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

Antimicrobial Activity of Amino Acid-Capped Zinc and Copper Sulphide Nanoparticles

The synthesis of polydispersed zinc sulphide and copper sulphide nanocrystals capped with polar L-alanine (Aln) and l-aspartic acid (Asp) molecules is reported. The resulting nanocrystals were characterized by UV-visible spectroscopy (UV-Vis), photoluminescence (PL), X-ray diffraction (XRD), transmission electron microscopy (TEM), and Fourier transform infrared spectroscopy (FT-IR). UV-Vis absorption spectra of all samples were blue-shifted from the bulk band edges due to quantum confinement effects. PL emission spectrum of the nanoparticles showed peaks at 453 and 433 nm for Aln-capped ZnS and CuS nanoparticles, respectively, while peaks for Asp-capped ZnS and CuS nanoparticles were observed at 455 and 367 nm, respectively. The average particle sizes for Aln-capped ZnS and Asp-capped ZnS nanoparticles synthesized at 35°C were measured to be 2.88 nm and 1.23 nm, respectively. The antibacterial properties were tested using different strains of both positive and negative bacteria and fungi. It was found that capped-copper sulphide nanoparticles were more effective against the bacteria than capped-zinc sulphide nanoparticles. Staphylococcus aureus (ATCC 25923) was the most susceptible one with an MIC of 0.05 mg/mL for uncapped-CuS nanoparticles while Pseudomonas aeruginosa (ATCC 15442) and Cryptococcus neoformans (ATCC 14116) were the least ones with the MIC of 3.125 mg/mL for both uncapped-CuS and Aln-capped CuS.

Chiral Ceramic Nanoparticles and Peptide Catalysis

The chirality of nanoparticles (NPs) and their assemblies has been investigated predominantly for noble metals and II-VI semiconductors. However, ceramic NPs represent the majority of nanoscale materials in nature. The robustness and other innate properties of ceramics offer technological opportunities in catalysis, biomedical sciences, and optics. Here we report the preparation of chiral ceramic NPs, as represented by tungsten oxide hydrate, WO_3-x·H₂O, dispersed in ethanol. The chirality of the metal oxide core, with an average size of ca. 1.6 nm, is imparted by proline (Pro) and aspartic acid (Asp) ligands via bio-to-nano chirality transfer. The amino acids are attached to the NP surface through C-O-W linkages formed from dissociated carboxyl groups and through amino groups weakly coordinated to the NP surface. Surprisingly, the dominant circular dichroism bands for NPs coated by Pro and Asp are different despite the similarity in the geometry of the NPs; they are positioned at 400-700 nm and 500-1100 nm for Pro- and Asp-modified NPs, respectively. The differences in the spectral positions of the main chiroptical band for the two types of NPs are associated with the molecular binding of the two amino acids to the NP surface; Asp has one additional C-O-W linkage compared to Pro, resulting in stronger distortion of the inorganic crystal lattice and greater intensity of CD bands associated with the chirality of the inorganic core. The chirality of WO_3-x·H₂O atomic structure is confirmed by atomistic molecular dynamics simulations. The proximity of the amino acids to the mineral surface is associated with the catalytic abilities of WO_3-x·H₂O NPs. We found that NPs facilitate formation of peptide bonds, leading to Asp-Asp and Asp-Pro dipeptides. The chiroptical activity, chemical reactivity, and biocompatibility of tungsten oxide create a unique combination of properties relevant to chiral optics, chemical technologies, and biomedicine.