Evidence for resonance-assisted hydrogen bonding. 2. Intercorrelation between crystal structure and spectroscopic parameters in eight intramolecularly hydrogen bonded 1,3-diaryl-1,3-propanedione enols

Bertolasi, Valerio; Gilli, Paola; Ferretti, Valeria; Gilli, Gastone

doi:10.1021/ja00013a030

Cited by 480 publications

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“…Moreover, the fact that molecule IV prefers to break the hydrogen bridge rather than to shorten the O · · · O distance when the steric effect is increased by forcing the 3-substituent phenyl group towards coplanarity with the chelate ring, suggests that the experimental data from X-ray diffraction are most likely affected by interactions and/or constrictions peculiar to the solid state rather than to an actual increase in the hydrogen bridge stability. That the intramolecular hydrogen bond strengthening due to the strong steric effect is not exceptional, notwithstanding the r O...O shortening, is also confirmed by the previously cited literature data concerning 1,3-diaryl-1,3-propanedione enols [27].…”

Section: Resultssupporting

confidence: 83%

“…In other words, the E HB increase is not so relevant as argued from the geometrical experimental findings: this conclusion is in line with the results of our previous study on the potential energy well of malondialdehyde and confirms that part of the steric strain can be dampened by the hydrogen bridge without dramatic geometrical and/or energetic changes. Support for the present findings comes from literature data concerning eight 1,3-diaryl-1,3-propanedione enols [27], where steric hindrance causes r O...O to decrease from 2.502 to 2.432Å accompanied by hydrogen bond strengthening much lower than the present ones (maximum strengthening of about 7 kJ mol −1 ). It is also noteworthy that E HB concerning III is only 11.8 kJ mol −1 higher than that of I according to 3-21G results, which scales to 5-6 kJ mol −1 according to the 6-31G** and B3LYP/6-31G** level.…”

Section: Hydrogen Bondingsupporting

confidence: 87%

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Importance of steric effect on the hydrogen bond strength of malondialdehyde and acetylacetone 3‐substituted derivatives. An ab initio study

Buemi¹,

Zuccarello²

1997

Elect J Theoret Chem

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SUMMARYThe molecular geometries of various 3-substituted malondialdehyde and acetylacetone derivatives, in their chelate, open and H-centred conformations, were optimized and the hydrogen bond energies evaluated, in order to estimate the effect of 3-substitution steric hindrance on the hydrogen bond strength. Calculations were performed at the ab initio 3-21G and 6-31G** level, with and without correlation energy inclusion, using the Møller-Plesset approach (where possible) and the B3LYP functional. The frequencies of the O-H stretching mode were evaluated, too. The obtained results indicate that the Cs chelate conformations are the most stable structures. The O · · · O distances are rather longer than the values typical of the H-centred conformers, at least in gas phase. The strengthening of the hydrogen bridge, on passing from the parent to the 3-substituted derivatives, is not so relevant as expected on the ground of literature data, the maximum increase being about 21 kJ mol −1 (in 3-t-butyl-acetylacetone). An increase of the steric effect to stress the O · · · O distance caused the breaking of the hydrogen bridge instead of strengthening, so indicating that the literature X-ray geometries (in particular the O · · · O distances) are governed, at least partially, by crystalline forces.

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Section: Resultssupporting

confidence: 83%

Section: Hydrogen Bondingsupporting

confidence: 87%

Importance of steric effect on the hydrogen bond strength of malondialdehyde and acetylacetone 3‐substituted derivatives. An ab initio study

Buemi¹,

Zuccarello²

1997

Elect J Theoret Chem

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“…6,8 This view has been challenged recently as more and more strong and unconventional hydrogen bonds have been recognized. [9][10][11][12] As a matter of fact, several types of strong hydrogen bonds have been investigated, for example, charge assisted hydrogen bonds (CAHBs), 12,13 low barrier hydrogen bonds (LBHBs), 14,15 dihydrogen bonds (DHBs), 8,16 and resonance-assisted hydrogen bonds (RAHBs). [10][11][12] In a CAHB, a positive or negative charge on the proton donating or accepting group remarkably increases the strength of the hydrogen bond.…”

