Carbohydrate-metal base complexes

III. Complexes from the Interaction of Carbohydrates with Metal Bases.237... 

Von Lippman1 reviewed much of the work on carbohydrate complexes published before 1904, and, for such complexes, Vogel and Georg3 compiled a comprehensive table based on work published before 1930. It is important to note that many of the chemical formulas suggested by early investigators for compounds formed by the interaction of carbohydrates with metal bases were mere assumptions, based on insufficient evidence. Similar tendencies exist in the literature even today. 

Bob s research interests and knowledge across chemistry were great. Throughout his career he retained an interest in biomimetic chemistry, specifically the study of metal ion-promoted reactions and reactions of molecules activated by metal ion coordination. His early interests in carbohydrate chemistry inspired him to study metal ion catalysis of both peptide formation and hydrolysis as well as studies in inorganic reaction mechanisms. He was particularly interested in the mechanisms of base-catalyzed hydrolysis within metal complexes and the development of the so-called dissociative conjugate-base (DCB) mechanism for base-catalyzed substitution reactions at inert d6 metal ions such as Co(III). 

In principle, mass spectrometry is not suitable to differentiate enantiomers. However, mass spectrometry is able to distinguish between diastereomers and has been applied to stereochemical problems in different areas of chemistry. In the field of chiral cluster chemistry, mass spectrometry, sometimes in combination with chiral chromatography, has been extensively applied to studies of proton- and metal-bound clusters, self-recognition processes, cyclodextrin and crown ethers inclusion complexes, carbohydrate complexes, and others. Several excellent reviews on this topic are nowadays available. A survey of the most relevant examples will be given in this section. Most of the studies was based on ion abundance analysis, often coupled with MIKE and CID ion fragmentation on MS " and FT-ICR mass spectrometric instruments, using Cl, MALDI, FAB, and ESI, and atmospheric pressure ionization (API) methods. 

The literature on metal complexes of carbohydrates through 1965 has been fully reviewed by Rendleman (I), and we shall therefore only discuss recent work. We shall not discuss the complexes formed with strong bases, such as calcium and barium oxide these are salts in which the sugar acts as a weak acid, losing one or several protons. Nor shall we discuss the complexes formed with anions of oxyacids—e.g., borate, stannate, periodate, etc. ions all these are compounds formed by covalent bonds in alkaline solution. We are concerned only with complexes formed with cations in neutral aqueous solution there is no evidence for the formation of complexes between sugars and simple anions in neutral aqueous solution. (For an example of complex formation between a sugar derivative and chloride ion in chloroform solution, see Reference 3.)... 

The results indicate that most of the carbohydrate residues, such as Gal and GalNAc, weakly interact with Gd " " and Mn. The cyclitols (inositols), on the other hand, form with these metal ions unique complexes that are based on the geometry (stereochemistry) of the multiple hydroxyl groups. Due to stereochemical requirements, a unique, metal-ion binding-site (for Gd ) on gluconamides is also observed, although this interaction is weak. 

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