Electrochemical polymerisation of 2-aminofluorene in ethylalcohol/water medium

Electrochemical polymerisation of 2-aminofluorene, 2AF, was investigated in ethylalcohol/water mixture (3:2, v:v) in the presence of HClO₄ as the supporting electrolyte via constant potential electrolysis, CPE. Prior to CPE, electrochemical behaviour of the monomer was investigated in the same solvent-electrolyte couple utilising cyclic voltammetry, CV. Electrochemical polymerisation of the monomer yielded insoluble, dark bluish-green, conducting polymer deposit on the electrode surface. Characterisation of the polymer film has been carried out using FT-IR spectroscopic technique and thermal behaviour was studied using differential scanning calorimetry, DSC. Spectroelectrochemical, SPEL, behaviour of the polymer on ITO working electrode was studied by recording the electronic absorption spectra, in situ, in monomer-free solution at different potentials and it is found that the film can be reversibly cycled between −0.1 and 1.1 V vs SCE. Paramagnetic behaviour of the polymer was monitored using in situ ESR spectroscopy. The temperature dependence of conductivity supported the Mott's variable range hopping, VRH, mechanism for poly(aminofluorene), PAF.     

Dielectrophoretic tweezers as a platform for molecular force spectroscopy in a highly parallel format

We demonstrated the application of a simple electrode geometry for dielectrophoresis (DEP) on colloidal probes as a form of molecular force spectroscopy in a highly parallel format. The electric field between parallel plates is perturbed with dielectric microstructures, generating uniform DEP forces on colloidal probes in the range of several hundred piconewtons across a macroscopic sample area. We determined the approximate crossover frequency between negative and positive DEP using electrodes without dielectric microstructures-a simplification over standard experimental methods involving quadrupoles or optical trapping. 2D and 3D simulations of the electric field distributions validated the experimental behavior of several of our DEP tweezers geometries and provided insight into potential improvements. We applied the DEP tweezers to the stretching of a short DNA oligomer and detected its extension using total-internal reflection fluorescence microscopy. The combination of a simple cell fabrication, a uniform distribution of high axial forces, and a facile optical detection of our DEP tweezers makes this form of molecular force spectroscopy ideal for highly parallel detection of stretching or unbinding kinetics of biomolecules.     

Optimization of the solid phase extraction method for determination of Cu(II) in natural waters by using response surface methodology

A solid-phase extraction method was proposed for the preconcentration of Cu(II) in different samples in a mini-column packed with functionalized multi-walled carbon nanotubes (MWCNTs-COOH) as an effective sorbent, without using any complexing reagent, prior to its determination by flame atomic absorption spectrometry using response surface methodology. The experimental optimization step was performed by both a two-level full factorial design, with a center point, and a Box-Behnken design combined with response surface methodology. Three variables (pH, amount of Cu(II), and sample volume) were regarded as factors in the optimization. It was found that pH is the most significant factor affecting the preconcentration of Cu(II). The preconcentration factor was obtained as 100. The linear range was 1-5 mg L(-1) (R(2) = 0.999). Under the optimized experimental conditions, the detection limit (3s) of the proposed method followed by FAAS was found to be 0.27 μg L(-1). The relative standard deviation for 10 replicate measurements of 50 and 100 μg L(-1) Cu(II) was 2.39% and 0.98%, respectively. The response surface methodology was successfully applied to the determination of Cu(II) in water samples and mussel samples, and in a certified standard reference material (BCR-320R, Channel sediment).     

Supramolecular strategies to construct biocompatible and photoswitchable fluorescent assemblies

We designed and synthesized an amphiphilic copolymer with pendant hydrophobic decyl and hydrophilic poly(ethylene glycol) chains along a common poly(methacrylate) backbone. This macromolecular construct captures hydrophobic boron dipyrromethene fluorophores and hydrophobic spiropyran photochromes and transfers mixtures of both components in aqueous environments. Within the resulting hydrophilic supramolecular assemblies, the spiropyran components retain their photochemical properties and switch reversibly to the corresponding merocyanine isomers upon ultraviolet illumination. Their photoinduced transformations activate intermolecular electron and energy transfer pathways, which culminate in the quenching of the boron dipyrromethene fluorescence. As a result, the emission intensity of these supramolecular constructs can be modulated in aqueous environments under optical control. Furthermore, the macromolecular envelope around the fluorescent and photochromic components can cross the membrane of Chinese hamster ovarian cells and transport its cargo unaffected into the cytosol. Indeed, the fluorescence of these supramolecular constructs can be modulated also intracellularly by operating the photochromic component with optical inputs. In addition, cytotoxicity tests demonstrate that these supramolecular assemblies and the illumination conditions required for their operation have essentially no influence on cell viability. Thus, supramolecular events can be invoked to construct fluorescent and photoswitchable systems from separate components, while imposing aqueous solubility and biocompatibility on the resulting assemblies. In principle, this simple protocol can evolve into a general strategy to deliver and operate intracellularly functional molecular components under optical control.     

