Analysis of aflatoxin B1-lysine adduct in serum using isotope-dilution liquid chromatography/tandem mass spectrometry

A method for quantitative analysis of aflatoxin B1-lysine adduct (B1-Lys) in serum by liquid chromatography using tandem mass spectrometry (LC/MS/MS) is presented. The protein in a 250-microL sample was digested in the presence of a stable-isotope internal standard during a 4-h incubation at 37 degrees C with Pronasetrade mark. B1-Lys and the internal standard were extracted using mixed-mode solid-phase extraction cartridges and eluted with 2% formic acid in methanol. Following evaporation and reconstitution, extracts were injected onto a Luna C-18(2) column and eluted with a step gradient of acetonitrile and 0.06% formic acid. The B1-Lys and the internal standard were detected in a positive ionization selective reaction monitoring mode with a ThermoFinnigan TSQ Quantum triple quadrupole mass spectrometer. Calibration curves were linear for concentrations from 0.05-8.0 ng/mL. The method was validated with aflatoxin B1 dosed rat serum diluted to anticipated high and low concentrations. Total imprecision determined from 30 measurements over 15 days was 5.6% and 9.1%, respectively. Recoveries of 78.8 +/- 6.4% for B1-Lys and 85.4 +/- 12.4% for the internal standard were based on the full extraction and reconstitution processes. The method can be used to quantitate B1-Lys at the 0.5 pg/mg albumin level and is suitable for routine analysis.     

Thermal decomposition of cycloadducts of vinylnaphthalenes with electron-deficient dienophiles

Light transmittance was measured during heating of thin NaPO₃ glass plates at different heating rates. According to the results, the crystallization of orthorhombic textured NaPO₃ glass proceeds from sample surfaces into their interior due to the foregoing surface nucleation. The glass surface crystallization process resulted in the sigmoidal decrease of the optical transmittance. Elaborated data lead to the activation energy of glass surface crystallization of the value of 182.8 kJ mol ^-1.     

Cleavage of Carbon Disulfide by n-Propyldiphenylphosphine and Nickel(II) Bromide

Carbon disulfide is cleaved by n-propyldiphenylphosphine and nickel(II) bromide in a one-step process, to form two unprecedented complexes: orange, [Ni(S₂C₂(PⁿPrPh₂)₂)Br(PⁿPrPh₂)]Br⋅CS₂ ( 1 ) and purple [Ni{η²-SC(PⁿPrPh₂)₂}Br(PⁿPrPh₂)]Br⋅0.5CS₂ ( 2 ). Orange ( 1 ) contains a dithiolene-related ligand that results from carbon–carbon bond formation, while purple ( 2 ) contains a remarkable ligand in which two n-propyldiphenylphosphine molecules have added to a carbon atom of a CS unit that is coordinated to nickel.     

Formation and analysis of particulate carbon in a synthetic lubricant

The formation of discrete carbonaceous particles has been investigated for a conventional synthetic ester-based lubricant degraded in thermal and thermal–oxidative environments. Experimental factors included oxidative and nonoxidative environments, high and low humidities, and the presence or lack of a metal catalyst surface, with all samples generated at 250 °C. Characterization performed for changes in antioxidant content, IR spectroscopy, molecular weight, total acid number, viscosity, and uv/vis absorbance spectrometry were used to determine the influences of the aforementioned variables on the rates of oil degradation and formation of high-molecular-weight species. Discrete carbonaceous particle formation was analyzed using Einstein's relationship for the viscoelastic behavior of particles in Newtonian fluids and by calculating associated radii of gyration. This viscoelastic behavior of the particles in solution is used to demonstrate how the absorption behavior of the carbonaceous degradation products tracks the discrete particulate species. The results show the formation of particulate species to be diffusion-limited after antioxidant depletion, and optical absorption analysis is shown to be a viable technique for monitoring the formation of discrete carbonaceous particles during lubricant degradation. Received: 29 February 2000/Accepted: 3 January 2000     

A dynamic soil chamber system coupled with a tunable diode laser for online measurements of δ13C, δ18O,and efflux rate of soil‐respired CO2

High frequency observations of the stable isotopic composition of CO₂ effluxes from soil have been sparse due in part to measurement challenges. We have developed an open‐system method that utilizes a flow‐through chamber coupled to a tunable diode laser (TDL) to quantify the rate of soil CO₂ efflux and its δ¹³C and δ¹⁸O values (δ¹³C_R and δ¹⁸O_R, respectively). We tested the method first in the laboratory using an artificial soil test column and then in a semi‐arid woodland. We found that the CO₂ efflux rates of 1.2 to 7.3 µmol m^?2 s^?1 measured by the chamber‐TDL system were similar to measurements made using the chamber and an infrared gas analyzer (IRGA) (R² = 0.99) and compared well with efflux rates generated from the soil test column (R² = 0.94). Measured δ¹³C and δ¹⁸O values of CO₂ efflux using the chamber‐TDL system at 2 min intervals were not significantly different from source air values across all efflux rates after accounting for diffusive enrichment. Field measurements during drought demonstrated a strong dependency of CO₂ efflux and isotopic composition on soil water content. Addition of water to the soil beneath the chamber resulted in average changes of +6.9 µmol m^?2 s^?1, ?5.0‰, and ?55.0‰ for soil CO₂ efflux, δ¹³C_R and δ¹⁸O_R, respectively. All three variables initiated responses within 2 min of water addition, with peak responses observed within 10 min for isotopes and 20 min for efflux. The observed δ¹⁸O_R was more enriched than predicted from temperature‐dependent H₂O‐CO₂ equilibration theory, similar to other recent observations of δ¹⁸O_R from dry soils (Wingate L, Seibt U, Maseyk K, Ogee J, Almeida P, Yakir D, Pereira JS, Mencuccini M. Global Change Biol. 2008; 14: 2178). The soil chamber coupled with the TDL was found to be an effective method for capturing soil CO₂ efflux and its stable isotope composition at high temporal frequency. Published in 2010 by John Wiley & Sons, Ltd.     

