High Shape Persistence in Single Polymer Chains Rigidified with Lateral Hydrogen Bonded Networks

Abstract

Exploiting tapping mode-scanning force microscopy (TM-SFM), we characterized single polymeric chains of poly(isocyanodipeptides) (PICs) equilibrated in quasi two-dimensions on the basal plane of mica surfaces. While the average contour length 〈L〉 of an acid-catalyzed PIC bearing L-alanine-D-alanine methyl ester groups was as high as 5.3 µm, the corresponding Ni-catalyzed product exhibited an 〈L〉 of 70 nm. With a newly devised method based on the statistical analysis of the curvature of polymeric chains on a length scale up to about 100 nm from SFM images, we determined their persistence length lp. The measured value of lp ) 76 ( 6 nm for both products, independent of the contour length, indicates that the single polymer molecules are very rigid, i.e., even more rigid than the double-stranded DNA. This rigidity is attributed to the helical structure of the polymer backbone and, in particular, to the hydrogen-bonded networks that are present between the alanine moieties in the side chains.

Polyisocyanides Derived from Tripeptides of Alanine

“…[15] Steric interactions between the amino acid side chains can prevent the formation of stable hydrogen bonds both in the helical prepolymer and in the supramolecular complex, which leads to a drastically decreased reaction rate or even an impairment of the reaction as a whole! Each of the three diastereomeric isocyanotripeptides was also subjected to an acid-initiated polymerization reaction.…”

Acid‐Initiated Stereospecific Polymerization of Isocyanopeptides

“…The molecular weights for the two block copolymers l,d-PIAA/l,d-PIAA and l,d-PIAA/l,l-PIAA were obtained by AFM studies of the molecules deposited on a mica surface. [8] It was observed that the molecular weight for the block homopolymer l,d-PIAA/l,d-PIAA only slightly increased upon addition of the second monomer, a result indicating that mainly new l,d-PIAA polymers are formed. In contrast, for the block copolymer l,d-PIAA/l,l-PIAA, the observed molecular weight was found to almost double; this indicates that the second block grows almost exclusively on from the first.…”

“…The resulting polymer was found to have exactly the same composition and conformation as poly(isocyano-l-alanyl-d-alanine methyl ester) (l,d-PIAA) prepared by using nickel(ii) catalysis. [8] Further studies revealed that this polymerization, which occurs in chloroform, is initiated by free protons in this solvent. In stark contrast, when identical polymerization conditions were applied to the diastereomeric l,l-IAA monomer, no polymerization was observed to take place.…”

Long‐range effects of chirality in aromatic poly(isocyanide)s

“…Chiral poly(isocyanide)s show interesting properties, such as second harmonic generation, 27,28 shape persist- ence, 46 as photonic wires, 47 and chiral memory. 48 Given these precedents, it is useful to use the longrange induction phenomenon to prepare chiral functional polymers in which the functional groups are arranged in pillars around the skeleton.…”