Water physicochemical parameters

The solubility of chemicals, drugs or pollutants in water (S ), in octanol (S ), their saturation concentration in air Qii), as well as their partitioning in the corresponding two-phase systems [octanol-water (P /w = Q/Cw), air-water (Pair/w = C IC ) and air-octanol (Paij/ = C /Co)] are important physicochemical parameters in medicinal chemistry and in environmental research. The following correlahons of those properties with HYBOT descriptors have been published recently [54—58] ... 

The log octanol-water partition coefficient (log Pq/w) probably is the most frequently used physicochemical parameter in medicinal chemistry [101 104]. Octanol, with a polar head and a flexible, nonpolar tail, has hydrogen-bonding capabilities and amphilicity similar to... 

In response to the concern expressed by the shellfish farmers operating in the Ebro River delta about the potential positive role of pesticides on the oyster and mussel mortalities observed in the area, our group, commissioned by and with the collaboration of the Catalan Water Agency (ACA), carried out a comprehensive study in which chemical and toxicity data were combined to assess potential toxic presures present in the delta. To this end, a combined approach scheme integrating the measurement of various general physicochemical parameters in water, quantitative chemical analysis of pesticides in water and biota, and ecotoxicity assays in water was applied to a series of samples collected at springtime (between mid-April and mid-June 2008) from six selected sites of the delta the two (northern and southern)... 

Data were divided into six different groups according to the physical compartment (water, SEs, and biota) and the analyzed variables (metals, organic compounds, and physicochemical parameters). Analyzed parameters and sampling sites were not the same for all compartments and years for reasons of data availability (see Fig. 4 for sample location and Table 1 for sample identification). SE and water sample data covering years from 1996 to 2003 were selected, since before 1996 the data set was too much incomplete. Time interval for biota was reduced, covering only years from 2000 to 2003 for metals and from 1999 to 2002 for organic compounds. 

As the logarithm of 1-octanol-water partition coefficient (log P) describes the hydrophobicity of molecules and the retention of solutes in RP-HPLC depends on the hydrophobicity, a strong correlation can be expected between the log V value and the retention of solutes in RP-HPLC. Besides log P, a considerable number of physicochemical parameters have been tested for their capacity to predict retention in RP-HPLC. Thus, Snyder s polarity index, fraction of positively and negatively charged surface area, molecular bulkiness, nonpolar surface area, electron donor and acceptor capacity, various ster-ical parameters, and the energy of highest occupied molecular orbit have all been included in QSRR calculations. 

As indicated earlier (Section 3.1.1) the sorption of organic compounds onto dissolved matter can significantly increase the solubility of the compound. This can in turn affect the fate of these chemicals in the environment. We can use physicochemical parameters such as distribution coefficients (log D), aqueous acid dissociation constants (pAia), and octanol-water partition coefficients (p/to )-These attributes are also linked to the acidity and alkalinity of the environment as well as lipohilicity of the compound. The mathematical relationships between these attributes are outlined below to explore how each of these impacts the fate of PPCPs in the environment. 

Pierlot C, Poprawski J, Catte M, Salager JL, Aubry JM (2003) Experimental design for the determination of the physicochemical parameters of optimum water-oil surfactant systems. Polym Int 52 614-618... 

Physicochemical parameters of the water (salinity, pH, and temperature) from all treatment tanks, and also heavy metal concentrations, were measured on a daily basis. 

A second physicochemical parameter influencing chemical penetration through membranes is the relative lipid solubility of the potential toxicant that can be ascertained from its known partition coefficient. The partition coefficient is a measure of the ability of a chemical to separate between two immiscible phases. The phases consist of an organic phase (e.g., octanol or heptane) and an aqueous phase (e.g., water). The lipid solvent used for measurement is usually octanol because it best mimics the carbon chain of phospholipids, but many other systems have been reported (chloroform/water, ether/water, olive oil/water). The lipid solubility and the water solubility characteristics of the chemical will allow it to proportionately partition between the organic and water phase. The partition coefficients can be calculated using the following equation ... 

Only a few physicochemical parameters can be measured by immersing the relevant instrument into a water body. In most cases a small fraction of a given water population or sample is collected and analyzed. The aim of taking samples or sampling is to extract a fraction of the water body that has chemical, physical, and biological properties identical to those of the bulk of the system to be studied. Ideally, all the characteristics of the sample, or at least, the parameters that are to be determined, should not change until the time of measurement. Only then can the results of the sample analysis be representative of the composition of the system under scrutiny. 

Skarzynska, K., Z. Polkowska, and J. Namiesnik. 2006. Samples handling and determination of physicochemical parameters in rime, hoarfrost, dew, fog and cloud water samples—a review. Pol. J. Environ. Stud. 15 185-209. 

