Doped sol-gel glasses as pH sensors

Rottman, Claudio; Ottolenghi, Michael; Zusman, Rivka; Lev, Ovadia; Smith, Mark E.; Gong, Guo; Kagan, Margarita; Avnir, David

doi:10.1016/0167-577x(92)90055-o

Cited by 107 publications

(62 citation statements)

References 16 publications

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“…In another type of study Izutsu et al [4] impregnated the pores of silica with L-tartaric acid, and they were able to separate chiral Co complexes on it. As for the entrapment of surfactants in sol-gel materials, this was extensively researched by Levy et al, [5] Rottman et al, [6,7] Frenkel-Mullerad and Avnir, [8] Brinker and co-workers, [9] and Stucky and co-workers.[10] One of the more interesting findings has been that the surfactant can significantly modify the cage properties, and therefore also the co-dopant properties and specific functionalities. [2] In this work it was reported that the transition between the surfactant monomer and aggregated forms develops continuously within the matrix without an abrupt phase transition (e.g., into micelles, as found in solution), an observation we use below.…”

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confidence: 99%

Enantioselective Sol–Gel Materials Obtained by Either Doping or Imprinting with a Chiral Surfactant

2007

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The formation of chiral porous materials is an on-going quest because of the numerous applications of such materials in separation science, chiral catalysis, and in pharmaceutics and so forth. Here, we describe two new methods for preparing bulk chiral silica materials, based on the use of a chiral surfactant. By one method the surfactant is used for the imprinting of chiral porosity, and by the second method we use the entrapped surfactant molecules as chiral centers within the silica. The chiral entity in the two types of matrices is different and therefore the enantioselective preferences before and after surfactant removal are not necessarily the same; indeed it was found that chiral discrimination changes before and after surfactant removal. Notably, these adsorbents are capable of recognizing chirality in molecules that have no structural similarity to the imprinting molecule. An additional attractive feature of these materials is their ability to enantioselect in both aqueous media and organic solvents. Specifically, phenylated silica sol-gel (PSG) matrices were doped with the chiral cationic surfactant, (-)-N-dodecyl-N-methylephedrinium bromide (DMB, 1, Scheme 1), and then the DMB was extracted with methanol. The powdered silica matrix was thus rendered chiral both before and after surfactant removal: before, by virtue of the entrapped chiral surfactant within the matrix; and after surfactant removal by forming chiral cavities. Both types of matrices showed general enantioselectivity by preferential adsorption of one enantiomer over several other molecules which are different from the surfactant. The pairs of enantiomers included (R)-and (S)-propranolol (2), (R)-and (S)-binaphthyl-2,2-diyl hydrogenphosphate (BINAP) (3), and (R)-and (S)-naproxen (4). In all cases good enantioselectivities were observed, both for the chirally imprinted powdered monoliths and for the chirally doped ones, with discrimination ratios in the range of 1.22-1.34. The chiral entity in the two types of matrices is different and therefore the enantioselective preferences before and after surfactant removal are not necessarily the same, as indeed was found to be the case. The fact that the discrimination changes before and after surfactant removal attests to the authenticity of the observed enantioselectivity in the two types of chiral materials.It is in order to cite some relevant background references now: Enantioselectivity towards the enantiomers of the imprinting molecule is more common [1] than enantioselectivity towards molecules different than the imprinting one, but which are still related to it. Thus, enantioselectivity towards morphine derivatives different than the imprinting derivative was demonstrated by Becket et al. [2] and by Bartels et al. [3] for silica prepared from sodium silicate. Enantioselective recognition of structurally related enantiomers is also known for organic polymers. We reiterate here that the enantioselectivity shown in this report is towards unrelated molecules. In another type of study Izutsu et a...

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Enantioselective Sol–Gel Materials Obtained by Either Doping or Imprinting with a Chiral Surfactant

2007

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“…As seen in Scheme 2, BCP has three protonated forms [44] . The equilibrium between the phenolic form (Ⅲ) in basic conditions and the hydroquinoic form (Ⅱ) in low concentration acids (pK a2 = 6.3) has led to its use as a pH indicator for low concentration acid sensors [45][46][47] . In our work we exploited the hydroquinonic (Ⅱ) to sulfonic form (I) transition with a pK a1 (sol-gel) value of −0.77 ± 0.02 (−2.06 ± 0.08 on the Hammett acidity scale [48] ).…”

Section: Optical Sol-gel Sensors For the Determination Of Concentratementioning

confidence: 99%

Optical and electrochemical sol-gel sensors for inorganic species

Dansby-Sparks

Ouyang

Chen

2009

Sci. China Ser. B-Chem.

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The use of sol-gels as a sensing matrix for the development of unique sensing strategies is discussed. Sol-gels offer almost limitless possibilities for sensing substrates due to the variety of physical properties that can be obtained by altering a number of discussed fabrication conditions and techniques. By careful consideration of the sensing requirements, novel detection methods have been developed for a variety of analytes and applications. Here, sol-gels have been used to monitor pH at the extreme ends of the scale ([H + ] = 1-11 M and [OH − ] = 1-10 M) and in mixed solvent/solute systems using dual sensing approaches. The use of ligand-grafted sol-gel monoliths for optical determination of metal ion species is also discussed. The electrochemical determination of Cr(Ⅵ) by electrodeposited sol-gel modified electrodes is also presented.sol-gel, organofunctional, acid, base, metal ions

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“…Immobilization of pH indicator molecules is critical in the fabrication process to avoid leaching and can be performed by adsorption, covalent binding or entrapment [6,7]. Phenol red based pH sensors have been prepared using sol-gel silica glasses via adsorption and entrapment [7][8][9][10], however, leakage of the dye is a problem [8].…”

Section: Introductionmentioning

confidence: 99%

Phenol red-silk tyrosine cross-linked hydrogels

et al. 2016

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Phenol red entrapped within hydrogels facilitates pH sensing in phenol red free environments. Leak-proof phenol red based pH sensors require covalent binding techniques, but are complicated due to the lack of amino or carboxyl groups on phenol red. Currently, there is no simple, reliable technique to covalently link phenol red to hydrogel matrices, for real-time pH sensing in cell culture environments. Herein, we take advantage of phenolic groups for covalent linkage of phenol red to silk tyrosine in the presence of HRP and H2O2. The novelty of the current system stems from its simplicity and the use of silk protein to create a cytocompatible, degradable sensor capable of real-time pH sensing in cell culture microenvironments.

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Doped sol-gel glasses as pH sensors

Cited by 107 publications

References 16 publications

Enantioselective Sol–Gel Materials Obtained by Either Doping or Imprinting with a Chiral Surfactant

Enantioselective Sol–Gel Materials Obtained by Either Doping or Imprinting with a Chiral Surfactant

Optical and electrochemical sol-gel sensors for inorganic species

Phenol red-silk tyrosine cross-linked hydrogels

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