Choice of organisms

Organic Chemistry Laboratory Manuals Brooks/Cole is pleased to offer a choice of organic chemistry laboratory manuals catered to fit individual needs. Visit www.thomsonedu.com. Customizable laboratory manuals also can be assembled—contact your Thomson representative to learn more. 

Researchers studying polypeptide and polypeptide hybrid systems have also processed vesicles using two solvents. This method usually involves a common organic solvent that solubilizes both blocks and an aqueous solvent that solublizes only the hydrophilic block. The two solvents can be mixed with the polypeptide or polypeptide hybrid system at the same time or added sequentially. The choice of organic solvent depends heavily upon the properties of the polypeptide material, and commonly used solvents include dimethylformamide (DMF) [46, 59], methanol (MeOH) [49], dimethyl sulfoxide (DMSO) [50, 72], and tetrahydrofuran (THF) [44, 55]. Vesicles are usually formed when the organic solvent is slowly replaced with an aqueous solution via dialysis or removed through evaporation however, some vesicles have been reported to be present in the organic/aqueous mixture [49]. 

Some advice can be formulated for the choice of organic modifier, (i) Acetonitrile as an aprotic solvent cannot interact with residual silanols, whereas the protic methanol can. Thus, when measuring retention factors, methanol is the cosolvent of choice, as it reduces the secondary interactions between the solutes and the free silanol groups, (ii) For the study of the performance of new stationary phases one should use acetonitrile, as the effects of free silanol groups are fuUy expressed [35]. (iri) Acetonitrile with its better elution capacity can be considered as the best organic modifier for Hpophilicity measurements of highly Hpophihc compounds with adequate stationary phases [36]. 

Various criteria can influence the choice of organic solvent that can be used in a biphasic bioreactor degree of solubility of substrates and/or products, inactivation effect, toxicity, flammability, and essentially reactant partition between the phases. Much research has been carried out on this topic [7,8,14,15,33,67]. 

Consumers are also likely to be influenced in their choice of organic products by the knowledge that an increase in organic farming will improve the welfare of farm animals, and that pollution of the rivers and the countryside generally will diminish. 

Care must be taken in the choice of organic solvent. Chloroform should never be used under the basic conditions due to the risk of the formation of isocyanides (see Chapter 7) and the use of carbon disulphide can lead to formation of dithiocarba-mates, e.g. dimethyl A -(ethoxycarbonylmethyl)iminodithiocarbonate is formed (35-39%), as the major product in high purity, in the liquiddiquid two-phase methyl-ation of ethyl glycinate in carbon disulphide [15]. The product is useful as an intermediate in the synthesis of thiazoles [15] and dihydrooxazoles [16]. 

The choice of organic solvent can also have a dramatic effect on selectivity.In contrast to enzyme activity, in the majority of examples reported there appears to be no correlation between solvent physical properties and enantioselectivity. In fact, investigating the effect of various solvents towards a number of lipases, Secundo et al also found that the optimal solvent differed with both enzyme and substrate. A number of theories have been postulated in order to explain these effects in individual cases, but none has any general predictive value. This is somewhat intriguing given that differences in enantioselectivity simply relate to a change in the relative rate of conversion of each enantiomer. 

The choice of organic diluent only affects the distribution constant, not the acid dissociation constant. 

The appropriate choice of organic counterion can result in reduced salt toxicity. There is evidence that salicylates may accumulate with chronic administration, which can be compounded if renal function is below normal (Lasslo et al., 1959). The nature and degree of absorption of tartrate from the human intestine has been questioned (Underhill et al., 1931 Pratt and Swartout, 1933), but the fact that several tartrates are reported to possess cathartic activity argues against substantial absorption from the intestinal tract (Lasslo et al., 1959), which cites Goodman and Gilman. 

At the same time these issues have underscored and publicised the choice of organic foods as a viable alternative. 

Thompson, Gary D., and Julia Kidwell. 1998. Explaining the Choice of Organic Produce Cosmetic Defects, Prices, and Consumer Preferences. American Journal of Agricultural Economics 80(2) 277-87. 

An early concern with the HPLC technique was the use of high pressures to achieve high flow rates of the mobile phase through a column packed with microparticulate silica. Recent improvements in column design and operating procedures, however, allow the purification of proteins at modest pressures (e.g., 500 psi) and flow rates (30-60 ml/h). Since it has been reported that C 3-alkyl chains are compatible with catalytic activity of adsorbed and eluted proteins, but larger alkyl substituents may cause denaturation (26), the use of reversed-phase columns of medium polarity, e.g., —C Hy-phenyl, when combined with a judicious choice of organic modifier and salt concentrations (e.g., isopropanol and phosphate) at pH... 

S.6 Choice of Organic Modifier. Selection of the organic modifier type could be viewed as relatively simple The usual choice is between acetonitrile and methanol (rarely THF). In Chapters 2 and 4 the principal difference in the behavior of methanol and acetonitrile in the column is discussed. In short, methanol shows more predictable influence on the analyte elution, and the logarithm of the retention factor shows linear variation with the concentration of methanol in the mobile phase. Often for the effective separation of complex mixtures of related compounds, this ideal behavior is not a benefit and greater effect of the type and organic concentration on the separation efficiency is required. Acetonitrile as an organic modifier may offer these variations due to the introduction of a dual retention mechanism. The dual retention mechanism was discussed in Chapter 2. 

The choice of organic solvents for interfacial polycondensation has an important effect on the molecular weight of the polymer that is made. Liquids which swell the polymer permit the formation of higher molecular weight products than media which are effectively nonsolvents for the polymer. If the polymer is insoluble in either phase, the migration of acid chloride will be hindered enough to limit the polymer yield and molecular weight. 

Porosity is a desirable characteristic of the particles in many applications of poly(vinyl chloride). If the product is to be used as a dry-blend resin, it is required to soak up substantial quantities of liquid plasticizers and still remain free-flowing. The structure and porosity of PVC granules is affected strongly by the choice of organic suspending agents, which are different types of partially hydrolyzed poly(vinyl alcohol). The required porosity is enhanced also by rapidly... 

---