Helix-sense-selective Polymerization of 3,5-bis(hydroxymethyl)phenylacetylene Rigidly Bearing Galvinoxyl Residues and Their Chiroptical Properties

Four kinds of newly synthesized achiral phenylacetylenes bearing a phenylhydrogalvinoxyl residue at 4-position were polymerized by using a chiral rhodium catalyst system, [Rh(nbd)B(C6H5)4] or [Rh(nbd)Cl]2 catalysts in the presence of chiral (R)-(+)- or (S)-(–)-1-phenylethylamine ((R)- or (S)-PEA) cocatalysts. Poly(m-HGDHPA) and poly(m-HGTHPA) in THF showed Cotton signals at the absorption regions of the main chain and hydrogalvinoxyl in the circular dichroism (CD) spectra. It indicated that excess of one-handed helical polyacetylene backbone was induced by helix-sense-selective polymerization (HSSP) under the asymmetric conditions despite the achiral monomer, and the hydrogalvinoxyl moieties were also arranged to form one-handed helical structure. However, there was no Cotton effect for poly(p-HGDHPA) and poly(p-HGTHPA) because the intramolecular hydrogen bonding did not act well to stabilize the helical conformation. The hydrogalvinoxyl units of poly(m-HGDHPA) and poly(m-HGTHPA) were converted to the corresponding galvinoxyl radicals after treatment with PbO2. In the CD spectra of the polyradicals, the Cotton effects decreased depending on their static stability of helical conformation, suggesting that reversal conformation of the polymer chain arose.

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Helix-Sense-Selective Polymerization of Phenylacetylenes Having a Porphyrin and a Zinc-Porphyrin Group: One-Handed Helical Arrangement of Porphyrin Pendants

Polymers ◽

10.3390/polym11020274 ◽

2019 ◽

Vol 11 (2) ◽

pp. 274 ◽

Cited By ~ 1

Author(s):

Masahiro Teraguchi ◽

Nobuyuki Nahata ◽

Takahiro Nishimura ◽

Toshiki Aoki ◽

Takashi Kaneko

Keyword(s):

Main Chain ◽

Helical Structure ◽

Spatial Arrangement ◽

Catalyst System ◽

Cd Spectra ◽

Absorption Region ◽

Zinc Porphyrin ◽

Stacking Effect ◽

The One ◽

Porphyrin Moiety

: Newly synthesized two kinds of achiral phenylacetylenes having a free-base- or a zinc-porphyrin (1 and Zn1, respectively) were polymerized by using a chiral rhodium catalyst system, Rh+(nbd)[(η6-C6H5)B–(C6H5)3] catalyst and (R)-(+)- or (S)-(–)-1-phenylethylamine ((R)- or (S)-PEA, respectively) cocatalyst. Poly(1) and poly(Zn1) in THF showed a Cotton signal at the absorption region of the porphyrin and the main chain in the circular dichroism (CD) spectra. This result suggests that poly(1) and poly(Zn1) exist in a conformation with an excess of one-handed helix sense and the porphyrin moiety arranged in chiral helical fashion. The one-handed helical structure of poly(1) could be sustained in a mixture of THF/HMPA (10/2, v/v) due to stabilizing by stacking effect of porphyrin moieties along the main chain. This is the first example about helix-sense-selective polymerization by using Rh+(nbd)[(η6-C6H5)B–(C6H5)3] catalyst. Additionally, poly(Zn1) showed about 10 times larger CD intensity in comparison with poly(1). This result suggests the regularity of arrangement of the porphyrin in poly(Zn1) is higher compared with poly(1). Spatial arrangement of porphyrins was achieved by utilizing a one-handed helical poly(phenylacetylenes) as a template.

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Solution Conformation of Konjac Glucomannan Single Helix

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.197-198.96 ◽

2011 ◽

Vol 197-198 ◽

pp. 96-104 ◽

Cited By ~ 2

Author(s):

Chao Wang ◽

Yu Zhang ◽

Hong Xia Huang ◽

Mao Bin Chen ◽

Dong Sheng Li

Keyword(s):

