Polarographic study on poly α-L-glutamic acid-Cd2+,Co2+ complexes in the helix–coil pH region

Abstract

Interactions between poly alpha- L-glutamic acid (PGA) and metal ions Cd(2+), Co(2+) were studied by direct current polarography. The diffusion currents of these ions decreased sharply in the presence of PGA in the pH region from 5.0 through neutral. A corresponding increase in the helix content of the PGA-metal ion complex was revealed by CD measurements on the same solutions. Helix contents determined by polarography were in good agreement with those by CD in the neutral pH region. On the contrary, the decrease of current in lower acidic pH regions was independent of helix formation and suggested that metal ions coordinate to sporadically-dissociated carboxylate groups to cause aggregation of the intra and/or inter polymer chains. The diffusion current of the ions, therefore, is a parameter sensitive to the conformational changes of PGA from acidic through neutral pH region.

Chemiluminescent and Chemiluminescence Resonance Energy Transfer (CRET) Detection of DNA, Metal Ions, and Aptamer–Substrate Complexes Using Hemin/G-Quadruplexes and CdSe/ZnS Quantum Dots

“…This is consistent with the selective opening of hairpins ( 9) or (10), respectively. In turn, treatment of the QDs mixture with all three analytes, (8), (11), and (12), results in the CRET emission of all three sized QDs at 490, 560, and 620 nm. Also, the interaction of the QDs mixture in the presence of different combinations of two target DNAs leads to the CRET signals from the respective QDs, as can be seen in Figure 9b.…”

“…Realizing that different sized QDs may be excited by the chemiluminescence wavelength generated by luminol, the sensing platform was further implemented for the multiplexed analysis of three different DNAs, Figure 8. Three different sized CdSe/ZnS QDs (λ em = 490 nm, λ em = 560 nm, λ em = 620 nm) were modified with the hairpin structures ( 7), (9), and (10); each of these hairpin structures includes in the duplex stem structure the blocked HRP-mimicking DNAzyme sequence, while the loop regions of ( 7), (9), and (10) are complementary to the DNA analytes ( 8), (11), and (12), respectively. As the chemiluminescence generated by the hemin/G-quadruplex is capable to stimulate the CRET to any of these QDs, the opening of any hairpin by the respective analyte will result in the chemiluminescence generation by the hemin/G-quadruplex, and the consequent triggering of the luminescence of the adjacent QDs.…”

“…As the chemiluminescence generated by the hemin/G-quadruplex is capable to stimulate the CRET to any of these QDs, the opening of any hairpin by the respective analyte will result in the chemiluminescence generation by the hemin/G-quadruplex, and the consequent triggering of the luminescence of the adjacent QDs. Figure 9a shows the luminescence features of the mixture of the three different sized QDs modified with hairpins (7), (9), and (10) after interaction with the DNA analytes ( 8), (11), and (12), in the presence of hemin and H 2 O 2 /luminol. The interaction of the QDs mixture with (8) triggers the luminescence of the 620 nm luminescent QDs, consistent with the selective opening of hairpin (7) and the formation of the hemin/G-quadruplex.…”

“…The interaction of the QDs mixture with (8) triggers the luminescence of the 620 nm luminescent QDs, consistent with the selective opening of hairpin (7) and the formation of the hemin/G-quadruplex. Similarly, the treatment of the modified-QDs mixture with the analytes (11) or (12) triggers the luminescence of the 560 or 490 nm luminescent QDs, respectively. This is consistent with the selective opening of hairpins ( 9) or (10), respectively.…”

“…The color changes upon the aggregation of Au nanoparticles provided a versatile method to detect DNA, aptamer–substrate recognition processes, − and metal ions − such as Hg 2+ . Different fluorescent and fluorescence resonance energy transfer DNA sensors and aptasensors − were developed. Similarly, semiconductor quantum dots (QDs) were used as luminescence labels for the detection of DNA , or as optical labels for following the dynamic replication and sensing of DNA, or the dynamic formation of aptamer–substrate complexes. , Catalytic nucleic acids (DNAzymes) attract substantial research efforts as amplifying labels for sensing events .…”