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At least 847 records · Page 47Linked to original sources
PubMed2005

A robust approach to studying the adsorption of Pluronic F108 on nonporous membranes.

A method for poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) desorption from synthetic nonporous polymeric membranes, using hexane:isopropanol treatment and subsequent colorimetric quantification, is described. The polymers polysulfone, poly(vinyldiene fluoride), and poly(ether imide) were used to fabricate solid adsorption matrices. The desorbed Pluronic F108 forms a color complex with ammonium ferrothiocyanate (NH4FeSCN) and is based on partitioning of a chromophore present in NH4FeSCN from an aqueous phase to a chloroform phase in the presence of Pluronic. The protocols for Pluronic desorption and detection are simple, sensitive, inexpensive, rapid, and reproducible over a wide range of Pluronic coating concentrations and membrane surface chemistries. A linear response over the concentration range from 3 to 130 microg ml(-1) is obtained. The adsorption isotherms for flat sheet membranes are also described and the Langmuir equation provides the best fit for the adsorption data obtained within the concentration range studied. The absence of any significant interference from certain proteins, vitamins, carbohydrates, plasma, and halogenated derivatives makes the assay equally suitable for the estimation of Pluronic F108 in the attendant Pluronic conjugates or in biomedical applications. Using nonporous hollow fine fibers and capillary membranes as model curved substrates we were also able to correlate an increase in the radius of curvature with a corresponding increase in the surface interfacial adsorption of Pluronic F108.

Adsorption↗
PubMed2005

Low-temperature ionic liquids immobilized in porous alumina.

The pores in an aluminum oxide matrix can be completely filled with 1-alkyl-3-methylimidazolium tetrafluoroborates, hexafluorophosphates, triflates, and bis(trifluoromethylsulfonyl)imides. This possibility can be utilized to produce solid electrolytes for batteries and fuel cells.

Journal Article↗
PubMed2005

Mono-layer of Ni(100-x)Fe(x) nanoparticles fabricated on a polyimide film under different curing atmospheres.

A mono-layer of nano-sized metal particles was prepared on the surface of a polyimide film by simply depositing a thin film of Ni80Fe20 on top of the polyamic acid that was spin coated onto a Si wafer. During thermal imidization of the polyamic acid film, Fe was selectively etched by reacting with the carbonyl group of the polyamic acid to leave behind uniformly distributed Ni-rich metallic particles. The average diameter of the particles was 4 nm and the particles were confined into a single layer on top of the polymer film. Moreover, it was also shown that the morphology of the nanoparticles can be substantially altered by curing the precursor film in a hydrogen atmosphere, without significantly damaging the polymer film. Thus produced nanoparticles lay exposed on top of the electrically insulating and chemically stable polymer film so that it is possible that the nanoparticles can be directly used for fabricating a nonvolatile flash memory device or as a template for building functional nano-structures.

Journal Article↗
PubMed2006

Mesoporous silica reinforced by silica nanoparticles to enhance mechanical performance.

Silica nanoparticle/mesoporous silica composite films were prepared by direct mixing with mechanical stirring and thermal imidization. The structural morphology was elucidated by scanning electron microscopy and the surface of the film was imaged by atomic force microscopy. The functional groups and desorption process of the films were elucidated by Fourier transform infrared spectroscopy and thermal desorption spectroscopy. The mechanical properties were investigated using a nanoindenter system. The gel matrix and the filler are very compatible because they have similar molecular content. The composite films had a higher mechanical strength than pure porous silica film. Their strength is related to the silica nanoparticle content. The interfacial compatibility, dispersion effect, and interfacial strength also affect the mechanical strength of composite films.

Journal Article↗
PubMed2006

Molecular details of Itk activation by prolyl isomerization and phospholigand binding: the NMR structure of the Itk SH2 domain bound to a phosphopeptide.

