Poster Abstracts - 2011

Structural analysis of proteins involved in the innate immune response of mosquitoes to malaria parasites. Richard Baxter, Yale University. 

Abstract: The immune system of the Anopheles gambiae mosquito plays a critical role in determining its capacity to transmit malaria, and is a potential target for novel malaria control strategies. The Baxter laboratory use structural methods including macromolecular x-ray crystallography and small-angle x-ray scattering to study the molecular basis of the A. gambiae immune response to Plasmodium. These methods have provided high resolution structures of the central components of the mosquito complement-like immune response, the proteins TEP1, LRIM1 and APL1, and information on how they may interact. Future studies aim to combine these structural approaches with chemical biology and in vivo validation to discover new chemical entities for vector-based malaria control.

Hydrogen-Bonding Capability of Nonpolar Difluorotoluene Nucleoside in Replication Complexes. Shuangluo Xia, Jimin Wang & William H. Konigsberg, Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, Connecticut 06520-8024. 

Abstract: Nucleoside analogs are used as chemotherapeutic agents as well as specific probes in chemogenetics to define structure-function relationships of nucleic acids at an atomic level. The introduction of difluorotoluene as a thymine isostere (dF) by Kool et al. challenged the Watson-Crick (W-C) dogma that hydrogen-bonds (H-bonds) between compementary bases (A/T or G/C) are an absolute requirement for accurate DNA replication. Results with dF and other isosteres prompted Kool et al. to hypothesize that the shape of nascent base-pairs was a more important factor for base discrimination than inter-base W-C H-bonds. Their hypothesis remains controversial because the underlying assumptions have never been validated by results from relevant replication complexes. Here we report high-resolution crystal structures and kinetic behavior of RB69 DNA polymerase (RB69pol) Y567A/L561A/S565G triple mutant ternary complexes with a templating dF opposite all four incoming dNTPs (dATP, dCTP, dGTP & dTTP). We show that: (i) dF has unexpected H-bonding capability; (ii) the shape of nascent base-pairs is distorted from canonic W-C nascent base-pairs and; (iii) the shapes of dATP/dF and dGTP/dF pairs differ from dA/dF and dG/dF pairs when they are embedded in duplex DNA. These findings provide an explanation for the observed selectivity of dF for dATP and strongly support the concept that H-bonding between incoming dNTPs and a templating base or base analog is crucial for dNTP discrimination. Thus it appears that, although the shape of the nascent base-pair has a role in nucleotide selectivity, its importance is overshadowed by H-bonding between the templating base and the incoming dNTP.

Timothy Schmeier, Yale University, New Haven, Connecticut 06520-8024. 

Abstract: Carbon dioxide is known publicly for its role in the atmosphere where it is responsible for regulating global temperatures and as the main chemical agent responsible for climate change. Less well known is the role carbon dioxide is envisioned to play in the future, as a cheap, safe, and abundant source of carbon for the production of commodity chemicals. By studying the mechanism of carbon dioxide insertion into transition metal complexes we hope to design catalysts which can exploit this C1 feedstock to produce a variety of commercially relevant chemicals. X-ray crystallography is used as an analytical tool to characterize synthesized complexes and reveal catalyst-substrate interactions which may be difficult to identify by other means.

Linking the Electronic and Atomic Structure of Epitaxial Complex Oxides on Semiconductors, Divine P. Kumah, Department of Applied Physics, Yale University, New Haven, Connecticut 

Abstract: Understanding the interfacial coupling between materials with different electronic properties is critical to achieve the integration of epitaxial complex oxides with semiconductors. Using a combination of synchrotron x-ray diffraction and first principles calculations, we show that the electronic properties and atomic structure of epitaxial SrTiO₃ films on Si, and BaTiO₃ films on Ge are directly linked to the chemical composition at their respective interfaces. Sub-angstrom [001] cation-anion displacements observed in the SrTiO₃/Si system, lead to a positively polarized film. The polar distortions are found to arise from an interplay between compressive strain and localized interface states. In contrast to SrTiO₃/Si, we find that the BaTiO3/Ge interface has a 2x1 structure that drives an in-plane polarization.

