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PubMed1998

Effect of polyamine analogues on hypusine content in JURKAT T-cells.

The availability of synthetic hypusine and deoxyhypusine has made it possible to develop analytical methods which allow for the measurement of these compounds in various tissues. The methods involve dansylation of extracts from the pellet remaining after perchloric acid precipitation of cell or tissue homogenates, followed by high-performance liquid chromatography. To demonstrate the utility of this approach, the impact of four polyamine analogues, N1,N11-diethylnorspermine (DENSPM), N1,N14-diethylhomospermine (DEHSPM), 1,6,12-triazadodecane [(4,5) triamine], and 1,7, 13-triazatridecane [(5,5) triamine], on hypusine levels in a human T-cell line (JURKAT) is evaluated. All four analogues are active in controlling cell growth and compete well with spermidine for the polyamine transport apparatus. After 144 h of exposure to JURKAT cells, DENSPM reduces putrescine to below detectable limits and spermidine to 10% of the level in control cells. The other three analogues diminish both putrescine and spermidine to below detectable limits. The effectiveness with which the compounds lower spermine levels is DENSPM > DEHSPM > (4,5) triamine > (5,5) triamine. The analogues decrease the activities of ornithine decarboxylase and S-adenosylmethionine decarboxylase in a similar fashion. Of the four polyamines, DENSPM and DEHSPM are potent at lowering intracellular hypusine levels after 144 h: 59 +/- 9% and 73 +/- 12% of control levels, respectively. The other two analogues have marginal effects.

Adenosylmethionine Decarboxylase↗
PubMed2001

A stereoselective synthesis of (+/-)-C-secolimonoid BCDE model compounds related to the insect antifeedant ohchinolide.

A short and stereoselective synthesis of a (+/-)-BCDE C-secolimonid model insect antifeedant related to ohchinolide and nimbolidin was accomplished in 13 (30% overall yield) and 15 (30% overall yield) steps, respectively, from ethyl drimanate. The key steps are the torquoselective electrocyclization of the divinyl ketone 6, induced by perchloric acid, and the stereoselective rearrangement of the hydroxy lactone 12, inspired in a biosynthetic proposal. An alternative route, which provides access to (+/-)-BCDE ohchinolide and nimbolidin isomers, is also described.

Animals↗
PubMed2005

Kinetics and mechanism of hydration of o-thioquinone methide in aqueous solution. Rate-determining protonation of sulfur.

o-Thioquinone methide, 2, was generated in aqueous solution by flash photolysis of benzothiete, 1, and rates of hydration of this quinone methide to o-mercaptobenzyl alcohol, 3, were measured in perchloric acid solutions, using H2O and D2O as the solvent, and also in acetic acid and tris(hydroxymethyl)methylammonium ion buffers, using H2O as the solvent. The rate profiles constructed from these data show hydronium-ion-catalyzed and uncatalyzed hydration reaction regions, just like the rate profiles based on literature data for hydration of the oxygen analogue, o-quinone methide, of the presently examined substrate. Solvent isotope effects on hydronium-ion catalysis of hydration for the two substrates, however, are quite different: k(H)/k(D) = 0.42 for the oxygen quinone methide, whereas k(H)/k(D) = 1.66 for the sulfur substrate. The inverse nature (k(H)/k(D) < 1) of the isotope effect in the oxygen system indicates that this reaction occurs by a preequilibrium proton-transfer reaction mechanism, with protonation of the substrate on its oxygen atom being fast and reversible and capture of the benzyl-type carbocationic intermediate so formed being rate-determining. The normal direction (k(H)/k(D) > 1) of the isotope effect in the sulfur system, on the other hand, suggests that protonation of the substrate on its sulfur atom is in this case rate-determining, with carbocation capture a fast following step. A semiquantitative argument supporting this hypothesis is presented.

Alkenes↗
PubMed2005

Ubiquitous strategy for probing ATR surface-enhanced infrared absorption at platinum group metal-electrolyte interfaces.

