Scanning force microscopy on monomolecular films of eicosylperfluorotetradecane, F(CF(2))(14)(CH(2))(20)H, on mica, silicon oxide, or water revealed spontaneous organization to well-defined nanoscopic ribbon and spiral or toroidal superstructures. Whether ribbons or nanospirals were formed depended on the solvent from which the molecular monofilm was cast. Ribbons were observed when a hydrocarbon or a perfluorocarbon solvent was used, e.g., decalin or perfluorodecalin. When the compound, however, was deposited from nonselective hexafluoroxylene, the molecules assembled into spirals of defined size. The spirals/toroids transformed to ribbons when exposed either to decalin or perfluorodecalin vapor, and the ribbons transformed to toroids when exposed to hexafluoroxylene vapor. These changes could be observed in situ. Scanning force microscopy yielded an identical height and width for the bands forming the spirals and for the parallel flat ribbons. X-ray reflectivity yielded a height of 3.61 +/- 0.05 nm, again identical for both morphologies. Yet, the length of the extended F(CF(2))(14)(CH(2))(20)H molecule, i.e., 4.65 nm, exceeds the layer thickness obtained from X-ray reflectometry. It is, however, consistent with an arrangement where the fluorinated chains are oriented normal to the surface layer and where the alkyl segments are tilted with a 122 degrees angle between the two segments. Within the plane defined by the tilt, this angle allows a dense packing of the alkyl segments compensating for the larger cross-section of the fluorocarbon segment. The tilt plane defines an "easy" direction along which the monolayer structure can preserve order. In the plane perpendicular to this axis, long-range ordered dense packing of the alkyl chains is not possible. Incommensurable packing can in principle explain the finite and regular width of the ribbons and the stepwise turn in the spirals.
Environment-controlled scanning force microscopy allowed us to study adsorption and desorption of single poly(methacrylate)-graft-poly(n-butyl acrylate) brush molecules on mica in real time. The molecules transform reversibly from a two-dimensional, extended wormlike state to a compact globular state. The dynamics of the conformational transition was sufficiently slow in order to allow its observation by scanning force microscope in real time. The reversible transformation is effected by coadsorption of water or ethanol, the latter introduces the collapse. Adsorbing ethanol and water from the vapour atmosphere results in a change of the surface properties of mica, either favouring adsorption or desorption of the graft polymer. When the extended, tightly adsorbed poly(n-butyl acrylate) brush molecules are exposed to ethanol vapour, the macromolecules swell and contract to form compact globules. Exchanging the ethanol vapour to a humid atmosphere caused the molecules to extend again to a wormlike two-dimensional conformation. Coexistence of collapsed and extended strands within the same molecule indicates a single-molecule first-order transition in agreement with observations on Langmuir films previously reported.
Small angle X-ray scattering (SAXS), an increasingly popular method for structural analysis of biological macromolecules in solution, is often hampered by inherent sample polydispersity. We developed an all-in-one system combining in-line sample component separation with parallel biophysical and SAXS characterization of the separated components. The system coupled to an automated data analysis pipeline provides a novel tool to study difficult samples at the P12 synchrotron beamline (PETRA-3, EMBL/DESY, Hamburg).
The synthesis of 4-N-[3',4',5'-tris(dodecyloxy)benzamido]benzene-4-sulfonic acid (1) and 4'-[3",4",5"-tris(dodecyloxy)benzoyloxy]azobenzene-4-sulfonic acid (2) is described. Pure acid 1 is stable, while 2 can be stored only in solution. Both acids were obtained from their sodium salts and were quantitatively transformed into the pyridinium salts. The phase behavior of these acids, as well as the sulfonates was investigated by differential scanning calorimetry and polarizing optical microscopy. The investigated compounds exhibit columnar mesophases. The formation of columnar superstructures was demonstrated for the sodium sulfonates by scanning force microscopy, gelation experiments, and proton magnetic resonance spectroscopy.
Summary: Comb‐like macromolecules were adsorbed on mica and imaged by scanning force microscopy in real time as they underwent a transition from an extended worm‐like conformation to globuli and vice versa. The conformational transition was effected by coadsorption of ethanol and water molecules. Coadsorption of the small molecules allowed manipulation of the adherence and spreading of the macromolecules, thus effecting the reptation like stretching and collapse of the single molecules.SFM images of three individual PMA‐g‐PnBuA brush molecules on mica 27 min (left, first collapse cycle) and 18 min (right, second collapse cycle) after injection of ethanol into the sample space.imageSFM images of three individual PMA‐g‐PnBuA brush molecules on mica 27 min (left, first collapse cycle) and 18 min (right, second collapse cycle) after injection of ethanol into the sample space.
