RESUMEN

Zeolitic imidazolate frameworks (ZIFs) have recently emerged as immobilization matrices for biomolecules, most notably enzymes. Understanding the key factors that dominate the enzyme's catalytic activity on/in ZIFs is crucial for the development of new immobilization matrices. In this work, a combination of the parallel tempering Monte Carlo simulation and all-atom molecular dynamics simulation is performed to study the orientation and conformation of the Candida rugose lipase (CRL) adsorbed on oppositely charged and neutral ZIF-8 (i.e., ZIF-8-COOH, ZIF-8-NH2, and ZIF-8-neutral) surfaces. The results show that CRL could adsorb on all ZIF-8 surfaces, with an ordered orientation obtained on charged ZIF-8 surfaces. ZIF-8-NH2 is a good candidate for CRL immobilization since it can maximize the catalytic activity of CRL. The native conformation of CRL is well preserved on all three surfaces due to the partially water-containing surface of ZIF-8. The results could provide theoretical support for the application of porous materials in enzyme immobilization.

Asunto(s)

Zeolitas , Adsorción , Lipasa , Simulación de Dinámica Molecular , Enzimas Inmovilizadas/metabolismo

RESUMEN

The efficiency of antibiotic oxidation by direct electrochemical processes based on transition metal electrodes is largely restricted by the adsorption capacity for single molecules on targeted active sites. Inspired by density functional theory (DFT) calculations, we found that the adsorption energy of sulfanilamide molecules on Ni sites could be markedly changed by regulating the local atomic environment of the Ni atoms (for NiCo2O4 and NiCoP, ΔGNi = -0.11 and +0.47 eV, respectively). The high electronegativity of oxygen changed the electron cloud density around the Ni atoms, leading to an oriented adsorption of SA on Ni sites. Moreover, the oriented adsorption on Ni sites occurs not only on NiCo2O4 but on the in situ-generated NiIIIOOH (ΔGNi = -0.09 eV). Consequently, utilizing NiCo2O4 as the anode resulted in superior removal performance (97% vs 55% efficiency) for SA oxidation, with a kinetic constant ∼10 times higher than that of NiCoP (0.031 min-1 vs 0.0029 min-1). Meanwhile, non-oriented adsorption reduced the competition between SA molecules and H+ for active sites, which benefitted the activity of the hydrogen evolution reaction at the NiCoP cathode (68 mV at j = 10 mA·cm-2, 0.5 mmol·L-1 SA added in). Furthermore, the in situ Raman spectra and DFT calculations confirmed that NiIIIOOH dominated the oxidation process and terminated it at the p-benzoquinone stage. These findings provide a feasible strategy to combine electrochemical antibiotic oxidation by Ni-based electrodes with hydrogen energy recovery.

RESUMEN

The adsorption of amyloidogenic peptides, amyloid beta 1-40 (Aß1-40), alpha-synuclein (α-syn), and beta 2 microglobulin (ß2m), was attempted over the surface of nano-gold colloidal particles, ranging from d = 10 to 100 nm in diameter (d). The spectroscopic inspection between pH 2 and pH 12 successfully extracted the critical pH point (pHo) at which the color change of the amyloidogenic peptide-coated nano-gold colloids occurred due to aggregation of the nano-gold colloids. The change in surface property caused by the degree of peptide coverage was hypothesized to reflect the ΔpHo, which is the difference in pHo between bare gold colloids and peptide coated gold colloids. The coverage ratio (Θ) for all amyloidogenic peptides over gold colloid of different sizes was extracted by assuming Θ = 0 at ΔpHo = 0. Remarkably, Θ was found to have a nano-gold colloidal size dependence, however, this nano-size dependence was not simply correlated with d. The geometric analysis and simulation of reproducing Θ was conducted by assuming a prolate shape of all amyloidogenic peptides. The simulation concluded that a spiking-out orientation of a prolate was required in order to reproduce the extracted Θ. The involvement of a secondary layer was suggested; this secondary layer was considered to be due to the networking of the peptides. An extracted average distance of networking between adjacent gold colloids supports the binding of peptides as if they are "entangled" and enclosed in an interfacial distance that was found to be approximately 2 nm. The complex nano-size dependence of Θ was explained by available spacing between adjacent prolates. When the secondary layer was formed, Aß1-40 and α-syn possessed a higher affinity to a partially negative nano-gold colloidal surface. However, ß2m peptides tend to interact with each other. This difference was explained by the difference in partial charge distribution over a monomer. Both Aß1-40 and α-syn are considered to have a partial charge (especially δ+) distribution centering around the prolate axis. The ß2m, however, possesses a distorted charge distribution. For a lower Θ (i.e., Θ <0.5), a prolate was assumed to conduct a gyration motion, maintaining the spiking-out orientation to fill in the unoccupied space with a tilting angle ranging between 5° and 58° depending on the nano-scale and peptide coated to the gold colloid.

Asunto(s)

Péptidos beta-Amiloides/química , Péptidos beta-Amiloides/ultraestructura , Proteínas Amiloidogénicas/química , Proteínas Amiloidogénicas/ultraestructura , Oro Coloide/química , Adsorción , Coloides/química , Oro/química , Concentración de Iones de Hidrógeno , Nanopartículas del Metal/química , Nanopartículas del Metal/ultraestructura , Microscopía Electrónica de Transmisión , Simulación de Dinámica Molecular , Nanogeles/química , Nanogeles/ultraestructura , Tamaño de la Partícula , Análisis Espectral , Propiedades de Superficie , alfa-Sinucleína/química , alfa-Sinucleína/ultraestructura , Microglobulina beta-2/química , Microglobulina beta-2/ultraestructura

RESUMEN

In which orientation does adenine adsorb on gold and silver surfaces? This question has been a matter of debate for over 30 years. Since the dawn of surface-enhanced Raman spectroscopy (SERS); it and other techniques such as tip-enhanced Raman spectroscopy (TERS), surface-enhanced infrared absorption spectroscopy (SEIRAS), scanning tunneling microscopy (STM), density functional theory (DFT) simulations, and more, have been used in many attempts to answer this seemingly straightforward, yet controversial, question. Herein, the timeline and recent advances on this topic are explored, and the frequently contradictory findings are put into context and discussed.