Retraction: Gate-induced superconductivity in a solution-processed organic polymer film.
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Retraction Notice↗
Biomedical subjects
Z Bao
Publications and source records attributed to Z Bao.
Conductance of small molecular junctions.
A new method of fabricating small metal-molecule-metal junctions is developed, approaching the single-molecule limit. The conductance of different conjugated molecules in a broad temperature, source-drain, and gate voltage regime is reported. At low temperature, all investigated molecules display sharp conductance steps periodic in source-drain voltage. The position of these steps can be controlled by a gate potential. The spacing corresponds to the energy of the lowest molecular vibrations. These results show that the low-bias conductance of molecules is dominated by resonant tunneling through coupled electronic and vibration levels.
Journal Article↗
Field-effect modulation of the conductance of single molecules.
Field-effect transistors based on two-component self-assembled monolayers of conjugated and insulating molecules were prepared; the conductance through them can be varied by more than three orders of magnitude by changing the applied gate bias. With very small ratios of conjugated to insulating molecules in the two-component monolayer, devices with only a few "electrically active" molecules can be achieved. At low temperatures, the peak channel conductance is quantized in units of 2e2/h (where e is the electron charge and h is Planck's constant). This behavior is indicative of transistor action in single molecules. On the basis of such single-molecule transistors, inverter circuits with gain are demonstrated.
Journal Article↗
Self-assembled monolayer organic field-effect transistors.
The use of individual molecules as functional electronic devices was proposed in 1974 (ref. 1). Since then, advances in the field of nanotechnology have led to the fabrication of various molecule devices and devices based on monolayer arrays of molecules. Single molecule devices are expected to have interesting electronic properties, but devices based on an array of molecules are easier to fabricate and could potentially be more reliable. However, most of the previous work on array-based devices focused on two-terminal structures: demonstrating, for example, negative differential resistance, rectifiers, and re-configurable switching. It has also been proposed that diode switches containing only a few two-terminal molecules could be used to implement simple molecular electronic computer logic circuits. However, three-terminal devices, that is, transistors, could offer several advantages for logic operations compared to two-terminal switches, the most important of which is 'gain'-the ability to modulate the conductance. Here, we demonstrate gain for electronic transport perpendicular to a single molecular layer ( approximately 10-20 A) by using a third gate electrode. Our experiments with field-effect transistors based on self-assembled monolayers demonstrate conductance modulation of more than five orders of magnitude. In addition, inverter circuits have been prepared that show a gain as high as six. The fabrication of monolayer transistors and inverters might represent an important step towards molecular-scale electronics.
Journal Article↗
High field-effect mobility oligofluorene derivatives with high environmental stability.
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Journal Article↗
Paper-like electronic displays: large-area rubber-stamped plastic sheets of electronics and microencapsulated electrophoretic inks.
Electronic systems that use rugged lightweight plastics potentially offer attractive characteristics (low-cost processing, mechanical flexibility, large area coverage, etc.) that are not easily achieved with established silicon technologies. This paper summarizes work that demonstrates many of these characteristics in a realistic system: organic active matrix backplane circuits (256 transistors) for large ( approximately 5 x 5-inch) mechanically flexible sheets of electronic paper, an emerging type of display. The success of this effort relies on new or improved processing techniques and materials for plastic electronics, including methods for (i) rubber stamping (microcontact printing) high-resolution ( approximately 1 microm) circuits with low levels of defects and good registration over large areas, (ii) achieving low leakage with thin dielectrics deposited onto surfaces with relief, (iii) constructing high-performance organic transistors with bottom contact geometries, (iv) encapsulating these transistors, (v) depositing, in a repeatable way, organic semiconductors with uniform electrical characteristics over large areas, and (vi) low-temperature ( approximately 100 degrees C) annealing to increase the on/off ratios of the transistors and to improve the uniformity of their characteristics. The sophistication and flexibility of the patterning procedures, high level of integration on plastic substrates, large area coverage, and good performance of the transistors are all important features of this work. We successfully integrate these circuits with microencapsulated electrophoretic "inks" to form sheets of electronic paper.
Journal Article↗
Gate-induced superconductivity in a solution-processed organic polymer film.
