Helical Structure Of Poly Research Articles

Single-molecule mechanics of synthetic aromatic amide helices: Ultrafast and robust non-dissipative winding

Summary Because of proteins’ many degrees of conformational freedom, programming protein folding dynamics, overall elasticity, and motor functions remains an elusive objective. Instead, smaller and simpler objects, such as synthetic foldamers, may be amenable to design. However, little is known about their mechanical performance. Here, we show that reducing molecular size may not compromise mechanical properties. We report that helical aromatic oligoamides as small as 1 nm possess outstanding elasticity and outperform most natural helices. Using single-molecule force spectroscopy, we characterize their folding trajectories and intermediate states. We show that they cooperatively and reversibly unwind at high forces. They extend up to 3.8 times their original length and rewind against considerable forces on a timescale of 10 μs. Pulling and relaxing cycles follow the same trace up to a very high loading rate, indicating that the mechanical energy accumulated during the stretching does not dissipate and is immediately reusable.

Long-Range Ordered Water Correlations between A–T/C–G Nucleotides

Summary The interactions between complementary base pairs are crucial to the helical duplex structure of DNA. Although base-base interactions have been widely reported, the study of long-range interactions in the base-pairing processes is still a major challenge in this field. Here, we first study the long-range interactions between the base pairs by atomic force microscopy-based single-molecule force spectroscopy (SMFS). The SMFS results of A–T/C–G imply that there are weak long-range interactions between them, which have a range of 15–25 nm. Raman spectroscopy results imply that these weak interactions can be attributed to multiplex hydrogen bond interaction of ordered water structure between A–T/C–G nucleotides. In addition, the theoretical calculations deduce that the ideal structure of these water molecules exhibits a specific helical structure. Our findings might open up a new understanding of biological assembly processes and provide helpful strategies for bio-nanotechnology.

Recyclable helical poly(phenylacetylene)‐supported catalyst for asymmetric aldol reaction in aqueous media

ABSTRACTA novel one‐handed helical poly(phenylacetylene) bearing L‐hydroxyproline pendants (poly(PA‐P)) was synthesized as an eco‐friendly polymer‐supported catalyst for asymmetric reactions. The helical poly(PA‐P) catalyzed the asymmetric aldol reactions of cyclohexanone with p‐nitrobenzaldehyde, and showed good recyclability and higher enantiomeric excess (ee) in aqueous medias than that in organic medias. The one‐handed helicity of poly(PA‐P) was clearly affected by the water content in the aqueous media. The helical poly(PA‐P) showed the higher enantioselectivity (ee = 99%) than its monomer PA‐P (ee = 54%) in THF/H2O (H2O vol % = 25.0 vol %). After the one‐handed helical structure of poly(PA‐P) was destroyed by grinding treatment, the ee of the reaction clearly decreased from 99 to 49%. These indicate that the one‐handed helical structure of poly(PA‐P) played an important role in the high enantioselectivity of the asymmetric aldol reactions in the aqueous media. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1024–1031

Cis-Cisoid Helical Structures of Poly(3,5-disubstituted phenylacetylene)s Stabilized by Intramolecular n → π* Interactions

A pair of enantiomeric cis-poly(phenylacetylene)s (PPAs) substituted at the meta-positions of pendant phenyl rings by an achiral methoxycarbonyl group and a chiral 1-methylpropyloxycarbonyl group (i.e., sP-Me-C4/rP-Me-C4) as well as two cis-PPAs bearing either just a methoxycarbonyl (i.e., m-aP-Me) or a 1-methylpropyloxycarbonyl (i.e., m-sP-C4) meta substituent were synthesized under the catalysis of [Rh(nbd)Cl]2 (nbd = norbornadiene). Various techniques including 1H NMR, FTIR, Raman, UV–vis, CD, DSC, STM, DLS/SLS, and computer calculation were applied to characterize the helical structures of these polymers in both solution and solid states. sP-Me-C4/rP-Me-C4 adopted contracted cis-cisoid helical conformations in THF, toluene, CH2Cl2, and ClCH2CH2Cl but cis-transoid ones in CHCl3 and Cl2CHCHCl2. The cis-cisoid helices were considered to be stabilized by the existence of six n → π* interaction bands along the polyene backbones between vicinal carbonyl groups. Such interactions were insensitive to the diel...

