Polyferrocenylsilane microspheres: synthesis,mechanism of formation,size and charge tunability,electrostatic self-assembly,and pyrolysis to spherical magnetic ceramic particles

Pt(0)-catalyzed ring-opening precipitation copolymerization of [1]silaferrocenophanes fcSiMe(2) (3) and the spirocyclic cross-linker fcSi(CH(2))(3) (4) (fc = Fe(eta(5)-C(5)H(4))(2)) was used to prepare polyferrocenylsilane microspheres (PFSMSs) under mild conditions. By varying the reaction conditions, a wide variety of other morphologies was obtained. The effects of temperature, monomer ratio, solvent composition, catalyst concentration, and time on the observed morphology were investigated and interpreted in terms of a mechanism for microsphere formation. The most well-defined particles were formed using equimolar amounts of 3 and 4, in a 50:50 mixture of xylenes and decane at 60 degrees C with gentle agitation. Chemical oxidation of the polymeric microspheres led to positively charged particles (OPFSMSs) which underwent electrostatically driven self-assembly with negatively charged silica microspheres to form core-corona composite particles. Redox titration with controlled amounts of the one-electron oxidant [N(C(6)H(4)Br-p)(3)][PF(6)] in acetonitrile led to the oxidation of the outer 0.15 microm (ca. 32%) of the PFSMSs. The resulting OPFSMSs were reduced back to their neutral form by reaction with hydrazine in methanol. Pyrolysis of the PFSMSs led to spherical magnetic ceramic replicas with tunable magnetic properties that organize into ordered 2-D arrays at the air-water interface under the influence of a magnetic field.     

A reinterpretation of the magnetic properties of the mixed-valence (Nb(V)/Nb(IV)) Zintl phase, Cs(9)Nb(2)As(6)

A new mixed-valent (Nb(V)/Nb(IV)) Zintl phase, Cs(9)Nb(2)As(6), has been prepared and characterized, recently (Gascoin, F.; Sevov, S. C. Inorg. Chem. 2002, 41, 5920). Niobium is present in the form of isolated, edge-sharing tetrahedral, Nb(2)As(6)(9)(-) dimers. The reported magnetic susceptibility features a broad maximum at approximately 36 K which has been interpreted as the onset of long-range antiferromagnetic order. Such a high transition temperature is difficult to understand as the compound is insulating and the interdimer Nb-Nb distance is 7.2 A. It is shown here that the observed magnetic properties follow straightforwardly from a statistical occupation of the equivalent intradimer Nb sites by equal concentrations of Nb(IV)(4d(1), S = (1)/(2)) and Nb(V)(4d(0)). From this analysis the broad maximum arises from intradimer antiferromagnetic exchange with an exchange constant, J/k = -40 K, and there is no long-range magnetic order except, possibly, below 5 K.     

Fluidic and air-stable supported lipid bilayer and cell-mimicking microarrays

As drug delivery, therapy, and medical imaging are becoming increasingly cell-specific, there is a critical need for high fidelity and high-throughput screening methods for cell surface interactions. Cell membrane-mimicking surfaces, i.e., supported lipid bilayers (SLBs), are currently not sufficiently robust to meet this need. Here we describe a method of forming fluidic and air-stable SLBs through tethered and dispersed cholesterol groups incorporated into the bottom leaflet. Achieving air stability allows us to easily fabricate SLB microarrays from direct robotic spotting of vesicle solutions. We demonstrate their application as cell membrane-mimicking microarrays by reconstituting peripheral as well as integral membrane components that can be recognized by their respective targets. These demonstrations establish the viability of the fluidic and air-stable SLB platform for generating content microarrays in high throughput studies, e.g., the screening of drugs and nanomedicine targeting cell surface receptors.     