The electrical and optical properties of conjugated polymers have received considerable attention in the context of potentially low-cost replacements for conventional metals and inorganic semiconductors. Charge transport in these organic materials has been characterized in both the doped-metallic and the semiconducting state, but superconductivity has not hitherto been observed in these polymers. Here we report a distinct metal-insulator transition and metallic levels of conductivity in a polymer field-effect transistor. The active material is solution-cast regioregular poly(3-hexylthiophene), which forms relatively well ordered films owing to self-organization, and which yields a high charge carrier mobility (0.05-0.1 cm2 V(-1) s(-1)) at room temperature. At temperatures below approximately 2.35 K with sheet carrier densities exceeding 2.5 x 10(14) cm(-2), the polythiophene film becomes superconducting. The appearance of superconductivity seems to be closely related to the self-assembly properties of the polymer, as the introduction of additional disorder is found to suppress superconductivity. Our findings therefore demonstrate the feasibility of tuning the electrical properties of conjugated polymers over the largest range possible-from insulating to superconducting.
Journal Article↗
Phosphorylation and regulation of G-protein-activated phospholipase C-beta 3 by cGMP-dependent protein kinases.
Among the drugs that are known to relax the vascular smooth muscle and regulate other cellular functions, beta-adrenergic agonists and nitric oxide-containing compounds are some of the most effective ones. The mechanisms of these drugs are thought to lower agonist-induced intracellular [Ca(2+)] by increasing intracellular cAMP and cGMP, activating their respective protein kinases. However, the physiological targets of cyclic nucleotide-dependent protein kinases are not clear. The molecular basis for the regulation of intracellular Ca(2+) by signaling pathways coupled to cyclic nucleotides is not well defined. G-protein-activated phospholipase C (PLC-beta) catalyzes the hydrolysis of phosphatidylinositol 4,5-bisphosphates to generate diacylglycerol and inositol 1,4,5-triphosphate, leading to the activation of protein kinase C and the mobilization of intracellular Ca(2+). In this study, we shown that G-protein-activated PLC enzymes are the potential targets of cGMP-dependent protein kinases (PKG). PKG can directly phosphorylate PLC-beta2 and PLC-beta3 in vitro with purified proteins and in vivo with metabolic labeling. Phosphorylation of PLC-beta leads to the inhibition of G-protein-activated PLC-beta3 activity by 50-70% in COS-7 cell transfection assays. By using phosphopeptide mapping and site-directed mutagenesis, we further identified two key phosphorylation sites for the regulation of PLC-beta3 by PKG (Ser(26) and Ser(1105)). Mutation at these two sites (S26A and S1105A) of PLC-beta3 completely blocked the phosphorylation of PLC-beta3 protein catalyzed by PKG. Furthermore, mutation of these serine residues removed the inhibitory effect of PKG on the activation of the mutant PLC-beta3 proteins by G-protein subunits. Our results suggest a molecular mechanism for the regulation of G-protein-mediated intracellular [Ca(2+)] by the NO-cGMP-dependent signaling pathway.
Animals↗
Synthetic chemistry for ultrapure, processable, and high-mobility organic transistor semiconductors.
An essential aspect of the development of organic-based electronics is the synthetic chemistry devised for the preparation of the semiconductor materials responsible for the activity of organic field-effect transistors. Access to organic semiconductors in sufficient purity and variety has led to breakthroughs in solid-state physics and circuit realization. In this Account, we review the synthetic methods that have been most useful for preparing a range of semiconductors, including thiophene-based oligomers, several kinds of fused rings, and polymers. The tradeoff between process efficiency and target purity is emphasized.
Organic Chemicals↗
Enhancement of biodegradability of polychlorinated dibenzo-p-dioxins.
Enhancement of biodegradability of polychlorinated dibenzo-p-dioxins (PCDDs) was studied with new isolated bacterial strains from soil and oxic-sediments contaminated by PCDDs. The results indicated that mono- and di-chlorinated dibenzo-p-dioxins could be utilized as a sole carbon source and degraded by isolated bacterial strains, but tri-chlorinated dibenzo-p-dioxin (TrCDD) was hardly degraded. The biodegradability of TrCDD and tetra-chlorinated dibenzo-p-dioxin (TCDD) by the strain Pseudomonas sp. EE41, a new isolated one, could be enhanced through primary nutrient of co-metabolism of o-dichlorobenzene (o-DCB). In this case, TrCDD (1.2mg/l for 3 weeks) was degraded by 33.1% and the degradation rate enhanced more than 2 fold; also TCDD (0.1 mg/l for 3 weeks) biodegraded by 37.8%. Most highly chlorinated, Penta-, Hexa-, Hepta-, and Octa-chlorinated, dibenzo-p-dioxins (P-CDD, H6, H7-CDD and OCDD) tested in this study could not be degraded while accumulated in bacterial cells.
