Control of Molecular Conformation and Crystal Packing of Biphenyl Derivatives

Superlong Metal-Organic Framework Micro-/Nanofibers for Selective Vitamin Absorption

Superlong MOF-74-type micro/nanofibers, which have aspect ratios much higher than 200, are synthesized via nanoparticulate MOF-mediated recrystallization. Co-MOF-74 microfibers have high crystallinity, whereas Co-MOF-74-II nanofibers are composed of nanocrystals and amorphous phases, even though they have nanofibrous morphology. Both MOFs consist of plenty of micropores with diameters in the range of 1.0 to 2.0 nm, and they exhibit high thermal stability with a decomposition temperature higher than 260.0 °C. The MOFs are demonstrated for selective absorption of some vitamins including riboflavin, folic acid, and 5-methyltetrahydrofolate. Co-MOF-74-II nanofibers can efficiently absorb riboflavin and folic acid from their aqueous solution with absorption percentages approaching 90.0%, and they have enhanced capability for absorbing tocopherol in methanol. The micro/nanofibrous morphology, together with the capability for selective vitamin absorption, makes the novel MOFs highly promising for applications in micro-solid-phase extraction.

Facile Synthesis of Rigid Binuclear Manganese Complexes for Magnetic Resonance Angiography and SLC39A14-Mediated Hepatic Imaging

Manganese(II)-based contrast agents (MBCAs) are potential candidates for gadolinium-free enhanced magnetic resonance imaging (MRI). In this work, a rigid binuclear MBCA (Mn2-PhDTA2) with a zero-length linker was developed via facile synthetic routes, while the other dimer (Mn2-TPA-PhDTA2) with a longer rigid linker was also synthesized via more complex steps. Although the molecular weight of Mn2-PhDTA2 is lower than that of Mn2-TPA-PhDTA2, their T1 relaxivities are similar, being increased by over 71% compared to the mononuclear Mn-PhDTA. In the presence of serum albumin, the relaxivity of Mn2-PhDTA2 was slightly lower than that of Mn2-TPA-PhDTA2, possibly due to the lower affinity constant. The transmetalation reaction with copper(II) ions confirmed that Mn2-PhDTA2 has an ideal kinetic inertness with a dissociation half-life of approximately 10.4 h under physiological conditions. In the variable-temperature 17O NMR study, both Mn-PhDTA and Mn2-PhDTA2 demonstrated a similar estimated q close to 1, indicating the formation of monohydrated complexes with each manganese(II) ion. In addition, Mn2-PhDTA2 demonstrated a superior contrast enhancement to Mn-PhDTA in in vivo vascular and hepatic MRI and can be rapidly cleared through a dual hepatic and renal excretion pattern. The hepatic uptake mechanism of Mn2-PhDTA2 mediated by SLC39A14 was validated in cellular uptake studies.

The Ehrenfest force field: A perspective based on electron density functions

The topology of the Ehrenfest force field (EhF) is investigated as a tool for describing local interactions in molecules and intermolecular complexes. The EhF is obtained by integrating the electronic force operator over the coordinates of all but one electron, which requires knowledge of both the electron density and the reduced pair density. For stationary states, the EhF can also be obtained as minus the divergence of the kinetic stress tensor, although this approach leads to well-documented erroneous asymptotic behavior at large distances from the nuclei. It is shown that these pathologies disappear using the electron density functions and that the EhF thus obtained displays the correct behavior in real space, with no spurious critical points or attractors. Therefore, its critical points can be unambiguously obtained and classified. Test cases, including strained molecules, isomerization reactions, and intermolecular interactions, were analyzed. Various chemically relevant facts are highlighted: for example, non-nuclear attractors are generally absent, potential hydrogen-hydrogen interactions are detected in crowded systems, and a bifurcation mechanism is observed in the isomerization of HCN. Moreover, the EhF atomic basins are less charged than those of the electron density. Although integration of the EhF over regions of real space can also be performed to yield the corresponding atomic forces, several numerical drawbacks still need to be solved if electron density functions are to be used for that purpose. Overall, the results obtained support the Ehrenfest force field as a reliable descriptor for the definition of atomic basins and molecular structure.