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

A series of novel N-propargylamides bearing substituted azobenzene pendant groups (RC6H4NNC6H4CONHCH(CH3)CONHCH2CCH, R=CH3CH2N(CH2)2OOC(CH2)3CH3 (V1), R=CH3CH2N(CH2)2OOCCH2NHCOCH3 (V2), R=H (V3)) were synthesized and polymerized with [Rh(nbd)Cl]2 as a catalyst to obtain the corresponding polymers (Poly(V1–3)). The azobenzene chromophores in the side chains of Poly(V1,2) contained bulky electron-donating substituents, while the azobenzene in Poly(V3) did not bear this kind of substituent. The introduction of substituted azobenzene chromophores into the side chains of poly(N-propargylamides) was found to increase the hydrogen bond strength, steric repulsion and electrostatic interactions between the neighboring side chains. These factors worked together to improve the helical stability of poly(N-propargylamides). The solubility of these poly(N-propargylamides) was increased by introducing substituents into the azobenzene chromophores. CD and UV–vis spectra showed that all the poly(N-propargylamides) took the helical structures with predominantly one-handed screw sense, which were tight helices. Furthermore, the unsubstituted azobenzene groups in the side chains of Poly(V3) also arranged to form the helical conformation. The helical structures of Poly(V1–3) remained stable at various temperatures (5–60°C). Poly(V1,2) exhibited good helicity in polar solvent, which indicated that the bulky substituents, electrostatic and steric repulsion between the adjacent side chains lessened the effect of polar solvent on the hydrogen bonding. The main chains of Poly(V1,3) still kept helical sense after the isomerization of trans-azobenzene to the cis form upon UV irradiation. The helical array of azobenzene side chains in Poly(V3) experienced reversible arrangement–disarrangement upon photoirradiation.

Synthesis and helical structures of poly(ω-alkynamide)s having chiral side chains: effect of solvent on their screw-sense inversion.

New ω-alkynamides, (S)-HC≡CCH2CONHCH2CH(CH3)CH2CH3 (1) and (S)-HC≡CCH2CH2CONHCH(CH3)CH2CH2CH2CH2CH3 (2) were synthesized and polymerized with a rhodium catalyst in CHCl3 to obtain cis-stereoregular poly(ω-alkynamide)s (poly(1) and poly(2)). Polarimetric, CD, and IR spectroscopic studies revealed that in solution the polymers adopted predominantly one-handed helical structures stabilized by intramolecular hydrogen bonds between the pendent amide groups. This behavior was similar to that of the corresponding poly(N-alkynylamide) counterparts (poly(3) and poly(4)) reported previously, whereas the helical senses were opposite to each other. The helical structures of the poly(ω-alkynamide)s were stable upon heating similar to those of the poly(N-alkynylamide)s, but the solvent response was completely different. An increase in MeOH content in CHCl3/MeOH resulted in inversion of the predominant screw-sense for poly(1) and poly(2). Conversely, poly(3) was transformed into a random coil, and poly(4) maintained the predominant screw-sense irrespective of MeOH content. The solvent dependence of predominant screw-sense for poly(1) and poly(2) was reasonably explained by molecular orbital studies using the conductor-like screening model (COSMO).

Copolymerization of chiral propargylethers and N-propargylamide and conformational control of the copolymers

The novel acetylene monomers, L-proline-derived chiral propargylether (PA, PC, PL, and PM) were synthesized. The copolymerization of L-proline-based propargylether having amide group (PR) with N-(tert-butoxycarbonyl)-L-alanine-N-propargylamide (LA) by different unit ratio and the control of conformation of poly(LA-co-PR) were discussed. The copolymerization catalyzed by (nbd)Rh+[η 6-C6H5B−(C6H5)3] afforded copolymers with medium M n. The specific rotation of poly(LA88-co-PA12), poly(LA88-co-PC12), and poly(LA88-co-PL12) was 250°, 967°, and 1117°, respectively. The specific rotation of poly(LA-co-PC) ranged from −967° to −167°. Conformation change of poly(LA88-co-PR12) and poly(LA-co-PC) in different solvents was studied and it was found that the intramolecular hydrogen bonding in the side chain significantly contribute to the stabilization of helical conformation of the copolymers and that solvent polarity strongly affected the stability of helical conformation. The helical structure of poly(LA88-co-PL12) was affected by temperature change.

Synthesis and Helical Structure of Poly(1‐methylpropargyl ester)s with Various Side Chains

Optically active 1-methylpropargyl esters bearing various substituents were polymerized with [(nbd)Rh](+)[eta(6)-C(6)H(5)B(C(6)H(5))(3)](-) (nbd=norbornadiene) as a catalyst to afford the corresponding poly(1-methylpropargyl ester)s with moderate molecular weights in good yields. The polymers have a cis-stereoregular structure, which was determined by (1)H NMR spectroscopy. Large optical rotations and clear CD signals demonstrated that all these polymers take on a helical structure with a predominantly one-handed screw sense. The polymers exhibited large viscosity indices in the range 1.14-1.75. Chiral amplification was observed in R/S copolymerization. Conformational analysis revealed that the polymers form a tightly twisted helical structure with a dihedral angle of 70 degrees at the single bond of the main chain.

