The Effects of Octanol on the Late Photointermediates of Rhodopsin

Membrane suspensions of unperturbed rhodopsin and rhodopsin perturbed with 2.5 niM octanol were photo-lyzed with 477 nm laser pulses at 20^OC and 35°C. Changes in absorbance were monitored at times ranging from 1 u-s to 80 ms after excitation. The data were analyzed using singular value decomposition, global exponential fitting and kinetic modeling. A recently proposed model involving the photointermediate Meta-I₃₈₀ (T. E. Thorgeirsson, J. W. Lewis, S. E. Wallace-Williams, and D. S. Kliger, Biochemistry 32,13861–13872, 1993) fits data for samples with and without octanol. Comparison of the microscopic rates shows this alcohol accelerates the formation of Meta-II via Meta-I₃₈₀. Activation and equilibrium thermodynamic parameters obtained from Ar-rhenius plots suggest that octanol reduces the entropy increase in forming both Meta-I_3g0 and Meta-II. It also lowers the enthalpy of Meta-1, _SI, relative to Lumi and of Meta-II relative to Meta-I₄₈₀. To help determine whether octanol affects the protein directly or indirectly through the lipid bilayer, similar experiments were conducted using rhodopsin solubilized in 0.13% dodecyl maltoside with and without octanol. Spectral shifts in the presence of octanol suggest that a direct protein interaction exists in addition to previously reported effects dependent on membrane free volume.     

Experiments on arrays of globally coupled chaotic electrochemical oscillators: Synchronization and clustering

Experiments on chaotically oscillating arrays of 64 nickel electrodes in sulfuric acid were carried out. External resistors in parallel and series are added to vary the extent of global coupling among the oscillators without changing the other properties of the system. The array is heterogeneous due to small variations in the properties of the electrodes and there is also a small amount of noise. The addition of global coupling transforms a system of independent elements to a state of complete synchronization. At intermediate coupling strengths stable clusters, or condensates of elements, form. All the elements in a cluster follow the same chaotic trajectory but each cluster has its own dynamics; the system is thus temporally chaotic but spatially ordered. Many cluster configurations occur under the same conditions and transitions among them can be produced. For values of the coupling parameter on either side of the stable cluster region a non-stationary behavior occurs in which clustered and synchronized states alternately form and break up. Some statistical properties of the cluster states are determined. (c) 2000 American Institute of Physics.     

Chaotic advection,diffusion, and reactions in open flows

We review and generalize recent results on advection of particles in open time-periodic hydrodynamical flows. First, the problem of passive advection is considered, and its fractal and chaotic nature is pointed out. Next, we study the effect of weak molecular diffusion or randomness of the flow. Finally, we investigate the influence of passive advection on chemical or biological activity superimposed on open flows. The nondiffusive approach is shown to carry some features of a weak diffusion, due to the finiteness of the reaction range or reaction velocity. (c) 2000 American Institute of Physics.     

Conformation and geometry of 2-thiophenesulphonyl chloride as studied by electron diffraction

The molecular conformation of 2-thiophenesulphonyl chloride is characterized by the perpendicular arrangement of the plane of the five-member ring and the CSCl plane, according to electron diffraction data. The sulphur bond configuration in the sulphonyl chloride moiety is consistent with the structural variations observed in a series of sulphonyl chlorides.     

On Stochastic Differential Equations with Locally Unbounded Drift

We study the regularizing effect of the noise on differential equations with irregular coefficients. We present existence and uniqueness theorems for stochastic differential equations with locally unbounded drift.     

An Intricate Molecule: Aluminum Triiodide. Molecular Structure of AlI3 and Al2I6 from Electron Diffraction and Computation.

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