Search

Environmental stability remains a major challenge for the commercialisation of organic solar cells and degradation pathways remain poorly understood. Designing materials for improved device stability requires an understanding of the relationship between the properties of the donor or acceptor molecule and different degradation mechanisms. Here we study the correlations between various molecular parameters of the fullerene derivative bis-PCBM and the degradation rate of polymer:bis-PCBM organic solar cells, based on the same carbazole-alt-benzothiadiazole polymer, in aerobic and anaerobic conditions. We compare eight high purity bis-PCBM isomers with different electronic, chemical and packing properties along with PCBM and the mixture of bis isomers. In the case of aerobic photodegradation, we find that device degradation rate is positively correlated to the LUMO energy of the bis-PCBM isomer and to the degree of crystallinity of the isomer, while the correlation of degradation with driving force for epoxide formation is unclear. These results support the idea that in these samples, aerobic photodegradation proceeds via superoxide formation by the photogenerated polaron on the fullerene, followed by further chemical reaction. In the absence of air, photodegradation rate is correlated with molecular structure, supporting the mechanism of microstructural degradation via fullerene dimerization. The approach and findings presented here show how control of specific molecular parameters through chemical design can serve as a strategy to enhance stability of organic solar cells.

We review attempts to evaluate Pivotal Politics and related theories in light of the social sciences’ movement toward causal empiricism. To accommodate limitations of available data, most existing ...

We conduct a preliminary analysis of the first 200 days of the Donald Trump presidency, to determine who his principal allies in the US House have been. We build our analysis around three groups of Republicans, based on caucus affiliations: members of the Republican Main Street Partnership (RMSP), the Republican Study Committee (RSC), and the House Freedom Caucus (HFC). We find that House Republicans, regardless off caucus membership, broadly support President Trump and largely shared in the his electoral success. Yet, we also uncover suggestive evidence that the HFC is maneuvering into a position of influence with President Trump. Freedom Caucus members are more closely tied to his electoral performance than members of other conservative groups, and they appear to receive more time with the President relative to a comparable group of House Republicans. While these results are interesting, they are also initial and more time is needed to assess how President Trump builds a winning coalition with Republican House members.

Though considerable research focuses on formal institutions in Congress, scholars have long acknowledged that much of what guides legislative behavior is unwritten. To advance this area, we leverage a tool that allows appropriators to redirect billions of dollars from mandatory programs to discretionary projects. Changes in mandatory program spending—known as “CHIMPs”—show that existing institutions are often maintained by the strategic action of legislators. In the case of CHIMPs, we find their use is largely a response to formal constraints and that they are preserved through avoidance of minimum reform coalitions. This highlights that the legislative process—and budgetary outcomes in particular—cannot be understood without attention to procedures which remain “off the books.”

We compared the gastrointestinal effects of milk-based diets in which the β-casein component was either the A1 or A2 type in male Wistar rats fed the experimental diets for 36 or 84 h. Gastrointestinal transit time was significantly greater in the A1 group, as measured by titanium dioxide recovery in the last 24 h of feeding. Co-administration of naloxone decreased gastrointestinal transit time in the A1 diet group but not in the A2 diet group. Colonic myeloperoxidase and jejunal dipeptidyl peptidase (DPP)-4 activities were greater in the A1 group than in the A2 group. Naloxone attenuated the increase in myeloperoxidase activity but not that in DPP-4 activity in the A1 group. Naloxone did not affect myeloperoxidase activity or DPP-4 activity in the A2 group. These results confirm that A1 β-casein consumption has direct effects on gastrointestinal function via opioid-dependent (gastrointestinal transit and myeloperoxidase activity) and opioid-independent (DPP-4 activity) pathways.

