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PubMed2006

Adsorption and hybridization of oligonucleotides on mercaptoacetic acid-capped CdSe/ZnS quantum dots and quantum dot-oligonucleotide conjugates.

Interest in the unique optical properties of quantum dots (QDs) has resulted in the development QD-bioconjugates for imaging and diagnostics. Although these applications are numerous, considerably less is known about the interactions between QDs and biomolecules. In this work, we describe hydrogen-bonding interactions between oligonucleotides and CdSe/ZnS quantum dots capped with mercaptoacetic acid ligands. The strength of the interactions can be modulated by changes in the pH and ionic strength, the addition of formamide, and differences between ssDNA and dsDNA. Fluorescence resonance energy transfer experiments have shown that conjugated oligonucleotides adopt a conformation that lies across the surface of the QD. The hydrogen-bonding interactions also affect the kinetics of hybridization with QD-DNA conjugates and the thermal stability of QD-conjugated dsDNA. The former is analogous to conventional solid-phase hybridization, where stronger oligonucleotide adsorption leads to faster kinetics. With respect to the latter, interactions with the QD surface can sharpen the melt transition and alter the melt temperature of dsDNA. These effects are largely absent when adsorptive interactions are minimized.

Adsorption↗
PubMed2007

General synthesis and delamination of highly crystalline transition-metal-bearing layered double hydroxides.

In this paper, we describe a general process for the synthesis and delamination of a family of highly crystalline Al-based and transition-metal-bearing layered double hydroxides (LDHs). Large-sized and monodispersed hexagonal platelike particles of binary-component M(II)-Al-CO3 and ternary-component M(II)-M'(II)-Al-CO3 LDHs (M(II) and M'(II) = Fe, Co, Ni, or Zn) were prepared at first by the urea method under optimized conditions. These CO32--LDHs were converted into other monovalent-anion-containing LDHs by means of a salt-acid treatment and subsequent anion-exchange processes. Finally, well-defined LDH nanosheets were obtained by delamination of NO3--LDHs in formamide.

Journal Article↗
PubMed2002

Equilibrating isomers: bromoindoles and a seco-xanthine encountered during a study of nematocides from the southern Australian marine sponge Hymeniacidon sp.

Bioassay-directed fractionation of a Hymeniacidon sp. yielded as nematocidal agents the equilibrating E/Z bromoindole ethyl esters 1 and 2 and corresponding methyl esters 3 and 4. Also isolated for the first time as a natural product was an equilibrating mixture of seco-xanthine formamides, attributed the trivial name hymeniacidin (5). The structure for 5 was assigned on the basis of detailed spectroscopic analysis and total synthesis.

Animals↗
PubMed1993

Evaluation of marine sponge metabolites for cytotoxicity and signal transduction activity.

Twenty-four metabolites derived from marine sponges were evaluated for their cytotoxicities against two human tumor cell lines, non-small cell lung carcinoma A549 and colon adenocarcinoma HT-29, and against one murine leukemia cell line, P-388, and evaluated for their ability to effect signal transduction in a newly developed cell adhesion assay using an EL-4 cell line. The compounds included latrunculin A [1], batzelline A [2], chondrillin [3], aureol [4], epihippuristanol, theonellamine B, discorhabdins A and C, kabiramide C, dercitin, meridine, manzamines A, B, and C, 8,15-diisocyano-11(20)-amphilectene and the corresponding C-15 formamide, a 20-carbon acetylenic alcohol, 4,5-dihydro-6"-deoxybromotopsentin, epispongiadiol, isospongiadiol, puupehenone, reiswigin A, and demethyl- and demethyloxyaaptamine. Latrunculin A [1], batzelline A [2], chondrillin [3], and aureol [4] expressed the desired profile of a greater than five-fold level of cytotoxicity against A549 relative to P-388, and an effect in the cell adhesion assay. In this group of compounds, cytotoxicity toward A549 was equal to or more pronounced than against HT-29. Latrunculin A was evaluated in an sc-implanted human A549 lung tumor xenograft mouse model and yielded a T/C of 146%. Batzelline A was evaluated in the cancer cell line panel at the National Cancer Institute and found to express selective cytotoxicity against several melanoma cancer cell lines.