A versatile two-step wet process to fabricate Pt, Pd, Rh, and Ru nanoparticle films (simplified as nanofilms hereafter) for in situ attenuated total reflection Fourier transform infrared (ATR-FTIR) study of electrochemical interfaces is presented, which incorporates an initial chemical deposition of a gold nanofilm on the basal plane of a silicon prism with the subsequent electrodepostion of desired platinum group metal overlayers. Galvanostatic electrodeposition of Pt, Rh, and Pd from phosphate or perchloric acid electrolytes, or potentiostatic electrodeposition of Ru from a sulfuric acid electrolyte, yields sufficiently "pinhole-free" overlayers as evidenced by electrochemical and spectroscopic characterizations. The Pt group metal nanofilms thus obtained exhibit strongly enhanced IR absorption. In contrast to the corresponding metal films electrochemically deposited directly on glassy carbon and bulk metal electrodes, the observed enhanced absorption for the probe molecule CO exhibits normal unipolar band shapes. Scanning tunneling microscopic (STM) images reveal that fine nanoparticles of Pt group metals are deposited around wavy and stepped bunches of Au nanoparticles of relatively large sizes. This ubiquitous strategy is expected to open a wide avenue for extending ATR surface-enhanced IR absorption spectroscopy to explore molecular adsorption and reactions on technologically important transition metals, as exemplified by successful real-time spectroscopic and electrochemical monitoring of the oxidation of CO at Pd and that of methanol at Pt nanofilm electrodes. The spectral features of free water molecules coadsorbed with CO on Pt, Pd, Rh, and Ru are also discussed.

Journal Article↗
PubMed2005

Hydration of Cm3+ in aqueous solution from 20 to 200 degrees C. A time-resolved laser fluorescence spectroscopy study.

Time-resolved laser fluorescence spectroscopy (TRLFS) is used to study the hydration of the Cm3+ ion in acidified (0.1 M perchloric acid) H2O and D2O from 20 to 200 degrees C. Strong temperature dependency is found for several of the spectroscopic quantities associated with the 6D'(7/2) --> 8S'(7/2) photoemission spectra, with similar relative changes in both solvents. The emission band shifts to lower energy with increasing temperature, which is attributed to an equilibrium between hydrated Cm3+ ions with different numbers of water molecules in the first coordination sphere, namely [Cm(H2O)9]3+ and [Cm(H2O)8]3+. Comparison with crystalline reference compounds and the analysis of hot bands corroborates the assignment of these species. The molar fraction of the octahydrated species increases from approximately 10% at room temperature to approximately 40% at 200 degrees C, indicating an entropy driven reaction. The corresponding thermodynamic parameters are obtained as Delta H degrees = + 13.1 +/- 0.4 kJ mol(-1), Delta S degrees = + 25.4 +/- 1.2 J mol(-1) K(-1), and Delta G298 = + 5.5 +/- 0.6 kJ mol(-1). Both the emission intensity and lifetime decrease with increasing temperature. The temperature dependency of the nonradiative decay rate of the emitting 6D'(7/2) level follows an Arrhenius equation with the activation energy 26.5 kJ mol(-1) (2250 cm(-1)) in both H2O and D2O, which is somewhat lower than the energy gap between 6D'(7/2) and 6P'(5/2) exited state levels.

Journal Article↗
PubMed2005

The impact of geometric and surface electronic properties of pt-catalysts on the particle size effect in electrocatalysis.

The particle size effect on the formation of OH adlayer, the CO bulk oxidation, and the oxygen reduction reaction (ORR) have been studied on Pt nanoparticles in perchloric acid electrolyte. From measurements of the CO displacement charge at controlled potential, the corresponding surface charge density versus potential curves yielded the potentials of total zero charge (pztc), which shifts approximately 35 mV negative by decreasing the particle size from 30 nm down to 1 nm. As a consequence, the energy of adsorption of OH is more enhanced, that is, at the same potential the surface coverage with OH increases by decreasing the particle size, which in turn affects the catalytic reactions thereon. The impact of the electronically induced potential shift in the OH adsorption is demonstrated at the CO bulk oxidation, in which adsorbed OH is an educt species and promotes the reaction, and the ORR, where it can act as a surface site blocking species and inhibits the reaction.

