Equilibrium Spatial Distribution of Aqueous Pullulan: Small-Angle X-ray Scattering and Realistic Computer Modeling

Conformation of Pullulan in Aqueous Solution Studied by Small-Angle X-Ray Scattering

Small-angle X-ray scattering functions were measured for six pullulan samples with molecular weights ranging from 2.3 × 10⁴ to 7.4 × 10⁵ in 0.05 M aqueous NaCl at 25 °C and fitted by the perturbed wormlike chain model, comprising touched-bead sub-bodies, to obtain wormlike chain parameters. The parameter values determined were consistent with those determined from previously reported dilute solution properties of aqueous pullulan. Because radii of gyration of not only pullulan polymers, but also pullulan oligomers were consistently explained by the touched-bead wormlike chain model perturbed by the excluded volume effect, the pullulan chain takes a local conformation considerably different from the amylose chain, although both polysaccharides are flexible polymers with an approximately same characteristic ratio.

Spectroscopic characterization of bioactive Cu(II) complexes with polysaccharides by modern FTIR microspectroscopy

Investigations of bioactive copper complexes are of great interest for the pharmaceutical industry from the aspect of therapy of hypochromic microcitary anemia and hypocupremia. The structure of bioactive copper complexes with oligosaccharides has not yet been explained in details despite a number of studies. This work represents further development in the research of the complex structure and pharmacobiological activity of the copper complexes. Different copper complexes with dextran and pullulan oligosaccharides, as well as reduced derivatives, have been analyzed by IR spectroscopy. Characterization of the complexes has been performed by using modern spectroscopic techniques: RT-FTIR, LNT-FTIR, D2O-FTIR, ATR-FTIR and FTIR microspectroscopy. Results of FTIR microspectroscopic investigations show that the structural form of complexes and copper content depend considerably on constitution and ligands conformation, degree of crystallinity, polymerization, polydispersity, and linearity of macromolecules. Also, stability of the synthesized complexes, as well as their pharmacological effect, depend on these parameters. Based on IR testing results, structures of the synthesized Cu(II) complexes with polysaccharides were confirmed.

Challenges for the modern analytical ultracentrifuge analysis of polysaccharides

This article reviews some of the recent advances in analytical ultracentrifugation and how these advances have impacted--and can impact--on our understanding of the size, shape through conformation modelling, interactions and charge properties of polysaccharides in solution, particularly when used in combination with other solution techniques and also imaging techniques. Specifically we look at (1) polysaccharide polydispersity and simple shape analysis by sedimentation velocity, and in particular using new approaches such as SEDFIT analysis; (2) polysaccharide molecular-weight analysis by sedimentation equilibrium and MSTAR analysis and how this complements analysis of size exclusion chromatography coupled to multi-angle laser light scattering; (3) polysaccharide conformation analysis using traditional procedures such as the Wales-van Holde ratio, power law or 'scaling' relations, more specialised treatments for rigid cylindrical structures, semi-flexible chains and worm-like coils and complications through draining effects; (4) Analysis of polysaccharide interactions and in particular complex formation phenomena, focusing on interesting applications in the areas of mucoadhesion and sedimentation fingerprinting; and (5) the possibilities for macromolecular charge and charge screening measurement.

Proton fluctuations and water diffusion in dextran chemical hydrogels studied by incoherent elastic and quasielastic neutron scattering

Proton fluctuations reporting local motions of the glycosidic linkages of chemically crosslinked dextran hydrogels with well defined pore-size distributions are studied by static and dynamic neutron-scattering approaches. The dependence of the dynamic behaviour of water on the pore sizes is also discussed.

Dynamics of the Escherichia coli O91 O-Antigen Polysaccharide in Solution as Studied by Carbon-13 NMR Relaxation

The dynamics of the O-antigen part of the lipopolysaccharide from the enterohemorrhagic Escherichia coli O91 has been determined in solution using (13)C NMR relaxation measurements at two magnetic field strengths, 9.4 and 14.1 T, thereby facilitating the testing of several dynamical models. The biological repeating unit, consisting of five sugar residues and substituents, could be determined by spectral analysis of different (1)H,(13)C correlations and corroborated by the relaxation data. The site specifically (13)C-labeled material was shown to have approximately 10 repeating units with a narrow distribution. A model-free analysis of the relaxation data revealed a complex dynamical behavior where the sugar residues could be described by a global correlation time (tau(m) = 5.4 ns), generalized order parameters (S(2) approximately 0.63), and different correlation times for internal motions related to their position in the repeating unit along the polymer (tau(e) approximately 360-520 ps). One of the sugar residues showed, in addition, a chemical exchange contribution. Furthermore, a substituent on another sugar residue was described by two order parameters (S(f)(2) = 0.51 and S(s)(2) = 0.21). The solution dynamics of the polysaccharide are thus described by highly intricate motions, both in amplitude and time scales. These results are of significance in the general description of polysaccharides surrounding bacterial cell surfaces and in the presentation of antigenic epitopes to the immune system of an invaded host.

