A microsystem for sensing and patterning oxidative microgradients during cell culture

We present the design, modeling, fabrication and testing of a microsystem for the electrolytic patterning and sensing of oxidative microgradients within 1 x 1 mm2 area during cell culture. The system employs an array of microfabricated electrodes (3-40 microm in width) embedded in gas-permeable microchannels to generate precise doses of dissolved oxygen (ranging from 10 fmol O2 mm(-2) s(-1) to 100 nmol O2 mm(-2) s(-1)) via electrolysis. The microgradients generated by different microelectrodes in the array can be superimposed to pattern multi-dimensional oxygen profiles not possible with other methods. We demonstrate the patterning, sensing and quantification of dissolved oxygen microgradients in the 0 to 40% dO2 range using this microsystem. Reactive oxygen species generation and dosing is also quantified. Lastly, we demonstrate how the microtechnology enables new types of experiments in three different cell culture models: localized hyperoxia-induced apoptosis in C2C12 myoblasts, dynamic aerotaxis assays of Bacillus subtilis, and studies of calcium release in an ischemia/re-oxygenation myoblast model.     

Characterization of the tryptophan residues of human placental ribonuclease inhibitor and its complex with bovine pancreatic ribonuclease A by steady-state and time-resolved emission spectroscopy

Human placental ribonuclease inhibitor (hRI) containing six tryptophan (Trp) residues located at positions 19, 261, 263, 318, 375, and 438 and its complex with RNase A have been studied using steady-state and time-resolved fluorescence (298 K) as well as low-temperature phosphorescence (77 K). Two Trp residues in wild-type hRI and also in the protein-protein complex with RNase A are resolved optically. The accessible surface area values of Trp residues in the wild-type hRI and its complex and consideration of inter-Trp energy transfer in the wild-type hRI reveal that one of the Trp residues is Trp19, which is located in a hydrophobic buried region. The other Trp residue is tentatively assigned as Trp375 based on experimental results on wild-type hRI and its complex. This residue in the wild-type hRI is more or less solvent exposed. Both the Trp residues are perturbed slightly on complex formation. Trp19 moves slightly toward a more hydrophobic region, and the environment of Trp375 becomes less solvent exposed. The complex formation also results in a more heterogeneous environment for both the optically resolved Trp residues.     

Ti(III)-mediated radical cyclization of β-aminoacrylate containing epoxy alcohol moieties: synthesis of highly substituted azacycles

Ti(III)-mediated radical cyclization of β-aminoacrylate containing 2,3-epoxy alcohol moieties led to the formation of highly substituted piperidine and pyrrolidine rings. The pyrrolidine ring system was then transformed into an indolizidine framework present in many natural products.     

Quantitative studies of pyrocarbon‐coated materials using synchrotron radiation

Phase‐contrast imaging provides enhanced image contrast and is important for non‐destructive evaluation of structural materials. In this paper, experimental results on in‐line phase‐contrast imaging using a synchrotron source (ELETTRA, Italy) for objects required in material science applications are discussed. Experiments have been carried out on two types of samples, pyrocarbon‐coated zirconia and pyrocarbon‐coated alumina microspheres. These have applications in both reactor and industrial fields. The phase‐contrast imaging technique is found to be very useful in visualizing and determining the coating thickness of pyrocarbon on zirconia and alumina microspheres. The experiments were carried out at X‐ray energies of 16, 18 and 20 keV and different object‐to‐detector distances. The results describe the contrast values and signal‐to‐noise ratio for both samples. A comprehensive study was carried out to determine the thickness of the pyrocarbon coating on zirconia and alumina microspheres of diameter 500 µm. The advantages of phase‐contrast images are discussed in terms of contrast and resolution, and a comparison is made with absorption images. The results show considerable improvement in contrast with phase‐contrast imaging as compared with absorption radiography.     

Universal iterative strategy for the divergent synthesis of dendritic macromolecules from conventional monomers by a combination of living radical polymerization and irreversible TERminator multifunctional INItiator (TERMINI)

A new synthetic concept named TERMINI that stands for irreversible TERminator Multifunctional INItiator is reported. Suitable combinations of TERMINI and living polymerizations provide access to strategies for the design and synthesis of unprecedented complex molecular and macromolecular architectures from a diversity of commercial monomers. TERMINI represents a masked multifunctional initiator designed to quantitatively and irreversibly interrupt a chain organic reaction or a living polymerization. After demasking, the TERMINI repeat unit enables the quantitative reinitiation, in the presence or absence of a catalyst, of the same or a different living polymerization or a chain organic reaction in more than one direction, thus becoming a branching point. The demonstration of this concept was made by using a combination of metal-catalyzed living radical polymerization (LRP) and (1,1-dimethylethyl)[[1-[3,5-bis(S-phenyl 4-N,N'-diethylthiocarbamate)phenyl]ethenyl]oxy]dimethylsilane as TERMINI, to elaborate a novel iterative divergent method for the synthesis of dendritic macromolecules based on methyl methacrylate (MMA).     

