Correlating the scattered intensities of P3HT and PCBM to the current densities of polymer solar cells

Grazing-incidence X-ray diffraction and rocking scans have quantified the structure of poly(3-hexylthiophene) and [6,6]-phenyl-C(61)-butyric acid methyl ester in the active layers of organic solar cells. Our study reveals that the device J(SC) correlates with the local structural development of pure PCBM and, to second order, the extent of out-of-plane P3HT π-stacking.     

Green chemical functionalization of single-walled carbon nanotubes in ionic liquids

Single walled carbon nanotubes (SWNTs) are exfoliated and functionalized predominantly as individuals by grinding them for minutes at room temperature with aryldiazonium salts in the presence of ionic liquids (ILs) and K(2)CO(3). This constitutes an extremely rapid and mild green chemical functionalization process for obtaining the individualized nanotube structures. A number of ILs and various reaction conditions were surveyed. Raman, XPS, UV/vis/NIR spectroscopies, thermogravimetric analysis, and atomic force and transmission electron microscopies were used to characterize the products.     

Protonated (protosolvated) onium ions (onlum dications)

In this short review we have shown the importance of protosolvation of onium ions (containing non-bonded pairs of electrons) in superacid catalyzed reactions. Such activation can result in unusual reactions such as aromatic alkylation with Meerwein’s salts, aliphatic nitration with nitronium ion, alkylation of saturated hydrocarbons, greatly enhanced activity of acyl cations, etc. Possibly such phenomena may be operative in hydroxylation reactions using protonated hydrogen peroxide in strong acid solutions. Even the reactivity of halonium ions could be enhanced by protosolvation. Consequently, electrophilic protosolvation may play a significant role in strogg acid catalyzed reactions.     

Surface-initiated synthesis of poly(3-methylthiophene) from indium tin oxide and its electrochemical properties

Poly(3-methylthiophene) (P3MT) was synthesized directly from indium tin oxide (ITO) electrodes modified with a phosphonic acid initiator, using Kumada catalyst transfer polymerization (KCTP). This work represents the first time that polymer thickness has been controlled in a surface initiated KCTP reaction, highlighting the utility of KCTP in achieving controlled polymerizations. Polymer film thicknesses were regulated by the variation of the solution monomer concentration and ranged from 30 to 265 nm. Electrochemical oxidative doping of these films was used to manipulate their near surface composition and effective work function. Doped states of the P3MT film are maintained even after the sample is removed from solution and potential control confirming the robustness of the films. Such materials with controllable thicknesses and electronic properties have the potential to be useful as interlayer materials for organic electronic applications.     

Poly(ethylene imine)s as Antimicrobial Agents with Selective Activity

We report the structure–activity relationship in the antimicrobial activity of linear and branched poly(ethylene imine)s (L‐ and B‐PEIs) with a range of molecular weights (MWs) (500–12 000). Both L‐ and B‐PEIs displayed enhanced activity against Staphylococcus aureus over Escherichia coli. Both B‐ and L‐PEIs did not cause any significant permeabilization of E. coli cytoplasmic membrane. L‐PEIs induced depolarization of S. aureus membrane although B‐PEIs did not. The low MW B‐PEIs caused little or no hemolysis while L‐PEIs are hemolytic. The low MW B‐PEIs are less cytotoxic to human HEp‐2 cells than other PEIs. However, they induced significant cell viability reduction after 24 h incubation. The results presented here highlight the interplay between polymer size and structure on activity.

