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
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.
Available from: Yvonne Williams
- "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 . 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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ABSTRACT: Nanomaterials such as SiO2 nanoparticles (SiO2NP) are finding increasing applications in the biomedical and biotechnological fields such as disease diagnostics, imaging, drug delivery, food, cosmetics and biosensors development. Thus, a mechanistic and systematic evaluation of the potential biological and toxic effects of SiO2NP becomes crucial in order to assess their complete safe applicability limits.
In this study, human monocytic leukemia cell line THP-1 and human alveolar epithelial cell line A549 were exposed to a range of amorphous SiO2NP of various sizes and concentrations (0.01, 0.1 and 0.5 mg/ml). Key biological indicators of cellular functions including cell population density, cellular morphology, membrane permeability, lysosomal mass/pH and activation of transcription factor-2 (ATF-2) were evaluated utilizing quantitative high content screening (HCS) approach and biochemical techniques. Despite the use of extremely high nanoparticle concentrations, our findings showed a low degree of cytotoxicity within the panel of SiO2NP investigated. However, at these concentrations, we observed the onset of stress-related cellular response induced by SiO2NP. Interestingly, cells exposed to alumina-coated SiO2NP showed low level, and in some cases complete absence, of stress response and this was consistent up to the highest dose of 0.5 mg/ml.
The present study demonstrates and highlights the importance of subtle biological changes downstream of primary membrane and endocytosis-associated phenomena resulting from high dose SiO2NP exposure. Increased activation of transcription factors, such as ATF-2, was quantitatively assessed as a function of i) human cell line specific stress-response, ii) SiO2NP size and iii) concentration. Despite the low level of cytotoxicity detected for the amorphous SiO2NP investigated, these findings prompt an in-depth focus for future SiO2NP-cell/tissue investigations based on the combined analysis of more subtle signalling pathways associated with accumulation mechanisms, which is essential for establishing the bio-safety of existing and new nanomaterials.
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ABSTRACT: A sea ice dynamics/thermodynamics model is validated using a
one-year time series of data from the C-band synthetic aperture radar
(SAR) instrument aboard Earth Resources Satellite 1 (ERS-1). Common
validation problems using geophysical parameter estimates produced by
operational algorithms are avoided by coupling a simple backscatter
model to the physical model to generate a time series of estimated SAR
backscatter values, which can be directly compared to the observed time
series. Comparison of actual and estimated SAR backscatter shows good
agreement during the winter and spring seasons. Differences during the
summer and early autumn period are attributed to surficial changes,
namely wet snow, meltponds, and young ice covered by frost flowers, that
are not included in the ice physics model but affect the C-band
backscatter. After adding these effects to the backscatter model, very
good agreement is observed throughout the year between the sea
ice/backscatter model and the ERS-1 time series, with RMS differences
about 10% of the full range of backscatter values. The paper
demonstrates the utility of the forward simulation approach for model
validation and discusses potential future improvements and applications
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ABSTRACT: Polarization resolved fluorescence from single molecules was measured from rhodamine 6G (R6G), sulforhodamine B (SRB), Oregon Green 514 (ORG), and didodecyl-3,3,3‘,3‘-tetramethylindocarbocyanine (DilC12) embedded in silica sol−gel thin films in contact with water and ethanol. Positively charged R6G was found to be firmly immobilized, regardless of the solvent medium. Despite its net negative charge, zwitterionic SRB was found mostly immobilized in both solvent media. The immobilization of SRB was attributed to a delicate balance of Coulombic interaction, hydrogen bonding, and molecular imprinting effect. While R6G showed a significant decrease in photostability in a solvent medium because of enhanced solvent interactions, hydrogen bonding appeared to effectively retard the molecular motions of solvated SRB such that its photostability exceeded those in dry films. The mobility of negatively charged ORG was found to be moderately enhanced through repulsion, but Coulombic force was not as influential as hydrophobic interaction, which was responsible for the high mobility found for DiIC12 in dry films. When in water and ethanol, the hydrophobic chains of DiIC12 were pushed by the solvent toward the less polar silica matrix, forcing DiIC12 to the solid−liquid interface and transforming a substantial amount of tumbling DiIC12 into intermediate DiIC12. Since the photostability of DiIC12 is closely related to the dynamics associated with its hydrophobic chains, DiIC12 in both water-covered and ethanol-covered films displayed comparable photostability because of the similar silica environment surrounding the hydrophobic chains.
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