Individually addressable microelectrode array for monitoring oxygen and nitric oxide release

We have fabricated a six individual addressable gold working electrode microarray. The device is wirebonded to an eight-pin DIL package that can be easily interconnected to an external multi-channel potentiostat. A polyion complex film coating on the electrode surface provides a suitable coating for the growth of cells. The responses of oxygen and nitric oxide were assessed on uncoated and coated devices using electroanalytical methods. The film coating reduced the diffusion current by approximately 20% in both cases. No changes in the electrochemical mechanism were observed. Simultaneous recordings were obtained for 2 h in the presence of the cells, thus the device is stable for the duration of the bioanalytical measurements. Measurements were conducted to study the simultaneous changes in oxygen and nitric oxide levels in cultured fibroblast cells in the presence of growth hormones that cause cell proliferation. Increases in oxygen consumption of the cells were coupled with increases in nitric oxide levels when in the presence of the growth hormones. Use of a biological detergent to cause an oxidative burst resulted in a large increase in the current for potentials set to detect nitric oxide and oxygen.     

Expression of chirality in salicyloxazolinate complexes of zirconium

Treatment of chiral non-racemic salicyloxazoline proligands HL with tetrabenzylzirconium(IV) gave species [L₂Zr(CH₂Ph)₂]. Reactions of KL with ZrCl₄(THF)₂ gave similar chloro complexes. One example of a benzyl complex was shown to exist as the Λ-trans,cis,cis diastereomer by X-ray crystallography. DFT calculations showed the observed isomer to be the most stable by 35 kJ mol⁻¹, indicating that thermodynamic diastereoselection for this species is excellent. Examination of the chiral environment about the benzyl co-ligands indicates however that the degree of expression of the chirality of the structure in what would be the site of metal-based reactions is poor in comparison to related systems. Variable temperature ¹H NMR data are consistent with this in that the low temperature spectrum exhibits a very small chemical shift difference between the chemically inequivalent benzylic CH atoms, and at higher temperatures dissociation of the portion of the ligand that contains the chiral information, i.e., the oxazoline unit, leads to apparent equivalence.     

Energy transfer in thermal and hyperthermal collisions between CN(X2Sigma+, v = 2) in selected rotational levels (Ni = 0, 1, 6, 10, 15 and 20) and N2

We report rate coefficients (k(tot,N(i))) for total removal of CN(X(2)Sigma(+), v = 2, N(i)) radicals from selected rotational levels (N(i) = 0, 1, 6, 10, 15 and 20) and for state-to-state rotational energy transfer (k(i-->f)) between levels N(i) and other rotational levels N(f) in single collisions with N(2). CN radicals have been generated using two sources: (a) the pulsed laser photolysis of ICN at 266 nm, which generates translationally 'hot' CN radicals; and (b) the pulsed laser photolysis of NCNO at 570 nm, which generates CN radicals with translational energies close to the average value at 298 K. Comparison of the values of k(tot,N(i)) obtained using these two sources of CN demonstrates: firstly, that the same results are obtained as long as time is allowed for the translationally hot CN radicals generated from ICN to be thermalised before radicals are promoted to a specific rotational level in v = 2 using a tuneable infrared 'pump' laser operating at ca. 2.45 micro m; and secondly, that the rate coefficients decrease, but the averaged cross-sections remain approximately constant, as the excess translational energy in CN radicals is moderated by collisions. With NCNO as the source of CN radicals, the observed values of k(tot,N(i)) do not depend on the delay between the pulses from the photolysis and pump lasers. Finally, we demonstrate that, for the non-reactive collision partner N(2) and with allowances made for the rate coefficients that are too small to measure directly, the sum of the state-to-state rate coefficients, Sigma(f)k(i-->f), for rotational energy transfer from a selected initial level N(i) agrees quite well with the value of k(tot,N(i)) for total transfer from the same initial level. The values of k(tot,N(i)) and of the state-to-state rate coefficients are compared with similar, earlier, results in which helium and argon were the collision partners. The relevance of these results to the study of collisions of CN with reactive collision partners is briefly discussed.     

