Complications in the Use of the Taylor Dispersion Method for Ternary Diffusion Measurements: Methanol + Acetone + Water Mixtures

The Taylor dispersion technique is used to measure the ternary mutual diffusion coefficients of aqueous nonelectrolyte solutions at 25°C. The dispersion of the injected solutes is recorded by a differential refractometer and an ultraviolet-visible detector. The diffusion coefficients are calculated directly by fitting the theoretical dispersion equations to about six experimental curves simultaneously. If the ternary diffusion effects in the measured dispersion profiles are not confused by the inaccuracy of the experimental method or an unfavorable relative detector sensitivity, the diffusion coefficients are precise. For the system methanol + acetone + water, it is shown that the Taylor dispersion method is unsuitable for the determination of all the diffusion coefficients if the methanol mole fraction is less than 0.45 or the acetone mole fraction if more than 0.001.     

Influence of connectivity and porosity on ligand-based luminescence in zinc metal-organic frameworks

Applications of metal-organic frameworks (MOFs) require close correlation between their structure and function. We describe the preparation and characterization of two zinc MOFs based on a flexible and emissive linker molecule, stilbene, which retains its luminescence within these solid materials. Reaction of trans-4,4'-stilbene dicarboxylic acid and zinc nitrate in N,N-dimethylformamide (DMF) yielded a dense 2-D network, 1, featuring zinc in both octahedral and tetrahedral coordination environments connected by trans-stilbene links. Similar reaction in N,N-diethylformamide (DEF) at higher temperatures resulted in a porous, 3-D framework structure, 2. This framework consists of two interpenetrating cubic lattices, each featuring basic zinc carboxylate vertices joined by trans-stilbene, analogous to the isoreticular MOF (IRMOF) series. We demonstrate that the optical properties of both 1 and 2 correlate with the local ligand environments observed in the crystal structures. Steady-state and time-resolved spectroscopic measurements reveal that the stilbene linkers in the dense structure 1 exhibit a small degree of interchromophore coupling. In contrast, the stilbenoid units in 2 display very little interaction in this low-density 3-D framework, with excitation and emission spectra characteristic of monomeric stilbenes, similar to the dicarboxylic acid in dilute solution. In both cases, the rigidity of the stilbene linker increases upon coordination to the inorganic units through inhibition of torsion about the central ethylene bond, resulting in luminescent crystals with increased emission lifetimes compared to solutions of trans-stilbene. The emission spectrum of 2 is found to depend on the nature of the incorporated solvent molecules, suggesting use of this or related materials in sensor applications.     

Rh(I)-catalyzed carbonylative ring opening of diazabicycles with acyl anion equivalents

A catalytic desymmetrization of strained alkenes by ring-opening of meso-diazabicycles with acyl anion nucleophiles is reported. Densely functionalized trans-1,2-hydrazinoacyl cyclopentene building blocks are obtained stereoselectively. The acyl anion equivalent is generated in situ under very mild conditions from readily available organoboron precursors.     

Critical evaluation of electrode design and matrix effects on monitoring organophosphate pesticides using composite carbon nanotube-modified electrodes

Carbon nanotubes (CNT)/Nafion-modified glassy carbon (GC) electrodes were used to immobilize the enzyme acetylcholinesterase (AChE) by crosslinking with glutaraldehyde. The CNT-modified electrodes exhibited a sensitive and stable electrocatalytic behavior towards thiocholine (TCh). Compared to ordinary GC electrodes modified with Nafion, a substantial (500-mV) decrease in the overvoltage of the TCh oxidation reaction is observed, along with a tenfold enhancement in the amperometric response. The CNT/Nafion/AChE electrode has very good stability of at least a month compared to surfaces made without crosslinking in the absence and presence of Nafion. Under optimal loadings of CNT, Nafion, AChE, and glutaraldehyde, a solution of CNT/Nafion in N,N-dimethylformamide (DMF) containing 4 mg/mL CNT and 0.01% Nafion was used to construct the electrodes in order to maximize the sensitivity of the biosensor for inhibition studies. An optimal enzyme loading of 0.137 U and crosslinking in 0.01% glutaraldehyde for 1 h was also needed to achieve this goal. The prepared electrodes had very good reproducibility to 1.0 mM acetylthiocholine (ATCh) (relative standard deviation [RSD] <5% for eight electrodes). Using paraoxon as a model pesticide, the biosensor was able to detect as low as 1.0 nM after 30 min of incubation at 30 °C. Using a log scale, the biosensor had good linearity in the concentration range 50?C800 nM, with a correlation coefficient of 0.99. The prepared biosensor was used to test real water samples spiked with paraoxon and showed good correlation with a calibration curve using phosphate buffer.     

A Multivalent Ligand for the Mannose‐6‐Phosphate Receptor for Endolysosomal Targeting of an Activity‐Based Probe

The ubiquitously expressed mannose‐6‐phosphate receptors (MPRs) are a promising class of receptors for targeted compound delivery into the endolysosomal compartments of a variety of cell types. The development of a synthetic, multivalent, mannose‐6‐phosphate (M6P) glycopeptide‐based MPR ligand is described. The conjugation of this ligand to fluorescent DCG‐04, an activity‐based probe for cysteine cathepsins, enabled fluorescent readout of its receptor‐targeting properties. The resulting M6P‐cluster–BODIPY–DCG‐04 probe was shown to efficiently label cathepsins in cell lysates as well as in live cells. Furthermore, the introduction of the 6‐O‐phosphates leads to a completely altered uptake profile in COS and dendritic cells compared to a mannose‐containing ligand. Competition with mannose‐6‐phosphate abolished all uptake of the probe in COS cells, and we conclude that the mannose‐6‐phosphate cluster targets the MPR and ensures the targeted delivery of cargo bound to the cluster into the endolysosomal pathway.     

