Abstract A polyacrylate‐based monolithic column bearing cationic functionalities and designed for capillary electrochromatography (CEC) has been prepared via photopolymerization of a mixture of hexyl acrylate, butanediol diacrylate, 2‐(acryloyloxy) ethyltrimethyl ammonium chloride (monomers), azobisisobutyronitrile (photoinitiator), acetonitrile, phosphate buffer, and ethanol (porogens). The polymerization process was initiated with UV light at 360 nm. The column performance was evaluated via the separations of alkylbenzenes, substituted anilines, basic drugs, peptides, and a protein digest. The separation of complex peptide mixtures was then studied since such separations constitute a promising application of capillary electrochromatograhy. In particular, the effects of mobile phase composition, including ionic strength of the buffer solution and the percentage of acetonitrile on the retention factor, the column efficiency, and the resolution were determined. The separations were affected by both interaction of the peptides with the stationary phase and their own electrophoretic mobility. Excellent separations with column efficiencies of up to 160 000 plates/m were achieved for both a mixture of ten well‐defined peptides and a tryptic digest of cytochrome c. The fractions of eluent containing peptides of the digest separated in the monolithic column were collected and characterized using matrix‐assisted laser desorption ionization mass spectrometry.

A comparison of three samples of poly(3-hexylthiophene) having regioregularities of 86, 90, and 96% is used to elucidate the effect of regioregularity on polymer-fullerene-composite solar cell performance. It is observed that polymer samples with lower regioregularity are capable of generating fullerene composites that exhibit superior thermal stability. The enhanced thermal stability of the composites is attributed to a lower driving force for polymer crystallization in the less regioregular polymer samples, which is supported with two-dimensional grazing incidence X-ray scattering and differential scanning calorimetry measurements. Furthermore, it is demonstrated that all three polymer samples are capable of generating solar cells with equivalent peak efficiencies of approximately 4% in blends with [6,6]-phenyl-C61-butyric acid methyl ester. While it may be non-intuitive that polymers with lower regioregularity can exhibit higher efficiencies, it is observed that the charge-carrier mobility of the three polymers is on the same order of magnitude (10(-4) cm2 V(-1) s(-1)) when measured from the space-charge-limited current, suggesting that highly regioregular and crystalline polythiophenes are not required in order to effectively transport charges in polymer solar cells. Overall, these results suggest a design principle for semicrystalline conjugated polymers in fullerene-composite solar cells in which crystallization-driven phase separation can be dramatically suppressed via the introduction of a controlled amount of disorder into the polymer backbone.

The types of the immune responses generated against an antigen are determined by the intracellular fate of the antigen. Endogenous antigens are processed in the cytoplasm and initiate cytotoxic T lymphocyte (CTL) activation. In contrast, exogenous antigens are degraded in the lysosome (or phagolysosome) of antigen presenting cells (APCs), and induce antibody-mediated immune responses and assist CTL activation. Therefore, maximizing a desired response by controlling delivery pathways is indispensable in vaccine development and immunotherapy. New cleavable microparticles have been prepared for use as protein-based vaccine carriers by polymerizing water soluble monomers including a newly developed aliphatic monomer with a pendant primary amine group and a cleavable acetal linkage with a wholly aliphatic cleavable acetal cross-linker. Incorporation of the cleavable amine monomer in the polymerization mixture increased the encapsulation efficiency of a model antigen, ovalbumin. Ex vivo assays showed that the composition of the particles greatly affected the magnitude and the pathway of antigen presentations, which determine the type of immune responses. The degradable particles synthesized with the new cross-linker enhanced MHC I antigen presentation 2-3-fold over nondegradable particles. It was also found that, by adding 10% cationic cleavable monomers to the microparticles, MHC I restricted antigen presentation was enhanced ca. 75 times over that achieved with nondegradable particles. The microparticles introduced in this study can be further used for targeting and gene delivery due to functionalizable and cleavable cationic monomers in addition to degradability.

