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991.
Kwon M Jeong S Lee KH Park YK Yu J 《Journal of the American Chemical Society》2002,124(47):13996-13997
Our approach to multivalent peptide construction relies on tentacle peptides, also known as a multiple antigenic peptides, which contain two and four repeats of a selected peptide. In this communication, we report the results of preliminary studies aimed at (1) the selection of short peptides against the carbohydrate, sLeX, (2) the synthesis of tentacle dimers and tetramers of the selected peptides, and (3) the determination of affinities and specificities of the peptides to several related carbohydrates by using the surface plasmon resonance (SPR) and the equilibrium dialysis techniques. Binding affinity studies, as well as assays of in vitro binding of the peptides to a sLeX-specific cell line, have shown that the tetrameric peptides bind to the cell surface sugars. 相似文献
992.
993.
During radiotherapy of cancer, neighboring normal cells may receive sub-lethal doses of radiation. To investigate whether such low levels of radiation modulate normal cell responses to death stimuli, primary cultured human fibroblasts were exposed to various doses of gamma-rays. Analysis of cell viability using an exclusion dye propidium iodide revealed that the irradiation up to 10 Gy killed the fibroblasts only to a minimal extent. In contrast, the cells efficiently lost their viability when exposed to 0.5-0.65 mM H(2)O(2). This type of cell death was accompanied by JNK activation, and was reversed by the use of a JNK-specific inhibitor SP600125. Interestingly, H(2)O(2) failed to kill the fibroblasts when these cells were pre-irradiated, 24 h before H(2)O(2) treatment, with 0.25-0.5 Gy of gamma-rays. These cytoprotective doses of gamma-rays did not enhance cellular capacity to degrade H(2)O(2), but elevated cellular levels of p21(Cip/WAF1), a p53 target that can suppress H(2)O(2)-induced cell death by blocking JNK activation. Consistently, H(2)O(2)-induced JNK activation was dramatically suppressed in the pre-irradiated cells. The overall data suggests that ionizing radiation can impart normal fibroblasts with a survival advantage against oxidative stress by blocking the process leading to JNK activation. 相似文献
994.
Lee SH Williams MV DuBois RN Blair IA 《Rapid communications in mass spectrometry : RCM》2003,17(19):2168-2176
There is an increasing need to be able to conduct quantitative lipidomics analyses as a complement to proteomics studies. The highest specificity for proteomics analysis can be obtained using methodology based on electrospray ionization (ESI) or atmospheric pressure chemical ionization (APCI) coupled with liquid chromatography/tandem mass spectrometry (LC/MS/MS). For lipidomics analysis it is often necessary to be able to separate enantiomers and regioisomers. This can be very challenging when using methodology based on conventional reversed-phase chromatography. Normal-phase chromatography using chiral columns can provide dramatic improvements in the resolution of enantiomers and regioisomers. However, conventional ESI- and APCI-MS/MS has limited sensitivity, which makes it difficult to conduct studies in cell culture systems where only trace amounts of non-esterified bioactive lipids are present. The use of electron capture APCI-MS/MS overcomes this problem. Enantiomers and regioisomers of diverse bioactive lipids can be quantified using stable isotope dilution methodology coupled with normal-phase chiral chromatography and electron capture APCI-MS/MS. This methodology has allowed a lipidomics profile from rat epithelial cells maintained in culture to be delineated and allowed the effect of a non-selective lipoxygenase inhibitor to be assessed. 相似文献
995.
A 3D network [Cu(tmen)(tp)(H2O)2]n (1) (tmen = N,N,N′,N′-tetramethylethylenediamine; tp = terephthalate) and a 2D sheet [Cu(pyrazole)2(tp)]n (2), featuring 1D chains interwoven by hydrogen bonds, have been prepared and characterized by means of X-ray analyses and magnetic measurements. For 1, coordinative zigzag chains contain Cu(II) centers capped by the chelate ligand tmen, in which the tetragonal structure is elongated due to Jahn–Teller distortion. Coordinated water molecules are hydrogen-bonded to two free carboxylate oxygens of tp bridges, leading to the observed 3D structure. The use of the non-chelating capping ligand pyrazole produced the covalent-bonded 1D linear compound 2 with hydrogen bonds. A severe octahedral distortion of the Cu(II) center arises from a small bite angle (52.3(1)°) of two carboxylate oxygen atoms of tp, which are in turn hydrogen-bonded to the N–H groups of pyrazole ligands coordinated to Cu(II) atoms in neighboring chains. Magnetic data were fitted with the high-temperature series expansion for the Heisenberg chain spin Hamiltonian H = −J∑iSi · Si + 1 together with consideration of the molecular field approximation (zJ′). Both compounds interestingly exhibit ferromagnetic interactions with g = 2.17, J = 4.08 cm−1, zJ′ = −0.28 cm−1 for 1 and g = 2.09, J = 1.47 cm−1, zJ′ = −0.04 cm−1 for 2. By taking into account structural parameters of distances between Cu atoms, it is reasonably assigned that the ferromagnetic couplings (J > 0) in these systems originate from the hydrogen bonds. The spin density of the dx2-y2 orbital on a Cu(II) atom in a chain is propagated and induced over the dz2 orbital of another Cu(II) atom in an adjacent chain. This orbital orthogonality gives rise to such interactions. The negative zJ′ term suggests that the tp bridges communicate only tiny antiferromagnetic interactions. 相似文献
996.