Journal Article↗
PubMed2006

Medium effects for very fast electron transfer reactions at electrodes: the [Ru(NH3)6]3+/2+ system in water.

The reduction kinetics of [Ru(NH(3))(6)](3+) was studied at Au(111) and Au(100) single-crystal ultramicroelectrodes in dilute perchloric acid electrolytes. Both heterogeneous rate constants and experimental transfer coefficients varied with the crystallographic orientation of the gold surface. The value of the heterogeneous rate constant at Au(111) was significantly larger than that at Au(100). The experimental transfer coefficients also increased but in the opposite order. Standard rate constants at both electrodes increased with an increase in electrolyte concentration. Using double-layer data obtained in 0.01 M HClO(4), it is shown that the true transfer coefficient for this reaction is 0.5 within experimental error. The effective charge on the reactant which has a nominal charge of +3 is close to +1. The latter result reflects the distribution of charge within the polyatomic reactant.

Journal Article↗
PubMed2006

Structure sensitivity of methanol electrooxidation pathways on platinum: an on-line electrochemical mass spectrometry study.

By monitoring the mass fractions of CO(2) (m/z 44) and methylformate (m/z 60, formed from CH(3)OH + HCOOH) with on-line electrochemical mass spectrometry (OLEMS), the selectivity and structure sensitivity of the methanol oxidation pathways were investigated on the basal planes--Pt(111), Pt(110), and Pt(100)--and the stepped Pt electrodes--Pt(554) and Pt(553)--in sulfuric and perchloric acid electrolytes. The maximum reactivity of the MeOH oxidation reaction on Pt(111), Pt(110), and Pt(100) increases in the order Pt(111) < Pt(110) < Pt(100). Mass spectrometry results indicate that the direct oxidation pathway through soluble intermediates plays a pronounced role on Pt(110) and Pt(111), while, on Pt(100), the indirect pathway through adsorbed carbon monoxide is predominant. In 0.5 M H(2)SO(4), introducing steps in the (111) plane increases the total reaction rate, while the relative importance of the direct pathway decreases considerably. In 0.5 M HClO(4), however, introducing steps increases both the total reaction rate and the selectivity toward the direct oxidation pathway. Anion (sulfate) adsorption on (111) leads to a more prominent role of the direct pathway, but, on all the other surfaces, (bi)sulfate seems to block the formation of soluble intermediates. For both electrolytes, increasing the step density results in more methylformate being formed relative to the amount of CO(2) detected, indicating that the [110] steps themselves catalyze the direct oxidation pathway. A detailed reaction scheme for the methanol oxidation mechanism is suggested based on the literature and the results obtained here.

Journal Article↗
PubMed1996

Systematic study on the chemical stability of the prodrug antitumor agent carzelesin (U-80,244)

The chemical stability of the novel anticancer agent carzelesin in aqueous buffer/acetonitrile (1:1, v/v) mixtures has been investigated utilizing a stability-indicating reversed-phase high-performance liquid chromatographic assay. The degradation kinetics of carzelesin has been studied as a function of pH, buffer composition, ionic strength, and temperature. Degradation of carzelesin follows (pseudo-) first-order kinetics. A pH-rate profile, using rate constants extrapolated to zero buffer concentration, was constructed demonstrating that carzelesin is most stable in the pH region 1-4. The degradation rate of carzelesin was not significantly affected by buffer components and by the ionic strength. In addition to the formation of the degradation products U-76,073, U-76,074, and aniline in alkaline medium and in acetate buffer solution, another degradation product was formed in acetate buffer solution. In perchloric acid buffer solution (pH* < 3), U-76,073 and U-76,074 could not be detected as degradation products.

Antineoplastic Agents↗
PubMed2005

In-situ scanning tunneling microscopy of carbon monoxide adsorbed on Au(111) electrode.

