Pyrimidines electrochemical methods

Several techniques have been developed for the determination of purine and pyrimidine derivatives in food sample and in particular for hypoxanthine quantification biosensors (220-223) and electrochemical methods making use of immobilized enzyme electrode (224 -227), electrochemical enzymatic-based HA methods (228,229), enzyme reaction with fluorimetric detection (230), radioimmunoassay (231), colorimetric methods (232), capillary electrophoresis (233), and TLC (234). Many HPLC methods have also been developed and are reported in Table 4 (235-247) the most recent ones are described next. 

Faraggi M, Klapper MH (1993) Reduction potentials determination of some biochemically important free radicals. Pulse radiolysis and electrochemical methods. J Chim Phys 90 711-744 Faraggi M, Klapper MH (1994) One electron oxidation of guanine and 2 -deoxyguanosine by the azide radical in alkaline solutions. J Chim Phys 91 1062-1069 Faraggi M, Broitman F, Trent JB, Klapper MH (1996) One-electron oxidation reactions of some purine and pyrimidine bases in aqueous solutions. Electrochemical and pulse radiolysis studies. J Phys Chem 100 14751-14761... 

Head of the Department, Adrien Albert (1907-89), was an international authority on biologically-active acridines, which included the antimalarial substances I had studied earlier, and now he was concerned with the purines and pyrimidines of the nucleic acids and other biochemically-important substances. My role was to extend the physico-chemical methods for studying organic structures and reactions from the electrochemical methods I had used in Oxford to the spectroscopic, using the infrared (IR) and ultraviolet (UV) spectrophotometers newly available commercially. 

Compared with other methods, electrochemical ones have a wider range of application, which makes it possible to study the details of the reaction s mechanism. They are suitable for unique syntheses and for the solution of analytical problems. The use of electrochemical methods made it possible to obtain detailed information about the thermodynamics (redox potentials), kinetics (number of electrons, etc.) and mechanism of reactions with the participation of heterocyclic nitrogen compounds (purines, pyrimidines, porphyrines, etc.). [For more details see 2]. Capacity measurements provided important information [see, for example 3] on the adsorption properties of low-molecular and high-molecular bio-logically-active compounds (proteins, DNA, RNA). 

Following these pioneering studies on electrochemical and optical chemical sensors based on functionalized poly thiophenes, many researchers decided to address the detection of small molecules of biomedical interest. For instance, in 1998, Bauerle and Emge described a method to detect the binding of purine or pyrimidine bases by covalently attaching a pyrimidine or triazine unit to polymers 6 or 7 (Scheme 22.1) [29]. Here, the addition of small concentrations of a complementary purine or pyrimidine resulted in an increase in the oxidation potential, and also a decrease in the electroactivity. 

At carbon electrodes, purine bases produce well-defined oxidation peaks within a wide pH range (0-12.5) [142,143]. Purine nucleosides and nucleotides are oxidized at potentials more positive than the parent bases [144]. Signals corresponding to the oxidation of purine bases, nucleotides, and nucleotides have also been obtained using chemically modified carbon electrodes [145,146] (for more details see Sect. 12.4.3). Recently, Cai and coworkers [147] proposed a method for trace A determination using an electrochemically/chemically modified (in alkahne sodium nitrate solution) carbon paste electrode (CPE). Pyrimidines are considered to be electroinactive on carbon electrodes however, Oliveira-Brett and Matysik recently reported [148] specific anodic peaks observed in solutions of T and C bases (but not their nucleosides). Sugar components of nucleotides can be oxidized at copper electrodes [149]. 

In a similar procedure, electrochemically induced Sj l reactions have been employed for the synthesis of aryl uracils from ArX and the uracd anion 61 in DMSO (Eq. 10.22) [54], where the substitution always took place at the carbon leading to C-5-arylated uracils 62. This approach offers a mild method to obtain pyrimidine nucleosides substituted at the 5-position without requiring the preparation of specific reagents ... 

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