Halogen bonding (XB) in complexes of diiodine with heteroaromatic N-oxides was examined via a combination of UV–vis spectral and X-ray structural measurements, as well as computational analysis. While all of these associates were formed by analogous I···O bonds, they showed considerable variations of formation constants (5–1500 M–1) and intermolecular I···O bond length (2.3–3.2 Å). In the solid state, both atoms of I2 molecules were involved in XB, and the I···O separations were determined by the electron-donor abilities of N-oxides and the strength of the bonding on the opposite side of the ditopic XB donor. The solution-phase formation constants of 1:1 complexes, K, as well as magnitudes of the calculated interaction energies, ΔE, increased with the shift of the values of the most negative potentials on the surfaces of N-oxides’ oxygen atoms, V min, toward more negative values. Yet, the interatomic contacts consistently deviated from the locations of V min. Instead, the structures of complexes were well suited for highest occupied molecular orbital/lowest unoccupied molecular orbital interactions of reactants. The values of K, ΔE, and the intermolecular distances d I···O in the calculated complexes were highly correlated with the charge-transfer interaction energies derived from the natural bond orbital analysis. This indicated that, besides electrostatic, molecular orbital interactions play a substantial role in XB between diiodine and N-oxides. This conclusion was supported by the analysis of the complexes using the quantum theory of atoms in molecules, noncovalent interaction index, and density overlap region indicator, which showed that the covalent character of I···O bonding increases with the rise of interaction energies in the complexes.
The copper(I), silver(I), and gold(I) metals bind π‐ligands by σ‐bonding and π‐back bonding interactions. These interactions were investigated using bidentate ancillary ligands with electron donating and withdrawing substituents. The π‐ligands span from ethylene to larger terminal and internal alkenes and alkynes. Results of X‐ray crystallography, NMR, and IR spectroscopy and gas phase experiments show that the binding energies increase in the order Ag
A new air and moisture stable antimony thiolate compound has been prepared that spontaneously forms stable hollow vesicles.
Bis- and tris-pyridyl borate ligands containing pyridyl donor arms, a methylated boron cap, and a fluorine-lined coordination pocket have been prepared and utilized in coinage metal chemistry. The tris(pyridyl)borate ligand has been synthesized using a convenient boron source, [NBu4][MeBF3]. These N-based ligands permitted the isolation of group 11 metal–ethylene complexes [MeB(6-(CF3)Py)3]M(C2H4) and [Me2B(6-(CF3)Py)2]M(C2H4) (M = Cu, Ag, Au). The gold complexes display the largest coordination-induced upfield shifts of the ethylene 13C resonance relative to that of the free ethylene in their NMR spectra, while the silver complexes show the smallest shift. Solid-state structures of five of these metal–ethylene complexes as well as the related free ligands were established by X-ray crystallography. Surprisingly, all three [MeB(6-(CF3)Py)3]M(C2H4) adopt the rare κ2 coordination mode rather than the typical κ3 coordination mode of facial capping tridentate ligands. Computational analyses indicate that κ2 coordination mode is favored over the κ3-mode in these coinage metal–ethylene complexes and point to the effects CF3-substituents have on κ2/κ3-energy difference. The M–C and M–N bond distances of [MeB(6-(CF3)Py)3]M(C2H4) follow the trend expected based on covalent radii of M(I) ions. The calculated ethylene–M interaction energy of κ2-[MeB(6-(CF3)Py)3]M(C2H4) indicated that the gold(I) forms the strongest interaction with ethylene. A comparison to the related poly(pyrazolyl)borates is also presented.
Halogen- and hydrogen-bonded complexes between trihalomethanes, CHX3, and (pseudo-)halide anions, A-, co-existing in acetonitrile solutions were identified and characterized via a combination of UV-vis and NMR spectral measurements with the results of X-ray structural and computational analyses. Halogen-bonded [CHX3, A-] complexes displayed strong absorption bands in the UV range (showing Mulliken correlations with the frontier orbital energies of the interacting species) and a decreased shift of the NMR signal of trihalomethanes' protons. Hydrogen bonding led to the opposite (increased) NMR signal shift and the UV-vis absorption bands of the hydrogen-bonded [CHX3, A-] complexes were similar in intensity to those of the separate CHX3 molecules. The simultaneous multivariable treatment of the results of UV-vis and NMR titrations of CHX3 with A- anions afforded formation constants of both halogen- and hydrogen-bonded complexes between these species, which existed side-by-side in the acetonitrile solutions. The relative values of the formation constants were consistent with the magnitudes of the positive potentials on the surfaces of the halogen or hydrogen atoms if the effects of the polarization of the trihalomethanes due to the presence of the anions were taken into account.
Triple pnictogen bonding refers to the ability of a pnictogen atom to engage in three simultaneous pnictogen bonds (PnBs) to a complementary partner through a single pnictogen atom. This supramolecular strategy was recently introduced as a unique facet of pnictogen bonding as compared to other named supramolecular interactions. Here, the ability of bismuth to participate in this phenomenon is demonstrated using Bi((NC 9 H 7 ) 3 CH 3 ). The study reveals that Bi engages in stronger PnBs than the analogous Sb system. The results have been contrasted with Bi systems that form strong coordination bonds, and analysis of the electron density along the bond path reveals key differences. The solution behavior of these newly synthesized supramolecules were studied by PFGSE NMR spectroscopy and they are found to remain intact in solution. Molecular design strategies that allow for triple pnictogen bonding should find use in the fields of molecular recognition and crystal engineering.
No abstract
Bidirectional cell-cell communication via paracrine mechanisms involving nano-sized extracellular vesicles have emerged as a predominant mechanism of cellular signaling. Unlike other shedding vesicles of similar size, exosomes selectively package their cargo using defined mechanisms within the cells. Recent research on exosome signaling describes a messenger-recipient cell dichotomy. The heterogeneous origin of exosome populations, although previously described, has as-yet been incompletely characterized using this dichotomy and thus does not currently provide a complete understanding of exosome populations. In this work, we outline the fundamentally bidirectional nature of exosomes and replace this dichotomy with a messenger-recipient-effector network formed by repackaging and rerelease events. This network further confounds the determination of messenger cell identity among an already heterogeneous exosome population and has major implications for future clinical application. Redefining the axiom of exosome signaling provides a route for future research to consider a multi-system-based approach and underscores a need for enhanced identification methods. This shift also has implications for the use of exosomes as therapeutic agents. Exosome biogenesis and its manipulation will be crucial for the development of curative endogenous exosomes and their synthetic, exogenously produced counterparts. Directed cargo loading, optimal shell composition, and robust production platforms are just some of the design aspects that need to be considered. As tissue-specific therapeutic agents, exosome design will also need to incorporate repackaging mechanics to prevent off-target effects and increase efficacy. A comprehensive current understanding of exosome biogenesis mechanisms amidst the heterogenous EV population will propel the field towards clinical viability.
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