PubMed Health⌕ Search

Biomedical subjects

Xiaojun Peng

Publications and source records attributed to Xiaojun Peng.

12 recordsLinked to original sources
PubMed2007

Fluorescence sensing of anions based on inhibition of excited-state intramolecular proton transfer.

Condensation of 2-(2'-aminophenyl)benzoxazole with p-toluenesulfonyl chloride and phenyl isocyanate yields two new anion sensors (TABO and PUBO), which can undergo excited-state intramolecular proton transfer (ESIPT) upon excitation. For the acid receptor TABO, the ESIPT process can be readily disturbed by basic anions such as F-, CH3COO-, and H2PO4- by deprotonating the sulfonamide unit, whereas in the case of PUBO, a good hydrogen-bonding donor, the ESIPT process is inhibited either by the fluoride-induced deprotonation of the urea unit or by the formation of a strong CH3COO--urea intermolecular hydrogen bond complex, and these two types of inhibition mechanisms consequently result in different ratiometric responses. But other anions with less hydrogen-bonding acceptor abilities cannot inhibit the ESIPT. Interestingly, the different inhibition abilities of F-, CH3COO-, and H2PO4- produce different spectral behaviors in PUBO, so this new sensor successfully distinguishes the subtle difference in these three anionic substrates of similar basicity and surface charge density.

Anions↗
PubMed2007

Simple bis-thiocarbono-hydrazones as sensitive, selective, colorimetric, and switch-on fluorescent chemosensors for fluoride anions.

Bis-thiocarbono-hydrazones are found to be a class of sensitive, selective, ratiometric, and colorimetric chemosensors for anions such as fluoride (F(-)) or acetate (Ac(-)). The sensitivities, or the binding constants of the sensors with anions, were found to be strongly dependent on the substituents appended on the pi-conjugation framework, the delocalization bridge CH==N, the aromatic moiety, and the hetero atom in the C==X group (X=O, S) of the sensors. Single-crystal structures and (1)H NMR titration analysis shows that the --CH==N-- moiety is a hydrogen-bond donor, and it is proposed that an additional CHF hydrogen bond is formed for the sensors in the presence F(-). A sensor bearing anthracenyl groups is demonstrated as a switch-on fluorescent chemosensor for F(-) and Ac(-). The recognition of F(-) in acetonitrile (MeCN) by a sensor with nitrophenyl substituents is tolerant to MeOH (MeCN/MeOH=10:1, v/v) and water (MeCN/H(2)O=30:1, v/v); at these solvent ratios the absorption intensity of the sensor-F(-) complex solution at maximal absorption wavelength was attenuated to half of the original value in pure MeCN.

Absorption↗
PubMed2006

A ratiometric fluorescent sensor for phosphates: Zn2+-enhanced ICT and ligand competition.

A pyrene-terpyridine-Zn conjugate has been synthesized and characterized, where Zn2+ acts as an electron acceptor to enhance molecular ICT with a large emission red-shift (>100 nm). It showed a ratiometric fluorescence change upon addition of phosphate anions in buffered aqueous solution. The selective response to phosphates or pyrophosphates involved ICT and ligand competition processes.

Journal Article↗
PubMed2005

Colorimetric and ratiometric fluorescence sensing of fluoride: tuning selectivity in proton transfer.

[reaction: see text] Phenyl-1H-anthra[1,2-d]imidazole-6,11-dione (1) and its derivatives (2 and 3) have been investigated as new colorimetric and ratiometric fluorescent chemosensors for fluoride. Acute spectral responses of 1 and 3 to fluoride in acetonitrile have been observed: an approximately 100 nm red shift in absorption and fluorescence emission and a very large ratiometric fluorescent response (Rmax/Rmin is 88 for sensor 1 and 548 for sensor 3). From the changes in the absorption, fluorescence, and 1H NMR titration spectra, proton-transfer mechanisms have been deduced. In ground states, a two-step process has been observed: first, the formation of the sensor-fluoride hydrogen-bond complex [LH...F]- and then the fluoride-induced deprotonation of the complex to form L- and FHF-. In excited states, the excited-state intermolecular proton-transfer made a contribution to the deprotonation. The selectivity for F- can be tuned by electron push-pull properties of the substituents on the phenyl para position of the sensors. Sensor 1 shows the best selectivity. The excellent selectivity of 1 for F- is attributed to the fitness in the acidity of its NH-group, which is tuned to be able to distinguish the subtle difference in the affinity of F-, CH3CO2(-), and H2PO4(-) to proton.

Journal Article↗
PubMed2005

Heptamethine cyanine dyes with a large stokes shift and strong fluorescence: a paradigm for excited-state intramolecular charge transfer.

New heptamethine cyanine dyes with an alkylamino group at the central position were found to exhibit a large Stokes shift (>140 nm) and strong fluorescence. They were suggested to be a new paradigm for excited-state intramolecular charge transfer (ICT). The configuration change of the bridgehead amine accompanying ICT was investigated in different viscosity and pH media.

Biosensing Techniques↗
PubMed2005

Boron dipyrromethene fluorophore based fluorescence sensor for the selective imaging of Zn(II) in living cells.

