Thermal motions, coupling

The average indicated on the right is the average over the thermal motion of the solution with the solute positioned at SAn, with no coupling between these subsystems. 

In the absence of specific adsorption of anions, the GCSG model regards the electrical double layer as two plate capacitors in series that correspond respectively, to two regions of the electrolyte adjacent to the electrode, (a) An inner compact layer of solvent molecules (one or two layers) and immobile ions attracted by Coulombic forces (Helmholtz inner plane in Fig. 2). Specific adsorption of anions at the electrode surface may occur in this region by electronic orbital coupling with the metal, (b) An outer diffuse region of coulombically attracted ions in thermal motion that complete the countercharge of the electrode. 

Examining these structures and the fact that they are all powered by ATP, the question remains as to how force is actually produced. Geeves and Holmes (2005) argue that myosin acts by the specific coupling between different myosin head states and different positions of the lever arm on the motor domain, so that, once attached to actin, the myosin acts as an ATP-driven motor where the energy released by ATP hydrolysis is direcdy coupled to the performance of mechanical work. However, Marx et al. (2005) argue that in some cases the kinesins appear to act as thermal ratchets. In this case, the attachment of a second head, once the first head has bound, is an event controlled by thermal motion, but, presumably for steric reasons, the head is more likely to bind to the microtubule in the... 

Figure 2. Schematisation of amorphous polymeric material. Macromolecules are coupled with weak van der Waals forces. At T > Tg, the system is in a fluid state, and the thermal motion makes the macromolecules move besides each other. At T < Tg, the system is in a glassy state, large-scale conformations of the chains are frozen, and a macromolecule can change its neighbours at the deformation of the material only.

Figure 10 shows the proposed ubiquinol oxidation and electron bifurcation mechanism at Qp site. (A) In the absence of the ubiquinone, the side chain of Glu-271 is connected to the solvent in the mitochondrial intermembrane space via a water chain. (B) As a reduced ubiquinol molecule binds to the site, the side chain of Glu-271 flips to form a hydrogen bond to the bound ubiquinone. (C) Now, the ISP, which is moving around the intermediate position by thermal motion is trapped at the b" position by a hydrogen bond to the bound ubiquinone. (D,E) Coupled to deprotonation, the first electron transfer occurs. Since the Rieske FeS cluster has a much higher redox potential (ca. +300 mV) than heme bl (ca. 0 mV), the first electron is favorably transferred to ISP. This yields ubisemiquinone, (F,G). After ubisemiquinone formation, the hydrogen bond to the His-161 of ISP is destabilized. The ISP moves to the c position, where the electron is transferred from the Rieske FeS cluster to heme c. Now unstable ubisemiquinone is left in the Qp pocket. The redox potential of the deprotonated ubisemiquinone is assumed to be several hundred millivolts. Now the electron transfer to the heme bl is a downhill reaction. (H) Coupled to the second electron transfer, the second proton is transferred to Glu-271 and subsequently to the mitochondrial intermembrane space. The fully oxidized ubiquinone is released to the membrane. 

A comment must be made about the cis— trans thermal isomerization rate at pressure. At room temperature, the thermal back reaction of DRl-PMMA follows a complex, nonexponential recovery, most of which is completed after a few seconds with a rate of 0.25 s" and deviates from a single exponential decay after the first 10 seconds.Larger relaxation times at Tg -98°C include slow polymer motion coupled with the chromophores rotational diffusion. We confirmed that this behavior is true in the polymer... 

Fig. 12.6. Direct determination of mechano-chemical coupling of myosin, (a) An experimental arrangement for simultaneous measurement. Single-headed myosin in the co-filament with an excess myosin rod is immobilized on the pedestal of the slide glass. An actin filament is manipulated by a trapped laser through two beads attached at both ends to interact with a myosin head in the correct arrangement. The ATP turnover is measured by monitoring the fluorescence from Cy3-ATP (Cy3-ADP) associated to and dissociated from the myosin head using TIRF microscopy, (b) Time trajectory of the displacement of the myosin head and the ATP turnover. The upper, middle, and bottom trace show the time course of displacements, changes in stiffness, which was calculated from the variance of the thermal motion of the beads, and changes in the fluorescence intensity of Cy3-nucleotide at the position of the myosin head...

If isotropic thermal motion is considered and if symmetry relations are established for coupling the different Fourier components, we obtain the... 

---