Isotope Effects on Hydrogen Bonding and CH/CD−π Interaction

Abstract

We study the isotope effect by liquid chromatography (LC) with a variety of separation media under reversed and normal phase conditions using the protiated and/or deuterated compounds as the solutes. Results of reversed phase LC (RPLC) suggested that the protiated compounds were more hydrophobic than that of deuterated compounds due to the isotope effect based on the hydrogen bonding between hydrogen atoms of isotopologues and hydroxy groups in the mobile phase. The importance of the hydrogen bonding was also supported by the separation of isotopologues with a silica stationary phase on normal phase LC (NPLC), where the deuterated compounds showed stronger hydrogen bonding to hydroxy groups on silanol. Additionally, we investigated the difference of the strength between CH−π and CD−π interactions. Comparison of free energies of isotopologues by RPLC suggested that the CH−π interaction was slightly stronger than CD−π interaction. Finally, we demonstrated the separation of a few isotopologues on NPLC using a column coated with C70-fullerene, which is capable of strong π-based interactions, by effective CH/CD−π interactions.

Polarizability and isotope effects on dispersion interactions in water

“…Isotope effect on dispersion interaction. Although a lot of efforts have been made [39][40][41][42][43][44][45][46][47][48][49][50][51][52] , the H/D isotope effect on intermolecular interactions is still in debate. Under Born-Oppenheimer approximation, the potential energy surfaces of complexes with different isotope(s) are the same, so the difference in the thermodynamic stability between the two isotopomers arises from the vibrational frequency of C-H and C-D bonds.…”

“…Due to smaller vibrational frequency of C-D bond, the average C-D bond distance is slightly shorter than the C-H bond distance by 0.005 Å and C-H bond is more polarizable than C-D bond [49][50][51] . The studies on the encapsulation of protic and deuterated guest molecules in molecular capsules led to the conclusion that CD···π interaction is stronger than CH···π interaction 39,40,52 , while those based on chromatographic analysis led to the opposite conclusion 41,42 . Other studies indicate very small or nondetectable difference between the isotopes 43,[53][54][55] .…”

Separation of saccharides using fullerene-bonded silica monolithic columns via π interactions in liquid chromatography

“…C60-or C70-conjugated molecules were successfully synthesized using the methods of our previous studies 41,43 . Then, C60-or C70-bonded silica monolithic capillaries (C60 column or C70 column) were also prepared (see Scheme S1, S2, and Fig.…”

Separation of halogenated benzenes enabled by investigation of halogen–π interactions with carbon materials

“…The logarithm of the retention factor was plotted in order to correspond to the potential energy based on the equation of distribution equilibrium. 63 Both di-and tribrominated structural isomers showed stronger retentions and larger contributions of the p-p interaction as the dipole moment strength increased. The theoretical considerations also supported the notion that di-and tri-brominated benzenes express different strengths of p-p interactions based on the magnitude of their dipole moments.…”