¹³C‐NMR Spectroscopic Detection of Malto‐oligosaccharide Complexes

Abstract

Fragments of amylose were enzymatically synthesized and purified to α‐(a→4)‐glucans of well defined degress of polymerization by preparative size exclusion chromatography. Maltooligosaccharides from DP 3 to 12 were subjected to 13C‐NMR‐spectroscopy. The addition of iodine as a complexing agent selectively affected the carbon atoms involved in the glycosidic bond. Resonances of C‐1 and C‐4 experienced a dramatic downfield shift. This is interpreted as a change of conformation of the amylose helix. The shift differences can be measured conveniently and be used for calculations of complex stability constants. Maltohexaose and higher saccharides gave strong effects upon complexation, indicating that one helical turn brings about a gain in helical stability. No lower chain‐length limit for the complex‐forming capacity was observed. Even the smallest fragments of amylose showed complexing behaviour.

Complexation between Amylodextrin Oligomers and Selected Pharmaceuticals Measured through Capillary Electrophoresis

“…These experiments confirmed that the end-labels provide the basic force for electromigration, keeping the rest of the labeled molecule unperturbed for interaction with the hydrophobic ligands. If, under the conditions used for CE, the oligosaccharides behave essentially as stretched random coils, then the conformational changes (observed previously through 13 C NMR 9,21,29 ) must be induced by the presence of the model pharmaceuticals.…”

“…Several recent publications − have dealt with the potential of using linear polysaccharides as chiral selectors. It has also been shown that amylose, just like the cyclodextrins, is capable of forming inclusion complexes with numerous small molecules, with possibly the most commonly known and extensively studied example being the iodine−amylose complex. − A wide range of organic molecules exhibit this complexation behavior: free fatty acids, , linear and branched alcohols, dimethyl sulfoxide, sodium myristate, sodium dodecyl sulfate, α-naphthol, organic dyes, etc. It has been reasoned that such complexes utilize an inner hydrophobic cavity, while the hydroxy groups of the sugar rings are pointed outward.…”

“…While the cavity inclusion model of complexation has been generally accepted, the opinions vary as to whether the amylose chain must assume its helical conformation prior to introduction of the guest molecules or the helical shape is actually induced by them. Various methods have been employed to explore the conformation of amylose in aqueous solutions: 13 C NMR, , circular dichroism, viscosity 18 and potentiometric 27 measurements, calorimetry, spectrophotometry, , use of a fluorescent probe, and surface tension measurements . While X-ray data have clearly shown amylose featuring strictly helical forms in its crystalline state, the situation in aqueous solutions is somewhat nebulous.…”

Influence of molecular configuration and conformation on the electromigration of oligosaccharides in narrow bore capillaries

“…This transition to a linear‐like migration time increment per ΔGU is indicated by the excellent least‐squares fit from GU 9 throughout 29 ( r 2 = 0.9995). Such distinctive electromigration behavior of maltooligosaccharides was originated from their tendency to form a full helical turn upon reaching DP 6 . Due to the fluorescent labeling reaction via reductive amination, the glucose at the reducing termini was present in its open form and consequently influenced the unit numbers required to close the first helical turn.…”

Matrix-Assisted Laser Desorption/Ionisation Time-of-Flight Mass Spectrometry. A Comparison of Fragmentation Patterns of Linear Dextran Obtained by In-Source Decay, Post-Source Decay and Collision-Induced Dissociation and the Stability of Linear and Cyclic Glucans Studied by In-Source Decay

“…26 The helical structure of maltodextrins and the cyclic structure of cyclodextrins is why they form inclusion complexes with various pharmaceutical chemicals, a fact confirmed by proton-and carbon-NMR studies. 27,28 The unit structure of a maltodextrin heptasaccharide and corresponding MALDI spectrum ( Figure 6) show that both sodium and potassium cations are present as evidenced by the two adjacent peaks (16 mass units apart) and the corresponding series of peaks with spacings of 162 mass units, which is the mass of an anhydroglucose unit. Peaks that correspond to the B n (Z n )-series of fragments of the [M + Na] + ion were observed together with C n (Y n )-series fragments of [M + Na]…”