Determination of Acid-Extractable Phenols and Organochlorine Pesticides in Laguna Lake by Gas Chromatography-Mass Spectrometry

The presence of eight acid-extractable phenols and sixteen organochlorine pesticides (OCPs) in Laguna Lake water was determined. The acid-extractable phenols which were analyzed included: phenol, 2-chlorophenol, 2-nitrophenol 2,4-dichlorophenol, 4-chloro-3-methylphenol, 2,4,6-trichlorophenol, 4-nitrophenol, and pentachlorophenol. The OCPs were as follows: α-BHC, β-BHC, γ-BHC (lindane), δ-BHC, heptachlor, aldrin, heptachlor epoxide, endosulfan I, 4,4\u27-DDE, dieldrin, endrin, endosulfan II, 4,4-DDD, endrin aldehyde, endosulfan sulfate, and 4,4-DDT.Water samples trom five different sites in Laguna Lake were collected in October and November 1996, and February and May 1997. The phenols and OCPs were extracted separately by liquid-liquid extraction. Identification and quantification were done by capillary gas chromatography-mass spectrometry (GC-MS). None of the sixteen OCPs was detected in any of the water samples. On the other hand, phenol and 4-nitrophenol were detected in some samples collected in February and May 1997. These analytes, however, could not be quantified because they were below this study\u27s practical quantification limits (PQL) of 1.8 µg/L for phenol and 1.2 µg/L for 4-nitrophenol. The PQLs were based on the actual method detection limits (MDL) of the acid-extractable phenols and OCPs

The Analysis of Volatile Organic Compounds from Fresh and Dried Leaves of Vitex negundo by Thermal Desorption-Gas Chromatography

The generation and analysis of volatile organic compounds (VOCs) from fresh and dried leaves of Vitex negundo (lagundi) by thermal desorption-gas chromatography (TD-GC) is described. The leaves were heated at 80 to 120°C in a tube to release the VOCs. The VOCs were cryofocused into the gas chromatography (GC) column and analyzed. Five compounds were identified in the VOC by electron impact-MS and chemical ionization-MS analysis: β-phellandrene, hexenal, hexenol, octenol, and β-caryophyllene. The VOCs were quantified by flame ionization detection-GC. The profiles produced by TD-GC were compared with GC analysis of the oil obtained by steam distillation. TD-GC was found to be superior to steam distillation in its ability to differentiate fresh from dried leaves

Elucidating a Relationship between Conformational Sampling and Drug Resistance in HIV‑1 Protease

Enzyme targets in rapidly replicating systems, such as retroviruses, commonly respond to drug-selective pressure with mutations arising in the active site pocket that limit inhibitor effectiveness by introducing steric hindrance or by eliminating essential molecular interactions. However, these primary mutations are disposed to compromising pathogenic fitness. Emerging secondary mutations, which are often found outside of the binding cavity, may or can restore fitness while maintaining drug resistance. The accumulated drug pressure selected mutations could have an indirect effect in the development of resistance, such as altering protein flexibility or the dynamics of protein–ligand interactions. Here, we show that accumulation of mutations in a drug-resistant HIV-1 protease (HIV-1 PR) variant, D30N/M36I/A71V, changes the fractional occupancy of the equilibrium conformational sampling ensemble. Correlations are made among populations of the conformational states, namely, closed-like, semiopen, and open-like, with inhibition constants, as well as kinetic parameters. Mutations that stabilize a closed-like conformation correlate with enzymes of lowered activity and with higher affinity for inhibitors, which is corroborated by a further increase in the fractional occupancy of the closed state upon addition of inhibitor or substrate-mimic. Cross-resistance is found to correlate with combinations of mutations that increase the population of the open-like conformations at the expense of the closed-like state while retaining native-like occupancy of the semiopen population. These correlations suggest that at least three states are required in the conformational sampling model to establish the emergence of drug resistance in HIV-1 PR. More importantly, these results shed light on a possible mechanism whereby mutations combine to impart drug resistance while maintaining catalytic activity