Conversion of colloidal aggregates into polymer networks on aging

After long-term aging, surfactant-mediated colloidal aggregates of sulfonated polyaniline (S-PANI) and poly(vinylidene fluoride) (PVF₂) converted into three-dimensional polymer networks, whereas colloidal crystals prepared from pure PVF₂ remained unaltered. A model, where the surfactant tails anchored from the colloidal particles interdigitate with time resulting in coalescence of the particles to form the network morphology, has been proposed. X-ray photoelectron spectroscopy (XPS) revealed higher relative abundances of carbon atoms on the surface of the polymer networks than those of the colloidal aggregates, which adequately supports the proposed model.     

Substituent Effects on Hydrogen Bonding in Watson–Crick Base Pairs. A Theoretical Study

We have theoretically analyzed Watson–Crick AT and GC base pairs in which purine C8 and/or pyrimidine C6 positions carry a substituent X = H, F, Cl or Br, using the generalized gradient approximation (GGA) of density functional theory at BP86/TZ2P. The purpose is to study the effects on structure and hydrogen bond strength if X = H is substituted by a halogen atom. Furthermore, we wish to explore the relative importance of electrostatic attraction versus orbital interaction in the above multiply hydrogen-bonded systems, using a quantitative bond energy decomposition scheme. We find that replacing X = H by a halogen atom has relatively small yet characteristic effects on hydrogen bond lengths, strengths and bonding mechanism. In general, it reduces the hydrogen-bond-accepting- and increases the hydrogen-bond-donating capabilities of a DNA base. The orbital interaction component in these hydrogen bonds is found for all substituents (X = H, F, Cl, and Br) to contribute about 41% of the attractive interactions and is thus of the same order of magnitude as the electrostatic component, which provides the remaining 59% of the attraction.     

Reactivity of the dinuclear platina-β-diketone [Pt2{(COMe)2H}2(μ-Cl)2] towards chelating ligands - Bridge cleavage versus formation of acetyl(chloro)platinum(II) complexes

The dinuclear platina-β-diketone [Pt₂{(COMe)₂H}₂(μ-Cl)₂] (1) was found to react with 2-(ROCH₂)C₅H₄N (R =  Me, 2a; H, 2b) yielding a cationic mononuclear platina-β-diketone [Pt{(COMe)₂H}{2-(MeOCH₂)C₅H₄N}]Cl (3) and an acetyl(chloro)platinum(II) complex [Pt(COMe)Cl{2-(HOCH₂)C₅H₄N}] (4), respectively. The reaction of 1 with 8-(methylthio)quinoline (5) resulted in the formation of [Pt(COMe)Cl{8-(MeS)C₉H₆N}] (6). The identities of all complexes were established by microanalysis, ¹H, and ¹³C NMR spectroscopy. Single-crystal X-ray diffraction analysis showed 6 to be square-planar platinum(II) complex with N and C atoms as well as Cl and S atoms in mutually trans positions (configuration index: SP-4-2). In accordance with this, quantum chemical calculations on the DFT level of theory revealed a higher stability of complex 6 having a SP-4-2 configuration vs. the analogous complex in SP-4-3 configuration. The distinctly different reactivity of 1 with 2a on the one hand and with 2b and 5 on the other is discussed in terms of the HSAB concept and a deprotonation/reprotonation reaction.     

ESPT of 2-(2'-pyridyl)benzimidazole at the Micelle-Water interface: selective enhancement and slow dynamics with sodium dodecyl sulfate

The effect of micellar environment on the excited state proton transfer (ESPT) of 2-(2'-pyridyl)benzimidazole (2PBI) has been investigated by steady state and time resolved fluorescence spectroscopy. The ESPT, which occurs to a rather small extent at pH 7, is found to be enhanced remarkably at the interface of sodium dodecyl sulfate (SDS) micelles and water. Such an enhancement is not observed for the cationic cetyl trimethyl ammonium bromide (CTAB) or neutral Triton X-100 micelles. This selective enhancement is explained in the light of a modification of pK(a) and a more acidic local pH in the micelle-water interface. A rise time of about 890 ps is observed in the region of tautomer emission. The origin of this rise time is explored, considering three factors, namely, diffusion controlled protonation of the normal form of 2PBI, slow and possibly incomplete solvation of the transition state, leading to a slowing down of the proton transfer process and a similar slow dynamics of the tautomeric excited state.     

Synthesis and characterization of the first diorganotin(IV) complexes containing mixed arylazobenzoic acids and having skew trapezoidal bipyramidal geometry

Three diorganotin(IV) complexes of the type, [R₂Sn(L^aH)(L^bH)] (R = ⁿBu or Me and, L^aH and L^bH are two different 5-[(E)-2-(aryl)-1-diazenyl]-2-hydroxybenzoate residues; a: aryl = 4′-Cl-(held constant) and b: aryl = 4′-Me or 4′-Br) have been prepared either by reacting ⁿBu₂SnO, L^aHH′ and L^bHH′ (1:1:1) in anhydrous toluene or by reacting Me₂SnCl₂, L^aHNa and L^bHNa (1:1:1) in anhydrous methanol. The products were characterized by microanalysis, IR, NMR (¹H, ¹³C, ¹¹⁹Sn) and ^119mSn Mössbauer spectroscopy. A full characterization of the structures of the complexes [ⁿBu₂Sn(L^aH)(L^bH)] (1 and 2) and [Me₂Sn(L^aH)(L^bH)] (3) in the solid state were accomplished by single crystal X-ray crystallography. These complexes were found to adopt the usual dicarboxylato structural type with a skew-trapezoidal bipyramidal arrangement around the tin atom.