Effects of Odd–Even Side Chain Length of Alkyl-Substituted Diphenylbithiophenes on First Monolayer Thin Film Packing Structure

Because of their preferential two-dimensional layer-by-layer growth in thin films, 5,5′bis(4-alkylphenyl)-2,2′-bithiophenes (P2TPs) are model compounds for studying the effects of systematic chemical structure variations on thin-film structure and morphology, which in turn, impact the charge transport in organic field-effect transistors. For the first time, we observed, by grazing incidence X-ray diffraction (GIXD), a strong change in molecular tilt angle in a monolayer of P2TP, depending on whether the alkyl chain on the P2TP molecules was of odd or even length. The monolayers were deposited on densely packed ultrasmooth self-assembled alkane silane modified $SiO_2$ surfaces. Our work shows that a subtle change in molecular structure can have a significant impact on the molecular packing structure in thin film, which in turn, will have a strong impact on charge transport of organic semiconductors. This was verified by quantum-chemical calculations that predict a corresponding odd–even effect in the strength of the intermolecular electronic coupling.Chemistry and Chemical BiologyEngineering and Applied Science

Depletion of Human Papilloma Virus E6- and E7-Oncoprotein-Specific T-Cell Responses in Women Living With HIV

Background: Cervical cancer - caused by persistent High Risk Human Papilloma Virus (HR HPV) infections - is the second most common cancer affecting women globally. HIV infection increases the risk for HPV persistence, associated disease progression and malignant cell transformation. We therefore hypothesized that this risk increase is directly linked to HIV infection associated dysfunction or depletion of HPV-oncoprotein-specific T-cell responses. Methods: The 2H study specifically included HIV+ and HIV- women with and without cervical lesions and cancer to analyze HPV oncogene-specific T cell responses in relation to HPV infection, cervical lesion status and HIV status. Oncoprotein E6 and E7 specific T-cell responses were quantified for the most relevant types HPV16, 18 and 45 and control antigens (CMV-pp65) and M.tb-PPD in 373 women, using fresh peripheral blood mononuclear cells in an IFN-γ release ELISpot assay. Results: Overall, systemic E6- and E7-oncoprotein-specific T-cell responses were infrequent and of low magnitude, when compared to CMV-pp65 and M.tb-PPD (p < 0.001 for all HR HPV types). Within HIV negative women infected with either HPV16, 18 or 45, HPV16 infected women had lowest frequency of autologous-type-E6/E7-specific T-cell responses (33%, 16/49), as compared to HPV18 (46% (6/13), p = 0.516) and HPV45 (69% (9/13), p = 0.026) infected women. Prevalent HPV18 and 45, but not HPV16 infections were linked to detectable oncoprotein-specific T-cell responses, and for these infections, HIV infection significantly diminished T-cell responses targeting the autologous infecting genotype. Within women living with HIV, low CD4 T-cell counts, detectable HIV viremia as well as cancerous and precancerous lesions were significantly associated with depletion of HPV oncoprotein-specific T-cell responses. Discussion: Depletion of HPV-oncoprotein-specific T-cell responses likely contributes to the increased risk for HR HPV persistence and associated cancerogenesis in women living with HIV. The low inherent immunogenicity of HPV16 oncoproteins may contribute to the exceptional potential for cancerogenesis associated with HPV16 infections

Simulation of Graphene Nanoribbon Aggregation and Its Mediation by Edge Decoration

Large polyaromatic molecules, including synthetic graphene nanoribbons (GNRs), are the subject of considerable interest for a variety of electronic applications. For GNRs in particular, functional groups can be bonded along the ribbon edges to modify their dispersibility, self-assembly behavior, and electronic properties. However, these side chains are usually chosen in a “trial and error” fashion, without an underlying molecular-scale picture of the conformations they will adopt in solution and the resulting influence of such structures on macroscopically observable phenomena, particularly aggregation. In this study, we use molecular dynamics (MD) to predict the behavior of various side chains in different solvents as a means to understand how this influences aggregate morphologies and binding energies. Specifically, oligomeric PEG and <i>n</i>-alkoxy chains of varying lengths and grafting densities are examined in vacuum, water, and <i>N</i>-methylpyrrolidone. Examining the binding energies and side chain dispositions that occur with different sets of parameters allows us to suggest a combination of these variables that will minimize aggregational tendencies for the GNRs. The results underscore the value of molecular-scale computational techniques to understand the aggregational tendencies of 2D materials and guide the design of future polyaromatic edge modifications

Ice nucleation by surrogates of Martian mineral dust: What can we learn about Mars without leaving Earth?