Fluorescence and Mass Spectrometry Studies of Meta-tetra(hydroxyphenyl)chlorin Photoproducts

The meta-tetra(hydroxyphenyl)chlorin (m-THPC), a second-generation sensitizer used in photodynamic therapy (PDT), is currently under clinical trial. In vivo fluorometry provides direct evidence that photobleaching processes are induced at the tumor site during PDT. Photoproduct formation has thus to be taken into account to fully understand PDT treatment. A preliminary step is to determine the fluorescence characteristics of photoproducts formed in solution. Solutions of m-THPC irradiated at 514 nm have been separated by HPLC using absorption and fluorescence detection. Six main photoproducts have been isolated. According to matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOFMS) results, five fluorescent photoproducts emitting at 652 nm have been attributed to three mono-, one di- and one tri-hydroxy derivatives (m/z 697, 713 and 729, respectively). Fluorescence characteristics of mono-hydroxy forms were found to be similar to those of m-THPC, whereas fluorescence yields in di- and tri-hydroxy derivatives were very low. Another product, corresponding to a MALDI-TOF MS main signal at m/z 542, showed an absorption spectrum maximum at 522 nm while a weak fluorescence was detected at 480 nm. The loss of the Soret band suggests that this photoproduct results from the opening of the reduced pyrrole ring. The part played by each of these products in the photobleaching phenomenon of m-THPC is discussed.     

Complexes of divalent transition metal chlorides with the tetradentate Schiff base ligand 1,2-bis(2′-pyridylmethyleneimino)-benzene

Summary Transition metal(II) chloro complexes of the new Schiff base ligand 1,2-bis(2-pyridylmethyleneimino)benzene (L), derived from 2-pyridinecarboxaldehyde and 1,2-phenylenediamine, were prepared. Compounds of [MnLCl₂]-H₂O, [CoLCl₂]·2H₂O, [NiLCl₂] and [Zn₃L₂Cl₄]Cl₂ were prepared. Details are given of the formation of the complex [Cu(L·EtOH)Cl₂], in which one molecule of EtOH adds across only one of the Schiff base {ie531-01} groups to give the coordinated ligand L·EtOH. The rationalization of this type of reaction by considering the steric requirements of the ligand is given. The complexes were characterized by elemental analyses, conductivity measurements, thermal techniques, mass spectra, magnetic susceptibilities and spectroscopic (i.r., ligand field, e.s.r., ¹H n.m.r.) studies. The nitrogen donor atoms of the tetradentate ligands L and L·EtOH are assumed to adopt an essentially planar arrangement about manganese(II), cobalt(II), nickel(II) and copper(II), with the remaining axial coordination sites occupied by chloro ligands to yield high-spin octahedral molecules. A trinuclear structure, based on tetrahedrally coordinated metal ions, is proposed for the zinc(II) complex.     

Development,validation, and implementation of an UHPLC–MS/MS method for the quantitation of furosemide in infant urine samples

Furosemide is a diuretic drug used to increase urine flow in order to reduce the amount of salt and water in the body. It is commonly utilized to treat preterm infants with chronic lung disease of prematurity. There is a need for a simple and reliable quantitation of furosemide in human urine. We have developed and validated an ultra-high performance liquid chromatography–tandem mass spectrometry method for furosemide quantitation in human urine with an assay range of 0.100–50.0 μg/ml. Sample preparation involved solid-phase extraction with 10 μl of urine. Intra-day accuracies and precisions for the quality control samples were 94.5–106 and 1.86–10.2%, respectively, while inter-day accuracies and precision were 99.2–102 and 3.38–7.41%, respectively. Recovery for furosemide had an average of 23.8%, with an average matrix effect of 101%. Furosemide was stable in human urine under the assay conditions. Stability for furosemide was shown at 1 week (room temperature, 4, −20 and −78°C), 6 months (−78°C), and through three freeze–thaw cycles. This robust assay demonstrates accurate and precise quantitation of furosemide in a small volume (10 μl) of human urine. It is currently being implemented in an ongoing pediatric clinical study.     

Pore structure of glasses derived from a leachable borosilicate precursor

The aim of the present study was the pore structure characterization of porous glass derived from a leachable precursor. Two independent techniques were applied on this purpose. The interpretation of the results obtained by these techniques, i.e. thermoporometry and nitrogen porosimetry was indicative for their supplementary character in what concerns the calculation of pore size distributions. The experimental work described in this study gives an example for the monitoring of the compositional evolution of phase separating compact-glass precursors of porous glasses. This revised version was published online in July 2006 with corrections to the Cover Date.