Molecular modeling and experimental studies of the thermodynamic and transport properties of pyridinium-based ionic liquids

A combined experimental and molecular dynamics study has been performed on the following pyridinium-based ionic liquids: 1-n-hexyl-3-methylpyridinium bis(trifluoromethanesulfonyl)imide ([hmpy][Tf(2)N]), 1-n-octyl-3-methylpyridinium bis(trifluoromethanesulfonyl)imide ([ompy][Tf(2)N]), and 1-n-hexyl-3,5-dimethylpyridinium bis(trifluoromethanesulfonyl)imide ([hdmpy][Tf(2)N]). Pulsed field gradient nuclear magnetic resonance spectroscopy was used to determine the self-diffusivities of the individual cations and anions as a function of temperature. Experimental self-diffusivities range from 10(-11) to 10(-10) m(2)/s. Activation energies for diffusion are 44-49 kJ/mol. A classical force field was developed for these compounds, and molecular dynamics simulations were performed to compute dynamic as well as thermodynamic properties. Evidence of glassy dynamics was found, preventing accurate determination of self-diffusivities over molecular dynamics time scales. Volumetric properties such as density, isothermal compressibility, and volumetric expansivity agree well with experiment. Simulated heat capacities are within 2% of experimental values.     

Elliptic phases: a study of the nonlinear elasticity of twist-grain boundaries

We develop an explicit and tractable representation of a twist-grain-boundary phase of a smectic-A liquid crystal. This allows us to calculate the interaction energy between grain boundaries and the relative contributions from the bending and compression deformations. We discuss the special stability of the pi/2 grain boundaries and discuss the relation of this structure to the Schwarz D surface.     

The structure of harmonizable isotropic random fields

The class of harmonizable processes and fields are a natural extension of the class of stationary processes and fields. Random fields admit an additional property called isotropy. The classical spectral and covariance representations for stationary isotropic random fields are extended to the harmonizable isotropic case. A classification of these fields is obtained based upon the smoothness properties of their covariances. In contrast to the stationary case, it is also shown that there exist non-trivial harmonizable isotropic fields which satisfy the Laplace operator in the L ²-sense     

Stable,Reactive, and Orthogonal Tetrazines: Dispersion Forces Promote the Cycloaddition with Isonitriles

The isocyano group is a structurally compact bioorthogonal functional group that reacts with tetrazines under physiological conditions. Now it is shown that bulky tetrazine substituents accelerate this cycloaddition. Computational studies suggest that dispersion forces between the isocyano group and the tetrazine substituents in the transition state contribute to the atypical structure–activity relationship. Stable asymmetric tetrazines that react with isonitriles at rate constants as high as 57 L mol^?1 s^?1 were accessible by combining bulky and electron‐withdrawing substituents. Sterically encumbered tetrazines react selectively with isonitriles in the presence of strained alkenes/alkynes, which allows for the orthogonal labeling of three proteins. The established principles will open new opportunities for developing tetrazine reactants with improved characteristics for diverse labeling and release applications with isonitriles.     

Electroweak Sudakov corrections using effective field theory

Electroweak Sudakov corrections of the form alphanlogms/MW,Z2 are summed using renormalization group evolution in soft-collinear effective theory. Results are given for the scalar, vector, and tensor form factors for fermion and scalar particles. The formalism for including massive gauge bosons in soft-collinear effective theory is developed.     

Aspartate‐Based CXCR4 Chemokine Receptor Binding of Cross‐Bridged Tetraazamacrocyclic Copper(II) and Zinc(II) Complexes

The CXCR4 chemokine receptor is implicated in a number of diseases including HIV infection and cancer development and metastasis. Previous studies have demonstrated that configurationally restricted bis‐tetraazamacrocyclic metal complexes are high‐affinity CXCR4 antagonists. Here, we present the synthesis of Cu²⁺ and Zn²⁺ acetate complexes of six cross‐bridged tetraazamacrocycles to mimic their coordination interaction with the aspartate side chains known to bind them to CXCR4. X‐ray crystal structures for three new Cu²⁺ acetate complexes and two new Zn²⁺ acetate complexes demonstrate metal‐ion‐dependent differences in the mode of binding the acetate ligand concomitantly with the requisite cis‐V‐configured cross‐bridged tetraazamacrocyle. Concurrent density functional theory molecular modelling studies produced an energetic rationale for the unexpected [Zn(OAc)(H₂O)]⁺ coordination motif present in all of the Zn²⁺ cross‐bridged tetraazamacrocycle crystal structures, which differs from the chelating acetate [Zn(OAc)]⁺ structures of known unbridged and side‐bridged tetraazamacrocyclic Zn²⁺‐containing CXCR4 antagonists.     

Hierarchically porous organic polymers: highly enhanced gas uptake and transport through templated synthesis

Porous organic polymers (POPs) possessing meso- and micropores can be obtained by carrying out the polymerization inside a mesoporous silica aerogel template and then removing the template after polymerization. The total pore volume (tpv) and specific surface area (ssa) can be greatly enhanced by modifying the template (up to 210% increase for tpv and 73% for ssa) as well as by supercritical processing of the POPs (up to an additional 142% increase for tpv and an additional 32% for ssa) to include larger mesopores. The broad range of pores allows for faster transport of molecules through the hierarchically porous POPs, resulting in increased diffusion rates and faster gas uptake compared to POPs with only micropores.