Animals↗
PubMed1999

Oxidized welwitindolinones from terrestrial fischerella spp

3-Hydroxy-N-methylwelwitindolinone C isonitrile (3), 3-hydroxy-N-methylwelwitindolinone C isothiocyanate (4), and the novel cyclic ether N-methylwelwitindolinone D isonitrile (6) are three new alkaloids from two terrestrial Fischerella spp. belonging to the Stigonemataceae. Photooxidation of N-methylwelwitindolinone C isonitrile (1) leads to isonitriles 3 and 6. Isonitrile 3 is readily hydrated to 3-hydroxy-N-methylwelwitindolinone C formamide (5), an artifact produced during the isolation procedure.

Journal Article↗
PubMed2001

Rhodium complex-catalyzed reaction of isonitriles with carbonyl compounds: catalytic synthesis of pyrroles.

[figure: see text] Low-valent rhodium complexes are efficient catalysts for the activation of alpha-C-H bond of isonitriles. Addition of isonitriles to carbonyl compounds proceeds under mild and neutral conditions to give the corresponding alpha,beta-unsaturated formamides. Catalytic synthesis of pyrroles can be performed by cyclocondensation of isonitriles with 1,3-dicarbonyl compounds.

Journal Article↗
PubMed2002

Predicting experimental complexation-induced changes in (1)H NMR chemical shift for complexes between zinc-porphyrins and amines using the ab initio/GIAO-HF methodology.

Ab initio calculations were carried out on zinc-porphyrins complexed to several amines: N-(3,5-dimethyl-pyridin-4-yl)-formamide, 1,4-diazabiciclo[2.2.2]octane (DABCO), and 1-azabiciclo[2.2.2]octane (quinuclidine). The proton chemical shifts of these complexes were calculated ab initio at the GIAO-HF/6-311G//HF/3-21G level of theory, and the obtained values agree satisfactorily with experimental results. The complexation-induced changes in (1)H NMR chemical shifts correlate well with differences in association constants of several host-guest complexes.

Journal Article↗
PubMed2002

An efficient route to alkyl chlorides from alcohols using the complex TCT/DMF.

[reaction: see text] Efficient conversion of alcohols and beta-amino alcohols to the corresponding chlorides (and bromides) can be carried out at room temperature in methylene chloride, using 2,4,6-trichloro[1,3,5]triazine and N,N-dimethyl formamide. This procedure can also be applied to optically active carbinols.

Journal Article↗
PubMed2003

Intramolecular titanium-mediated aminocyclopropanation of terminal alkenes: easy access to various substituted azabicyclo[n.1.0]alkanes.

[reaction: see text] A variety of substituted azabicyclo[n.1.0]alkanes were synthesized by intramolecular titanium-mediated cyclopropanation of N-benzyl-N-(2-alkylalk-3-enyl)formamides and N-benzyl-N-alkadienylformamides. N-Benzylpyrroline upon treatment with Grignard reagents undergoes a titanium-mediated carbomagnesiation to yield N-benzyl-N-(2-alkylbut-3-enyl)amines.

Journal Article↗
PubMedDate not supplied

Mass spectrometric peptide fingerprinting of proteins after Western blotting on polyvinylidene fluoride and enhanced chemiluminescence detection.

