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EFFECT OF IONIC STRENGTH ON ACID-BASE PROPERTIES OF VICINAL WATER
Citation:
Galloway, J. R. AND G W. Bailey. EFFECT OF IONIC STRENGTH ON ACID-BASE PROPERTIES OF VICINAL WATER. Presented at Annual Biomedical Research Conference for Minority Students, San Diego, CA, October 15-18, 2003.
Impact/Purpose:
This task is divided into four major research areas: (1) Development of computational tools and databases for screening-level modeling of the environmental fate of organic chemicals; (2) Metabolism of xenobiotics: Enhancing the development of a metabolic simulator; (3) Metabonomics: The use of advanced analytical tools to identify toxicity pathways; and (4) Software infrastructure to support development and application of transformation/metabolic simulators.
For many chemicals, multiple transformation/metabolic pathways can exist. Consequently, transformation/metabolic simulators must utilize transformation rate data for prioritization of competing pathways. The prioritization process thus requires the integration of reliable rate data. When this data is absent, it is necessary to generate a database with metabolic and transformation rate constants based on: (1) experimentally measured values, including those requiring the use of advanced analytical techniques for measuring metabolic rate constants in vivo and in vitro; (2) rate constants derived from SPARC and mechanistic-based QSAR models; and (3) data mined from the literature and Program Office CBI. A long-term goal of this project is to build this database. This information will be used to enhance the predictive capabilities of the transformation/metabolic simulators. As indicated previously, exposure genomics, which provide early signs of chemical exposure based on changes in gene expression, will be used to guide chemical fate and metabolism studies. The incorporation of exposure genomics into fate studies will provide information concerning (1) the minimal concentrations at which biological events occur; and (2) the identification of biologically relevant chemicals(s) in mixtures.
The capability of categorizing chemicals and their metabolites based on toxicity pathway is imperative to the success of the CompTox Research Program. Metabonomics, which is the multi-parametric measurement of metabolites in living systems due to physiological stimuli and/or genetic modification, provides such a capability. The application of metabonomics to toxicity testing involves the elucidation of changes in metabolic patterns associated with chemical toxicity based on the measurement of component profiles in biofluids, and enables the generation of spectral profiles for a wide range of endogenous metabolites. Metabolic profiles can provide a measure of the real outcome of potential changes as the result of xenobiotic exposure.
Description:
Surface research over the past 75 years has clearly shown that water under the influence of electrical and magnetic force fields (vicinal water) does not have the same properties as bulk water. Vicinal water is vital in influencing and maintaining the critical spatial and conformational intramolecular relationships in macromolecules. If the structure of the water molecule changes, it may not positively influence the conformation, chemical reactivity, and function of the macromolecule.
Our objective was to determine the thermodynamic activity of both innersphere and outersphere water surrounding metal cations. Stock solutions of Li- and CaNO3 were made up having a minimum purity of 99.995%; metal concentrations used were:
9 M, 5.24 M, 3.4 M, 1.9 M, 1.1 M, and 0.6 M. Near-infrared spectroscopy monitored the change in the OH vibrational peaks of the H2O molecule as a function of cation type and ionic strength. The scan range was 4000- 8000 cm-1. For CaNO3 the band at 4400 cm-1 was attributed to innersphere water while the band at 5200 cm-1 is attributed to bulk water. For LiNO3 the O-H band at 7200 cm-1shifted up field, and the absorbency decreases as the metal concentration increases. Ultra-violet spectroscopy and an organic molecular probe were used to measure the Lewis acid-base character of vicinal water. The breaking of the O-H bonds created free protons in the presence of an organic Lewis base, resulting in the formation of a monovalent cation. Solution driven acid-catalyzed hydrolysis was not observed. We conclude that the water activity was lowered due to the elevated salt concentrations, and that proton activity was enhanced. The decrease in activity lowered the strength of the O-H bonds, causing them to have a higher dissociation constant. Three different types of water were observed, innersphere water, outersphere water (water bonded to water), and free water.