The unique physicochemical properties and biocompatibility of zinc oxide nanocrystals (ZnO NCs) are strongly dependent on the nanocrystal/ligand interface, which is largely determined by synthetic procedures. Stable ZnO NCs coated with a densely packed shell of 2-(2-methoxyethoxy)acetate ligands, which act as miniPEG prototypes, with average core size and hydrodynamic diameter of 4-5 and about 12 nm, respectively, were prepared by an organometallic self-supporting approach, fully characterized, and used as a model system for biological studies. The ZnO NCs from the one-pot, self-supporting organometallic procedure exhibit unique physicochemical properties such as relatively high quantum yield (up to 28 %), ultralong photoluminescence decay (up to 2.1 μs), and EPR silence under standard conditions. The cytotoxicity of the resulting ZnO NCs toward normal (MRC-5) and cancer (A549) human lung cell lines was tested by MTT assay, which demonstrated that these brightly luminescent, quantum-sized ZnO NCs have a low negative impact on mammalian cell lines. These results substantiate that the self-supporting organometallic approach is a highly promising method to obtain high-quality, nontoxic, ligand-coated ZnO NCs with prospective biomedical applications.
The surface organic ligands have profound effect on modulation of different physicochemical parameters as well as toxicological profile of semiconductor nanocrystals (NCs). Zinc oxide (ZnO) is one of the most versatile semiconductor material with multifarious potential applications and systematic approach to in-depth understand the interplay between ZnO NCs surface chemistry along with physicochemical properties and their nano-specific toxicity is indispensable for development of ZnO NCs-based devices and biomedical applications. To this end, we have used recently developed the one-pot self-supporting organometallic (OSSOM) approach as a model platform to synthesize a series of ZnO NCs coated with three different alkoxyacetate ligands with varying the ether tail length which simultaneously act as miniPEG prototypes. The ligand coating influence on ZnO NCs physicochemical properties including the inorganic core size, the hydrodynamic diameter, surface charge, photoluminescence (quantum yield and decay time) and ZnO NCs biological activity toward lung cells was thoroughly investigated. The resulting ZnO NCs with average core diameter of 4-5 nm and the hydrodynamic diameter of 8-13 nm exhibit high photoluminescence quantum yield reaching 33% and a dramatic slowing down of charge recombination up to 2.4 µs, which is virtually unaffected by the ligand’s character. Nano-specific ZnO NCs-induced cytotoxicity was tested using MTT assay with normal (MRC-5) and cancer (A549) human lung cell lines. Noticeably, no negative effect has been observed up to the NCs concentration of 10 µg/mL and essentially very low negative toxicological impact could be noticed at higher concentrations. In the latter case, the MTT data analysis indicate that there is a subtle interconnection between inorganic core-organic shell dimensions and toxicological profile of ZnO NCs (strikingly, the NCs coated by the carboxylate bearing a medium ether chain length exhibit the lowest toxicity level). The results demonstrate that, when fully optimized, our organometallic self-supporting approach can be a highly promising method to obtain high-quality and bio-stable ligand-coated ZnO NCs.
The synthesis and structural characterization of a new series of ethylzinc carboxylates are reported. Structurally diverse complexes were derived from three monofunctional carboxylic acids with different numbers of phenyl groups on the α-carbon, and two bifunctional carboxylic acids with a neutral donor terminus, namely, methoxyacetic and diethylphosphonoacetic acids. Donor solvents are commonly used in various transformations of alkylzinc carboxylates; therefore, the effect of THF as a donor solvent on the reaction outcome was also investigated. Reactions of equimolar amounts of Et 2 Zn and the selected carboxylic acid in THF solutions gave ethylzinc carboxylates with a large variety of structures. In the cases of triphenylacetic and diphenylacetic acids, THF solvated products of stoichiometry [EtZn-(O 2 CR)(THF)] were isolated as a dimer and a 1D coordination polymer, respectively, whereas, with methoxyacetic acid, a novel solvent-free hexanuclear structural motif with a butterfly-like framework was formed, ([EtZnO 2 CCH 2 OCH 3 ] 6 ). The corresponding reaction with diethylphosphonoacetic acid produced a rare example of a nonanuclear organozinc oxo carboxylate cluster, [(EtZn) 8 Zn(μ 3 -O) 2 (O 2 CCH 2 (O)P(OEt) 6 )].
Reactions of organomagnesium halides with group 13 metal halides lead to the formation of R3M type compounds (R = alkyl, aryl; M = Al, Ga, In) and are considered as the simplest methods of R3M compound syntheses. These seemingly simple reactions reveal a much more complex chemistry involving mixed magnesium‐group 13 metal compounds. To elucidate the reaction course of reactions of organomagnesium halides with group 13 metal halides, we have studied reactions of R3M with organomagnesium halides. The interaction of Et3M with R1MgX led to the formation of following products being mixtures of crystalline ionic complexes with the general composition of [Et4‐nR1nM]−[XMg (thf)5]+·(thf): [Et2.2Al(CH=CH2)1.8]−[BrMg (thf)5]+·(thf) (1), [Et3Ga(CH=CH2)]−[BrMg (thf)5]+·(thf) (2), [Et4Al]−[BrMg (thf)5]+·(thf) (3), [Et4Ga]−[BrMg (thf)5]+·(thf) (4), [Et2.9Al(C6H5)1.1]−[BrMg (thf)5]+·(thf) (5), [Et2.9Ga(C6H5)1.1]−[BrMg (thf)5]+·(thf) (6), [Et3.4GaMe0.6]−[IMg (thf)5]+·(thf) (7) and [Et4In]−[BrMg (thf)5]+·(thf) (8). A comparison of the production course of group 13 metal trialkyls R3M with a thermal decomposition of 1–8 products showed that reactions of MX3 with RMgX (X = Br, I; R = alkyl, aryl) yield initially intermediate ionic compounds, which must then be thermally decomposed to obtain pure R3M compounds. If group 13 metal bromides and iodides, and alkyl (aryl)magnesium bromides and iodides in thf are used, only intermediate products with the [R4M]−[XMg (thf)5]+·(thf) structure are formed.
One‐pot self‐supporting organometallic (OSSOM) method was successfully extended towards an efficient “safe‐by‐design” strategy for the preparation of bio‐friendly quantum‐sized ZnO crystals coated by densely packed ligand shell. The observed unique physicochemical properties, such as ultra‐long photoluminescence decay, EPR silence under standard condition, inertness in biological environment, and negligible negative impact on the selected mammalian cell lines, clearly demonstrated that the OSSOM approach gives ZnO nanocrystals with exceptional nanocrystal–ligand interface and facilitates their use in biology. More information can be found in the Full Paper by J. Lewiński et al. on page 4033.
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