Efficient complexation of pyrrole-bridged dizinc(II) bisporphyrin with fluorescent probe pyrene: synthesis, structure, and photoinduced singlet-singlet energy transfer

A diethylpyrrole‐bridged dizinc(II) bisporphyrin (Zn₂DEP) is reported that encapsulates fluorescent probe pyrene molecules through strong π–π interactions, which can relay information about the chemical environment in the interior of the host–guest supramolecular assembly. X‐ray structures of both Zn₂DEP and the encapsulated pyrene complex are reported, which provides a rare opportunity to investigate the structural changes upon guest binding. A comparative structural analysis demonstrated the exceptional ability of this bisporphyrin platform to open its binding pocket for pyrene encapsulation by a vertical displacement of more than 2.45 Å, although both Zn₂DEP and the pyrene complex have nearly parallel porphyrin ring orientations. The ¹H NMR spectrum of the encapsulated pyrene complex in solution shows the upfield shifts of the pyrene protons due to a strong ring current effect, which demonstrates the retention of the solid‐state structure in solution. To further assess the extent to which pyrene guests remain encapsulated in solution, a known fluorescence quencher, dimethylaniline, was added to the host–guest assembly, which shows no exciplex formation for days in nonpolar solvents. Thus, the assembly also retained the structural integrity in solution for a long time. The association constant (K_asso) for such a complexation process in solution was observed to be 1.78×10⁵ M ^?2 for 1:2 binding. Steady‐state fluorescence and lifetime studies indicate significant photoinduced singlet–singlet energy transformation from the excited state of pyrene to zinc bisporphyrin.     

S K-edge XAS and DFT calculations on SAM dependent pyruvate formate-lyase activating enzyme: nature of interaction between the Fe4S4 cluster and SAM and its role in reactivity

S K-edge X-ray absorption spectroscopy on the resting oxidized and the S-adenosyl-l-methionine (SAM) bound forms of pyruvate formate-lyase activating enzyme are reported. The data show an increase in pre-edge intensity, which is due to additional contributions from sulfide and thiolate of the Fe(4)S(4) cluster into the C-S σ* orbital. This experimentally demonstrates that there is a backbonding interaction between the Fe(4)S(4) cluster and C-S σ* orbitals of SAM in this inner sphere complex. DFT calculations that reproduce the data indicate that this backbonding is enhanced in the reduced form and that this configurational interaction between the donor and acceptor orbitals facilitates the electron transfer from the cluster to the SAM, which otherwise has a large outer sphere electron transfer barrier. The energy of the reductive cleavage of the C-S bond is sensitive to the dielectric of the protein in the immediate vicinity of the site as a high dielectric stabilizes the more charge separated reactant increasing the reaction barrier. This may provide a mechanism for generation of the 5'-deoxyadenosyl radical upon substrate binding.     

Biomimetic postcapillary expansions for enhancing rare blood cell separation on a microfluidic chip

Blood cells naturally auto-segregate in postcapillary venules, with the erythrocytes (red blood cells, RBCs) aggregating near the axis of flow and the nucleated cells (NCs)--which include leukocytes, progenitor cells and, in cancer patients, circulating tumor cells--marginating toward the vessel wall. We have used this principle to design a microfluidic device that extracts nucleated cells (NCs) from whole blood. Fabricated using polydimethylsiloxane (PDMS) soft lithography, the biomimetic cell extraction device consists of rectangular microchannels that are 20-400 μm wide, 11 μm deep and up to 2 cm long. The key design feature is the use of repeated expansions/contractions of triangular geometry mimicking postcapillary venules, which enhance margination and optimize the extraction. The device operates on unprocessed whole blood and is able to extract 94 ± 4.5% of NCs with 45.75 ± 2.5-fold enrichment in concentration at a rate of 5 nl s(-1). The device eliminates the need to preprocess blood via centrifugation or RBC lysis, and is ready to be implemented as the initial stage of lab-on-a-chip devices that require enriched nucleated cells. The potential downstream applications are numerous, encompassing all preclinical and clinical assays that operate on enriched NC populations and include on-chip flow cytometry (A. Y. Fu et al., Anal. Chem., 2002, 74, 2451-2457; A. Y. Fu et al., Nat. Biotechnol., 1999, 17, 1109-1111), genetic analyses (M. M. Wang et al., Nat. Biotechnol., 2005, 23, 83-87; L. C. Waters et al., Anal. Chem., 1998, 70, 5172-5176) and circulating tumor cell extraction (S. Nagrath et al., Nature, 2007, 450, 1235-1241; S. L. Stott et al., Proc. Natl. Acad. Sci. U. S. A., 2010, 18392-18397; H. K. Lin et al., Clin. Cancer Res., 2010, 16, 5011-5018).     

