Studies of the Structure and Reactivity of Soot

Vibrational spectroscopy, supplemented with other techniques, is providing a comprehensive picture of the structure and reactivity of soot. Reactions such as soot-NO₂/N₂O₄, soot-O₃, and soot-SO₂, at atmospheric and subatmospheric pressures and at different temperatures, have been studied. Determination of the kinetics and mechanisms of the formation of CO and CO₂ during the soot-O₃ reaction, and the effect of temperatures and the concentrations of soot and ozone on this reaction, have led to further insights about the soot structure. Examination of the identity and role of linkages bonding carbon layers together is underway. Application of the Elovich equation to determine initial rates for the formation of surface species in these reactions indicates that the soot-O₃ reaction is faster than the rapid soot-NO₂/ N₂O₄ reaction which, in turn, is faster than that of soot-SO₂. Oxidation of SO₂ to ionic sulfate, confirmed by isotopic substitution, occurs in the presence of soot, water vapor, and oxygen. The presence of simulated solar radiation results in the formation of both ionic and covalent sulfate species. The substrate, whether it is carbon black, cab-o-sil, or the glass walls of the reaction vessel, seems to play a role in the nonphotochemical oxidation of SO₂ to sulfate. The miscibilities of the reaction products of soot-O₃, soot-NO₂/N₂O₄, soot-SO₂, with water vary greatly and have implications for the depletion of tropospheric ozone in the presence of soot-containing particulates.     

Early detection of recurrent prostate cancer with an ultrasensitive chemiluminescent prostate-specific antigen assay

OBJECTIVES: Treatment failure after radical prostatectomy is most commonly heralded by an increase in serum prostate-specific antigen (PSA) to detectable levels. We evaluated the clinical utility of an ultrasensitive chemiluminescent PSA assay. METHODS: We evaluated the assay in banked sera obtained from 170 men after radical prostatectomy. Controls consisted of 142 females, 29 men who had undergone cystoprostatectomy without evidence of prostate cancer, and 25 men without evidence of recurrent disease at least 5 years after prostatectomy for organ-confined disease. Lead time to diagnosis of recurrence was based on comparisons with the IMx or Tandem E assays using a cutoff of 0.1 ng/mL (100 pg/mL). RESULTS: The biologic level of detection of this assay is 8 pg/mL. Serum PSA levels were undetectable in 82.4% of females, 86.2% of the cystoprostatectomy patients, and 96% of the radical prostatectomy controls. After radical prostatectomy, PSA levels were undetectable at last check in 104 of 168 (61.9%) men. In the 24 men with prostate cancer recurrence, the enhanced sensitivity of 8 pg/mL provided a mean lead time based on conservative calculations of 12.7 to 22.5 months over conventional assays. Thirty-four of the 41 men with detectable PSA levels and no evidence of disease recurrence had PSA levels of 30 pg/mL or less. CONCLUSIONS: PSA levels are undetectable in most men who do not have recurrence of disease after radical prostatectomy. Low but detectable serum PSA levels less than or equal to 30 pg/mL can be produced by nonmalignant sources of PSA. PSA assays with enhanced sensitivity can detect recurrent prostate cancer with significant lead time over conventional assays.     

Channeling of three newly introduced antidepressants to patients not responding satisfactorily to previous treatment

