Fragmentation method reveals a wide spectrum of intramolecular hydrogen bond energies in antioxidant natural products

Detailed solvent and temperature effects on the experimental 1H-NMR chemical shifts of the natural products chrysophanol (1), emodin (2), and physcion (3) are reported for the investigation of hydrogen bonding, solvation and conformation effects in solution. Very small chemical shift of │Δδ│ < 0.3 ppm and temperature coefficients │Δδ/ΔΤ│ ≤ 2.1 ppb/K were observed in DMSO-d6, acetone-d6 and CDCl3 for the C(1)–OH and C(8)–OH groups which demonstrate that they are involved in a strong intramolecular hydrogen bond. On the contrary, large chemical shift differences of 5.23 ppm at 298 K and Δδ/ΔΤ values in the range of −5.3 to −19.1 ppb/K between DMSO-d6 and CDCl3 were observed for the C(3)–OH group which demonstrate that the solvation state of the hydroxyl proton is a key factor in determining the value of the chemical shift. DFT calculated 1H-NMR chemical shifts, using various functionals and basis sets, the conductor-like polarizable continuum model, and discrete solute-solvent hydrogen bond interactions, were found to be in very good agreement with the experimental 1H-NMR chemical shifts even with computationally less demanding level of theory. The 1H-NMR chemical shifts of the OH groups which participate in intramolecular hydrogen bond are dependent on the conformational state of substituents and, thus, can be used as molecular sensors in conformational analysis. When the X-ray structures of chrysophanol (1), emodin (2), and physcion (3) were used as input geometries, the DFT-calculated 1H-NMR chemical shifts were shown to strongly deviate from the experimental chemical shifts and no functional dependence could be obtained. Comparison of the most important intramolecular data of the DFT calculated and the X-ray structures demonstrate significant differences for distances involving hydrogen atoms, most notably the intramolecular hydrogen bond O–H and C–H bond lengths which deviate by 0.152 tο 0.132 Å and 0.133 to 0.100 Å, respectively, in the two structural methods. Further differences were observed in the conformation of –OH, –CH3, and –OCH3 substituents.

Download Full-text

Experimental observations and CNDO/2 calculations for hydroxy stretching frequency shifts, intensities, and hydrogen bond energies of intramolecular hydrogen bonds in ortho-substituted phenols

Journal of the Chemical Society Perkin Transactions 2 ◽

10.1039/p29790001743 ◽

1979 ◽

pp. 1743 ◽

Cited By ~ 28

Author(s):

Mamoru Takasuka ◽

Yoshiki Matsui

Keyword(s):

Hydrogen Bond ◽

Hydrogen Bonds ◽

Bond Energies ◽

Substituted Phenols ◽

Frequency Shifts ◽

Intramolecular Hydrogen Bonds ◽

Intramolecular Hydrogen ◽

Hydrogen Bond Energies

Download Full-text

Intramolecular hydrogen bonding as reflected in the deuterium isotope effects on carbon-13 chemical shifts. Correlation with hydrogen bond energies

Journal of the American Chemical Society ◽

10.1021/ja00268a003 ◽

1986 ◽

Vol 108 (8) ◽

pp. 1735-1738 ◽

Cited By ~ 57

Author(s):

Jacques. Reuben

Keyword(s):

Hydrogen Bond ◽

Hydrogen Bonding ◽

Chemical Shifts ◽

Isotope Effects ◽

Intramolecular Hydrogen Bonding ◽

Bond Energies ◽

Deuterium Isotope Effects ◽

Intramolecular Hydrogen ◽

Hydrogen Bond Energies

Download Full-text

A DFT-D study on the stability and intramolecular interactions of the energetic salts of 3,6-dihydrazido-1,2,4,5-tetrazine

Canadian Journal of Chemistry ◽

10.1139/cjc-2015-0346 ◽

2016 ◽

Vol 94 (1) ◽

pp. 28-34

Author(s):

Xueli Zhang ◽

Xuedong Gong

Keyword(s):

Hydrogen Bond ◽

Density Functional ◽

Lattice Energy ◽

Intramolecular Interactions ◽

Bond Energies ◽

Dispersion Energy ◽

Linear Relationships ◽

The Stability ◽

Intramolecular Hydrogen ◽

Hydrogen Bond Energies

Structures of the salts I–IV formed by 3,6-dihydrazido-1,2,4,5-tetrazine with HNO3, HN(NO2)2, HClO4, and HC(NO2)3, respectively, were studied using dispersion-corrected density functional theory. The intramolecular hydrogen bond energies of I–IV were estimated using the quantum theory of atoms in molecules. The total hydrogen bond energies (EH,tot) have the order of I (65.60 kcal/mol) > II (46.24 kcal/mol) > III (39.13 kcal/mol) > IV (19.68 kcal/mol). In addition, the charge transfer (q), binding energy (Eb), lattice energy (HL), dispersion energy (Edis), and second-order perturbation energy (E2) were evaluated for studying the intramolecular interactions between the cation and anion. Linear relationships exist between any two of EH,tot, qtot, Eb, and E2,tot. HLs have the same variation trend as h50s (characteristic height) and may be used as the indicator of impact sensitivity. The HOMOs and LUMOs of I–IV are derived from the HOMOs of the isolated anions and the LUMOs of the isolated cations, respectively. Ultraviolet spectra of I–IV have the strongest absorptions at around 442, 445, 427, and 587 nm, respectively. The excitations HOMO→LUMO to HOMO–7→LUMO play important roles in the first three excited states.

Download Full-text