Noble metals in polyoxometalate chemistry: palladium-containing derivatives of the monolacunary Keggin and Wells-Dawson tungstophosphates

We have prepared the three novel Pd(II)-containing tungstophosphates [Pd(2)(α-PW(11)O(39)H(0.5))(2)](9-) and two structural isomers of [Pd(2)(α(2)-P(2)W(17)O(61)H(n))(2)]((16-2n)-) via simple synthetic procedures and characterized their potassium salts by single-crystal X-ray diffraction, elemental analysis, and IR and multinuclear ((31)P and (183)W) NMR spectroscopy. This study sheds light on the long-standing question about the nature and structure of the actual products formed in the reaction of Pd(II) ions with monolacunary Keggin-type [α-XW(11)O(39)](n-) and Wells-Dawson-type [α(2)-P(2)W(17)O(61)](10-) heteropolytungstates.     

2,7-Diaminofluorene-based organic dyes for dye-sensitized solar cells: effect of auxiliary donor on optical and electrochemical properties

New organic dyes containing a diarylaminofluorene unit as an electron donor and cyanoacrylic acid as acceptor and anchoring group in a donor-π-donor-π-acceptor architecture have been synthesized and characterized as sensitizers for nanocrystalline TiO(2)-based dye-sensitized solar cells. They have shown three major electronic absorptions originating from the π-π* and charge-transfer transitions covering the broad visible range (250-550 nm) in solution. The charge-transfer transition of the dyes exhibited negative solvatochromism, suggesting a polarized ground state. They have also displayed acidochromism in solution owing to the presence of a protonation-deprotonation equilibrium. On comparison with the triphenylamine and carbazole-based parent dyes (E)-2-cyano-3-(4-(diphenylamino)phenyl)acrylic acid and (E)-2-cyano-3-(9-ethyl-9H-carbazol-3-yl)acrylic acid they exhibited longer wavelength absorptions and facile oxidation, indicating the stronger electron-donating ability of the auxiliary chromophores. In addition, they exhibited nearly two times larger light-to-electron conversion efficiency under simulated AM 1.5 G irradiation (100 mW cm(-2)) with an aperture mask when compared to the parent dyes. Among the new dyes, the one containing the naphthylphenylamine segment showed better device characteristics attributable to the higher HOMO energy level which probably facilitates the regeneration of the dye and effective suppression of the back reaction of the injected electrons with the I(3)(-) in the electrolyte. The optical properties of the dyes were modeled using TDDFT simulations employing different theoretical models (B3LYP, CAM-B3LYP, and MPW1K), and the best correlations with the observed parameters have been found for CAM-B3LYP and MPW1K calculations. The electron lifetimes extracted from the electrochemical impedance measurements of the dye-sensitized solar cells were used to interpret the solar cell efficiency alternations.     

Thermal analyses of organic powders made from precipitation polymerization of triallyl monomers

Organic solids have been prepared from radical-initiated activation of solutions composed of tetradecane and triallyl trimesate (TAM) monomer or triallyl phosphate (TAP) monomer using a recently developed variation of precipitation polymerization methods. The powders, which comprise fused aggregates, are shown to be rich in monomer (83–88 wt% TAM or 86–92 wt% TAP), and are believed to be formed by a combination of hydrocarbon addition and allyl group oligomerization. TAM-g-tetradecane primary particles are on the order of 500 nm in diameter, while TAP-g-tetradecane particles are on the order of 100–200 nm diameter. These products are thermochemically assessed using a combination of differential scanning calorimetry, thermogravimetry and pyrolysis combustion flow calorimetry. The phosphorus-containing TAP-g-tetradecane shows exothermic activity around 230 °C, likely due to thermal decomposition of the trialkyl phosphate moiety, and may find use in advanced materials applications.     

Thermal conduction through loose and granular two-phase materials at normal pressure

The integrated theory derived for the lattice-type dispersions is modified and extended to estimate the effective thermal conductivity of loose and granular two-phase materials at normal pressure assuming an effective continuous media approximation. A comparison of calculated values ofλ _e with the reported experimental results over a wide range of loose and granular two-phase materials shows a good agreement.     

Effective thermal conductivity of granulated two-phase systems at interstitial air pressures

Considering the htermal conduction through molecular collisions an expression for the effective thermal conductivityλ _e of loose and granular two-phase materials at different interstitial air pressure has been derived. The dependence ofλ _e on pore and particle sizes, characteristic pressure and radiative heat transfer is also discussed. Calculated values ofλ _e of glass beads and loose building materials are compared with reported results.     

Heat transfer for laminar flow through parallel porous disks of different permeability

The problem of temperature distribution and heat transfer for laminar flow through two parallel porous disks of different permeability, has been investigated when the flow is entirely due to injection and/or suction at the two disks. Viscous dissipation terms have been included in the energy equation and the injection and/or suction velocities at the two disks are assumed to be small. The boundaries are kept at constant temperatures. The variation of temperature and Nusselt numbers at the two disks has been graphically depicted for various values of the injection and suction velocities.