15N enrichment of ammonium, glutamine-amide and urea, measured via mass isotopomer analysis of hexamethylenetetramine.

Ammonium is an important intermediate of protein metabolism and is a key component of acid-base balance. Investigations of the metabolism of NH(4)(+) in vivo using isotopic techniques are difficult because of the low concentration of NH(4)(+) in biological fluids and because of frequent artifactual isotopic dilution of the enrichment of NH(4)(+) during the assay. A new gas chromatographic mass spectrometric method was designed to monitor the (15)N enrichment and concentration of NH(4)(+) in vivo. These are both calculated from the mass isotopomer distribution of hexamethylenetetramine (HMT) formed by reacting NH(4)(+) with formaldehyde. The enrichment of NH(4)(+) is amplified four times since the HMT molecule contains four atoms of nitrogen derived from NH(4)(+). This allows the measurement of low (15)N enrichment of NH(4)(+), down to 0.1%. (15)N enrichment of urea and of the amide N of L-glutamine are measured by enzymatic release of NH(4)(+) and conversion of the latter to HMT. These new techniques facilitate in vivo investigations of the metabolism of NH(4)(+) and related compounds.     

Diels-alder reactions of 3-(2-nitrovinyl)indoles: Formation of carbazoles and bridged carbazoles

The Diels-Alder reactions of 1-substituted-3-(2-nitrovinyl)indoles 3 with quinones and acetylenes give aromatized 1:1 adducts (- nitrous acid) ( 1 ) or (- nitrous acid, -2 hydrogens) 2,5 . Likewise, dimerization (-2 nitrous acids) of 3 gives aromatized 2-(3-indolyl)carbazoles 4 . In contrast, 3 reacts with maleimides 6 to give 1:2 adducts (- nitrous acid or -2 hydrogens) 10 and 11 , respectively, along with smaller amounts of 1:1 adducts (- nitrous acid, -2 hydrogens; or -4 hydrogens) 12 and 13 , respectively. A mechanism for formation of the nitro products 11 and 13 is discussed. A 1:2 adduct (-2 hydrogens) 19 was also obtained from a Diels-Alder reaction between maleimide and the vinylindole produced in situ by condensing 1-methylindole with acetone. The stereochemisty of this 1:2 adduct has been determined by X-ray crystallography.     

The Li2CrO4---CaCrO4 binary phase diagram

Phase equilibria in the Li₂CrO₄---CaCrO₄ system were determined by differential thermal analysis and X-ray powder diffraction. The phase diagram is characterized by a eutectic reaction at 489°C and 5 mole% CaCrO₄, and a monotectic reaction at 570°C and 80 mole% CaCrO₄. The solubility of Li₂CrO₄ in CaCrO₄ was ≈15 mole% at the eutectic temperature and declined to <5 mole% at the monotectic temperature. No double salt was formed between the end members. The immiscibility observed in the system is rationalized in terms of the cation coordination polyhedra.

Thermal events indicative of a solid state phase change in Li₂CrO₄ as reported in some references are judged to be the result of a Li₂CO₃ impurity.     

IMPROVED SURVIVAL FROM INTRACAVITARY PHOTODYNAMIC THERAPY OF RAT GLIOMA

The effectiveness of intratumoral photoradiation in photodynamic therapy (PDT) using a polyporphyrin photosensitizer was studied in the RT-2 rat glioma model. One week after intracerebral implantation of RT-2 cells, experimental rats received a single i.p. injection of 2 mg/kg of Photofrin. After administration of the photosensitizer (48 h), the tumors were partially resected and the exposed cavity was irradiated with 15 J of laser light at a wavelength of 630 nm. Further treatment with a large craniectomy significantly enhanced rat survival. Control rats which received no photosensitizer but were treated with surgery, alone or in combination with laser irradiation, succumbed from early tumor recurrence. Photodynamic therapy without decompressive surgery resulted in hemorrhagic infarction of residual tumor and adjacent brain with focal cerebral edema which resulted in cerebral herniation and early death. Our results indicate that photodynamic therapy is effective in treating residual brain tumor but at the expense of brain tissue surrounding the tumor. Unless relieved, intracranial pressure from photodynamic therapy-associated cerebral edema in this animal model resulted in shortened survival.