Three different β‐cyclodextrins direct the emulsion copolymerization of a highly fluorinated methacrylate toward distinctive nanostructured particle morphologies

Stable colloidal dispersions of nanostructured semifluorinated acrylic particles with an unfluorinated core and an outer layer consisting of copolymers of the highly hydrophobic and lipophobic heptadecafluorodecyl methacrylate (FMA) were successfully synthesized with the assistance of three different cyclodextrins as phase‐transfer catalysts: β‐cyclodextrin (β‐CD), hydroxypropyl β‐cyclodextrin (HpCD), and methyl β‐cyclodextrin (MeCD). While all the cyclodextrins form a stable inclusion complex (IC) with FMA, only the ICs with the more hydrophilic HpCD and MeCD are soluble in water. Nevertheless, incorporation of FMA in the particle shell copolymer could be achieved also when using β‐CD. On the other hand, the morphology of the nanostructured particles was characterized by a “patchy” fluorinated shell dependent on the cyclodextrin used, the best results being obtained with MeCD. A monomer‐starved semicontinuous emulsion polymerization procedure was essential to favor the CD‐mediated incorporation of FMA into the copolymer structure and to achieve a stable colloidal dispersion even in the presence of small amounts of mixed anionic–nonionic surfactants. The thermal and surface properties of the latex films showed a good correlation with the shell composition and patchy nanostructured morphology of the particles. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Size‐Tunable Highly Luminescent SiO2 Particles Impregnated with Number‐Adjusted CdTe Nanocrystals

Highly luminescent SiO₂ particles impregnated with CdTe nanocrystals (NCs) are prepared by a sol–gel procedure. Partial ligand exchange from thioglycolic acid to 3‐mercaptopropyltrimethoxysilane (MPS) on the NCs enables retention of the initial photoluminescence (PL) efficiency of the NCs in water, while the simultaneous addition of a poor solvent (ethanol) results in regulated assembly of the NCs through condensation of hydrolyzed MPS. The SiO₂ particles thus prepared have, for example, a diameter of 16 nm and contain three NCs each. The PL efficiency of these particles is 40 %, while the initial efficiency is 46 % in a colloidal solution. The redshift and narrowed spectral width in PL observed after impregnation indicate that the concentration of NCs in these nearly reaches the ultimate value (on the order of 10²¹ particles per liter). The porosity of these particles is investigated by means of N₂ adsorption–desorption isotherms. Due to the SiO₂ shell, these particles have higher stability in phosphate‐buffered saline buffer solution than the initial NCs. Their potential use for labeling in bio‐applications is investigated by conjugating biotinylated immunoglobulin G to them by using streptavidin maleimide as linker. Successful conjugation is confirmed by electrophoresis in agarose gel. This preparation method is an important step towards fabricating intensely emitting biocompatible SiO₂ particles impregnated with semiconductor NCs.     

Electrochemical Investigation of Binding of Heavy Metal Ions to Turkish Lignites

Adsorption and desorption of Cu²⁺, Pb²⁺, Cd²⁺, Ni²⁺ and Zn²⁺ ions on samples of lignites (young brown coal) from three areas in the vicinity of Konya (Anatolia, Turkey) were followed using the polarographic method of analysis. This method enables the determination of free metal ions in suspensions containing both small and colloidal particles of lignite. Effects of pH, nature of the metal ion, and origin of the lignite on its adsorption capacity were followed. Binding is only between 5 and 30% reversible, indicating that ion exchange is not the predominant factor. The role of the size and shape of cavities inside pulverized lignite and of the functional groups inside these cavities was considered.     

Nucleation and Growth Synthesis of Siloxane Gels to Form Functional,Monodisperse, and Acoustically Programmable Particles

Nucleation and growth methods offer scalable means of synthesizing colloidal particles with precisely specified size for applications in chemical research, industry, and medicine. These methods have been used to prepare a class of silicone gel particles that display a range of programmable properties and narrow size distributions. The acoustic contrast factor of these particles in water is estimated and can be tuned such that the particles undergo acoustophoresis to either the pressure nodes or antinodes of acoustic standing waves. These particles can be synthesized to display surface functional groups that can be covalently modified for a range of bioanalytical and acoustophoretic sorting applications.     

