Water nonessential

Nonessential water is retained by the solid as a consequence of physical forces. It is not necessary for characterization of the chemical constitution of the sample and therefore does not occur in any sort of stoichiometric proportion. 

Adsorbed water is a type of nonessential water that is retained on the surface of solids. The amount adsorbed is dependent on humidity, temperature, and the specific surface area of the solid. Adsorption of water occurs to some degree on all solids. 

A second type of nonessential water is called sorbed water and is encountered with many colloidal substances, such as starch, protein, charcoal, zeolite minerals, and silica gel. In contrast to adsorption, the quantity of sorbed water is often large, amounting to as much as 20% or more of the total mass of the solid. Solids containing even this amount of water may appear to be perfectly dry powders. Sorbed water is held as a condensed phase in the interstices or capillaries of the colloidal solid. The quantity contained in the solid is greatly dependent on temperature and humidity. 

Nonessential water is the water that is physically retained by a solid. 

Adsorbed water Nonessential water that is held on the surface of solids. 

Nonessential water Water that is retained in or on a solid by physical, rather than chemical, forces. 

Occluded water Nonessential water that has been entrained in a growing crystal. 

Sorbed water Nonessential water that is retained in the inter- stices of solid materials. 

Solid samples will usually contain variable amounts of adsorbed water. With inorganic materials, the sample will generally be dried before weighing. This is accomplished by placing it in a drying oven at 105 to 110°C for 1 or 2 h. Other nonessential water, such as that entrapped within the crystals, may require higher temperatures for removal. 

The reduction of water limits mold formation, but only slightly affects the aroma or pungency. The dried product maintains its character and pound for pound is stronger in aroma and flavor than the fresh spice, since a nonessential component has been substantially removed. In areas where a spice is grown, the same product that is dried for storage and shipment is often used fresh for flavoring. 

Contaminating CO2. The ubiquitous presence of CO2 causes a great difficulty to the experiment. Normal atmosphere contains 0.03% CO2, and a 5-6 ml portion of pure water equilibrated with atmosphere contains 0.06 pmol of CO2. However, the amount of CO2 in buffers and luciferase solutions is much greater. For example, 5 ml of freshly prepared Tris-HCl buffer, pH 7.8, contained 0.13 pmol of CO2 after 20 min degassing, and the value increased to 0.23 pmol when the same buffer was tested one week later (Shimomura et al., 1977). It is strongly advised to eliminate all nonessential CO2 sources from the experimental environment. 

Tyrosine. Phenylalanine hydroxylase converts phenylalanine to tyrosine (Figure 28-10). Provided that the diet contains adequate nutritionally essential phenylalanine, tyrosine is nutritionally nonessential. But since the reaction is irreversible, dietary tyrosine cannot replace phenylalanine. Catalysis by this mixed-function oxygenase incorporates one atom of O2 into phenylalanine and reduces the other atom to water. Reducing power, provided as tetrahydrobiopterin, derives ultimately from NADPH. 

Tyrosine is formed from phenylalanine by phenylalanine hydroxylase. The reaction requires molecular oxygen and the coen zyme tetrahydrobiopterin, which can be synthesized by the body. One atom of molecular oxygen becomes the hydroxyl group of tyro sine, and the other atom is reduced to water. During the reaction, tetrahydrobiopterin is oxidized to dihydrobiopterin. Tetrahydro biopterin is regenerated from dihydrobiopterin in a separate reaction requiring NADPH. Tyrosine, like cysteine, is formed from an essen tial amino acid and, is therefore, nonessential only in the presence of adequate dietary phenylalanine. 

Covalent Attachment The covalent attachment of enzyme molecules via nonessential amino acid residues (that is, amino acids minus water) to water-insoluble, functionalized supports are the most widely used method for immobilizing enzymes. Functional groups of the nonessential amino acid residues that are suitable for the immobilization process are free a-, /3-, or y-carboxyl groups, a- or /3-amino groups, and phenyl, hydroxyl, sulfhydryl, or imidazole groups.2... 

With unusually hot weather lasting longer than two days, heat can build up in the enviromnent both at work and at home, and the body can become progressively dehydrated. Chronic dehydration can occur without any signs of thirst in its early stages it may be indicated by a lack of alertness. During heat spells, increase water consumption both on and off the job, and postpone nonessential tasks likely to cause severe heat strain until after the heat speU is over. For tasks which cannot be postponed, special measures should be taken, such as ... 

A third type of nonessential moisture is occluded water, liquid water entrapped in microscopic pockets spaced irregularly throughout solid crystals. Such cavities often occur in minerals and rocks (and in gravimetric precipitates). 

All in all, there are at least forty-one elements in most human bodies, of which only twenty-one are known to be essential. We cannot assume that just because an element is found in the human body, it must serve some purpose. Our natural defenses, such as the white blood cells, antibodies, antioxidants, and macrophages, don t attack or immobilize toxic or nonessential chemical elements and remove them from the body as they do with harmful bacteria or viruses.We pick up some of these unneeded or unwanted elements from our food, water, and air, and they simply settle in the body, usually in the fatty tissue, liver, or bones. There are ways of getting them out, which I will mention later. 

Many nonessential trace elements are found in the body. Depending on the local environment, at least 43 elements are normally incorporated into developing teeth another 25 elements are seen less frequently. The rest, notably the heavy metals, have never been detected in teeth. Many trace elements, particularly the heavy metals, are considered when testing for metal poisoning. Many plants concentrate essential and nonessential elements from soil and water, including aluminum (several species of subtropical plants), selenium (many plants), strontium (mesquite beans), and lithium (wolfberries, used by Native Americans in the southwestern United States for jam). Ingestion of these plants can cause toxicity for the element involved. 

---