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Biomedical subjects

Daoben Zhu

Publications and source records attributed to Daoben Zhu.

At least 19 recordsLinked to original sources
PubMed2007

Amination of [60]fullerene by ammonia and by primary and secondary aliphatic amines--preparation of amino[60]fullerene peroxides.

Ammonia and aliphatic amines react readily in the oxygen-rich regions of the Cs symmetric fullerene peroxides C60(O)(OOtBu)4 (1) and C60(OH)(Br)(OOtBu)4 (2 c). Michael addition-type hydroamination of the 1,4-diene moiety on the central skew-pentagon was observed when 1 was treated with ammonia or with nonbulky primary amines, while sterically demanding primary amines opened the epoxy moiety to form vicinal aminohydroxy fullerene compounds with the amino group on the central pentagon. In 2 c the bromo group was replaced under similar conditions by ammonia and primary amines. Cyclic secondary amines showed different reaction patterns, forming hydrogenation products or aminoketal-fullerenes when treated with 1 and 2 c, respectively. Single-electron transfer (SET) is the key step in all the proposed mechanisms. The compounds were characterized by their spectroscopic data, and in addition, three single-crystal X-ray structures were obtained.

Journal Article↗
PubMed2006

High-performance low-cost organic field-effect transistors with chemically modified bottom electrodes.

The characteristics of organic field-effect transistors (OFETs) were dramatically improved by chemically modifying the surface of the bottom-contact Ag or Cu source-drain (D-S) electrodes with a simple solution method. The contact resistance and energetic mismatch typically observed with Ag D-S electrodes in pentacene bottom-contact OFETs can be properly eliminated when modified by the Ag-TCNQ (TCNQ = 7,7,8,8-tetracyanoquinodimethane). The pentacene transistors with low-cost Ag-TCNQ-modified Ag bottom-contact electrodes exhibit outstanding electrical properties, which are comparable with that of the Au top-contact devices. It thus provides a novel way toward high-performance low-cost bottom-contact OFETs.

Journal Article↗
PubMed2006

A cyclic triphenylamine dimer for organic field-effect transistors with high performance.

A cyclic ethylene linked triphenylamine dimer formed highly crystalline thin film via vapor deposition. Meanwhile, the corresponding linear molecule only resulted in amorphous films under the same condition. The performance as FET semiconductor also improved significantly when the molecular structure derived from linear to cyclic type. The cyclic molecule displayed mobilities in excess of 10-2 cm2 V-1 s-1 and high on/off ratios up to 107.

Chemistry, Organic↗
PubMed2006

Direct visualization of enzymatic cleavage and oxidative damage by hydroxyl radicals of single-stranded DNA with a cationic polythiophene derivative.

A new method has been developed for the label-free, convenient, and real-time monitoring of the cleavage of single-stranded DNA by single-strand-specific S1 nuclease and hydroxyl radical based on cationic water-soluble poly[3-(3'-N,N,N-triethylamino-1'-propyloxy)-4-methyl-2,5-thiophene hydrochloride](PMNT). The PMNT can form an interpolyelectrolyte complex with ssDNA (duplex) through electrostatic interactions, in which PMNT takes a highly conjugated and planar conformation, and thus PMNT exhibits a relatively red-shifted absorption wavelength. When ssDNA is hydrolyzed by S1 nuclease or hydroxyl radical into small fragments, the PMNT/ssDNA duplex cannot form. In this case, the PMNT remains in random-coil conformation and exhibits a relatively short absorption wavelength. The nuclease digestion or oxidative damage by hydroxyl radical of DNA can be monitored by absorption spectra or just visualized by the "naked-eye" in view of the observed PMNT color changes in aqueous solutions. This assay is simple and rapid, and there is no need to label DNA substrates. The most important characteristic of the assay is direct visualization of the DNA cleavage by the "naked-eye", which makes it more convenient than other methods that rely on instrumentation. The assay also provides a promising application in drug screening based on the inhibition of oxidative damage of DNA.

Base Sequence↗
PubMed2006

1-Imino nitroxide pyrene for high performance organic field-effect transistors with low operating voltage.

Organic field-effect transistors (OFETs) fabricated with vapor-deposited films of 1-imino nitroxide pyrene show excellent p-type FET characteristics, with mobility up to 0.1 cm2 V-1 s-1 and an on/off ratio of nearly 5 x 104. Most remarkable feature of the FETs is their low operating voltage due to the low threshold voltage (about -0.6 V) and inverse subthreshold slope (about 540 mV decade-1).

