Highly conductive electrostatically assembled porphyrazine films

The electrochemical and photoelectrochemical response of molecular films formed by (3,4-pyridyl)porphyrazine coordinated to four peripheral [Ru(bipy)₂Cl]⁺ groups (TRPz) has been investigated, in comparison with the corresponding electrostatic assembled bilayer films generated in the presence of the tetrasulfonate phthalocyaninatecopper(II) complex (CuTSPc). Both types of films are redox conductors, but an additional electron conduction mechanism through the stacked rings π system has been observed in the bilayer films, based on impedance spectroscopy. Their combined action promotes an enhanced photoaction response for the bilayer films in the presence of dissolved dioxygen.     

Four-way-branched DNA-porphyrin conjugates for construction of four double-helix-DNA assembled structures

[reaction: see text] DNA-porphyrin conjugates having four DNA strands were designed and synthesized. Four double helices were assembled using two DNA-porphyrin conjugates and their complementary strands, and the formation of the four double-helix assembled structures with the two DNA-porphyrin units was examined by gel electrophoresis and spectroscopic analysis. The interaction between two porphyrin chromophores in the complex was investigated by measurement of fluorescence lifetimes, and the singlet energy transfer between the two different phorphyrin units (Zn-porphyrin and H2-porphyrin) was observed. These results indicate that multiple and different porphyrin chromophores can be integrated into the DNA structures by programming the sequences of the DNA strands.     

Release of a dye from hydrogen-bonded and electrostatically assembled polymer films triggered by adsorption of a polyelectrolyte

The absorption of dyes within hydrogen-bonded and electrostatically assembled multilayers and subsequent release of the dyes from the films were studied in situ using FTIR-ATR. Multilayers were composed of poly(methacrylic acid), PMAA, and poly(ethylene oxide), PEO (hydrogen-bonded multilayers), or of PMAA and 22% quarternized copolymer of N-ethyl-4-vinylpyridium bromide and 4-vinylpyridine, Q22 (electrostatically stabilized multilayers). After multilayer deposition, the solution pH was changed to produce excess charge within the films. Dyes with charge opposite to the excess charge of the film (Rhodamine 6G for hydrogen-bonded films or Bromophenol Blue for electrostatically assembled multilayers) were then allowed to absorb within multilayers. In both systems, the dyes were uniformly included within the films. The top layers largely affected the loading capacity of the multilayers, suggesting weaker binding of the dyes with the top layers. Dye release into a 0.01 M phosphate buffer was significantly smaller as compared to release in the presence of 0.05-0.5 mg/mL solutions of adsorbing polymers whose charge was the same as the excess charge within the films. We found that with the PMAA/PEO films, dye release did not depend on the concentration of polymer in solution, but was largely controlled by the amount of charge accumulated within the adsorbing polymer layer on the top of the film. For electrostatically stabilized PMAA/Q22 systems, dye release increased with increasing concentration of Q22 in solution, suggesting a significant contribution of the competition of solution species in the release mechanism. Our findings contribute to the understanding of interactions of small molecules with polymer multilayers and might have ramifications for novel applications of multilayer films as new materials for the controlled delivery of chemicals.     

Charge transfer excitations in cofacial fullerene-porphyrin complexes

Porphyrin and fullerene donor-acceptor complexes have been extensively studied for their photo-induced charge transfer characteristics. We present the electronic structure of ground states and a few charge transfer excited states of four cofacial porphyrin-fullerene molecular constructs studied using density functional theory at the all-electron level using large polarized basis sets. The donors are base and Zn-tetraphenyl porphyrins and the acceptor molecules are C(60) and C(70). The complexes reported here are non-bonded with a face-to-face distance between the porphyrin and the fullerene of 2.7 to 3.0 A?. The energies of the low lying excited states including charge transfer states calculated using our recent excited state method are in good agreement with available experimental values. We find that replacing C(60) by C(70) in a given dyad may increase the lowest charge transfer excitation energy by about 0.27 eV. Variation of donor in these complexes has marginal effect on the lowest charge transfer excitation energy. The interfacial dipole moments and lowest charge transfer states are studied as a function of face-to-face distance.     

Distorted fused porphyrin-phthalocyanine conjugates: synthesis and photophysics of supramolecular assembled systems with a pyridylfullerene

