Evidence for the preservation of the particle identity in miniemulsion polymerization

A combination of small‐angle neutron scattering (SANS), conductivity, and surface tension measurements is used to show that the primary droplets in miniemulsion polymerization have the same size and the same size distribution as the final particles. It is also shown that hexadecane employed as a cosurfactant is homogeneously dispersed in the droplets and does not possess any interface activity. The presented data support that a 1 : 1 copy from monomer droplets to polymer particles is achieved.     

Photochemistry of Methane on Pd/Al2O3 Model Catalysts: Control of Photochemistry on Transition Metal Surfaces

The mean size of the Pd clusters deposited on an Al₂O₃ thin film influences the efficiency of photodissociation of CD₄ into CD₃ and D as well as the photodesorpion upon irradiation with 193-nm laser light. The picture shows the degree of desorption on Pd clusters of various sizes (as well as on a Pd(111) single-crystal surface) as a function of temperature; the values given refer to the average thickness of the evaporated metal layer.     

Rembrandt's Old Woman Praying, 1629/30: A look below the surface using X-ray fluorescence mapping

Rembrandt's painting Old Woman Praying, 1629/30, is the most valuable and exceptional work of art of the Residenzgalerie Salzburg (RGS). It is painted on a gilded copper plate with dimensions of only approximately 15 × 12 cm. The painting probably belongs to a series of three small-scale tronies, all executed on gilded copper plates. This particular picture preparation, which represents a special feature in Rembrandt's work, is quite unusual in the history of art. Previous investigations on the comparable paintings The Laughing Man, 1629/30, in the Mauritshuis, The Hague and the Self Portrait, 1630, in the National Museum, Stockholm showed that the gilding of the copper plate was applied over a lead white ground. To characterize the painting in the RGS, X-ray fluorescence (XRF) mapping was performed in a collaboration between the Research Office Residenzgalerie, Land Salzburg, the XGLab S.R.L, Milan, and the Conservation Science Department of the Kunsthistorische Museum Vienna (KHM). The results indicate a different structure for this painting than that used for The Laughing Man and the Self Portrait. The gilding was applied directly onto the copper plate, but with three areas with the gilding missing. It seems likely that in these sections, the gold was purposely removed to provide a different darker effect. XRF mapping yielded valuable insights into the structure of the painting and its technique as well as the principal pigments used for its composition.     

Benzene formation in premixed fuel-rich 1,3-butadiene flames

Detailed kinetic modeling and flame-sampling molecular-beam time-of-flight mass spectrometry are combined to unravel important pathways leading to the formation of benzene in a premixed laminar low-pressure 1,3-butadiene flame. The chemical kinetic model developed is compared with new experimental results obtained for a rich (? = 1.8) 1,3-butadiene/O₂/Ar flame at 30 Torr and with flame data for a similar but richer (? = 2.4) flame reported by Cole et al. [Combust. Flame 56 (1) (1984) 51-70]. The newer experiment utilizes photoionization by tunable vacuum-ultraviolet synchrotron radiation, which allows for the identification and separation of combustion species by their characteristic ionization energies. Predictions of mole fractions as a function of distance from the burner of major combustion intermediates and products are in overall satisfactory agreement with experimentally observed profiles. The accurate predictions of the propargyl radical and benzene mole fractions permit an assessment of potential benzene formation pathways. The results indicate that C₆H₆ is formed mainly by the C₃H₃ + C₃H₃ and i-C₄H₅ + C₂H₂ reactions, which are roughly of equal importance. Smaller contributions arise from C₃H₃ + C₃H₅. However, given the experimental and modeling uncertainties, other pathways cannot be ruled out.     

Si@Al14(N(Dipp)SiMe3)6: Ein Si‐zentrierter metalloider Aluminiumcluster und ergänzende Untersuchungen zur Strukturproblematik des Si@Al14Cp*6‐Clusters

The preparation and X‐ray structure of Si@Al₁₄R₆ (R = Cp*, N(Dipp)SiMe₃; Dipp = 2,6‐iPr₂–C₆H₃) are described via the disproportionation and substitution reaction of a metastable AlCl solution. One silicon atom occupies the center of an Al₈ cube. This central unit is stabilized through capping of six AlR moieties above the faces of the cube. These findings open the door for a reinvestigation of Si@Al₁₄Cp*₆ through MALDI, DFT and X‐ray investigations: Caused by the preparation procedure a small part of the Si@Al₁₄Cp*₆ clusters are partially oxidized by chlorine and one of the eight aluminum atoms of the cube is substituted by a Si atom: Thus, within the crystal about ¹/₃ of the SiAl₁₄Cp*₆ clusters are Si₂Al₁₃Cp*₆Cl species causing a more unsymmetrical arrangement of all cluster species than those observed in crystalline SiAl₁₄(N(Dipp)SiMe₃)₆. The serious problems during the solution of the crystal structure of Si@Al₁₄Cp*₆ caused by only slightly modified cluster species may be a strong hint at being careful with the interpretation of any nanoscale species: Even very small modifications (e.g. a single silicon atom i.e. neighbor element of aluminum containing only one more electron and proton substitutes one aluminum atom) cause drastical structural changes and consequently also different e.g. electric properties can be expected.     

