Fluorophores of lipofuscin granules responsible for human eye fundus autofluorescence

Individual fluorophores and/or their groups contained in a chloroform extract of lipofuscin granules isolated from retinal pigment epithelium of human cadaver eyes were studied by HPLC. Their spectral characteristics were studied, which made it possible to evaluate the contribution of particular fluorophores and/or their groups to the general image of human eye fundus autofluorescence. Many components, being conjugates of all-trans-retinal of different nature, contribute to the total fluorescence spectrum of the chloroform extract. The fluorophore A2E is not predominant.     

Novel example of a chain structure formed by 1,4-dioxane and cobalt(II) links. Chain [Co3(mu-OOCCF3)4(mu-H2O)2(OOCCF3)2(H2O)2(C4H8O2)].2C4H8O2

The trimer [Co3(mu-OOCCF3)4(mu-H2O)2(OOCCF3)2(H2O)2(C4H8O2)].2C4H8O2. (1) is composed of three tetragonally distorted Co(II) centers bridged by four trifluoroacetates and two bridging water molecules. 1,4-Dioxane is coordinated at a distance of 2.120(3) A from the terminal cobalt Co2; the remaining oxygen of this 1,4-dioxane links the terminal cobalt to a neighbor trimer, forming a one-dimensional chain. The crystal structure displays a network of hydrogen bonds between four noncoordinated 1,4-dioxane molecules and the coordinated terminal water molecules. The magnetic properties of 1 were analyzed with the use of the Hamiltonian including isotropic exchange interactions between real spins of a high-spin Co(II), spin-orbit coupling and a low-symmetry crystal field acting within the (4)T(1g) ground manifold of each cobalt ion. A weak antiferromagnetic exchange interaction between cobalt ions in 1 was found. The results of the magnetic model are in good agreement with the experimental observations.     

On the Limit Lognormal and Other Limit Log-Infinitely Divisible Laws

The limit log-infinitely divisible multifractals of Muzy and Bacry (Phys. Rev. E 66:056121, 2002) are reviewed and shown to possess novel invariance relations that translate into functional Feynman-Kac equations for the corresponding probability distributions. In the special case of the limit lognormal process of Mandelbrot (in Statistical Models and Turbulence, M. Rosenblatt, C. Van Atta (Eds.), Springer, New York, 1972), the limit distribution is represented exactly in an operator form using the technique of intermittency expansions. A novel representation for the Mellin transform of the limit distribution is derived and related to the Hurwitz zeta function. For application, the cumulants of the logarithm of the limit lognormal distribution are computed explicitly.     

Density of prelocalized states in mesoscopic NS systems

The semiclassical theory of the proximity effect predicts the formation of a gap E _g ～?D/L ² in the excitation spectrum of a diffusive contact between a normal metal and a superconductor (NS). Mesoscopic fluctuations lead to the emergence of states localized anomalously in the normal metal and weakly linked with the superconducting bank, creating a nonzero density of states for energies lower than E _g . In this review, the behavior of the density of quasiparticle states below a quasi-classical gap is considered for various geometries of the NS system (special attention is paid to SNS junctions) and for the problem of a superconductor with a low concentration of magnetic impurities, in which a similar effect is observed. Analysis is mainly carried out on the basis of a fully microscopic method of the supermatrix σ model; in this method, a nonzero density of states emerges due to instanton configurations with broken supersymmetry. In addition, the results of an alternative approach proceeding from the idea of universality of the spectra of random Hamiltonians with the given symmetry are reviewed. In situations studied using both methods, the results are identical. They include the exact expression for the mean density of states of an NS system in the vicinity of E _g . In the framework of 1D and 2D σ models, the subgap density of states is determined with an exponential accuracy. The contacts with a poor transparency of the NS interface are also considered. It is shown that the number of subgap states in the case of low transparency is much greater than unity.

     

Coulomb effects in a nanoscale SINIS junction

We study a system of two superconductors connected by a small normal grain. We consider the modification of the Josephson effect by the Coulomb interaction on the grain. Coherent charge transport through the junction is suppressed by Coulomb repulsion. An optional gate electrode may relax the charge blocking and enhance the current leading to the single Cooper pair transistor effect. Temperature dependences of critical current and of the minigap induced in the normal grain by the proximity to superconductor are studied. Both temperature and Coulomb interaction suppress critical current and minigap, but their interplay may lead to the nonmonotonic and even reentrant temperature dependence.     

