Comparative Study of Guest Charge−Charge Interactions within Silica Sol−Gel

Department of Chemistry, State University of New York College at Geneseo, Geneseo, New York, United States
The Journal of Physical Chemistry B (Impact Factor: 3.3). 04/2005; 109(11):4816-23. DOI: 10.1021/jp0458957
Source: PubMed


We investigated the effect of charge-charge interactions on the mobilities of rhodamine 6G (R6G), Nile Red, sulforhodamine B, and Oregon Green 514 (ORG) guest molecules within a silica sol-gel host as the guest charge progressed from positive to neutral to negative. Through classification of the mobility as fixed, tumbling, or intermediate behavior, we were able to distinguish differences in surface attraction as the guest charge was varied. On the basis of our results, an attractive charge (as tested by cationic R6G) does not contribute significantly to mobility within dry films. However, an increase in the cationic influence is observed in water-equilibrated environments. A comparison of ORG in dry and water- and phosphate-buffer-equilibrated films indicates that charge repulsion does significantly increase dye rotational mobility (to a maximum of 24 +/- 3% tumbling molecules). However, in view of the percentage of tumbling molecules found, charge-charge interactions do not appear to be the dominant force controlling guest mobility.

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    • "These were synthesised via a co-condensation reaction where Rhodamine 6G soluble dye was incorporated into the silica framework during the synthesis of the nanoparticles. It is known that by the incorporation of the dye within the silica framework, the dye release is prevented by the lack of charge transfer which is usually associated with a surface functionalisation of the fluorescent dye [47]. Therefore, in our study when dispersed in biological, or water based solutions no obvious difference between the unlabelled and Rhodamine 6G labelled amorphous SiO2NP was found due to the complete amorphous nature of the mesoporous silica. "
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