The combined use of sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and mass spectrometry has become a powerful and widely used tool in proteome studies. Following separation by electrophoresis, proteins can be transferred to an inert support such as polyvinylidene fluoride (PVDF) or nitrocellulose (NC) for the visualization of individual or specific classes of proteins by immunochemical detection methods. We developed a method that allows the mass spectrometric analysis of peptides derived from proteins detected by Western blotting on PVDF. Proteolysis buffer containing either dimethyl formamide (DMF) or Triton X-100 to recover peptides amenable to mass spectrometry was investigated. Although either one can be used, the buffer containing DMF required less sample handling prior to mass spectrometry. The approach was tested using commercially available proteins and serine-phosphorylated proteins from an HEK-293 nuclear extract.

Blotting, Western↗
PubMed2002

Bioactivation of benzylamine to reactive intermediates in rodents: formation of glutathione, glutamate, and peptide conjugates.

The in vivo and in vitro disposition of benzylamine was investigated in rats. Benzylamine was metabolized to only a small extent by rat liver subcellular fractions. In contrast, it was extensively metabolized in vivo in rats. In vivo studies performed with stable isotope-labeled benzylamine enabled rapid mass spectrometric identification of metabolites present in rat bile and urine. The major metabolite of benzylamine was the hippuric acid formed by glycine conjugation of benzoic acid. LC/MS analysis of bile and urine obtained from rats dosed with 1:1 equimolar mixture of either d(0):d(7)- or d(0):d(2)-benzylamine showed the presence of several glutathione adducts in addition to the hippuric acid metabolite. The presence of various glutathione adducts indicated that benzylamine was metabolized to a number of reactive intermediates. Various metabolic pathways, including those independent of P450, were found to produce these intermediates. A previously undocumented pathway included the formation of a new carbon-nitrogen bond that led to a potentially reactive intermediate, Ar-CH(2)-NH(CO)-X, capable of interacting with various nucleophiles. The origin of this reactive intermediate is postulated to occur via the formation of either a formamide or carbamic acid metabolites. Metabolites which were produced by the reaction of this intermediate, Ar-CH(2)-NH(CO)-X with nucleophiles included S-[benzylcarbamoyl] glutathione, N-acetyl-S-[benzylcarbamoyl]cysteine, S-[benzylcarbamoyl] cysteinylglycine, S-[benzylcarbamoyl] cysteinylglutamate, N-[benzylcarbamoyl] glutamate, and an oxidized glutathione adduct. Bioactivation of amines via this pathway has not been previously described. The oxidative deamination of benzylamine yielding the benzaldehyde was demonstrated to be a precursor to the hippuric acid metabolite and S-benzyl-L-glutathione. The formation of the S-benzyl-L-glutathione conjugate showed that a net displacement of amine from benzylamine had taken place with a subsequent addition of glutathione at the benzylic position. In addition to these novel pathways, a number of other glutathione-derived adducts formed as a result of epoxide formation was characterized. It was demonstrated that benzylamine was converted by rat P450 2A1 and 2E1 to benzamide that was rapidly metabolized to an epoxide. Mechanisms are proposed for the formation of various GSH adducts of benzylamine.

Animals↗
PubMed2000

In vivo gene delivery to the liver using novel galactosylated cationic liposomes.

PURPOSE: The purpose of this study is to elucidate the in vivo gene transfer for galactosylated liposomes containing cholesten-5-yloxy-N-(4-((1-imino-2-beta-D-thiogalactosyle thyl)amino)butyl)formamide(Gal-C4-Chol) in relation to lipid composition and charge ratio. METHODS: Galactosylated cationic liposomes containing N-[1-(2,3-dioleyloxy)propyl]-n,n,n-trimethylammonium chloride(DOTMA), Gal-C4-Chol and cholesterol(Chol), and similar liposomes were prepared. Plasmid DNA complexed with a galactosylated liposome preparation was injected intraportally into mice. The mice were sacrificed after 6 hours. The tissues were subjected to luciferase assay. RESULTS: A markedly higher gene expression in the liver following injection of plasmid DNA that has been complexed with DOTMA/ Chol/Gal-C4-Chol(1:0.5:0.5) and DOTMA/Gal-C4-Chol(1:1) liposomes was observed. The effect was one order of magnitude higher than naked DNA and DOTMA/Chol(1:1) liposomes. Pre-exposing with galactosylated bovine serum albumin significantly reduced the hepatic gene expression. By comparison, the gene expression for galactosylated cationic liposomes containing 3beta[N-(N',N'-dimethylaminoethane)carbamoyl]cholesterol, Gal-C4-Chol and dioleoylphosphatidylethanolamine was 10 times lower. As far as the charge ratio of DOTMA/ Chol/Gal-CA-Chol(1:0.5:0.5) liposomes to plasmid DNA(1.6-7.0) was concerned, complexes with charge ratios of 2.3-3.1 produced maximal gene expression in the liver. Whereas, higher ratios resulted in enhanced expression in the lung. CONCLUSIONS: By optimizing lipid composition and charge ratio, galactosylated liposome/DNA complexes allow superior in vivo gene transfection in the liver via asialoglycoprotein receptor-mediated endocytosis.