The Src homology 2 (SH2) domain of interleukin-2 tyrosine kinase (Itk) is a critical component of the regulatory apparatus controlling the activity of this immunologically important enzyme. To gain insight into the structural features associated with the activated form of Itk, we have solved the NMR structure of the SH2 domain bound to a phosphotyrosine-containing peptide (pY) and analyzed changes in trans-hydrogen bond scalar couplings ((3h)J(NC')) that result from pY binding. Isomerization of a single prolyl imide bond in this domain is responsible for simultaneous existence of two distinct SH2 conformers. Prolyl isomerization directs ligand recognition: the trans conformer preferentially binds pY. The structure of the SH2/pY complex provides insight into the ligand specificity; the BG loop in the ligand-free trans SH2 conformer is pre-arranged for optimal contacts with the pY+3 residue of the ligand. Analysis of (3h)J(NC') couplings arising from hydrogen bonds has revealed propagation of structural changes from the pY binding pocket to the CD loop containing conformationally heterogeneous proline as well as to the alphaB helix, on the opposite site of the domain. These findings offer a structural framework for understanding the roles of prolyl isomerization and pY binding in Itk regulation.

Amino Acid Sequence↗
PubMed2006

Lenalidomide inhibits proliferation of Namalwa CSN.70 cells and interferes with Gab1 phosphorylation and adaptor protein complex assembly.

Lenalidomide (Revlimid, CC-5013) belongs to a line of compounds known as immunomodulatory drugs (IMiDs) that are under clinical investigation in hematopoietic and solid tumor cancers. Lenalidomide efficacy has been reported in clinical trials of multiple myeloma and myelodysplastic syndromes (MDS), particularly in MDS patients with a del 5q cytogenetic abnormality, with or without other cytogenetic abnormalities. Here we report that lenalidomide inhibits proliferation of chromosome 5 deleted hematopoietic tumor cell lines in vitro, whether from the B cell, T cell, or myeloid lineage. There was diversity in the responses of the various cell lines to lenalidomide, with one undergoing cell cycle arrest, and others undergoing apoptosis. In the most lenalidomide-sensitive chromosome 5 deleted cell line, Namalwa CSN.70, the compound induced G0/G1 cell cycle arrest, inhibited Akt and Gab1 phosphorylation, and inhibited the ability of Gab1 to associate with a receptor tyrosine kinase. Lenalidomide also enhanced AP-1 transcriptional activity in Namalwa, but not in the other cell lines tested. These studies provide evidence for the mechanism of action of lenalidomide in chromosome 5 deleted hematopoietic tumors in vitro, and may provide a better understanding of the drug's activity in clinical applications.

Adaptor Protein Complex 1↗
PubMed2005

Orally administered lenalidomide (CC-5013) is anti-angiogenic in vivo and inhibits endothelial cell migration and Akt phosphorylation in vitro.

The thalidomide analogue and immunomodulatory drug (IMiD) lenalidomide (CC-5013, REVLIMID) is emerging as a useful treatment for a number of cancers and has recently entered phase III trials for multiple myeloma. It has been suggested that the anti-tumor effect of lenalidomide is related to its anti-angiogenic potency. In this regard, we have previously shown that lenalidomide inhibits angiogenesis in both rat and human in vitro models but does not affect endothelial cell proliferation. We now show that oral administration of lenalidomide attenuates growth factor-induced angiogenesis in vivo; the rat mesenteric window assay was utilized to show that lenalidomide significantly inhibits vascularization in a dose-dependent manner. We also found that lenalidomide significantly inhibits growth factor-induced endothelial cell migration. This correlates with the inhibitory effect of lenalidomide on growth factor-induced Akt phosphorylation, thereby providing a potential mechanism for its anti-migratory and subsequent anti-angiogenic effects. These data further support the use of lenalidomide as an orally administered drug for the effective treatment of angiogenesis-dependent conditions, including cancer, and suggest a potential mechanism of action.

Administration, Oral↗
PubMed2005

Discovery of a novel N-iminylamidase activity: substrate specificity, chemicoselectivity and catalytic mechanism.

Enzymatic hydrolysis of the N-iminylamide was investigated in this study. An enzyme possessing N-iminylamidase activity from pig liver was purified to electrophoretic homogeneity. This enzyme was also active, however, with imides and appears to be identical to pig liver imidase. The identification was confirmed by copurification of enzyme activities and by specificities of typical substrates of mammalian imidase, such as phthalimide, dihydrouracil, and maleimide. The hydrolysis of 3-iminoisoindolinone was further analyzed by HPLC, (13)C NMR spectrometry, and LC-MS measurements to determine its chemicoselectivity. All data indicated that this enzyme chemicoselectively catalyzed the hydrolysis of the N-iminylamide to produce the compound bearing the diamine and carboxylate group. The pH profiles of this enzyme suggest that one of the protons of 3-iminoisoindolinone was important to promote the ring-opening process of this substrate. These results constituted a first study on the enzymatic hydrolysis of compounds bearing the N-iminylamide functional group.