A sensitive technique for the determination of trace Cu(II) in various samples after column preconcentration by adsorbing
onto pulverized Amberlite XAD-4 loaded with N-benzoylphenylhydroxylamine (BPHA) was developed. Several experimental conditions,
such as the size of XAD-4, adsorption flow rate, pH of sample solution, and so forth, were optimized. The interfering effects
of diverse concomitant ions were investigated. Al(III), Fe(III), Ni(II), and Co(II) interfered, but the interference by these
ions was completely eliminated by adjusting the amount of XAD-4-BPHA resin to 0.30 g. The dynamic range, the correlation coefficient
(R2), and the detection limit obtained by the proposed technique were 1.0–60, 0.9953, and 0.83 ng/mL, respectively. For validating
the technique, the aqueous samples (stream water, reservoir water, and wastewater), the diluted brass sample, and the plastic
sample were used as real samples. Recovery yields of 94–102% were obtained. These measured data were not different from ICP-MS
data at the 95% confidence level. This method was also validated by rice flour CRM (normal, fortified) samples. Based on the
results of the experiment, it has been found that the proposed technique can be applied to the determination of Cu(II) in
various real samples.
The text was submitted by the authors in English. 相似文献
997.
Jang‐Hee Yoon G. Muthuraman JeeEun Yang Yoon‐Bo Shim Mi‐Sook Won 《Electroanalysis》2007,19(11):1160-1166
Pt‐nanoparticles were synthesized and introduced into a carbon paste electrode (CPE), and the resulting modified electrode was applied to the anodic stripping voltammetry of copper(II) ions. The synthesized Pt‐nanoparticles were characterized by cyclic voltammetry, scanning electron microscopy and X‐ray photoelectron spectroscopy techniques to confirm the purity and the size of the prepared Pt‐nanoparticles (ca. 20 nm). This incorporated material seems to act as catalysts with preconcentration sites for copper(II) species that enhances the sensitivity of Cu(II) ions to Cu(I) species at a deposition potential of ?0.6 V in an aqueous solution. The experimental conditions, such as, the electrode composition, pH of the solution, pre‐concentration time, were optimized for the determination of Cu(II) ion using as‐prepared electrode. The sensitivity changes on the different binder materials and the presence of surfactants in the test solution. The interference effect of the coexisted metals were also investigated. In the presence of surfactants, especially TritonX‐100, the Cu(II) detection limit was lowered to 3.9×10?9 M. However, the Pt‐nanoparticle modified CPE begins to degrade when the period of deposition exceeds to 10 min. Linear response for copper(II) was found in the concentration range between 3.9×10?8 M and 1.6×10?6 M, with an estimated detection limit of 1.6×10?8 M (1.0 ppb) and relative standard deviation was 4.2% (n=5). 相似文献
998.
Investigation of the root extract of Antidesma pentandrum var. barbatum led to the isolation of seven new compounds, antidesmol ( 1 ), antidesmanins E ( 2 ) and F ( 3 ), antidesnone ( 4 ), antidesnol ( 5 ), barbatumols A ( 6 ) and B ( 7 ), together with 14 known compounds including sodium aristolochate‐I ( 10 ) and aristolochic acid‐I methyl ester ( 11 ). 相似文献
999.
1000.
Since alkynes have higher symmetry than olefins, it is not easy to infer the mechanism of a triplet carbene’s addition to
an alkyne by traditional product analysis studies. Specifically, no stereochemical information which might offer insight into
the carbene’s spin state can be extracted from the cyclopropene products. In 1971, Hendrick, Baron, and Jones showed that
diphenylcarbene reacts with terminal alkynes in solution to produce indenes via a “self-trapping” vinylcarbene. They also examined the diphenylcarbene reaction with disubstituted alkynes and found at most
trace amounts of the “self-trapping” indene product.
In this work, we report the direct observation by organic matrix EPR of the vinylcarbenes generated from triplet fluorenylidene
and terminal alkynes. Our efforts to confirm the identities of these intermediates by independent synthesis, intermolecular
trapping, and an intramolecular “self-trapping” method-halogen-migration-are also recounted. These findings are among the
few instances in which fluorenylidene undergoes carbon-carbon bond formation rather than atom abstraction reactions in a low-temperature
matrix, and in which the biradical adduct of a triplet carbene and a π-bonded substrate can be directly observed. 相似文献