In the current work, we report on the synthesis and photophysical features of supramolecular hybrid systems that are based on newly fused porphyrin-phthalocyanine (P-Pc) conjugates and a pyridylfullerene. The ZnP-ZnPc conjugate was synthesized in three steps starting with a Diels-Alder reaction between β-vinylporphyrin and fumaronitrile. The resulting mixture of isomeric adducts was then dehydrogenated to yield the corresponding benzo[b]porphyrin-2(1),2(2)-dicarbonitrile. In the final step, cyclotetramerization with 4-tert-butylphthalonitrile, in the presence of zinc acetate, afforded the bis-metalated conjugate. Selective demetallation of ZnP led to the H(2)P-ZnPc conjugate. For both conjugates steric hindrance is the inception to a bent configuration, which does, however, not preclude enlargement of the π-conjugated system, that is, the porphyrins and the phthalocyanines. The two conjugates coordinate N-(4-pyridyl)fullero[c]pyrrolidine giving rise to the corresponding supramolecular porphyrin-phthalocyanine-fullerene systems. Photophysical measurements corroborate a sequential deactivation in the excited state, namely an initial intramolecular energy transfer from ZnP or H(2)P to ZnPc followed by an intramolecular charge transfer to yield ZnP-(ZnPc)˙(+)-(C(60))˙(-) and H(2)P-(ZnPc)˙(+)-(C(60))˙(-), respectively.     

Synthesis of self‐assembled sphingolipid conjugates and their morphology effect on anticancer therapeutic potency

The shape of self‐assembling polymer–drug conjugates, influencing the cellular uptake, is one of the important factors to be considered for effective drug delivery. In this study, we described synthesis of polymeric drug conjugates of different morphologies with phytosphingosine (PHS) as a hydrophobic model drug and poly(amino acid) as a hydrophilic host polymer. By varying the amount of PHS grafted to poly(amino acid), PHS–poly(amino acid) conjugates exhibited morphological transition from spherical to worm‐like micellar aggregates in the aqueous media. We investigated the physicochemical properties of self‐assembled structures in terms of hydrodynamic size, surface charge, and critical aggregation concentration. The anticancer therapeutic potency of these self‐assembled structures was also discussed in terms of cellular uptake and cytotoxicity of prodrug micelles as a function of dose and time by in vitro cell study. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

A stable fullerene-azide building block for the construction of a fullerene-porphyrin conjugate

A stable C₆₀ derivative bearing an azide functional group was prepared and used as a building block under the copper-mediated Huisgen 1,3-dipolar cycloaddition conditions for the preparation of a fullerene-porphyrin conjugate.     

Colloid stability of electrostatically stabilized sols

 The dependence of the stability of SiO₂ and Al₂O₃ sols on the pH of their medium has been studied. Vapor adsorption isotherms on powders were prepared from acidic and basic sols, the immersion enthalpy (heat) of samples containing preadsorbed water have been determined and, also, the reversibility of the sol ⇌ xerogel transformation, i.e. the peptizability of the powders, has been investigated. Based on the flocculation values determined with KCl, the sols have been classified into three groups. The stability of highly hydrophilic sols (acidic SiO₂- and Al₂O₃-sols) is ensured by a thick continuous diffuse lyosphere formed around the particles, as the continuity principle by Ostwald–Buzágh suggests. In this case, no electric charge is needed for ensuring stability. These sols are thermodynamically stable (group 1). Sols with medium stability are stabilized by the electrical double layer around the particles and by 1–2 layers of adsorbed water. The flocculation value of these sols is determined by the electrostatic interaction, whereas the peptizability of the flocs is related to formation of water layers. Such sols are the basic SiO₂- and Al₂O₃-sols (group 2). Sols of low stability are of hydrophobic nature. Their flocculation value with 1:1 electrolytes is smaller than 0.1 molkg^-1. The transformation process sol ⇒ floccule ⇒ xerogel is mostly irreversible. There are a lot of such sols (group 3). The existence of a hydrosphere is proved by the almost identical value of the hydration energy for both the acidic and the basic SiO₂ sols, in spite of an order of magnitude difference in the flocculation value. The remnants of adsorbed water after drying hinders sintering of the particles and ensures the peptizability of powders. The highly hydrophilic sols (sequence of hydrophilicity: SiO₂> Al₂O₃>FeO OH ⋅ 0.5 H₂O) are all oxides which are formed in acidic media. Received: 25 May 1997 Accepted: 13 October 1997     

Supramolecular fullerene-porphyrin chemistry. Fullerene complexation by metalated "jaws porphyrin" hosts

Porphyrins and fullerenes are spontaneously attracted to each other. This new supramolecular recognition element is explored in discrete, soluble, coordinatively linked porphyrin and metalloporphyrin dimers. Jawlike clefts in these bis-porphyrins are effective hosts for fullerene guests. X-ray structures of the Cu complex with C60 and free-base complexes with C70 and a pyrrolidine-derivatized C60 have been obtained. The electron-rich 6:6 ring-juncture bonds of C60 show unusually close approach to the porphyrin or metalloporphyrin plane. Binding constants in toluene solution increase in the order Fe(II) < Pd(II) < Zn(II) < Mn(II) < Co(II) < Cu(II) < 2H and span the range 490-5200 M-1. Unexpectedly, the free-base porphyrin binds C60 more strongly than the metalated porphyrins. This is ascribed to electrostatic forces, enhancing the largely van der Waals forces of the pi-pi interaction. The ordering with metals is ascribed to a subtle interplay of solvation and weak interaction forces. Conflicting opinions on the relative importance of van der Waals forces, charge transfer, electrostatic attraction, and coordinate bonding are addressed. The supramolecular design principles arising from these studies have potential applications in the preparation of photophysical devices, molecular magnets, molecular conductors, and porous metal-organic frameworks.     

