Individual Acidic Organelle pH Measurements by Capillary Electrophoresis

This report describes the pH measurement of individual acidic organelles isolated from the human leukemia CCRF-CEM and CEM/C2 cells. These cells were allowed to endocytose fluorescein tetramethylrhodamine dextran (FRD), a ratiometric probe that has fluorescein as a pH-dependent fluorophore and tetramethylrhodamine as a pH-independent fluorophore. Isolated organelle fractions from these cells were then subjected to capillary electrophoresis with laser-induced fluorescence detection (CE-LIF) analysis. The detection of individual organelle fluorescence at two different wavelengths, selected on the basis of the emission range of the FRD probe, gives a fluorescence intensity ratio used to calculate the pH from a calibration curve. This curve was constructed from CE-LIF measurements of individual liposomes loaded with several pH buffer standards. The respective median pH values are 5.1 ± 0.2 in CEM/C2 cells and 6.1 ± 0.4 in CCRF-CEM cells. These measurements compare well with pixel-based epifluorescence microscopy measurements of whole cells where the corresponding average pH values are 5.0 ± 0.6 (n = 15) and 6.2 ± 0.7 (n = 15). A pH comparison between the two cell types suggests that the lower pH in the CEM/C2 cells may be relevant to the protonation and sequestration of weak base anticancer drugs such as doxorubicin. The determination of the pH of individual vesicles, liposomes, and acidic organelles is a new resource for measuring and investigating the role of the acid−base properties of subcellular-size compartments

Photoluminescent and Electrochemical Properties of Novel Poly(aryl ether)s with Isolated Hole-Transporting Carbazole and Electron-Transporting 1,3,4-Oxadiazole Fluorophores

Four novel poly(aryl ether)s consisting of alternate isolated hole-transporting carbazole and electron-transporting 1,3,4-oxadiazole segments were synthesized from the nucleophilic displacement reaction of bis(fluoride) monomers with bis(phenol) monomers. These poly(aryl ether)s are soluble in common organic solvents and exhibit good thermal stability with 5% weight loss temperature above 400 °C under a nitrogen atmosphere. The photoluminescent (PL) spectra and quantum yields of these polymers are dependent on the composition of the two isolated fluorophores. The formation of exciplex in P3 was observed in the film and solution state and resulted in the lower quantum yield. The quantum yields of P4 in solutions can increase from 0.04 of P3 to 0.36, due to the dilute effect, by introducing the inert bisphenol A segments. However, the PL spectra of P4 only showed a little blue shift in the film state. This means the interchain exciplex still dominated the emission of polymeric films. The HOMO and LUMO energy levels of these polymers have been measured from cyclic voltammetry. All the observations directly proved that the oxidation in polymers started at the hole-transporting segments. Both the electron and hole affinities of these polymers could be enhanced simultaneously due to the introduction of isolated hole-transporting carbazole and electron-transporting 1,3,4-oxadiazole segments

Copolyfluorenes Containing Bipolar Groups: Synthesis and Application To Enhance Electroluminescence of MEH−PPV

Enhancing electroluminescence of conventional MEH−PPV {poly[2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylenevinylene]} is desirable due to its popularity in polymeric emitting materials. The enhancement is much readily attained by simple blending with functional polymers instead of tedious structural modification. In response to this, three copolyfluorenes (P1−P3) containing bipolar groups (3.1−11.2 mol %), directly linked hole-transporting triphenylamine and electron-transporting 1,2,4-triazole, are synthesized by Suzuki coupling reaction. The bipolar groups not only suppress undesirable green emission of polyfluorene under thermal annealing but also increase hole and electron affinity of the resulting copolyfluorenes. Blending the bipolar copolyfluorenes with MEH−PPV effectively improves the emission efficiency of its electroluminescent devices [ITO/PEDOT:PSS/polymer blend/Ca(50 nm)/Al(100 nm)]. The maximum luminance and maximum luminance efficiency are significantly enhanced from 3120 cd/m2 and 0.49 cd/A (MEH−PPV device) to 19 560 cd/m2 and 1.08 cd/A (blend device with ca. 0.5 wt % of bipolar groups), respectively. Our results demonstrate the efficacy of the bipolar copolyfluorenes in enhancing electroluminescence of MEH−PPV

Individual Electrophoretic Mobilities of Liposomes and Acidic Organelles Displaying pH Gradients Across Their Membranes

This report focuses on measuring the individual electrophoretic mobilities of liposomes with different pH gradients across their membrane using capillary electrophoresis with laser-induced fluorescence detection (CE-LIF). The results from the individual analysis of liposomes show that, using surface electrostatic theories and the electrokinetic theory as the first approximation, ζ potential contributes more significantly to the electrophoretic mobility of liposomes than liposomal size. For liposomes with an outer pH 7.4 (pHo 7.4) and a net negative outer surface charge, the most negative electrophoretic mobilities occur when the inner pH (pHi) is 6.8; at higher or lower pHi, the electrophoretic mobilities are less negative. The theories mentioned above cannot explain these pH-induced electrophoretic mobility shifts. The capacity theory, predicting an induced electrical charge on the surface of liposomes, can only explain the results at pHi > 6.8. In this report, we hypothesize that there is a flip-flop process of phospholipids, which refers to the exchange of phospholipids between the outer and inner layers of the membrane. This flip-flop is caused by the pH gradient and membrane instability and results in the observed electrophoretic mobility changes when pHi is <6.8. Furthermore, it is found that the mobilities of acidic organelles are consistent with the predictions of liposome models we used here

