Perturbation of fluorescence by nonspecific interactions between anionic poly(phenylenevinylene)s and proteins: implications for biosensors

The use of anionic water-soluble conjugated polymers (CPs) for sensing the presence of avidin by use of a biotin-modified fluorescence quencher was studied. The molecules involved in the study included poly[2-methoxy-5-(3'-propyloxysulfonate)-1,4-phenylenevinylene] with either lithium (Li+-MPS-PPV) or sodium (Na(+)-MPS-PPV) countercations, the well-defined oligomer pentasodium 1,4-bis(4'(2",4"-bis(butoxysulfonate)-styryl)-styryl)2-butoxysulfonate-5-methoxybenzene (5R5-), the quenchers N-methyl-4,4'-pyridylpyridinium iodide (mMV+) and [N-(biotinoyl)-N'-(acetyl 4,4'-pyridylpyridinium iodide)] ethylenediamine (BPP+), which contains a molecular recognition fragment (biotin) attached to a unit that accepts an electron from a CP excited state, and the proteins avidin, tau, BSA, and pepsin A. Fluorescence quenching experiments were examined in a variety of conditions. Experiments carried out in water and in ammonium carbonate buffer (which ensures avidin/biotin complexation) reveal that nonspecific interactions between the CP and the proteins cause substantial perturbations on the CP fluorescence. The overall findings are not consistent with a simple mechanism whereby avidin complexation of BPP+ leads to encapsulation of the quencher molecule and recovery of Li+-MPS-PPV fluorescence. Instead, we propose that binding of BPP+ to avidin results in the quenching unit attaching to a positively charged macromolecule. Electrostatic attraction to the negatively charged conjugated polymer results in closer proximity to the quencher. Therefore, more enhanced fluorescence quenching is observed.     

Diffraction characteristics of planar absorption gratings

Planar (co)sinusoidal conductivity (absorption) transmission gratings are analyzed using rigorous coupled-wave theory. The first-order and higher-order diffraction efficiencies are determined over the entire range of possible conductivities and Bragg angles of incidence (or equivalently, grating periods) for H-mode polarization incident plane waves. The maximum possible first diffracted order efficiency is found to be 5.26%. Rigorous results are compared to approximate results from the Raman-Nath theory and the two-wave first-order coupled-wave (Kogelnik) theory. A regime parameter, , is defined which delineates the regions of Raman-Nath diffraction behavior ( < 1) and the region of two-wave first-order diffraction theory behavior ( > 1). Likewise, the angular selectivity characteristics of conductivity gratings are determined from rigorous theory and are compared with corresponding results from approximate theory.     

Effect of chromophore-charge distance on the energy transfer properties of water-soluble conjugated oligomers

The synthesis of 1,4-bis(9,9'-bis(3"-(N,N,N-trimethylammonium)-propyl)-2'-fluorenyl)benzene tetrabromide (C3), 1,4-bis(9,9'-bis(4"-(N,N,N-trimethylammonium)-butyl)-2'-fluorenyl)benzene tetrabromide (C4), 1,4-bis(9,9'-bis(6"-(N,N,N-trimethylammonium)-hexyl)-2'-fluorenyl)benzene tetrabromide (C6), and 1,4-bis(9,9'-bis(8"-(N,N,N-trimethylammonium)-octyl)-2'-fluorenyl)benzene tetrabromide (C8) is reported. Fluorescence energy transfer experiments between C3-C8 and the acceptors pentasodium 1,4-bis(4'(2",4"-bis(butoxysulfonate)-styryl)styryl)-2-(butoxysulfonate)-5-methoxybenzene (3), fluorescein labeled single-stranded DNA and fluorescein labeled double-stranded DNA in water, buffer, and methanol reveal the importance of hydrophobic and electrostatic forces in determining chromophore-chromophore close proximity. In water, the oligomers with longer side chain length show better energy transfer, as well as higher Stern-Volmer quenching constants (K(sv)), largely due to a stronger hydrophobic attraction between the optically active components. In methanol, the differences in energy transfer are leveled, and the oligomers with shorter side chain lengths show higher K(sv) values. Compounds C3, C4, C6, and C8 were also used to dissect the different contributors to DNA hybridization assays based on cationic conjugated polymers.     