OBJECTIVE: Trifluoromethane and CO are produced simultaneously during the breakdown of isoflurane and desflurane by dry CO2 absorbents. Trifluoromethane interferes with anesthetic agent monitoring, and the interference can be used as a marker to indicate anesthetic breakdown with CO production. This study tests representative types of gas monitors to determine their ability to provide a clinically useful warning of CO production in circle breathing systems. METHODS: Isoflurane and desflurane were reacted with dry Baralyme at 45 degrees C. Standardized samples of breakdown products were created from mixtures of reacted and unreacted gases to simulate the partial degrees of reaction which might result during clinical episodes of anesthetic breakdown using 1% or 2% isoflurane and 6% or 12% desflurane. These mixtures were measured by the monitors tested, and the indication of the wrong agent or a mixture of agents due to the presence of trifluoromethane was recorded and related to the CO concentration in the gas mixtures. RESULTS: When presented with trifluoromethane from anesthetic breakdown, monochromatic infrared monitors displayed inappropriately large amounts of isoflurane or desflurane. Agent identifying infrared and Raman scattering monitors varied in their sensitivity to trifluoromethane. Mass spectrometers measuring enflurane at mass to charge = 69 were most sensitive to trifluoromethane. CONCLUSION: Monochromatic infrared monitors were unable to indicate anesthetic breakdown via interference by trifluoromethane, but did indicate falsely elevated anesthetic concentrations. Agent identifying infrared and Raman monitors provided warning of desflurane breakdown via the interference of trifluoromethane by displaying the wrong agent or mixed agents, but may not be sensitive enough to warn of isoflurane breakdown Some mass spectrometers provided the most sensitive warnings to anesthetic breakdown via trifluoromethane, but additional data processing by some patients monitor units reduced their overall effectiveness.     

Configurations of diastereomeric hydroxyethylene isosteres strongly affect biological activities of a series of specific inhibitors of human-immunodeficiency-virus proteinase

Human immunodeficiency virus (HIV) proteinase (PR) represents an important target for antiviral chemotherapy. We present an analysis of inhibitory activities of a series of pseudopeptide inhibitors of HIV-1 PR. All inhibitors were N-protected tetrapeptides with the scissile bond replaced by a nonhydrolysable hydroxyethylene or hydroxyethylamine isostere. To elucidate subtle structural requirements of the PR binding cleft, we synthesised inhibitors with four combinations of configurations at the asymmetric carbons of the isostere. Compounds were tested in vitro using purified recombinant enzyme and a chromogenic peptide substrate. The differences in inhibition constants between individual diastereoisomers reached three orders of magnitude. The most active hydroxyethylene-containing inhibitor possessed the 2R,4S,5S configuration at the isostere. Inhibitor activity was also tested in mammalian cell culture by analysing reduction of viral polyprotein processing and virus infectivity. The results obtained in tissue culture were generally in agreement with the in vitro data, giving a similar order of potency for the individual diastereoisomers. The most active compounds completely blocked production of infectious virus. A simulation method for interaction was employed to build a model of the inhibitors in the PR active site, to identify the interactions responsible for the differences in activities of individual stereoisomers, and to estimate the relative contribution of individual structural features to the overall inhibitory activity.     

Purification and specificity of lipases fromGeotrichum candidum

A crude, commercialGeotrichum candidum lipase (EC 3.1.1.3) preparation (Amano GC-20) was purified by hydrophobic interaction chromatography on Octyl Sepharose. The purified enzyme is a microheterogeneous glycoprotein containing isozymes varying in molecular weight, pI and specificity. It consists of 64, 62 and 59 kDa species as determined by denaturing polyacrylamide gel electrophoresis. Five isozymes (pI 4.40, 4.47, 4.58, 4.67 and 4.72) are detected by isoelectric focusing using both silver and activity stains. Chromatofocusing was used to separate the isozymes according to pI. Although all the isozymes are specific for oleatevs stearate esters, one isozyme (pI 4.72) is also specific for oleatevs palmitate. The number of isozymes is reduced to two (pI 4.67 and 4.72) after carbohydrate removal using endoglycosidase F/N-glycosidase. These isozymes may be products of two lipase genes. Presented in part at the Annual Meeting of the American Oil Chemists' Society, Baltimore, MD, April 22–25, 1990     

Cathode performance: The influence of design, operations, and operating conditions

There have been tremendous advances in the materials, knowledge, design, and construction of cathodes; however, widelydivergent cell operations and operating conditions present a challenge for selecting the right materials and lining design for good cell life. Cathode wear is frequently becoming the life-determining step, and, although there are questions still to be answered, it is probable that particulate detachment (physical wear) plays an important role in parallel with carbide dissolution. If wear cannot be controlled by smart design and operations, coating technology may offer benefits for extending the life of cathode linings by reducing or eliminating wear. Thus, it would also enable softer graphitic materials to be utilized more readily, and this advantage will become more important if the trend toward higher current density continues.