Amidohydrolases↗
PubMed2005

Vibrational spectra of saccharin nitranion and its orientation on the surface of silver metal particles.

Infrared-reflectance spectra of the saccharin nitranion adsorbed on silver powder was observed. Surface-Enhanced Raman Scattering (SERS) spectra of the saccharin nitranion were also recorded using cellulose acetate films doped with fine silver particles. The spectra suggested that the saccharin nitranion is bonded to the silver metal surface through the oxygen atom of carbonyl and the nitrogen atom of the imide ring groups and that the nitranion tilts at the surface.

Acetates↗
PubMed2004

Spectroscopic and DFT studies to understand the liquid formation mechanism in the LiTFSI/acetamide complex system.

It is interesting that although both lithium bis(trifluoromethane sulfone) imide (LiN(SO2CF3)2, LiTFSI) and acetamide (CH3CONH2) are solid, their mixture is a liquid in an appropriate molar ratio range at room temperature. The liquid formation mechanism of the LiTFSI/acetamide complex has been investigated by FT-IR and FT-Raman spectroscopy. The spectroscopic studies show that the Li+ ions coordinate with the C=O group of acetamide whereas the SO2 group in TFSI- anions interacts with the NH2 group of acetamide via hydrogen bonding. These interactions lead to the breakage of the hydrogen bonds between acetamide molecules and to the dissociation of LiTFSI, resulting in the formation of this molten salt. Furthermore, it has been found that moderate interaction between LiX and RCONH2 (R = -NH2, -CH3 and -CF3) is favorable for forming a LiX/RCONH2 molten salt system with low eutectic temperature and high conductivity based on density functional theory (DFT) calculational and experimental comparison for different R groups in RCONH2 and different lithium salts.

Acetamides↗
PubMed2006

[Delayed infection after Bio-alcamid implantation].

Bio-alcamid (Polymekon) is a gelatinous endoprothesis constituted of poly-alkyl-imide and water that is used for correction of aesthetic alterations. It presents very good tolerance with few adverse effects. We present a case of localized infection in one of the sites of injection, three months after the implant was placed in the nasolabial furrows and lips. It would be the first case of a delayed infection following injection of this material, although there are few references in this field.

Acrylic Resins↗
PubMed1983

Buthiobate: a potent inhibitor for yeast cytochrome P-450 catalyzing 14 alpha-demethylation of lanosterol.

Buthiobate (S-n-butyl S'-p-tert-butylbenzyl N-3-pyridyldithiocarbon-imidate), a fungicide, inhibited 14 alpha-demethylation of lanosterol catalyzed by a reconstituted enzyme system consisting of cytochrome P-450 (P-450(14)-DM) and NADPH-cytochrome P-450 reductase both purified from Saccharomyces cerevisiae. Concentration of buthiobate necessary for the 50% inhibition was 0.3 microM and this value was markedly lower than those of metyrapone and SKF-525A. Buthiobate bound stoichiometrically to P-450(14)-DM and induced Type II spectral change of the cytochrome. Buthiobate inhibited lanosterol-dependent enzymatic reduction of the cytochrome. These facts indicate that buthiobate binds to P-450(14)-DM with high affinity and acts as a potent inhibitor on the cytochrome.

Cytochrome P-450 Enzyme Inhibitors↗
PubMed2000

Roles of mitogen-activated protein kinase pathways for mediator release from human cultured mast cells.

