Boric acid, carbohydrate complexation with

Infrared and Raman spectroscopy are in current use fo r elucidating the molecular structures of nucleic acids. The application of infrared spectroscopy to studies of the structure of nucleic acids has been reviewed,135 as well as of Raman spectroscopy.136 It was noted that the assignments are generally based on isotopic substitution, or on comparison of the spectrum of simple molecules that are considered to form a part of the polynucleotide chain to that of the nucleic acid. The vibrational spectra are generally believed to be a good complementary technique in the study of chemical reactions, as in the study76 of carbohydrate complexation with boric acid. In this study, the i.r. data demonstrated that only ribose forms a solid complex with undissociated H3B03, and that the complexes are polymeric. 

Buffers of boric acid are useful in the pH range 8.5 to 10. Borate has the major disadvantage of complex formation with many metabolites, especially carbohydrates. 

The reactions of boric acid solutions with diols have been used for almost a century to examine structural differences among carbohydrates. The complexity of these reactions seems to arise not only from simple structural differences but also from differences in carbohydrate configuration and conformation. The precise nature of these reactions is not clear. Recent studies of the chemistry of polyol-boric acid solutions have clarified some aspects of these reactions that have important bearing on the structure of carbohydrates in solution. Nevertheless, some of the most fundamental questions about the nature of the reaction are still unanswered. 

If it is true that the structural form of D-glucose which reacts with boric acid is the a-D-pyranose form, then that form probably exists in a boat or twist conformation in the complex. This implies that the study of the stability constants of sugar borate ester might give information about the ability of various carbohydrates to form such boat or twist conformations (10, 21). 

Another possibility is the separation of carbohydrates after complexation with boric acid [99], Although such separations are characterized by high selectivities, the kinetics for complex formation are very slow. Thus, low flow rates are required which again result in long analysis times. 

Sihca impregnated with saturated and unsaturated hydrocarbons (squalene, paraffin oil) silicone and plant oils complexing agents (silver ions, boric acid, and borates carbohydrates unsaturated and aromatic compounds) chelating compounds [ethylene diamine tetra-acetic add (EDTA), digitonin] transition metal salt synthetic peptides 18-crown-6 and ammonium sulfate silanized sdica gel impregnated with anionic and cationic surfactants Cross-hnked, polymeric dextran gels (Sephadex)... 

The ionization of boric acid is enhanced in solutions containing carbohydrates (143). This effect is variable, apparently depending upon the individual complexing ability of the sugar. Khym and Zill (144) have used this effect to separate sugars by removing their borate complexes from ion-exchange resins in columns by differential elution with acid developers... 

The reaction of polyhydroxy compounds with boric acid or boronic acids has been used for derivatization and separation of carbohydrates and other compounds containing vicinal diols using different chromatographic and electrophoretic techniques (1,9,69). The mechanism of reaction is a complex between cis diol moieties and borate or boronate groups. It has been demonstrated that it is the borate ion, rather than boric acid, which is complexed by the polyol (70,71). The reaction is pH dependent and the optimum conditions are usually at pH > 8.0. In a pH ranging from 8 to 12, aqueous borate solutions contain tetrahydroxyborate ions and also more highly condensed polyanions such as triborate and tetraborate. Equilibrium between the different species depends on the pH and the total borate concentration. 

By complexing with boric acid, the carbohydrates become negatively charged, thus elute faster from the column by means of ion exclusion and are separated because the complexation capacity with boric acid differs from one carbohydrate to another. An excellent separation between ribose, ribulose and arabinose was achieved with concentrations between 0.1 and 10 gl of discrete sugar (22). 

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