Determination of average degree of polymerisation and distribution of oligosaccharides in a partially acid-hydrolysed homopolysaccharide: A comparison of four experimental methods applied to mannuronan

The average degree of polymerisation (DP) and distribution of oligosaccharides in partially acid hydrolysed mannuronans were quantitatively evaluated by 1H NMR, electrospray ionisation mass spectrometry (ESI-MS), micellar electrokinetic capillary chromatography with UV detection (MEKC-UV), and high-pressure anion-exchange chromatography with pulsed amperometric detection (HPAEC-PAD). Our investigation shows that 1H NMR, MEKC-UV and, in particular, HPAEC-PAD can be used as quantitative tools to aid the investigation of polysaccharide structure, function and synthesis. For the latter two techniques, especially, this represents a significant new development as it enables calculation of the quantity of individual oligomers of nominal DP by direct analysis of a defined oligomer mixture. Appropriate statistical averages of number and weight distributions were also calculated and found to fit very well to predicted Kuhn distributions that assume random depolymerisation.

Current knowledge on biosynthesis, biological activity, and chemical modification of the exopolysaccharide, pullulan

The article presents an overview of the latest advances in investigations of the biosynthesis, molecular properties, and associated biological activity of pullulan. The literature survey on the pullulan biosynthesis is intended to illustrate how the great variety of environmental conditions as well as variability in strain characteristics influences the metabolic pathways of the pullulan formation and effects structural composition of the biopolymer. Molecular properties of pullulan as alpha-(1-->4)- and alpha-(1-->6)-glucan are discussed in terms of similarities with amylose and dextran structures, and an emphasis is made on the inherent biological activity of pullulan molecules. The author also attempts to summarize the concepts, options, and strategies in chemical modification of the biopolymer and to delineate future prospects in designing new biologically active derivatives.

(13)C nuclear magnetic relaxation study of segmental dynamics of the heteropolysaccharide pullulan in dilute solutions

(13)C spin-lattice relaxation times (T(1)) and nuclear Overhauser enhancements (NOE) were measured as a function of temperature and magnetic field strength for the heteropolysaccharide pullulan in two solvents, water and dimethyl sulfoxide. The relaxation data of the endocyclic ring carbons were successfully interpreted in terms of chain segmental motions by using the bimodal time-correlation function of Dejean de la Batie, Laupretre, and Monnerie. On the basis of the calculated correlation times for segmental motion, the flexibilities of the pullulan chain at a repeat-unit level have been studied and compared with the segmental mobility of the homopolysaccharides amylose and dextran in the same solvents. The internal rotation of the free hydroxymethyl groups about the exocyclic C-5 [bond] C-6 bonds superimposed on segmental motion has been described as a diffusion process of restricted amplitude. The rate and amplitude of the internal rotation of the free hydroxymethyl groups were not affected by the local geometry of the pullulan chain.

Determination of structural peculiarities of dexran, pullulan and gamma-irradiated pullulan by Fourier-transform IR spectroscopy

Deconvoluted IR-absorbance spectra of dextran, pullulan and gamma-irradiated pullulan were analyzed in order to find the most specific spectral peculiarities that allow one to obtain information about the structure and conformation of these macromolecules in solvents that exhibit different influences on the system of intra- and intermolecular interactions. The changes in intensity and width of the IR bands at about 1040, 1020 and, in the case of pullulan, also at 996 cm(-1), were related to changes in conformation and short-range interactions of the polysaccharides. Furthermore, certain bands within the 1200-900 cm(-1) region were considered as a characteristic for the type of glycosidic linkage. The results of the FTIR spectroscopy study allowed one to suggest a predominant cleavage of the alpha-(1-->4) linkages upon the radiation-chemical destruction of pullulan.

Novel approaches to the analysis of polysaccharide structures

Recently, atomic force microscopy has been used to image a variety of polysaccharides and map their distribution on cell surfaces. The mechanical response of polysaccharides to tensile stress has been investigated in single-molecule force spectroscopy experiments. Small-angle X-ray scattering has provided a probe of polysaccharide structure operating in a size range (2-25 nm) that is intermediate between those accessible using nuclear magnetic resonance and light scattering.