Influence of the Mixed Adsorption Layer 1-Butanol/Thiourea on the Two-step Electroreduction of Zinc(II) Ions

Influence of a constant 1-butanol (BuOH) concentration and various thiourea (TU) concentrations in the bulk on the two consecutive one-electron transfer steps in the electroreduction of Zn2+ ions at Hg electrode is described. It was found that in the range of Zn2+ ions reduction potentials BuOH has the predominant effect on formation of the adsorption mixed layer. The values determined for the total surface excesses of BuOH and TU in the function of Φr potential are linear and, except for the highest TU concentrations, insignificantly depend on the potential. As it follows from the dependence ktf = f(Φr), in the presence of 0.11 mol dm-3 BuOH even the smallest amounts of TU accelerate Zn2+ ion reduction compared with 1 mol dm-3 NaClO4 solution. However, in a solution containing 0.33 mol dm-3 or 0.55 mol dm-3 BuOH this effect takes places only for cTU ≥ 0.033 mol dm-3. The course of the kts1 = f(Γ) and kts2 = f(Γ) dependence indicates that one kind of active complex is formed on the electrode surface in the 0.11 mol dm-3 BuOH solution but in Solutions of a larger amount of BuOH two kinds of active complexes are formed, differing in the extent of hydration. The obtained results indicate that the stage of the first electron transfer is less susceptible to inhibition by BuOH than the stage of the second electron transfer

Properties of the Mixed Polyethyleneglycoles-iodide Ions Adsorption Layers on a Mercury Electrode

Adsorption of a mixture of I- ions and polyethyleneglycoles of molecular weights 400 (PEG 400) and 10 000 (PEG 10 000) on a mercury electrode from NaClO4 solution of constant ionic strength is described. Parallel courses of linear dependences of the potential of zero charge with the increase of I- ion concentration in the Solutions with PEG and without PEG indicate removal of water molecules by adsorption of I- ions and not PEG molecules. The standard Gibbs energy of adsorption ΔadG° and parameter B obtained from the virial isotherm do not depend on PEG 10 000 concentration. This can be associated with the full coverage of the electrode surface with its molecules already at a concentration of 10-4 mol dm-3. For PEG 400, a dependence of adsorption parameters on its concentration was observed. Lower repulsive interaction between the adsorbed I- ion in PEG Solutions indicates a favourable effect of PEG molecules on I- ion adsorption compared with H2O. The values of rate constants ksapp of Zn2+ ion reduction as a piloting ion were determined. Acceleration of the processes inhibited by PEG 400 or PEG 10 000 by I- ions is based on formation of ion pairs Zn2+−I- on the mercury surface. Kinetic measurements con-firm stronger adsorption of PEG 10 000 compared with PEG 400

Adsorption of Tetramethylthiourea in the Presence of Cationic Detergent at Interface Electrode / Aqueous Perchlorate Solutions

The mixed adsorption layers of tetramethylthiourea and a cationic detergent formed at electrode surface in NaClO4 (1 mol dm–3) are described. The systems were characterized by the measurement of differential capacity, zero charge potential, and surface tension at this potential. The data were analyzed to obtain the surface pressure and relative surface excess of tetramethylthoiurea as a function of electrode charge at bulk concentration of studied compounds. It was stated that the adsorbing tetramethylthoiurea molecule pushed out the water molecule instead of the detergent molecule from the electrode surface. The constants of the Frumkin and corrected Flory-Huggins isotherm point to a decreased TMTU adsorption energy in the cationic detergents presence and stronger repulsive interaction. Electrostatic parameters of the inner layer were assigned. In the range of more negative potentials, mixed adsorption layers were described by investigating the kinetics of the Zn2+ ions electroreduction as a piloting ion. (doi: 10.5562/cca1791

FACTORS ASSOCIATED WITH ADHERENCE TO RECOMMENDATIONS FOR SCREENING MAMMOGRAPHY AMONG AMERICAN INDIAN WOMEN IN COLORADO

Objective: To compare adherence to screening mammography recommendations of American Indian and non-Hispanic White women in the Denver, Colorado, area. Design/Setting/Participants: This study retrospectively examined adherence patterns in 229 American Indian and 60,197 non-Hispanic White women $40 years and older, with at least one screening mammogram in the Colorado Mammography Project (CMAP), from January 1, 1999, to December 31, 2003. The CMAP was a prospective study of women receiving mammograms at participating clinics around Denver. Main Outcome Measures: Using logistic mixed models, we defined two dependent variables as annual and biennial adherence from the intervals between screening mammograms for each woman. Results: Biennial adherence was substantially higher than annual adherence for both American Indian and non-Hispanic White women in our analyses. American Indian women were less likely than non-Hispanic White women to adhere to biennial recommendations in multivariate models controlling for age, family history of breast cancer, and economic status (zip code): odds ratio (OR) .4 and 95% confidence interval (CI) .2–.6. The association between American Indian race/ethnicity and annual adherence was similar, although not as strong (OR .5, 95% CI .3–.8). Conclusions: American Indian women in the CMAP cohort were less likely than non- Hispanic White women to adhere to recommendations for screening mammography, both annually and biennially. Additional research is needed to explore the effect of biennial screening and other barriers among American Indian women