Quantification of copper and zinc species fractions in legume seeds extracts by SEC/ICP-MS: validation and uncertainty estimation

Fractions of Cu and Zn species in legume samples (common white bean, pea, chick pea and lentil seeds and defatted soybean flour) were analysed by on-line hyphenation of size exclusion chromatography and inductively coupled plasma-mass spectrometry. Samples were extracted by 0.02 mol l⁻¹ Tris–HCl buffer solution, pH 7.5. The extraction efficiency lay in the region 60–90 and 60–80% for Cu and Zn, respectively. Quantification of elements in the individual chromatographic fractions was carried out by isotope dilution (ID) and external calibration (EC) techniques. For ID analysis the chromatographic effluent was mixed with the flow of ⁶⁵Cu and ⁶⁸Zn isotope enriched solution and the isotope ratio values ⁶³Cu/⁶⁵Cu and (⁶⁴Zn+⁶⁶Zn)/⁶⁸Zn were measured. In the case of EC technique calibration solutions of elements were injected to the flow of mobile phase by the second injector. Prior entering detector the effluent was mixed with the flow of internal standard solution (In, 50 μg l⁻¹). Both methods have similar precision, however the behaviour of both studied elements was not the same. The chromatographic analysis itself was the main source of variability in the case of Cu. For Zn species analysis, the extraction process and the manipulation with the extract, played the significant role too. It was probably caused by lower stability of the present zinc chelates. The total amounts of Zn found in all chromatographic fractions represented 85–95% of Zn in sampled extract whereas those of Cu approached 100%. In case of small peaks the results of ID and EC were not the same. The EC results were lower then ID results. The great deal of results uncertainty accounts for the precision.     

Characterization of the early stages of programmed cell death in maize root cells by using comet assay and the combination of cell electrophoresis with annexin binding

An emerging topic in plant biology is whether plant cells display similar elements of programmed cell death (PCD) as animal cells do. We have studied cell death in maize roots exposed to cold stress by using fluorescence microscopy, terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick end labeling (TUNEL), DNA gel electrophoresis, single cell gel electrophoresis (SCGE), cell electrophoresis, and annexin binding techniques. The results showed that cell death in maize root cells triggered by cold stress was accompanied by a subset of features characteristic of animal PCD such as nuclear condensation and fragmentation, and oligonucleosomal DNA fragmentation. In addition to DNA laddering and TUNEL positivity, a "comet" pattern indicative of DNA breakage appeared as short as after one day of treatment. The maize root cell PCD process was also accompanied by an increase in negative surface charge of the dying cells due to exposure of phosphatiolylserine (PS) from inner to outer membrane. After annexin binding, however, the enhanced electrophoretic mobility (EPM) of the dying cells decreased nearly to normal values. This result suggests that the combination between cell electrophoresis and annexin binding provides a quantitative method for monitoring PS exposure during plant PCD.     

Chemical Processes Involving 18-Crown-6-Ether in Activated Noncovalent Complexes with Protonated Peptides

These last decades, it has been widely assumed that 18-crown-6-ether (CE) plays a spectator role during the chemical processes occurring in isolated host-guest complexes between peptides or proteins and CE after activation in mass spectrometers. Our present experimental and theoretical results challenge this hypothesis by showing that CE can abstract a proton or a protonated molecule from protonated peptides after activation by collisions in argon or electron capture/transfer. Furthermore, thanks to comparison between experimental and calculated values of collision cross-sections, we demonstrate that CE can change binding site after electron transfer. We also propose detailed mechanisms for these processes.     

Polymicrobial Biofilm Inhibition Effects of Acetate‐Buffered Chitosan Sponge Delivery Device

Polymicrobial biofilm‐associated implant infections present a challenging clinical problem. Through modifications of lyophilized chitosan sponges, degradable drug delivery devices for antibiotic solution have been fabricated for prevention and treatment of contaminated musculoskeletal wounds. Elution of amikacin, vancomycin, or a combination of both follows a burst release pattern with vancomycin released above minimum inhibitory concentration for Staphylococcus aureus for 72 h and amikacin released above inhibitory concentrations for Pseudomonas aeruginosa for 3 h. Delivery of a vancomycin, amikacin, or a combination of both reduces biofilm formation on polytetrafluoroethylene catheters in an in vivo model of contamination. Release of dual antibiotics from sponges is more effective at preventing biofilm formation than single‐loaded chitosan sponges. Treatment of pre‐formed biofilm with high‐dose antibiotic release from chitosan sponges shows minimal reduction after 48 h. These results demonstrate infection‐preventive efficacy for antibiotic‐loaded sponges, as well as the need for modifications in the development of advanced materials to enhance treatment efficacy in removing established biofilm.