Colloidal Microcapsules: Self‐Assembly of Nanoparticles at the Liquid–Liquid Interface

Colloidal microcapsules (MCs) are highly modular, inherently multiscale constructs of capsules stabilized by nano‐/microparticle shells, with applications in many areas of materials and biological sciences, such as drug delivery, encapsulation, and microreactors. Until recently, fabrication of colloidal MCs focused on the use of submicron‐sized particles because the smaller nanoparticles (NPs) are inherently unstable at the interface owing to thermal disorder. However, stable microcapsules can now be obtained by tuning the interactions between the nanometer‐sized building blocks at the liquid–liquid interface. This Review highlights recent developments in the fabrication of colloidal MCs using NPs.     

Polyaniline dispersions 7. Dynamic light scattering study of particle formation

 When aniline is oxidized in the presence of colloidal silica, composite polyaniline–silica particles of submicrometer size are obtained. Dynamic light scattering was used to monitor the course of dispersion polymerization of aniline and the formation of particles. The increase of a hydrodynamic radius of particles was observed as polyaniline had been produced. Additional increase in particle size after polymerization has also been recorded. The rate of aniline polymerization was found to increase with increasing temperature in the range 0–50 °C. Well-defined particles are formed below 30 °C while above this temperature the colloidal stability of the resulting systems is limited. The activation energy of aniline polymerization was estimated. Received: 24 February 1997 Accepted: 7 May 1997     

Synthesis, characterization and SERS activity of Au-Ag nanorods

The formation mechanism and morphology of Au-Ag bimetallic colloidal nanoparticles depend on the composition. Ag coated Au colloidal nanoparticles have been prepared by deposition of Ag through chemical reduction on performed Au colloid. The composition of the Au(100-x)-Ag(x) particles was varied from x=0 to 50. The obtained colloids were characterized by UV-vis spectroscopy and transmission electron microscopy (TEM). The Au(80)-Ag(20) colloid consists of alloy nanorods with dimension of 25nmx100nm. The activity of these nanorods in surface enhanced Raman spectroscopy (SERS) was checked by using sodium salicylate as an adsorbate probe. Intense SERS bands are observed indicating its usefulness as a SERS substrate in near infrared (NIR) laser excitation.     

A Single‐Step Reaction for Silicon and Germanium Nanorods

A single‐step reaction has been developed for colloidal quantum‐size silicon (Si) and germanium (Ge) nanorods. The nanorods are formed by solution–liquid–solid (SLS) growth from tin (Sn) seed particles prepared by in situ reduction of a molecular tin(II) complex by trisilane, the reactant for Si nanorod growth. Using the same procedure, Ge nanorods can be grown by including a diphenyl germane reactant. The nanorod length could be adjusted from several nanometers to more than a micrometer without significant increase of diameter by manipulating reactant concentrations.     

Characteristic ion clusters as determinants for the identification of pyrrolizidine alkaloid N‐oxides in pyrrolizidine alkaloid–containing natural products using HPLC–MS analysis

Pyrrolizidine alkaloid (PA)–containing plants are widely distributed in the world. PAs are hepatotoxic, affecting livestock and humans. PA N‐oxides are often present together with PAs in plants and also exhibit hepatotoxicity but with less potency. HPLC–MS is generally used to analyze PA‐containing herbs, although PA references are unavailable in most cases. However, to date, without reference standards, HPLC–MS methodology cannot distinguish PA N‐oxides from PAs because they both produce the same characteristic ions in mass spectra. In the present study, the mass spectra of 10 PA N‐oxides and the corresponding PAs were systemically investigated using HPLC–MS to define the characteristic mass fragment ions specific to PAs and PA N‐oxides. Mass spectra of toxic retronecine‐type PA N‐oxides exhibited two characteristic ion clusters at m/z 118–120 and 136–138. These ion clusters were produced by three unique fragmentation pathways of PA N‐oxides and were not found in their corresponding PAs. Similarly, the nontoxic platynecine‐type PA N‐oxides also fragmented via three similar pathways to form two characteristic ion clusters at m/z 120–122 and 138–140. Further application of using these characteristic ion clusters allowed successful and rapid identification of PAs and PA N‐oxides in two PA‐containing herbal plants. Our results demonstrated, for the first time, that these characteristic ion clusters are unique determinants to discriminate PA N‐oxides from PAs even without the availability of reference samples. Our findings provide a novel and specific method to differentiate PA N‐oxides from PAs in PA‐containing natural products, which is crucial for the assessment of their intoxication. Copyright © 2012 John Wiley & Sons, Ltd.     

pH‐Controlled Formation of a Stable β‐Sheet and Amyloid‐like Fibers from an Amphiphilic Peptide: The Importance of a Tailor‐Made Binding Motif for Secondary Structure Formation