Human cultured mast cells (HCMC) secrete histamine, sulfidoleukotrienes (LTs), and prostaglandin D(2) (PGD(2)), and produce a variety of cytokines after aggregation of high-affinity receptors for IgE (FcepsilonRI). With respect to the mitogen-activated protein kinase (MAPK) family, extracellular signal-regulated kinases (ERKs), c-Jun NH(2)-terminal kinases (JNKs), and p38 mitogen-activated protein kinase (p38 MAPK) are known. To investigate the roles of these kinase pathways for mediator release from human mast cells, we examined the participation of the activation of these kinases in mediator release, using 1,4-diamino-2, 3-dicyano-1,4-bis(2-aminophenylthio)butadiene (U0126), an ERK pathway inhibitor, and 4-(4-fluorophenyl)-2-(4-methylsulfinylphenyl)-5-(4-pyridyl)1H-imid azo le (SB203580), a p38 MAPK pathway inhibitor. U0126 inhibited ERK activation, LT and PGD(2) release, and granulocyte macrophage-colony stimulating factor (GM-CSF) production after stimulation of HCMC. SB203580, on the other hand, potentiated JNK activation and GM-CSF production. The findings of the present study demonstrated that: (i) the release of arachidonic acid metabolites is mediated by the ERK pathway; (ii) GM-CSF production may be driven by both the ERK and JNK pathways; and (iii) the p38 MAPK pathway negatively regulates the JNK pathway. This suggests that MAPK pathways play important roles in mediator release from human mast cells.

Butadienes↗
PubMed2000

Reversible and syntopic interaction between angiotensin receptor antagonists on Chinese hamster ovary cells expressing human angiotensin II type 1 receptors.

Evidence for a competitive type of interaction between angiotensin II type 1 (AT(1)) antagonists on Chinese hamster ovary cells expressing the human AT(1) receptor (CHO-AT(1)) was obtained by analyzing the binding of [(3)H]-2-ethoxy-1-[(2'-(1H-tetrazol-5-yl)biphenyl-4-yl)methyl]-1H- ben zimidazoline-7-carboxylic acid ([(3)H]candesartan) and by measuring the AT-induced production of inositol phosphates. The AT(1) antagonists candesartan, 2-n-butyl-4-chloro-1-[(2'-(1H-tetrazol-5-yl)biphenyl-4-yl)methyl]+ ++imid azole-5-carboxylic acid (EXP3174), or 2-n-butyl-4-chloro-5-hydroxymethyl-1-[(2'-(1H-tetrazol-5-yl)bip hen yl- 4-yl)methyl]imidazole (losartan) produced a concentration-dependent increase in the apparent K(d) values of [(3)H]candesartan in saturation binding experiments, while the B(max) values were unchanged. Furthermore, the dissociation rate of the radioligand initiated by 1 microM unlabelled candesartan was not changed in the presence of 10 microM losartan, 10 microM EXP3174, or 10 microM irbesartan (2-n-butyl-4-spirocyclopentane-1-[(2'-(1H-tetrazol-5-yl)b iph enyl-4-yl) methyl]2-imidazolin-5-one)). Preincubation of the CHO-AT(1) cells with candesartan, EXP3174, and irbesartan caused a reduction in the maximal AT-induced inositol mono-, bis-, and trisphosphate production. This insurmountable effect was reversed in the presence of 1 microM losartan. In line with this finding, the insurmountable antagonist concentration-inhibition curves at 10 microM AT were shifted to the right in the presence of losartan. For candesartan this effect was concentration-dependent, yielding a pK(B) value for losartan of 7.7, which is similar to the pK(B) from previously obtained AT concentration-response curves. Finally, the dissociation rate of candesartan, EXP3174, irbesartan, and losartan was determined by measuring the recovery of AT responses after antagonist pretreatment and washing of the cells with medium containing 1 microM losartan to prevent re-association of the insurmountable antagonists. In addition, similar kinetic data were obtained from the slowing of the [(3)H]candesartan association rate to antagonist preincubated cells.

Angiotensin Receptor Antagonists↗
PubMed1999

Solid-state NMR and hydrogen-deuterium exchange in a bilayer-solubilized peptide: structural and mechanistic implications.

Hydrogen-deuterium exchange has been monitored by solid-state NMR to investigate the structure of gramicidin M in a lipid bilayer and to investigate the mechanisms for polypeptide insertion into a lipid bilayer. Through exchange it is possible to observe 15N-2H dipolar interactions in oriented samples that yield precise structural constraints. In separate experiments the pulse sequence SFAM was used to measure dipolar distances in this structure, showing that the dimer is antiparallel. The combined use of orientational and distance constraints is shown to be a powerful structural approach. By monitoring the hydrogen-deuterium exchange at different stages in the insertion of peptides into a bilayer environment it is shown that dimeric gramicidin is inserted into the bilayer intact, i.e., without separating into monomer units. The exchange mechanism is investigated for various sites and support for a relayed imidic acid mechanism is presented. Both acid and base catalyzed mechanisms may be operable. The nonexchangeable sites clearly define a central core to which water is inaccessible or hydroxide or hydronium ion is not even momentarily stable. This provides strong evidence that this is a nonconducting state.

