Synthesis and characterization of pyrene bearing amphiphilic miktoarm star polymer and its noncovalent interactions with multiwalled carbon nanotubes

A novel amphiphilic miktoarm star polymer, polystyrene‐poly(ethylene glycol)‐poly(methyl methacrylate), bearing a pyrene group at the end of PS arm (Pyrene‐PS‐PEG‐PMMA) was successfully synthesized via combination of atom transfer radical polymerization and click chemistry. The structure and composition of the amphiphilic miktoarm star polymer were characterized by gel permeation chromatography and ¹H NMR. The functionalization of multiwalled carbon nanotubes (MWCNTs) via “π–π” stacking interactions with pyrene‐PS‐PEG‐PMMA miktoarm star polymer was accomplished and the resulting polymer‐MWCNTs hybrid was analyzed by using ¹H NMR, UV–vis, fluorescence spectroscopy, and thermal gravimetric analysis. The high‐resolution transmission electron microscopy and analytical techniques aforementioned confirmed that the noncovalent functionalization of MWCNT's with the amphiphilic miktoarm star polymer was successfully achieved. The MWCNT/pyrene‐PS‐PEG‐PMMA exhibited significant dispersion stability in common organic solvents such as dimethyl formamide, chloroform, and tetrahydrofuran. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Synthesis of tadpole polymers via triple click reactions: Copper‐catalyzed azide–alkyne cycloaddition,diels–alder,and nitroxide radical coupling reactions

We designed a trifunctional initiator ( 3 ) containing anthracene, bromide, and OH functionalities and subsequently used as an initiator in atom transfer radical Polymerization (ATRP) of styrene to yield linear polystyrene (PS) with α‐anthracene, OH, and ω‐bromide terminal groups, of which bromide is later transformed into azide to result in the linear anthracene‐, OH‐, and azide‐terminated PS (l‐α‐anthracene‐OH‐ω‐azide‐PS). The copper‐catalyzed azide–alkyne cycloaddition reaction between l‐α‐anthracene‐OH‐ω‐azide‐PS and α‐furan‐protected‐maleimide‐ω‐alkyne linkage, 4 afforded the linear anthracene‐, OH‐, and maleimide‐terminated PS. The cyclization via intramolecular Diels–Alder click reaction of this linear PS and the subsequent conversion of the hydroxyl into bromide resulted in the cyclic PS with one bromide located on the ring, (c‐PS)‐Br. Finally, the c‐PS‐Br was clicked with either well‐defined tetramethylpiperidine‐1‐oxyl‐terminated poly(ethylene glycol) (PEG) or poly(ε‐caprolactone) (PCL) yielding the tadpole polymer, (c‐PS)‐b‐PEG or (c‐PS)‐b‐PCL. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Model fluorous polyurethane surface modifiers having co-polyoxetane soft blocks with trifluoroethoxymethyl and bromomethyl side chains

Polyurethanes containing poly(2-trifluoroethoxymethyl-2-methyl)-co-(2-bromomethyl-2-methyl)-1,3-propylene oxide (co-polyoxetane) soft blocks, P[3FOx:BrOx-m:n], were prepared and used (0.5-2 wt %) to modify the surface properties of a conventional polyurethane. The substrate polyurethane was composed of an isophorone diisocyanate/butanediol hard block and a polytetramethylene oxide soft block [IPDI/BD(50%)-PTMO(2000)]. A combination of tapping mode atomic force microscopy (TM-AFM), X-ray photoelectron spectroscopy (XPS), and dynamic contact angle (DCA) studies showed that the fluorous polyurethane surface modifiers confer surface properties similar to those of the parent at 0.5-1.0 wt %. The retention of initial wetting behavior in water was enhanced with higher ratios of 3FOx:BrOx that corresponds to increasing fluorous character. A semifluorinated chaperone is necessary to surface concentrate -CH2Br groups. Negligible Br was detected by XPS when the P[BrOx]-soft block polyurethane was used as a surface modifier (0.5%) and the wetting behavior was similar to that of the bulk polyurethane. Despite being hydrophobic (theta adv = 102 degrees) the P[BrOx]-soft block polyurethane is not a polymer surface modifier under the conditions described herein. The calculated solubility parameters for PTMO and P[BrOx], which are similar, support the notion of BrOx miscibility with the base polyurethane. The combination of miscibility of BrOx repeat units and lack of an end-group-like architecture minimizes BrOx surface concentration in the chosen bulk polyurethane.     

Water makes it hydrophobic: contraphilic wetting for polyurethanes with soft blocks having semifluorinated and 5,5-dimethylhydantoin side chains

