Donor-acceptor phthalocyanine nanoaggregates

A novel donor-acceptor bisphthalocyanine (bis-Pc, 1) in which two different Pc units (Zn(II)-Pc and Ni(II)-Pc) are linked via vinylene spacers to the pseudopara positions of a central [2.2]paracyclophane moiety is described. The synthesis of 1 is achieved by two successive Heck reactions of pseudopara-divinyl[2.2]paracyclophane 9 with, sequentially, a zinc(II)- and a nickel(II)-iodophthalocyanine (4 and 5, respectively). The self-assembly ability of 1, which is the result of the complementary donor-acceptor character of its phthalocyanine units, has been assessed by a variety of techniques. It is revealed that 1 forms one-dimensional aggregates of nanometer-sized dimension, whereas equimolar mixtures of the donor and acceptor Pc subunits 2 and 3, although strongly interacting, do not give large arrays. The aggregates of 1 represent a novel type of supramolecular polymers based mainly upon donor-acceptor interactions.     

Highly negative homotropic allosteric binding of viologens in a double-cavity porphyrin

The synthesis of a double-cavity porphyrin with interesting allosteric binding properties toward viologens (N,N'-disubstituted 4,4'-bipyridines) is described. The porphyrin host forms very strong 1:2 complexes with viologens, displaying a negative allosteric behavior. The first viologen guest binds exceptionally tight (K > 107 M-1), and the second guest binds much more weakly (DeltaDeltaG = 9-15 kJ mol-1). The allosteric effect, one of the highest reported so far, originates in structural changes upon binding the first ligand, closely following the sequential (or induced-fit) theory of allosteric interactions by Koshland, Némethy, and Filmer (the KNF-model).     

Creating effective refractive index gradients within polyelectrolyte multilayer films: molecularly assembled rugate filters

We demonstrate the use of aqueous-based layer-by-layer (LbL) processing and in situ nanoreactor chemistry for creating polyelectrolyte multilayer (PEM) nanocomposites in which the concentration of a nanoparticle species is modulated throughout the depth of the film in a complex way. Using the in situ growth of silver nanoparticles to selectively increase the refractive index of precisely defined regions of the PEM film, we have produced a digitized rugate filter, a special type of dielectric mirror possessing many thin layers that approximate a continuous, periodic refractive index profile. The design of the digital rugate from an initial smooth index profile was aided by a computer, and construction of the device was accomplished entirely by automated means. Poly(allylamine hydrochloride) (PAH) and poly(acrylic acid) (PAA) bilayer regions within the film supported subsequent nanoreactor chemistry and created the high refractive index regions of the film, while PAH and poly(styrenesulfonate) (PSS) bilayer regions remained unmodified and served as the low index regions. Spectroscopic results obtained from the assembled device confirm the presence of a reflection band that grows in amplitude with increasing silver incorporation, reaching a peak reflectance of 75% after five silver loading and exchange cycles. The rugate structure suppresses reflection sidebands, features common to Bragg reflectors and simpler dielectric mirror designs. Cross-sectional TEM reveals nanoscale control of the size and location of silver-containing domains within the PEM film. The ability of this method to control the placement of nanoparticles within PEMs enables the inexpensive, easy production of conformable optical coatings with tunable properties. In addition, these nanocomposite films may have applications in a number of other fields where precise control of effective gradients in physical properties throughout thin films has been shown to affect the overall performance in a desirable way.     

Observation of new nuclides37Si,40P,41S,42S produced in deeply inelastic reactions induced by40Ar on238U

A non-relativistic quantum-mechanical system is studied which consists ofN identical bosons interacting by pair potentials of the form 〈r¦V¦r ¹〉=?π/2ν ₀ a ^?3 f(r/a)f ^*(r ¹/a). General upper and lower bounds to the ground-state energyE _N are provided for alla, V ₀ andN, and detailed results are given in the case of the Yamaguchi potential for whichf(x)=e ^?x/x. It is shown that the ratioE _N /E ₂ diverges both under the limit (i) a↓0,E ₂ =arbitrary constant <0, and (ii) (V ₀ a ²)↓(V ₀ a ²)_c, where (V ₀ a ²) _c corresponds toE ₂=0. The results complement recent studies of the Efimov effect via scattering theory.     

Eine projektive Spiegelungsgruppe,welche S-Gruppe ist

Let be a projective plane with the flag (A,b). Assume that there exist all involutory homologies with centres on b and axis through A. Let G be the collineation group generated by the set S of all these involutory homologies. It is shown that is a pappian plane if (G,S) is an S - group.     

Construction of supramolecular multi-component assemblies by using allosteric interactions

Supramolecular complexes between two cavity-appended porphyrin hosts and three bifunctional guests are described. The host with a single cavity exclusively forms dimers with the bifunctional guests, while the double cavity host yields tetramers and higher order assemblies. The role of allosteric interactions in the binding and assembly process is highlighted.     

Surface solitons at interfaces of arrays with spatially modulated nonlinearity

We address the properties of two-dimensional surface solitons supported by the interface of a waveguide array whose nonlinearity is periodically modulated. When the nonlinearity strength reaches its minima at the points where the linear refractive index attains its maxima, we found that nonlinear surface waves exist and can be made stable only within a limited band of input energy flows and for lattice depths exceeding a lower threshold.     

Angular surface solitons in sectorial hexagonal arrays

We report on the experimental observation of corner surface solitons localized at the edges joining planar interfaces of hexagonal waveguide array with uniform nonlinear medium. The face angle between these interfaces has a strong impact on the threshold of soliton excitation as well as on the light energy drift and diffraction spreading.     

Functional imaging in photorefractive tissue speckle holography

Cellular motion produces highly dynamic speckle in wide-field depth-gated holographic optical coherence imaging. The speckle provides cell scale information such as cell membrane and organelle motion, even though the spatial resolution of the optics is above the cell scale. The statistical properties of dynamic speckle can be used for functional imaging of motile activity at depth within tissue. In this paper we develop a motility metric using time autocorrelation to create a three-dimensional motility map of tissue. The effect of noise and the shimmering showerglass effect in functional optical coherence imaging are evaluated quantitatively, and we demonstrate that meaningful motility information can be extracted from functional imaging using dynamic speckle.