In-situ scanning tunneling microscopy (STM) coupled with cyclic voltammetry was used to examine the adsorption of carbon monoxide (CO) molecules on an ordered Au(111) electrode in 0.1 M HClO4. Molecular resolution STM revealed the formation of several commensurate CO adlattices, but the (9 x radical 3) structure eventually prevailed with time. The CO adlayer was completely electrooxidized to CO2 at 0.9 V versus RHE in CO-free 0.1 M HClO(4), as indicated by a broad and irreversible anodic peak which appeared at this potential in a positive potential sweep from 0.05 to 1.6 V. A maximal coverage of 0.3 was estimated for CO admolecules from the amount of charge involved in this feature. Real-time in-situ STM imaging allowed direct visualization of the adsorption process of CO on Au(111) at 0.1 V, showing the lifting of (radical 3 x 22) reconstruction of Au(111) and the formation of ordered CO adlattices. The (9 x radical 3) structure observed in CO-saturated perchloric acid has a coverage of 0.28, which is approximately equal to that determined from coulometry. Switching the potential from 0.1 to -0.1 V restored the reconstructed Au(111) with no change in the (9 x radical 3)-CO adlattice. However, the reconstructed Au(111) featured a pairwise corrugation pattern with two nearest pairs separated by 74 +/- 1 A, corresponding to a 14% increase from the ideal value of 65.6 A known for the ( radical 3 x 22) reconstruction. Molecular resolution STM further revealed that protrusions resulting from CO admolecules in the (9 x radical 3) structure exhibited distinctly different corrugation heights, suggesting that the CO molecules resided at different sites on Au(111). This ordered structure predominated in the potential range between 0.1 and 0.7 V; however, it was converted into new structures of (7 x radical 7) and ( radical 43 x 2 radical 13) on the unreconstructed Au(111) when the potential was held at 0.8 V for ca. 60 min. The coverage of CO adlayer decreased accordingly from 0.28 to 0.13 before it was completely removed from the Au(111) surface at more positive potentials.

Journal Article↗
PubMed2005

Enhanced and selective adsorption of mercury ions on chitosan beads grafted with polyacrylamide via surface-initiated atom transfer radical polymerization.

Enhanced and selective removal of mercury ions was achieved with chitosan beads grafted with polyacrylamide (chitosan-g-polyacrylamide) via surface-initiated atom transfer radical polymerization (ATRP). The chitosan-g-polyacrylamide beads were found to have significantly greater adsorption capacities and faster adsorption kinetics for mercury ions than the chitosan beads. At pH 4 and with initial mercury concentrations of 10-200 mg/L, the chitosan-g-polyacrylamide beads can achieve a maximum adsorption capacity of up to 322.6 mg/g (in comparison with 181.8 mg/g for the chitosan beads) and displayed a short adsorption equilibrium time of less than 60 min (compared to more than 15 h for the chitosan beads). Coadsorption experiments with both mercury and lead ions showed that the chitosan-g-polyacrylamide beads had excellent selectivity in the adsorption of mercury ions over lead ions at pH < 6, in contrast to the chitosan beads, which did not show clear selectivity for either of the two metal species. Mechanism study suggested that the enhanced mercury adsorption was due to the many amide groups grafted onto the surfaces of the beads, and the selectivity in mercury adsorption can be attributed to the ability of mercury ions to form covalent bonds with the amide. It was found that adsorbed mercury ions on the chitosan-g-polyacrylamide beads can be effectively desorbed in a perchloric acid solution, and the regenerated beads can be reused almost without any loss of adsorption capacity.

Adsorption↗
PubMed2003

1H NMR pattern recognition and 31P NMR studies with d-Serine in rat urine and kidney, time- and dose-related metabolic effects.

