N-H…X (X = F, Cl, Br, and I) hydrogen bonding in aromatic amide derivatives in crystal structures

Thermodynamically and Dynamically Boosted Electrocatalytic Iodine Conversion with Hydroxyl Groups for High-Efficiency Zinc-Iodine Batteries

Rechargeable zinc-iodine (Zn-I2) batteries have shown immense potential for grid-scale energy storage applications, but there remain challenges of improving efficiency and cycling stability due to the sluggish iodine reduction reaction (IRR) kinetics and serious shuttle problem of polyiodides. We herein demonstrate an efficient metal-free hydroxyl (-OH)-functionalized carbon catalyst that effectively boosts the performance of Zn-I2 batteries. It has been found that the obtained electrocatalytic performance is strongly correlated with the surface oxygen chemical environment in the carbon matrix. Both theoretical calculations and experimental measurements have uncovered that the -OH group, rather than carbonyl (-C═O) and carboxyl (-COOH), provides the active electrocatalytic site for IRR, improves the iodine redox kinetics and the electrochemical reversibility, and facilitates I2 nucleation. As confirmed by a series of in situ and ex situ spectroscopy techniques, due to the favorable reaction thermodynamics and the lowered energy barrier for I3- dissociation, the O-H···I channels can effectively trigger the direct transformation of I2/I- and avoid the formation of stable polyiodides. As a result, the as-assembled battery of I2/oxygen-functionalized carbon cloth (I2/OCC-2)//Zn exhibits a high capacity of 2.27 mA h cm-2 at 1 mA cm-2, outstanding rate capability with 89.0% capacity retention at 20 mA cm-2, and long-term stability of 10,000 cycles.

"Magic Chloro": Profound Effects of the Chlorine Atom in Drug Discovery

Chlorine is one of the most common atoms present in small-molecule drugs beyond carbon, hydrogen, nitrogen, and oxygen. There are currently more than 250 FDA-approved chlorine-containing drugs, yet the beneficial effect of the chloro substituent has not yet been reviewed. The seemingly simple substitution of a hydrogen atom (R = H) with a chlorine atom (R = Cl) can result in remarkable improvements in potency of up to 100,000-fold and can lead to profound effects on pharmacokinetic parameters including clearance, half-life, and drug exposure in vivo. Following the literature terminology of the "magic methyl effect" in drugs, the term "magic chloro effect" has been coined herein. Although reports of 500-fold or 1000-fold potency improvements are often serendipitous discoveries that can be considered "magical" rather than planned, hypotheses made to explain the magic chloro effect can lead to lessons that accelerate the cycle of drug discovery.

Effect of Hydrogen Bonds and π...π-interactions on the Crystallization of Phenyl-perfluorophenyl Amides: Understanding the Self-organization of a Cocrystal

A series of N-arylbenzamides containing amide group and phenyl−perfluorinated rings were used as the smallest molecules to investigate the direct influence of hydrogen bond and aromatic donor-acceptor complementarity in the...

Theoretical, Solid-State, and Solution Quantification of the Hydrogen Bond-Enhanced Halogen Bond

Proximal noncovalent forces are commonplace in natural systems and understanding the consequences of their juxtaposition is critical. This paper experimentally quantifies for the first time a Hydrogen Bond-Enhanced Halogen Bond (HBeXB) without the complexities of protein structure or preorganization. An HBeXB is a halogen bond that has been strengthened when the halogen donor simultaneously accepts a hydrogen bond. Our theoretical studies suggest that electron-rich halogen bond donors are strengthened most by an adjacent hydrogen bond. Furthermore, stronger hydrogen bond donors enhance the halogen bond the most. X-ray crystal structures of halide complexes (X^- =Br^- , I^- ) reveal that HBeXBs produce shorter halogen bonds than non-hydrogen bond analogues. ¹⁹ F NMR titrations with chloride highlight that the HBeXB analogue exhibits stronger binding. Together, these results form the foundation for future studies concerning hydrogen bonds and halogen bonds in close proximity.

Supramolecular hydrogen-bonding patterns in the organic-inorganic hybrid compound bis(4-amino-5-chloro-2,6-dimethylpyrimidinium) tetrathiocyanatozinc(II)-4-amino-5-chloro-2,6-dimethylpyrimidine-water (1/2/2)

Zinc thiocyanate complexes have been found to be biologically active compounds. Zinc is also an essential element for the normal function of most organisms and is the main constituent in a number of metalloenzyme proteins. Pyrimidine and aminopyrimidine derivatives are biologically very important as they are components of nucleic acids. Thiocyanate ions can bridge metal ions by employing both their N and S atoms for coordination. They can play an important role in assembling different coordination structures and yield an interesting variety of one-, two- and three-dimensional polymeric metal-thiocyanate supramolecular frameworks. The structure of a new zinc thiocyanate-aminopyrimidine organic-inorganic compound, (C6H9ClN3)2[Zn(NCS)4]·2C6H8ClN3·2H2O, is reported. The asymmetric unit consist of half a tetrathiocyanatozinc(II) dianion, an uncoordinated 4-amino-5-chloro-2,6-dimethylpyrimidinium cation, a 4-amino-5-chloro-2,6-dimethylpyrimidine molecule and a water molecule. The Zn(II) atom adopts a distorted tetrahedral coordination geometry and is coordinated by four N atoms from the thiocyanate anions. The Zn(II) atom is located on a special position (twofold axis of symmetry). The pyrimidinium cation and the pyrimidine molecule are not coordinated to the Zn(II) atom, but are hydrogen bonded to the uncoordinated water molecules and the metal-coordinated thiocyanate ligands. The pyrimidine molecules and pyrimidinium cations also form base-pair-like structures with an R2(2)(8) ring motif via N-H...N hydrogen bonds. The crystal structure is further stabilized by intermolecular N-H...O, O-H...S, N-H...S and O-H...N hydrogen bonds, by intramolecular N-H...Cl and C-H...Cl hydrogen bonds, and also by π-π stacking interactions.

Supramolecular chemistry: from aromatic foldamers to solution-phase supramolecular organic frameworks

This mini-review covers the growth, education, career, and research activities of the author. In particular, the developments of various folded, helical and extended secondary structures from aromatic backbones driven by different noncovalent forces (including hydrogen bonding, donor-acceptor, solvophobicity, and dimerization of conjugated radical cations) and solution-phase supramolecular organic frameworks driven by hydrophobically initiated aromatic stacking in the cavity of cucurbit[8]uril (CB[8]) are highlighted.