Chiroptical study and conformation analysis of helical polymers surrounded by helical hydrogen-bonding strands

Sanda, Fumio; Tabei, Junichi; Shiotsuki, Masashi; Masuda, Toshio

doi:10.1016/j.stam.2006.04.013

Cited by 15 publications

(10 citation statements)

References 29 publications

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“…The addition of acetylacetone (acac) reversed the helicity, causing the recovery of the original CD spectra in all cases. [8] AFM also shows multistranded lefthanded helices, in which interchain hydrogen bonds are likely to play a main role [9] (Figure 2 b). The images show two types of structures ( Figure 2): individual and associated chains.…”

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confidence: 99%

“…w1 % + 1488, Figure 2 c). [8] AFM also shows multistranded lefthanded helices, in which interchain hydrogen bonds are likely to play a main role [9] (Figure 2 b). [8] AFM also shows multistranded lefthanded helices, in which interchain hydrogen bonds are likely to play a main role [9] (Figure 2 b).…”

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confidence: 99%

“…This value justifies the right-handedness of the backbone (Figure 2 d) and allows intrachain hydrogen bond formation between the nth and (n + 2)th amide groups (essential to stabilize the helical structure). [8] AFM also shows multistranded lefthanded helices, in which interchain hydrogen bonds are likely to play a main role [9] (Figure 2 b). The AFM images show, after the partial addition of Ba(ClO 4 ) 2 (1.0 equiv), the coexistence of both senses of handedness (see the Supporting Information).…”

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confidence: 99%

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Control of the Helicity of Poly(phenylacetylene)s: From the Conformation of the Pendant to the Chirality of the Backbone

et al. 2010

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Dedicated to Professor Pelayo Camps on the occasion of his 65th birthdaySince the seminal work of Percec and co-workers, [1a] the design, synthesis, and applications of helical polymers with a controlled helix sense has become a field of major interest in recent years. [1b,c, 2] The possibility of controlling and switching the helicity of these polymers by an external agent [2,3] (e.g. temperature, [3a,b] solvent, [3c-e] light [3f,g] ) makes them suitable [4] for several applications. [1b,c, 2] We now present a novel reversible way to control the helicity of poly(phenylacetylene)s with phenylglycine methyl ester pendant groups (poly-(R)-1 and poly-(S)-1; Figure 1). We show herein that the manipulation of the conformational equilibrium of the pendant allows one to choose the right-or left-handed sense of the helix. This phenomenon is achieved by complexation with appropriate metal cations or by solvent polarity effects [2,5] and is based on the characteristics of the conformational equilibrium of the pendants. We performed variable-temperature circular dichroism (CD) experiments in a variety of solvents, atomic force microscopy (AFM) on highly oriented pyrolytic graphite (HOPG), NMR, IR, and Raman spectroscopy, and theoretical calculations (MM (MMFF94), DFT (B3LYP), PCM).(R)-and (S)-Phenylglycine methyl esters were chosen as suitable pendants for the planned studies. Accordingly, poly-(R)-1 and poly-(S)-1 ( Figure 1) were prepared by following known procedures [5a] with [Rh(nbd)Cl] 2 (nbd = 2,5-norbornadiene) as catalyst from monomer 2 and obtained with stereoregular cis-transoid CD spectra of the two polymers after addition of a series of perchlorates of mono-and divalent metal cations (Li + , Na + , Ag + , Mg 2+ , and Ba 2+ ) showed, in all cases, that inversion of the helicity had taken place (opposite CD signs); Ba 2+ gave the strongest response. The addition of acetylacetone (acac) reversed the helicity, causing the recovery of the original CD spectra in all cases. [6] To reveal the mechanism beyond this inversion of helicity, a series of studies were performed: 1) AFM (HOPG) [7] gave important insights into the helicity and morphology of poly-(R)-1 (see the Supporting Information for details). The images show two types of structures (Figure 2): individual and associated chains.The single chains, packed parallel one after another, display a left-handed (counterclockwise) pendant disposition [3b] (Figure 2 a,d) with the periodic oblique strips forming angles close to 458 (i.e. w1 % + 1488, Figure 2 c). This value justifies the right-handedness of the backbone (Figure 2 d) and allows intrachain hydrogen bond formation between the nth and (n + 2)th amide groups (essential to stabilize the helical structure).[8] AFM also shows multistranded lefthanded helices, in which interchain hydrogen bonds are likely to play a main role [9] (Figure 2 b). The AFM images show, after the partial addition of Ba(ClO 4 ) 2 (1.0 equiv), the coexistence of both senses of handedness (see the Supporting Information).

