Presence Of Organosulfur Compounds Research Articles

Preventing SOx Emissions through Process Control: Interdigital Capacitors for On-Site Monitoring of Thiophene-Based Environmental Pollutants in Oil Refineries

The presence of organosulfur compounds in fossil fuels is a major source of environmental pollution (SOx emissions) and deteriorates the catalytic exhaust systems of automobiles. Therefore, the development of miniaturized, low-cost, robust interdigital capacitors (IDC) is required to precisely monitor organosulfur compounds in petroleum products. Based on the Pearson concept of hard/soft acids/bases (HSAB), NiS nanoparticles were prepared and integrated into chemical, heat, and wear-resistant TiO2 coatings to fabricate sensitive layers on IDC for the detection of benzothiophene (BT) and dibenzothiophene (DBT) in gasoline samples. Compared to NiS nanoparticles and pristine TiO2 sol, TiO2-NiS nanocomposites exhibit distinctive morphology with homogeneous distribution of NiS nanoparticles, high surface roughness, and greater localized nanoscale variations. Therefore, HSAB chemistry and spatially distinctive features of TiO2-NiS/IDC sensors yield excellent response and sensitivity toward BT/DBT. The reproducibility of sensor layers, selectivity, repeatability, and stability of TiO2-NiS/IDC sensor were studied before calibrating the devices for real-time measurements in refined gasoline samples. TiO2-NiS/IDC sensors exhibit a wide-range linear response, high sensitivity, and low detection limits in gasoline. Real-time sensor measurements show a 90.7% recovery of BT/DBT from gasoline samples. The sensors were calibrated in gasoline samples for potential process and quality control applications during crude oil refining.

Evaluation of the Effects of <i>S</i>-Allyl-L-cysteine, <i>S</i>-Methyl-L-cysteine, <i>trans</i>-<i>S</i>-1-Propenyl-L-cysteine, and Their <i>N</i>-Acetylated and <i>S</i>-Oxidized Metabolites on Human CYP Activities

Three major organosulfur compounds of aged garlic extract, S-allyl-L-cysteine (SAC), S-methyl-L-cysteine (SMC), and trans-S-1-propenyl-L-cysteine (S1PC), were examined for their effects on the activities of five major isoforms of human CYP enzymes: CYP1A2, 2C9, 2C19, 2D6, and 3A4. The metabolite formation from probe substrates for the CYP isoforms was examined in human liver microsomes in the presence of organosulfur compounds at 0.01-1 mM by using liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis. Allicin, a major component of garlic, inhibited CYP1A2 and CYP3A4 activity by 21-45% at 0.03 mM. In contrast, a CYP2C9-catalyzed reaction was enhanced by up to 1.9 times in the presence of allicin at 0.003-0.3 mM. SAC, SMC, and S1PC had no effect on the activities of the five isoforms, except that S1PC inhibited CYP3A4-catalyzed midazolam 1'-hydroxylation by 31% at 1 mM. The N-acetylated metabolites of the three compounds inhibited the activities of several isoforms to a varying degree at 1 mM. N-Acetyl-S-allyl-L-cysteine and N-acetyl-S-methyl-L-cysteine inhibited the reactions catalyzed by CYP2D6 and CYP1A2, by 19 and 26%, respectively, whereas trans-N-acetyl-S-1-propenyl-L-cysteine showed weak to moderate inhibition (19-49%) of CYP1A2, 2C19, 2D6, and 3A4 activities. On the other hand, both the N-acetylated and S-oxidized metabolites of SAC, SMC, and S1PC had little effect on the reactions catalyzed by the five isoforms. These results indicated that SAC, SMC, and S1PC have little potential to cause drug-drug interaction due to CYP inhibition or activation in vivo, as judged by their minimal effects (IC50>1 mM) on the activities of five major isoforms of human CYP in vitro.

Chemostat approach for the directed evolution of biodesulfurization gain-of-function mutants.

Chemostat enrichment is a classical microbiological method that is well suited for use in directed-evolution strategies. We used a two-phase sulfur-limited chemostat to select for gain-of-function mutants with mutations in the biodesulfurization (Dsz) system of Rhodococcus erythropolis IGTS8, enriching for growth in the presence of organosulfur compounds that could not support growth of the wild-type strain. Mutations arose that allowed growth with octyl sulfide and 5-methylbenzothiophene as sole sulfur sources. An isolate from the evolved chemostat population was genetically characterized and found to contain mutations in two genes, dszA and dszC. A transversion (G to T) in dszC codon 261 resulted in a V261F mutation that was determined to be responsible for the 5-methylbenzothiophene gain-of-function phenotype. By using a modified RACHITT (random chimeragenesis on transient templates) method, mutant DszC proteins containing all possible amino acids at that position were generated, and this mutant set was assayed for the ability to metabolize 5-methylbenzothiophene, alkyl thiophenes, and dibenzothiophene. No mutant with further improvements in these catalytic activities was identified, but several clones lost all activity, confirming the importance of codon 261 for enzyme activity.