Complex dispersions

Dipyridiue-chromium(VI) oxide2 was introduced as an oxidant for the conversion of acid-sensitive alcohols to carbonyl compounds by Poos, Arth, Beyler, and Sarett.3 The complex, dispersed in pyridine, smoothly converts secondary alcohols to ketones, but oxidations of primary alcohols to aldehydes are capricious.4 In 1968, Collins, Hess, and Frank found that anhydrous dipyridine-chromium(VI) oxide is moderately soluble in chlorinated hydrocarbons and chose dichloro-methane as the solvent.5 By this modification, primary and secondary alcohols were oxidized to aldehydes and ketones in yields of 87-98%. Subsequently Dauben, Lorber, and Fullerton showed that dichloro-methane solutions of the complex are also useful for accomplishing allylic oxidations.6... 

The number of the constituent phases of a disperse system can be higher than two. Many commercial multiphase pharmaceutical products cannot be categorized easily and should be classified as complex disperse systems. Examples include various types of multiple emulsions and suspensions in which solid particles are dispersed within an emulsion base. These complexities influence the physicochemical properties of the system, which, in turn, determine the overall characteristics of the dosage forms with which the formulators are concerned. 

Nonionic Cotton Wool, nylon Polyester Direct, vat, azoic Milling acid, metal-complex Disperse... 

To illustrate the problems encountered in supported sensors we present data of two actual systems that we have studied in detail. We focus on oxygen quenching of metal complex dispersed in a silicone rubber and on a hydrophilic silica. 

The cyclodimerization of 1,3-butadiene and isoprene by zinc reduction of an iron nitrosyl complex dispersed in [BMIM]BF4 (and alternatively [BMIMJPFg) showed... 

A similar chiral environment is given by inclusion to cyclodextrins (CDs), cyclic oligosaccharides (3). The outside of the host molecule is hydrophilic and the inside hydrophobic. The diameters of the cavities are approximately 6 (a), 7-8 (j3), and 9-10 A (7), respectively. Reduction of some prochiral ketone-j3-CD complexes with sodium boro-hydride in water gives the alcoholic products in modest ee (Scheme 2) (4). On the other hand, uncomplexed ketones are reduced with a crystalline CD complex of borane-pyridine complex dispersed in water to form the secondary alcohols in up to 90% ee, but in moderate chemical yields. Fair to excellent enantioselection has been achieved in gaseous hydrohalogenation or halogenation of a- or /3-CD complexes of crotonic or methacrylic acid. These reactions may seem attractive but currently require the use of stoichiometric amounts of the host CD molecules. 

Platinum, ruthenium, and mixed platinum-ruthenium species supported on silica Various alumina-supported nickel complexes Dispersion of metallic species during treatments in 02 and H2 at temperatures up to 473 K Reaction of nickel complexes and interaction with support at temperatures... 

Because most foods are complex disperse systems, there are great difficulties in establishing objective criteria for texture measurement. It is also difficult in many cases to relate results obtained by instrumental techniques of measurement to the type of response obtained by sensory panel tests. 

The cases of complex dispersion shown in Fig. 2 can be handled in this way (Yang and Doty, 1957), but a more systematic approach became possible at the same time as complex dispersion was first observed for helical polypeptides (Doty and Yang, 1956). This is the treatment originating in the theoretical work of Moffitt (1956a). 

This form will give complex dispersion, but since the same dispersion constant, X., occurs in both terms, it is the unusual wavelength dependence... 

The simplest way of isolating the dispersion of the helix is a straightforward subtraction of the dispersion of the disordered chain from that of the helical polypeptide. In order to carry out this subtraction, however, both simple and complex dispersion must be cast in the same mathematical form. The relation between these two types of dispersion and the manner in which they may be assimilated to one another will therefore be examined in some detail, for the results will be essential not only to the question at hand but also to a quantitative consideration of the central problem posed at the outset of this review, the dispersion of a mixture of helically arranged and disordered regions. 

The c values of many random coils are in fact close to Xo, 212 m u. If Xc is assumed to equal Xo, then this difference reduces to a two-term equation, thus assimilating the simple dispersion of the disordered chain to the complex dispersion of helical polypeptides. 

This expression, which purports to characterize the helix alone, suggests that it has complex dispersion of the Moffitt type characterized by bo, Xo and a third constant, (of — a ), as well as making a definite rotatory contribution at each wavelength, A[ n ]x . 

The origin of nonzero bo values in these cases is not entirely clear, but it can be formally traced to the difference between Xo and values for the simple dispersion of random coils and hence to a failure of the assumption that Xo equals Xo. If K equals Xo, then the first term of the Moffitt equation will of course be the same as the simple Drude expression known to describe the data and, there being no necessity for a second term, bo will vanish. However, if Xo differs from Xo, the Moffitt plot may still be linear but with a nonvanishing slope. Thus dispersion data that are simple when referred to one dispersion constant may appear complex when plotted against another by a form that sees matters as complex, thereby generating what may be properly suspected as pseudocomplexity. The Moffitt equation was initially intended to describe the complex dispersion of polypeptides for which the simple Drude equation is inadequate, but, as will be seen, its form is also applied to protein dispersions which can be expressed equally well by either formula. It is therefore important to examine more fully the relation of the two equations for cases in which both fit the data. 

If the dispersion of an isolated helix is plotted from a Moflitt equation with the coefficients found by Doty and Lundberg, it shows a point of inflection and a maximum near 400 m/i and becomes progressively levorota-tory below 300 mju, indicating that the contribution of the helical form is indeed the anomalous variety of complex dispersion. The anomalous character of the dispersion of poly-7-benzyl-L-glutamate is especially evident in wi-cresol (Fig. 1), a solvent in which Downie et al. (19.57) suggest that... 

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