The stability of the helix of amylose and amylopectin in DMSO and water solutions

Abstract

The DMSO molecule behaves as a zwitterion having a n electrostatic charge density on its oxygen atom comparable to that of the fluoride ion. Therefore the DMSO anion interacts with water to form an A-region having two water molecules, i.e., a DMSO.2H2O complex a t 66% DMSO. Studies on amylose and amylopectin show that DMSO.2H2O as well as anhydrous DMSO help to stabilize the helix structure of amylose and amylopectin. Because this helix structure is absent in dextran and hydroxyethyl cellulose, their properties in DMSO/water solutions are different from those of starch. The proposed model for the interaction of DMSO or hydrated DMSO with the starch helix shows how these molecules stabilize the helix by interacting with only one hydroxyl group of the C-2 and C'-3 hydrogen bonded hydroxyl groups. The a-helix of amylose and amylopectin is more stable at acid p H values of 90 and 100 yo DMSO solutions than alkaline values because of the formation of the (CH,),S+-OH cation. The hydroxyl group of this cation salts-out the hydrogen bonds just as the case of the hydrated A-regions of Li+ and Na+ cations. Optical rotation studies show that the addition of hydrated Na+ ions also stabilizes the a-helix just as a decrease in apparent pH. The greater stability of the helix in these DMSO solutions predicts that its average segment length will also increase. The decrease in the corrected specific rotation of am)lose in going from water to DMSO solutions is most likely due to an increase in the thermal motion of the amylose rather than any decrease in the helix stability. The DMSO disperses starch because, unlike the hydrogen bonds in the helix, both of the hydrox>l groups involved in intermolecular hydrogen bonds can become complexed to DMSO anions. The lower pK of such intermolecular hydrogen bonds also allows alkali in DMSO to increase the dispersion power of DMSO. Salt (NaCI) decreases the dispersion power of DMSO because of the formation of interchain linkages through the unhydrated C1-ion. The (CH,),S+-OH cation increases the dispersion power of DMSO by favoring the formation of those hydrogen bonds involved in the helix. ZUSAMMENFASSUNG:Das DMSO-Molekul verhalt si-h als Zwitterion und tragt am Sauerstoffatom eine elektrostatische Ladungsdichte, die mit der des Fluoridions vergleichbar ist. Daher reagiert das DMSO-Anion mit Wasser und bildet eine A-Region mit zwei Wassermolekiilen, d. h., einen DMSO ' Stability of the Helix of Amylose and Amylopectin in DMSO and H,O Solutions Helixstruktur von Amylose und Amylopektin stabilisieren. Da diese Helixstruktur in Dextran und in Hydroxyathylcellulose fehlt, sind die Eigenschaften dieser Verbindungen in DMSO/Wasser-Losungen von denen der Sttirke verschieden. Das vorgeschlagene Modell fii die Wechselwirkung von DMSO oder hydratisiertem DMSO mit der Starke-Helix zeigt, in welcher Art diese Molekiile die Helix stabilisieren; es tritt dabei nur eine der durchWasserstofiriicken verbundenen Hydroxylpppen am C-2 und C'-3 in Wechselwirkung.Die a-Helix von Amylose und Amylopektin ist bei s...

The Mechanism for the Synthesis of Starch and Its Relationship to the Newly Proposed Structural Model for DNA. Part I.

“…Addition of salt reduces the viscosity of D N A by decreasing the size of the segment length. The decrease in viscosity goes according to the ability of the added cation to destroy the ionic bond (Mg++ > Li+ > Na+ > K+ > Cs+) and not according to the ability of the cation to reduce the electrostatic charge [44]. And as noted, addition of sufficient salt will destroy the D N A helix as observed by Vold [63].…”

Erratum: “The Effects of Counterion Size on the Equilibrium Properties of Charged Interfaces” [J. Electrochem. Soc., 123, 1325 (1976)]

“…For negatively charged head groups, these properties depend both on the nature of the head group and on the nature of the cation in solution. Examination of the literature on cation effects at negatively charged coIi:oids reveals that cation interaction depends very much on the nature of the anionic group and that more than one interaction sequence for alkali metal cations is observed experimentally (35). Cation interaction with BLNI does not appear to have been studied in any detail (29,30) but electrical properties such as BLM capacitance have been found to depend on the nature and concentration of the electrolyte in the surrounding solution (29).…”

Levans. III. A light‐scattering study of Streptococcus salivarius levan in dimethyl sulfoxide

“…The value observed for levan is of the same magnitude as the d n l d c of amylose and amylopectin in Me2SO-0.066. 16,17 The value of the d n l d c of levan in 0.1 M NaCl MezSO was assumed to be the same as in Me2SO. This is reasonable in view of the observation that the presence of 0.1 M NaCl does not alter the d n l d c of dextran polysaccharide in water17 and its validity is verified by the fact that the Mr of unfractionated levan, LI, was observed to be the same in MezSO as in 0.1 M NaCl in MeZSO, within the experimental error of 5%.…”