Metalated sugar

Considerable studies have been done on the effects of the most important chemical and physical factors involved in the degradation of anthocyanins (temperature, light, pH, SO2, metal, sugar, and oxygen) in model systems and food extracts. In addition, anthocyanin concentrations, its chemical structures, and media compositions are fundamental factors influencing stability. 

It was in 1971, just 100 years later, that there appeared the first paper to discuss the relationship between structure and complex-formation of neutral carbohydrates with cations. Most of the developments during the intervening 100 years were covered in an article by Rendleman in this Series. The present discussion is an updating of Rendleman s chapter, and it covers the renaissance of interest in metal - sugar complexes. The information given by Rendleman will not be repeated here unless it is required for the understanding of subsequent developments. 

This article, therefore, deals with complexes (briefly designated as metal-sugar complexes ) that are formed, in detectable proportions, in aqueous solution from cations and un-ionized carbohydrates. As an excep- tion, we shall briefly discuss (in Section III,5) complexes of cations with aldonic and alduronic acids, because of their structural similarities to metal-sugar complexes. 

N.m.r. studies of the binding of calcium and lanthanum ions to o-lyxose and D-ribose in aqueous solutions show the existence of 1 1 metal-sugar complexes. It has been suggested that the pyranose has a conformation which has ax-eq-ax arrangements of the three consecutive cis-hydroxy-groups. 

To illustrate the specific position of D-fructose in these metal-sugar interactions, the instability constants of several sugars are listed in Table II, and the difference is at least 100 times in favor of the D-fructose com-... 

Solid state C-n.m.r. by the c.p.-m.a.s. technique has been used to study the metal-sugar complexes (1) and (2). Related cop er(II) complexes of Schiff s bases from chitosan were also studied. 

Together, these examples show that the metals, sugars, and microbes in our bodies and food interact with chemical logic. Because the laws of chemistry have been constant over time, even human history has been ordered by chemistry in predictable and understandable patterns. 

We know that functional groups are commonly the major factors controlling the reaction system. The reaction mechanism shown in Fig. 4 suggests that the intermediate ternary complex, nickel/diamine/sugar, governs the epimerization. It indicates that aldoses cannot be epimerized by a nickel ion or ethylenediamine alone. Formation of a ternary complex comprising of metal, sugar, and a diamine derivative is indispensable and a minimum requirement for the epimerization. We have carried out experiments to clarify whether an amine-type base... 

Scheme 11.53 Trans-selective aldol reaction to metal sugar-vinylcarbenes.

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