The new amphiphilic peptide 1 is composed of alternating cyclohexyl side chains and guanidiniocarbonyl pyrrole (GCP) groups. In contrast to analogue 2 , which contains lysine instead of the GCP groups and only exists as a random coil owing to charge repulsion, peptide 1 forms a stable β‐sheet at neutral pH in aqueous medium. The weakly basic GCP groups (pK_a≈7) are key for secondary structure formation as they stabilize the β‐sheet through mutual interactions (formation of a “GCP zipper”). The β‐sheets further aggregate into left‐handed helically twisted fibers. However, β‐sheet formation is completely reversible as a function of pH. At low pH (ca. 4), peptide 1 is unstructured (random coil) as all GCP units are protonated. Only round colloidal particles are observed. The amyloid nature of the fibers formed at neutral pH was confirmed by staining experiments with Congo Red and thioflavin T. Furthermore, at millimolar concentrations, peptide 1 forms a stable hydrogel.     

Collapse transitions of a supersized neutral chain due to irreversibly adsorbed small colloidal particles

 We performed Monte Carlo simulations to study the destabilization processes of large neutral and flexible polymer chains due to irreversibly adsorbed colloidal particles attached to the chains like beads on a necklace. The particles are modeled as charged spherical units which interact with each other via repulsive electrostatic and attractive van der Waals (vdW) potentials. The usual Monte Carlo search procedure is extended and carefully checked to completely sample the chain conformational space and achieve dense conformations in the limit of both strong attractive and repulsive interaction potentials. Configurational properties, such as the radius of gyration, the end-to-end length, and the Kuhn length, are calculated as a function of the intensity of the vdW interactions and ionic strength values. It is observed that chains exhibit a new range of possible conformations compared to the classical random walk and self avoiding walk chains or polyelectrolytes. In the limit of low salt concentration, by gradually increasing vdW interactions, chains undergo a cascade of transitions from extended structures to dumbbells, from dumbbells to pearl necklaces, and from pearl necklaces to collapsed coils. Because of strong competition between the vdW and electrostatic forces, the distance along the chain between the interacting particles, and the sampling limitations, these transitions are found to sample metastable domains and to depend on the initial conformations. To gain insight into the spatial organization of the collapsed conformations, the pair correlation functions of both monomers and particles are calculated. It is shown that collapsed conformations which are the result of strong particle–particle interactions exhibit two distinct parts: a hard core mainly composed of particles and a surrounding polymeric shell composed of loops and tails. Possible effects of such a collapsed transition on the kinetics of flocculation of a mixture containing large flexible chains and small adsorbing colloidal particles are discussed. Received: 26 July 1999 Accepted in revised form: 9 November 1999     

Synthesis and Characterization of (2E,2 E)‐3,3‐((9,9‐diocyl‐9H‐flourene‐2,7‐diyl)bis(4,1‐phenylene))bis(2‐cyanoacylic acid) as a Symmetrical Metal‐free Organic Dye

In this study a novel symmetrical metal‐free organic dye for applications in dye‐sensitized solar cells (DSSCs) was synthesized. This dye ( D ) was designed with A–π–D–π–A framework and synthesized with 9,9‐dioctylfluorene as electron donor, phenylene as π‐spacer and cyanoacetic acid as electron acceptor. The chemical structure of product was determined using UV‐Vis, FT‐IR, CNMR, HNMR spectroscopy techniques. The presence of a phenylene π‐bridge between the donor and the acceptor units and the di‐anchoring moieties in this structure led to enhancement of conjugation lengths and molar extinction coefficient (ε) that is promising for further improvement of the conversion efficiency of DSSCs.     

The disproportionation of Cu(I)X mediated by ligand and solvent into Cu(0) and Cu(II)X2 and its implications for SET‐LRP

Disproportionation of Cu(I)X is the major step in Single‐Electron Transfer Living Radical Polymerization (SET‐LRP). The disproportionation of Cu(I)X mediated by Me₆‐TREN in various solvents was studied through UV–vis spectroscopy and Dynamic Light Scattering (DLS). UV–vis experiments reveal that disproportionation is dependent on both solvent composition and concentration of Me₆‐TREN, consistent with a revised equilibrium expression and corroborated by mathematical models. Electrochemistry data do not accurately predict the extent of disproportionation in the presence of Me₆‐TREN. Exemplified by DMSO, a favored solvent for SET‐LRP, UV–vis spectroscopy shows that under certain conditions disproportionation is four‐orders of magnitude greater than the value reported from electrochemistry experiments. Through UV–vis and DLS analysis, it was demonstrated that DMSO, DMF, DMAC, and NMP, stabilize colloidal Cu(0), while acetone, EtOH, EC, MeOH, PC, and H₂O facilitate agglomeration of Cu(0) particles. Additionally, for colloidal Cu(0) stabilizing solvents, the amount of ligand and solvent composition decide the particle size distribution. Therefore, the kinetics of SET‐LRP are cooperatively and synergistically determined by the complex interplay of solvent polarity, the extent of disproportionation in the solvent/ligand mixture, and the ability of that mixture to stabilize colloidal Cu(0) or control particle size distribution. The implications of these results for SET‐LRP are discussed. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5606–5628, 2009     

