Orthogonal, convergent syntheses of dendrimers based on melamine with one or two unique surface sites for manipulation

An orthogonal, convergent route for the introduction of substoichiometric numbers of latent surface sites into dendrimers based on melamine is used to prepare targets that display one or two Boc-protected amines on the periphery. Asymmetry is the result of the stepwise incorporation of functionalized and unfunctionalized dendrons onto the triazine cores, a highly selective process due to the different reactivities of the substituted triazines. The routes to the dendrons rely on iterative reactions of the growing dendrons with triazine cores and diamine linkers. p-Aminobenzylamine is used as a linking group to avoid functional group interconversions or protecting group manipulations. Addition of the benzylamine group to the monochlorotriazine of the dendron proceeds cleanly leaving a less reactive aniline for subsequent reaction with trichlorotriazine. The routes to these targets proceed in 5 or 6 linear steps (11 or 12 total steps) in 40% overall yield. The unique surface sites can be deprotected and subjected to additional chemistries. Reaction of the monofunctionalized dendrimer with trichlorotriazine yields the desired dimer, a molecule whose increased size is evident from light scattering and tapping mode atomic force microscopy, and corroborated with computation.     

Electrogenerated chemiluminescence of conjugated polymer films from patterned electrodes

A new phenomenon is presented in which electrogenerated chemiluminescence (ECL) is generated and propagates laterally as self-reinforcing waves as a result of the oxidation of a poly(9,9-dioctylfluorene-co-benzothiadiazole) thin film. In an ordered array of Au electrode posts that act as effective ECL nucleation sites, soliton-like waves were observed to expand from each site and annihilate upon collision with each other. Simulations of the ECL response supported the experimental observations that the ECL waves propagate at a constant speed. A correlated diffusion mechanism involving the correlated motion of ions, injected holes, and solvent molecules is proposed to interpret the experimental data qualitatively. A rapid increase in the diffusion coefficient of these species in the polymer results in a sharp interface between non-oxidized and oxidized polymer phases wherein the electrochemical (EC) oxidation and mass transport of all pertinent species take place. EC oxidation of conjugated polymers of this type has important implications for the understanding of these materials and their modes of operation in EC conjugated polymer devices.     

Links between microscopic and macroscopic fluid mechanics

The microscopic and macroscopic versions of fluid mechanics differ qualitatively. Microscopic particles obey time-reversible ordinary differential equations. The resulting particle trajectories {q(t)} may be time-averaged or ensemble-averaged so as to generate field quantities corresponding to macroscopic variables. On the other hand, the macroscopic continuum fields described by fluid mechanics follow irreversible partial differential equations. Smooth particle methods bridge the gap separating these two views of fluids by solving the macroscopic field equations with particle dynamics that resemble molecular dynamics. Recently, nonlinear dynamics have provided some useful tools for understanding the relationship between the microscopic and macroscopic points of view. Chaos and fractals play key roles in this new understanding. Non-equilibrium phase-space averages look very different from their equilibrium counterparts. Away from equilibrium the smooth phase-space distributions are replaced by fractional-dimensional singular distributions that exhibit time irreversibility.     

Gaussian Property of the Rings R(X) and R〈X〉

The content of a polynomial f over a commutative ring R is the ideal c(f) of R generated by the coefficients of f. A commutative ring R is said to be Gaussian if c(fg) = c(f)c(g) for every polynomials f and g in R[X]. A number of authors have formulated necessary and sufficient conditions for R(X) (respectively, R?X?) to be semihereditary, have weak global dimension at most one, be arithmetical, or be Prüfer. An open question raised by Glaz is to formulate necessary and sufficient conditions that R(X) (respectively, R?X?) have the Gaussian property. We give a necessary and sufficient condition for the rings R(X) and R?X? in terms of the ring R in case the square of the nilradical of R is zero.     

A Simple Lithographic Approach for Preparing Patterned,Micron-Scale Corrals for Controlling Cell Growth

Hydrophobic n -alkanethiolate bottoms and walls consisting of hydrophilic three-layer poly(acrylic acid)/poly(ethylene glycol) nanocomposite polymers are used for making patterned corrals having lateral dimensions of 63 μm. Macrophage cells are confined within these corrals and are unable to grow over the corral walls (see picture).     

Electrogenerated Chemiluminescence of Pure Polymer Films and Polymer Blends

We recently reported the discovery of soliton‐like electrogenerated chemiluminescence (ECL) waves from pure conjugated polymer films and gold‐nanoparticles‐doped polymer films. In addition to a more detailed study of these polymer systems by changing the film thickness and the distribution of local leaks, we also apply the ECL wave phenomenon to polymer blends of conjugated and nonconjugated polymers. Poly(9,9‐dioctylfluorene‐co‐benzothiadiazole) (F8BT) is used as the active material that is oxidized and produces ECL with the presence of a co‐reactant, tri‐n‐propylamine (TPA). Several factors such as film thickness, artificial leaks, and solubility of doped polymers are examined for their effects on the ECL behavior. When polystyrene (PS), less soluble in the electrolyte, is blended with F8BT, dotted ECL signals are observed and transported as waves. When poly(methyl methacrylate) (PMMA), more soluble in the electrolyte, is blended with F8BT, PMMA serves as local scratches and ECL waves are triggered simultaneously from the whole film.

     

Solubilization chromatography: Ethers,carboxylic acids,and hydrocarbons

Synthetic mixtures of aliphatic and aromatic ethers, satmated fatty acids, and substituted benzenes and naphthalenes were separated by elution through columns of ion-exchange resins with aqueous solutions of acetic acid as eluent An attempt was made to use a resin of low capacity for the separation of such mixtures, and the results of this attempt are used to help elucidate the theory of solubilization chromatography     

Corona discharge ion sources for fine particle charging

Charging of aerosol droplets and solid particles is applied in many industrial processes such as electrostatic painting, particle separation and electrostatic precipitation. In most of charging devices, electrical discharges are used as a source of ions, which are deposited onto the particles. In the present paper, the charging process by ionic current in alternating electric field was optimized experimentally. Alternating electric field charger was used as a charging device in these experiments. The current voltage characteristics of electrical discharge in this device, and the charge imparted to the particles were determined. The level of charge was measured at the outlet of the charger and was compared to the Pauthenier limit for different supply voltages, and frequencies. MgO powder was used as a source of particles in these experiments. It was noticed that higher supply voltage of the charger gives higher level of particle charge, but at the same time, the particle deposition on the charger elements was increased, decreasing the particle penetration. A compromise between these two tendencies is therefore necessary. As a result we have proposed a criterion maximizing the total charge born by the particles which is a product of relative particle charge and particle penetration.