Congo Red ◽

Helical Structure ◽

Konjac Glucomannan ◽

Helical Conformation ◽

Urea Solution ◽

Cd Spectra ◽

Solution Conformation ◽

Random Coils ◽

The Stability ◽

Single Helix

The possibility of the existence of konjac glucomannan (KGM) single helix in dilute solution was discussed finely by ultraviolet-visible spectrophotometer (UV-Vis) with Congo red complex, viscosimetry and circular dichroism (CD). KGM bound to Congo red and the λmaxcharacteristic shifted markedly to longer wavelength (514 nm) in 0.25 M aq NaOH. The shifts of λmaxand intrinsic viscosity were also compared in different mediums, such as different concentrations of KGM, NaOH, urea solutions or temperatures. The results indicated that KGM had an ordered, single-helical conformation in neutral, slight NaOH (<0.15 M) and urea (<3.0 M) solutions or at a moderate temperature (T<55ºС ), while it was transformed disorder, random coils in high NaOH (>0.45 M), urea (>4.0 M) solutions or at a high temperature (T>60ºС ). So it can be conclude that the outside factors play an important role on the stability of the single-helix conformation for KGM solution. The induced CD spectra by Congo red and the CD spectra of KGM in aqueous and urea solution indicated further that KGM had a single-helical structure. The new conclusion laid the foundation of determining helical radius, pitch and length of KGM in the future studies.

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Conjugated Oligomers Containing Imidazole in Main Chain with Intramolecular Hydrogen Bonding

Polymer Journal ◽

10.1295/polymj.pj2008045 ◽

2008 ◽

Vol 40 (7) ◽

pp. 614-621 ◽

Cited By ~ 6

Author(s):

Koji Takagi ◽

Kenta Sugihara ◽

Junya Ohta ◽

Yasuo Yuki ◽

Shin-ichi Matsuoka ◽

...

Keyword(s):

Hydrogen Bonding ◽

Main Chain ◽

Intramolecular Hydrogen Bonding ◽

Conjugated Oligomers ◽

Intramolecular Hydrogen

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A Facile Synthetic Route to Amphiphilic Poly(Meta-Phenylene Ethynylene) and Poly(Meta-Phenylene Ethynylene)-Block-Polyisocyanide Using a Single Catalyst

Polymers ◽

10.3390/polym10090936 ◽

2018 ◽

Vol 10 (9) ◽

pp. 936 ◽

Cited By ~ 2

Author(s):

Chonglong Li ◽

Xunhui Xu ◽

Lei Xu ◽

Na Liu

Keyword(s):

Conformational Changes ◽

Mixed Solvents ◽

Cotton Effect ◽

Optically Active ◽

Amphiphilic Block Copolymers ◽

Helical Conformation ◽

Mixing Ratio ◽

Phenylene Ethynylene ◽

Synthetic Route ◽

Cotton Effects

An optically active, amphiphilic meta-phenylene ethynylene (m-PE) bearing a chiral amide pendant was designed and synthesized. Living polymerization of m-PE using alkyne-Pd(II) as the initiator afforded well-defined poly(meta-phenylene ethynylene) (m-PPE). These m-PPEs were found to have a stable helical conformation in THF, 1,4-dioxane, and CH3CN and showed split Cotton effects over the range of 245–400 nm. The positive first Cotton effect was observed at a wavelength of approximately 308 nm, and the negative second Cotton effect was observed at a wavelength of approximately 289 nm. The m-PPEs exhibited helical conformational changes in different mixed solvents and showed effective solvent-dependent helix inversion in CHCl3/THF solutions. The sign of the Cotton effect of m-PPE was inverted at 25 °C by varying the mixing ratio of THF and CHCl3. Finally, amphiphilic poly(meta-phenylene ethynylene)-block-polyisocyanide containing hydrophilic PPE and hydrophobic PPI segments were facilely prepared using Pd(II)-terminated m-PPE as the macroinitiator. This block copolymer can self-assemble into well-defined spherical nanostructures in a selective THF/CH3OH solution. This efficient polymerization will open up enormous opportunities for the preparation of functional amphiphilic block copolymers in a wide variety of fields.

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The Influence of Secondary Structure on Electron Transfer in Peptides

Australian Journal of Chemistry ◽

10.1071/ch13276 ◽

2013 ◽

Vol 66 (8) ◽

pp. 848 ◽

Cited By ~ 12

Author(s):

Jingxian Yu ◽

John R. Horsley ◽

Andrew D. Abell

Keyword(s):