Structure−Property Relationships of Polyselenoethers [−(CH2)ySe−]x (y = 1, 2, and 3) and Related Polyethers and Polysulfides

Conformational characteristics, solution (melt) properties, and thermal properties of polyselenoethers [-(CH2)ySe-]x ( y=1, 2, and 3) have been revealed by the rotational isomeric state analysis of ab initio molecular orbital calculations and (1)H and (13)C NMR experiments for monomeric model compounds and compared with those of typical polyethers and polysulfides. The comparative results are summarized here as correlations in conformation among model compounds and unperturbed and crystalline states of the polymers, and thermal properties of the polymer crystals are discussed in terms of intramolecular and intermolecular interactions. By ab initio molecular orbital calculations under periodic boundary conditions, helical structures of poly(methylene oxide), poly(methylene sulfide), and poly(methylene selenide), and the crystal structure of poly(ethylene selenide) have been optimized, and their electronic structures have been predicted. A systematic methodology to predict and characterize up to higher-order structures and various physical properties of polymers incorporated in different phases has been attempted to be developed.

Synthesis and Helical Structure of Poly(N-butynylamide)s Having Various Side Chains, Where the Helix Is Highly Affected by the Methyl Branch and the Lactone Moiety

N-Butynylamides, (S)-HC⋮CCH2CH2NHCOCH2CH(CH3)CH2CH3 (1), (R)-HC⋮CCH2CH2NHCOCH2CH(CH3)CH2CH2CH2CH(CH3)2 (2), (S)-HC⋮CCH2CH2NHCOCH(CH3)CH2CH2CH2CH2CH2CH3 (3), (1S)-HC⋮CCH2CH2NHCOC9H13O2 (4, COC9H13O2...

Helical polyacetylenes carrying 2,2,6,6‐tetramethyl‐1‐piperidinyloxy and 2,2,5,5‐tetramethyl‐1‐pyrrolidinyloxy moieties: Their synthesis, properties, and function

Abstract2,2,6,6‐Tetramethyl‐1‐piperidinyloxy (TEMPO)‐ and 2,2,5,5‐tetramethyl‐1‐pyrrolidinyloxy (PROXYL)‐containing (R)‐1‐methylpropargyl TEMPO‐4‐carboxylate (1), (R)‐1‐methylpropargyl PROXYL‐3‐carboxylate (2), (rac)‐1‐methylpropargyl PROXYL‐3‐carboxylate (3), (S)‐1‐propargylcarbamoylethyl TEMPO‐4‐carboxylate (4), and (S)‐1‐propargyloxycarbonylethyl TEMPO‐4‐carboxylate (5) (TEMPO, PROXYL) were polymerized to afford novel polymers containing the TEMPO and PROXYL radicals at high densities. Monomers 1–3 and 5 provided polymers with moderate number‐average molecular weights of 8200–140,900 in 49–97% yields in the presence of (nbd)Rh+[η6‐C6H5B−(C6H5)3], whereas 4 gave no polymer with this catalyst but gave polymers possessing low Mn (3800–7500) in 56–61% yield with [(nbd)RhCl]2‐Et3N. Poly(1), poly(2), and poly(4) took a helical structure with predominantly one‐handed screw sense in THF and CHCl3 as well as in film state. The helical structure of poly(1) and poly(2) was stable upon heating and addition of MeOH, whereas poly(4) was responsive to heat and solvents. All of the free radical‐containing polymers displayed the reversible charge/discharge processes, whose capacities were in a range of 43.2–112 A h/kg. In particular, the capacities of poly(2)–poly(5)‐based cells reached about 90–100% of the theoretical values regardless of the secondary structure of the polymer, helix and random. Poly(1), poly(2), and poly(4) taking a helical structure exhibited better capacity tolerance towards the increase of current density than nonhelical poly(3) and poly(5) did. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5431–5445, 2007

Homo- and R/S-copolymerizations of chiral methylpropargyl esters carrying pyrene moieties, and optical properties of the formed polymers