Surface micromachined electrostatically actuated micro peristaltic pump

An electrostatically actuated micro peristaltic pump is reported. The micro pump is entirely surface micromachined using a multilayer parylene technology. Taking advantage of the multilayer technology, the micro pump design enables the pumped fluid to be isolated from the electric field. Electrostatic actuation of the parylene membrane using both DC and AC voltages was demonstrated and applied to fluid pumping based on a 3-phase peristaltic sequence. A maximum flow rate of 1.7 nL min(-1) and an estimated pumping pressure of 1.6 kPa were achieved at 20 Hz phase frequency. A dynamic analysis was also performed with a lumped-parameter model for the peristaltic pump. The analysis results allow a quantitative understanding of the peristaltic pumping operation, and correctly predict the trends exhibited by the experimental data. The small footprint of the micro pump is well suited for large-scale integration of microfluidics. Moreover, because the same platform technology has also been used to fabricate other devices (e.g. valves, electrospray ionization nozzles, filters and flow sensors), the integration of these different devices can potentially lead to versatile and functional micro total analysis systems (microTAS).     

Colloidal stability of electrostatically stabilized sol particles.

The colloid stability of ferric hydroxide sol has been investigated at three different HCl concentrations. The total HCl concentration in the sols was A>B>C, the amount of HCl adsorbed was A=B>C. The parameters which characterize the stability (flocculation value, gelation concentration, repeptizability) are related to the amount of adsorbed HCl, because this property governs the hydrophility of the sols. In contrast, the peptizability of powders after drying the sols depends on the total concentration of HCl in the system. The hydrochloric acid impedes the condensation of surface groups to Fe–O–Fe bonds.From water vapor adsorption and heat of immersion data the hydration potential barrier is constructed which is comparable to the barrier according to the DLVO theory The differences and anomalies in the stability of sols are interpreted as differences in the hydrophility of samples.     

糖类的毛细管电泳及芯片毛细管电泳

 糖类化合物在生物体内发挥多方面的作用。糖研究的复杂性在于其结构的复杂多变。高效毛细管电泳作为一种快速、高效的分离分析手段已广泛应用于糖的研究。芯片毛细管电泳是近几年来发展起来的新的分析技术 ,并已经在生命科学的研究中得到较广泛的应用。就各种糖类化合物的毛细管电泳的分析策略、检测条件及糖类化合物的芯片毛细管电泳进行了阐述 ,共 4 8篇。     

Surface plasmon resonance spectroscopy study of electrostatically adsorbed layers

The use of 4-(dimethylamino)pyridine to form an adhesion layer for the adsorption of anionic polyelectrolytes on gold surfaces is investigated. In situ surface plasmon resonance spectroscopy is used to monitor the changes in thickness of the adsorbed layers as a function of pH changes. Weak (poly(acrylate)) and strong (poly(styrenesulfonate)) polyelectrolytes have been studied. Although 4-(dimethylamino)pyridine is weakly bound to gold, it is not displaced by these polyelectrolytes and acts as an adhesion layer. The relationship of the interaction of anionic polyelectrolytes with 4-(dimethylamino)pyridine-modified planar gold and gold nanoparticles is discussed.     

Reduction kinetics of hydrogen ion immobilized electrostatically on polystyrene latex

The reduction current of the hydrogen ion immobilized electrostatically by the sulfonated polystyrene latex charge showed much larger temperature dependence of an Arrhenius type than that of a free hydrogen ion when the latex suspension included no supporting electrolyte. The activation energy, 14 kJ mol⁻¹, suggests that the immobilization should be attained by a local potential minimum and a maximum rather than a monotonic attractive potential between the hydrogen ion and the latex particle. The temperature dependence decreased with the addition of supporting electrolyte. The mono-dispersed latex particle was synthesized so that the charge number (27 200e) became large. Its diameter was 134 nm and the uniformity ratio was 1.01.     

Structure and dynamics of electrostatically interacting magnetic nanoparticles in suspension

We investigate the structure and dynamics of charge-stabilized CoFe(2)O(4)-SiO(2) core-shell magnetic nanoparticles in suspensions. Small angle x-ray scattering and x-ray photon correlation spectroscopy allow us to analyze the intraparticle (core-shell) and interparticle structure of the suspension, as well as their dynamic and hydrodynamic behavior. Due to the weak magnetic interactions, the liquidlike structure is governed by screened Coulomb interactions. The hydrodynamic interactions of the measured systems are significantly stronger than predicted by current theories.