Temperature effects on the adsorption of polyvinyl alcohol on silica

The influence of temperature on the adsorption of polyvinyl alcohol (PVA) on a silica surface was studied from 15–35°C. The structure of the polymer adsorption layer was determined from spectrophotometric, viscosity and thermogravimetric measurements. The amount of PVA adsorbed, macromolecules’ conformation in solution, thickness of the polymer adsorption layer, and changes in the heating curve of SiO₂ with adsorbed polymer were determined. Temperature influences the PVA chain conformation in solution and the structure of the polymer adsorption layer. A temperature rise causes relaxation of polymer coils which results in an increase in the linear dimensions of PVA chains in the solution, the creation of a thicker adsorption layer, and an increase in polymer adsorbed. Polymer adsorption on the silica surface also causes changes in the heating curve of these systems. The mass losses due to heating are smallest for the systems obtained at 15°C because the least polymer is adsorbed at this temperature.      

Synthesis, crystal, molecular and electronic structures of ruthenium complexes with a benzoxazole derivative ligand

[RuCl₂(HBO)(PPh₃)₂] and [RuCl(CO)(HBO)(PPh₃)₂] complexes with the 2-(2-hydroxyphenyl)benzoxazole (C₁₃H₉NO₂) ligand were synthesized and characterized by infra red, proton and phosphorus nuclear magnetic resonances, electronic absorption and emission spectroscopies and X-ray crystallography. The experimental studies were completed by theoretical calculations. The calculations show that the donor properties of the carbonyl group predominates the π-acceptor ability in the ruthenium(II) complex. The small transfer of electron density to the acceptor π^∗ carbonyl orbitals is compensated by the presence of the chloride acceptor ligand. The electronic structures of these complexes, presented in particular by density of states diagrams, have been correlated with their ability to fluorescence and have been used to analyze the UV-Vis spectra.     

Ligand field-tuned single-molecule magnet behaviour of 2p-4f complexes

Three new 2p-4f complexes of [Ln(acac)(3)(NIT-2Py)]·0.5NIT-2Py [Ln(III) = Gd(1), Dy(2)] and [Dy(tfa)(3)(NIT-2Py)]·0.5C(7)H(16) (3) (NIT-2Py = 2-(2'-pyridyl)- 4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide; acac = acetylacetonate and tfa = trifluoroacetylacetonate) have been synthesized, and structurally and magnetically characterized. The X-ray structural analysis exhibits that the three complexes show similar mononuclear structures, in which NIT-2Py radical chelates the Ln(III) ion through the oxygen atom of the NO group and the nitrogen atom from the pyridine ring. The static magnetic measurements on the three complexes exhibit ferromagnetic coupling between the lanthanide ion and the radical. Compared to the silence of the out-of-phase ac susceptibility of complex 3, the magnetic relaxation behavior of complex 2 is observed, suggesting single-molecule magnet behavior. The different magnetic relaxation behaviours of 2 and 3 are due to their slightly different crystal structure around the Dy(III) ions. It was demonstrated that the spin dynamic can be modified by the careful adjustment of the ligand field around the metal center.     

Enantiomeric separation and determination of the enantiomeric impurity of armodafinil by capillary electrophoresis with sulfobutyl ether-β-cyclodextrin as chiral selector

A selective capillary electrophoresis method using sulfobutyl ether-β-cyclodextrin as a chiral selector was developed and validated for the determination of the enantiomeric impurity of (R)-modafinil, i.e., armodafinil. Several parameters were optimized for a satisfactory enantioresolution, including the type and concentration of chiral selector and organic modifier, pH of background electrolyte (BGE), capillary temperature. The finally adopted condition was: 20 mmol/L phosphate buffer at pH 7.5, containing 20 mmol/L sulfobutyl ether-β-cyclodextrin and 20% methanol, at temperature of 25 °C. A good resolution of 3.3 for the two enantiomers of modafinil was achieved by applying the optimal conditions. The limit of detection (LOD) and limit of quantification (LOQ) of (S)-modafinil were 1.25 μg/mL and 2.50 μg/mL, respectively. The established method was also proven to display good selectivity, repeatability, linearity and accuracy. Finally, the method was used to investigate the enantiomeric purity of armodafinil in bulk samples.     

Effect of surface oxidation on the interaction of 1-methylaminopyrene with gold nanoparticles

The effect of the surface chemistry of gold nanoparticles (GNPs) on the GNP-amine (-NH(2)) interaction was investigated via conjugating an amine probe--1-methylaminopyrene (MAP) chromophore--with three Au colloidal samples of the same particle size yet different surface chemistry. The surface of laser-irradiated and ligand-exchanged-irradiated GNPs is covered with acetonedicarboxylic ligands (due to laser-introduced citrate oxidization) and citrate ligands, respectively, and both surfaces contain oxidized Au species which are essentially lacking for the citrate-capped GNPs prepared by the pure chemical approach. Both laser-irradiated samples show inferior adsorption capacity of MAP as compared with the purely chemically prepared GNPs. Detailed investigations indicate that MAP molecules mainly complex directly with Au atoms via forming Au-NH(2)R bonds, and the oxidization of the GNP surface strongly influences the ratio of this direct bonding to the indirect bonding originating from the electrostatic interaction between protonated amine (-NH(3)(+)) and negatively charged surface ligands. The impact of the oxidized GNP surface associated with the laser treatment is further confirmed by aging experiment on GNP-MAP conjugation systems, which straightforwardly verifies that the surface oxidation leads to the decrease in the MAP adsorption on GNPs.     

