Preparation of magnetic polymer colloids with Brownian magnetic relaxation

Magnetic polymer colloids (MPCs) consisting of CoFe₂O₄ nanoparticles (NPs) embedded in a poly(methyl methacrylate) (PMMA) matrix were synthesized by magnetic miniemulsion polymerization. CoFe₂O₄ NPs were modified with 3-trimethoxysilylpropylmethacrylate and directly emulsified with different concentrations of sodium dodecyl sulfate under ultrasonication for subsequent miniemulsion polymerization. The average diameter of the CoFe₂O₄/PMMA spheres (about 200 nm) was controlled by varying the amount of surfactant. Thermogravimetric analysis indicated that the magnetic content was in the range of 44 to 73 %. Magnetic properties of the dispersions were investigated by measuring equilibrium magnetization curves and the dynamic magnetic susceptibility as a function of frequency. The MPCs were found to follow the Debye model for the dynamic magnetic susceptibility, with a characteristic time given by the rotational hydrodynamic resistance and thermal energy through the Stokes-Einstein relation. This demonstrates that the MPCs respond to applied magnetic fields by rotating. Due to their uniform size and high magnetic loading, these colloids may be suitable in a variety of applications, including nanoscale mechanical probes and actuators in complex fluids and biological systems.     

Partial molar volume and partial molar compressibility of four homologous α-amino acids in aqueous sodium fluoride solutions at different temperatures

Density and ultrasonic speed of four amino acids (glycine, l-alanine, l-valine, and l-leucine) in aqueous sodium fluoride solutions {(0.1 to 0.5) M} have been measured at T = (308.15, 313.15, and 318.15) K. Apparent molar volumes (V_φ), partial molar volumes $\left(V_{\phi }^0\right)$, transfer volumes $\left(\mathrm{\Delta }{V}_{\phi }^0\right)$ and hydration number (n_H) are evaluated using density data. Adiabatic compressibility (β_s), change (Δβ_s), and relative change in compressibility (Δβ_s/β₀), apparent molar compressibility (K_φ), partial molar compressibility $\left(K_{\phi }^0\right)$, transfer compressibility $\left(\mathrm{\Delta }{K}_{\phi }^0\right)$, and hydration number (n_H) have been calculated using ultrasonic speed data. The linear correlation of $V_{\phi }^0\text{,}\mathrm{\Delta }{V}_{\phi }^0\text{,}{K}_{\phi }^0$ and $\mathrm{\Delta }{K}_{\phi }^0$ for a homologous series of amino acids have been used utilised to calculate the contribution of charged end groups (${\text{NH}}_3^{+}$, COO^?), CH₂ group and other alkyl chain of the amino acids. The analysis shows that the ion–ion interactions are much stronger than ion–hydrophobic interactions over the entire concentration range of sodium fluoride. It is observed that sodium fluoride has a strong dehydration effect on amino acids.     

Poly[(μ4‐2,5‐dimethoxybenzene‐1,4‐dicarboxylato)manganese(II)] and its zinc(II) analogue: three‐dimensional coordination polymers containing unusually coordinated metal centres

The title compounds, [Mn(C₁₀H₈O₆)]_n and [Zn(C₁₀H₈O₆)]_n, are isomorphous coordination polymers prepared from 2,5‐dimethoxyterephthalic acid (H₂dmt) and the respective metal(II) salts. Both complexes form three‐dimensional metal–organic frameworks with each M^II centre bridged by four 2,5‐dimethoxyterephthalate (dmt²⁻) anions, resulting in the same type of network topology. The asymmetric unit consists of one M^II cation on a twofold axis and one half of a dmt²⁻ anion (located on a centre of inversion). In the crystal structure, the M^II centres are coordinated in a rather unusual way, as there is a distorted tetrahedral inner coordination sphere formed by four carboxylate O atoms of four different dmt²⁻ anions, and an additional outer coordination sphere formed by two methoxy and two carboxylate O atoms, with each of the O atoms belonging to one of the four different dmt²⁻ anions forming the inner coordination sphere. Consideration of both coordination spheres results in a super‐dodecahedral coordination geometry for the M^II centres. Besides the numerous M^II...O interactions, both structures are further stabilized by weak C—H...O contacts.     

X-ray crystal structures of <Emphasis Type=Italic>p</Emphasis>-halogenated 6,6-diphenylfulvenes

Crystal structures of a series of p-halogenated 6,6-diphenylfulvenes 2–5 are reported and comparatively discussed including the known structure of the non-halogenate parent compound 1. The molecular structures show twisted conformations of the plane aryl and fulvene subunits against each other, rather unaffected by the different halogen substituents. The packing structures exclusively involve C–H···X (X = F, Cl, π) contacts while Hal···Hal and π-stacking interactions do not occur.     

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.     

A robust method to quantify low molecular weight contaminants in heparin: detection of tris(2-n-butoxyethyl) phosphate

Recently, oversulfated chondroitin sulfate (OSCS) was identified in contaminated heparin preparations, which were linked to several adverse clinical events and deaths. Orthogonal analytical techniques, namely nuclear magnetic resonance (NMR) and capillary electrophoresis (CE), have since been applied by several authors for the evaluation of heparin purity and safety. NMR identification and quantification of residual solvents and non-volatile low molecular contaminants with USP acceptance levels of toxicity was achieved 40-fold faster than the traditional GC-headspace technique, which takes ~120 min against ~3 min to obtain a (1)H NMR spectrum with a signal/noise ratio of at least 1000/1. The procedure allowed detection of Class 1 residual solvents at 2 ppm and quantification was possible above 10 ppm. 2D NMR techniques (edited-HSQC (1)H/(13)C) permitted visualization of otherwise masked EDTA signals at 3.68/59.7 ppm and 3.34/53.5 ppm, which may be overlapping mononuclear heparin signals, or those of ethanol and methanol. Detailed NMR and ESI-MS/MS studies revealed a hitherto unknown contaminant, tris(2-n-butoxyethyl) phosphate (TBEP), which has potential health risks.     

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.     

Fluxionality in the chemical reactions of transition metal oxide clusters: the role of metal, spin state, and the reactant molecule

The phenomenon of fluxionality in the reactions of transition metal oxide clusters provides many opportunities in various catalytic and industrial processes. To gain a better understanding into the various factors influencing this phenomenon, we have carried out an electronic structure investigation of the fluxionality pathways when W(3)O(6)(-) and Mo(3)O(6)(-) clusters react with hydrogen sulfide and ammonia. The study illustrates how the metal (W vs Mo), different spin states of the anionic metal oxide cluster (doublet vs quartet), and the nature of the nonmetal in the small molecule (O vs S vs N), all affect the fluxionality pathway. The thermodynamically facile fluxionality pathway with H(2)S detaches both the hydrogens from hydrogen sulfide and can thus be very useful in the petrochemical and desulfurization industries. The fluxionality pathway with NH(3) results in interesting metal-bound imines and bridged amines. However, the overall fluxionality process with NH(3) is found to be thermodynamically unfavorable.     

Synthesis of silicophosphates containing SiO6-octahedra under ambient conditions--reactions of anhydrous H3PO4 with alkoxysilanes

Anhydrous H(3)PO(4) reacts in diethylether solution at room temperature with ethoxysilanes to form silicophosphates which contain SiO(6)-units. A single crystal X-ray structure provides evidence for silicophosphate structures comprised of alternating SiO(4)- and PO(4)-tetrahedra as well as SiO(6)-octahedra.