Morphological characterization has been used to explain the previously observed strong correlation between charge carrier mobility measured with thin-film transistors and the number-average molecular weight (MW) of the conjugated polymer regioregular poly(3-hexylthiophene). Atomic force microscopy and X-ray diffraction show that the low-mobility, low-MW films have a highly ordered structure composed of nanorods and the high-mobility, high-MW films have a less ordered, isotropic nodule structure. Modifying the morphology for a constant MW by changing the casting conditions or annealing the samples strongly affects the charge transport and morphology in the low-mobility, low-MW films, but has little effect on the high-MW films. In-plane grazing incidence X-ray scattering shows the in-plane π-stacking peak increases when the mobility increases for a constant MW. When the MW is changed, this correlation breaks down, confirming that in-plane π-stacking does not cause the mobility−MW relationship. We believe a combination of disordered domain boundaries and inherent effects of chain length on the electronic structure cause the mobility−MW relationship.

Monolithic poly(butyl methacrylate-co-ethylene dimethacrylate) columns have been prepared in capillaries ranging in inner diameter from 5 to 75 microm using thermally initiated free-radical polymerization of a mixture of butyl methacrylate, ethylene dimethacrylate, and porogens at different temperatures. Scanning electron microscopy and the measurement of hydrodynamic properties reveal that the downward scalability of the monolithic columns is greatly affected by the confinement effect of the capillary wall resulting from the decreased volume-to-surface ratio as the capillary diameter is decreased. The downscaling process is affected most by the polymerization temperature, the diffusion of the propagating radicals, and the density of coverage of polymerizable groups on the inner walls of the capillary. Optimization of all these factors enables the preparation of monolithic structures in capillaries with inner diameters as low as 5 microm while retaining the desirable properties of monoliths prepared in much larger capillaries. Under these conditions, formation of undesired dense polymer layers attached to the capillary wall was minimized. The chromatographic performance of 10, 25, and 50 microm capillaries evaluated in the reversed phase gradient separation of three proteins showed no change in elution times at identical flow velocities and gradient times, while peak elution width was the smallest with the narrowest capillary.

Despite the promise of precisely targeted or otherwise functionalized polymeric particulate drug delivery vehicles, typical biocompatible particles are generally not amenable to facile and selective surface modification. Herein, we report the development of a simple, mild, and chemoselective strategy for the conjugation of biologically active molecules to the surface of dextran-based microparticles. Alkoxyamine-bearing reagents were used to form stable oxime conjugates with latent aldehyde functionality present in reducing carbohydrate chain ends. We demonstrate the functionalization of dextran-based microparticles with a fluorophore as well as a cell-penetrating peptide sequence, which facilitated the delivery of cargo to nonphagocytic cells leading to a 60-fold increase in the expression of a reporter gene when plasmid DNA-loaded particles were used.

The active sites of metalloenzymes are often deeply buried inside a hydrophobic protein sheath, which protects them from undesirable hydrolysis and polymerization reactions, allowing them to achieve their normal functions. In order to mimic the hydrophobic environment of the active sites in bacterial monooxygenases, diiron(II) compounds of the general formula [Fe2([G-3]COO)4(4-RPy)2] were prepared, where [G-3]COO- is a third-generation dendrimer-appended terphenyl carboxylate ligand and 4-RPy is a pyridine derivative. The dendrimer environment provides excellent protection for the diiron center, reducing its reactivity toward dioxygen by about 300-fold compared with analogous complexes of terphenyl carboxylate ([G-1]COO-) ligands. An FeIIFeIII intermediate was characterized by electronic, electron paramagnetic resonance, Mössbauer, and X-ray absorption spectroscopic analyses following the oxygenation of [Fe2([G-3]COO)4(4-PPy)2], where 4-PPy is 4-pyrrolidinopyridine. The results are consistent with the formation of a superoxo species. This diiron compound, in the presence of dioxygen, can oxidize external substrates.

Biopharmaceuticals, such as proteins and DNA, have demonstrated their potential to prevent and cure diseases. The success of such therapeutic agents hinges upon their ability to cross complex barriers in the body and reach their target intact. In order to reap the full benefits of these therapeutic agents, a delivery vehicle capable of delivering cargo to all cell types, both phagocytic and non-phagocytic, is needed. This article presents the synthesis and evaluation of a microparticle delivery vehicle capable of cell penetration and sub-cellular triggered release of an encapsulated payload. pH-sensitive polyacrylamide particles functionalized with a polyarginine cell-penetrating peptide (CPP) were synthesized. The incorporation of a CPP into the microparticles led to efficient uptake by non-phagocytic cells in culture. In addition, the CPP-modified particles showed no cytotoxic effects at concentrations used in this study. The results suggest that these particles may provide a vehicle for the successful delivery of therapeutic agents to various cell types.

