Water-soluble chemical compounds

Hexavalent chromium (Cr+6) is the most biologically active chromium chemical species, although little is known about the properties of organochromium compounds, water-soluble species, or their interactions in complex mixtures... 

The underlying principle of the pro-drug approach consists in chemically modifying water-soluble contrast agents such that the new compounds exhibit... 

Once a chemical is in systemic circulation, the next concern is how rapidly it is cleared from the body. Under the assumption of steady-state exposure, the clearance rate drives the steady-state concentration in the blood and other tissues, which in turn will help determine what types of specific molecular activity can be expected. Chemicals are processed through the liver, where a variety of biotransformation reactions occur, for instance, making the chemical more water soluble or tagging it for active transport. The chemical can then be actively or passively partitioned for excretion based largely on the physicochemical properties of the parent compound and the resulting metabolites. Whole animal pharmacokinetic studies can be carried out to determine partitioning, metabolic fate, and routes and extent of excretion, but these studies are extremely laborious and expensive, and are often difficult to extrapolate to humans. To complement these studies, and in some cases to replace them, physiologically based pharmacokinetic (PBPK) models can be constructed [32, 33]. These are typically compartment-based models that are parameterized for particular... 

There are a number of factors that affect the absorption of foreign compounds from the gut or their disposition one factor, which is of particular importance, is the aqueous solubility of the compound in the nonionized form. With very lipid-soluble compounds, water solubility may be so low that the compound is not well absorbed (Table 2), because it is not dispersed in the aqueous environment of the gastrointestinal tract. In relation to this, a factor of particular importance in absorption of chemicals from the gut is the presence of bile, which is produced in the liver and secreted into the small intestine. This contains detergent-like substances, which will facilitate the dispersal of lipid-soluble chemicals in the aqueous medium of the intestine. 

When one has to deal with a real new target, the only way to progress is to practice enough syntheses to identify the molecular features that are favorable and those that are detrimental to the activity. Such molecular variation programs can be practiced in several manners. Usually the predominant parameter wanted first is potency, but other qualities of the future drug molecules are relevant of drug optimization. One can mention selectivity, satisfactory ADME (absorption, distribution, metabolism, and excretion) and toxicity profiles, optimal physicochemical properties such as chemical stability, water solubility, and absence of polymorphs, finally the compounds must be patentable. Table 19.5, due to Baxter et al summarizes the different criteria practiced at the Astra-Zeneca company. 

Sulfonylurea herbicides (SUHs) are relatively new herbicides, introduced in the 1980s. Chlorsulfuron was the first sulfonylurea marketed in the United States, in 1982. World-wide, 19 sulfonylureas had been commercialized by 1994, and five more are being developed. This rapid increase is due to their very high and specific herbicidal activity, which results in extremely low application rates of 10 to 40 g/ha. Furthermore, as compared to other herbicides, sulfonylureas are less toxic and degrade more rapidly. Chemical structures of some representative sulfonylureas are presented in Figure 25.2. From a chemical point of view, these herbicides are labile and weakly acidic compounds. The common names, chemical formulas, water solubility, pKa, half-life in soil, and leaching potential through the soil (when available) of the most representative sulfonylureas are reported in Table 25.2. 

Rates of degradation in wetland systems depend on the interplay of a number of environmental factors including chemical characteristics of organic compounds (water solubility, oxidation... 

Argon is two and one half times as soluble in water as nitrogen, having about the same solubility as oxygen. Argon is colorless and odorless, both as a gas and liquid. Argon is considered to be a very inert gas and is not known to form true chemical compounds, as do krypton, xenon, and radon. 

Eyrol 51 is a water-soluble Hquid containing about 21% phosphoms. It is made by a multistep process from dimethyl methylphosphonate, phosphoms pentoxide, and ethylene oxide. The end groups are principally primary hydroxyl and the compound can thus be incorporated chemically into aminoplasts, phenoHc resins, and polyurethanes. Eyrol 51, or 58 if diluted with a small amount of isopropanol, is used along with amino resins to produce a flame-retardant resin finish on paper used for automotive air filters, or for backcoating of upholstery fabric to pass the British or California flammabiHty standards. 

