The role of water molecules in a resorcinarene capsule as probed by NMR diffusion measurements

[structure: see text] NMR diffusion measurements were used to probe the role of water molecules in a resorcinarene capsule in a CDCl(3) solution. It was found that the water/resorcinarene ratio affects both the chemical shift and the diffusion coefficient of the water molecules. From the NMR diffusion measurements we could conclude that the major species in the chloroform solution is the hexamer having eight water molecules that are in fast exchange, on the NMR time scale, with the bulk water.     

Excitation wavelength dependence of the proton-transfer reaction of the green fluorescent protein

Picosecond time-correlated single-photon counting was used to measure the proton-transfer rate of green fluorescent protein (GFP) excited by several wavelengths between 266 and 405 nm. When samples of GFP in water and D2O are excited at short wavelengths, lambda(ex) < 295 nm, the fluorescence properties are largely modified with respect to excitation at a wavelength around 400 nm, the peak of the absorption band of the S0 --> S1 transition of the ROH form of the chromophore. The shorter the excitation wavelength, the longer the decay time of the ROH emission band at 450 nm and the longer the rise time of the RO- emission band at 512 nm. The proton transfer is slower by an order of magnitude and about a factor of 3 when GFP in water and D2O are excited by 266 nm, respectively.     

Asymptotic Behaviour of C0–Semigroups with Bounded Local Resolvents

Let {T(t)}_t≥0 be a C₀–semigroup on a Banach space X with generator A, and let H^∞_T be the space of all x ∈ X such that the local resolvent λ ↦ R(λ, A)x has a bounded holomorphic extension to the right half–plane. For the class of integrable functions ϕ on [0, ∞) whose Fourier transforms are integrable, we construct a functional calculus ϕ ↦ T_ϕ, as operators on H^∞_T. Weshow that each orbit T(·)T_ϕx is bounded and uniformly continuous, and T(t)T_ϕx → 0 weakly as t → ∞, and we give a new proof that ∥T(t)R(μ, A)x∥ = O(t). We also show that ∥T(t)T_ϕx∥ → 0 when T is sun –reflexive, and that ∥T(t)R(μ, A)x∥ = O(ln t) when T is a positive semigroup on a normal ordered space X and x is a positive vector in H^∞_T.     

Optical losses in dielectric apertured terahertz VCSEL

The resonant wavelength and mode radius of the fundamental modes supported by an oxide apertured terahertz vertical surface emitting laser are determined from Gaussian resonant theory and scalar variational method. The reflectivity of the Bragg mirror is calculated for the lowest modes and it decreases as the aperture size decreases. The aperture radius, thickness, and axial position in the cavity are shown to be an important factor for high efficiency vertical cavity surface emitting lasers and single mode operation. When the aperture size is much larger than the emitting wavelength, the optical loss is negligible. However, the optical loss strongly depends on the aperture size and thickness when aperture size is similar to or smaller than emitting wavelength.     

Long relaxation times and tilt sensitivity in Rayleigh Bénard turbulence

We study the influence of a small tilt angle ( rd) on the Nusselt number in a 1/2 aspect ratio Rayleigh-Bénard cell, at high Rayleigh number (5 x 10¹¹ < Ra < 4 x 10¹²). The small decrease observed is interpreted as revealing a two rolls structure of the flow. Transitions between different global flows are also observed, on very long times, comparable to the diffusion time on the whole cell. The consequence is that the Nusselt number observed in most high Ra experiments should significantly depend on initial conditions.Received: 19 May 2004, Published online: 12 August 2004PACS: 92.60.Ek Convection, turbulence, and diffusion - 47.27.Te Convection and heat transfer - 44.25. + f Natural convection     

Convergence to steady states of solutions of semilinear evolutionary integral equations

We study the convergence and decay rate to a steady state of bounded solutions of the nonlinear evolutionary integral equation and we apply our abstract results to the viscoelastic Euler-Bernoulli beam and to Kelvin-Voigt solids.Received: 25 March 2003, Accepted: 5 April 2004, Published online: 16 July 2004This work was partially supported by the DFG project Regularität und Asymptotik für elliptische und parabolische Probleme and by the grants GAR 201/01/D094, MSM 113200007.     

Complexation in pseudorotaxanes based on alpha-cyclodextrin and different alpha,omega-diaminoalkanes by NMR diffusion measurements

The interactions of 1,4-diaminobutane (1), 1,6-diaminohexane (2), 1,8-diaminooctane (3), 1,10-diaminodecane (4), and 1,12-diaminododecane (5) with alpha-cyclodextrin (alpha-CD) were studied in aqueous solutions by NMR diffusion measurements before and after protonation. The correlation between the association constant and the length of the alkyl chain of the diamine unit was studied. The assumption that protonation on the amino groups can be used as a stopper and, as a result, to convert the pseudorotaxanes into rotaxanes was tested. In addition, other factors that can affect the pseudorotaxane stability, such as the effects of temperature, were tested. On the basis of these measurements, the following conclusions could be reached: (1) The association constant increases with the increase in the alkyl chain length. (2) For the salts (2b-5b), both in neutral and in acidic solutions, the binding constants increase as the number of CH(2) units increases. (3) The association constants of the complexes of the diaminoalkane salts and alpha-CD are lower than those of the corresponding neutral diaminoalkanes. (4) This difference between the binding constants of the diaminoalkanes and their respective salts decreases as the chain length increases. (5) By examining the effects of temperature on the (1)H NMR spectra, it was found that after addition of DCl the energy barrier for the threading-dethreading process of the salt of 5a is larger than that for the salt of 4a.     

Self‐Assembled Cyclic d,l‐α‐Peptides as Generic Conformational Inhibitors of the α‐Synuclein Aggregation and Toxicity: In Vitro and Mechanistic Studies

Many peptides and proteins with large sequences and structural differences self‐assemble into disease‐causing amyloids that share very similar biochemical and biophysical characteristics, which may contribute to their cross‐interaction. Here, we demonstrate how the self‐assembled, cyclic d,l ‐α‐peptide CP‐2 , which has similar structural and functional properties to those of amyloids, acts as a generic inhibitor of the Parkinson′s disease associated α‐synuclein (α‐syn) aggregation to toxic oligomers by an ?off‐pathway“ mechanism. We show that CP‐2 interacts with the N‐terminal and the non‐amyloid‐β component region of α‐syn, which are responsible for α‐syn′s membrane intercalation and self‐assembly, thus changing the overall conformation of α‐syn. CP‐2 also remodels α‐syn fibrils to nontoxic amorphous species and permeates cells through endosomes/lysosomes to reduce the accumulation and toxicity of intracellular α‐syn in neuronal cells overexpressing α‐syn. Our studies suggest that targeting the common structural conformation of amyloids may be a promising approach for developing new therapeutics for amyloidogenic diseases.