Animals↗
PubMedDate not supplied

Modulation of adenosine 5'-monophosphate adsorption onto aqueous resident pyrite: potential mechanisms for prebiotic reactions.

The adsorption of adenosine 5'-monophosphate (5'-AMP) onto pyrite (FeS2) and its modulation by acetate, an organic precursor of complex metabolic pathways, was studied in aqueous media that simulate primitive environments. 5'-AMP adsorption requires divalent cations, indicating that a cationic bridge mediates its attachment to negatively charged sites of the mineral surface. The isotherm of 5'-AMP adsorption exhibits a strong cooperative effect at low nucleotide concentrations in acetate-rich medium, whereas high levels of adsorption were only found at high nucleotide concentrations in a model of primitive seawater (acetate free). The modulating role of acetate is also evidenced in the presence of high dipolar moment molecules: dimethyl sulfoxide (Me2SO) and dimethyl formamide (DMF) strongly inhibit 5'-AMP adsorption in acetate-rich media, whereas no effect of DMF was found in artificial seawater. The observation that exogenous divalent cations are not needed for acetate attachment onto FeS2 reveals that organic acids can interact with the Fe2+ atoms in the mineral surface. All considered, the results show that complex and flexible ironsulfide/biomonomers interactions can be modulated by molecules that accumulate in the interface layer.

Acetates↗
PubMed1990

Chemical stability of pentostatin (NSC-218321), a cytotoxic and immunosuppressant agent.

Pentostatin, an unusual nucleoside of natural origin, has been used for the treatment of hairy cell leukemia, as an immunosuppressant agent, and as an inhibitor of adenosine deaminase. The studies of the physicochemical properties and solution stability of pentostatin are important to the development of a parenteral formulation for extensive preclinical and clinical testing. Pentostatin displayed apparent pKa values at 25 +/- 0.1 degree C and ionic strength of 0.15 M of 2.03 +/- 0.03 and 5.57 +/- 0.14 (spectrophotometric) and 5.50 +/- 0.02 (potentiometric) for N1 and the amidine nitrogen in the seven-membered ring, respectively, which are the most likely protonation sites. The rates of degradation of pentostatin were determined as a function of pH, buffer concentration, and temperature. In the pH range 1.0-4.0, pentostatin undergoes acid-catalyzed glycosidic cleavage leading to the formation of the base compound, and 2-deoxyribose. A carbonium ion mechanism in which C-N bond cleavage was the rate-determining step was consistent with the data. In the pH range 6.5-10.5, the imine bond at C5 position in pentostatin is hydrolyzed to form the corresponding formamide. Pentostatin hydrolysis in this pH range was independent of pH. At pH greater than 11, pentostatin decomposes to nonchromophoric products probably through multiple-step base-catalyzed hydrolytic mechanisms. Pentostatin appears to be quite stable after reconstitution of a lyophilized experimental dosage form. Care must be taken if pentostatin is extensively diluted with 5% dextrose in water, as pentostatin stability is compromised at pH values less than 5.