Electron Transfer ◽

Secondary Structure ◽

Chain Length ◽

Intramolecular Hydrogen Bonding ◽

Electrochemical Analysis ◽

Helical Conformation ◽

Intramolecular Electron Transfer ◽

Helical Structures ◽

Redox Active ◽

Intramolecular Hydrogen

A series of synthetic peptides containing 0–5 α-aminoisobutyric acid (Aib) residues and a C-terminal redox-active ferrocene was synthesised and their conformations defined by NMR and circular dichroism. Each peptide was separately attached to an electrode for subsequent electrochemical analysis in order to investigate the effect of peptide chain length (distance dependence) and secondary structure on the mechanism of intramolecular electron transfer. While the shorter peptides (0–2 residues) do not adopt a well defined secondary structure, the longer peptides (3–5 residues) adopt a helical conformation, with associated intramolecular hydrogen bonding. The electrochemical results on these peptides clearly revealed a transition in the mechanism of intramolecular electron transfer on transitioning from the ill-defined shorter peptides to the longer helical peptides. The helical structures undergo electron transfer via a hopping mechanism, while the shorter ill-defined structures proceeded via an electron superexchange mechanism. Computational studies on two β-peptides PCB-(β3Val-β3Ala-β3Leu)n–NHC(CH3)2OOtBu (n = 1 and 2; PCB = p-cyanobenzamide) were consistent with these observations, where the n = 2 peptide adopts a helical conformation and the n = 1 peptide an ill-defined structure. These combined studies suggest that the mechanism of electron transfer is defined by the extent of secondary structure, rather than merely chain length as is commonly accepted.

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CONFORMATIONAL STUDIES ON SYNTHETIC POLY-α-AMINO ACIDS: THE HELICAL SENSE OF POLY-L-TRYPTOPHAN: OPTICAL ROTATORY DISPERSION STUDIES

Canadian Journal of Chemistry ◽

10.1139/v65-210 ◽

1965 ◽

Vol 43 (5) ◽

pp. 1588-1598 ◽

Cited By ~ 38

Author(s):

Gerald D. Fasman ◽

Margarete Landsberg ◽

Manuel Buchwald

Keyword(s):

Wavelength Range ◽

Cotton Effect ◽

Optical Rotatory Dispersion ◽

Rotatory Dispersion ◽

Helical Conformation ◽

Optical Rotatory ◽

Negative Cotton Effect ◽

Cotton Effects ◽

The Right ◽

Tryptophanyl Residue

The synthesis of high molecular weight (100 000 to 200 000) polymers and copolymers of L-tryptophan and γ-benzyl-L-glutamate is reported. The optical rotatory dispersion (o.r.d.) of these polypeptides is recorded in the wavelength range 540–320 mμ and the b0 values of the Moffitt equation, using λ0 = 212ν, are listed. Poly-L-tryptophan has a b0 value of +570 in dimethylformamide (DMF). A linear relationship exists between this value, b0 values of copolymers of various ratios of L-tryptophan and γ-benzyl-L-glutamate, and the value of− 670 found for poly-γ-benzyl-L-glutamate. The o.r.d. curve of a poly-L-tryptophan film, in the 330–200 mμ wavelength range, reveals two positive Cotton effects in the 270–290 mμ region and a large negative Cotton effect at 233 mμ. Thus, despite the positive b0 value, these data prove that poly-L-tryptophan, in DMF, has the right-handed helical conformation. Hypochromicity was found for the tryptophanyl residue in the helical polypeptide. The rotatory contribution of chromophores, such as tryptophan or coenzymes, when bound asymmetrically to a protein, can be very significant, and caution is advised in the interpretation of such o.r.d. curves.

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DNA polymorphism in crystals: three stable conformations for the decadeoxynucleotide d(GCATGCATGC)

Acta Crystallographica Section D Structural Biology ◽

10.1107/s2059798316006306 ◽

2016 ◽

Vol 72 (6) ◽

pp. 780-788 ◽

Cited By ~ 3

Author(s):

Arunachalam Thirugnanasambandam ◽

Selvam Karthik ◽

Gunanithi Artheswari ◽

Namasivayam Gautham

Keyword(s):

Metal Ion ◽

Helical Structure ◽

Mixed Population ◽

Helical Conformation ◽

Cd Spectra ◽

X Ray ◽

X Ray Crystallography ◽

Double Helical Structure ◽

Flexible Molecule ◽

Dna Fragment

High-resolution structures of DNA fragments determined using X-ray crystallography or NMR have provided descriptions of a veritable alphabet of conformations. They have also shown that DNA is a flexible molecule, with some sequences capable of adopting two different structures. Here, the first example is presented of a DNA fragment that can assume three different and distinct conformations in crystals. The decanucleotide d(GCATGCATGC) was previously reported to assume a single-stranded double-fold structure. In one of the two crystal structures described here the decamer assumes both the double-fold conformation and, simultaneously, the more conventional B-type double-helical structure. In the other crystal the sequence assumes the A-type double-helical conformation. These results, taken together with CD spectra, which were recorded as the decamer was titrated against four metal ions and spermine, indicate that the molecule may exist as a mixed population of structures in solution. Small differences in the environmental conditions, such as the concentration of metal ion, may decide which of these crystallizes out. The results also support the idea that it may be possible for DNA to change its structure to suit the binding requirements of proteins or drugs.

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