Interaction between small colloidal particles and polymer chains in a semidilute solution: Monte Carlo simulation

 Interaction between flexible-chain polymers and small (nanometric) colloidal particles is studied by Monte Carlo simulation using two-dimensional and three-dimensional lattice models. Spatial distribution of colloidal particles and conformational characteristics of chains in a semidilute solution are considered as a function of the segment adsorption energy, ɛ. When adsorption is sufficiently strong, it induces effective attraction of polymer segments, which results in contraction of macromolecular coils. The strongly adsorbing polymer chains affect the equilibrium spatial distribution of the colloidal particles. The average size of colloidal aggregates <m> exhibits a nontrivial behavior: with ɛ increasing, the value of <m> first decreases and then begins to grow. The adsorption polycomplex formed at strong adsorption exhibits a mesoscopic scale of structural heterogeneity. The results of computer simulations are in a good agreement with predictions of the analytic theory [P.G. Khalatur, L.V. Zherenkova and A.R. Khokhlov (1997) J Phys II (France) 7:543] based on the integral RISM equation technique. Received: 4 August 1997 Accepted: 16 April 1998     

Tuning the Colloidal Crystal Structure of Magnetic Particles by External Field

Manipulation of the self‐assembly of magnetic colloidal particles by an externally applied magnetic field paves a way toward developing novel stimuli responsive photonic structures. Using microradian X‐ray scattering technique we have investigated the different crystal structures exhibited by self‐assembly of core–shell magnetite/silica nanoparticles. An external magnetic field was employed to tune the colloidal crystallization. We find that the equilibrium structure in absence of the field is random hexagonal close‐packed (RHCP) one. External field drives the self‐assembly toward a body‐centered tetragonal (BCT) structure. Our findings are in good agreement with simulation results on the assembly of these particles.     

Synthesis and characterization of nonaqueous dispersion particles with photolabile α‐heptadecylphenacyl ester stabilizer chains

We describe a new method for the synthesis of core–shell photolabile nanoparticles. The synthesis begins with the batch emulsion copolymerization of n‐butyl methacrylate (BMA) and ethylene glycol dimethacrylate to form small (20‐nm‐diameter) crosslinked particles with a narrow size distribution. These seeds are then used for a second‐stage emulsion copolymerizations in which BMA and various polar monomers, including methacrylic acid, are added under monomer‐starved conditions. After characterization of the particles, they are transferred to an N,N‐dimethylformamide solution. The cesium salt of the carboxylic acid groups is reacted with 2‐bromo‐1‐phenyl‐octadecan‐1‐one to convert various fractions of the ? COOH groups to the corresponding 2‐benzoylheptadecyl ester groups. These aliphatic ester groups render the surface sufficiently hydrophobic that the particles can be dispersed in common aliphatic hydrocarbons solvents to yield colloidal dispersions, sterically stabilized by the dangling aliphatic chains. Ester groups with a phenyl ketone attached to the β‐carbon are photolabile. Irradiation of the particles with UV light detaches the sterically stabilizing chains from the particle and transforms the surface groups back to COOH groups. This leads to flocculation of the particles. The emphasis in this article is on the optimization of the particle synthesis and the characterization of the particles obtained. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2642–2657, 2001     

The performance of density functional theory for LnF (Ln=Nd,Eu, Gd,Yb) and YbH

Different density functional theory (DFT) functionals have been evaluated by studying geometries and bond strengths of YbH, YbF, EuF, GdF, and NdF and compared with accurate CCSD(T) results and, when available, experiment. The agreement between the CCSD(T) results and experiment, when available, is good. The agreement is also good between bond strengths calculated at the DFT level using relativistic effective core potentials and the CCSD(T) results. However, the all-electron ADF calculations systematically overestimate binding energies. The geometries obtained by both the all-electron and the effective-core-potential-based DFT calculations are generally in good agreement with the CCSD(T) results.Contribution to the Björn Roos Honorary Issue     