Buffers↗
PubMed2002

Tubular localization of silent calcium channels in crustacean skeletal muscle fibers.

Ca2+-induced Ca2+ release (CICR) in the superficial abdominal flexor muscle of the crustacean Atya lanipes appears to be mediated by a local control mechanism similar to that of vertebrate cardiac muscle, but with an unusually high gain. Thus, Ca2+ influx increases sufficiently the local concentration of Ca2+ in the immediate vicinity of the sarcoplasmic reticulum Ca2+ release channels to trigger the highly amplified release of Ca2+ required for contraction, but is too low to generate a macroscopic inward current (i.e., the Ca2+ channels are silent). To determine the localization of the silent Ca2+ Channels, the mechanical, electrophysiological and ultrastructural properties of the muscle were examined before and after formamide treatment, a procedure that produces the disruption of transverse tubules of striated muscle. We found that tubular disruption decreased tension generation by about 90%; reduced inward current (measured as Vmax, the maximum rate of rise of Sr2+ action potentials) by about 80%; and decreased membrane capacitance by about 77%. The results suggest that ca. 80% of the silent Ca2+ channels are located in the tubular system. Thus, these studies provide further evidence to support the local control mechanism of CICR in crustacean skeletal muscle.

Action Potentials↗
PubMed2002

Targeting efficiency of galactosylated liposomes to hepatocytes in vivo: effect of lipid composition.

PURPOSE: To investigate the effects of the lipid composition of galactosylated liposomes on their targeted delivery to hepatocytes. METHODS: Several types of liposomes with a particle size of about 90 nm were prepared using distearoyl-L-phosphatidylcholine (DSPC), cholesterol (Chol) and cholesten-5-yloxy-N-(4-((1-imino-2-D- thiogalactosylethyl)amino)butyl)formamide (Gal-C4-Chol), and labeled with [3H]cholesterol hexadecyl ether. Their tissue disposition was investigated in mice following intravenous injection. The binding and internalization characteristics were also studied in HepG2 cells. RESULTS: Compared with [H]DSPC/Chol (60:40) liposomes, [3H]DSPC/Chol/Gal-C4-Chol (60:35:5) liposomes exhibit extensive hepatic uptake. Separation of the liver cells showed that galactosylated liposomes are preferentially taken up by hepatocytes, whereas those lacking Gal-C4-Chol distribute equally to hepatocytes and nonparenchymal cells (NPC). Increasing the molar ratio of DSPC to 90% resulted in enhanced NPC uptake of both liposomes, suggesting their uptake via a mechanism other than asialoglycoprotein receptors. DSPC Chol/Gal-C4-Chol (60:35:5) and DSPC/Chol/Gal-C4-Chol (90:5:5) liposomes exhibited similar binding to the surface of HepG2 cells, but the former were taken up faster by the cells. CONCLUSIONS: The recognition of galactosylated liposomes by the asialoglycoprotein receptors is dependent on the lipid composition. Cholesterol-rich galactosylated liposomes, exhibiting less non-specific interaction and greater receptor-mediated uptake, are better for targeting drugs to hepatocytes in vivo.

Animals↗
PubMed2003

Enzymatic synthesis of hydrophilic undecylenic acid sugar esters and their biodegradability.

To enhance water solubility of 10-undecylenic acid, which has anti-fungus, anti-bacterial and anti-virus activity, D-glucose, trehalose and sucrose were regioselectively esterified with vinyl 10-undecylenic acid ester in dimethyl formamide by a commercial protease, Bioprase conc., from Bacillus subtilis. 6-O-(10-Undecylenoyl) D-glucose, 6-O-(10-undecylenoyl) trehalose and 1'-O-(10-undecylenoyl) sucrose were obtained. The influence of structural variation by changing the sugar moiety was analyzed the surface tension and biodegradability.

Bacillus subtilis↗