Synthesis and characterization of new oxazoline-based palladacycles with bridging or terminal imidate ligands. Crystal structures of [{Pd(μ-dibromomaleimidate)(Phox)}2], [Pd(dibromomaleimidate)(Phox)(PPh3)] and [Pd(glutarimidate)(Phox)(PPh3)] (Phox = 2-(2-oxazolinyl)phenyl))

The dinuclear hydroxo complex [{Pd(μ-OH)(Phox)}₂] (I) (Phox = 2-(2-oxazolinyl)phenyl) reacts in a 1:2 molar ratio with several imidate ligands to yield new cyclometallated palladium complexes [{Pd(μ-NCO)(Phox)}₂] containing asymmetric imidate –NCO– bridging units. [–NCO– = succinimidate (succ) (1), phtalimidate (phtal) (2), maleimidate (mal) (3), 2,3-dibromomaleimidate (2,3-diBrmal) (4) and glutarimidate (glut) (5)]. The reaction of these complexes with tertiary phosphines provides novel mononuclear N-bonded imidate derivatives of the general formula [Pd(imidate)(Phox)(PR₃)] [R = Ph (a), 4-F–C₆H₄ (b) or CH₂CH₂CN (c)]. The new complexes were characterized by partial elemental analyses and spectroscopic methods (IR, FAB, ¹H, ¹³C and ³¹P). The single-crystal structures of compounds 4, 4a and 5a have been established.     

Structure of iron and manganese ions substituted in the framework of nanoporous AlPO-5 material

The structure of iron and managanese ions substituted in the framework of nanoporous AlPO-5 is determined by ex situ and in situ X-ray absorption spectroscopy. Fe K-edge XANES and EXAFS studies clearly indicate that iron ions are present as Fe(III) in octahedral coordination in the assynthesised material and tetrahedral coordination in the calcined material in both pure FeAlPO-5 and FeMnalPO-5. XANES and EXAFS results also indicate that reaction with hydrogen peroxide causes the removal of Fe(III) ions from the framework. Mn K-edge XANES and EXAFS of FeMnAlPO-5 samples indicate that Mn(II) ions are present in the framework, tetrahedrally coordinated, in the as-synthesised material but upon calcination it is found that the Mn(II) ions are removed from the framework, suggesting a different synthesis strategy is necessary to stabilise the Mn(II) ions in the framework simultaneously with Fe(III) ions.     

Quantification of the In Vitro and In Vivo Metabolic Fates of 2-, 3- and 4-Bromobenzoic Acids Using High Temperature LC Coupled to ICP-MS and Linear Ion Trap MS

High temperature liquid chromatography (HTLC), with water as the mobile phase, combined with ICP-MS tuned to the detection of Br, for quantification, and a linear ion trap MS, for structural identification, were applied to determine the disposition and metabolic fate of 2-, 3- and 4-bromobenzoic acids (BBAs) following in vitro incubation with rat hepatocytes at 4 mM. The separation of the metabolites was performed using a thermal gradient to increase the eluotropic strength of the aqueous mobile phase through the run to elute less polar components. The use of highly aqueous solvents for separations involving ICP-MS is advantageous because the water does not change the conductivity of the plasma thereby providing a more stable system. The improved system stability resulted in better sensitivity, as shown by the increased signal intensity for HTLC compared to conventional reversed-phase separations. Using HTLC to investigate the in vitro metabolic fate of the BBAs showed the major route of metabolism to be glycine conjugation, irrespective of the structure of the parent, but with different amounts produced depending on the positional isomer. The comparison of HTLC with the conventional methodology showed that chromatography at elevated temperatures had no effect on the observed metabolite profile. HTLC was also applied to urine obtained from an in vivo sample and showed an improved chromatographic peak shape compared to conventional liquid chromatography (LC) whilst providing the same analytical result.     

