Role of Host-Guest Charge Transfer in Cyclodextrin Complexation : A Computational Study

• Charge transfer (CT) was proposed to play a role in the cyclodextrin (CD) complexation with guest molecules. To elucidate the importance of CT interactions, here we used computational methods of quantum mechanics, docking, and molecular dynamics (MD) to investigate alpha-CD complexes with aromatic guest molecules of nitrobenzene, carboxybenzene, benzoate, 4-nitrophenol, and 4-nitrophenolate. Considering host guest CT in the docking has more of a chance to search reasonable guest orientations relative to alpha-CD matching the experiment, compared to that without CT. The CT interaction enlarges the difference in binding affinities of varied guests, as evidenced from potential of mean force (PMF) MD calculations. Energy decomposition of the total enthalpy and entropy shows the CT influence on the binding reactions in detail and indicates that there are considerable compensating effects of individual contributions from the binding partners and surrounding water. Charge transfer reduces the total dipole of alpha-CD by 9% on average and alters its dipole direction thereby affecting guest association. Gas-phase zeroth-order symmetry-adapted perturbation theory calculations show host guest CT amounts to approximately 6% of the total binding energy. The continuum solvation model based on the quantum mechanical charge density predicts binding energies comparable with the well depth of PMF profiles in explicit water. The abnormal binding strength of alpha-CD with the similar guests can be rationalized in terms of hydrogen bonding, extent of host guest CT, and dipole arrangement of guest relative to host.

Ämnesord

NATURVETENSKAP  -- Kemi -- Fysikalisk kemi (hsv//swe)

NATURAL SCIENCES  -- Chemical Sciences -- Physical Chemistry (hsv//eng)

NATURVETENSKAP  -- Kemi -- Teoretisk kemi (hsv//swe)

NATURAL SCIENCES  -- Chemical Sciences -- Theoretical Chemistry (hsv//eng)

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