Pyrene-functionalized chiral methylpropargyl esters, (R)-3-butyn-2-yl-1-pyrenebutyrate [(R)-1], (S)-3-butyn-2-yl-1-pyrenebutyrate [(S)-1], (R)-3-butyn-2-yl-1-pyrenecarboxylate [(R)-2], and 3-butyn-2-yl-1-pyrenecarboxylate [(R,S)-2] were polymerized with (nbd)Rh+[η6-C6H5B−(C6H5)3] to obtain the corresponding polymers with moderate molecular weights (Mn: 10 500–66 500) in good yields (82–97%). All the polymers were soluble in CHCl3, CH2Cl2, and THF. The polarimetric and CD spectroscopic data indicated that poly[(R)-1], poly[(S)-1], and poly[(R)-2] existed in a helical structure with predominantly one-handed screw sense in these solvents. The helical structure of poly[(R)-1] and poly[(S)-1] was stable upon heating and addition of MeOH, while that of poly[(R)-2] changed upon MeOH addition. The copolymerization of (R)-1 with (S)-1 was also conducted to obtain the copolymers satisfactorily. Poly[(R)-1], poly[(S)-1], and poly[(R)-2] emitted fluorescence smaller than the corresponding racemic copolymers. The fluorescence intensity was tuned by the addition of MeOH to THF solutions of the polymers.

Synthesis and electro-optical properties of helical polyacetylenes carrying carbazole and triphenylamine moieties

Novel chiral acetylene monomers bearing carbazole and triphenylamine groups, namely, ( S)-3-butyn-2-yl 2-(9-carbazolyl)ethyl carbonate ( 1) and ( S)-3-butyn-2-yl 4-(diphenylamino)benzoate ( 2) were synthesized, and polymerized with Rh +(nbd)[η 6-C 6H 5B −(C 6H 5) 3] catalyst to give the corresponding polymers with moderate molecular weights ( M n 13.0 × 10 3 and 15.5 × 10 3) in good yields (86% and 88%). CD spectroscopic studies revealed that poly( 1) and poly( 2) took predominantly one-handed helical structure in CHCl 3. The helical structures of poly( 1) and poly( 2) were very stable against heating and addition of MeOH. The solution of poly( 1) and poly( 2) emitted fluorescence in 0.52% and 7.2% quantum yields, which were lower than those of the corresponding monomers 1 and 2 (22.5% and 76.5%). The cyclic voltammograms of the polymers indicated that the oxidation potentials of the polymers were lower than those of the monomers. The polymers showed electrochromism and changed the color from pale yellow to pale blue by application of voltage, presumably caused by the formation of polaron at the carbazole and triphenylamine moieties. The onset temperatures of weight loss of poly( 1) and poly( 2) were 225 and 270 °C under air.

Synthesis and Properties of Helical Polyacetylenes Carrying Cholesteryl Moieties

AbstractNovel acetylene monomers containing cholesteryl groups, N‐cholesteryloxycarbonyl‐2‐ethynylcarbazole (1) and cholesteryl N‐propargylcarbamate (2) were synthesized and polymerized with an Rh catalyst to give the corresponding polymers [poly(1) and poly(2)] with $\overline M _{\rm n} $ of 22 600 and 26 600 in 56% and 95% yields, respectively. CD spectroscopic studies revealed that poly(1) and poly(2) took predominantly one‐handed helical structure in CHCl3, THF, and toluene. The helical structure of poly(1) remarkably changed upon temperature, while that of poly(2) was stable against heating. The helix of poly(2) was relatively stable to the addition of MeOH, but largely affected by the composition of CHCl3 and toluene. Poly(1) exhibited no clear oxidation peak, but a clear reduction peak at 0.65 V in cyclic voltammetry. Poly(1) and poly(2) showed liquid crystalline properties.magnified image

Synthesis and properties of helical polyacetylenes containing carbazole

Novel acetylene monomers containing carbazole with chiral menthyl and bornyl groups, 9-(1 R,2 S,5 R)-menthyloxycarbonyl-2-ethynylcarbazole ( 1), 9-(1 S,2 R,5 S)-menthyloxycarbonyl-2-ethynylcarbazole ( 2), 9-(1 R,2 S,5 R)-menthyloxycarbonyl-3-ethynylcarbazole ( 3) and 9-(1 S)-bornyloxycarbonyl-2-ethynylcarbazole ( 4) were synthesized and polymerized with a Rh catalyst to give the corresponding polymers [poly( 1)–poly( 4)] with moderate M n value of (11.5–92.2) × 10 3 in good yields (77–89%). CD spectroscopic studies revealed that poly( 1), poly( 2) and poly( 4) took predominantly one-handed helical structure in CHCl 3, THF, toluene, and CH 2Cl 2, while poly( 3) did not. Addition of methanol to CHCl 3 solutions of poly( 1) and poly( 2) resulted in the formation of aggregates showing smaller CD signals at 275 and 320 nm. The helical structure of poly( 1) and poly( 2) was very stable against heating. The polymers emitted fluorescence in 0.40–2.90% quantum yields. Poly( 4) exhibited an obvious oxidation peak at 1.10 V. The polymers were thermally stable below 300 °C.