Diamagnetic Alignment: Toward Ordered Ion-conducting Block Copolymer Membranes and Supramolecular Polymers, Manesh Gopinadhan, Pawel W. Majewski, Evan S. Beach and Chinedum Osuji, Department of Chemical and Environmental Engineering, Yale University, New Haven, Connecticut 

Abstract: The use of magnetic fields is presented as a facile and scalable approach to impose long-range order in a novel block copolymer electrolyte membrane and a hydrogen bonded supramolecular polymer. Our approach allows us to produce highly aligned hexagonally packed cylindrical or lamellar polymer microdomains over macroscopic areas. For the ion conducting membranes, we systematically explore the influence of several parameters; the magnetic field strength, lithium ion content and temperature on the ion conductivity etc. A surprising order of magnitude increase in conductivity is found in films aligned in the conduction direction relative to the non-aligned case. The data suggest that domain-confined ion transport in hexagonally packed cylindrical systems differs greatly in anisotropy compared to lamellar systems. Our findings advance the creation of well aligned arrays of amorphous PEO domains over large length scales and offer a route to functional materials, in particular for selective transport applications such as solid ionic electrolytes. We also demonstrate that non-covalent interactions can be used to enable facile alignment of hierarchical self-assembled morphologies in block copolymer systems. We show that hydrogen bonding between a rigid biphenyl species and one block of a diblock copolymer render the system susceptible to strong alignment by magnetic fields in a composition dependent manner. This finding has important implications for the directed self-assembly of stimuli responsive supramolecular polymer systems, particularly those involving rigid chromophores and other electro-optically active species as recently advanced in literature. This work is funded by the NSF under DMR-0847534.

Synthesis and Characterization of Dispersible ZrO₂/Multi-Walled Carbon Nanotubes Catalyst in Aviation Fuels and Related Mechanistic Studies, Changchang Liu, Sungchul Lee, Charles McEnally, Lisa D. Pfefferle, and Gary L. Haller,* Department of Chemical Engineering, Yale University, New Haven, Connecticut 

Abstract: In this paper, we developed a strong solid acid catalyst that would catalyze endothermic reactions in aviation fuel and would be dispersible in the fuel after functionalization. We used multi-walled carbon nanotubes (MWCNT) as the catalyst support and graft zirconium onto the nanotubes to form nano-scale ZrO₂ particles followed by sulfation (i.e., the S-ZrO₂/MWCNT catalyst). The ZrO₂ particle sizes calculated through XRD peak-fitting correlate well with TEM results. Moreover, using X-ray Absorption Spectroscopy (carbon and oxygen K-edge NEXAFS), we were not only able to prove the formation of covalent bonding between the ZrO₂ and MWCNT, which will stablize the ZrO₂ against sintering, but also see the various functionalizations of the MWCNT surface. This paper would only focus on the XRD and XAS analysis on our catalysts, while the catalytic reaction activity and selectivity results will not be included. 

Magnetic Fields for Long-range Ordering of Amphiphilic Block Copolymers, Pawel Majewski, Manesh Gopinadhan and Chinedum Osuji, Department of Chemical Engineering, Yale University, New Haven, Connecticut 

Abstract: We present a diamagnetic interactions-based approach to impose long range order in Li ion-conducting liquid crystalline diblock copolymers of two distinct morphologies. Our technique allows us to control the orientation of Li-doped PEO domains within a non-conducting liquid crystalline matrix that is responsive to the magnetic field. The orientation and the degree of alignment are quantified by X-ray scattering, electrical impedance spectroscopy. The conductivity of the cylindrical samples with PEO domains aligned perpendicular to electrodes is an order of magnitude greater than randomly orientated samples, an extent greater than predicted by the microstructured model developed by Sax and Ottino. During temperature scans the conductivities of three differently aligned cylindrical samples follow distinct pathways merging at the order-disorder transition temperature. The observed conductivity ratios for orthogonally aligned lamellar system are much smaller and temperature dependence of conductivity is mostly influenced by PEO melting and crystallization.

Magnetically aligned soft mesophases for applications in templated synthesis and ionic transport, Pawel Majewski, Yale University

Abstract: We present a diamagnetic interactions-based approach to impose long range order in self-assembled soft materials. We discuss two chemically different systems which have been successfully aligned with the use of a magnetic field. The orientation and the degree of alignment are quantified by the analysis of two dimensional small-angle X-ray scattering patterns (2D SAXS), polarized optical microscopy (POM) and electrical impedance spectroscopy (EIS). In a lamellar surfactant-water system, the method which we term "rotational annealing," is used to obtain highly ordered structure which can be further utilized as a template for nanomaterials synthesis. Our second system is a Li ion-conducting block copolymer. In this material hexagonally closed-packed PEO domains are embedded in a non-conducting liquid crystalline matrix that is responsive to the field. Our technique allows us to control the orientation of PEO channels across the sample. The electrical conductivity of the samples with PEO domains aligned perpendicular to electrodes is an order of magnitude greater than for samples featuring randomly orientated domains.