Repeatable/versatile

Because almost any diacid can be leaddy converted to the acid chloride, this reaction is quite versatile and several variations have been developed. In the interfacial polymerization method the reaction occurs at the boundary of two phases one contains a solution of the acid chloride in a water-immiscible solvent and the other is a solution of the diamine in water with an inorganic base and a surfactant (48). In the solution method, only one phase is present, which contains a solution of the diamine and diacid chloride. An organic base is added as an acceptor for the hydrogen chloride produced in the reaction (49). Following any of these methods of preparation, the polymer is exposed to water and the acid chloride end is converted to a carboxyhc acid end. However, it is very difficult to remove all traces of chloride from the polymer, even with repeated washings with a strong base. 

The polymer 21 contains a reactive olefinic linkage in its repeating unit, and can be modified chemically in various manners. In particular, it is expected that the polymer can be used as a versatile precursor for the chemical synthesis of polysaccharide... 

A rapid and versatile covalent assembly technique starting from DEE oligomers has provided the 11.9 nm long hexadecameric poly(triacetylene) rod 20.1481 With its linearly conjugated 16 double and 32 triple bonds spanning in-between the terminal silicon atoms, compound 20 is currently the longest linear, fully Jt-conjugated molecular wire without aromatic repeat units in the backbone. 

Kobe, B., and Deisenhofer, J. (1994). The leucine-rich repeat A versatile binding motif. 

Many polymer conformations can be described in terms of atoms regularly spaced along helices. Methods for analysing the diffraction patterns from helical structures provide a highly versatile technique for the determination of the repeat unit in such polymers. 

Note how the process may be modihed to extend its versatility. Thus, using " C-labelled potassium cyanide with D-erythrose yields a mixture of [l- " C]-D-ribose and [l- " C]-D-arabinose. The sequence could then be repeated on the latter product, using unlabelled KCN, to give [2- " C]-D-glucose. 

Coming back to the molecular structures of SOAz (I), SOAz (II A) and SOAz (IIB), it is noticeable that the conformations of their aziridinyl ligands differ drastically from one allotropic form to the other. In other words, the molecule of SOAz appears to be a versatile molecule with respect to its aziridinyl groups. There is, at the moment, no ready explanation for the adoption of either the one or the other conformation when the synthesis is repeated under exactly the same experimental conditions. However, the SOAz molecule seems to be extremely flexible with regard to the orientation of its wings , even more flexible than that of N3P3AZg 3 15>... 

A polymer is considered to be a copolymer when more than one type of repeat unit is present within the chain. There are a variety of copolymers, depending on the relative placement of the different types of repeat units. These are broadly classified as random, block, graft, and alternating copolymers (see Fig. 2.1 for structural details Cheremisinoff 1997 Ravve 2000 Odian 2004). Among these stmctures, block copolymers have attracted particular attention, because of their versatility to form well-defined supramolecular assemblies. When a block copolymer contains two blocks (hydrophobic and hydrophilic), it is called an amphiphilic diblock copolymer. The immiscibility of the hydrophilic and lipophilic blocks in the polymers provides the ability to form a variety of assemblies, the stmctures and morphologies of which can be controlled by tuning the overall molecular weight and molar ratios of the different blocks (Alexandridis et al. 2000). 

When using the continuous flow method, however, some additional versatility is available in chemisorption measurements. For example, when data is required at an adsorbate pressure of 0.1 atm, a 10 % mixture of adsorbate, mixed with an inert carrier gas, is passed through the apparatus with the sample cooled to a temperature at which no chemisorption can occur. Upon warming the sample to the required temperature, adsorption occurs producing an adsorbate-deficient peak that is calibrated by injecting carrier gas into the flow stream. Equation (15.9) is then used to calculate the quantity adsorbed. This process is repeated for each concentration required. Caution must be exercised to avoid physical adsorption when the sample is cooled to prevent chemisorption. Should this occur, the adsorption peak due to chemisorption can be obscured by the desorption peak of physically bound adsorbate when the sample is heated. 

L-Tetrahydrofolic acid is a versatile intermediate for the manufacture of various folates, e.g., L-leucovorin [19], which is used in cancer therapy, or Metafolin , which is used as a vitamin in functional food. To our knowledge optically pure L-tetrahydrofolic acid is still obtained by repeated fractional crystallization from an equimolar mixture of diastereoisomers formed by nondiastereoselective hydrogenation of folic acid. In order to increase the yield of l-tetrahydrofolic acid and to avoid recrystallization steps, we checked the utility of our ligand for the diastereoselective hydrogenation of folic acid dimethyl ester benzenesulfonate (Scheme 1.4.4). 

The other important aspect of MS/MS is that it can perform any of these types of scans during a particular analysis. In other words, you can perform a precursor ion scan and a neutral loss scan then repeat the entire cycle as frequently as the data sensitivity allows and for as long as the compound is present. This makes for a very versatile and powerful instrument. 

Recently flow coulometry, which uses a column electrode for rapid electrolysis, has become popular [21]. In this method, as shown in Fig. 5.34, the cell has a columnar working electrode that is filled with a carbon fiber or carbon powder and the solution of the supporting electrolyte flows through it. If an analyte is injected from the sample inlet, it enters the column and is quantitatively electrolyzed during its stay in the column. From the peak that appears in the current-time curve, the quantity of electricity is measured to determine the analyte. Because the electrolysis in the column electrode is complete in less than 1 s, this method is convenient for repeated measurements and is often used in coulometric detection in liquid chromatography and flow injection analyses. Besides its use in flow coulometry, the column electrode is very versatile. This versatility can be expanded even more by connecting two (or more) of the column electrodes in series or in parallel. The column electrodes are used in a variety of ways in non-aqueous solutions, as described in Chapter 9. 

In addition to sulfone, phenyl units, and ether moieties, the main backbone of polysulfones can contain a number of other connecting units. The most notable such connecting group is the isopropylidene linkage which is part of the repeat unit of the well-known bisphenol A-based polysulfone. It is difficult to clearly describe the chemical makeup of polysulfones without reference to the chemistry used to synthesize them. There are several routes for the synthesis of polysulfones, but the one which has proved to be most practical and versatile over the years is by aromatic nucleophilic substitution. This polycondensation route is based on reaction of essentially equimolar quantities of 4,4,-dihalodiphenylsulfone (usually dichlorodiphenylsulfone (DCDPS)) with a bisphenol in the presence of base thereby forming the aromatic ether bonds and eliminating an alkali salt as a by-product. This route is employed almost exclusively for the manufacture of polysulfones on a commercial scale. 

Native HNLs from bitter almonds (Prunus amygdalus), cassava (Manihot escu-lenta), millet (Sorghum bicolor), and flax (Linum usitatissimum) were repeatedly used in the synthesis of chiral cyanohydrins [39, 41, 197]. Cyanohydrins are versatile building blocks in natural product synthesis, giving organic chemists the possibility of introducing all kinds of functional groups (Fig. 38) [198]. 

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