Design of Helical Poly(N-propargylamides) that Switch the Helix Sense with Thermal Stimuli

Copolymerization of chiral N-propargylamides, (S)-N-propargyl-2-methyldecanamide (1), and either (R)-N-propargyl-3,7-dimethyloctanamide (2) or (1S)-N-propargyl-3-oxo-2-oxa-4,7,7-trimethyl-2-bicyclo[2.2.1]heptan-1-acetamide (3) were conducted with (nbd)Rh + [η 6 -C 6 H 5 B - (C 6 H 5 ) 3 ] catalyst to obtain the corresponding copolymers with moderate molecular weights (M n = 19 000-56 000) in good yields. The CD spectroscopic study showed that these two types of copolymers with various compositions formed helical structure and underwent a helix-helix transition driven by temperature change. In all cases, the optical activity became zero at certain temperatures, which depended on copolymer composition. The temperature dependence of helix sense of the copolymers allowed the determination of thermodynamic parameters. The helical structure of poly(1-co-2), which has long alkyl pendants, was affected by external stimuli more than poly(1-co-3) was. The thermodynamic parameters of helix inversion were also influenced by solvent polarity.

Synthesis and Structure of Poly(N-propargylbenzamides) Bearing Chiral Ester Groups

N-Propargylbenzamides having chiral ester groups on the benzene ring, 1−6, were polymerized with (nbd)Rh+[η6-C6H5B-(C6H5)3] to afford soluble polymers with moderate molecular weights (Mn = 34 000−100 000) in good yield. The 1H NMR spectra demonstrated that the polymers have stereoregular structures (cis = 91−100%). The influence of the substitution position for the chiral ester group on the secondary structure was examined. From the comparison of the CD effects of poly(1)−poly(3), the meta-substituted polymer was proven to possess a one-handed helical conformation. When the chiral center was closer to the benzene ring or chiral ester group was bulkier, the polymers showed more intense chiroptical properties. A variable temperature CD spectroscopic study showed that the helical structure of poly(2) and poly(6) was thermally stable. However, the CD spectra of poly(4) and poly(5) were inverted in sign on temperature change in chloroform or toluene, meaning that the helix inversion took place. The temperature of helix inversion could be controlled by copolymerizing with N-propargylbenzamide (7).

A study on the effect of Cu2+ ions on the stability of triple helix poly[(riboadenylic acid):2 poly(riboinosinic acid)

AbstractThe effect of Cu2+ on the stability of the triple‐stranded helical structure of poly[(riboadenylic acid): 2 poly(riboinosinic acid)] poly(A : 21) was studied by means of circular dichroism spectroscopy and ultraviolet spectroscopy. The experimental results show that Cu2+ induces the hyperchromicity of poly(A : 2I) and causes the melting temperature Tm of poly(A : 2I) to decrease with increasing Cu2+ concentration. At the ratio of the concentration of Cu2+ to that of phosphate in poly(A : 2I), rt = 0, poly(A : 2I) is stable, is stable, at rt = 0.27, poly(A : 2I) decays in poly(A) and 2 poly(I), and at rt = 1.6, there is a racemate.

Study on the reaction of triple helix poly(A:2I) with Cu2+

AbstractThe effect of Cu2+ on the triple‐stranded helical structure of poly(A:2I) was studied by means of circular dichroism spectral method with the help of ultraviolet spectral and ethidium bromide fluorescence probe methods. It was found that Cu2+ destabilizes the structure of the triple helix poly(A:2I) and induces its structural transformations, meanwhile, the transformations can be partially reversed by a higher NaCl concentration. The structural transformations may be expressed by the following scheme: poly(A:2I)·poly(A:I) + poly (I) · poly(A) + 2poly(I)

RAMAN SPECTROSCOPIC STUDY OF NONIONIC SURFACTANTS. MOLECULAR CONFORMATIONS OF TRI- THROUGH OCTAETHYLENE GLYCOL MONODODECYL ETHERS IN THE SOLID STATE

Abstract Raman spectra of n-C12H25 (OCH2CH2)mOH with m=3–8 measured in the solid state. Molecular conformations of these surfactants were examined by utilizing normal coordinate treatment; the conformation of the oxyethylene chain is fundamentally identical with the helical structure of poly(oxyethylene).