Molecular basis of binding and stability of curcumin in diamide-linked γ-cyclodextrin dimers

J Phys Chem B. 2013 Oct 17;117(41):12375-82. doi: 10.1021/jp406125x. Epub 2013 Oct 4.

Abstract

Curcumin is a naturally occurring molecule with medicinal properties that is unstable in water, whose efficacy as a drug can potentially be enhanced by encapsulation inside a host molecule. In this work, the thermodynamics and mechanism of binding of curcumin to succinamide- and urea-linked γ-cyclodextrin (γ-CD) dimers in water are investigated by molecular dynamics simulations. The simulated binding constants of curcumin to succinamide- and urea-linked γ-CD dimers at 310 K are 11.3 × 10(6) M(-1) and 1.6 × 10(6) M(-1), respectively, matching well with previous experimental results of 8.7 × 10(6) M(-1) and 2.0 × 10(6) M(-1). The simulations reveal structural information about the encapsulation of curcumin inside the diamide-linked γ-CD dimers, with distinct qualitative differences observed for the two dimers. In particular, (1) the predominant orientation of curcumin inside the urea-linked γ-CD dimer is perpendicular to that in the succinamide-linked γ-CD dimer; (2) the magnitude of the angle between the planes of the cyclodextrins is larger for the succinamide-linked γ-CD dimer; and (3) curcumin exhibits greater configurational freedom inside the urea-linked γ-CD dimer. A consequence of some of these structural differences is that the dimer interior is more accessible to water in the succinamide-linked γ-CD dimer. These observations explain the higher stability and lower binding constant observed experimentally for curcumin in the urea-linked cyclodextrin γ-CD dimer compared with the succinamide-linked γ-CD dimer. More generally, the results demonstrate how stability and binding strength can be decoupled and thus separately optimized in host-guest systems used for drug delivery.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Binding Sites
  • Curcumin / chemistry*
  • Diamide / chemistry*
  • Dimerization
  • Models, Molecular
  • Molecular Structure
  • gamma-Cyclodextrins / chemistry*

Substances

  • gamma-Cyclodextrins
  • Diamide
  • Curcumin
  • gamma-cyclodextrin