AA. Preferential killing of bacterial cells by surface-modified organosilane-treated ZnO quantum dots synthesized through a co-precipitation method

The aim of this study was to screen and determine the significant antibacterial/antiviral activities of surface-modified ZnO@MPS QDs owing to their impressive activities against microorganisms.

Nanocrystal-ligand interactions deciphered: the influence of HSAB and pK a in the case of luminescent ZnO

Despite all the efforts made by the scientific community to rationalize the interaction of organic molecules with nanocrystals (Ncs), we are still at the level of the empirical recipe when the material behavior in solution is concerned. In an effort to address this issue, the analysis of the luminescence measurements of ZnO Ncs in the presence of various organic substrates using a Langmuir adsorption model was carried out to determine for the first time the affinity constants and the number of binding sites as well as to rank the interaction strengths of these substrates with regard to ZnO Ncs. The results were confirmed by NMR spectroscopic studies, which, besides, provided a deep understanding of the substrate-ZnO Nc interactions. Analysis of the results using pK _a and HSAB theory demonstrates that the interaction of a given substrate can be determined by its pK _a versus the pK _a of the organic molecules present at the surface of pristine Ncs and that the hard or soft character of the substrates can govern the emission intensity of the ZnO Ncs.

Catalytic Effect of Photoluminescent Zinc Oxide Nanoparticles Formed in the Presence of Quaternary Ammonium Salts

The comparative effect of two quaternary ammonium salts from 1,2-bis(4-pyridyl)ethane (PyQAs), namely N,N′-diphenacyl-1,2-bis(4-pyridinium)ethane dibromide (PyQAs1) and N,N′-di(p-methoxyphenacyl)-1,2-bis(4-pyridinium)ethane dibromide (PyQAs2), upon the size and photoluminescence of zinc oxide nanoparticles (ZnO NPs) was investigated. The formation of ZnO NPs took place in the presence of variable amounts of the two PyQAs species (1, 2.5, and 5%), according to the chemical precipitation of zinc(II) acetate with potassium hydroxide in ethanol under reflux. The obtained ZnO NPs were structurally characterized by means of X-ray powder diffraction, infrared, and Raman spectroscopy. The fluorescence of all supernatant solutions, observed under ultraviolet light, determined us to make an investigation of the solutions by means of liquid chromatography coupled with electrospray ionization mass spectrometry (LC-MS-ESI) in order to elucidate the identity of the newly formed fluorescent species. Such an occurrence thus allowed the invocation of the catalytic effect of zinc(II) ions towards the organic transformation of both nonfluorescent PyQAs surfactants into new fluorescent organic species.

Insight into the molecular mechanism behind PEG-mediated stabilization of biofluid lipases

Bioconjugates established between anionic polyethylene glycol (PEG) based polymers and cationic proteins have proven to be a promising strategy to engineer thermostable biocatalysts. However, the enzyme activity of these bioconjugates is very low and the mechanism of non-covalent PEG-stabilization is yet to be understood. This work presents experimental and molecular dynamics simulation studies, using lipase-polymer surfactant nanoconjugates from mesophile Rhizomucor miehei (RML), performed to evaluate the effect of PEG on enzyme stability and activity. Results demonstrated that the number of hydrogen bonds between the cationized RML and PEG chain correlates with enzyme thermostability. In addition, an increase of both the number of PEG-polymers units and cationization degree of the enzyme leads to a decrease of enzyme activity. Modelling with SAXS data of aqueous solutions of the biofluid lipases agrees with previous hypothesis that these enzymes contain a core constituted of folded protein confined by a shell of surfactants. Together results provide valuable insight into the mechanism of non-covalent PEG mediated protein stabilization relevant for engineering active and thermostable biofluids. Furthermore, the first biofluids RML with activity comparable to their cationized counterpart are presented.

Preparation of Monodisperse Hydrophilic Quantum Dots with Amphiphilic Polymers

Monodisperse hydrophilic quantum dots (QDs) are promising labeling materials for biomedical applications. However, the controllable preparation of monodisperse hydrophilic QDs with amphiphilic polymers remains a challenge. Herein, the molecular structures of amphiphilic polymers assembled on different-sized QDs are investigated. Both the experimental results and the molecular dynamics (MD) calculation suggest that the grafting ratio of amphiphilic polymers assembled on QDs increases as the size of QDs increases. Thus, the controllable preparation of different-sized monodisperse hydrophilic QDs can be achieved by simply varying the grafting ratio of amphiphilic molecules and applied in the simultaneous labeling of three tumor biomarkers.

NMR Observation of Mobile Protons in Proton-Implanted ZnO Nanorods

The diffusion properties of H(+) in ZnO nanorods are investigated before and after 20 MeV proton beam irradiation by using (1)H nuclear magnetic resonance (NMR) spectroscopy. Herein, we unambiguously observe that the implanted protons occupy thermally unstable site of ZnO, giving rise to a narrow NMR line at 4.1 ppm. The activation barrier of the implanted protons was found to be 0.46 eV by means of the rotating-frame spin-lattice relaxation measurements, apparently being interstitial hydrogens. High-energy beam irradiation also leads to correlated jump diffusion of the surface hydroxyl group of multiple lines at ~1 ppm, implying the presence of structural disorder at the ZnO surface.