Synthesis of an Anionically Chargeable, High-Molar-Mass, Second-Generation Dendronized Polymer and the Observation of Branching by Scanning Force Microscopy

Abstract

An efficient synthesis of a methacrylate-based, second-generation (G2) dendronized macromonomer and its free radical polymerization to the corresponding high-molar-mass G2 dendronized polymer are described. The molar mass is determined by gel permeation chromatography (GPC), light-scattering, and analytical ultracentrifugation and compared with values estimated from a scanning force microscopy (SFM) contour lengths analysis of individualized polymer strands on mica. The polymer carries terminal tert-butyl-protected carboxyl groups, the degree of deprotection of which with trifluoroacetic acid is quantified by NMR spectroscopy using the highest molar mass sample. SFM imaging of both protected (noncharged) and unprotected (charged) dendronized polymers on solid substrates reveals mostly linear chains but also some with main-chain branches. The nature of these branches is investigated and the degree roughly estimated to which they are formed. Finally, a synthetic model experiment is described which sheds some light on the aspect of whether chain transfer, a process that could lead to covalent branching, is of importance in the synthesis of the present dendronized polymers.

A new adaptive grid-size algorithm for the simulation of sedimentation velocity profiles in analytical ultracentrifugation

“…At a given sedimentation coefficient, the boundary will have the velocity dr/dt = sω 2 r, such that the time required for the boundary to arrive at a given radial point r 1 * is on the order of τ∼(r 1 *-m)/sω 2 r* (neglecting the small radial-dependence of the force and velocity). It follows that when the boundary has reached a radius r 1 *, the spread is approximately (9) , with the identity on the right-hand side using the Svedberg relationship [1] between s, D, and the buoyant molar mass M b . Straightforward corrections can be applied to account for the slightly increased extent of diffusion arising from the time lag caused by the acceleration phase of the rotor.…”

“…In sedimentation velocity analytical ultracentrifugation (SV), an optical system allows monitoring the evolution of macromolecular concentration gradients in free solution caused by the application of a gravitational force. In the eight decades following Svedberg's Nobel prize in 1926, it found wide-spread applications and is still an important today tool in many traditional areas of protein biochemistry [1][2][3], synthetic polymer chemistry [4], molecular biology [5], protein interactions [6], as well as more recently emerging fields such as supramolecular chemistry [7], dendritic polymers [8,9], the characterization of nanoparticles for drug or gene delivery and biomaterials [10][11][12][13], amyloid formation of proteins [14], and the development of formulation conditions for protein therapeutics in pharmaceutical industry [15][16][17][18]. In the last decade, the increasing potential for computational data analysis, in particular, the highly detailed mathematical analysis of the sedimentation boundary shape *Address for correspondence Dr. Peter Schuck National Institutes of Health Bldg.…”

Self‐Folding of Charged Single Dendronized Polymers

“…[14] Dendronized polymers (denpols), [15] when turned into amphiphilic polyelectrolytes by charging their peripheral functional groups, exhibit patterns of hydrophobic and hydrophilic regions on the nanometer scale. [16] With cryo-transmission electron microscopy (TEM) double-helices of cationically charged polymers of this sort were discovered, the driving force for which was suggested to be hydrophobic interactions.[17] Additionally, scanning force microscopy (SFM) revealed several structural and mechanical properties of single denpols adsorbed onto solid substrates in air. [16,[18][19][20][21] These observations triggered more systematic studies on supramolecular structure formation with denpols aiming at, first, an understanding of the underlying principles and, second, the rational use of these polymers for the construction of predetermined complex architectures as was impressively shown, for example, by Seeman with DNA.…”

“…[16] With cryo-transmission electron microscopy (TEM) double-helices of cationically charged polymers of this sort were discovered, the driving force for which was suggested to be hydrophobic interactions.…”

“…Furthermore, the effort to decomplex the self-folded duplex through annealing, vacuum drying, and SFM tip manipulation will be described as an additional proof for the proposed duplex structures. The samples of PG2a [16] and PG3a [24] were synthesized as reported. Charged samples were obtained from them by subsequent treatment with trifluoroacetic acid and potassium hydroxide.…”