The main goal of this chapter is to present the theoretical background of some basic chemometric methods as a tool for the assessment of surface water quality described by numerous chemical and physicochemical parameters. As a case study, long-term monitoring results from the watershed of the Struma River, Bulgaria, are used to illustrate the options offered by multivariate statistical methods such as CA, principal components analysis, principal components regression (models of source apportionment), and Kohonen s SOMs. 

During both Phases I and II, 71 piezometers were installed to monitor groundwater. A total of 221 water samples were collected and 9463 analyses were carried out. Seven field surveys sampled shallow and deep groundwater, analyzing various physicochemical parameters (e. g., pH, Eh, dissolved 02, temperature, conductivity), and the presence of potentially harmful elements and compounds (e.g., heavy metals, hydrocarbons, PAH). The hydrogeological survey carried out by the Bagnoli SpA, concluded that... 

The partition coefficient logP or the distribution coefficient logD between water and n-octanol are determined traditionally by the shake flask method (see chapter about physicochemical parameters). The shake flask method is a rather labour intensive method and not suited for high throughput analysis needed in pharmaceutical research. 

Based on the earlier work of Meyer and Overton, who showed that the narcotic effect of anesthetics was related to their oil/water partition coefficients, Hansch and his co-workers have demonstrated unequivocally the importance of hydrophobic parameters such as log P (where P is, usually, the octanol/water partition coefficient) in QSAR analysis.28 The so-called classical QSAR approach, pioneered by Hansch, involves stepwise multiple regression analysis (MRA) in the generation of activity correlations with structural descriptors, such as physicochemical parameters (log P, molar refractivity, etc.) or substituent constants such as ir, a, and Es (where these represent hydrophobic, electronic, and steric effects, respectively). The Hansch approach has been very successful in accurately predicting effects in many biological systems, some of which have been subsequently rationalized by inspection of the three-dimensional structures of receptor proteins.28 The use of log P (and its associated substituent parameter, tr) is very important in toxicity,29-32 as well as in other forms of bioactivity, because of the role of hydrophobicity in molecular transport across cell membranes and other biological barriers. 

Example 2.7 Several physicochemical parameters vary with temperature. For example, at 100°C the pH of pure water is approximately 6. Under these conditions,... 

When the library individuals are filtered with physicochemical parameters, the nature of the scaffold becomes fundamental. As an example, if a maximum accepted value of log P (partition coefficient between n-octanol and water) of 4 is set as a limit, the use of a functionalized scaffold with log P = 6 will enormously limit the selection of monomers to highly hydrophilic structures, while the selection of a more appropriate scaffold would allow a higher degree of diversity while respecting the imposed filter. The same is true for monomers. For example, if an upper hmit of 600 is imposed for the molecular weight (MW) of the final library components, the use of monomers with an MW higher than 250-300 will not be acceptable. 

The pKa is an important physicochemical parameter. The analyte pKa values are especially important in regard to pharmacokinetics (ADME—absorption, distribution, metabolism, excretion) of xenobiotics since the pKa affects the apparent drug lipophilicity [59]. Potentiometric titrations and spectrophome-tric analysis can be used for pKa determination however, if the compound is not pure, is poorly soluble in water, and/or does not have a significant UV chromophore and is in limited quantity, its determination may prove to be challenging. 

Figure 13. Simulation of the genesis of a roll-type uranium deposit and of the weathering of a pyrite-rich sandstone. Twenty boxes model at logi = —1 with Vx = 10, In the upper part we present an instant view of the alteration profile with neoformed minerals. Numbers in brackets correspond to the molar percentage of the neoformed minerals vs. total neoformed minerals in each box. In the lower part we present the major physicochemical parameters PE, pH, and [O2] (mol/1) in the percolating water in the above boxes. The scale is the same in the upper part and the lower part. IPW = initial percolating water.

C represents the equipotent concentration, k and m are constants for a particular system, and A is a physicochemical constant representative of phase distribution equilibria such as aqueous solubility, oil/water partition coefficient, and vapor pressure. In examining a large and diverse number of biological systems, Hansch and coworkers defined a relationship (Equation 1.62) that expressed biological activity as a function of physicochemical parameters (e.g., partition coefficients of organic molecules) (19). 

The empirical physicochemical parameters have a good informative value for determining the mechanism of retention operating in a given chromatographic sy.stem. There are exhaustive compilations of such parameters like >/-octanol-water partition coefficients [45,46] or the LSER-based analyte parameters [47,48]. The problem is. however, that there is a lack of such descriptors for many analytes of interest in actual QSRR studies. 

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