Section: Introductionmentioning

confidence: 99%

“…8 RAHB highlights the co-operativity between the -electron delocalization and hydrogen bonds and the term was coined by Gilli and coworkers in the late 1980s, who have continued to refine their theory through a series of papers. [10][11][12] In RAHB, the hydrogen bond donor and acceptor atoms are connected through -conjugated double bonds. A typical example of RAHB is -diketone enols which form intramolecular ÁÁÁO¼ ¼CÀ ÀC¼ ¼CÀ ÀOHÁÁÁ hydrogen bonds enhanced by the resonance with OÁÁÁO distances as short as 2.39-2.44 Å .…”

Section: Introductionmentioning

confidence: 99%

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How resonance assists hydrogen bonding interactions: An energy decomposition analysis

Beck

2006

J Comput Chem

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Block-localized wave function (BLW) method, which is a variant of the ab initio valence bond (VB) theory, was employed to explore the nature of resonance-assisted hydrogen bonds (RAHBs) and to investigate the mechanism of synergistic interplay between delocalization and hydrogen-bonding interactions. We examined the dimers of formic acid, formamide, 4-pyrimidinone, 2-pyridinone, 2-hydroxpyridine, and 2-hydroxycyclopenta-2,4-dien-1-one. In addition, we studied the interactions in -diketone enols with a simplified model, namely the hydrogen bonds of 3-hydroxypropenal with both ethenol and formaldehyde. The intermolecular interaction energies, either with or without the involvement of resonance, were decomposed into the Hitler-London energy (DE HL ), polarization energy (DE pol ), charge transfer energy (DE CT ), and electron correlation energy (DE cor ) terms. This allows for the examination of the character of hydrogen bonds and the impact of conjugation on hydrogen bonding interactions. Although it has been proposed that resonance-assisted hydrogen bonds are accompanied with an increasing of covalency character, our analyses showed that the enhanced interactions mostly originate from the classical dipoledipole (i.e., electrostatic) attraction, as resonance redistributes the electron density and increases the dipole moments in monomers. The covalency of hydrogen bonds, however, changes very little. This disputes the belief that RAHB is primarily covalent in nature. Accordingly, we recommend the term ''resonance-assisted binding (RAB)'' instead of ''resonance-assisted hydrogen bonding (RHAB)'' to highlight the electrostatic, which is a long-range effect, rather than the electron transfer nature of the enhanced stabilization in RAHBs.

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Conformational flexibility of the catalytic Asp dyad in HIV-1 protease: An ab initio study on the free enzyme

2000

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The enzyme protease from the human immunodeficiency virus type 1 (HIV-1 PR) is one of the main targets for therapeutic intervention in AIDS. Computer modeling is useful for probing the binding of novel ligands, yet empirical force field-based methods have encountered problems in adequately describing interactions of the catalytic aspartyl pair. In this work we use ab initio dynamic methods to study the molecular interactions and the conformational flexibility of the Asp dyad in the free enzyme. Calculations are performed on model complexes that include, besides the Asp dyad, the conserved Thr26 and Gly27 residues and water molecules present in the active site channel. Our calculations provide proton location and binding mode of the active-site water molecule, which turn out to be different from those of the eukariotic isoenzyme. Furthermore, the calculations reproduce well the structural features of the aspartyl dyad in the protein. Finally, they allow the identification of both dipole/charge interactions and a low-barrier hydrogen bond as important stabilizing factors for the peculiar conformation of the active site. These findings are consistent with site-directed mutagenesis experiments on the 27, 27; positions (Bagossi et al., Protein Eng 1996;9:997-1003). The electric field of the protein frame (included in some of the calculations) does not affect significantly the chemical bonding at the cleavage site. Proteins 2000;39:26-36.

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Evidence for resonance-assisted hydrogen bonding. 2. Intercorrelation between crystal structure and spectroscopic parameters in eight intramolecularly hydrogen bonded 1,3-diaryl-1,3-propanedione enols

Cited by 480 publications

References 0 publications

Importance of steric effect on the hydrogen bond strength of malondialdehyde and acetylacetone 3‐substituted derivatives. An ab initio study

Importance of steric effect on the hydrogen bond strength of malondialdehyde and acetylacetone 3‐substituted derivatives. An ab initio study

How resonance assists hydrogen bonding interactions: An energy decomposition analysis

Conformational flexibility of the catalytic Asp dyad in HIV-1 protease: An ab initio study on the free enzyme

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