Journal Article↗
PubMed2006

Controlling the growth of single crystalline nanoribbons of copper tetracyanoquinodimethane for the fabrication of devices and device arrays.

In this paper, (1) a simple and controllable method to synthesize single crystalline nanoribbons of CuTCNQ in a large area was demonstrated by using a physical and chemical vapor combined deposition technique. (2) Nanoribbons synthesized by this method were identified to belong to phase I. (3) Devices and device arrays of nanoribbons were in situ fabricated by this method using gap electrodes and gap electrode arrays. (4) Current-voltage characteristics of crystalline devices and device arrays of nanoribbons exhibited semiconductor properties, and this conclusion was further confirmed by the results of devices based on an individual nanoribbon or microribbon of CuTCNQ (phase I). The controllable synthesis of nanoribbons for the in situ fabrication of crystalline nanodevices and device arrays will be attractive for nanoelectronics. Moreover, semiconductor current-voltage characteristics of the nanoribbons will be beneficial to the understanding of CuTCNQ.

Journal Article↗
PubMed2006

Formation of the intermediate nitronyl nitroxide-anthracene dyad sensing saccharides.

We design a new saccharides sensor based on the ensemble of compound 2 with a boronic group and compound 3 with two phenolic -OH groups, taking advantage of the fluorescence quenching ability of nitronyl nitroxides and reversible boronate formation between boronic acid and diol. The results show that the fluorescence of compound 2 was largely quenched upon addition of compound 3 due to the formation of the intermediate nitronyl nitroxide-anthracene dyad 1. Sequential addition of saccharides such as fructose to the ensemble of compounds 2 and 3 together with dyad 1 induced the fluorescence enhancement. These results clearly demonstrate the possibility to employ the ensemble of compounds 2 and 3 (with dyad 1) to sense saccharides.

Anthracenes↗
PubMed2006

Novel diethynylcarbazole macrocycles: synthesis and optoelectronic properties.

Diethynylcarbazole macrocycles 1b and 2b have been synthesized by oxidative coupling of appropriate precursors. In particular, macrocycle 2b was prepared by bimolecular Pd-catalyzed oxidative coupling in 35% isolated yield. The spectroscopic properties of these macrocycles and their precursors were measured in detail. The films of these macrocycles by the dipping method and the Langmuir-Blodgett technique were fabricated to study their photoinduced charge-transfer properties. A rapid and steady cathodic photocurrent of these films was produced in a three-electrode cell when irradiated with white light. A possible mechanism of the photoinduced electron-transfer pathway was suggested.

Journal Article↗
PubMed2006

A new morphology of copper 7,7,8,8-tetracyano-p-quinodimethane.

Morphology control is a long-standing problem that needs to be solved for making the switching mechanism of copper 7,7,8,8-tetracyano-p-quinodimethane (CuTCNQ) understood all the time, but up till now how many morphologies CuTCNQ possesses and which morphology should be responsible for the on/off switching phenomenon are still unclear. A new morphology of CuTCNQ, namely the tubular structure, has been obtained and characterized in our experiment, whose formation mechanism has also been investigated. Through characterizing, we can conclude that the tubular structure belongs to the phase I, which can be further confirmed by the electrical measurements. From the I-V plots, the carrier mobility of the tubular structure is estimated to be approximately 0.1 cm2 V-1 s-1, which suggests the potential application of CuTCNQ in devices.

Journal Article↗
PubMed2006

A new redox-resettable molecule-based half-adder with tetrathiafulvalene.

A new redox molecule-based half-adder with tetrathiafulvalene (TTF) was reported for the first time. This half-adder employs electrochemical and chemical oxidations (NOPF6) as input signals and absorbances at 350 and 435 nm as output signals. It is interesting to note that this new molecule-based half-adder shows reset capability by making use of the unique redox behaviors of TTF.

Electrochemistry↗
PubMed2006

Photomodulation of the electrode potential of a photochromic spiropyran-modified Au electrode in the presence of Zn2+: a new molecular switch based on the electronic transduction of the optical signals.

The electrode potential of a photochromic spiropyran-modified Au electrode could be reversibly modulated by UV/visible light irradiation in the presence of Zn2+, and a new molecular switch and an "AND" logic gate based on this electronic transduction of the optical signals were established.

