Chemical-defined

There are no simple rules for chemically defining a good odorant. Table 2 and Figure 1 present a number of widely used aroma chemicals by chemical type. Table 2. Typical Aroma Chemicals by Functional Group... 

It is hoped that these volumes will be useful not only to the chemist who wishes to carry out synthesis in the steroid field, but also to the broader group of organic chemists who are interested in carrying out selective and stereo-chemically defined reactions, as well as protective chemistry on extraneous functional groups, during a broad range of synthetic applications. The chapter on the introduction of deuterium and by inference tritium into steroids was included because of the importance of this technique in mechanistic and metabolic studies both in the steroid and nonsteroid field. 

In more recent times chemically defined basal media have been elaborated, on which the growth of various lactic acid bacteria is luxuriant and acid production is near-optimal. The proportions of the nutrients in the basal media have been determined which induce maximum sensitivity of the organisms for the test substance and minimize the stimulatory or inhibitory action of other nutrilites introduced with the test sample. Assay conditions have been provided which permit the attainment of satisfactory precision and accuracy in the determination of amino acids. Experimental techniques have been provided which facilitate the microbiological determination of amino acids. On the whole, microbiological procedures now available for the determination of all the amino acids except hydroxy-proline are convenient, reasonably accurate, and applicable to the assay of purified proteins, food, blood, urine, plant products, and other types of biological materials. On the other hand, it is improbable that any microbiological procedure approaches perfection and it is to be expected that old methods will be improved and new ones proposed by the many investigators interested in this problem. 

Vitamin B2 or riboflavin is chemically defined as 7,8-dimethyl-10-(lY-D-tibityl)isoalloxazine. Figure 1 shows the oxidized and reduced form of the vitamin. The ending flavin (from the latin word flavus—yellow) refers to its yellowish color. 

Vitamin C or L-ascorbic acid (Fig. 1) is chemically defined as 2-oxo-L-theo-hexono-4-lactone-2,3-enediol. Ascorbic acid can be reversibly be oxidized to semidehydro- L-ascorbic acid and further to dehydroas-corbic acid. 

Fig. 7-13 Physical transformations of trace substances in the atmosphere. Each box represents a physically and chemically definable entity. The transformations are given in F, (from the ith to the /th box). Q, represents sources contributing to the mass or burden, M,> in the ith box. Rd, and Rw, are dry and wet removals from M,. The dashed box represents what may be called the fine-particle aerosol and could be a single box instead of the set of four sub-boxes (i = 1,2,3,4). The physical transformations are as follows ...

Elores-Cotera, L.B., Martin, R., and Sanchez S., Citrate, a possible precursor of astaxanthin in Phaffia rhodozyma influence of varying levels of ammonium, phosphate and citrate in a chemically defined medium, Appl. Microbiol. BiotechnoL, 55, 341, 2001. 

The oligomeric formulas are also known as chemically defined formulas. This class of formulas can be subcategorized based on whether the formula contains all free amino acids (elemental formulas) or peptides (peptide-based) as the protein source. Some of these formulas contain a combination of free amino acids and small peptides. Actually, dipeptides and tripeptides in these formulas are absorbed more efficiently than free amino acids. Oligomeric formulas may be better tolerated than polymeric formulas for patients with defects in GI function and maybe particularly useful in patients with severe pancreatic dysfunction or significantly decreased GI surface area (e.g., short bowel syndrome). 

The terms of the fractions are more likely to be operationally, rather than chemically, defined. However, each extractant in the sequentially selective procedure mostly targets one major solid-phase component. Therefore, trace elements bound to the targeted fraction can be either... 

S. A. Kalovidouris, O. Blixt, A. Nelson, S. Vidal, W. B. Turnbull, J. C. Paulson, and J. F. Stoddart, Chemically defined sialoside scaffolds for investigation of multivalent interactions with sialic acid binding proteins, /. Org. Chem., 68 (2003) 8485-8493. 

Nelson YM, Lion LW, Ghiorse WC, Shuler ML (1999) Production of biogenic Mn oxides by Leptothrix discophora SS-1 in a chemically defined growth medium and evaluation of their Pb adsorption characteristics. Appl Environ Microbial 65 175-180... 

Although plant cell culture is not as cost effective as plant cultivation in the open field, it will become an economical process if higher protein yields can be achieved [58]. The cultivation medium of plants is chemically defined, consisting of a carbon source, minerals, vitamins and phytohormones [69]. Furthermore, it is protein-free and relatively inexpensive. In contrast, animal cells often require complex supplements such as fetal calf serum and/or expensive growth factors, although serum-free cultivation is possible in case of Chinese hamster ovary (CHO) cells [70]. 

The principal method by which aluminium adjuvanted vaccines are prepared entails mixing the antigen in solution with a preformed aluminium phosphate (or hydroxide) precipitate under chemically defined conditions (e.g. of pH). Adsorption of the antigen to the aluminium-based gel ensues, with such preparations being generally termed aluminium-adsorbed vaccines 1 mg of aluminium hydroxide will usually adsorb in the order of 50-200 pg of protein. 

An overview of chemicals defined as chemical weapons. Main... 

Figure 5.43 Phase contrast optical micrographs of typical helical structures in chemically defined lipid concentrate system, (a) Low-pitch helical ribbon with pitch angle i r = 11 2°. (b) High-pitch helical ribbons with pitch angle t t = 54 2°. (c) Intermediate-pitch helical ribbons with pitch angle i r = 40.8 3.8°. Reprinted with permission from Ref. 162. Copyright 1999 by the National Academy of Sciences, U.S.A.

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