Biodegradation, Environmental↗
[Microbial degradation of polychlorinated dibenzo-p-dioxins].
PCDDs-degrading bacterial strains were isolated from soil and oxic-sediments polluted by PCDDs. One of them was identified as Pseudomonas sp. EE41. They are capable of growing on and degrade mono- and di-chlorinated dibenzo-p-dioxins as a sole carbon source. The biodegradability of TrCDD and TCDD can be enhanced through primary nutrient of co-metabolism of o-CDB, thus, 1,2,3-TrCDD and 2,3,7,8-TCDD were degraded by 33% (at the concentration of 1.2 mg/L, within 3 weeks) and 37.8% (at the concentration of 0.1 mg/L, within 3 weeks) respectively. Most highly chlorinated dibenzo-p-dioxins (P-CDD, H6-, H7-CDD and OCDD) tested in this study were accumulated in bacterial cells, but could not be degraded.
Biodegradation, Environmental↗
Human cytochrome P450 CYP2A13: predominant expression in the respiratory tract and its high efficiency metabolic activation of a tobacco-specific carcinogen, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone.
The human CYP2A subfamily comprises three genes, CYP2A6, CYP2A7, and CYP2A13. CYP2A6 is active toward many carcinogens and is the major coumarin 7-hydroxylase and nicotine C-oxidase in the liver, whereas CYP2A7 is not functional. The function of CYP2A13 has not been characterized. In this study, a CYP2A13 cDNA was prepared by RNA-PCR from human nasal mucosa and was translated using a baculovirus expression system. In a reconstituted system, the expressed CYP2A13 was more active than CYP2A6 in the metabolic activation of hexamethylphosphoramide, N,N-dimethylaniline, 2'-methoxyacetophenone, and N-nitrosomethylphenylamine but was much less active than CYP2A6 in coumarin 7-hydroxylation. Of particular interest, CYP2A13 was highly active in the metabolic activation of a major tobacco-specific carcinogen, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone, with a catalytic efficiency much greater than that of other human cytochrome P450 isoforms examined previously. The tissue distribution of CYP2A13 was determined with isoform-specific RNA-PCR. CYP2A13 mRNA was detected in liver and a number of extrahepatic tissues, including nasal mucosa, lung, trachea, brain, mammary gland, prostate, testis, and uterus, but not in heart, kidney, bone marrow, colon, small intestine, spleen, stomach, thymus, or skeletal muscle. Quantitative PCR analysis further revealed that CYP2A13 mRNA is expressed at the highest level in the nasal mucosa, followed by the lung and the trachea. Together, these findings suggest that CYP2A13 plays important roles in xenobiotic toxicity and tobacco-related tumorigenesis in the human respiratory tract.
Adolescent↗
Ultrafast spectroscopy of even-parity states in pi-conjugated polymers
Relaxation dynamics of even parity ( A(g)) states in poly( p-phenylene vinylene) derivatives are studied using a novel fsec transient spectroscopy, in which two different excitation pulses successively generate odd parity ( 1 (1)B(u)) excitons at 2.2 eV and then reexcite them to higher A(g) states. For reexcitation energies Planck's over 2piomega<1.1 eV ultrafast internal conversion back to 1 (1)B(u) takes place in accordance with Vavilov-Kasha's rule. However, for Planck's over 2piomega>1.1 eV the decay occurs in a nonemissive state identified as a polaron pair, showing that the A(g) states above 3.3 eV mediate charge transfer.
Journal Article↗
GCIP, a novel human grap2 and cyclin D interacting protein, regulates E2F-mediated transcriptional activity.
