Biological Toxicities and Aggregation Effects of ʟ-Glycine and ʟ-Alanine Capped ZnS:Mn Nanocrystals in Aqueous Solution

Abstract

In this study, water-dispersible ZnS:Mn nanocrystals were synthesized by capping the surface with conventional and simple structured amino acid ligands: L-Glycine and L-Alanine. The ZnS:Mn-Gly and ZnS:Mn-Ala nanocrystal powders were characterized by XRD, HR-TEM, EDXS, ICP-AES, and FT-IR spectroscopy. The optical properties were measured by UV-Visible and photoluminescence (PL) spectroscopy. The PL spectra for the ZnS:Mn-Gly and ZnS:Mn-Ala showed broad emission peaks at 599 nm and 607 nm with PL efficiencies of 6.5% and 7.8%, respectively. The measured average particle size from the HR-TEM images were 6.4 ± 0.8 nm (ZnS:Mn-Gly) and 4.1 ± 0.5 nm (ZnS:Mn-Ala), which were also supported by Debye-Scherrer calculations. In addition, the degree of aggregation of the nanocrystals in aqueous solutions were measured by a hydrodynamic light scattering method, which showed formation of sub-micrometer size aggregates for both ZnS:Mn-Gly (273 ± 94 nm) and ZnS:Mn-Ala (233 ± 34 nm) in water due to the intermolecular attraction between the capping amino acids molecules. Finally, the cytotoxic effects of ZnS:Mn-Gly and ZnS:Mn-Ala nanocrsystals over the growth of wild type E. coli were investigated. As a result, no toxicity was shown for the ZnS:Mn-Gly nanocrystal in the colloidal concentration region from 1 µg/mL to 1000 µg/mL, while ZnS:MnAla showed significant toxicity at 100 µg/mL.

Application of L-Aspartic Acid-Capped ZnS:Mn Colloidal Nanocrystals as a Photosensor for the Detection of Copper (II) Ions in Aqueous Solution

“…These agglomerates likely formed from the intermolecular interaction (mostly hydrogen bonding) between the COO and NH groups in the capping aspartic acid molecules on neighboring ZnS:Mn NCs, since the NCs were originally observed to form 5 nm-sized particles in the solid state according to the previously shown HR-TEM image and the Debye-Scherrer’s XRD calculation. Similar intermolecular attractions between the capping molecules on the NC surface for L-glycine and L-alanine capped ZnS:Mn NCs have been reported [ 18 ], in which the intermolecular interaction (also mainly hydrogen bonding) between the amino acid molecules caused the formation of huge agglomerates of the corresponding ZnS:Mn-aminoacid nanocrystals (from 250 nm to a few micrometer in size) in water. However, the degree of aggregation for the ZnS:Mn-Asp NCs was relatively low in water compared to other aminoacids capped ZnS:Mn NCs, which was probably due to the electrostatic repulsion between the negatively-charged NC surfaces.…”

“…In this regard, there have been several papers published regarding the attempt to synthesize water-soluble semiconductor nanocrystals by the modification of their surfaces with polar organic molecules [ 15 ]. Among these, thioglycolic acid [ 16 , 17 ] and conventional amino acids [ 18 , 19 ] were found to be effective capping agents in the synthesis of water-soluble and non-toxic semiconductor nanocrystals. However, the ligand-dependent surface properties of water-dispersible nanocrystals are not yet fully understood.…”

Surface Properties and Photocatalytic Activities of the Colloidal ZnS:Mn Nanocrystals Prepared at Various pH Conditions

“…These agglomerates probably formed by the intermolecular interaction between the capping molecules on the neighboring ZnS:Mn nanocrystals, because these nanocrystals were originally found as 5 nm sized particles in the solid state according to the HR-TEM images and the Debye-Scherrer’s XRD calculations. Previously, we reported very similar intermolecular attractions between the surface capping molecules on the nanocrystal surfaces for l -glycine and l -valine capped ZnS:Mn nanocrystals [ 42 ], in which the intermolecular interaction (majorly hydrogen bonding) between the aminoacid molecules caused the formation of huge aggregates of the ZnS:Mn-aminoacid nanocrystals (from 250 nm to few micrometer sizes) in water. Compared to other water-dispersed nanocrystals, the degree of aggregation for the ZnS:Mn-MAA nanocrystals was relatively low in water, probably because of the electrostatic repulsion between the negatively charged nanocrystal surfaces [ 43 ].…”

Influence of Zinc and Ammonium Compounds on the Growth and Characterisation of L Alanine NLO Crystals

“…Comparative band assignments of grown crystals are given in Table II. For the crystal ZLA the peaks at 2291 and 2252 cm −1 correspond to asymmetric stretching of zinc coordinated NH 2 and COO − [16]. The incorporation of sulphur was confirmed in both the crystals ZLA and ALA by the presence of vibrations corresponding to S=O, S-O and SO − 4 as shown in Table II [17].…”