Water and carbon dioxide ice clouds have been observed in the Martian atmosphere where they are dynamic parts of that planet's water and carbon cycles. Many Martian atmospheric models struggle to correctly predict clouds and, with insufficient data, some use untested simplifications that cloud formation occurs exactly at the saturation point of the condensed phase or at the same conditions as terrestrial cirrus clouds. To address the lack of data, we have utilized an 84 m3 cloud chamber built for studies of high altitude cirrus and polar stratospheric ice clouds in the Earth's atmosphere and adapted to Martian conditions. Using this chamber, we have been able to produce water ice clouds from aerosol in an inert and low pressure atmosphere mimicking that of Mars. At temperatures between 189 and 215 K, we investigated cloud formation by mineral dust particulates of a similar composition and size to those found on Mars. We show that these surrogate materials nucleate effectively at the higher temperatures, with minor temperature dependence at saturations ratios with respect to the ice phase of ~1.1, similar to what has been found for terrestrial cirrus. At the lower end of the temperature range, this saturation rises to ~1.9, a result consistent with previous studies.MIT International Science and Technology Initiatives (MISTI-Germany)EUROCHAMP-2 (Transnational Access Activity E2-2012- 05-14-0075)Deutsche Forschungsgemeinschaft (DFG HALO priority program SPP 1294 (contract number MOEH 668/1-2)

Simultaneous Determination of Critical Micelle Temperature and Micelle Core Glass Transition Temperature of Block Copolymer–Solvent Systems via Pyrene-Label Fluorescence

The critical micelle temperature (CMT) and micelle core glass transition temperature (<i>T</i>_g) for a poly­(methyl methacrylate) (PMMA)-poly­(<i>tert</i>-butyl methacrylate) (PtBMA) diblock copolymer system were measured by fluorescence via single temperature (<i>T</i>) ramps. Synthesis yielded identical block lengths in unlabeled and pyrene-labeled diblocks, the latter with dye at the PMMA block terminus. Studies were conducted at 5–18 wt % diblock in 2-ethylhexanol (2EH) with a trace of labeled diblock (0.2 wt % of total copolymer). The <i>T</i> dependence of pyrene-label fluorescence intensity yielded the CMT and micelle core <i>T</i>_g in systems where the PMMA-block and the 2EH within the cores constituted 1.9–7.8% of sample mass. While the CMT can be measured by many methods, this is the first direct measurement of micelle core <i>T</i>_g at low core content (e.g., 1.9 wt %) in a block copolymer/solvent system. Differential scanning calorimetry was done on diblock samples, showing severe limitations for sensing and characterizing core <i>T</i>_g. Fluorescence from trace levels of labeled diblock was used with 5–20 wt % PMMA–poly­(<i>n</i>-butyl acrylate)–PMMA triblocks in 2EH. The micelle core <i>T</i>_g is important in triblock systems that form thermoreversible gels because it fundamentally underlies the viscoelastic to elastic gel transition. Fluorescence results demonstrated the dependence of the CMT and the near invariance of the micelle core <i>T</i>_g on core-block molecular weight in these diblock and triblock systems for PMMA blocks with <i>M</i>_n = 15–25 kg/mol and solvent in the micelle core

Halogenation of a Nonplanar Molecular Semiconductor to Tune Energy Levels and Bandgaps for Electron Transport

Though peripheral halogen substitution is a known strategy to lower the lowest unoccupied (LUMO) and highest occupied (HOMO) molecular orbital energy levels of planar molecular semiconductors, this strategy has not been explored in conformationally contorted systems. We demonstrate that substitution of peripheral hydrogens with fluorine and chlorine can effectively lower the energy levels of contorted hexabenzocoronene (cHBC) despite its nonplanar conformation. The HOMO energy level lowers comparably with fluorine and chlorine substitution. Due to chlorine’s ability to accommodate more electron density than fluorine, chlorination lowers the LUMO energy level more effectively compared to fluorination (31–60 meV/F versus 53–83 meV/Cl), resulting in a narrowing of the optical bandgap. We find the preference for electron transport to increase with increasing halogenation of cHBC. As an example, thin-film transistors fabricated with 8F-8Cl-cHBC demonstrated electron mobilities as high as 10^–2 cm²/(V s) and solar cells with 8F-8Cl-cHBC and poly­(3-hexylthiophene), P3HT, showed power-conversion efficiencies as high as 1.2%