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Fluorescent Probes and the Structural Evolution of Hybrid and Nonhybrid Sol-Gel Systems

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L. M. Ilharco , J. M. Gaspar Martinho and C. I. Martins

Complexo I, Instituto Superior Tecnico, Centro de Quimica-Fisica MolecularAv. Rovisco Pais,Lisboa Codex 1096,PORTUGAL

J. Chem. Educ., 1998, 75 (11), p 1466

DOI: 10.1021/ed075p1466

Publication Date (Web): November 1, 1998

Abstract

A pedagogical approach to the sol-gel process is suggested, taking into account the interest of such an interdisciplinary subject for an advanced undergraduate course in chemistry. A comparison is made between pure inorganic and hybrid sol-gel systems, obtained by incorporation of polymers and exhibiting interesting properties. In these systems, the structural evolution during the sol-gel-dry gel (xerogel) process is a conditioning factor of the final properties. As case studies, we have selected sol-gel systems consisting of tetraethyl orthosilicate (TEOS, a widely used precursor), water, and ethanol at pH 1.2 and 2.5, and the same systems modified by addition of polytetrahydrofuran (PTHF). The sol-gel-xerogel structural evolution was followed using a carefully chosen fluorescent probe, Py-(CH₂)₁₂-Py, incorporated in a very low concentration (of the order of 10^-6 M). The ratio between fluorescence intensities of excimer and monomer of pyrene, I_E/I_M, was followed with time. The increase of this ratio with time for pH 1.2, in contrast to pH 2.5, has been interpreted in terms of the different sizes of the primary silica particles, which have a hydrophobic character, and in which the fluorescent probe is encapsulated. A slower increase of the I_E/I_M ratio for hybrid systems was explained by the presence of PTHF: the polymer acts as a spacer between silica particles, and, owing to its higher hydrophobic character when compared to the solvent, retains a significant part of the probe molecules. Based on the fluorescence results, structural models are proposed for the two types of systems.

Keywords (Audience):

Upper-Division Undergraduate

Keywords (Domain):

Laboratory Instruction

Keywords (Pedagogy):

Hands-On Learning / Manipulatives

Keywords (Subject):

Fluorescence Spectroscopy

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This article has been cited by 3 ACS Journal articles (3 most recent appear below).

Biocatalysis with Sol−Gel Encapsulated Acid Phosphatase
Suhasini Kulkarni, Vu Tran, Maggie K.-M. Ho, Chieu Phan, Elizabeth Chin, Zeke Wemmer and Monika Sommerhalter
Journal of Chemical Education2010 87 (9), 958-960
- Biocatalysis with Sol−Gel Encapsulated Acid Phosphatase
  Suhasini Kulkarni, Vu Tran, Maggie K.-M. Ho, Chieu Phan, Elizabeth Chin, Zeke Wemmer and Monika Sommerhalter
  Journal of Chemical Education2010 87 (9), 958-960
  This experiment was performed in an upper-level undergraduate biochemistry laboratory course. Students learned how to immobilize an enzyme in a sol−gel matrix and how to perform and evaluate enzyme-activity measurements. The enzyme acid phosphatase (APase)...
  Abstract | Full Text HTML | Hi-Res PDF | PDF w/ Links
Flavin Mononucleotide as a Probe for Dopant Encapsulation in Sol−Gel Silicates
Trent H. Galow, Nathan Fuller, Claire T. Cohen, Raymond J. Thibault, and Vincent M. Rotello
Langmuir2002 18 (24), 9149-9152
- Flavin Mononucleotide as a Probe for Dopant Encapsulation in Sol−Gel Silicates
  Trent H. Galow, Nathan Fuller, Claire T. Cohen, Raymond J. Thibault, and Vincent M. Rotello
  Langmuir2002 18 (24), 9149-9152
  Flavin mononucleotide (FMN, 1) provides a dynamic conformational probe for studying the covalent cross-linking of dopants into silica. Excitation of FMN 1 leads to photodecomposition only when the side chain is in an appropriate geometry to allow a six-...
  Abstract | Full Text HTML | Hi-Res PDF | PDF w/ Links
Applications of the Sol-Gel Process Using Well-Tested Recipes
A. Celzard and J. F. Marêché
Journal of Chemical Education2002 79 (7), 854
- Applications of the Sol-Gel Process Using Well-Tested Recipes
  A. Celzard and J. F. Marêché
  Journal of Chemical Education2002 79 (7), 854
  Simple syntheses of glassy materials are proposed in this article. All of them are based on the sol–gel process and the polycondensation of metallo-organic molecular precursors in a solvent. The basic chemical reactions are reviewed, and the main steps of ...
  Abstract | Hi-Res PDF | PDF w/ Links