Influence of the glycosidic linkage on the solution conformation of glucans

Abstract

In order to gain a better understanding of the influence of β‐glycosidic linkages on the solution conformation of glucans, a comparison was made between the carboxymethyl derivatives of cellulose (CMC, 100% 1,4‐), barley glucan (CMGG, 30 : 70 1,3 : 1,4‐) and curdlan (CMCd, 100% 1,3‐glycosidic), each with an average degree of substitution of DS = 1.0–1.5 and molar masses of 144 000–720 000 g mol–1. For this purpose curdlan and barley glucan were chemically modified, whereas carboxymethylcellulose was available as a commercial sample. Via congo red analysis it was proved for the microbial β‐1,3‐glucans curdlan (unsubstituted) and scleroglucan (one β‐1,6‐linked glucose side group on every third monomer unit) that substituents in glucan derivatives weaken an existing helical structure but that reduction of the molar mass with ultrasound has no influence on the helices. The molecular parameters Mw, Mn, RG, LP and [η] were determined by means of SEC/MALLS measurements and viscometry and the chain mobility was quantified using the 13C NMR relaxation times, T1, of the different polymers. From this it was possible to derive [η]‐Mw relationships. For all samples, the exponent ν of the RG‐MW relationship lay in the range 0.54–0.59, from which it is possible to deduce a coiled solution structure. However, β‐1,3‐glucans occupy 25% less volume than β‐1,4‐glucans and exhibit less chain mobility. Hence β‐1,4‐glucans should be considerably more viscous than β‐1,3‐glucans, as was indeed demonstrated by rheological flow curves of 6% solutions of the carboxymethylglucan derivatives. The zero‐shear viscosity, η0, decreases by 3 decades in the order of CMC > CMGG > CMCd.

Effects of thermal, alkaline and ultrasonic treatments on scleroglucan stability and flow behavior

“…If necessary, at the end of solution preparation, volume was corrected by addition of distilled water, and blend was left aside to reach room temperature (25 • C). In all cases, NaN 3 (0.02%, w/v) was added as preservative, in the presence of NaNO 3 (0.1 M) as electrolyte (Kath, Lange, & Kulicke, 1999).…”

Influence of glycosidic linkage on solution conformational entropy of oligosaccharides: Malto‐ vs. isomalto‐ and cello‐ vs. laminarioligosaccharides

“…Glycosidic linkage, through its influence on carbohydrate flexibility in solution, is known to affect properties such as solution viscosity,1 bacterial selectivity,2 and hydration,3 and has also been shown to play a key role in slowing the spread of diseases such as the H5N1 influenza A virus 4. To date, most studies of the influence of glycosidic linkage on carbohydrate flexibility have employed molecular dynamics (MD) computer modeling, oftentimes in conjunction with nuclear magnetic resonance spectroscopy to analyze mono‐ and disaccharides (e.g., references 3, 5, and 6).…”

Structural stability ofSclerotium rolfsiiATCC 201126 β-glucan with fermentation time: a chemical, infrared spectroscopic and enzymatic approach

“…For the herein described EPSs, chemical analyses led to the confirmation of a β‐1,3‐β‐1,6‐glycosidic structure (Scheme 1, I), where β‐1,6‐glycosidic linkages were esential for solubility. The lack of branching in the Smith‐degraded glucan (Scheme 1, IV) would have enabled the molecules to close to each other in such an extent that extensive H‐bonding took place and aggregated forms started to precipitate (Kath et al. 1999).…”