Ethylene glycol, trapped electrons

A detailed study of the effect of temperature on the reaction kinetics of etr with a set of acceptors over a broad time interval of 10 5-l s in the region of ultralow temperatures (4.2-100 K) was performed in ref. 79. For the acceptors CrO, Fe(CN)jF, and N02, the decay curves for electrons et stabilized in deep traps of a water-alkaline (8M NaOH) matrix were found to vary only slightly with variation of temperature. The same result was obtained for the reactions of these acceptors with e stabilized in deep traps of vitrified mixtures of water with ethylene glycol [105]. Thus, at temperatures of 4-100 K, the main contribution of the reaction of et with the above acceptors in both matrices is made by a temperature-independent channel of electron tunneling. 

Crown ethers are cyclic polyethers and their structure permits a conformation with certain sized holes in which cations can be trapped by co-ordination with the lone pair electrons on the oxygen atoms. These are used as phase transfer catalysts. The cyclic polymers of ethylene glycol (0CH2CH2) are named as X-crown-Y. X refers to total number of atoms in the ring and Y to the total number of oxygens in the ring. 

The introduction of QDs into aqueous media is usually accompanied by drastic decreases in the luminescence yields of the QDs. This effect presumably originates from the reaction of surface states with water, a process that yields surface traps for the conduction-band electrons [63]. As biorecognition events or biocat-alytic transformations require aqueous environments for their reaction medium, it is imperative to preserve the luminescence properties of QDs in aqueous systems. Methods to stabilize the fluorescence properties of semiconductor QDs in aqueous media (Figure 6.2) have included surface passivation with protective layers, such as proteins [64, 65], as well as the coating of QDs with protective silicon oxide films [66, 67] or polymer films [43, 68, 69). Alternatively, they can be coated with amphiphilic polymers, which have both a hydrophobic side chain that interacts with the organic capping layer of the QDs and a hydrophilic component, such as a poly(ethylene glycol) (PEG) backbone, for water solubility [70, 71). Such water-soluble QDs may retain up to 55% of their quantum yields upon transfer to an aqueous medium. 

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