Biomedical subjects

E Beltran

Publications and source records attributed to E Beltran.

9 recordsLinked to original sources

PubMed2001

Kinetics of chemical degradation of isoxaflutole: influence of the nature of aqueous buffers (alkanoic acid/sodium salt vs phosphate).

A kinetic study of the chemical degradation of isoxaflutole (5-cyclopropyl-1,2-oxazol-4-yl alpha alpha alpha-trifluoro-2-mesyl-p-tolyl ketone) into its diketonitrile derivative (DKN), which is its active herbicide principle, in organic buffers at different pH values was carried out using a HPLC/UV detection method. The values of the pseudo-first-order rate constants Kobs for the reaction were calculated and compared with those previously obtained in inorganic buffers. In both cases, Kobs was found to be dependent on pH and temperature, but at pH 5.2 the degradation of isoxaflutole in CH3COOH/CH3COONa buffers was considerably faster than in KH2PO4/Na2HPO4 buffers, indicating that the compound was sensitive to the nature of the reagents used to prepare buffered solutions. The influence of phosphate and acetate concentrations and the influence of the R-substituent in RCOOH/RCOONa buffers were investigated. For the HA/A- buffers studied, the values of Kobs were linearly dependent on HA and A- concentrations, which meant that the degradation of isoxaflutole was subject to general catalysis. The values of Kobs were also found to be dependent on the number and the position of the CH3 groups of the R-substituent. The known degradation product of DKN (a benzoic acid derivative) was not detected throughout this study.

Biodegradation, Environmental↗

PubMed2001

Fate of a phenylpyrazole in vegetation and soil under tropical field conditions.

The fate of fipronil, a phenylpyrazole insecticide, and its metabolites under tropical conditions was studied in soil and in vegetation after treatment for locust control. Two different plots were treated with a formulation of fipronil at doses of 5 and 10 g of active ingredient ha(-)(1), respectively. Vegetation and soil at depths of 0-5 and 5-20 cm were sampled for up to 2 months after treatment. After extraction and purification on fipronil immunoaffinity cartridges, residues were analyzed by gas chromatography using electron capture and mass detectors. In soil, a rapid initial decrease of fipronil was observed with a rapid formation of the sulfone and the photodegradate; the amide and the sulfide were not detected. In vegetation, a rapid initial decrease of fipronil was also observed with a rapid formation of mostly the sulfone; the photodegradate and the sulfide were also detected but at much lower concentrations. The metabolites resulting from the degradation of fipronil were similar in both soil and vegetation, but their relative concentrations were different.

Animals↗

PubMed2000

Kinetics of abiotic hydrolysis of isoxaflutole: influence of pH and temperature in aqueous mineral buffered solutions.

A kinetic study of the chemical hydrolysis of isoxaflutole [5-cyclopropyl-4-(2-methanesulfonyl-4-trifluoromethylbenzoyl)is oxazol e (IFT)], a new herbicide recently developed by Rhône-Poulenc Agro, in buffered, sterile aqueous solutions was carried out in the dark at 295, 308, and 323 K and at nine pH values between 1.8 and 10.1. Samples were analyzed by HPLC-UV. The decrease in IFT concentration was accompanied by an increase in the concentration of its diketonitrile derivative (DKN). Obeying pseudo-first-order kinetics, isoxaflutole hydrolysis increased with increasing pH and temperature: for 295 K and pH 9.3 the rate of degradation was 100-fold faster than at pH 3.8. Using the Arrhenius equation, the rate constants K(obsd), activation energies E(a), and entropies DeltaS() were calculated, and plotting log(K(obsd)) against pH showed that the effect of pH varied with temperature. According to DeltaS() values the mechanism of the reaction was found to be different with respect to pH range. The benzoic acid derivative, known as a degradation product of DKN in plants, was not detected in the present study.

Buffers↗

PubMed1999

An evaluation of NHANES III estimates of early childhood caries.