Binding Sites↗
PubMed1976

Tryptophanyl and carboxylic acid residues in the active centre of glucoamylase I from Aspergillus niger.

The pH-dependence of the photo-oxidation of L-tryptophan, in the presence of Rose Bengal and Methylene Blue, has been investigated. True, initial rate constants were determined in order to circumvent errors due to secondary processes. Photo-oxidation of glycoamylase I from A. niger in the presence of Methylene Blue or Rose Bengal resulted in a pH-dependent loss of enzymic activity, which was analogous to the destruction of free L-tryptophan during photo-oxidation. The loss of enzymic activity was closely associated with the destruction of tryptophan residues in the enzyme. Significant protection of both enzymic activity and tryptophanyl residues in the enzyme molecule was achieved by performing the photo-oxidation in the presence of maltose, which is a substrate for the enzyme. The tryptophanyl residues of glucoamylase I, which had been inactivated by reaction of its carboxylic acid residues with glycine methyl ester in the presence of a water-soluble carbodi-imide, were also substantially protected by maltose. It is concluded that the active centre of glucoamylase I is a cleft lined with tryptophanyl residues that participate in the binding of the substrate. One or more carboxylic acid residues are involved in bond cleavage.

Aspergillus↗
PubMed1985

Structural and conformational features of the Escherichia coli K92 capsular polysaccharide.

Escherichia coli K92 polysaccharide, an alternating (2----8)-alpha- and (2----9)-alpha-linked heteropolymer of sialic acid, undergoes lactonisation (10-20%) at low pH or on treatment with a water-soluble carbodi-imide (greater than 90%). Under the latter conditions, the formation of O-acylisourea is a minor pathway. The antigenicity of the K92 polysaccharide is unaffected by lactonisation of approximately 10% of the residues, but is abolished by lactonisation of approximately 90% of the residues. The unexpected, relative resistance of the K92 polysaccharide to periodate oxidation contrasts with the behaviour of the meningococcal non-O-acetylated (O-Ac-) C polysaccharide, a (2----9)-alpha-linked homopolymer of sialic acid. Two-dimensional 13C-1H-n.m.r. correlation spectroscopy has been used to assign 1H chemical shifts which have aided the interpretation of a resolution-enhanced one-dimensional spectrum. This has led to a determination of conformational features of the K92 polysaccharide in solution. The side-chain adopts a conformation such that H-7 and H-8 are gauche in the (2----8)-alpha-linked residues (1a or 1b), but antiperiplanar in the (2----9)-alpha-linked residues (2). Molecular correlation times have been calculated and some aspects of internal motion elucidated.

Carbohydrate Conformation↗
PubMed2001

Synthesis of Neu5Ac- and Neu5Gc-alpha-(2-->6')-lactosamine 3-aminopropyl glycosides.

In order to prepare 3-aminopropyl glycosides of Neu5Ac-alpha-(2-->6')-lactosamine trisaccharide 1, and its N-glycolyl containing analogue Neu5Gc-alpha-(2-->6')-lactosamine 2, a series of lactosamine acceptors with two, three, and four free OH groups in the galactose residue was studied in glycosylations with a conventional sialyl donor phenyl [methyl 5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-2-thio-D-glycero-alpha- and beta-D-galacto-2-nonulopyranosid]onates (3) and a new donor phenyl [methyl 4,7,8,9-tetra-O-acetyl-5-(N-tert-butoxycarbonylacetamido)-3,5-dideoxy-2-thio-D-glycero-alpha- and beta-D-galacto-2-nonulopyranosid]onates (4), respectively. The lactosamine 4',6'-diol acceptor was found to be the most efficient in glycosylation with both 3 and 4, while imide-type donor 4 gave slightly higher yields with all acceptors, and isolation of the reaction products was more convenient. In the trisaccharides, obtained by glycosylation with donor 4, the 5-(N-tert-butoxycarbonylacetamido) moiety in the neuraminic acid could be efficiently transformed into the desired N-glycolyl fragment, indicating that such protected oligosaccharide derivatives are valuable precursors of sialo-oligosaccharides containing N-modified analogues of Neu5Ac.

Carbohydrate Conformation↗