High Molecular Weight Mixed-Linkage Glucan as a Mechanical and Hydration Modulator of Bacterial Cellulose: Characterization by Advanced NMR Spectroscopy.

Bacterial cellulose (BC) consists of a complex three-dimensional organization of ultrafine fibers which provide unique material properties such as softness, biocompatibility, and water-retention ability, of key importance for biomedical applications. However, there is a poor understanding of the molecular features modulating the macroscopic properties of BC gels. We have examined chemically pure BC hydrogels and composites with arabinoxylan (BC-AX), xyloglucan (BC-XG), and high molecular weight mixed-linkage glucan (BC-MLG).

Polymer sequencing by molecular machines: a framework for predicting the resolving power of a sliding contact force spectroscopy sequencing method.

We evaluate an AFM-based single molecule force spectroscopy method for mapping sequences in otherwise difficult to sequence heteropolymers, including glycosylated proteins and glycans. The sliding contact force spectroscopy (SCFS) method exploits a sliding contact made between a nanopore threaded over a polymer axle and an AFM probe. We find that for sliding α- and β-cyclodextrin nanopores over a wide range of hydrophilic monomers, the free energy of sliding is proportional to the sum of two dimensionless, easily calculable parameters representing the relative partitioning of the monomer inside the nanopore or in the aqueous phase, and the friction arising from sliding the nanopore over the monomer.

Supramolecular Amino Acid Based Hydrogels: Probing the Contribution of Additive Molecules using NMR Spectroscopy.

Supramolecular hydrogels are composed of self-assembled solid networks that restrict the flow of water. l-Phenylalanine is the smallest molecule reported to date to form gel networks in water, and it is of particular interest due to its crystalline gel state. Single and multi-component hydrogels of l-phenylalanine are used herein as model materials to develop an NMR-based analytical approach to gain insight into the mechanisms of supramolecular gelation.

Sliding Contact Dynamic Force Spectroscopy Method for Interrogating Slowly Forming Polymer Cross-Links.

Dynamic single-molecule force spectroscopy (SMFS), conducted most commonly using AFM, has become a widespread and valuable tool for understanding the kinetics and thermodynamics of fundamental molecular processes such as ligand-receptor interactions and protein unfolding. Where slowly forming bonds are responsible for the primary characteristics of a material, as is the case in cross-links in some polymer gels, care must be taken to ensure that a fully equilibrated bond has first formed before its rupture can be interpreted. Here we introduce a method, sliding contact force spectroscopy (SCFS), that effectively eliminates the kinetics of bond formation from the measurement of bond rupture.

Single molecule investigation of the onset and minimum size of the calcium-mediated junction zone in alginate.

One of the principal roles of alginate, both natively and in commercial applications, is gelation via Ca(2+)-mediated crosslinks between blocks of guluronic acid. In this work, single molecule measurements were carried out between well-characterised series of nearly monodisperse guluronic acid blocks ('oligoGs') using dynamic force spectroscopy. The measurements provide evidence that for interaction times on the order of tens of milliseconds the maximum crosslink strength is achieved by pairs of oligoGs long enough to allow the coordination of 4Ca(2+) ions, with both shorter and longer oligomers forming weaker links.

Mechanistic and Kinetic Insight into Spontaneous Cocrystallization of Isoniazid and Benzoic Acid.

Solid-state cocrystallization is of contemporary interest because it offers an easy and efficient way to produce cocrystals, which are recognized as prospective pharmaceutical materials. Research explaining solid-state cocrystallization mechanisms is important but still too scarce to give a broad understanding of factors governing and limiting these reactions. Here we report an investigation of the mechanism and kinetics of isoniazid cocrystallization with benzoic acid.

Non-covalent duplex to duplex crosslinking of DNA in solution revealed by single molecule force spectroscopy.

