Density of Grafted Chains in Thioglycerol-Capped CdS Quantum Dots Determines Their Interaction with Aluminum(III) in Water.

We aimed to quantify the interaction of water-soluble-functionalized CdS quantum dots (QDs) with metal cations from their composition and physical properties. From the diameter of thioglycerol-capped nanoparticles (TG-CdS QDs) measured by electronic microscopy ( D = 12.3 ± 0.3 nm), we calculated the molecular mass of the individual particle MAQD = (3 ± 0.5) × 106 g·mol-1 and its molar absorption coefficient ε450 = 21 × 106 M-1·cm-1. We built a three-dimensional model of the TG-CdS QDs in agreement with the structural data, which allowed us to quantify the number of thioglycerol grafted chains to ∼2000 per QD. This value fully matches the saturation binding curve of Al3+ cations interacting with TG-CdS QDs. The reaction occurred with a slow association rate ( kon = 2.1 × 103 M-1·s-1), as expected for heavy QDs. The photophysical properties of the functionalized QDs were studied using an absolute QD concentration of 7 nM, which allowed us to investigate the interaction with 14 metallic cations in water. The fluorescence intensity of TG-CdS QDs could be quenched only in the presence of Al3+ ions in the range 0.2-10 µM but not with other cations and was not observed with other kinds of grafting chains.

The control of nitric oxide dynamics and interaction with substituted zinc-phthalocyanines.

Phthalocyanines are artificial macrocycles that can harbour a central metal atom with four symmetric coordinations. Similar to metal-porphyrins, metal-phthalocyanines (M-PCs) may bind small molecules, especially diatomic gases such as NO and O2. Furthermore, various chemical chains can be grafted at the periphery of the M-PC macrocycle, which can change its properties, including the interaction with diatomic gases. In this study, we synthesized Zn-PCs with two different substituents and investigated their effects on the interaction and dynamics of nitric oxide (NO). Time-resolved absorption spectroscopy from picosecond to millisecond revealed that NO dynamics dramatically depends on the nature of the groups grafted to the Zn-PC macrocycle. These experimental results were rationalized by DFT calculations, which demonstrate that electrostatic interactions between NO and the quinoleinoxy substituent modify the potential energy surface and decrease the energy barrier for NO recombination, thus controlling its affinity.

Use of MPA-capped CdS quantum dots for sensitive detection and quantification of Co2+ ions in aqueous solution.

Water soluble CdS quantum dots (QDs) were synthesized by a simple aqueous chemical route using mercaptopropionic acid (MPA) as a stabilizer. These QDs had a fluorescence emission band maximum at 540 nm with a FWHM ∼130 nm and a quantum yield of ∼12%. Transmission electronic microscopy images were used to determine the QD diameter of 8.9 ±â€¯0.4 nm. From this value we calculated the molecular mass M(QD) = 1.17 × 106 g mol-1 and the extinction coefficient at the band edge (450 nm) ε450 = 4.7 × 106 cm-1 M-1, which allowed to determine the true molar concentration of 17 nM for spectroscopic measurements in solution. The fluorescence intensity of MPA-CdS QDs was quenched only in the presence of Co2+ ions, but not in the presence of thirteen other metal cations. The fluorescence quenching of MPA-CdS QDs appeared proportional to the Co2+ concentration in the range 0.04-2 µM. Based on a fluorescence peak position and a lifetime both independent from Co2+ concentration, the quenching mechanism of MPA-CdS QDs appeared static. Because the strong electronic absorption of Co2+ overlaps the emission of QDs, our results can be explained by Förster energy transfer from QD to the bound Co2+ cations.