Heterogenization method

Davenport, L. 1997. Fluorescence probes for studying membrane heterogeneity. Methods Enzymol. 278 487-512. 

The present work considers the chemical physical, thermal, and mechanical properties of CPVC obtained with various types of heterogeneous methods and of blends of CPVC with a high chlorine content. In fact, these blends are used widely in industry because their processability is better than that of pure CPVC containing the same amount of chlorine. 

Many of the comments related to C=0 reduction in this section also apply to the homogeneous reductions of C=N bonds, a process for which heterogeneous methods predominate192. This section will therefore concentrate on recent developments and, in particular, on asymmetric transformations. Transfer hydrogenations of C=N bonds by homogeneous catalysts have been reported264. 

Owing to the good solubility of many monomers and initiators in C02, dispersion polymerization is today the most investigated heterogeneous method used for the synthesis of high-molecular-weight C02-insoluble polymers. One central role for the performance of a successful dispersion polymerization is the surfactant. 

Most types of polymerizations can be performed in liquid and supercritical C02. The two major types of polymerizations, chain-growth and step-growth, have been demonstrated in C02. Reviews in the literature (Canelas and DeSimone, 1997b Kendall et al., 1999) have described numerous polymerizations in C02, many of which will not be discussed in this chapter. Since only amorphous or low-melting fluoropolymers and silicones show appreciable solubility at relatively mild temperatures and pressures (T< 100 °C, P<400 bar), only these two classes of polymers can be synthesized by a homogeneous polymerization in C02. All other types of polymers, including semicrystalline fluoropolymers and lipophilic or hydrophilic polymers, must be made by heterogeneous methods, such as precipitation, dispersion, emulsion, and suspension, since the polymers are insoluble in C02 (when T< 100 °C and P<400 bar). Some semicrystalline fluoropolymers and hydrocarbon polymers can be dissolved at more extreme temperatures and pressures and are discussed in Chapter 7 of this book. 

Kao, C., Riidisser, S., and Zheng, M. (2001). A simple and efficient method to transcribe RNAs with reduced 3 heterogeneity. Methods 23, 201—205. 

Possible multiple washing with buffer solution (in heterogeneous methods). 

In the preparation of Zr(OH>4, the homogeneous precipitation method using urea can be applied. Namely, Zr(OH)4 is prepared by hydrolyzing with an aqueous solution of 10% urea at 368-370 K. to precipitate the hydroxide [15]. In the next section the morphology and surface properties are compared with Zr(OH >4 prepared by the usual heterogeneous method using aqueous ammonia. 

Separation-free, homogeneous immunoassay protocols offer several advantages in comparison to heterogeneous methods. Because no separation is involved, the number of procedural steps is decreased, which decreases the time required per assay. Additionally, because the physical transfer step is avoided, potential sample loss related to this step is eliminated. Drugs with low molecular weights (amphetamines, digoxin) are commonly measured by separation-free homogeneous immunoassay protocols. ... 

Nauck M, Marz W, Wieland H. New immunosepara-tion-based homogeneous assay for HDL-cholesterol compared with three homogeneous and two heterogeneous methods for HDL-cholesterol. Clin Chem 1998 44 1443-51. 

Both, homogeneous and heterogeneous methods produce surfaces with a relatively low amount of organic groups, typically about 0.5 mmol of organic groups per gram of modified sfiica. 

Torok, B., Felfoldi, K., Balazsik, K., Bartok, M. (1999) New synthesis of a useful C3 chiral building block by a heterogeneous method enantioselective hydrogenation of pyruvaldehyde dimethyl acetal over cinchona modified Pt-Al203 catalysts, Chem. Commun. 1725-1726. 

We have also shown that copper(I)-modified zeolites can be used as catalysts for the [3+2] cycloaddition of pyrazol-3-one ylides with alkynes. This heterogeneous method offers a mild and efficient access to tetrahydropyrazolo[l,2-a]pyrazol-3-ones with a reasonably wide scope, tolerating various functional groups, and with high regioselectivity. 

In general, homogeneous methods are preferable due to their simplicity and kinetic methods are preferable due to their enabling kinetic features. Until recently, the only mixture-based heterogeneous method with comprehensive kinetic capabilities was SPR. In this chapter, kinetic capillary electrophoresis (KCE) is described as a conceptual platform for separation-based homogeneous methods with comprehensive kinetic capabilities, which will find multiple applications in chemistry, biology, medicine, and drug discovery. 

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