Metallo-vesicular catalysis: A mixture of vesicular cysteine/iron mediates oxidative pH switchable catalysis

Abstract

The design of heme and non-heme active centers, which resemble peroxidase enzymes, has recently received a significant attention. Herein, a cystein-metal complex was designed and encapsulated in a vesicular mixture (1:4; SDS/DTAB) in order to imitate a chloroperoxidase (CLP) enzyme via chlorination of thionine at pH 3. This artificial enzyme behaved both as a catalase and CLP at pH 3, and as a peroxidase at pH 1. The shape of the metallo-vesicular catalyst at each pH value was obtained by dynamic light scattering, and was confirmed by transmission electron microscopy (TEM). The different fluidities as interior structure property of catalyst aggregates at pH 3 and 1 were obtained by differential scanning calorimetry (DSC). IR, 1 H and 13 C NMR spectroscopies were utilized to investigate the structural properties of the vesicular catalyst. These studies demonstrated that the cysteine/iron (III) center acted as a multifunctional catalyst. In addition, the sulfur and ammonium moieties of L-Cys interacted in the presence of metal ion at pH 1. However, the ammonium side chain was replaced with the carboxylate group at pH 3. Collectively, we engineered two distinct vesicular cysteinate-Fe 3+/2+ complexes, which functioned as a pH-switchable catalyst.

Effect of Chiral Ligand Concentration and Binding Mode on Chiroptical Activity of CdSe/CdS Quantum Dots

“…At the higher Cys concentration (Figure b, green lines), the 13 C NMR spectrum presents three sets of peaks: (i) the first one, with three intense signals at the same positions as free Cys; (ii) the second one, with three weak peaks corresponding to the low concentration ones; and (iii) the third one, where 13 C 1 remains almost in the same position, but 13 C 2 and 13 C 3 are shifted from 59 ppm to 55 ppm and from 29 ppm to 44 ppm, respectively. Similar shifts have been reported for a NH 2 –SH bidentate mode; therefore, we attribute these signals to Cys molecules that are bound to the QD surface in a S – –NH 2 bidentate configuration …”

“…Similar shifts have been reported for a NH 2 −SH bidentate mode; 67 therefore, we attribute these signals to Cys molecules that are bound to the QD surface in a S − −NH 2 bidentate configuration. 67 Investigation of Cys Binding Modes by FTIR Spectroscopy. To determine the binding mode of the amino group, which was not obvious from NMR analysis, we have also performed FTIR analysis of our QD samples.…”

Effects of Amino Acids on Iron-Silicate Chemical Garden Precipitation

“…In order to determine if there was any new organic product formation or polymer formation, 1 H NMR spectroscopy was conducted on the chemical garden solution after chemical garden formation for 20 mM cysteine, alanine, glycine, lysine, and a control. When NMR spectra were taken of the remaining solution, we primarily observed only the amino acids that were added to the solution, with the exception of the control, where no organics were observed . If polymers were present, we would expect the appearance of new 1 H shifts.…”

“…When NMR spectra were taken of the remaining solution, we primarily observed only the amino acids that were added to the solution, with the exception of the control, where no organics were observed. 41 If polymers were present, we would expect the appearance of new 1 H shifts. The NMR signals were relatively broad, likely due to the dissolved iron remaining in solution.…”

Iron‐Porphyrin/Cysteine/PEG as Pseudo‐Chloroperoxidase Nanozyme

“…Here a mixture including Fe‐TPP complex was provided at low pH to design a suitable microenvironment for catalytic reaction. Cysteine was used as an axial ligand for iron center to imitate the native CLP active site . As shown in Figure , the activity of Fe‐TPP‐cysteine complex at pH 3 has promoted the CLP‐like activity respect to alone iron‐porphyrin.…”