Moonhee Ryu

Carbon nanotubes (CNT) were dispersed into homemade silicone–polyurethane (SPU) resin in order to enhance their mechanical and anticorrosion ability. Before mixing with SPU, CNT were modified by four different approaches to improve their dispersion in SPU, and the surface of CNT were covered by SiO₂–TiO₂ nanoparticles, -NH₂ groups, epoxy groups or isocyanate groups, respectively. The structures of the modified CNTs were checked by XRD, FTIR, and SEM. After being dispersed in SPU to form a composite coating, the one with SiO₂–TiO₂ nanoparticles modified CNT exhibited the best mechanical properties and chemical resistance (low water absorption), and its corrosion current density (i_corr) was only 9.246 × 10⁻⁹ A cm², which is four orders of magnitude lower than the i_corr value of the coating with unmodified CNT (1.599 × 10⁻⁵ A/cm²). This may be because the covered SiO₂–TiO₂ nanoparticle increased the roughness of the CNT surface, which can improve their dispersion in SPU resin.

Arginine kinase (AK) plays a crucial role in the survival of Daphnia magna, a water flea and a common planktonic invertebrate sensitive to water pollution, owing to the production of bioenergy. AK from D. magna (DmAK) has four highly conserved histidine residues, namely, H90, H227, H284, and H315 in the amino acid sequence. In contrast to DmAK WT (wild type), the enzyme activity of the H227A mutant decreases by 18%. To identify the structure-function relationship of this H227A mutant enzyme, the crystal 3D X-ray structure has been determined and an unfolding assay using anilino-1-naphthalenesulfonic acid (ANS) fluorescence has been undertaken. The results revealed that when compared to the DmAK WT, the hydrogen bonding between H227 and A135 was broken in the H227A crystal structure. This suggests that H227 residue, closed to the arginine binding site, plays an important role in maintaining the structural stability and maximizing the enzyme activity through hydrogen bonding with the backbone oxygen of A135.

Biodegradation has been considered as an ideal technique for total petroleum hydrocarbon (TPH) contamination, but its efficiency is limited by its application in the field. Herein, an original TPH-degrading strain, SCYY-5, was isolated from contaminated oil sludge and identified as Acinetobacter sp. by 16S rDNA sequence analysis. The biological function of the isolate was investigated by heavy metal tolerance, carbon, and nitrogen source and degradation tests. To enhance its biodegradation efficiency, the response surface methodology (RSM) based on a function model was adopted to investigate and optimize the strategy of microbial and environmental variables for TPH removal. Furthermore, the performance of the system increased to 79.94% with the further addition of extra nutrients, suggesting that the RSM and added nutrients increased the activity of bacteria to meet the needs of the co-metabolism matrix during growth or degradation. These results verified that it is feasible to adopt the optimal strategy of combining bioremediation with RSM to improve the biodegradation efficiency, for contaminated oil sludge.