effects or by mutations on the distal side of the heme pocket. Our transient absorption kinetics of different proximal mutants of both sperm whale myoglobin (Mb) and soybean leghemoglobin (Lba) reveal very little influence of the proximal pocket on the geminate recombination of NO. However, the first ever study of distal pocket mutations in Lba, show profound effects of the distal amino acid(s) on NO recombination on the geminate timescale.;Solvation dynamics of five different room temperature ionic liquids using coumarin 153 as the fluorescent probe reveal an initial phase of rapid solvation due to the polarizability of the cationic part of the ionic liquids. The amplitude of the rapidly decaying components correlates well with the viscosity of the ionic liquids. Finally, the complex of coumarin 153 with apomyoglobin has been exhaustively characterized. This is the first step towards analyzing the contribution of the individual amino acid residues in the heme pocket towards the total protein dielectric response.