Tapping mode atomic force microscopy of scleroglucan networks

Abstract

Tapping mode Atomic Force Microscopy (TmAFM) has been used to study the fungal polysaccharide scleroglucan deposited from aqueous solution and dimethyl sulfoxide (DMSO) onto a mica surface. The solutions from which the microscope samples were produced were prepared by first dissolving the solid scleroglucan in 0.1M NaOH, then neutralizing the solution with HCl, followed by dilution to the required concentration in either water or DMSO. It was found that from the aqueous solution described above, scleroglucan forms networks. Based on a comparison of the denatured‐renatured and aqueous solution samples, network formation is due to the imperfect registration between the chains forming the triple helices. The relatively large stiffness of the scleroglucan triple helix is also assumed to contribute to the formation of the extended networks. The triple helix diameter was measured to be 0.92 ± 0.27 nm, which is in the same range as that obtained by other researchers using similar techniques. Denatured scleroglucan, deposited from DMSO onto mica, forms a web‐like layer on top of which there are sphere‐like structures. These morphologies are believed to be due to triple helix denaturation yielding highly flexible single chains in DMSO, which results in coiling and web‐like dense packing of scleroglucan upon deposition onto mica. Most interestingly after addition of water to the samples deposited from DMSO, some of the chains can be renatured into short, stiff rod‐like structures which are similar to the structures observed by other researchers. The imaging data for aqueous solution deposition can be analyzed by plotting maximum end‐to‐end distance versus the perimeter of the networks deposited onto mica. This yields a Flory‐like exponent of 0.67, which is almost similar in value to that obtained by other researchers for linear structures of scleroglucan but less than that expected for a polymer chain following a self‐avoiding walk (v = 0.75) model on a two‐dimensional surface. The fractal dimension that can be used to characterize the networks was determined graphically to be 1.22 ± 0.06. © 1997 John Wiley & Sons, Inc. Biopoly 42: 89–100, 1997

Terraced self assembled nano-structures from laminarin

“…Scleroglucan has been shown to exhibit strand heights of 0.8 ± 0.5 nm for the native triple-helical form [16]. The difference in these numbers is thought to be due to flattening and spreading of the biopolymer on the surface during the drying process [17,18].…”

“…End to end association of the helices must therefore occur when the dilute solutions of laminarin are dried onto mica as the observed helices are considerably longer than the 12.5 nm contour length. Linking of helices has previously been observed in polysaccharide systems [12,17,21,22]. This indicates that the structures are formed from end associated helices or microfibrils.…”

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

“…6 C) or at NaOH concentrations above 0.1 N (data not shown). ␤-(1,3)-glucan microfibrils have been described in the literature as associations of triple helices which held together (Cheeseman & Brown, 1995;Gawronski et al, 1999;McIntire & Brant, 1997;Vuppu, Garcia, & Vernia, 1997). As temperature increased under alkaline environment, disappearance of microfibrils could be related to the increase in single strands proportion and the simultaneous decline or disappearance of triple helical conformation.…”

Network structure of curdlan in DMSO and mixture of DMSO and water

“…Vuppu et al reported on the rod-like structure of ␤-(1,3)(1,6)-glucan, scleroglucan, by tapping mode atomic force microscopy. 8 Previously, we have clarified from the static light scattering (SLS) measurements for curdlan solutions in various concentrations of NaOH that the curdlan molecules associate at 25°C, and the molecular associations dissociate at 60°C. 9 We have reported that a decrease in the concentrations of NaOH promotes the molecular association.…”