| 1. |
|
|
| 2. |
- Edman, Peter, et al.
(author)
-
On determining intramolecular distances from donor–donor energy migration (DDEM) within bifluorophoric macromolecules
- 2000
-
In: PHYSICAL CHEMISTRY CHEMICAL PHYSICS. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 2, s. 1789-94
-
Journal article (peer-reviewed)abstract
- Recently a model based on donor–donor energy migration (DDEM) was developed for examining structure–function properties of biomacromolecules such as proteins (J. Chem. Soc., Faraday Trans., 1996, 92, 1563). Unlike the extended Förster theory (EFT; J. Chem. Phys., 1996, 105, 10896) the DDEM model is straightforward to apply in the analyses of fluorescence depolarisation experiments, as obtained by the time-correlated single photon counting (TCSPC) technique. In order to test the validity of the DDEM model, the EFT was used to create synthetic depolarisation data. These mimic true TCSPC experiments and cover a wide range of physical conditions, which are difficult to arrange for in real experiments with model systems. In particular, the relative rate of DDEM () and the rotation correlation time () of the donor molecules was examined. The DDEM rates obtained from the analyses were compared to the true rates. From these results the relative error of the intramolecular distances were calculated. For values 1<12<25, the DDEM model is slightly overestimating the distances. Typically, the distances determined with the DDEM model are overestimated by 5–10%.
|
|
| 3. |
- Usova, N, et al.
(author)
-
Theory of slow-motion EPR lineshapes for studies of membrane curvature
- 2000
-
In: PHYSICAL CHEMISTRY CHEMICAL PHYSICS. - 1463-9076. ; 2:12, s. 2785-93
-
Journal article (peer-reviewed)abstract
- The direct calculation method of slow-motion EPR spectra is presented based on the stochastic Liouville equation in the Langevin form, using the trajectories of Brownian dynamics (BD) simulations. We have developed a model of EPR slow-motion lineshapes describing a probe molecule residing in a curved bilayer system. Two dynamic processes are active: one is local reorientation motion of the lipid chain, and the second is the lateral diffusion of the spin probe along the curved lipid bilayer surface. The trajectories of two independent BD simulations are combined in order to describe the stochastic fluctuation of the electron spin-lattice Hamiltonian. The method of obtaining the Langevin equation describing lateral diffusion from the diffusion equation is discussed in detail. We solve the stochastic Liouville-von Neumann equation in the semiclassical approximation. EPR slow-motion lineshapes are obtained together with electron spin correlation functions. The synthesis of classical simulation methods and the lineshape model is illustrated by calculating a number of curvature dependent EPR lineshapes. Two curved model surfaces are considered namely the rippled z=a sin(bx) surface and the so called "Baltic Sea" z=a[sin(bx)+sin(by)].
|
|
| 4. |
- Westlund, Per-Olof
(author)
-
Line shape analysis of NMR powder spectra of (H2O)-H-2 in lipid bilayer systems
- 2000
-
In: JOURNAL OF PHYSICAL CHEMISTRY B. ; 104:25, s. 6059-64
-
Journal article (peer-reviewed)abstract
- A NMR line shape/spin relaxation model is developed for (H2O)-H-2 studies of structure and dynamics of the lipid-water interfaces of phosphatidylcholine bilayers. A line shape function describing the orientational dependence of (H2O)-H-2 is derived. In addition, also expressions of the observed quadrupole splitting and the spin-lattice relaxation rate are derived within the same dynamic model. The model comprises two chemically interchanging fractions of water namely, "free", and "bound". There are four molecular parameters characterizing the "bound" water of the lipid water interface, namely, (1) the fraction water molecules bound to lipid molecules, (2) the local water order parameter S-0(Pd), (3) the order parameter S-0(dD) which describes the averaged "bound" water, and an effective correlation time (4) tau(c), characterizing water translational diffusion at the interface. This model allows for analyzing quadrupole splittings, spin-lattice relaxation rates, and water powder line shapes. Thus, dynamics as well as structural information about the water molecules residing in the water lipid interface may be extracted. In the reinterpretation of (H2O)-H-2 powder spectra obtained for lamellar phases of dipalmitoylphosphatidylcholine (DPPC), the results clearly indicate that S-0(dD)(L-alpha) > S-0(dD)(L-beta') when comparing the liquid crystalline phase with 10-11 water molecules per lipid molecule and the gel phase with 3.5-4.2 water molecules per lipid molecule. Whereas the order of the perturbed water is similar in both phases, S-0(Pd)(L-alpha) approximate to S-0(Pd)(L-beta'). The lateral diffusion is characterized by a correlation time tau(c) > 60 ns but cannot be determined without measuring the spin-lattice relaxation measurements.
|
|
