DCDPS

The diphenylsulfone group is suppHed to the repeat unit of aU polysulfones by DCDPS the differentiating species between various polysulfones comes from the choice of bisphenol. There are three commercially important polysulfones referred to genericaHy by the common names polysulfone (PSF), polyethersulfone (PES), and polyphenylsulfone (PPSF). The repeat units of these polymers are shown in Table 1. 

The reaction of NaOH with bisphenol A generates water. This water must be thoroughly removed from the system to allow the reaction to be driven to completion, and more importandy, to preclude any residual water in the system from hydrolyzing part of the DCDPS monomer (2). Before the introduction of DCDPS for the polymerization step, all but traces of water must be removed. Failure to do so results in regeneration of NaOH, which rapidly reacts with DCDPS to form the monosodium salt of 4-chloro-4 -hydroxydiphenylsulfone [18995-09-0] (3) (6). 

Table 11 describes the thermal properties of polyether sulfone based on DCDPS and heteroarylenediol. The TgS range from 230 to 315°C and the decomposition temperature is higher than 450°C. Their thermal stability depends on the bisphenol and activated difluoride used in the polymer synthesis (Tables 10 and 11). 

The SnAt reactions were first successfully used in the synthesis of high-molecular-weight poly(arylene etherjs by Johnson et al.4,5 This reaction represents a good example for poly(ether sulfonejs in general, either in laboratory -or industrial-scale preparations. In this procedure, the bisphenol A and sodium hydroxide with an exact mole ratio of 1 2 were dissolved into dimethyl sulfoxide (DMSO)-chlorobenzene. The bisphenol A was converted into disodium bisphenolate A, and water was removed by azeotropic distillation. After the formation of the anhydrous disodium bisphenolate A, an equal molar amount of 4,4,-dichlorodiphenyl sulfone (DCDPS) was added in chlorobenzene under anhydrous conditions and the temperature was increased to 160°C for over 1 h... 

Preparing bisphenolates by using a strong base is often feasible, and the phenolate readily reacts widi activated dihalides (DCDPS or DFDPS) at high temperature to yield high-molecular-weight in a short period of time. 

Unfortunately, the method is only suitable for fluorinated systems such as DFDPS. Using chloro monomers generally affords low molecular weight, because a weak base like KF or CsF is needed and DCDPS is not reactive enough under these reaction conditions. However, the activated dichloro compounds can be successfully polymerized in NMP in the presence of equimolar amounts of K2C0371. 

A few functional dihalides have been prepared. Some of these monomers are tabulated in Table 6.2. The monomers could be nitrated and then reduced to amine-functionalized monomers (Scheme 6.26).203 This approach was used to nitrate DCDPS or bis-4-fluorophenyl phenyl phosphine oxide.204 These monomers were used to copolymerize with some other activated dihalides as the comonomers. 

Robeson and Matzner were the first to report the synthesis of the sulfonation of DCDPS.205 This work makes it possible to synthesize sulfonated poly(arylene ether sulfone) with well-controlled structures. Ueda et al. used this monomer (Scheme 6.27) as a comonomer of DCDPS to react with bisphenol A and high-molecular-weight bisphenol-A-based copolymers with up to 30 mol % sulfonation achieved.206 Biphenol-based copolymers with up to 100 mol % sulfonation were recently reported by Wang et al.207... 

Wang et al. also successfully sulfonated DFDPS (Scheme 6.28).208 Since the DFDPS is more reactive than DCDPS, it is expected that the sulfonated DFDPS... 

Recently, Liu et al. used DCDPS to prepare thiobisphenol S (TBPS) by hydrolysis.258 DTPS can be used to react with DCDPS in a dipolar aprotic solvent with K2C03 as the weak base at 165°C and high molecular weight can be obtained due to higher reactivity of TBPS compared with its BPS counterpart. 

Cytosine Deoxycytidine Deoxyeytidyiic acid Deoxycytidine. monophosphate (dCMP) Deoxycytidine diphosphate (dCDP) Deoxycytidine triphosphate (dCTP)... 

The biosynthetic pathways for the pyrimidine nucleotides (2) are more complicated. The first product, UMP, is phosphorylated first to the diphosphate and then to the triphosphate, UTP. CTP synthase then converts UTP into CTP. Since pyrimidine nucleotides are also reduced to deoxyribonucleotides at the diphosphate level, CTP first has to be hydrolyzed by a phosphatase to yield CDP before dCDP and dCTP can be produced. 

This enzyme [EC 3.6.1.12], also known as dCTP pyrophosphatase, catalyzes the hydrolysis of dCTP to produce dCMP and pyrophosphate (or, diphosphate). The enzyme can also utilize dCDP as a substrate, producing CMP and orthophosphate. 

The enzyme is also responsible for converting cytidine diphosphate (CDP) to 2 -dCDP and uridine diphosphate (UDP) to 2 -dUDP for use in making nucleotides for DNA synthesis. 

The answer is D. Impaired immune function in severe combined immunodeficiency (SCID) is the direct result of blocked DNA synthesis due to inadequate supplies of de-oxyribonucleotides in B and T cells. This effect arises by dATP-induced allosteric inhibition of ribonucleotide reductase, which catalyzes reduction of the 2 -hydroxyl groups on ADP and GDP to form dADP and dCDP. The ultimate cause of many cases of SCID is adenosine deaminase deficiency, which leads to accumulation of dATP and consequent inhibition of ribonucleotide reductase. Although the other enzymes mentioned are also involved in purine nucleotide metabolism, their deficiencies do not lead to SCID. 

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