Virtual Substance availability

The sensitivity of cellular constituents to environmental extremes places another constraint on the reactions of metabolism. The rate at which cellular reactions proceed is a very important factor in maintenance of the living state. However, the common ways chemists accelerate reactions are not available to cells the temperature cannot be raised, acid or base cannot be added, the pressure cannot be elevated, and concentrations cannot be dramatically increased. Instead, biomolecular catalysts mediate cellular reactions. These catalysts, called enzymes, accelerate the reaction rates many orders of magnitude and, by selecting the substances undergoing reaction, determine the specific reaction taking place. Virtually every metabolic reaction is served by an enzyme whose sole biological purpose is to catalyze its specific reaction (Figure 1.19). 

The sunblocks zinc oxide, titanium dioxide, and iron oxide are inorganic chemicals that are not absorbed into the skin. These substances consist of opaque particles that reflect both visible and ultraviolet light. In addition, zinc oxide blocks virtually the entire UVA and UVB spectrum and thus offers overall protection. The particulate nature of these sunblocks enhances their effectiveness at reflecting sunlight. The smaller the particle size, the greater the surface area available for reflection, and the more effective the sun protection offered by the formulation. 

Sulphuric acid (sp. gr 1.84) and oleum (20-25%) should be virtually free from lead sulphate which is liable to be present in old installations constructed of lead, and also from sulphates of iron, as these substances hinder the separation of nitroglycerine and acid. Since such acid is not always available storage of sulphuric add and oleum in spedal cast iron tanks is recommended in order to allow impurities to settle. Acid is drawn from the upper part of the tank so that the slime composed of iron and lead sulphates remains on the bottom. Similarly, the mixed acid is stored in tanks so designed that the predpitate can collect on the bottom. 

FSH has been commercially available since the 1960s. It was first extracted from the urine of postmenopausal women, which contains a substance with FSH-like properties (but with 4% of the potency) and an LH-like substance. This purified extract of FSH and LH, derived from the urine of postmenopausal women, remains available and is known as menotropins, or human menopausal gonadotropins (hMG). A purified preparation of human FSH, also extracted from the urine of postmenopausal women, contains virtually no LH and is know as urofollitropin, or urinary FSH (uFSH). In 1996, a synthetic modified form of FSH became available, known as follitropin alpha, or recombinant FSH (rFSH). Preparations of rFSH have batch-to-batch consistency and are free from possible urinary contaminants. The cost of rFSH is about three times that of hMG. It is controversial whether in vitro fertilization protocols using rFSH are significantly more successful than protocols using uFSH or hMG. 

Inadvertent human intrusion into hazardous waste. Inadvertent human intrusion is relevant to disposal of virtually all hazardous substances, especially in near-surface facilities. Typical scenarios assume that an unknowing individual (1) digs or drills into the waste and brings some of it to the surface where it is then available for dispersal and uptake, or (2) lives on the disposal site after waste has been exhumed or the cover removed, and consumes contaminated plant and animal products. Scenarios for inadvertent intrusion usually are assumed to occur after some period of active institutional control over the disposal site, which is typically 100 to 300 y. Intrusion scenarios are not very sensitive to site-specific parameters because the nature of intrusion (by digging or drilling) effectively bypasses the site-specific protection features, such as small amounts of groundwater,... 

In the interest of conserving space in this handbook, a compact tabular presentation format has been adopted. Table 5.1.5.1 lists the chemical name, and its freon number (if applicable), molecular formula, molar weight and melting and boiling points. These data are available for virtually all substances in this group. Also shown in this table is the availability, expressed as a tick mark, of data on vapor pressure, solubility in water, octanol-water partition coefficient (Kqw) and the second order reaction rate constant with hydroxyl radicals. This rate constant is the critical determinant of persistence in the atmosphere. Tables 5.1.5.2 to Table 5.1.5.5 list the compounds and give the available property data with citations. 

Rapid quantification of products and substrates in a fermentation process is essential for process development and optimization. Most fermentation laboratories have access to HPLC equipment with possibilities to couple them to quite inexpensive diode-array-detectors, and this equipment could be used for quantitative monitoring of the process. Because HPLC can allow multi-component analyses, i.e., several analytes in the same sample can be determined virtually simultaneously, and since it is often necessary to monitor more than one substance at a time, this technique is an important tool for bioprocess monitoring. HPLC coupled to expensive MS does not represent standard equipment at fermentation laboratories. Even if mass spectrometers are available, DAD is often sufficient for quantification because product concentrations are relatively high, so the MS could be used for other issues. In paper II the goal was to develop and validate a method for analytical quantification of both the product and the substrate to enable the proper characterization of the kinetics of the process i.e., the determination of the values of substrate conversion and product formation. 

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