AlEt3–metal soap catalysts for the polymerization of epoxides

Epoxides, propylene oxide in particular, were polymerized by a catalyst system consisting of AlEt₃–metal soap, to high molecular weight polyethers in high conversion. Carboxylic acid salts of Ti, V, Cr, Zr, Mo, Co, and Ni, transition metals of groups IV–VIII in the Periodic Table, were most preferable. Metal salts of stearic, octanoic, lauric and naphthenic acid were examined as catalyst components and proved to be very active for the polymerization of epoxides when used with an organoaluminum compound such as AlEt₃ or AlEt₂Cl. Copolymerization of propylene oxide and allyl glycidyl ether was successfully carried out with an AlEt₃–Zr octoate catalyst.     

Cyclo- and cyclized diene polymers. XII. Cationic polymerization of isoprene

Polymerization of isoprene with Lewis acids in n-heptane is a process leading to a quasiequilibrium which is characterized by very low conversions. Polymerization rates in aromatic solvents are much higher due to extensive chain transfer with solvent with regeneration of the original active centers. The rate of monomer disappearance in benzene or toluene when aluminum bromide is the catalyst is second order with respect to monomer concentration. The reaction order with respect to the catalyst depends on the reaction conditions; at constant monomer concentration it is approximately one. Polymerization rates in halogenated solvents with the use of syringe techniques are much higher than those in aromatic solvents. Polymers obtained with various cationic catalysts ranged from oils to white powders having molecular weights up to more than 100,000 depending on reaction conditions. All polymers exhibited infrared spectra characteristic of cyclopolydienes, and the content of linear structures usually did not exceed 20%, irrespective of the nature of the catalyst or solvent. In solvents of higher polarity, such as o-dichlorobenzene, more linear structures were detected. Among residual linear forms the trans-1,4 addition was found to prevail. Residual unsaturation in polymers did not exceed 30%.     

Sorption of inorganic nanoparticles in woven cellulose fabrics

Titanium dioxide was deposited from aqueous suspension onto cellulosic surfaces.Titania was sourced from Degussa (P25TM,70:30 anatase:rutile).Dry uptake of particles was shown to be rapid and dominant with one-third of the deposition occurring in less than 30 s and over one-half in the first minute.Isotherms were recorded to compare the rate of titanium deposition on dry and pre-wetted cotton.In the dry case uptake reached a maximum in 30 min whereas in the pre-wetted case the uptake was seen to continue beyond 180 min.A broad trend of higher deposition occurring at lower pH was seen,corresponding to the region where surface charges were opposite and thus attractive.Dry pickup was less significant at high pH.The response to varying ionic strength was complex and was attributed to the combined effect of charge screening,particle aggregation and consequent particle entrapment or occlusion.Titania deposition into the interstices of woven cotton sheets resulted in the formation of inorganic,nanoparticulate skeletons which could be isolated by controlled combustion of the cellulose and thus cotton was suggested to have potential for the templated synthesis of high surface area semiconductor materials.     

Loss measurement of plasmonic modes in planar metal-insulator-metal waveguides by an attenuated total reflection method

We report experimental excitation and characterization of surface plasmon modes in planar metal-insulator-metal (MIM) waveguides. Our approach is based on determining the width of the reflection angular spectrum in the attenuated total reflection (ATR) configuration. Owing to its transverse character, the ATR configuration provides a more straightforward and simpler way to determine the loss of plasmonic modes in MIM structures, compared to using tapered end couplers with multiple waveguide samples or scanning near-field optical microscopy. In this Letter, two waveguide structures with Au claddings and 50/200 nm SiO(2) cores are investigated. The propagation lengths measured at λ = 1.55 μm are 5.7 and 18 μm, respectively, in agreement with the theoretical predictions.     

Donor-Acceptor-Gleichgewichte bei der Copolymerisation. 44. Mitt. Copolymerisation von Styrol und α-Methylstyrol mit Acrylaten und (α-substituierten Acrylaten mit Al-Verbindungen

Ohne Zusammenfassung     

Digital processing capabilities using holographically recorded data pages in electro-optic crystals

Digital logic operations on holographically recorded binary data pages in electro-optic crystals as previously reported by others are summarized and extended. The basic logic operations available and processing capabilities are identified and discussed.