Acid−Base Equilibria inside Amine-Functionalized Mesoporous Silica

Abstract

Acid-base equilibria and effective proton concentration inside a silica mesopore modified with a trimethyl ammonium (TMAP) layer were studied by steady-state fluorescence experiments. The mesoporous silica with a dense TMAP layer (1.4 molecules/nm(2)) was prepared by a post grafting of N-trimethoxysilylpropyl-N,N,N-trimethylammonium at surfactant-templated mesoporous silica (diameter of silica framework =3.1 nm). The resulting TMAP-modified mesoporous silica strongly adsorbed of anionic fluorescence indicator dyes (8-hydroxypyrene-1,3,6-trisulfonate (pyranine), 8-aminopyrene-1,3,6-trisulfonate (APTS), 5,10,15,20-tetraphenyl-21H,23H-porphinetetrasulfonic acid disulfuric acid (TPPS), 2-naphthol-3,6-disulfonate (2NT)) and fluorescence excitation spectra of these dyes within TMAP-modified mesoporous silica were measured by varying the solution pH. The fluorescence experiments revealed that the acid-base equilibrium reactions of all pH indicator dyes within the TMAP-modified silica mesopore were quite different from those in bulk water. From the analysis of the acid-base equilibrium of pyranine, the following relationships between solution pH (pH(bulk)) and the effective proton concentration inside the pore (pH(pore)) were obtained: (1) shift of pH(pore) was 1.8 (ΔpH(pore)=1.8) for the pH(bulk) change from 2.1 to 9.1 (ΔpH(bulk)=7.0); (2) pH(pore) was not simply proportional to pH(bulk); (3) the inside of the TMAP-modified silica mesopore was suggested to be in a weak acidic or neutral condition when pH(bulk) was changed from 2.0 to 9.1. Since these relationships between pH(bulk) and pH(pore) could explain the acid-base equilibria of other pH indicator dyes (APTS, TPPS, 2NT), these relationships were inferred to describe the effective proton concentration inside the TMAP-modified silica mesopore.

Trinucleotide duplex formation inside a confined nanospace under supercooled conditions

“…A dense TMAP monolayer (1.4 molecules nm À 2 ) was formed on the inner pore surface of the mesoporous silica using the post-grafting method (Fig. 1) 22 . The resulting TMAP-modified HMM (TMAP-HMM) has a silica mesophase with a quasi-hexagonal pore arrangement ( Supplementary Fig.…”

“…The details of TMAP-HMM preparation are described in our previous papers [20][21][22] . A mixture of ethanol (7.68 g), TEOS (11.57 g) and 1 ml of HCl aqueous solution (2.8 mM) was refluxed at 60°C for 90 min.…”

“…After calcination to remove the template surfactant, the calcined membrane (HMM) was immersed in a mixture of 8.9 ml of 1,4-dioxane, 20.8 ml of 1-hexanol, and 0.3 ml of N-trimethoxysilylpropyl-N,N,Ntrimethylammonium chloride (50 wt% in methanol) and heated under reflux for 12 h at 102°C (ref. 22). After refluxing, the TMAP-modified HMM was rinsed with acetone and water three times each.…”

Microviscosity of Supercooled Water Confined within Aminopropyl-modified Mesoporous Silica as Studied by Time-resolved Fluorescence Spectroscopy

“…The mesoporous silica specimen used in this study had a quasi-hexagonal pore arrangement and the pore diameter was 3.1 nm, 30,31,34 and RhB molecules were covalently bound to part of the AsP groups on the inner pore surface (Fig. 1).…”

Pore-forming Compounds as Signal Transduction Elements for Highly Sensitive Biosensing

“…Such sensing strategy provides a highly sensitive and practical method because the marker is enriched in the pores and fluorescence emission from the solid phase can be directly measured. In addition, the confined nanospace has unique chemical and optical properties 97 that are different from a bulk solution because of the restricted freedom of dye movement, 98 a shift in acid-base equilibrium 99 and suppressed dimerization of dyes. [100][101][102] Such chemical features will be interesting for biosensing applications.…”