Mechanical stimulation of epithelial cells using polypyrrole microactuators

The importance of mechanotransduction for physiological systems is becoming increasingly recognized. The effect of mechanical stimulation is well studied in organs and tissues, for instance by using flexible tissue culture substrates that can be stretched by external means. However, on the cellular and subcellular level, dedicated technology to apply appropriate mechanical stimuli is limited. Here we report an organic electronic microactuator chip for mechanical stimulation of single cells. These chips are manufactured on silicon wafers using traditional microfabrication and photolithography techniques. The active unit of the chip consists of the electroactive polymer polypyrrole that expands upon the application of a low potential. The fact that polypyrrole can be activated in physiological electrolytes makes it well suited as the active material in a microactuator chip for biomedical applications. Renal epithelial cells, which are responsive to mechanical stimuli and relevant from a physiological perspective, are cultured on top of the microactuator chip. The cells exhibit good adhesion and spread along the surface of the chip. After culturing, individual cells are mechanically stimulated by electrical addressing of the microactuator chip and the response to this stimulation is monitored as an increase in intracellular Ca(2+). This Ca(2+) response is caused by an autocrine ATP signalling pathway associated with mechanical stimulation of the cells. In conclusion, the present work demonstrates a microactuator chip based on an organic conjugated polymer, for mechanical stimulation of biological systems at the cellular and sub-cellular level.     

NMR of heparin API: investigation of unidentified signals in the USP-specified range of 2.12–3.00 ppm

This article addresses the identification and quantification of the chemical species resulting in resonances at 2.17 and 2.25 ppm in the ¹H nuclear magnetic resonance (NMR) spectrum of pharmaceutical-grade heparin sodium. The NMR signals in question were first confirmed to arise from chemical moieties covalently attached to the heparin molecule through NMR diffusion experiments as well as chemical treatment of heparin active pharmaceutical ingredient (API) containing the resonances. The material responsible for the extra NMR signals was then demonstrated by NMR spiking studies to be something other than oversulfated chondroitin sulfate and was finally identified as an O-acetylation product of heparin through ¹³C labeling experiments with subsequent NMR analysis. The extent of O-acetylation was quantified using three orthogonal techniques: ¹H NMR, ion chromatography, and headspace gas chromatography/mass spectrometry. The results of this work showed good agreement between the three quantitative methods developed to analyze the signals in the United States Pharmacopeia-specified region of 2.12–3.00 ppm for heparin API.     

The role of low levels of water in the electrochemical oxidation of α-tocopherol (vitamin E) and other phenols in acetonitrile

The phenol, α-tocopherol, can be electrochemically oxidised in a -2e(-)/-H(+) process to form a diamagnetic cation that is long-lived in dry organic solvents such as acetonitrile and dichloromethane, but in the presence of water quickly reacts to form a hemiketal. Variable scan rate cyclic voltammetry experiments in acetonitrile with carefully controlled amounts of water between 0.010 M-0.6 M were performed in order to determine the rate of reaction of the diamagnetic cation with water. The water content of the solvent was accurately determined by Karl Fischer coulometric titrations and the voltammetric data were modelled using digital simulation techniques. The oxidation peak potential of α-tocopherol measured during cyclic voltammetry experiments was found to shift to less positive potentials as increasing amounts of water (0.01-0.6 M) were added to the acetonitrile, which was interpreted based on hydrogen-bonding interactions between the phenolic hydrogen atom and water. Several other phenols were examined and they displayed similar voltammetric features to α-tocopherol, suggesting that interactions of phenols with trace amounts of water were a common occurrence in acetonitrile. The H-bonding interactions of α-tocopherol with water were also examined via NMR and UV-vis spectroscopies, with the voltammetric and spectroscopic studies extended to include other coordinating solvents (dimethyl sulfoxide and pyridine).     

A class of nonlinear nonseparable continuous knapsack and multiple-choice knapsack problems

This paper considers a general class of continuous, nonlinear, and nonseparable knapsack problems, special cases of which arise in numerous operations and financial contexts. We develop important properties of optimal solutions for this problem class, based on the properties of a closely related class of linear programs. Using these properties, we provide a solution method that runs in polynomial time in the number of decision variables, while also depending on the time required to solve a particular one-dimensional optimization problem. Thus, for the many applications in which this one-dimensional function is reasonably well behaved (e.g., unimodal), the resulting algorithm runs in polynomial time. We next develop a related solution approach to a class of continuous, nonlinear, and nonseparable multiple-choice knapsack problems. This algorithm runs in polynomial time in both the number of variables and the number of variants per item, while again dependent on the complexity of the same one-dimensional optimization problem as for the knapsack problem. Computational testing demonstrates the power of the proposed algorithms over a commercial global optimization software package.     

6,6′-Dimethoxygossypol: molecular structure,crystal polymorphism,and solvate formation

6,6′-Dimethoxygossypol (DMG) is a naturally occurring derivative of gossypol that is found in relatively high concentration in some Gossypium barbadense cotton varieties. Like gossypol, DMG forms an equimolar solvate with acetic acid, but it was not known if, like gossypol, the compound would also form clathrates with other molecules. To test for this, the compound was crystallized from different solvents. Four new structures of DMG were found that include two polymorphic and two solvated forms. The polymorphs include two monoclinic structures with P2₁/c and C2/c space groups (P1 and P2, respectively). Packing of the DMG molecules P1 is similar to packing of the gossypol molecules in the P1 polymorphic form of gossypol. The DMG molecules in P2 pack in a highly ordered arrangement that has not been previously observed among gossypol structures. DMG forms equimolar solvates with water (S1) and cyclohexanone (S2). Both structures are triclinic with P [`1]P \bar {1} space groups. The DMG molecules in S2 assemble in a manner that is similar to the gossypol molecules of gossypol–cyclohexanone (1:1), and the DMG molecules in S1 pack in a manner that is similar to the DMG molecules in DMG–acetic acid (1:1) as well as the gossypol molecules in gossypol–acetic acid (1:1). Although DMG is not as versatile a host compound as gossypol, it still forms solvates under many crystallization conditions. Consequently, some care is needed to be sure that one understands exactly which form is recovered when the compound is isolated.     