OBJECTIVES: The purposes of this study were to estimate and evaluate the prevalence for the United States of early childhood caries (ECC) among children 12 to 23 months of age. METHODS: The 1988-94 National Health and Nutrition Examination Survey (NHANES III) public-use data set was analyzed using SUDAAN. Two ECC case definitions were used. Definition #1 was restricted to the caries score called by the examiner. Definition #2 liberally included children identified by definition #1 and those possibly having questionable caries scores. RESULTS: The NHANES III six-year prevalence estimates of caries in the maxillary anterior incisors of children 12 to 23 months of age were 1.0 percent for definition #1 and 1.7 percent for definition #2. Mexican-American and economically disadvantaged children were disproportionally represented with ECC. CONCLUSIONS: The prevalence of ECC among children 12 to 23 months of age is barely detectable at the national level. Alternative study designs and improved case definitions are needed for further advances in ECC.

Chi-Square Distribution↗

PubMed1994

Sexual behavior research on a cohort of gay men, 1984-1990: can we predict how men will respond to interventions?

In 1984, over 1000 gay and bisexual men volunteered to participate in both the Chicago Multicenter AIDS Cohort Study (MACS) and a companion psychosocial study, the Coping and Change Study (CCS). Participants in the semiannual Chicago MACS/CCS evaluations comprise the largest cohort of high-risk men under continuous medical, behavioral, and psychosocial observation. Chicago MACS/CCS researchers prospectively chart the sexual behavior change patterns of the cohort and relate those behavioral changes to psychosocial correlates and actual HIV infection risk. This report summarizes the behavioral natural history of the Chicago MACS/CCS cohort from 1984 to 1990, focusing on receptive anal sex practices and use patterns for alcohol and the most frequently used recreational drugs. As these are prospective observational and not controlled intervention studies, psychosocial correlates of sexual behavior change by members of the cohort are suggestive of factors influencing behavior change rather than indicative of causal relationships. However, the voluntary availability to participants in the Chicago MACS/CCS of HIV-1 antibody test results beginning in late 1985 provided the opportunity to examine whether demographic, psychosocial, or behavioral factors were indicators of sexual behavior change following disclosure and counseling about HIV-1 serostatus. Recommendations for promotion and maintenance of safer sexual behavior for the long run, and limitations in the generalizability of these findings to the much more diverse populations of men who have sex with other men conclude this article.

Acquired Immunodeficiency Syndrome↗

PubMed1993

A retrospective analysis of the cost-effectiveness of dental sealants in a children's health center.

A retrospective patient record analysis was conducted to study the cost-effectiveness of dental sealants placed under routine, unrestricted practice condition in a fluoridated community. The 26 dentists who provided care at the clinic over the period of the study used their own clinical judgement to determine sealant placement or alternative treatment. Dental services for 275 patients at a children's dental clinic for low-income families were evaluated. All children had at least 3 years between their first and last dental visit (mean = 5.8 years). A lifetable analysis was conducted to compare the probability of survival (restoration-free tooth years) and costs incurred to first molars of children who did not receive sealants, received any sealants, or received sealants on all first molars. Among the children with sealants, comparisons were also made between sealed and unsealed teeth in children who did and did not have a first molar restoration prior to sealant placement. Costs included the costs of sealants and restorative treatments for these teeth over time. Depending on the conditions under which sealants were placed, cost-savings or improving cost-effectiveness with time were found. A strategy of identifying children with prior restorations and sealing the remaining molars showed cost-savings within 4-6 years. For other comparisons, incremental cost-effectiveness ratios became more favorable over time.

Child↗

PubMed1992

Ectopic somatic endoderm in secondary human yolk sac.

Three secondary human yolk sacs (SHYSs) showing heterotopic endodermal tubular structures of the gut-forming type were analyzed from a series of 180 SHYSs. These structures were similar to the early somatic endoderm involved in the formation of gut and lung. They may have arisen either as sequestrations in growth-disorganized embryos or as a phenomenon of differentiation from extraembryonal endoderm, which would indicate that extraembryonal tissues such as the SHYSs retain the capacity to differentiate somatic endoderm in developmentally altered embryos. It is possible that these structures may be the precursors of placental hepatic tissue and teratomas. Their morphologic resemblance to similar structures found in glandular, polyvesicular, and intestinal human yolk sac tumors provides yet another example of the similarity between SHYSs and yolk sac tumors.

Abortion, Spontaneous↗

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Americas↗

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Historiography↗