Enzymatic Esterification in Aqueous Miniemulsions

Just a drop of water : Esterification in water is possible by confining the reactants in small miniemulsion droplets protected by nonionic surfactants. A lipase located at the interface between the droplet and aqueous surroundings catalyzes the esterification and expels generated water from the reaction site (see picture). High yields of the ester can be obtained after short reaction times under ambient conditions.

     

Novel diazadienes based on 1,3,4-oxadiazines: Ligands in iron carbonyl complexes and substrates in catalytic [2+2+1] cycloaddition reactions

N,N′-(4-methyl-4H-1,3,4-oxadiazine-5,6-diylidene)-bis-aniline derivatives react with Fe₂(CO)₉ to give dinuclear iron carbonyl complexes. One of the iron atoms is bonded symmetrically to both exocyclic imine nitrogen atoms. The second iron atom shows a side-on coordination towards the CN bond next to the oxadiazine oxygen atom. In addition, the iron atoms are connected via a metal metal bond. The same oxadiazine derivatives produce chiral spiro-lactams in a ruthenium catalyzed formal [2+2+1] cycloaddition reaction with carbon monoxide and ethylene.     

Miniemulsion Polymerization and the Structure of Polymer and Hybrid Nanoparticles

The miniemulsion process allows the formation of complex polymer nanoparticles and the encapsulation of widely varying materials into a polymer shell (see examples). Functionalization of the nanoparticles can be easily carried out, and polymerization to form polymer nanoparticles can be performed in environmentally friendly solvents, such as water.

     

Fluorescent Polyurethane Nanocapsules Prepared via Inverse Miniemulsion: Surface Functionalization for Use as Biocarriers

The functionalization of well‐defined PU nanocapsules with an aqueous core prepared by performing a polyaddition at the interface of inverse (water‐in‐oil) miniemulsion droplets is demonstrated. The miniemulsion technique involving the nanoreactor concept allows one to obtain an encapsulation efficiency as high as 90% within the nanocapsules. A pH independent fluorescent dye is used as a model system for the aqueous core. By varying the molar ratio of the diol to the diisocyanate at a fixed surfactant concentration, the shell thickness of the nanocapsules can be finely tuned. The carboxy‐ and amino‐functionalized surface of the nanocapsules can be tailored by an in‐situ carboxymethylation reaction and by physical adsorption of a cationic polyelectrolyte, i.e. PAEMA or PEI. The increased uptake of amino‐functionalized fluorescent nanocapsules by HeLa cells clearly demonstrates the potential of the functionalized nanocapsules to be successfully exploited as biocarriers.

     

Stability of arsenic peptides in plant extracts: off-line versus on-line parallel elemental and molecular mass spectrometric detection for liquid chromatographic separation

The instability of metal and metalloid complexes during analytical processes has always been an issue of an uncertainty regarding their speciation in plant extracts. Two different speciation protocols were compared regarding the analysis of arsenic phytochelatin (As^IIIPC) complexes in fresh plant material. As the final step for separation/detection both methods used RP-HPLC simultaneously coupled to ICP-MS and ES-MS. However, one method was the often used off-line approach using two-dimensional separation, i.e. a pre-cleaning step using size-exclusion chromatography with subsequent fraction collection and freeze-drying prior to the analysis using RP-HPLC–ICP-MS and/or ES-MS. This approach revealed that less than 2% of the total arsenic was bound to peptides such as phytochelatins in the root extract of an arsenate exposed Thunbergia alata, whereas the direct on-line method showed that 83% of arsenic was bound to peptides, mainly as As^IIIPC₃ and (GS)As^IIIPC₂. Key analytical factors were identified which destabilise the As^IIIPCs. The low pH of the mobile phase (0.1% formic acid) using RP-HPLC–ICP-MS/ES-MS stabilises the arsenic peptide complexes in the plant extract as well as the free peptide concentration, as shown by the kinetic disintegration study of the model compound As^III(GS)₃ at pH 2.2 and 3.8. But only short half-lives of only a few hours were determined for the arsenic glutathione complex. Although As^IIIPC₃ showed a ten times higher half-life (23 h) in a plant extract, the pre-cleaning step with subsequent fractionation in a mobile phase of pH 5.6 contributes to the destabilisation of the arsenic peptides in the off-line method. Furthermore, it was found that during a freeze-drying process more than 90% of an As^IIIPC₃ complex and smaller free peptides such as PC₂ and PC₃ can be lost. Although the two-dimensional off-line method has been used successfully for other metal complexes, it is concluded here that the fractionation and the subsequent freeze-drying were responsible for the loss of arsenic phytochelatin complexes during the analysis. Hence, the on-line HPLC–ICP-MS/ES-MS is the preferred method for such unstable peptide complexes. Since freeze-drying has been found to be undesirable for sample storage other methods for sample handling needed to be investigated. Hence, the storage of the fresh plant at low temperature was tested. We can report for the first time a storage method which successfully conserves the integrity of the labile arsenic phytochelatin complexes: quantitative recovery of As^IIIPC₃ in a formic acid extract of a Thunbergia alata exposed for 24 h to 1 mg As^v L⁻¹ was found when the fresh plant was stored for 21 days at 193 K. Figure On-line HPLC–ICP-MS/ES-MS (bottom) is the preferred method for MS determination of unstable arsenic peptide complexes in plant extracts, since this avoids fractionation and subsequent freeze-drying that are responsible for loss of arsenic phytochelatin complexes in the 2D off-line method (top) Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.