Volatilization. The susceptibility of a herbicide to loss through volatilization has received much attention, due in part to the realization that herbicides in the vapor phase may be transported large distances from the point of application. Volatilization losses can be as high as 80—90% of the total applied herbicide within several days of application. The processes that control the amount of herbicide volatilized are the evaporation of the herbicide from the solution or soHd phase into the air, and dispersal and dilution of the resulting vapor into the atmosphere (250). These processes are influenced by many factors including herbicide application rate, wind velocity, temperature, soil moisture content, and the compound s sorption to soil organic and mineral surfaces. Properties of the herbicide that influence volatility include vapor pressure, water solubility, and chemical stmcture (251). 

The covalent character of mercury compounds and the corresponding abiUty to complex with various organic compounds explains the unusually wide solubihty characteristics. Mercury compounds are soluble in alcohols, ethyl ether, benzene, and other organic solvents. Moreover, small amounts of chemicals such as amines, ammonia (qv), and ammonium acetate can have a profound solubilizing effect (see COORDINATION COMPOUNDS). The solubihty of mercury and a wide variety of mercury salts and complexes in water and aqueous electrolyte solutions has been well outlined (5). 

In order to obtain a homogenous and stable latex compound, it is necessary that insoluble additives be reduced in particle size to an optimum of ca 5 )Tm and dispersed or emulsified in water. Larger-size chemical particles form a nucleus for agglomeration of smaller particles and cause localized dispersion instabiHty particles <3 fim tend to cluster with similar effect, and over-milled zinc oxide dispersions are particularly prone to this. Water-soluble ingredients, including some accelerators, can be added directly to the latex but should be made at dilute strength and at similar pH value to that of the latex concentrate. 

Wet-Chemical Determinations. Both water-soluble and prepared insoluble samples must be treated to ensure that all the chromium is present as Cr(VI). For water-soluble Cr(III) compounds, the oxidation is easily accompHshed using dilute sodium hydroxide, dilute hydrogen peroxide, and heat. Any excess peroxide can be destroyed by adding a catalyst and boiling the alkaline solution for a short time (101). Appropriate ahquot portions of the samples are acidified and chromium is found by titration either using a standard ferrous solution or a standard thiosulfate solution after addition of potassium iodide to generate an iodine equivalent. The ferrous endpoint is found either potentiometricaHy or by visual indicators, such as ferroin, a complex of iron(II) and o-phenanthroline, and the thiosulfate endpoint is ascertained using starch as an indicator. 

Included in this grouping are D C Green No. 5 (13), a water-soluble sulfonate, D C Green No. 6 (14), an unsulfonated water-insoluble compound, and D C Violet No. 2 (29), a water-insoluble hydroxyanthraquinone. Anthraquinone color additives, in general, are light stable and have good physical and chemical properties for use in cosmetics (see Dyes, ANTHRAQUINONE). 

Acid Dyes. These water-soluble anionic dyes ate appHed to nylon, wool, sUk, and modified acryHcs. They ate also used to some extent for paper, leather, food, and cosmetics. The original members of this class aU had one or mote sulfonic or catboxyHc acid groups in thein molecules. This characteristic probably gave the class its name. Chemically, the acid dyes consist of azo (including preformed metal complexes), anthraquiaone, and ttiaryHnethane compounds with a few azHie, xanthene, ketone imine, nitro, nitroso, and quHiophthalone compounds. 

Square planar. There are two compounds with the formula Pt(NH3)2Cl2, differing in water solubility, melting point, chemical behavior, and biological activity. Their structures are... 

The reverse of Example 16.4 involves finding Rq, of a compound given its solubility. The solubilities of many ionic compounds are determined experimentally and tabulated in chemical handbooks. Most solubility values are given in grams of solute dissolved in 100 grams of water. To obtain the molar solubility in moles/L, we have to assume that the density of the solution is equal to that of water. Then the number of grams of solute per 100 g water is equal to the number of grams of solute per 100 mL of solution. This assumption is valid because the mass of the compound in solution is small. To solve for IQp, find the molar solubility of the solute and determine the concentration of its component ions. Substitute into the IQp expression. 

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