Synthesis of low grafting density molecular brush from a poly(N‐alkyl urea peptoid) backbone

The synthesis of a molecular brush was accomplished by combining step‐growth polymerization and reversible addition fragmentation chain transfer (RAFT) polymerization in a “grafting from” methodology. A symmetrical N‐alkyl urea peptoid sixmer containing alkyne functional groups was prepared using a divergent strategy, and the structure of the product was confirmed using NMR spectroscopy and mass spectrometry. A step‐growth process was used to prepare a linear poly(N‐alkyl urea peptoid) by reacting the diamine‐functionalized N‐alkyl urea peptoid sixmer with a diisocyanate. RAFT chain transfer agents were coupled to the poly(N‐alkyl urea peptoid) backbone through a copper‐catalyzed azide/alkyne cycloaddition reaction. The afforded macro‐RAFT agent was used to sequentially polymerize styrene and tert‐butyl acrylate block copolymer arms from the poly(N‐alkyl urea peptoid) backbone. The tert‐butyl groups were removed using dilute trifluoroacetic acid affording hydrophilic polyacrylic acid segments. The molecular brushes were observed to generate micelles in aqueous solution. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Thermal,structural and optical properties of Al2CoO4-Crocoite composite nanoparticles used as pigments

Novel zinc(II) complex compounds of general formula Zn(C₆H₅COO)₂·L₂ (where L=caffeine (caf) and urea (u)) were synthesized and characterized by elemental analysis and IR spectroscopy. The thermal behaviour of the complexes was studied during heating in air by thermogravimetry. It was found that the thermal decomposition of the anhydrous Zn(II) benzoate compounds with bioactive ligands was initiated by the release of organic ligands at various temperatures. On further heating of the compounds up to 400°C the thermal degradation of the benzoate anions took place. Zinc oxide was found as the final product of the thermal decomposition of all zinc(II) benzoate complex compounds heated to 600°C. Results of elemental analysis, infrared spectroscopy, mass spectroscopy and thermogravimetry are presented.     

Enthalpic interactions of -alanine and -serine in aqueous urea solutions

The enthalpies of dilution of -alanine and -serine in various aqueous urea solutions have been determined by flow microcalorimetry at 298.15 K. The homogeneous enthalpic interaction coefficients over the whole range of aqueous urea solutions have been calculated according to the excess enthalpy concept. The results were interpreted from the point of view of solute–solute interactions moderated by solvent effects.     

Kinetic and equilibrium studies of urea adsorption onto activated carbon: Adsorption mechanism

We found that activated carbon effectively removed urea from solution and that urea adsorption onto activated carbon followed a pseudo-second-order kinetic model. We classified the urea adsorption on activated carbon as physical adsorption and found that it was best described by the Halsey adsorption isotherm, suggesting that the multilayer adsorption of urea molecules on the adsorption sites of activated carbon best characterized the adsorption system. The mechanism of adsorption of urea by activated carbon involved two steps. First, an amino (–NH₂) group of urea interacted with a carbonyl (–C?O) group and a hydroxyl (?OH) group on the surface of activated carbon via dipole–dipole interactions. Next, the –C?O group of the urea molecule adsorbed to the activated carbon interacted with another –NH₂ group from a second urea molecule, leading to multilayer adsorption.     

Hydrothermal synthesis of nitrogen-doped carbon dots as a sensitive fluorescent probe for the rapid,selective determination of Hg2+

In the present work, a green synthetic method for producing nitrogen-doped carbon dots (NCDs) by using ammonium citrate and urea is introduced. The obtained NCDs were characterised by transmission electron microscopy, Fourier transform infrared spectra, UV–vis absorption and fluorescence spectra. The results showed that the prepared NCDs were spherical with a size of about 3.5 nm, emitting strong and stable blue fluorescence when excited at 352 nm. It was noting that the NCDs enable sensitive and selective determination of Hg²⁺ in tap water with a linear range of 0.01–5 mg L^?1 based on a possible charge transfer process. The detection limit was 9.4 µg L^?1.     

An efficient and mild protocol for the synthesis of unsymmetrical ureas in the absence of catalyst and additives

<正>A new practical method for the synthesis of unsymmetrical ureas was achieved by reaction of phenylurea with primary and secondary amines under neutral and mild condition in very good yields.The reaction took place in refluxing dioxane and does not require any catalyst or additives.     

Homogeneous methylation of wood pulp cellulose dissolved in LiOH/urea/H2O

Spruce sulphite cellulose (number average degree of polymerization 620) dissolved in an aqueous solution of 8% (w/w) LiOH*H₂O and 12% (w/w) urea was methylated with dimethyl sulphate (DMS). By varying the reaction temperature between 22 and 50 °C, the molar ratio between 9 and 15 mol DMS per mol anhydroglucose unit, and the reaction time from 4 to 24 h, methyl cellulose (MC) with degree of substitution (DS) values in the range of 1.07 and 1.59 was prepared. The chemical structure of MC was analysed by FTIR and ¹H NMR spectroscopy. The turbidity (given in nephelometric turbidity units, NTU) of the aqueous solution of MC reached an optimum of 10 NTU for a product obtained with 12 mol DMS/mol AGU at 50 °C. GPC measurements revealed polymer degradation to a certain extent. The intrinsic viscosity and the Huggins constant k of the MC samples increased with increasing DS value. The MC samples possess k values higher than 0.8, indicating association of the polymer chain. The zero-shear viscosity decreased with increase of both temperature and the amount of methylation agent due to the depolymerization. During the heating/cooling cycle (20-90 °C) of the aqueous solutions of MC, it was observed that samples synthesized at 22 °C with DS values lower than 1.3 did not undergo phase separation in aqueous solution. Phase separation hysteresis with a precipitation temperature up to 80 °C was obtained for aqueous solutions of MC with DS values between 1.07 and 1.66 synthesized at higher temperatures. The functionalization pattern determined by GLC of the corresponding partially methylated glucitol acetates is close to randomness and comparable with those of commercial MC samples.     

Effect of Some Urea Derivatives on Measurement of pH with Glass Electrodes

Abstract

In solutions containing some urea or thiourea derivatives and alkali metal hydroxides at pH 6 to 10, the pH value measured with glass electrodes changes with time. The degree of change varies between 0.1 and 1.0 pH units and depends on the structure of the urea derivative, its initial concentration, and the glass electrode used, but not on the cation of the alkali metal hydroxide added. In contrast, pH measured in the same solution with a quinhydrone electrode or the UV spectra remain time-independent. It is proposed that urea derivatives are adsorbed in the gel at the surface of the glass electrode and there affect the ion-exchange process.