     

Comparison of micro- and mesoporous inorganic materials in the uptake and release of the drug model fluorescein and its analogues

The uptake of the three species of the drug model fluorescein (fluorescein sodium salt (FNa), fluorescein free acid (F), and fluorescein diacetate (FDA)) by zeolite NaX and the mesoporous zeotype MCM-41 was investigated as well as their release rates into solutions at pH 7 and pH 4.5. UV/Vis analysis was carried out at a wavelength of 490 nm. Uptakes of the sodium salt of 9 % for zeolite X and 14 % for MCM suggest little penetration of the pores. The use of ethanol as the loading solvent for F resulted in little uptake for both zeolitic materials due to the successful competition of the ethanol for binding sites. Use of acetone (weaker proton acceptor) as loading solvent significantly improved the uptake of F to 17 % and 12 % for zeolite X and MCM, respectively, whilst the uptake of FDA in acetone increased still further to 22 % and 17 % for zeolite X and MCM, respectively. Generally there was a large initial release of the fluorescein analogues from the surface of the zeolites with very little further increase over time. The prescence of an esterase enzyme in the release medium of FDA tripled the release from MCM to 15 % but left the release from zeolite X unaffected at 6 %. The results obtained show that uptake of fluorescein and its analogues is dependent on the loading solvent used, the amount released is influenced by not only the solvent but the pH and the presence of enzymes in the release medium.     

Quantitative measurements of recombinant HIV surface glycoprotein 120 binding to several glycosphingolipids expressed in planar supported lipid bilayers

The interaction of recombinant HIV-1 surface glycoprotein gp120 (rgp120) with natural isolates of lactosylceramide (LacCer), glucosylceramide (GlcCer), and galactosylceramide (GalCer) has been quantitatively measured under equilibrium conditions using total internal reflection fluorescence (TIRF) spectroscopy. The binding affinity (K(a)) of rgp120 to these glycosphingolipids (GSLs), reconstituted at 5 mol % in supported planar lipid bilayers composed of 95 mol % POPC, is ca. 10(6) M(-1) for dissolved rgp120 concentrations greater than 25 nM. In contrast, at concentrations of rgp120 between 0.2 and 15 nM, rgp120 does not bind significantly to LacCer and GlcCer, but has a high affinity for GalCer with a measured K(a) value of 1.6 x 10(9) M(-1). However, protein surface coverage measurements show that this strong binding process accounts for very little of the total protein adsorbed over the entire concentration range studied. At a protein concentration of ca. 20 nM, the surface coverage is only 3% of that achieved at apparent saturation (i.e., when the protein concentration is ca. 220 nM). Thus the "high affinity" binding sites comprise only a small fraction of the total number of binding sites. Several other variables were investigated. Rgp120 binding behavior at membranes doped with alpha-hydroxygalactosylceramide (alpha-GalCer) was very similar to that observed with GalCer, showing that the presence/absence of an alpha-hydroxy moiety does not significantly affect galactosylceramide recognition. Phase segregation of GalCer, which occurs when the mole fraction of this GSL in a POPC bilayer exceeds ca. 0.1, was also investigated and showed no effect on binding affinity at low rgp120 concentrations. To investigate the influence of fatty acid chain length, GSLs with monodisperse C(18) and C(24) chain lengths, both with and without an alpha-hydroxy moiety, were synthesized, and their binding affinity to rgp120 was examined. Relative to the natural isolates (which contain a mixture of chain lengths), minimal differences were observed; thus among the compounds tested, fatty acid chain length does not affect GSL recognition. The results of this work should aid efforts to design anti-HIV-1 agents based on membrane-tethered, carbohydrate-based receptors for rgp120.     

Synthesis of the ABC ring system of manzamine A

A synthesis of the core ABC ring system of the manzamine alkaloids is described, starting from arecoline. The key steps involve a Claisen rearrangement to set up a 4-substituted-3-methylenepiperidine and a stereoselective azomethine ylide dipolar cycloaddition reaction. Condensation of the aldehyde 6 and sarcosine ethyl ester hydrochloride salt gives an intermediate azomethine ylide, which undergoes an intramolecular cycloaddition reaction to set up two new rings and three new chiral centers stereoselectively. The aldehyde 6 was not a suitable substrate for related azomethine ylide cycloaddition reactions with other amines. However, the related dimethyl acetal 26 could be condensed with a variety of amines to give the desired tricyclic products. The cycloaddition reaction with N-methyl or N-allyl glycine ethyl ester gave almost exclusively the exo adduct, whereas cycloaddition with glycine ethyl ester gave the endo adduct.