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Control of the Helicity of Poly(phenylacetylene)s: From the Conformation of the Pendant to the Chirality of the Backbone

et al. 2010

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“…Interestingly, earlier computational studies 13,14 had found that overlapping adjacent monomers yield helical conformations. Also protein-like folds are adopted by a host of non-biological polymers 15,16,17,18,19,20,21 (see Appendix).…”

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First-principles design of nanomachines

Banavar

Cieplak

Hoang

et al. 2009

Proc. Natl. Acad. Sci. U.S.A.

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Learning from nature's amazing molecular machines, globular proteins, we present a framework for the predictive design of nanomachines. We show that the crucial ingredients for a chain molecule to behave as a machine are its inherent anisotropy and the coupling between the local Frenet coordinate reference frames of nearby monomers. We demonstrate that, even in the absence of heterogeneity, protein-like behavior is obtained for a simple chain molecule made up of just 30 hard spheres. This chain spontaneously switches between 2 distinct geometries, a single helix and a dual helix, merely because of thermal fluctuations.anisotropy ͉ Frenet frame ͉ globular proteins ͉ molecular switching S ignificant advances in laboratory techniques for tailoring and processing materials at the atomic scale have resulted in nanotechnology becoming an increasingly mature field with great promise. One of the exciting goals of the field is the design of powerful machines, such as functional entities that can switch reversibly between distinct geometries (1-4). Such machines would not only be of great use on their own but also could yield novel emergent behavior upon networking them together (5). The existence of life in its myriad forms provides a proof-of-concept of what one might aspire to accomplish with nanotechnology.Proteins are complex water-soluble chain molecules made up of tens or hundreds of 20 types of naturally occurring amino acids and exhibit conformational switching (6) triggered by influences such as ligand binding. At the nanoscale, thermal fluctuations yield forces with magnitudes comparable with those involved in chemical reactions catalyzed by the proteins (7). How might one design a machine whose functionality is structure based? In its simplest form, we seek an object that takes on just a few distinct geometries in a reproducible manner and is able to switch reversibly between them because of thermal fluctuations. Such a situation would allow external stabilizing influences to favor a given conformation over the others and allow for the development of powerful machines at the nanoscale.A collection of hard spheres constitutes the simplest model of matter and exhibits both a crystalline phase and a fluid phase on varying the density of spheres (8). A linear chain of hard spheres is the simplest connected object with the fewest constraints and, thus, the greatest flexibility (9). Such a chain, at high temperatures or when there are no interactions promoting compaction, would occupy a random-coil phase in which all self-avoiding conformations are equally likely. This situation is not conducive for machine design. In the presence of intersphere interactions promoting compaction and when there are no frustrating influences from the sphere tethering, one would expect a generic compact phase in which, at least locally, the preferred conformation is that of a face-centered cubic (fcc) lattice. It was conjectured by Kepler, and proven more recently by Hales, that the fcc structure provides for optimal packing of unconst...

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“…In the former pattern, it forms between the amide groups at nth and (n + 2)th units, while in the latter one, it forms between the amide groups at nth and (n + 3)th units. The CD signals of these two types of helical patterns appear around 390 and 300 nm, respectively [38]. In the present study, the main chains of Poly(V 1-3 ) could be considered to form a tight helix according to the CD and UV spectra.…”

Section: Conformation Of Poly(v 1-3 ) In Solutionmentioning

confidence: 68%

Synthesis of novel helical poly(N-propargylamides) containing azobenzene pendant groups and effects of substitution groups on azobenzene on the stability of helix

Ren

Zhang

et al. 2015

European Polymer Journal

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Chiroptical study and conformation analysis of helical polymers surrounded by helical hydrogen-bonding strands

Cited by 15 publications

References 29 publications

Control of the Helicity of Poly(phenylacetylene)s: From the Conformation of the Pendant to the Chirality of the Backbone

Control of the Helicity of Poly(phenylacetylene)s: From the Conformation of the Pendant to the Chirality of the Backbone

First-principles design of nanomachines

Synthesis of novel helical poly(N-propargylamides) containing azobenzene pendant groups and effects of substitution groups on azobenzene on the stability of helix

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