A series of polyurethanes with novel copolymer soft blocks display a new surface phenomenon, contraphilic wetting, in which the dry surface is hydrophilic and the wetted surface is hydrophobic. A precursor polymer was prepared with copolymer soft blocks containing semifluorinated (trifluoroethoxy, 3FOx, or pentafluoropropoxy, 5FOx) and bromomethyl functional pendant groups with 2:1, 1:1, and 1:2 semifluorinated/bromomethyl ratios. The hard block consists of isophorone diisocyanate (IPDI) and 1,4-butanediol (BD). 5,5-Dimethylhydantoin was introduced by the substitution of Br via reaction-on-polymer. The composition, structure, and percent of 5,5-dimethylhydantoin substitution for both the precursor and the 5,5-dimethylhydantoin-substituted polyurethanes were analyzed by 1H NMR. The difference between the advancing contact angle on the wetted surface and that on the dry surface (deltaC) is highest (38 degrees ) for the polyurethane with the highest ratio of semifluorinated/hydantoin soft block side chains. A model is proposed according to which contraphilic wetting is driven enthalpically by hydrogen bonding. For the dry surface, hydrogen bonding of 5,5-dimethylhydantoin amide carbonyl groups to methylene hydrogens of semifluorinated groups disrupts the normal surface concentration of semifluorinated groups, whereas the geometric arrangement of hydantoin N-H results in availability for hydrogen bonding with water. Upon exposure to water, amide groups switch from hydrogen bonding to -CH2CF2CF3 to stronger hydrogen bonding with water. As a result, semifluorinated groups are "released", and the surface becomes hydrophobic. Drying the coating (50 degrees C) reversibly restores hydrophilic character. Coatings stored at ambient temperature and humidity have deltaC values intermediate between dry and wet states.     

Evaluation of Antibacterial and Antifungal Effects of Calcium Hydroxide Mixed with Two Different Essential Oils

Background: Calcium hydroxide is a routinely used material for root canal disinfection during root canal treatment. Natural products have great potential in terms of their antibacterial effects. This study aimed to establish an effective alternative intracanal medicament using Origanum dubium (O. dubium) and Mentha spicata (M. spicata) essential oils. Materials and Methods: O. dubium and M. spicata, collected from Lefke, Cyprus, were separately subjected to hydrodistillation. The obtained essential oil compositions were analysed simultaneously by gas chromatography (GC) and gas chromatography/mass spectrometry (GC-MS). The compositions were then divided into groups and mixed with calcium hydroxide at a 1:1 concentration; after that, the pastes were tested on Enterococcus faecalis (E. faecalis) and Candida albicans (C. albicans), which are the most common resistant pathogenic microorganisms in the root canal. The antibacterial activity of the pastes was measured using a disk diffusion assay. Results: The GC and GC-MS analyses revealed that O. dubium and M. spicata had major compositions of carvacrol (75.8%) and carvone (71.3%), respectively. Antimicrobial activity was found to be significantly higher when study groups with O. dubium essential oil were applied to both E. faecalis and C. albicans. The results also show that M. spicata, together with calcium hydroxide, demonstrated a significant antifungal effect on C. albicans when incubated for 72 h. Conclusions: M. spicata was found to be an effective antimicrobial agent on C. albicans, whereas O. dubium was found to be very effective on both E. faecalis and C. albicans. These data demonstrate that these natural essential oils may be promising candidates for alternative intracanal medicament in future routine clinical applications.     

Mineralogical,geochemical and radiological characterisation of Selmo Formation in Batman area,Turkey

This work deals with the mineralogical, geochemical and radiological characterisations of Selmo Formation in Batman neighbourhood. The upper Miocene–Pliocene Selmo Formation is common in the centre of Batman and composed of carbonated sandy claystones and silty–sandy stone lenses. The common whole minerals of the samples are quartz, feldspars, calcite and dolomite. The clay minerals are smectite, illite, chlorite and mixed-layer clay (chlorite–smectite). The geochemical mean values of the samples are 51.7% SiO₂; 12.6% Al₂O₃; 6.2% Fe₂O₃; 3.6% MgO; 6.3% CaO; 1.1% Na₂O; 1.7% K₂O; 0.8% TiO₂; 0.2% P₂O₅; 0.1% MnO; and 0.03% Cr₂O₃. In addition, baseline maps for the concentrations of each radionuclide, the radium equivalent activity and the outdoor gamma dose rate distributions have been plotted for the study area. The mean activity concentrations of ²²⁶Ra, ²³²Th, ⁴⁰K and ¹³⁷Cs were determined to be 32, 24, 210 and 9 Bq kg^?1, respectively. The assessments of the radiological hazard indices, such as radium equivalent activity, absorbed dose rate in air, annual effective dose equivalent, excess lifetime cancer risk, external hazard index and internal hazard index, were calculated and compared with the internationally accepted reference values. This study shows that the concentrations of radioactivities in the measured samples were within the recommended safety limits and did not pose to be any significant source of radiation hazard.     

A computational exploration of the oxygen reduction reaction over a carbon catalyst containing a phosphinate functional group

Oxygen reduction reaction (ORR) over a carbonaceous catalyst (1) with a phosphinate (>P(=O)OH) moiety was explored computationally. Under the acidic environment of a fuel cell, 1 could be active for ORR and be converted to 2 with a >P(OH)(2) moiety. An edge phosphinate could be active for both 2- and 4-electron ORR.     

Diode-pumped, high-average-power femtosecond Cr3+ :LiCAF laser

We demonstrate a high-average-power continuous wave (cw) and cw mode-locked Cr3+ :LiCAF laser pumped by broad-area laser diodes. In cw lasing experiments, up to 580 mW of output was obtained with 4.35 W of incident pump. A semiconductor saturable absorber mirror was used to initiate stable, self-starting, mode locking. In the cw mode-locked regime, the Cr3+ :LiCAF laser produced nearly transform-limited, 67 fs long pulses near 800 nm with an average output power of 300 mW. The pulse repetition rate was 120 MHz, with a pulse energy of 2.5 nJ.