Small molecules that interact with DNA, disrupting the binding of transcription factors or crosslinking DNA into larger structures, have significant potential as cancer therapies and in nanotechnology. Bisintercalators, including natural products such as echinomycin and rationally designed molecules such as the bis-9-aminoacridine-4-carboxamides, are key examples. There is little knowledge of the propensity of these molecules to crosslink duplex DNA.

A rapid screen for molecules that form duplex to duplex crosslinks in DNA.

We describe a gold nanoparticle based assay that can rapidly determine the crosslinking of DNA duplexes by ligands. Such compounds have potential in targeting highly compacted DNA such as that found in the nucleosome.

Lamellar structures of MUC2-rich mucin: a potential role in governing the barrier and lubricating functions of intestinal mucus.

Mucus is a ubiquitous feature of mammalian wet epithelial surfaces, where it lubricates and forms a selective barrier that excludes a range of particulates, including pathogens, while hosting a diverse commensal microflora. The major polymeric component of mucus is mucin, a large glycoprotein formed by several MUC gene products, with MUC2 expression dominating intestinal mucus. A satisfactory answer to the question of how these molecules build a dynamic structure capable of playing such a complex role has yet to be found, as recent reports of distinct layers of chemically identical mucin in the colon and anomalously rapid transport of nanoparticles through mucus have emphasized.

The development of thermal nanoprobe methods as a means of characterizing and mapping plasticizer incorporation into ethylcellulose films.

Purpose: The phase composition and distribution of ethylcellulose (EC) films containing varying amounts of the plasticizer fractionated coconut oil (FCO) were studied using a novel combination of thermal and mapping approaches.

Methods: The thermal and thermomechanical properties of films containing up to 30% FCO were characterized using modulated temperature differential scanning calorimetry (MTDSC) and dynamic mechanical analysis (DMA). Film surfaces were mapped using atomic force microscopy (AFM; topographic and pulsed force modes) and the composition of specific regions identified using nanothermal probes.

A new view of pectin structure revealed by acid hydrolysis and atomic force microscopy.

Individual pectin polymers and complexes, isolated from the pericarp of unripe tomato (Lycopersicon esculentum var. Rutgers), were subjected to a mild acid hydrolysis and visualised and characterised by atomic force microscopy (AFM). The AFM images confirm earlier studies showing that individual pectic polysaccharides often possess long branches.

Mapping the positions of beads on a string: dethreading rotaxanes by molecular force spectroscopy.

The direct manipulation by atomic force microscopy (AFM) of individual macrocycles within a rotaxane offers a potential route to a new sequencing tool for complex macromolecules such as polysaccharides, glycoproteins and nucleic acids. In this paper we demonstrate for the first time that a sliding contact made between a macrocycle, α-cyclodextrin, and its polymer axle by an AFM tip can be used to map the positions of specific groups along the polymer as if they were beads along a string, thereby generating sequence information. We find very good agreement (linear fit with slope = 1.

The isolated MUC5AC gene product from human ocular mucin displays intramolecular conformational heterogeneity.

Atomic force microscopy (AFM) has been used to show that human ocular mucins contain at least three distinct polymer conformations, separable by isopycnic density gradient centrifugation. In this work we have used affinity purification against the anti(mucin peptide core) monoclonal antibody 45M1 to isolate MUC5AC gene products, a major component of human ocular mucins. AFM images confirm that the affinity-purified polymers adopt distinct conformations that coidentify with two of those observed in the parent population, and further reveal that these two different conformations can be present within the same polymer.

Glycopolymer charge density determines conformation in human ocular mucin gene products: an atomic force microscope study.

Atomic force microscopy (AFM) has been applied to the study of heterogeneity in the structure and function of individual biopolymers with complex structures such as glycoproteins, polysaccharides and nucleic acids. In this work we describe experiments which shed light on the heterogeneity of human ocular mucin gene products. By separating samples of native human ocular mucins on a caesium chloride density gradient, at least three populations consisting predominantly of products of the gene MUC5AC can be identified.