Ionic Strength, Surface Charge, and Packing Density Effects on the Properties of Peptide Self-Assembled Monolayers

The various environmental parameters of packing density, ionic strength, and solution charge were examined for their effects on the properties of the immobilized peptide mimotope CH19 (CGSG­SGSQL­GPYEL­WELSH) that binds with the therapeutic antibody Trastuzumab (Herceptin) on a gold substrate. The immobilization of CH19 onto gold was examined with a quartz crystal microbalance (QCM). The QCM data showed the presence of intermolecular interactions resulting in the increase of viscoelastic properties of the peptide self-assembled monolayer (SAM). The CH19 SAM was diluted with CS7 (CGSGSGS) to decrease the packing density as CH19/CS7. The packing density and ionic strength parameters were evaluated by atomic force microscopy (AFM), ellipsometry, and QCM. AFM and ellipsometry showed a distinct conformational difference between CH19 and CH19/CS7, indicating a relationship between packing density and conformational state of the immobilized peptide. The CH19 SAM thickness was 40 Å with a rough topology, while the CH19/CS7 SAM thickness was 20 Å with a smooth topology. The affinity studies showed that the affinity of CH19 and CH19/CS7 to Trastuzumab were both on the order of 10⁷ M^–1 in undiluted PBS buffer, while the dilution of the buffer by 1000× increased both SAMs affinities to Trastuzumab to the order of 10¹⁵ M^–2 and changed the binding behavior from noncooperative to cooperative binding. This indicated that ionic strength had a more pronounced effect on binding properties of the CH19 SAM than packing density. Electrochemical impedance spectroscopy (EIS) was conducted on the CH19/CS7 SAM, which showed an increase in impedance after each EIS measurement cycle. Cyclic voltammetry on the CH19/CS7 SAM decreased impedance to near initial values. The impact of the packing density, buffer ionic strength, and local charge perturbation of the peptide SAM properties was interpreted based on the titratable sites in CH19 that could participate in the proton transfer and water equilibrium

Hydrogen Electrooxidation in Ionic Liquids Catalyzed by the NTf₂ Radical

Hydrogen electrooxidation via a “hydrogen abstraction” mechanism in an aprotic ionic liquid 1-butyl-1-methylpyrrolidinium bis­(trifluoromethylsulfonyl) [Bmpy]­[NTf₂] under anaerobic conditions was investigated using cyclic voltammetry and density functional theory (DFT). It is found that a platinum bound NTf₂ radical (NTf₂^<b>•</b>) formed by the oxidation of NTf₂^– at anodic potential can catalyze the oxidation of hydrogen and enhance its reaction rate. Both experimental and theoretical studies (DFT) have supported a mechanism involving a NTf₂^<b>•</b> radical intermediate that catalyzes the hydrogen redox processes

Antimicrobial effects of Na₂CO₃ in combination with 10 μg/mL CDots on <i>E</i>.<i>coli</i> cells.

<p>Different letters above the columns indicate statistically significant differences (p<0.05).</p

SEM images of <i>E</i>.<i>coli</i> cells with different treatments.

<p>(A) Untreated control samples; (B) CDots (10 μg/mL) treated samples; (C) H₂O₂ (8.82 mM) treated samples; (D) CDots (10 μg/mL) and H₂O₂ combination treated samples. </p

The MICs and FICs of individual agents in the combination treatments of CDots with H₂O₂, and the total FICs of combination treatments, obtained using the microdilution checkerboard method.

<p>The MICs and FICs of individual agents in the combination treatments of CDots with H₂O₂, and the total FICs of combination treatments, obtained using the microdilution checkerboard method.</p

The MICs and FICs of individual agents in the combination treatments of CDots with AcOH, and the total FICs of combination treatments, obtained using the microdilution checkerboard method.

<p>The MICs and FICs of individual agents in the combination treatments of CDots with AcOH, and the total FICs of combination treatments, obtained using the microdilution checkerboard method.</p

The MICs and FICs of individual agents in the combination treatments of CDots with H₂O₂, and the total FICs of combination treatments, obtained using the microdilution checkerboard method.

<p>The MICs and FICs of individual agents in the combination treatments of CDots with H₂O₂, and the total FICs of combination treatments, obtained using the microdilution checkerboard method.</p

The combination of different concentrations of AcOH and CDots used in the microdilution checkerboard method for treatments to <i>E</i>. <i>coli</i> cells, and the growth status of the cells at 24 h incubation after they were treated.

<p>The combination of different concentrations of AcOH and CDots used in the microdilution checkerboard method for treatments to <i>E</i>. <i>coli</i> cells, and the growth status of the cells at 24 h incubation after they were treated.</p

Inhibitory effects of H₂O₂ alone and H₂O₂/CDots combination on <i>E</i>. <i>coli</i> cells.

<p>CDots concentration was 8 μg/mL or 16 μg/mL. Bacterial cell growth was measured by OD value at wavelength 595 nm. Data is presented by the mean of 3–5 replicated samples and Error bars are ±SD of the replicated measurements. Different letters above the columns indicate statistically significant differences (p<0.05).</p

Isobologram of the interaction between CDs and H₂O₂ against <i>E</i>.<i>coli</i> cells.

<p>Isobologram of the interaction between CDs and H₂O₂ against <i>E</i>.<i>coli</i> cells.</p