Photobleaching-based flow measurement in a commercial capillary electrophoresis chip instrument

For microfluidic analytical instruments, a facile, fast, and accurate instrument test is highly demanded. The test includes the quantitative verification of the relationship between pressure drop and flow velocity for the hydrodynamic pump, between the electric voltage and electroosmotic flow (EOF) for the high-voltage supply, and the chip quality. The key point for the test is the measurement of the flow velocity. However, most currently available velocimetries cannot be directly used without any instrumental modification or adding extra instruments. We applied a recently developed Laser Induced Fluorescence Photobleaching Anemometer (LIFPA) for the instrument test through measuring fluid flow velocity in a microfluidic instrument with optical measurement without any modification and extra instrument. We have successfully used the method to test Caliper HTS 250 System from Caliper Life Sciences (Hopkinton, MA) with its own light source and detector. The experimental result demonstrates that this single-point method of measuring flow velocity can be easily used for accurate test of a microfluidic instrument in less than 10 min at extremely low cost without any modification and extra instrument.     

How to realize the linear scale-up process for rapid purification using high-performance counter-current chromatography

This study used the isolation of six constituents from Selaginella tamariscina as an example to demonstrate how to achieve rapid and predictable linear scale-up processes in both normal- and reversed-phase high-performance counter-current chromatography. After systematic optimization of solvent systems, sample concentration, sample loading volume, rotation speed and flow rate on the analytical Mini-DE centrifuge, the optimized parameters obtained were directly transferred to the preparative Midi-DE centrifuge, with nearly the same purities, resolutions and elution times but with 50 times the throughput. Amentoflavone (446.7 mg, 97.8%), robustaflavone (21.6 mg, 89.4%), bilobetin (80.7 mg, 92.7%), hinokiflavone (15.1 mg, 85.5%), isocryptomerin (34.8 mg, 89.6%) and an apigenin-diglucoside (46.3mg, 96.4%) were obtained with amounts and purities shown in parentheses as analysed by HPLC. The process, therefore, offers an efficient and rapid method of obtaining sufficient quantities of target compounds with significantly increased throughput after a linear scale-up.     

Impurities in commercial phytantriol significantly alter its lyotropic liquid-crystalline phase behavior

The lyotropic liquid-crystalline phase behavior of phytantriol is receiving increasing interest in the literature as a result of similarities with glyceryl monooleate, despite its very different molecular structure. Some differences in the phase-transition temperature for the bicontinuous cubic to reverse hexagonal phase have been reported in the literature. In this study, we have investigated the influence that the commercial source and hence the purity has on the lyotropic phase behavior of phytantriol. Suppression of the phase-transition temperatures (by up to 15 degrees C for the bicontinuous cubic to reverse hexagonal phase transition) is apparent with lower-purity phytantriol. In addition, the composition boundaries were also found to depend significantly on the source and purity of phytantriol, with the bicontinuous cubic phase + excess water boundary occurring at a water content above that reported previously (i.e., >5% higher). Both the temperature and compositional changes in phase boundaries have significant implications on the use of these materials and highlight the impact that subtle levels of impurities can play in the phase behavior of these types of materials.     

Cucurbit[7]uril host-guest complexes with small polar organic guests in aqueous solution

The host-guest stability constants for the inclusion of a series of small neutral polar organic guests in cucurbit[7]uril (CB[7]) have been determined in aqueous solution by (1)H NMR titrations. The dependence of the stability constant on the nature of the guests indicates that hydrophobic and dipole-quadrupole interactions are responsible for the binding. The complexation-induced chemical shift changes in the guest proton resonances, coupled with energy-minimization calculations, suggest that the guests are located such that their dipole moment is aligned perpendicular with the quadrupole moment of the CB[7] host. The stability constants for acetone and acetophenone decrease in the presence of Na(+) or K(+) cations as a result of cation capping of the CB[7] portals.