Peroxidase-like Catalytic Activity of Copper-Mediated Protein-Inorganic Hybrid Nanoflowers and Nanofibers of ß-Lactoglobulin and α-Lactalbumin: Synthesis, Spectral Characterization, Microscopic Features, and Catalytic Activity.

A free Cys-SH-containing protein, ß-lactoglobulin (ß-LG), and another protein not possessing the same, viz., apo-α-lactoglobulin (apo-α-LA), were used in studies to demonstrate the role of this amino acid, along with its secondary structure, in the formation of a protein dimer and a protein-inorganic hybrid nanoflower and in the creation of the peroxidase-like activity of the nanomaterials produced when the proteins were treated with varying Cu(2+) concentration under different pH conditions. An increase in the pH as well as the Cu(2+) mole ratio results in increasing dimer formation in case of ß-LG due to the presence of free Cys121-SH, while the dimer is not formed in case of apo-α-LA under the same conditions. The role of Cys in the dimer formation has been demonstrated both by MALDI and sodium dodecyl sulfate-polyacrylamide gel electrophoresis studies. Both of the proteins exhibited changes in their secondary structures to different extents as a function of pH, and the structures were stabilized by Cu(2+) interactions, as studied by CD and fluorescence spectroscopy. The small and spherical nanoparticles formed at pH 7 with lower equivalents of Cu(2+) join together to form larger aggregates at higher equivalents of Cu(2+). For the same concentration at pH 9, both the aggregates and the nanoflowers were noticed. However, at pH 12, the Cu(2+) binding induces the formation of fibers along with the flowers. Both the nanoflowers and nanofibers exhibited peroxidase-like activity in a catalytic manner. Nanoflowers were also shown to detect phenol in the concentration range from 10 to 200 µM. The copper-induced nanobiomaterial obtained in the case of apo-α-LA also exhibited peroxidase-like activity. Thus, this paper deals with the green synthesis of copper-induced protein (ß-LG/apo-α-LA)-inorganic hybrid nanomaterials that are important due to their applications as nanobiomaterials.

Quinoline driven fluorescence turn on 1,3-bis-calix[4]arene conjugate-based receptor to discriminate Fe3+ from Fe2+.

The synthesis and characterization of a triazole linked quinoline appended calix[4]arene conjugate, L, and its fluorescence turn on receptor property for Fe(3+) have been demonstrated. The selective and sensitive discrimination of Fe(3+) has been shown using fluorescence and absorption titration experiments. The Fe(3+) binding to L has been further shown by ITC and ESI MS. The mode of binding of Fe(3+) by calix[4]arene conjugate has been shown by absorption, (1)H NMR and visual color change and the species were modeled based on DFT computations. The {L + Fe(3+)} has been shown to label cells with fluorescence imaging. Moreover the utility of this conjugate has been demonstrated by the combination logic gate system.