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

Polymers ◽  
2018 ◽  
Vol 10 (9) ◽  
pp. 936 ◽  
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.

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

Polymers ◽  
2019 ◽  
Vol 11 (11) ◽  
pp. 1877 ◽  
Author(s):  
Shi ◽  
Wang ◽  
Teraguchi ◽  
Aoki ◽  
Kaneko
Keyword(s):  
Main Chain ◽  
Helical Structure ◽  
Intramolecular Hydrogen Bonding ◽  
Catalyst System ◽  
Static Stability ◽  
Cotton Effect ◽  
Helical Conformation ◽  
Cd Spectra ◽  
Cotton Effects ◽  
Intramolecular Hydrogen

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.

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

1965 ◽  
Vol 43 (5) ◽  
pp. 1588-1598 ◽  
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.

scholarly journals Optically active polyacetylene: Synthesis and helical conformation of a poly(phenylacetylene) carryingL-alanyl-L-alanine pendants

2005 ◽  
Vol 43 (16) ◽  
pp. 3701-3706 ◽  
Author(s):  
Lo Ming Lai ◽  
Jacky W. Y. Lam ◽  
Kevin K. L. Cheuk ◽  
Hermans H. Y. Sung ◽  
Ian D. Williams ◽  
...  
Keyword(s):  
Optically Active ◽  
Helical Conformation

Circulardichroismusuntersuchungen von Polyalkohol- und Zucker-Vanadat(V)-Komplexen / Circular Dichroism Studies of Polyalcohol and Sugar Vanadate(V) Complexes

1989 ◽  
Vol 44 (11) ◽  
pp. 1464-1472 ◽  
Author(s):  
Hermann Bauer ◽  
Jeanine Brun ◽  
Alexius R. Hernanto ◽  
Wolfgang Voelter ◽  
Spyridon Paraskewas
Keyword(s):  
Circular Dichroism ◽  
Wavelength Range ◽  
Optically Active ◽  
Hydroxyl Groups ◽  
Pyranose Ring ◽  
Cotton Effects ◽  
Circular Dichroïsm

The complexes of tetravanadate ions with optically active polyols and carbohydrates with suitable steric properties show up to four separate cotton effects in the wavelength range of λ = 200-350 nm. Thus it is possible to classify pyranoses into four groups according to their circular dichroitic behaviour and determine the configuration and the conformation of the hydroxyl groups attached to the pyranose ring.

Synthesis and Helical Conformation of Novel Optically Active Liquid Crystalline Poly(p-phenylene)s Containing Cyanoterphenyl Mesogen as Pendant

2009 ◽  
Vol 42 (14) ◽  
pp. 5053-5061 ◽  
Author(s):  
Lie Chen ◽  
Yiwang Chen ◽  
Kai Yao ◽  
Weihua Zhou ◽  
Fan Li ◽  
...  
Keyword(s):  
Liquid Crystalline ◽  
Optically Active ◽  
Helical Conformation ◽  
Active Liquid

Circular dichroism spectra of amino acid complexes. II. Chelated amino acid complexes with the CoN5O chromophore

1970 ◽  
Vol 23 (9) ◽  
pp. 1735 ◽  
Author(s):  
CJ Hawkins ◽  
PJ Lawson
Keyword(s):  
Amino Acids ◽  
Circular Dichroism ◽  
Amino Acid ◽  
Visible Region ◽  
Optically Active ◽  
Circular Dichroism Spectra ◽  
Amino Acid Complexes ◽  
Similar Series ◽  
Cotton Effects ◽  
Circular Dichroïsm

The circular dichroism spectra of a series of optically active (α-aminocarboxylato)tetraamminecobalt(111) complexes have been measured in aqueous solution, and in the presence of salts of polarizable anions. The observed spectra in the visible region have been analysed to determine the signs of the Cotton effects of the three components of the 1A1g ↔ 1T1g cobalt(111) transition. For L-amino acids, the transition with A2g(D4h) parentage is negative, and the two transitions with Eg(D4h) parentage have opposite signs. Published circular dichroism spectra of complexes of the type [Co(en)2(L-am)]2+ were similarly interpreted in terms of a perturbed tetragonal chromophore, and it was shown that the vicinal effect of the L-amino acids imposed the same signs onto the component transitions as for the tetraammines and for a similar series of pentaamminecobalt(111) complexes.

Linear tetrapyrroles as functional pigments in chemistry and biology

2004 ◽  
Vol 08 (03) ◽  
pp. 226-237 ◽  
Author(s):  
Tadashi Mizutani ◽  
Shigeyuki Yagi
Keyword(s):  
Conformational Changes ◽  
Materials Science ◽  
Redox Activity ◽  
Helical Conformation ◽  
Biological Functions ◽  
Experimental Conditions ◽  
Chiral Structure ◽  
Biliverdin Ix ◽  
Linear Tetrapyrroles ◽  
Single Bonds

1,19,21,24-tetrahydro-1,19-bilindione is the framework of pigments frequently found in nature, which includes biliverdin IX α, phytochromobilin and phycocyanobilin. 1,19-bilindiones have unique features such as (1) photochemical and thermal cis-trans isomerization, (2) excited energy transfer, (3) chiroptical properties due to the cyclic helical conformation, (4) redox activity, (5) coordination to various metals, and (6) reconstitution to proteins. 1,19-bilindione can adopt a number of conformations since it has exocyclic three double bonds and three single bonds that are rotatable thermally and photochemically. In solution, biliverdin and phycocyanobilin adopt a cyclic helical ZZZ, syn, syn, syn conformation, but other conformations are stabilized depending on the experimental conditions and substituents on the bilin framework. The conformational changes in 1,19-bilindiones are related to the biological functions of a photoreceptor protein, phytochrome. Structural and conformational studies of bilindiones are summarized both in solution and in protein. The conformational changes of bilins can be used for other functions such as a chirality sensor. The bilindiones and the zinc complexes of bilindiones can be employed as a chirality sensor due to the helically chiral structure and the dynamics of racemization of enantiomers. In this paper, we discuss the conformational equilibria and dynamics of bilindiones and its implications in photobiology and materials science.

A Mass Spectrometry Investigation of the Conformational Changes in Adrenocorticotropic Hormones

2002 ◽  
Vol 8 (5) ◽  
pp. 381-387 ◽  
Author(s):  
Hui Lin ◽  
Chhabil Dass
Keyword(s):  
Mass Spectrometry ◽  
Conformational Changes ◽  
Aqueous Media ◽  
Charge State Distribution ◽  
Random Coil ◽  
Helical Conformation ◽  
Ionization Mass ◽  
Time Resolved ◽  
Esi Ms ◽  
Α Helix

Electrospray ionization-mass spectrometry (ESI-MS) was employed to study methanol-induced conformational changes in adrenocorticotrophic hormone (ACTH). ACTH, a 39–residue peptide, is a member of the proopiomelanocortin family of peptides. Charge-state distribution (CSD) and hydrogen–deuterium (H/D) exchange were used to monitor the conformational changes as a function of methanol concentration. The latter experiments were conducted via time-resolved ESI-MS in a continuous-flow apparatus. The CSD and the H/D exchange experimental data both reveal that ACTH exists, presumably in a random coil open structure in aqueous media, but assumes a more compact helical conformation with increased concentration of methanol. The H/D exchange experiments also reveal that 79% of ACTH is present as α-helix in mixed water-methanol solvent media.

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