Complete statistical randomization of the direction of propagation of light trapped in semiconductor films can result in a large absorption enhancement. We have employed a calorimetric technique, photothermal deflection spectroscopy, to monitor the absorption of alpha-SiH(x) films textured by the natural lithography process. The observed enhancement factors, as high as 11.5, are consistent with full internal phase-space randomization of the incoming light.

Necessary and sufficient conditions are given for the uniqueness of solution of nonlinear resistive circuits made of strictly monotoneincreasing nonlinear resistors, dc sources, and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</tex> linear current-controlled current sources (CCCS's) or linear voltage-controlled voltage sources (VCVS's) whose controlling coefficients <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">{\alpha}_{\mu}</tex> are bounded by <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0&lt;{\alpha}_{\mu}&lt;{\alpha}_{\mu}max'{\mu} = 1,2,{\cdots}, k</tex> . These conditions are cast in explicit topological terms and are therefore easy to check.

This tutorial presents an in-depth introduction to chaos in dynamical systems, and presents several practical techniques for recognizing and classifying chaotic behavior. These techniques include the poincaré map, Lyapunov exponents, capacity, information dimension, correlation dimension, Lyapunov dimension, and the reconstruction of attractors from a single time series.

This paper provides a rigorous mathematical proof that the double scroll is indeed chaotic. Our approach is to derive a linearly equivalent class of piecewise-linear differential equations which includes the double scroll as a special case. A necessary and sufficient condition for two such piecewise-linear vector fields to be linearly equivalent is that their respective eigenvalues be a scaled version of each other. In the special case where they are identical, we have exact equivalence in the sense of linear conjugacy. An explicit normalform equation in the context of global bifurcation is derived and parametrized by their eigenvalues. Analytical expressions for various Poincaré maps are then derived and used to characterize the birth and the death of the double scroll, as well as to derive an approximate one-dimensional map in analytic form which is useful for further bifurcation analysis. In particular, the analytical expressions characterizing various half-return maps associated with the Poincaré map are used in a crucial way to prove the existence of a Shilnikov-type homoclinic orbit, thereby establishing rigorously the chaotic nature of the double scroll. These analytical expressions are also fundamental in our in-depth analysis of the birth (onset of the double scroll) and death (extinction of chaos) of the double scroll. The unifying theme throughout this paper is to analyze the double scroll system as an unfolding of a large family of piecewise-linear vector fields in <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R^3</tex> . Using this approach, we were able to prove that the chaotic dynamics of the double scroll is quite common, and is robust because the associated horseshoes predicted from Shilnikov's theorem are structurally stable. In fact, it is exhibited by a large family (in fact, infinitely many linearlyequivalent circuits) of vector fields whose associated piecewise-linear differential equations bear no resemblance to each other. It is therefore remarkable that the normalized eigenvalues, which is a local concept, completely determine the system's global qualitative behavior.

A detailed analysis is given of the geometric structure of a chaotic attractor observed from an extremely simple autonomous electrical circuit. It is third order, reciprocal, and has only one nonlinear element: a 3-segment piecewise-linear resistor. Extensive laboratory measurements from this circuit and a detailed geometrical analysis and computer simulation reveal the following rather intricate "anatomy" of the associated strange attractor. In addition to a microscopically infinite sheet-like composition the attractor has a macroscopic "double-scroll" structure, i.e., two sheetlike objects are curled up together into spiral forms with infinitely many rotations. (See frontispiece.) The chaotic nature of this circuit is further confirmed by calculating its associated Lyapunov exponents and Lyapunov dimension. The double-scroll attractor has one positive, one zero and one negative Lyapunov exponent. The Lyapunov dimension turns out to be a fractal between 2 and 3 which agrees with the observed structures. The power spectra of the three associated state variables obtained by both measurement and computer simulation show a continuous broad spectrum typical of chaotic systems.

Experimental evidence showing the existence of signal amplification via perturbation of periodic and chaotic orbits in an electronic circuit is presented.