Showing papers on "NQS published in 1994"

Mutagenicity and cytotoxicity of naphthoquinones for Ames Salmonella tester strains

Abstract: The molecular mechanisms involved in quinone cytotoxicity, especially mutagenicity, are still largely unknown. In order to better understand the molecular aspects of the mechanisms of quinone mutagenicity and cytotoxicity, we examined them by using a series of 13 simple structural naphthoquinone (NQ) derivatives for 9 Ames Salmonella mutagenicity tester strains in the presence of absence of liver homogenate S9 mix from rats induced with phenobarbital and 5,6-benzoflavone. Most NQs used in this study showed mutagenicity with and/or without S9 mix. The most potent mutagenic NQ was 2,3-dichloro-1,4-NQ, with mutagenicity of 18 induced revertants/nmol/plate for strain TA104 without S9 mix. Among the strains used, TA104, which is sensitive to oxidative mutagens, was the most sensitive to the NQs, and the second most sensitive strain was TA2637, which detects bulky DNA adducts. The relationship of mutagenic potency to the one-electron reduction potential with TA104 suggested that the higher redox potential NQs were more mutagenic than the lower redox potential NQs. Significant reduction of the mutagenicity of 1,4-naphthoquinone without S9 mix was observed in the presence of catalase. Enhancement of the mutagenic potential of the NQs by the pKM101 plasmid implicated in error-prone repair was also observed. The most cytotoxic NQ was 2,3-dichloro-5,8-dihydroxy-1,4-NQ, and the least cytotoxic NQ was beta-NQ-4-sulfonic acid potassium salt, a 700-fold range in potency. The cytotoxic effect of the NQs was largely dependent on the structures of their substituents.(ABSTRACT TRUNCATED AT 250 WORDS)

An efficient nonquasi-static diode model for circuit simulation

Abstract: Based on the partitioned-charge-based modeling approach, a general nonquasi-static dynamic charge element is derived to simulate both transient behavior and high-frequency characteristics of a semiconductor diode. A new model parameter /spl tau/ is introduced to describe the dynamic charge redistribution time for a diode. By partitioning the total base charge into quasi-static (QS) and nonquasi-static (NQS) terms, a single-/spl tau/ (level 2) diode model is first derived. By further dividing the NQS charge, a double-/spl tau/ (level 3) diode model is proposed to describe different reverse recovery processes. In addition, a voltage-dependent equation is incorporated to the double-/spl tau/ model into account for the dynamic charge partitioning. We show that the SPICE diode (level 1) model is included by setting /spl tau/ to zero as a special case of the proposed models. The new diode model has been implemented in MISIM, a model independent SPICE-like simulation framework. Significant improvement in accuracy over the traditional SPICE diode model in both time and frequency domain has been demonstrated, while achieving the same or even better simulation speed and reliability. >

Extractive-Spectrophotometric Determination of Ephedrine with Sodium 1,2-Naphthoquinone-4-Sulphonate in Pharmaceutical Formulations

Abstract: An extractive-spectrophotometric study based on the reaction of furosemide with 1,2-naphthoquinone-4-sulphonate (NQS) is described. Optimal conditions are: NaH2PO4-Na2HPO4 pH 7.5, NQS 7.7×...

Determination of methamphetamine in urine samples with sodium 1, 2-naphthoquinone-4-sulphonate

Abstract: Optimal conditions have been studied for the determination of methamphetamine in urine samples by an extractive-spectrophotometric method with sodium 1,2-naphthoquinone-4-sulphonate (NQS) as reagent These conditions are: NaHCO3 pH 10, NQS 63 × 10−3 mol/l and heating for 5 min at 45°C The accuracy and precision of the method were tested The detection limits were 02 mg/l in the standard and 09 mg/l when 5 ml of urine sample were taken The standard deviation of blank urine was evaluated from 12 different samples The relative errors found in the determination of methamphetamine in urine were lower than 10% if the methamphetamine-amphetamine ratio was higher than 4

Kinetic-spectrophotometric determination of primary and secondary amines by reaction with 1-2 naphthoquinone-4-sulphonate

Abstract: A kinetic-spectrophotometric method for the determination of primary and secondary amines is described. It is based on the coloured reaction of these amines with sodium 1,2 Naphthoquinone 4-sulphonate (NQS) in the presence of a non-ionic surfactant. For each determination the optimum conditions were studied and found to be as follows: pH 10.5. Carbonate-bicarbonate buffer 0.1M, Triton X-100 0.1%, Temperature 45°C, and NQS 6.4 × 10−3 M and interval of time 45–180s at wavelength 490 nm. The parameters used for the quantitative determinations are the reaction rate and the increase in the absorbance of the kinetic curves. This procedure has been applied to the determination of ephedrine and amphetamine in pharmaceutical samples.

Nonquasi-static effects in saturated bipolar circuits

Abstract: A nonquasi-static (NQS) model accounting for intrinsic carrier propagation delays in both B/E and B/C junctions is implemented in the ASTAP circuit simulator to evaluate the impact of non-quasi-static effects in saturated bipolar circuits. It is shown that while the extra delay introduced by the NQS effects during the turn-on transition is primarily due to the normal mode B/E NQS delay time, the more severe NQS delay in the turnoff transition is caused mainly by the removal of the saturation overdrive charges and the longer inverse mode B/C NQS delay time. >