Polymersomes in "gelly" polymersomes: toward structural cell mimicry

We demonstrate here the formation of compartmentalized polymersomes with an internal "gelly" cavity using an original and versatile process. Nanosize polymersomes of poly(trimethylene carbonate)-b-poly(L-glutamic acid) (PTMC-b-PGA), formed by a solvent displacement method are encapsulated with a rough "cytoplasm mimic" in giant polymersomes of poly(butadiene)-b-poly(ethylene oxide) PB-b-PEO by emulsion-centrifugation. Such a system constitutes a first step toward the challenge of structural cell mimicry with both "organelles" and "cytoplasm mimics". The structure is demonstrated with fluorescence labeling and confocal microscopy imaging with movies featuring the motion of the inner nanosize polymersomes in larger vesicles. Without "cytoplasm mimic", the motion was confirmed to be Brownian by particle tracking analysis. The inner nanosize polymersomes motion was blocked in the presence of alginate, but only hindered in the presence of dextran. With the use of such high molecular weight and concentrated polysaccharides, the crowded internal volume of cells, responsible for the so-called "macromolecular crowding" effect influencing every intracellular macromolecular association, seems to be efficiently mimicked. This study constitutes major progress in the field of structural biomimicry and will certainly enable the rise of new, highly interesting properties in the field of high-added value soft matter.     

Lanthanide doping-facilitated growth of ultrasmall monodisperse Ba2LaF7 nanocrystals with excellent photoluminescence

Lanthanide doping not only works as sensitizer and activator, but also plays an important role to facilitate the growth of nanocrystal and to control the size, shape, and property of nanocrystals. Here, reported was the synthesis of monodisperse Ba(2)LaF(7) nanocrystals with the size of sub-10nm through a solvothermal method. We found the dopants of Ho(3+), Er(3+), or Yb(3+) facilitated the growth of Ba(2)LaF(7) nanocrystals obviously to a certain size within a shorter reaction time. Similar phenomenon can also be observed in the synthesis of LaF(3) nanocrystals. We find that Ln(3+) (e.g., Ho(3+), Er(3+), or Yb(3+)) with smaller radius can reduce the nucleation energy and lead to heterogeneous nucleation, which favors the growth of Ba(2)LaF(7) nanocrystals obviously. In addition, intense upconversion emission can be observed from Ln(3+)-doped Ba(2)LaF(7) nanocrystals under the 980 nm laser excitation, providing great potential application in biological imaging. Especially, Ba(2)LaF(7):Yb/Er (20/1 mol%) nanocrystals present more intense upconversion emission than α-NaYF(4):Yb/Er (20/1 mol%) nanocrystals under the same conditions.     

Solvent effects on isomerization and spectral properties of photochromic-switching diarythene derivatives in polar and apolar solutions

The photocyclization behavior and dynamic conformational transition of photochromic switches of diarythene derivatives in solutions are investigated by using the density functional theory (DFT) and molecular dynamics (MD) simulations. Three possible conformations, antiparallel (anti), parallel (para), and twist, for the open-ring isomers of 1,2-bis(2-methylbenzothiophene-3-yl)maleic anhydride are located. Both PCM-B3LYP/6-31G* calculations and MD simulations demonstrate that anti and twist open-ring isomers can interconvert freely in n-hexane and acetonitrile solutions at room temperature. The statistical ratio of twist to anti isomers from MD simulations is 2.09 in n-hexane and 1.07 in CH(3)CN, in qualitative agreement with those (1.18 in n-hexane and 1.05 in CH(3)CN) estimated from Arrhenius analysis of DFT activation energies. The solvent polarity has little influence on the isomerization of open-ring isomers in the ground state. Due to the evident charge transfer upon excitations, the solvent effects on the electronic structures and absorption spectra of low-lying excited states (S(1) and S(2)) are more significant. For such charge-transfer excited states, the long-range corrected functional CAM-B3LYP gives better agreement with the experimental spectra than B3LYP. The solvent polarity and polarization of the charge-transfer excited states are crucial for fabricating the novel functionalized photochromic molecular switches.     

Label-free electrochemiluminescent immunosensor for α-fetoprotein: performance of Nafion-carbon nanodots nanocomposite films as antibody carriers

A simple and highly sensitive electrochemiluminescent immunosensor based on nanocomposite architecture of the one-pot synthesized carbon nanodots and Nafion composite film was proposed for the detection of α-fetoprotein.     

Influence of surface functionalization via chemical oxidation on the properties of carbon nanotubes

The surface of carbon nanotubes (CNTs) was functionalized in different chemical oxidants, hydrogen peroxide, mixed concentrated HNO(3)/H(2)SO(4) and acidic KMnO(4) solution. The influences on the properties of CNTs were systematically investigated, such as the structure, the kinds and the contents of the formed surface oxygen-containing functional groups, the pH(PZC) values and the surface hydrophilicity using XRD, HREM, FTIR and chemical titration. The results show that the kinds and the contents of the surface oxygen-containing groups are dependent on the functionalization methods. The formation of the oxygen-containing groups can decrease pH(PZC) values and improve surface hydrophilicity of CNTs. The dispersion of the supported Pd-Pt particles on the functionalized CNTs and their catalytic activity in the profile reaction of naphthalene hydrogenation to tetralin are both promoted due to the presence of these oxygen-containing groups.