Proton NMR spectroscopy of urine has previously been used to gain insight into the site and mechanism of toxic injury to the kidney. d-Serine injures the rat kidney, causing selective necrosis of the proximal straight tubules. Damage is accompanied by proteinuria, glucosuria, and amino aciduria, the latter preceding the onset of necrosis. This study has employed (1)H NMR spectroscopy of urine and (1)H NMR and (31)P NMR spectroscopy of kidney extracts to examine the nephrotoxic action of d-serine. Urine was collected 0-8 h (all doses) and 8-24, 24-48, 48-72, 72-96, and 96-120 h (500 mg/kg only) postdosing from Alderley Park rats given d-serine (62.5, 125, 250, and 500 mg/kg ip). (1)H NMR spectra were monitored for markers of tubular damage. Additionally, ATP and ADP were quantitated in kidney perchloric acid extracts, prepared after 0.5, 1, 2, 4, and 8 h (500 mg/kg) to assess energy status; serine was also measured in these samples. At 500 mg/kg, glucosuria, amino aciduria, and reduced citrate, alpha-ketoglutarate, and succinate were observed in urine at 0-8 h. Furthermore, serine and pyruvate levels were elevated at this time. After 8-24 h, similar changes were observed; however, they were more severe reflecting the development of the lesion prior to recovery. These perturbations were dose-related, in particular, for serine and pyruvate, with no alterations seen at 62.5 mg/kg. Kidney serine concentration rapidly increased, where it was maximal after 30 min and cleared by 8 h. A decline in ATP, to approximately 60-70% of control, was observed within the kidney at 2-4 h postdosing, when necrosis first becomes evident suggesting that mitochondrial function might be impaired in the early stages of d-serine-induced nephrotoxicity. The use of NMR spectroscopy has given a comprehensive overview of the effects of d-serine in vivo. Information on the excretion of serine and its effect on renal energy metabolism provides insight into the possible mechanism of renal tubule injury.

Animals↗
PubMed1997

Assessment of the mechanism of astrocyte swelling induced by the macrolide immunosuppressant sirolimus using multinuclear nuclear magnetic resonance spectroscopy.

The toxic effect of the macrolide immunosuppressant sirolimus on cell metabolism of primary astrocytes was studied by multinuclear NMR spectroscopy of viable cells and perchloric acid (PCA) extracts and compared to the effects of the immunosuppressant cyclosporine. The addition of 5 mg/L sirolimus (5.5 mumol/L) induced swelling of primary astrocytes to 110% of the original volume. Alteration in astrocyte volume in the presence of sirolimus was accompanied by reduction of the following important cell osmolytes and amino acid metabolites: myo-inositol, -58 +/- 12% (mean +/- standard deviation, n = 5); taurine, -44 +/- 5%; glutamine, -13 +/- 2%; compared with control. Sirolimus altered glucose metabolism and partially inhibited the tricarboxylic acid (TCA) cycle: sigma TCA/sigma glycolyse = 1.36 +/- 0.09 (control, n = 3), 0.96 +/- 0.08 (with sirolimus). The increased concentration of phosphodiesters by sirolimus addition (glycerophosphoethanolamine, 52 +/- 18%; glycerophosphocholine, 61 +/- 14%; compared with control, n = 5) indicated disorders in phospholipid metabolism of cellular membranes. Addition of sirolimus led to a decline of the energy state in astrocytes: the concentration of phosphocreatine (PCr) decreased to 75% of control value within 60 min of perfusion with sirolimus and the nucleotide triphosphate (NTP) concentration to 85% within 90 min (n = 3). The effect of sirolimus on the cell metabolism of astrocytes equals that of the immunosuppressants cyclosporine and tacrolimus, the neurotoxicity of which is well-established in clinical studies. The results of this in vitro study indicate that sirolimus possesses neurotoxic potential as well.

Animals↗
PubMed1997

Expression of IGF receptors on alveolar macrophages: IGF-induced changes in InsPi formation, [Ca2+]i, and pHi.

