Polydopamine-Assisted Rapid One-Step Immobilization of L-Arginine in Capillary as Immobilized Chiral Ligands for Enantioseparation of Dansyl Amino Acids by Chiral Ligand Exchange Capillary Electrochromatography

Sulfonic Functionalized Polydopamine Coatings with pH-Independent Surface Charge for Optimizing Capillary Electrophoretic Separations

Enhancing the pH-independence and controlling the magnitude of electroosmotic flow (EOF) are critical for highly efficient and reproducible capillary electrophoresis (CE) separations. Herein, we present a novel capillary modification method utilizing sulfonated periodate-induced polydopamine (SPD) coating to achieve pH-independent and highly reproducible cathodic EOF in CE. The SPD-coated capillaries were obtained through post-sulfonation treatment of periodate-induced PDA (PDA-SP) coatings adhered on the capillary inner surface. The successful immobilization of the SPD coating and the substantial grafting of sulfonic acid groups were confirmed by a series of characterization techniques. The excellent capability of PDA-SP@capillary in masking silanol groups and maintaining a highly robust EOF mobility was verified. Additionally, the parameters of sulfonation affecting the EOF mobilities were thoroughly examined. The obtained optimum SPD-coated column offered the anticipated highly pH-independent and high-strength cathodic EOF, which is essential for enhancing the CE separation performance and improving analysis efficiency. Consequently, the developed SPD-coated capillaries enabled successful high-efficiency separation of aromatic acids and nucleosides and rapid cyclodextrin-based chiral analysis of racemic drugs. Moreover, the SPD-coated columns exhibited a long lifetime and demonstrated good intra-day, inter-day, and column-to-column repeatability.

Hydrophilic arginine-functionalized mesoporous polydopamine-graphene oxide composites for glycopeptides analysis

Considering the importance of glycopeptides in the clinical diagnosis of cancer and some serious diseases, the identification of glycopeptides from complex biological samples has attracted considerable attention. Effective pre-enrichment before mass spectrometry analysis plays an important role. In this work, a kind of hydrophilic two-dimensional composites (denoted as GO@MPDA@Arg) based on mesoporous polydopamine-graphene oxide were used to selectively enrich glycopeptides in biological samples. The mesoporous polydopamine (MPDA) layer self-assembled with template Pluronic F127 provided more binding sites to load arginine, and bound arginine enhanced the hydrophilicity of the material. As a result, GO@MPDA@Arg composites exhibited excellent enrichment performance for glycopeptides, containing good selectivity (IgG digests : BSA digests = 1:50, molar ratio), low detection limit for IgG digests (10 fmol μL^-1), high loading capacity for IgG digests (200 μg mg^-1), and good size exclusion (IgG digests : IgG : BSA = 1:100:100, mass ratio). In addition, mouse brain tissue was selected as the actual biological sample to further study the enrichment effect of GO@MPDA@Arg composites. In three parallel experiments, a total of 401 glycopeptides belonging to 233 glycoproteins were enriched from 200 μg digestion of mouse brain extract. The enrichment results demonstrate that GO@MPDA@Arg composites have application potential for glycopeptides enrichment in protein post-translational modification research.

Enhancing bio-catalytic performance of lipase immobilized on ionic liquids modified magnetic polydopamine

In this study, imidazolium-based ionic liquid with [tf₂N]^- as the anion was successfully grafted to magnetic polydopamine nanoparticles (MPDA). The prepared materials were well characterized and used as supports for lipase immobilization. The immobilized lipase (PPL-ILs-MPDA) exhibited excellent activity and stability. The specific activity of PPL-ILs-MPDA was 2.15 and 1.49 folds higher than that of free PPL and PPL-MPDA. In addition, after 10 rounds of reuse, the residual activity of PPL-ILs-MPDA was 86.2 % higher than that of PPL-MPDA (75.4 %). Furthermore, the kinetic assay indicated that the affinity between PPL-ILs-MPDA and substrate had increased. Analysis of the secondary structure using circular dichroism was used to explain the mechanism underlying the improvement in the performance of PPL-ILs-MPDA. In addition, the immobilized lipase can be easily separated from the reaction system with a magnet. The observations regarding the development of new supports for lipase immobilization may provide new ideas regarding further studies in this field.