Interaction of pyridinium bis-retinoid (A2E) with bilayer lipid membranes

The accumulation of lipofuscin granules within the retinal pigment epithelium (RPE) cells is correlated with the progression of age-related macular degeneration. One of the fluorophores contained in lipofiscin granules is pyridinium bis-retinoid (A2E). To test its membrane-toxic effect, the interaction of A2E with bilayer lipid membranes (BLM) was studied. The incorporation of charged A2E molecules into the membranes has been detected as a change of either zeta-potential of multilayer liposomes or boundary potential of BLM. It was shown that the presence of up to 25mol% of A2E did not destabilize the bilayers made of saturated phosphatidylcholine (PC). However, the destabilizing effect became very significant when BLM contained negatively charged lipids such as cardiolipin or phosphatidylserine. The electrical breakdown measurements revealed that the A2E-induced decrease of BLM stability was primarily associated with the growing probability of lipid pore formation. It was found from the measurements of boundary potential of BLM that exposure of A2E to light initiates its transformation into at least two products. One of them is epoxy-A2E, which, being hydrophilic, moves from the membrane into water solution. The other product is a non-identified hydrophobic substance. Illumination of A2E-containing BLM made from unsaturated PC by visible light caused the membrane damage presumably due to oxidation of these lipids by singlet oxygen generated by excited A2E molecules. However, this effect was very weak compared to the effect of known photosensitizers. The illumination of BLM with A2E also leads to the damage of gramicidin incorporated into the membrane, as was detected by measuring the conductance of channels formed by this peptide.     

Functional Feynman-Kac Equations for Limit Lognormal Multifractals

A novel technique of functional Feynman-Kac equations is developed for the probability distribution of the limit lognormal multifractal process introduced by Mandelbrot [in Statistical Models and Turbulence, M. Rosenblatt and C. Van Atta, eds., Springer, New York (1972)] and constructed explicitly by Bacry, Delour, and Muzy [Phys. Rev. E 64:026103 (2001)]. The distribution of the process is known to be determined by the complicated stochastic dependence structure of its increments (SDSI). It is shown that the SDSI has two separate layers of complexity that can be captured in a precise way by a pair of functional Feynman-Kac equations for the Laplace transform. Exact solutions are obtained as power series expansions in the intermittency parameter using a novel intermittency differentiation rule. The expansion of the moments gives a new representation of the Selberg integral. The author wishes to express gratitude to the Mathematics Department of Lehigh University for generous support during his stay at Lehigh University, where this article was written.     

Wannier-Type Threshold Laws for Multifragmentation and Thomson’s Problem

Wannier-type threshold theory for multiple break-up processes is based on the existence of special classical trajectories which represent partial fixed points of the equations of motion in a system of charged particles. These trajectories preserve the shape of the initial configuration while only changing its overall size in time. The relation between such scaling configurations and Thomson’s (or surface Coulomb) problem is analyzed. In particular, it is shown that for eight electrons the twisted cube configuration solves Thomson’s problem and also governs the threshold break-up of eight electrons receding from a charged core. The relevant exponents for the threshold power law are evaluated.     

Short-chain peptides as a promising class of chaperone-like anticataract agents: Molecular mechanism of inhibition of crystallin aggregation by pantethine

The molecular mechanism of inhibition of UV-induced aggregation of a mixture of gA and gB_L-crystallins in the presence of pantethine, a representative of a new promising class of chap-erone-like anticataract agents, was studied in vitro. Pantethine (5–25 mmol L^-1) enhances the chaperone-like properties of gA-crystallin and also functions as an UV filter by decreasing the amount of UV light falling on gB_L-crystallin. Using a fluorescence probe, 1,1’-bis(4-anilino-naphthalene-5-sulfonic acid), it was found that pantethine considerably increases the number of binding sites for hydrophobic substrates on the gA-crystallin molecule. By dynamic light scattering, it was shown that the presence of pantethine increases the size of the gA-crystallin molecule.