Efficient Method for the Concentration Determination of Fmoc Groups Incorporated in the Core-Shell Materials by Fmoc–Glycine

Abstract

In this paper, we described the synthesis procedure of TiO2@SiO2 core-shell modified with 3-(aminopropyl)trimethoxysilane (APTMS). The chemical attachment of Fmoc–glycine (Fmoc–Gly–OH) at the surface of the core-shell structure was performed to determine the amount of active amino groups on the basis of the amount of Fmoc group calculation. We characterized nanostructures using various methods: transmission electron microscope (TEM), scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA) and X-ray photoelectron spectroscopy (XPS) to confirm the modification effectiveness. The ultraviolet-visible spectroscopy (UV-vis) measurement was adopted for the quantitative determination of amino groups present on the TiO2@SiO2 core-shell surface by determination of Fmoc substitution. The nanomaterials were functionalized by Fmoc–Gly–OH and then the fluorenylmethyloxycarbonyl (Fmoc) group was cleaved using 20% (v/v) solution of piperidine in DMF. This reaction led to the formation of a dibenzofulvene–piperidine adduct enabling the estimation of free Fmoc groups by measurement the maximum absorption at 289 and 301 nm using UV-vis spectroscopy. The calculations of Fmoc loading on core-shell materials was performed using different molar absorption coefficient: 5800 and 6089 dm3 × mol−1 × cm−1 for λ = 289 nm and both 7800 and 8021 dm3 × mol−1 × cm−1 for λ = 301 nm. The obtained results indicate that amount of Fmoc groups present on TiO2@SiO2–(CH2)3–NH2 was calculated at 6 to 9 µmol/g. Furthermore, all measurements were compared with Fmoc–Gly–OH used as the model sample.

Dansyl-Labelled Ag@SiO2 Core-Shell Nanostructures—Synthesis, Characterization, and Metal-Enhanced Fluorescence

“…The amino-functionalized core-shell silver nanomaterial was used for further modification based on the reaction with DNS chloride conducted in toluene in the presence of triethylamine at 80 °C for 24 h. The reaction was performed until all the used substrates in the reaction mixture were consumed ( Scheme 2 a). The number of the attached groups on the core-shell surface was about 6 to 9 µmol/g, which was calculated based on the method used in peptide chemistry [ 40 ]. Moreover, we determined the concentration of DNS present in Ag@SiO 2 -NH-DNS (2 × 10 −5 M).…”

Characterization and Cytotoxicity Comparison of Silver- and Silica-Based Nanostructures

“…The weight loss of 25.11% observed in the region within 200 to 350 °C could be assigned to hydrolysis and polycondensation reactions of the unreacted alkoxy and hydroxy groups [58]. The second peak observed in DTG curves centered at 460 °C with the weight loss of 4.99% mainly corresponds to the composition of organic groups from TEOS used in the synthesis [27]. The FT-IR spectrum of SiO 2 NPs contains several bands characteristic of silica.…”

“…The standard techniques are electron microscopy-including scanning (SEM) or transmission (TEM), Fourier-transform infrared spectroscopy (FT-IR), or thermogravimetric analysis (TG). In addition, all the methods are under constant development, which allows accurate characterization of the nanoparticle surfaces, including the determination of active groups number [27].…”

Analyzing the surface of functional nanomaterials—how to quantify the total and derivatizable number of functional groups and ligands

“…Fmoc can be used for the quantification of amino groups on NM by cleaving off the NM-bound Fmoc protecting groups with piperidine in DMF followed by photometric or fluorometric detection of the released dibenzofulvene-piperidine adduct [130][131][132][133][134][135][136]. Meanwhile, variations of the reaction solvent [137] and other suitable detection wavelengths [138] have been reported. To increase the sensitivity of the assays, that was initially read out photometrically, a Fmoc-Cl fluorescence assay was developed that can be performed in aqueous solution.…”