Expression of insulin-like growth factor-I (IGF-I) receptors and insulin-like growth factor-II/mannose-6-phosphate (IGF-II/Man6P) receptors in cultured bovine alveolar macrophages (BAM) was demonstrated by competitive binding studies and crosslinking experiments. Western blotting of protein extracts from cultured BAM using an anti bovine IGF-II/Man6P receptor antiserum (#66416) confirmed the presence of IGF-II/Man6P receptors on BAM. The effects of IGFs and Man6P on generation of inositol phosphates was measured by HPLC analysis of perchloric acid extracts from myo-[3H]inositol-labelled cultured BAM. IGF-I at nanomolar concentrations and Man6P (10[-8]-10[-3] M) stimulated the accumulation of both Ins(1,4,5)P3 and Ins(1,3,4,5)P4 after 30 sec. IGF-II (up to 2.3 x 10[-8] M) had no significant effect on inositol phosphate accumulation under the same conditions. Both IGFs and Man6P induced a rise in [Ca2+]i in cultured BAM. In addition, using the fluorescent dye SNARF-1/AM we could demonstrate rapid but small IGF-II (10[-9] M) triggered acidification (0.07 pH units) of cultured BAM. Taken together, our results indicate not only the presence of both IGF-I and IGF-II/Man6P receptors on BAM, but also provide evidence of the linkage of the IGF-I receptor to the inositol phosphate system.

Animals↗
PubMed1988

Determination of spectinomycin dihydrochloride by liquid chromatography with electrochemical detection.

Spectinomycin dihydrochloride is determined by liquid chromatography with electrochemical detection. The drug is chromatographed on a reverse-phase Nucleosil C18 column using an eluent containing 0.02 M sodium citrate and 0.0015 M octyl sodium sulfate (pH 6.10 with perchloric acid) and acetonitrile (100:4). Detection is performed using a coulometric detector (porous carbon working electrode) at +0.85 V. The drug and primary degradation product are detectable. Detector response is linear to at least 20 micrograms/ml, which is four times the assay level. The procedure has relative standard deviations of +/- 1.21 to +/- 2.72% for three lots of bulk drug. Sensitivity is greater than 0.1 microgram/ml of spectinomycin (5 ng on column). Repeatability at this level is +/- 4.94%.

Chromatography, Liquid↗
PubMed2002

Occurrence of histone H1 degrees protein in rat alveolar macrophages.

Histone H1 of rat alveolar macrophages, neutrophilic granulocytes and monocytes extracted with 5% (v/v) perchloric acid was studied in order to see whether a protein similar to histone H1 degrees of rat liver exists in these specialized cells. The biochemical methods used involved SDS and acid-urea polyacrylamide gel electrophoresis, gel filtration on BioGel P100 and raising antisera against chromatographically purified rat liver H1 degrees and histone H1. The antiserum was applied for further characterization of the presumptive H1 degrees fraction using ELISA and Western blot analysis. The results from our studies showed that histone H1 degrees protein is present in rat alveolar macrophages, monocytes and neutrophilic granulocytes, but its quantity in neutrophilic granulocytes is very much less than macrophages and monocytes.

Animals↗
PubMed2003

High mobility group-like proteins of the insect Plodia interpunctella.

Nuclei from Plodia interpunctella larvae contain four major proteins, which are extracted by 5% perchloric acid and 0.35 M NaCl. The proteins have been designated PL1, PL2, PL3, and PL4. The amino acid analyses of these proteins show that they have high proportions of acidic and basic amino acid residues, a property characteristic of the high mobility group (HMG) proteins isolated from vertebrate tissues. Immunological characterication of these proteins clearly shows that PL1, PL2, and PL4 are more closely related to HMG1 dipteran proteins, while PL3 is more closely related to HMG1 dipteran proteins. The possible relatedness of these proteins to HMG proteins is discussed.

Amino Acids↗
PubMed2003

A high mobility group protein from the Dipteran insects Ceratitis capitata and Bactrocera oleae.

Nuclei from Bactrocera oleae and Ceratitis capitata larvae contain a major protein that shares most of the characteristics of vertebrate high mobility group (HMG) proteins. Proteins are extracted from nuclei with 0.35 M NaCl, are soluble in 5% perchloric acid, are relatively small (molecular weight in the range of 10-16 kDa), and have both a high basic and a high acidic amino acid content. The amino acid constitution of these proteins is similar to that of the HMGB protein family of vertebrates. The proteins cross-react with antibodies raised against the HMGD chromosomal protein of Drosophila melanogaster. The possible relatedness of these proteins to high mobility group proteins is discussed.

Animals↗