Blocking Specific Functional Groups

The choice and application of a specific blocking reagent can produce a modified macromolecule with unique and useful properties. Many of the common blocking reagents are discussed 

Weigh out 1.25 mg of the carbodiimide EDC (l-ethyl-3-(3-dimethylamino-propyl)carbodiimide hydrochloride Pierce) into a microfuge tube. 

Add to the tube 7.5 xl of RNA or DNA containing a 5 phosphate group. The concentration of the oligonucleotide should be 7.5-15 nmol or total of about 57-115.5 JLg. Also, immediately add 5 pi of 0.25 M adipic acid dihydrazide or carbohydrazide dissolved in 0.1 M imidazole, pH 6. Because EDC is labile in aqueous solutions, the addition of the oligo and bis-hydrazide/imidazole solutions should occur quickly. 

Mix by vortexing, then place the tube in a microcentrifuge and spin for 5 min at maximal rpm. 

Add an additional 20 ml of 0.1 M imidazole, pH 6. Mix and react for at least 2 h at room temperature. The additional buffer prevents pH drift during the carbodiimide reaction. 

Purify the hydrazide-labeled oligo by gel filtration on Sephadex G-25 using 10 mM sodium phosphate, 0.15 M NaCl, 10 mM EDTA, pH 7.2. The hydrazide-containing probe now may be used to conjugate with a molecule containing an aldehyde reactive group. 

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Plasma polymerization is initiated via the dissociation of molecules caused by varieties of energetic species in the luminous gas phase as described in Chapter 4. It is important to recognize that the reactive species created in the luminous gas phase are not initiators of plasma polymerization. Some species, e.g., free radicals, could be initiators of some monomers that have specific functional groups under special conditions, e.g., in the off period of pulsed glow discharge and in the nonglow zone of a reactor (remote plasma). In most cases, the reactive species created in luminous gas phase are reactive building blocks of LCVD. 

For mesitylene and durene, the kinetics have been followed by specular reflectance spectroscopy [17]. The results indicated that mesitylene produces a fairly stable radical cation that dimerizes. That of durene, however, is less stable and loses a proton to form a benzyl radical, which subsequently leads to a diphenylmethane. The stability of the radical cation increases with increasing charge delocalization, blocking of reactive sites, and stabilization by specific functional groups (phenyl, alkoxy, and amino) [18]. The complex reaction mechanisms of radical cations and methods of their investigation have been reviewed in detail [19a]. Fast-scan cyclovoltammetry gave kinetic evidence for the reversible dimerization of the radical cations of thianthrene and the tetramethoxy derivative of it. Rate constants and enthalpy values are reported for this dimerization [19b]. 

Naturally occurring oxoanions like SO/ and H2P04 at concentrations representative of those encountered in natural waters can inhibit dissolution and weathering reactions. A very low concentration of inhibitors can often be effective, because it may suffice to block the functional groups of solution-active sites (such as the kink sites). The effect of specifically adsorbable cations on the reduction of dissolution (weathering) rates of minerals is important. A case was documented by Grandstaff (32), who showed that thorium, Pb(II),... 

Nonpolar block copolymers with functional polar groups combine the properties of a block copolymer with those of functionahzed homopolymers. End functionalized polymers can self-associate in solution in a manner analogous to low-molecular-weight surfactants, whereas the solid-state properties of the precursor polymer are greatly influenced by the presence of small amounts of polar groups since their aggregation persists in bulk [31]. The interaction of a polymer chain with a surface in solution can be altered and sometimes controlled by the nature and placement of specific functional groups. 

Since a POSS molecule has both defined structure and specific functional groups, it provides the possibility of preparing nanocomposites with controlled structures. There has been considerable effort using POSS cages as building blocks to make controlled structure materials. 

Synthesis of macrocycles needs Ugsons (starting blocks), the coupling of which proceeds through the interaction of specific functional groups. Macrocyclisation occurs through the formation of new bonds of three types carbon-heteroatom, heteroatom-heteroatom and carbon-carbon. 

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