SummaryThe antigen receptor for natural killer T cells (NKT TCR) binds CD1d-restricted microbial and self-lipid antigens, although the molecular basis of self-CD1d recognition is unclear. Here, we have characterized NKT TCR recognition of CD1d molecules loaded with natural self-antigens (Ags) and report the 2.3 Å resolution structure of an autoreactive NKT TCR-phosphatidylinositol-CD1d complex. NKT TCR recognition of self- and foreign antigens was underpinned by a similar mode of germline-encoded recognition of CD1d. However, NKT TCR autoreactivity is mediated by unique sequences within the non-germline-encoded CDR3β loop encoding for a hydrophobic motif that promotes self-association with CD1d. Accordingly, NKT cell autoreactivity may arise from the inherent affinity of the interaction between CD1d and the NKT TCR, resulting in the recognition of a broad range of CD1d-restricted self-antigens. This demonstrates that multiple self-antigens can be recognized in a similar manner by autoreactive NKT TCRs.

Post-translational modification of protein serines/threonines with N-acetylglucosamine (O-GlcNAc) is dynamic, inducible and abundant, regulating many cellular processes by interfering with protein phosphorylation. O-GlcNAcylation is regulated by O-GlcNAc transferase (OGT) and O-GlcNAcase, both encoded by single, essential, genes in metazoan genomes. It is not understood how OGT recognises its sugar nucleotide donor and performs O-GlcNAc transfer onto proteins/peptides, and how the enzyme recognises specific cellular protein substrates. Here, we show, by X-ray crystallography and mutagenesis, that OGT adopts the (metal-independent) GT-B fold and binds a UDP-GlcNAc analogue at the bottom of a highly conserved putative peptide-binding groove, covered by a mobile loop. Strikingly, the tetratricopeptide repeats (TPRs) tightly interact with the active site to form a continuous 120 A putative interaction surface, whereas the previously predicted phosphatidylinositide-binding site locates to the opposite end of the catalytic domain. On the basis of the structure, we identify truncation/point mutants of the TPRs that have differential effects on activity towards proteins/peptides, giving first insights into how OGT may recognise its substrates.

Natural killer T cells (NKT cells) are divided into type I and type II subsets on the basis of differences in their T cell antigen receptor (TCR) repertoire and CD1d-antigen specificity. Although the mode by which type I NKT cell TCRs recognize CD1d-antigen has been established, how type II NKT cell TCRs engage CD1d-antigen is unknown. Here we provide a basis for how a type II NKT cell TCR, XV19, recognized CD1d-sulfatide. The XV19 TCR bound orthogonally above the A' pocket of CD1d, in contrast to the parallel docking of type I NKT cell TCRs over the F' pocket of CD1d. At the XV19 TCR-CD1d-sulfatide interface, the TCRα and TCRβ chains sat centrally on CD1d, where the malleable CDR3 loops dominated interactions with CD1d-sulfatide. Accordingly, we highlight the diverse mechanisms by which NKT cell TCRs can bind CD1d and account for the distinct antigen specificity of type II NKT cells.

This study aimed to identify genes or gene products associated with high lean muscle mass in bovines that may serve as potential markers for selection. An animal with a genetic predisposition to high lean muscle mass, the Belgium Blue, was chosen as a model to compare with the Holstein Friesian, a model that does not. Two-dimensional polyacrylamide gel electrophoresis analysis was utilized to compare the exhibited skeletal muscle proteome between the two animal types at two stages of foetal development. A previously uncharacterized polymorphism of a high expression myofibrillar protein, myosin light chain 1 fast (MLC-1f), was observed. The characterization of this polymorphism revealed a two amino acid insertion in a part of the protein that has been implicated in modulating myosin S1 ATPase activity. Furthermore, this polymorphism was shown to be the product of two alleles that are codominant. Screening studies were carried out on selected herds and showed a very high frequency of one allele. Both isoforms of MLC-1f were produced by recombinant means and purified. The recombinant proteins were exchanged into purified myosin hexamers that were then subject to assays measuring ATP consumption. The sensitivity of the assay utilized could not reveal any significant difference in ATPase activity between hexamers containing one or the other isoform.