The fundamental mechanisms involved in photosynthesis provide an opportunity
to study physical principles that span over both classical and quantum scales. A
better understanding of these mechanisms will benefit the development of alternative
energy sources such as cheaper biofuel and more effective photovoltaics.
This dissertation describes the single molecule spectroscopy setup that was assembled
during my MSc-degree and the underlying theory required to understand
the technique, is discussed. The greatest part of the setup development involved
customised software development that performs the measurement. The code of
this software is briefly discussed. Thereafter the results of a series of single molecule
spectroscopy measurements of isolated light harvesting complex II (LHCII)
that undergo non-photochemical quenching (NPQ) are described. The fast, reversible,
energy-dependent component (qE) of NPQ is emulated by lowering the pH of
the solvent in which the complexes are diluted. Apart from fluorescence intensity
measurements, time correlated single photon counting is used to measure fluorescence
lifetimes, which serves as an indirect measurement of NPQ. It was found
that quenching could be taking place before the energy reaches the terminal emitter,
and a relationship between intermediate fluorescence states and high jumping
frequencies was established.
Die fundamentele meganismes wat by fotosintese betrokke is skep 'n ideale
geleentheid om beginsels te bestudeer wat oor beide klassieke en kwantumskale
strek. 'n Beter verstaan van hierdie meganismes sal die ontwikkeling
van alternatiewe energiebronne soos goedkoop biobrandstof en meer effektiewe
fotovoltaïese selle bevorder. Hierdie verhandeling beskryf die
enkelmolekuulspektroskopie-opstelling wat tydens my MSc-graad opgerig is en
die onderliggende teorie wat nodig is om die tegniek te verstaan, word bespreek.
Die grootste deel van die ontwikkeling van die opstelling het die
ontwikkeling van toepassingsgerigte sagteware behels. Die kode van hierdie
sagteware word oorsigtelik bepreek. Vervolgens word die resultate van 'n reeks
enkelmolekuulspektroskopie-metings beskryf waartydens nie-fotochemiesedowing
(NFD) in die geïsoleerde ligversamelingskompleks II (LHCII) van hoër
plante bestudeer is. Die vinnige, omkeerbare, energie-afhanklike komponent (qE)
van NFD is geëmuleer deur die pH van die oplossing waarin die komplekse opgelos
is, te verlaag. Buiten metings van die fluoressensie-intensiteite is tydsgekorreleerde
enkelfotontelling ook toegepas om fluoressensieleeftye te meet, wat as 'n
indirekte meting van die mate van NFD dien. Die moontlikheid dat dowing plaasvind
voordat die opwekkingsenergie die laagste energietoestand in die kompleks
bereik, is ontdek en 'n verwantskap tussen intermediêre fluoressensietoestande en
hoëfrekwensieskakeling word gelê.
