Synthesis and Properties of 2‑Halo-1,3-diether-propanes: Diversifying the Range of Functionality in Glycerol-Derived Compounds

Synthesis of value-added chemicals from glycerol derivatives has been of real interest due to the excess volumes of glycerol resulting from biofuel production. Previously, we have demonstrated the controlled synthesis of symmetric and asymmetric 1,3-diether-2-propanol compounds bearing glycerol skeletons, which, in addition to potential applications as CO2 capture solvents, are also versatile intermediates for a number of further chemical transformations. Here, we demonstrate the conversion of these compounds to corresponding 2-halo-1,3-diethers as a means of further diversifying the range and properties of glycerol-derived compounds. Thermophysical properties of these compounds (density, molar volume, and viscosity) were measured over a temperature range of 20–80 °C. The experimental work was augmented by theoretical calculations of density, viscosity, vapor pressure, and dipole moment for each of the synthsized compounds as well as additional species with similar structures that have not yet been synthesized. The data obtained in this work provide a useful guide for valorization of glycerol in the form of new solvents and building blocks for value-added chemicals

Electrostatically Regulated Active Site Assembly Governs Reactivity in Nonheme Iron Halogenases

Non-heme iron halogenases (NHFe-Hals) catalyze the direct insertion of a chloride ion at an unactivated carbon position using a high-valent haloferryl intermediate. Despite more than a decade of structural and mechanistic characterization, a rigorous understanding of the entire catalytic cycle of NHFe-Hals and how they facilitate binding, activation, and reactivity with specific substrates and functionalizing anions remains unclear. Here, we focus on understanding binding and active site assembly in freestanding halogenases, BesD and HalB, which directly catalyze the chlorination of lysine without the need for a partner protein. While the lysine and chloride binding affinities to BesD’s active sites are extremely weak (Kd values of ∼50 and 560 mM, respectively), we demonstrate strong positive heterotropic cooperativity (cooperativity constant, α ∼ 15,500) between the lysine and chloride binding events such that they bind efficiently when simultaneously present at physiologically relevant concentrations. Using a combination of computational and rational protein design studies, we identify a negatively charged residue, E119, in BesD that locks the active site assembly unless both the chloride anion and the positively charged lysine substrate are simultaneously present. Removing this electrostatic lock by mutating E119 to polar/neutral glutamine and alanine residues results in a 6.7- and 14-fold increase in affinity for the chloride anion, respectively. A concomitant order of magnitude decrease in chlorination yields is observed as lysine binding is impaired in these mutants, yet the chemoselectivity profile remains rather similar. Beyond such implications for the overall catalytic performance, we show that the electrostatically regulated active site assembly stage of BesD’s catalytic cycle can also determine its promiscuity for C–H functionalization with other anions such as bromide, azide, and nitrite. Overall, our studies highlight complex electrostatic effects at play during the active site assembly stage of charged substrates like lysine along with their implications for C–H functionalization performance in BesD-like halogenases

Synthesis, structural characterization, and solution properties of a 1-D Pb(II)-bipyridine coordination polymer

<div><p>A new one-dimensional (1-D) Pb(II) coordination polymer, [Pb(2,2′-bpy)(NO₃)₂(H₂O)]_n (<b>1</b>) (2,2′-bpy = 2,2′-bipyridine), has been synthesized and characterized by different spectroscopic techniques and X-ray single-crystal analysis. From the X-ray crystal structure of <b>1</b>, the Pb²⁺ can be best described as a highly distorted pentagonal bipyramid with O4 (water) and O6 (nitrate) at apical positions (O4–Pb–O6 of 143.7(1)°). Variability in bond distances reveals that Pb²⁺ is unsymmetrically surrounded by two nitrates, one 2,2′-bpy and one water. Nitrates bridge between monomers. The molecule crystallizes in the monoclinic <i>P</i>2₁<i>/n</i> (14) space group. This is the first example of a 1-D Pb(II) polymer in which nitrates show three different coordination motifs (terminal, chelating, and bridging). Solid state as well as solution phase UV–vis spectral analysis and mass spectrometric studies clearly reveal instability with breakdown of Pb(II) polymer in aqueous solution. The arrangement of the 2,2′-bpy, water, and nitrates leaves a coordination gap at the Pb(II) occupied probably by a stereo-active lone pair of electrons.</p></div

Silica–Conjugated Polymer Hybrid Fluorescent Nanoparticles: Preparation by Surface-Initiated Polymerization and Spectroscopic Studies

Organic/inorganic hybrid nanoscale materials possess fascinating optical, electronic, magnetic, and catalytic properties that are promising for a variety of practical applications. Such properties can be dramatically affected by the hierarchical structure and molecular organization in the nanomaterials. Herein, we employed surface-initiated Kumada catalyst-transfer polymerization to prepare hybrid materials consisting of shells of conjugated polymers (CPs)polythiophene or poly­(<i>p</i>-phenylene)and their block copolymers covalently attached to the surface of silica nanoparticles. Because of the controlled chain-growth mechanism of surface-initiated polymerization, we obtained structurally well-defined CP blocks in the diblock copolymer shells, which produced distinct spectroscopic properties related to the intraparticle excitation energy transfer between the nanoscale polymer shell components, as well as the formation of interfacial exciplex states. The spectroscopic phenomena were further understood via time-resolved transient absorption spectroscopy studies. Overall, the surface-initiated polymerization provided an efficient tool to prepare structurally defined and highly stable organic polymer shell–inorganic core nanoparticles with tunable spectroscopic characteristics not achievable from corresponding single-component systems

Liquid Crystalline Poly(3-hexylthiophene) Solutions Revisited: Role of Time-Dependent Self-Assembly

Poly­(3-hexylthiophene) (P3HT) in trichlorobenzene solution self-assembles and exhibits liquid crystal ordering when confined to rectangular capillaries. The relative proportion of polymer assemblies increases with time, as determined by UV–vis spectroscopic analysis. Polarized optical microscopy (POM) reveals development of birefringence and monodomainlike long-range ordering. Micro-Raman spectroscopy was used to calculate the orientational order parameters, ⟨P₂⟩ and ⟨P₄⟩, of the liquid-crystalline P3HT solutions. The order parameter ⟨P₂⟩ increased with time up to 0.35, indicating increased anisotropy. The calculated depolarization ratio (ρ_v) from depolarized dynamic light scattering measurements points to the time-dependent formation of highly ordered P3HT nanostructures, whereas cryogenic transmission electron microscopy was employed for the direct visualization of the rodlike assemblies. POM shows that the observed anisotropy can be preserved in P3HT films drawn from aged solutions. These results suggest that P3HT self-assembly leads to a liquid-crystalline solution of conjugated polymer aggregates, which may lead to a viable approach for optimization of processes for organic electronic device applications. Such ordered and oriented conjugated polymer assemblies have many desirable attributes for high-performance device applications, where the ability to control nano- through macroscale molecular ordering is required