Electrocatalysis on Shape-Controlled Palladium Nanocrystals: Oxygen Reduction Reaction and Formic Acid Oxidation

A systematic study was conducted on small Pd nanocrystals (5–6 nm) to understand the effects of catalyst structure and electrolyte on the oxygen reduction reaction (ORR) and formic acid oxidation (FAO). The ORR activities of Pd catalysts strongly depended on their structure and the electrolyte used. It was found that Pd cubes were 10 times more active than Pd octahedra for ORR in an aqueous HClO₄ solution due to higher onset potential of OH_ad formation on the cubic surface. In the case of a H₂SO₄ solution, the ORR activity of Pd cubes was 17 times higher than that of Pd octahedra due to the stronger adsorption of (bi)­sulfate on the surface of octahedral nanocrystals in addition to OH_ad. In alkaline solutions, however, no structure dependence was observed for ORR due to the outer-sphere electron-transfer mechanism in the potential region for Pd oxide formation. For FAO, no advantage was observed on shape-controlled Pd nanocrystals in comparison to conventional Pd catalysts. The FAO current densities, both at peak current and at 0.4 V, followed the order of conventional Pd > octahedral Pd > cubic Pd. It was hypothesized that steps and defects were more active for FAO than terraces, which could be used to explain why the shape-selective materials were less active than conventional Pd because they contained fewer defects and edge sites

Mapping of peptide 5-2-D3.

<p>Peptide 5-2-D3 could be mapped (orange) with AA E 168|N 164|D 152|G 153|T 150|K 146|L 144|A 141 on the three-dimensional model of a VSG LiTat 1.5 N-terminal domain monomer by means of 3DEX and Chimera.</p

Peptide sequences of phage clones selected with human anti-VSG LiTat 1.3 antibodies.

<p>3-3-H3(1) and 3-3-H3(2) are two different phage clones, na: not applicable, SD: standard deviation,</p>*<p>not withheld: similar to 3-2-G5 & 3-2-G10.</p><p>The phage clones were selected after two or three positive (pos) selections. The peptide sequences that were expressed by these phage clones are given in column three. The average OD_c in sandwich ELISA, using nine purified antibody fractions as capture antibody, is shown in column four. If the peptide sequence was synthesised, the name of the biotinylated peptide is given in column five.</p

Alignment on VSG LiTat 1.5 of peptides selected with anti-VSG LiTat 1.5 antibody fractions.

<p>Homologous sequences between phage displayed peptides and/or the protein sequence of VSG LiTat 1.5 are indicated in grey. Amino acids that are identical to those of the VSG protein sequence are in bold and grey. All peptide sequences include the GGGS-spacer at the C-terminus. Maximum % identity: percentage identity of the peptide sequence with a corresponding stretch of sixteen AA within the protein sequence of VSG LiTat 1.5. Synth peptide: name of the synthesised peptide.</p

Evaluation of the potential of the biotinylated peptides for diagnosis of <i>T.b. gambiense</i> HAT.

<p>The ability of biotinylated synthetic peptides to bind human serum antibodies in 102 HAT positive and 102 endemic negative control sera was assessed by indirect ELISA. The area under the receiver operator characteristics curve (AUC) and the sensitivity and specificity at maximum Youden index are shown with 95% confidence intervals (CI).</p

Peptide sequences of phage clones selected with human anti VSG LiTat 1.5 antibodies.

<p>na: not applicable, SD: standard deviation,</p>*<p>not withheld: similar to 5-3-C1.</p><p>The phage clones were selected after 1, 2 or 3 positive selections. The peptide sequences that were expressed by these phage clones are given in column three. The average OD_c in sandwich ELISA, using nine purified antibody fractions as capture antibody, is shown in column four. If the peptide sequence was synthesised, the name of the biotinylated peptide is given in column five.</p

Differential biopanning strategy to select conformational mimotopes of desired specificity.

<p>HIV gp160 was bound to ELISA plates under native or denaturing conditions. After incubation with serum of monkey RKl-8 (which was chronically infected with a clade C simian-human immunodeficiency virus (SHIV) <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0038943#pone.0038943-Humbert1" target="_blank">[25]</a> and had high titers of anti-HIV nAbs) followed by washing, Abs were eluted. Abs eluted from the native protein antigen (“conformational” Abs) were used for the positive selection rounds; Abs eluted from the denatured protein (“linear” Abs) were used for the negative rounds. A total of three biopanning rounds were performed and mimotopes selected by this strategy were tested for specificity and conformation dependence with rhesus monkey sera.</p

Strategy of isolation of epitope-specific Abs.

<p>After differential biopanning of phage display peptide library, mimotopes representing conformational epitopes are sequenced, and the inserts plus M13 flanking sequences are cloned into a bacterial expression vector encoding fluorescent protein. After purification of the resulting mimotope fusion proteins, binding assays to assure maintenance of the correct three-dimensional structure of mimotope insert are conducted. This is followed by single-cell sorting for specific IgG-positive memory B cells, single-cell RT-PCR and cloning of RM V_L and V_H regions into pFUSE2-type vectors encoding the backbone of human IgG1.</p

VH and VL CDR sequences of V3-specific mAbs.

<p>(A) 33B2 and 33C6 VH CDR amino acid sequences. (B) 33B2 and 33C6 VL CDR amino acid sequences.</p

Genetic characteristics of V3-specific mAbs.

<p>Genetic characteristics of V3-specific mAbs.</p