Benzopyrans↗
PubMed2006

Quadruplex-to-duplex transition of G-rich oligonucleotides probed by cationic water-soluble conjugated polyelectrolytes.

G-quartet DNA converts to duplex form in the presence of its complementary strand. This conformational change can be detected in real time by a homogeneous assay method based on the signal amplification of conjugated polyelectrolytes and the specific interaction of intercalating dyes with double-stranded DNA (dsDNA). The probe solution contains a cationic, conjugated polymer (CCP), G-quadruplex labeled with a fluorescein at the 5'-terminus (G-quadruplex-Fl), and ethidium bromide (EB). The addition of a complementary target results in the transition from G-quadruplex to duplex (dsDNA-Fl) and EB intercalation within the duplex structure. Excitation of the CCP leads to energy transfer from CCP to dsDNA-Fl (FRET-1) and then energy transfer from dsDNA-Fl to EB (FRET-2). Increasing the number of mismatched bases discourages dsDNA formation, which is detected in the assay.

Cations↗
PubMed2006

A new tetrathiafulvalene-anthracence dyad fusion with the crown ether group: fluorescence modulation with Na+ and C60, mimicking the performance of an "AND" logic gate.

In this Note, we describe a new TTF-anthracene dyad fusion with the crown ether unit. It is interesting to find that the fluorescence of this new dyad can be modulated with Na+ and C60, and its fluorescence intensity can be largely enhanced only in the presence of both Na+ and C60. Such fluorescence modulation behavior mimics the performance of a two-input "AND" logic gate.

Journal Article↗
PubMed2006

Syntheses, crystal structures, and magnetic characterization of five new dimeric manganese(III) tetradentate Schiff base complexes exhibiting single-molecule-magnet behavior.

Tetradentate Schiff base ligands H2L (H2saltmen, H2salen, H2-5-Brsalen, and H2-3,5-Brsalen), derived from the condensation of the corresponding salicylaldehyde or its derivatives with 1,1,2,2-tetramethylethyldiamine or 1, 2-diaminoethane, reacted with Mn(III) acetate or perchlorate salts and sodium azide or sodium cyanate to produce five Mn(III) dimer complexes, [Mn(saltmen)(O2CCH3)]2.2CH3CO2H (1), [Mn(saltmen)(N3)]2 (2), [Mn(salen)(NCO)]2 (3), [Mn(3,5-Brsalen)(3,5-Brsalicylaldehyde)]2 (4), and [Mn(5-Brsalen)(CH3OH)]2(ClO4)2 (5). These new complexes have been characterized by IR, elemental analyses, crystal structural analyses, and magnetic studies. Within these Mn(III) dimeric complexes, two Mn(III) ions are connected by phenolate oxygen atoms with acetate, azide, cyanate, a 3,5-Brsalicyladehyde anion, and a neutral methanol molecule as the axial ligands for complexes 1-5, respectively. Complexes 1-4 exhibit intradimer ferromagnetic exchange and display frequency dependence of ac magnetic susceptibility, possibly showing single-molecule-magnet (SMM) behavior. In contrast, complex 5 shows an intradimer antiferromagnetic coupling probably originating from the relatively shorter Mn-O distance, compared to those of complexes 1-4.

Journal Article↗
PubMed2006

X-shaped oligothiophenes as a new class of electron donors for bulk-heterojunction solar cells.

Four X-shaped oligothiophenes with different conjugation length were investigated as novel electron donors in single-layer bulk-heterojunction solar cells. The UV-vis absorption spectra of blends of compounds 1-4 with 1-(3-methoxycarbonyl)propyl-1-phenyl[6,6]C(61) show a remarkably red shift and broadening with increasing thiophene number at each of the four branches. The performance of the photovoltaic cells varied significantly with molecular structures of the four oligothiophenes. Conversion efficiencies increased from 0.008% to 0.8% with changing the electron donors from 1 to 4. The maximum incident photon-to-current conversion efficiency of the device based on 4 reaches 31.6%, much higher than those of three other compounds 1-3. Remarkable improvement of the device performance was achieved with increasing the substituted thiophene number. The results show that the photovoltaic effect is dependent on the structural characteristics and the film forming abilities of the X-shaped thiophenes.

Journal Article↗