Regulation of mammalian cell growth and proliferation is governed through receptor-mediated signaling networks that ultimately converge on the cell cycle machinery. Adaptor proteins play essential roles in the formation of intracellular signaling complexes, relaying extracellular signals from the plasma membrane to the nucleus of a cell. The leukocyte-specific adaptor protein Grap2 is a central linker protein in immune cell signaling and activation. Using Grap2 as bait protein, we identified a novel human protein, GCIP (Grap2 cyclin-D interacting protein). We found that GCIP bound to Grap2 in both yeast two-hybrid assays and in mammalian cells through binding to the COOH-terminal unique domain and SH3 domain (designated QC domain) of Grap2. GCIP also associated with cyclin D both in vitro and in vivo. The expression of GCIP was found in all human tissues examined with the highest level of expression in the heart, muscle, peripheral blood leukocytes, and brain. Furthermore, phosphorylation of retinoblastoma protein by cyclin D-dependent protein kinase was reduced and E2F1-mediated transcription activity was inhibited in cells transfected with GCIP. High level expression of GCIP in terminally differentiated tissues and the inhibition of E2F1 transcription activation suggest that GCIP could play an important role in controlling cell differentiation and proliferation.
Adaptor Proteins, Signal Transducing↗
Large-scale complementary integrated circuits based on organic transistors
Thin-film transistors based on molecular and polymeric organic materials have been proposed for a number of applications, such as displays and radio-frequency identification tags. The main factors motivating investigations of organic transistors are their lower cost and simpler packaging, relative to conventional inorganic electronics, and their compatibility with flexible substrates. In most digital circuitry, minimal power dissipation and stability of performance against transistor parameter variations are crucial. In silicon-based microelectronics, these are achieved through the use of complementary logic-which incorporates both p- and n-type transistors-and it is therefore reasonable to suppose that adoption of such an approach with organic semiconductors will similarly result in reduced power dissipation, improved noise margins and greater operational stability. Complementary inverters and ring oscillators have already been reported. Here we show that such an approach can realize much larger scales of integration (in the present case, up to 864 transistors per circuit) and operation speeds of approximately 1 kHz in clocked sequential complementary circuits.
Journal Article↗
Application of Live Monocells from Macroalgae to Shellfish Seed Production.
Monocells were isolated from several macroalgae, Porphyra yezoensis, Undaria pinnatifida, and Laminaria japonica, by digestion with alga-tool enzymes. The monocells were then used to feed the parents or larvae of bay scallop Argopecten irradians, blood cockle Arca inflata, and abalone Haliotis discus juveniles. Results showed that the parents of bay scallop and blood cockle fed with Porphyra monocells could mature and discharge eggs and spermatozoa and their larvae could metamorphose; the survival rate of abalone juveniles fed with isolated cells from Laminaria and Undaria increased by 100% compared with that of those fed with artificial food.
Journal Article↗
Expression of MacMARCKS restores cell adhesion to ICAM-1-coated surface.
To evaluate the role of MacMARCKS, a major substrate of protein kinase C, in cell adhesion, we selected a macrophage cell line, Wehi 274.1.7. Although surface expression of beta2-integrins can be detected on these cells, they lack the phorbol ester- or chemokine-induced adhesion to ICAM-1-coated surface, an event mediated by beta2-integrins. Concomitantly, these cells lack expression of both MacMARCKS and its homologue, MARCKS. When wild type MacMARCKS was expressed in these cells, the phorbol ester-induced adhesion to ICAM-1-coated surface increased approximately 5-fold compared to vector transfected control cells. To further investigate the potential physiological role of MacMARCKS in this adhesion event, we also tested the effect of monocyte chemotactic protein-1, and a 3-fold increase in the adhesion to ICAM-1-coated surface was observed with MacMARCKS-transfected cells. Therefore, these data suggest that MacMARCKS is an essential component in regulating cell adhesion.
Animals↗
Acetone catabolism by cytochrome P450 2E1: studies with CYP2E1-null mice.
Previous experiments in vitro have suggested that cytochrome P450 2E1 (CYP2E1) is involved in acetone catabolism by converting acetone to acetol and then to methylglyoxal, both intermediates in the gluconeogenic pathway. In the present study, CYP2E1-null mice were used to demonstrate the role of CYP2E1 in acetone catabolism in vivo. The blood acetone level in male CYP2E1-null mice was 3.3 +/- 0.9 microg/mL, which was similar to levels of their sex- and age-matched parental lineage strains C57BL/6N (2.3 +/- 0.2 microg/mL) and 129/Sv (3.5 +/- 0.3 microg/mL) mice (both are CYP2E1 wild-type). After fasting for 48 hr, the blood acetone levels in the CYP2E1 wild-type mice were increased by 2.5- to 4.4-fold, but that in the CYP2E1-null mice increased 28-fold. These results clearly demonstrate that CYP2E1 plays a vital role in the catabolism of acetone under fasting conditions.
Acetone↗