Individual Electrophoretic Mobilities of Liposomes and Acidic Organelles Displaying pH Gradients Across Their Membranes

This report focuses on measuring the individual electrophoretic mobilities of liposomes with different pH gradients across their membrane using capillary electrophoresis with laser-induced fluorescence detection (CE-LIF). The results from the individual analysis of liposomes show that, using surface electrostatic theories and the electrokinetic theory as the first approximation, ζ potential contributes more significantly to the electrophoretic mobility of liposomes than liposomal size. For liposomes with an outer pH 7.4 (pHo 7.4) and a net negative outer surface charge, the most negative electrophoretic mobilities occur when the inner pH (pHi) is 6.8; at higher or lower pHi, the electrophoretic mobilities are less negative. The theories mentioned above cannot explain these pH-induced electrophoretic mobility shifts. The capacity theory, predicting an induced electrical charge on the surface of liposomes, can only explain the results at pHi > 6.8. In this report, we hypothesize that there is a flip-flop process of phospholipids, which refers to the exchange of phospholipids between the outer and inner layers of the membrane. This flip-flop is caused by the pH gradient and membrane instability and results in the observed electrophoretic mobility changes when pHi is <6.8. Furthermore, it is found that the mobilities of acidic organelles are consistent with the predictions of liposome models we used here

Multifunctional Hyperbranched Oligo(fluorene vinylene) Containing Pendant Crown Ether: Synthesis, Chemosensory, and Electroluminescent Properties

Multifunctional hyperbranched oligo(fluorene vinylene) (HOFC) containing pendant crown ether was synthesized from 2,4,7-trivinyl-9,9-dihexylfluorene and 2,7-dibromo-9-(15-crown-4)-9H-fluorene via Heck coupling reaction. Their chemosensory, photophysical, and electrochemical properties were investigated and compared with those of linear oligo(fluorene vinylene) (LOFC) to elucidate the effect of hyperbranched structure. Both HOFC and LOFC exhibit selective fluorescence quenching toward Fe3+ and Ru3+, with the Stern−Volmer coefficients (Ksv) to Ru3+ being 2 × 104 and 1.9 × 104 M−1, respectively. The stability constant (Ks) of forming complex with Ru3+ are 3.1 × 103 and 5 × 103 M−1 for HOFC and LOFC. Moreover, hyperbranched HOFC reveals homogeneous film morphology due to its hyperbranched structure. After thermal treatment, the cured polymer (HFC) shows better thermal stability because of higher cross-linked density. Double-layer electroluminescent devices (ITO/PEDOT:PSS/HFC or LFC/Ca/Al), using thermally cross-linked HFC or LFC as emitting layer, were fabricated to investigate their optoelectronic properties. The turn-on voltage, maximum luminance and maximum luminance efficiency of HFC device (4.1 V, 7132 cd/m2 and 1.3 cd/A) are superior to those of LFC device (6.2 V, 331 cd/m2, 0.22 cd/A), which have been attributed to its homogeneous film morphology. Current results indicate that the hyperbranched oligo(fluorene vinylene) is a promising material for chemosensors and electroluminescent devices

Three-Dimensional Graphene-Carbon Nanotube Hybrid for High-Performance Enzymatic Biofuel Cells

Enzymatic biofuel cells (EBFCs) are promising renewable and implantable power sources. However, their power output is often limited by inefficient electron transfer between the enzyme molecules and the electrodes, hindered mass transport, low conductivity, and small active surface area of the electrodes. To tackle these issues, we herein demonstrated a novel EBFC equipped with enzyme-functionalized 3D graphene-single walled carbon nanotubes (SWCNTs) hybrid electrodes using the naturally abundant glucose as the fuel and oxygen as the oxidizer. Such EBFCs, with high stability, can nearly attain the theoretical limit of open circuit voltage (∼1.2 V) and a high power density ever reported (2.27 ± 0.11 mW cm^‑2)

Physiological features of reference and single deletion strains.

<p>Cell growth of reference strain (A) and mutant strains SCIYC05 (<i>acs1</i>Δ) (B), SCIYC06 (<i>cit2</i>Δ) (C) and SCIYC07 (<i>mls1</i>Δ) (D), cultured in shake flask with minimal medium containing 20 g L⁻¹ glucose as carbon source. All measurements are mean +/− standard error of three biological replicates.</p

List of strains and plasmid used in this study and their genotypes.

a<p>University of Frankfurt, Germany.</p

Growth phenotypes of <i>mls1</i>Δ and <i>acs1</i>Δ strains expressing an SKL-less or intact Mls1p variant.

<p>Cells were grown on minimal medium supplemented with glucose, glycerol, ethanol or acetate as carbon source. Uracil (20 µg ml⁻¹) was added as required (reference, SCIYC05 (<i>acs1</i>Δ) and SCIYC07 (<i>mls1</i>Δ)). The plates were recorded photographically after 10 days of incubation at 30°C.</p