Dissertation/Thesis Abstract

The Effect of Ligand and Counter Anion on the Fluorescence Efficiency of Cu (II) Complex during Nitric Oxide Sensing: Experimental Observations and Theoretical Predictions
by Fayissa, Mosissa Adi, Ph.D., Howard University, 2015, 167; 3742208
Abstract (Summary)

It has long been understood that nitric oxide (NO) is both benevolent and malevolent to human health. From the biological perspective, NO produced in the body regulates vasodilatation, neurotransmission, and fights the invading pathogens. However, from an air quality perspective, NO is one of the air pollutants directly emitted into the atmosphere and oxidized into nitrogen dioxide (NO2) and plays a key role in the formation of troposphere ozone in the presence of VOCs through photolysis. To predict the pollution levels and provide the level of sensitivity required for pollution alert information, much work has to be done in the development of passive NO sensors. Studies on Cu (II) complexes as fluorescent NO probes as a primary application objective in the detection of biological NO has shown remarkable sensitivities.

The objectives of this work are to synthesize Cu (II) complexes of various fluorescent ligands as well as complexes of same ligand but different Cu (II) salts (different counter anions) and to study their fluorescence response toward NO. Complexes (C2, C5, C6A, and C6B) with dansyl as a fluorophore moiety and pyridyl as recognition moiety were synthesized and characterized. C2, C6A, and C6B were investigated for sensing NO. Calibration gas and a G-Cal permeation device were used as a source of NO. Fluorescence enhancements of 1.504 (± 0.018)-, 1.315 (± 0.016)-, and 1.669 (± 0.002)- fold were obtained for C2, C6B(in-situ), and C6B respectively after exposure to excess NO. The relative quantum yields of the complexes after exposure to NO are 2.048(± 0.068), 1.107(± 0.014), and 1.060(± 0.004) for C2, C6A, and C6B respectively. The detection limits obtained are between 1 – 2 ppm with C6A performing better than the other two. Thin films of C6A complex were also investigated for detecting NO using AFM, SEM, and Raman spectroscopy.

Thin film properties indicate distinct differences between with and without NO. Finally, molecular orbital and excitation energies of the free ligand (L2), its complex (C2), and C2-NO were calculated to propose the mechanism of Cu (II) complex NO sensor.

Indexing (document details)
Advisor: Morris, Vernon R., Matthews, Jason S.
Commitee: Brewer, Greg, Gultneh, Yilma, Stockwell, William R.
School: Howard University
Department: Chemistry
School Location: United States -- District of Columbia
Source: DAI-B 77/05(E), Dissertation Abstracts International
Subjects: Analytical chemistry, Physical chemistry, Environmental science
Keywords: Cu (ii) complex, Excitation enegy, Fluorescence, Nitric oxide sensing, Optimized geometry, Quantum efficiency
Publication Number: 3742208
ISBN: 978-1-339-34734-9
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