Influence of CH3 substituents on tetrahydropyrimidin-2-ylidene: σ-donating properties and in situ catalytic activities of precursor salts/Pd(OAc)2 system for C-C coupling reactions

In this study, symmetrical and non-symmetrical 1,3-dialkyltetrahydropyrimidinium salts (1·HCl and 2·HBr, respectively), bearing two methyl groups at C₅ position of the pyrimidine ring were synthesized and characterized. One of the new salts 1,3-bis(2,4,6-trimethylbenzyl)-5,5-dimethyl-3,4,5,6-tetrahydropyrimidinium tetrafluoroborate (1a·HBF₄, 1a = 6-Bn∗-Me₂) was converted to cis-[RhCl(6-Bn∗-Me₂)(CO)₂] to determine the σ-donating properties in comparison to those of their 5-membered NHC complexes. Furthermore, the in situ catalytic activities of all salts, in combination with Pd(OAc)₂, were tested for the Heck-Mizoraki and Suzuki-Miyaura type C-C coupling reactions. In contrast to the expectation, only the substituents on N,N′-atoms were found to play an important role in the catalytic activity.     

Novel antifouling oligo(ethylene glycol) methacrylate particles via surfactant-free emulsion polymerization

The use of particle formulations with antifouling surface properties attracts increasing interest in several biotechnological applications. Majority of these studies utilize a poly(ethylene glycol) coating to render the corresponding surface nonrecognizable to biological macromolecules. Herein, we report a simple way to prepare novel antifouling colloids composed of oligo(ethylene glycol) backbones via surfactant-free emulsion polymerization. Monodisperse cross-linked poly(ethylene glycol) ethyl ether methacrylate particles were characterized by dynamic light scattering and transmission electron microscopy. The effects of monomer, cross-linker and initiator on particle characteristics were investigated. More importantly, a prominent blockage of bovine serum albumin adsorption was obtained for the poly(ethylene glycol)-based sub-micron (~200 nm) particles when compared with similar-sized poly(methyl methacrylate) counterparts.     

Stability analysis of parallel server systems under longest queue first

We consider the stability of parallel server systems under the longest queue first (LQF) rule. We show that when the underlying graph of a parallel server system is a tree, the standard nominal traffic condition is sufficient for the stability of that system under LQF when interarrival and service times have general distributions. Then we consider a special parallel server system, which is known as the X-model, whose underlying graph is not a tree. We provide additional “drift” conditions for the stability and transience of these queueing systems with exponential interarrival and service times. Drift conditions depend in general on the stationary distribution of an induced Markov chain that is derived from the underlying queueing system. We illustrate our results with examples and simulation experiments. We also demonstrate that the stability of the LQF depends on the tie-breaking rule used and that it can be unstable even under arbitrary low loads.     

Coefficient bounds for a subclass of starlike functions of complex order

In the present work, we determine coefficient bounds for functions in certain subclass of starlike functions of complex order b, which are introduced here by means of a multiplier differential operator. Several corollaries and consequences of the main results are also considered.     

Electrical spin injection from an organic-based ferrimagnet in a hybrid organic-inorganic heterostructure

We report the successful extraction of spin-polarized current from the organic-based room temperature ferrimagnetic semiconductor V[TCNE](x) (x～2, TCNE: tetracyanoethylene; T(C)～400 K, E(G)～0.5 eV, σ(300?K)～10(-2) S/cm) and its subsequent injection into a GaAs/AlGaAs light-emitting diode. The spin current tracks the magnetization of V[TCNE](x～2), is weakly temperature dependent, and exhibits heavy-hole-light-hole asymmetry. This result has implications for room temperature spintronics and the use of inorganic materials to probe spin physics in organic and molecular systems.