The electrochemical behavior of colloidal polypyrrole

 The electrochemical behavior and charge transport of colloidal polypyrrole particles (without stabilizer) modified electrode have been investigated. The voltam-metric results show that the electro-chemical behavior of colloidal polypyrrole is different from that of polypyrrole synthesized electro-chemically. The strong adsorption of the colloidal particles on substrate makes it easy to form a polypyrrole modified electrode. The charge transport of polypyrrole is controlled by the diffusion of counterions. Received: 13 December 1996 Accepted: 24 May 1997     

Preparation and chemical properties of soluble π‐conjugated poly(aryleneethynylene) consisting of azabenzothiadiazole as the electron‐accepting unit

A soluble charge‐transfer type poly(aryleneethynylene), PAE‐AzaBzTdz , consisting of a highly electron‐accepting azabenzothiadiazole unit was prepared in 99% yield by palladium‐catalyzed polycondensation between 4,7‐dibromo‐2,1,3‐azabenzothiadiazole ( Br₂‐AzaBzTdz ) and 1,4‐diethynyl‐2,5‐didodecyloxybenzene. PAE‐AzaBzTdz showed a number‐average molecular weight, M_n, of 6000 in gel‐permeation chromatography analysis and had good thermal stability as measured by TGA. UV–vis spectrum of PAE‐AzaBzTdz exhibited an absorption peak at 529 nm in chloroform, and the absorption peak shifted to a longer wavelength (601 nm) in film. Addition of MeOH to a CHCl₃ solution of PAE‐AzaBzTdz led to aggregation of the polymer to form stable colloidal particles. Results of filtration experiments using 0.2 and 0.02 μm membranes supported aggregation of the polymer. Addition of trifluoroacetic acid (TFA) to a chloroform solution of PAE‐AzaBzTdz led to a red‐shift of the UV–vis peak from 529 to 640 nm. An X‐ray diffraction pattern of powdery PAE‐AzaBzTdz indicated that the polymer assumed a layer‐to‐layer stacked structure with an interlayer distance of 3.4 Å in the solid state. An X‐ray diffraction pattern of cast film of PAE‐AzaBzTdz revealed that the polymer molecules in the cast film were ordered on the surface of Pt plate with the dodecyl side chain oriented toward the surface of the Pt plate. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2975–2982, 2008     

Novel lipid-based colloidal dispersions as potential drug administration systems – expectations and reality

 Colloidal drug carriers offer a number of potential advantages as delivery systems for, for example, poorly soluble compounds. The first generation of colloidal carriers, in particular liposomes and sub-micron-sized lipid emulsions, are, however, associated with several drawbacks which so far have prevented the extensive use of these carriers in drug delivery. As an alternative colloidal delivery system melt-emulsified nanoparticles based on solid lipids have been proposed. Careful physicochemical characterization has demonstrated that these lipid-based nanosuspensions (solid lipid nanoparticles) are not just “emulsions with solidified droplets”. During the development process of these systems interesting phenomena have been observed, such as gel formation on solidification and upon storage, unexpected dynamics of polymorphic transitions, extensive annealing of nanocrystals over significant periods of time, stepwise melting of particle fractions in the lower-nanometer-size range, drug expulsion from the carrier particles on crystallization and upon storage, and extensive supercooling. These phenomena can be related to the crystalline nature of the carrier matrix in combination with its colloidal state. Observation of the supercooling effect has led to the development of a second new type of carrier system: nanospheres of supercooled melts. This novel type of colloidal lipidic carrier represents an intermediate state between emulsions and suspensions. Moreover, these dispersions are particularly suited to the study of the basic differences between colloidal triglyceride emulsions and suspensions. For many decades drug carriers have represented the only group of colloidal drug administration systems. Nowadays a fundamentally different group of dispersions is also under investigation: drug nanodispersions. They overcome a number of carrier-related drawbacks, such as limitations in drug load as well as side effects due to the matrix material of the carrier particles. Utilizing this concept virtually insoluble drugs can be formulated as colloidal particles, of solid or supercooled nature. For example, coenzyme Q₁₀ (Q₁₀) has been successfully processed into a dispersion of a supercooled melt. Droplet sizes in the lower nanometer range and shelf lives of more than 3 years can easily be achieved for Q₁₀ dispersions. The drug load of the emulsion particles reaches nearly 100%. Received: 15 July 1999/Accepted: 11 November 1999