A simple PET fluorescence sensor (BDA) for Zn2+ that utilizes 1,3,5,7-tetramethyl-boron dipyrromethene as a reporting group and di(2-picolyl)amine as a chelator for Zn2+ has been synthesized and characterized. BDA has an excitation (491 nm) and emission wavelength (509 nm) in the visible range. The fluorescence quantum yields of the zinc-free and zinc-bound states of BDA are 0.077 and 0.857, respectively. With a low pKa of 2.1 +/- 0.1, BDA has the advantage of less sensitivity to pH than fluorescein-based Zn2+ sensors, and the fluorescence emission of zinc-binding is pH-independent in the range of pH 3-10. Under physiological conditions, metal ions such as Na+, K+, Ca2+, Mg2+, Mn2+ and Fe2+ have little interference. The apparent dissociation constant (Kd) is 1.0 +/- 0.1 nM. Using fluorescence microscopy, the sensor is shown to be capable of imaging intracellular Zn2+ changes.

Animals↗
PubMed2005

A novel fluorescent sensor for triplex DNA.

A triplex DNA fluorescent sensor based on PET is described. The sensor takes 4-aminonaphthalimide as a reporting group and a triplex-select intercalator as a recognizing group. The results show that it is a selective sensor for T.AT triplex DNA in compared with duplex and ssDNA by fluorescence enhancement in PIPES 20 buffer.

Biosensing Techniques↗
PubMed2004

Effects of triethylene tetraamine on telomerase activity and proliferation in HeLa cells.

Telomerase, which is required to maintain telomeres, has attracted considerable attention as a target for anticancer therapy. In this study, we investigated the inhibition of HeLa cell telomerase activity and cell cycle progression by triethylene tetraamine (TETA), using a modified telomeric repeat amplification protocol (TRAP) assay, and flow cytometry. TETA inhibited telomerase activity in HeLa cell extracts, with an IC50 of about 7.8 microM. Coupled with this inhibition, TETA also increased the proportion of cells in the G1 phase of the cell cycle in a dose-dependent manner. These findings demonstrate that TETA is a potent inhibitor of telomerase in micromolar concentrations, and inhibits the proliferation of HeLa cells by arresting them in G1.

Cell Cycle↗
PubMed2004

Electrospray ionization mass spectrometry studies of rhenium(I) bipyridyl complexes.

Electrospray ionization mass spectrometry (ESMS) has been employed to study the formation of fragment ions of a series of rhenium(I) bipyridyl complexes [(4,4'-di-(COOEt)2-bpy) Re(CO)3XPyPF6], where bpy is 2,2'-bipyridine, Py is pyridine, and X is H, 4-methyl, 3-methyl, 4-hydroxyl, 3-hydroxyl, 4-amino, or 3-amino of the pyridine ligand. The effects of substituents (X) on the stabilities of the complexes have been investigated with the increase of fragmentor voltages. For different X, the stabilities of the complexes increase as X become more electron-donating from H to CH3, OH, and NH2. For the same substituent, the p-substituted pyridines have stronger stabilizing effect than the corresponding m-substituted ones. Ligand exchange reaction was found in acetonitrile, where the pyridine ligand has been replaced by the solvent indicated by the formation of [M-PF6- XPy+MeCN]+ in the fragmentation.

2,2'-Dipyridyl↗
PubMed2003

Triethylene tetraamine: a novel telomerase inhibitor.

Telomerase inhibition can be achieved by stabilization of G-quadruplex structure. Triethylene tetraamine, a small linear molecule, has been identified as a potent telomerase inhibitor. It stabilizes both intra- and inter-molecular G-quadruplexes and shows a good differential between potent telomerase inhibition and acute cytotoxicity.

Animals↗
PubMed2002

Differential regulation of maturation and apoptosis of human monocyte-derived dendritic cells mediated by MHC class II.

Antigen-driven interaction of dendritic cells (DC) with CD4(+) T(h) cells results in the exchange of bidirectional activating signals. Cross-linking of TCR by MHC class II-bound antigen activates T(h) cells, resulting in their up-regulation of CD40 ligand. Here we show that MHC class II molecules, in addition to their passive role in DC-T(h) cell interaction, can also actively induce DC maturation. Cross-linking of MHC class II molecules on human monocyte-derived DC results in the up-regulation of the surface expression of CD83, CD80, CD86, CD54, CD1a and CD40 molecules, the typical DC maturation-associated markers. It also promotes a rapid homotypic aggregation of DC paralleled by the up-regulation of such adhesion molecules as VLA-4, tissue transglutaminase, CD54 and CD11c. The impact of MHC class II cross-linking upon DC was context dependent. The outcome of MHC class II signaling depends on the maturation status of DC. While the cross-linking of MHC class II on immature DC promoted their maturation, the dominant effect upon the DC that were previously matured was the induction of DC apoptosis. Our current observations indicate that, in addition to the previously reported negative impact of MHC class II-mediated signaling on DC function, it also promotes DC maturation, participating in the enhancement of DC stimulatory function. Importantly, MHC class II-induced DC maturation and apoptosis are mediated by different signaling pathways, sensitive to different sets of inhibitors. This opens the possibility of differential regulation of each of these events in immunotherapy.

Antibodies↗