Hydrogen Bonding

From Noncovalent Chalcogen–Chalcogen Interactions to Supramolecular Aggregates: Experiments and Calculations

“…The C–H···π distances recorded for these two ring systems (2.85 and 2.89 Å) compare well with other weak hydrogen bonds. − ,, The comparison of the data listed in Table reveals that the contributions of the E···E interactions increase in the sequence S-Se-Te, whereas the other weak interactions decrease from S to Se and Te. A comparison of the C–H···S and S···S bond lengths in Table , respectively, reveals very similar distances as reported for the thiabowls trithia-[3]-peristylane: C–H···S = 3.05 and 3.09 Å and tetrathia-[4]-peristylane: C–H···S = 2.93 Å and S···S = 3.61 Å. , …”

“…These results suggest that S···S interactions might be weaker than other weak forces such as CH−π interactions. − ,, Therefore, it is of interest to take a look at cyclic diynes with two CH 2 -CC-E instead of two E-CC-E (E = S, Se, Te) units, as discussed before. In Scheme the syntheses of the cyclic systems 60 ( m , n ), 61 ( m , n ), and 62 ( m , n ) are presented.…”

“…In Figure we show the optimized geometries of the three dimers and list their chalcogen–chalcogen distances together with the interaction energies. , A comparison between the three nonbonding species in Figure reveals bond lengths between 3.7 Å (S) and 4.0 Å (Te) which are equal (S) or smaller than the van der Waals distances (Se···Se 4.0 Å, Te···Te 4.4 Å). , The interaction energies of the three dimers vary between 2.79 (S), 2.82 (Se), and 3.4 kcal/mol (Te). All three values are small and in the order of weak hydrogen bonds, such as CH···O and OH···π. − Nevertheless, these weak bonds are important for the formation and structures of many types of condensed matter: As examples for molecules with noncovalent interactions we mention in this chapter the supramolecular assemblies to yield macrocycles, helices, and container molecules to name only a few. − On behalf of these supermolecules and their supramolecular assemblies, we have depicted in Figure C 16 S 8 ( 6 ) and its association in the solid state by noncovalent intermolecular S···S contacts between 3.2 and 3.5 Å . Further examples of crown ethers with S, Se, and Te as heteroatoms and their association to further species with and without inclusion of molecules will be discussed in section 2.…”

MD and QM/MM Study of the Quaternary HutP Homohexamer Complex with mRNA, l-Histidine Ligand, and Mg2+

“…the electronic structure communication between the interacting residues, including the weakening of the X–H covalent bonds. The X–H elongations correlate quite well with other descriptors of H-bonding, such as red shifts in the infrared spectrum (i.e., changes in the X–H vibrational frequencies) and electron topology analyses. − The MM description does not capture electronic structure effects, which are thus missing in MD simulations. While the MM approximation does in principle allow some elongation of X–H bonds upon H-bond formation too, the elongations are typically smaller than in QM calculations, especially for stronger H-bonds.…”

Classical Electrostatics Remains the Driving Force for Interanion Hydrogen and Halogen Bonding

“…The current consensus is that electrostatic attraction between H and A governs HB. , Certain energy analyses show that the attractive electrostatic interaction benefits from a comparable contribution from the quantum exchange-correlation energy component . Meanwhile, the minor charge transfer (CT) interaction, or n A → σ* H‑D , stabilizes HB as well and is responsible for the covalent features such as the directionality in HB. − Due to the dominance of electrostatics, electrostatic concepts, such as atomic charges, multipoles, and polarizability, have been successfully adopted in the force field description of HB. − Recently, the scope of HB has been noticeably expanded with various unconventional cases identified. − Among these unconventional HBs, interanion HB (IAHB) − is particularly intriguing as it seemingly violates the long-standing electrostatic explanation and thus challenges the force field description, as Coulombic repulsion would prevent the formation of such HB. Thus, insightful, and comprehensive theoretical studies on IAHB are highly desirable, in order to sort out the governing factors for the stability of IAHB and elucidate the key distinction from conventional HB.…”