25‐Allyloxy‐5,11,17,23‐tetra‐tert‐butyl‐26,27,28‐trihydroxycalix[4]arene chloroform disolvate

In the title solvated calixarene, C₄₇H₆₀O₄·2CHCl₃, the host chalice displays an almost undistorted cone conformation, stabilized by three strong O—H...O hydrogen bonds at the calixarene's lower rim. One chloroform solvent molecule is fixed in the calixarene cavity by C—H...π interactions, while the second is accommodated in a clathrate‐like mode in elliptical packing voids. These voids are spanned by six host molecules connected via C—H...π contacts and van der Waals interactions. Within the crystal structure, one tert‐butyl group of the calixarene host is disordered over two orientations, with occupancies of 0.884 (4) and 0.116 (4). Furthermore, both solvent molecules show disorder, with occupancies of 0.857 (2) and 0.143 (2) for the cavitate‐type, and 0.9359 (17) and 0.0641 (17) for the clathrate‐type chloroform solvent molecules.     

On-line analysis of volatile fatty acids in anaerobic treatment processes

In this paper, an on-line spectrofluorimetric system is proposed for a simple, rapid and accurate measurement of volatile fatty acids (VFA) in anaerobic treatment processes. The determination method is based on the derivatization of VFA with N-(1-naphthyl)ethylenediamine (EDAN) followed by a spectrofluorimetric detection of the corresponding amide. The analytical procedure is automated with a flow analysis technique, coupling multisyringe (MSFIA) and multi-pumping (MPFS) methods. Operative conditions have been investigated with a special attention paid to the activation and amidation steps and to the liquid-liquid extraction of the derivatized final product. Fluorescence intensities (λ_em = 335 nm, λ_ex = 395 nm) were found to be proportional to the concentration of VFA, expressed as acetic equivalent, in the range 19-1000 mg L⁻¹, with a detection limit (3σ) of 5.1 mg L⁻¹. Our results showed a good selectivity for VFA as compared to other organic and inorganic compounds usually found in sewage sludges. Validation of the on-line system developed has been assessed by application of the procedure to aqueous samples originating from sewage sludge treatment plants. The results were in good agreement with ion chromatography measurements.     

Superamphiphilic Janus fabric

Janus fabrics with superamphiphilicity were fabricated via electrospinning of polyacrylonitrile (PAN). PAN nanofibrous mats were formed on an aluminum foil substrate and then thermally treated to cause hydrolysis. An identical PAN solution was subsequently electrospun onto the hydrolyzed PAN layer, followed by peeling off of the bicomposite film from the collector substrate to produce a free-standing Janus fabric. On one side, the electrospun PAN mat exhibited superhydrophobic properties, with a water contact angle of 151.2°, whereas the initially superhydrophobic PAN sheet on the opposite side of the fabric was converted to a superhydrophilic surface (water contact angle of 0°) through hydrolysis of the surface functional groups induced by the thermal treatment. The resulting Janus fabrics exhibited both superhydrophobicity, repelling water on the one side, and superhydrophilicity, absorbing water on the other side. The organic solvent resistance of the PAN nanofibrous sheets was remarkably improved by incorporation of a tetraethyl orthosilicate. This facile and simple technique introduces a new route for the design and development of functional smart, robust fabrics from an inexpensive, commercially available polymer.     

Sol–gel derived Si/C/O/N‐materials: molecular model compounds,xerogels and porous ceramics

Polymeric Si/C/O/N xerogels, with the idealized polymer network structure comprising [Si O Si(NCN)₃]_n moieties, were prepared by reactions of hexachlorodisiloxane (Cl₃Si O SiCl₃) with bis(trimethylsilyl)carbodiimide (Me₃Si NCN SiMe₃, BTSC). NMR and FTIR spectra indicate the existence of ‐NCN‐ and Si O Si‐ units in the xerogels and also in the ceramic materials obtained upon pyrolysis. The feasibility of this reaction protocol was confirmed on the molecular level by the deliberate synthesis of the macrocyclic compound [SiPh₂ O SiPh₂(NCN)]₂, the crystal structure and spectroscopic data of which are reported. The influence of pyridine as a catalyst for the cross‐linking reaction was studied. The degree of cross‐linking increased within the polymers with the addition of pyridine. It was shown by the reaction of hexachlorodisiloxane with excess pyridine that the latter appears to activate only one out of the two ‐SiCl₃ moieties under formation of hexacoordinated silicon compounds. The crystal structure of Cl₃Si O SiCl₃(pyridine)₂ is presented. Quantum chemical calculations are in support of this adduct being a potential intermediate in the pyridine catalyzed sol–gel process. The ceramic yield after pyrolysis of the Si/C/O/N‐xerogels at 1000 °C, which reaches values up to 50%, was found to depend on the aging protocol (time, temperature), whereas no correlation was found with the amount of pyridine added for xerogel synthesis. The Si/C/N/O‐ceramics obtained after pyrolysis at 1000 °C under NH₃ are completely amorphous. Chemically they have to be considered as hybrids between an ideal [SiOSi(NCN)₃]_n network and glass‐like Si₂N₂O. The products are mesoporous with closed pores and a broad pore size distribution. Copyright © 2011 John Wiley & Sons, Ltd.