Summary We describe a technique to visualize and effect in real time motion and conformational transitions of single macromolecules. Two steps are involved. First, scanning force microscopy (SFM) was applied to detect in situ conformational transitions of single polymer molecules adsorbed on a substrate surface. Secondly, these changes were induced by controlled variations of environmental conditions in a microscope environmental chamber. In particular, we have revealed that exposure of a substrate with adsorbed macromolecules to vapours of different nature was able to increase molecular mobility and to stimulate conformational transitions of the polymer chains on the surface. Realization of SFM observation in a variable vapour environment was not as difficult as in liquid media. Variations of the vapour composition affected the oscillation dynamics of the cantilever with the scanning probe only to a small extent, and did not impede continuation of the scanning procedure. In fact, the characteristic times of the observed conformational changes were large enough (minutes to dozens of minutes) for sampling images repeatedly. Although recording of an SFM image was slow and required several minutes, we were able to visualize step‐by‐step the successive stages of the slow conformational transformation of the macromolecules adhering to the substrate, i.e. to investigate a molecular response to the environment changes in real time. Here, we studied the reversible collapse–decollapse transitions of cylindrical poly(methacrylate)‐graft‐poly(n‐butyl acrylate) brush‐like macromolecules exposed to different vapours. Single macromolecules on mica tended to assume a compacted globular conformation when exposed to the vapour of compounds, which due to their amphiphilic nature adsorb on mica and lower the surface energy of the substrate (e.g. alcohols). By contrast, the macromolecules adopted extended two‐dimensional worm‐like conformations in the vapours of compounds having high values of surface tension (such as water). In our opinion, the reason for the observed tendency was a competition in spreading on the substrate surface between the macromolecules and the co‐adsorbed vapour molecules. If the brush‐like macromolecules succeeded in the spreading, they acquired an extended conformation. Otherwise they collapsed to globuli in order to reduce the surface area per macromolecule. Thus, the enhanced mobility of synthetic macromolecules on a substrate observed in a vapour environment in combination with the possibility to manipulate the macromolecular conformation via changes in a vapour phase and the ability to visualize the transitions of the macromolecules individually, provides challenging prospects for SFM studies on the dynamics of single molecules under applied external stimuli.
Scaling exponents m, that describe the correlation between mean square end-to-end distances and contour lengths of macromolecules, were determined by statistical analysis of scanning force micrographs of single linear poly(2-vinylpyridine) and brush-like poly(butanoate-ethyl methacrylate)-graft-poly(n-butyl acrylate) macromolecules adsorbed on mica. Using an atmosphere-controlled scanning force microscope, single adsorbed molecules were collapsed and re-expanded upon being exposed to alcohol and water vapor, respectively. This manipulated collapse-unfolding was used to equilibrate the molecular structure/conformation. The in situ and real-time scanning force microscopy analysis allows the scientist to quantitatively characterize end-to-end distances and contour lengths of the molecules directly on the image and to observe differences in the spreading dynamics for the two types of macromolecules. A distinct difference has been observed between the expanded two-dimensional (2D) conformations of linear and brush-like polymer chains. Whereas a scaling exponent m of 0.73 was found for the expanded 2D conformation of the linear molecules, a m-value of 0.53 was determined for the expanded 2D conformation of the seemingly stiffer Correspondence to: M. Gallyamov
The biopolymer chitosan has shown great potential for a tremendous number of applications despite the fact that typical chitosan preparations are always mixtures of different chemical entities, natural impurities and process-induced impurities. However, chitosan preparations described in the literature or offered on the market are analytically highly undefined. Here we propose a T-SAR (thinking in terms of structure-activity-relationships) guided multi-dimensional analysis of distinct chitosan preparations with the aim a) to obtain the information needed for the production of reproducible chitosan preparations and b) to predict biological effects and technological properties of certain chitosan preparations. First, a physico-chemical description (molecular weight (M-W), polydispersity (M-W/M-N), fraction of acetylation (F-A), pattern of acetylation (P-A), hydrodynamic radius (R-h), intrinsic viscosity ([eta])) of six selected samples was done. Furthermore chitosan properties like solubility, crystallinity, conformation (Mark-Houwink-plot) and impurities of all the chitosan preparations from different origins were determined and biological effects were also analyzed using test systems with two different bacteria (Escherichia coli, Vibrio fischeri). It was found that the presence of HCl enabled the water solubility of chitosan, while chloride-free chitosan was only soluble in acetic acid. The pattern of acetylation P-A showed no impact on this behavior. The analyzed biological effects revealed growth inhibition within 30 minutes for E. coli and a decreased bioluminescence for V. fisheri (IC50 = 0.035 w%). Thus, the strategy to check biological effects within a multi-dimensional analysis kit proved to be effective for detecting general structure-property-relationships of chitosan in relation to its biological effects
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