Nuclear Magnetic Resonance Relaxation Study of Poly(γ-benzyl L-glutamate) Side-Chain Mobility in Helix-Coil Transition

Chien, Mingjien; Samulski, Edward T.; Wade, Charles G.

doi:10.1021/ma60034a032

Cited by 10 publications

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“…13 • 14 Though qualitatively, the dependence of the helical structure and its stability on the species of the side chain has been explained in terms of side chain-side chain and side chain-backbone interactions. 8 Recently, it has been reported that in a series of poly(y-monosubstituted-benzyl o-glutamate)s, in which a substituent is introduced into the phenyl ring at the end of the side chain of poly(y-benzyl oglutamate) (PBDG), the properties markedly depend on the species and the position of the substituent.10 -12 It has been also reported that the different position of the substitution affects the * 3 To whom all inquiries should be addressed.The purpose of the present investigation is to examine the effects of the substitution to the benzyl group of PBDG on side-chain motions of PBDG. Dielectric and broad-line nuclear magnetic resonance measurements were performed to observed molecular motions for the following seven samples of poly(y-monosubstituted -benzyl glutamate)s; poly(y--chlorobenzyl o-glutamate) (o-ClPBDG), poly(y-m-chlorobenzyl o-glutamate) (m-CIPBDG), poly(y-p-chlorobenzyl o-glutamate) (p-ClPBDG), poly(y-p-chlorobenzyl L-glutamate) (p-ClPBLG), poly(y-p-nitrobenzyl o-glutamate) (p-NPBDG), 583 …”

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Molecular Motions of Poly(γ-monosubstituted-benzyl D-glutamate) in the Solid State

Sasaki

Tsutsumi

Hikichi

et al. 1979

Polym J

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ABSTRACT:Dielectric measurements were performed at frequencies ranging from 30Hz to 300KHz and at temperatures between -150 and l20°C for the following poly(y-monosubstitutedbenzyl n-glutamate)s; poly(y-o-chlorobenzyl o-glutamate) (o-CIPBDG), poly(y-m-chlorobenzyl Dglutamate) (m-CIPBMDG), poly(y-p-chlorobenzyl D-glutamate) (p-CIPBDG), poly(y-p-nitrobenzyl o-glutamate) (p-NPBDG), poly(y-p-methylbenzyl o-glutamate) (pMePBDG) and a racemic mixture of p-CIPBDG and p-CIPBLG (p-CIPBDG+p-CIBLG). Each sample exhibited a dielectric loss maximum in the temperature range of These loss maxima were attributed to the onset of large scale motion of side chains. The temperatures of maximum loss (the dispersion temperature) are shifted by the introduction of substituents. The dispersion temperature is highest for p-CIPBDG among three monochlorosubstituted PBDGs. For p-monosubstituted-PBDGs, p-NPBDG, which has the side chain with the largest dipole moment among three p-substituents studied, showee the highest dispersion temperature. The results are explained in terms of restriction caused by dipole-dipole interaction among dipoles in the side chain. The enormous relaxation strength of o-CIPBDG was considered to reflect a certain conformation of the side chain originating from steric hindrance between the ester and the a-substituent of a side chain. Racemic mixtures of p-CIPBDG and p-CIPBLG showed no evidence of the first-order solid-solid transition observed for racemic mixtures of PBDG and PBLG.KEY WORDS Poly(y-monosubstituted-benzyl n-glutamate) I Side-ChainMotion I Dipole-Dipole Interaction I Steric Hindrance I Racemic Mixtures I It has widely been accepted that even in the solid state, long side chains of the ()(-helical poly(IJ(-amino acid) undergo considerable motions while ()(-helical main chain remains rigid. The importance of side-chain motions of the ()(-helical poly(1J(-amino acid) in determining properties in the solid state has been recognized. 1 -9 conformation of the ()(-helical backbone. 13 • 14 Though qualitatively, the dependence of the helical structure and its stability on the species of the side chain has been explained in terms of side chain-side chain and side chain-backbone interactions. 8 Recently, it has been reported that in a series of poly(y-monosubstituted-benzyl o-glutamate)s, in which a substituent is introduced into the phenyl ring at the end of the side chain of poly(y-benzyl oglutamate) (PBDG), the properties markedly depend on the species and the position of the substituent.10 -12 It has been also reported that the different position of the substitution affects the * 3 To whom all inquiries should be addressed.The purpose of the present investigation is to examine the effects of the substitution to the benzyl group of PBDG on side-chain motions of PBDG. Dielectric and broad-line nuclear magnetic resonance measurements were performed to observed molecular motions for the following seven samples of poly(y-monosubstituted -benzyl glutamate)s; poly(y--chlorobenzyl o-glutamate) (o-ClPBDG), poly(y...

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Molecular Motions of Poly(γ-monosubstituted-benzyl D-glutamate) in the Solid State

Sasaki

Tsutsumi

Hikichi

et al. 1979

Polym J

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“…The effect of adding halogenated organic acids to the liquid crystal phase, known to destroy the helical conformation at sufficient concentration, has been studied (105,106). The acid is fo und to effect the side chain motion, while leaving the twist constant unchanged.…”

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Stiff Chain Polymer Lyotropic Liquid Crystals

Miller¹

1978

Annu. Rev. Phys. Chem.

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“…This model suggests that the side-chain motion is affected by the side chain-side chain and the intramolecular backbone-side chain interactions. 17 The side chainside chain interaction provides cooperative properties to motions of the side chains. When a copolymer is composed of two different side chains with different mobilities, the relaxation process reflects the cooperative interaction between side chains.…”

Section: Models Of Interacting Side Chainsmentioning

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Cooperative Interaction on Side-Chain Motion of Poly(α-amino acid)

Yagihara

Hikichi

1982

Polym J

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ABSTRACT:Models of interacting side chains were proposed to explain the dielectric properties of poly( a-amino acid) in the solid state. Theoretical studies on these models were made by taking into account cooperative interactions among the side-chain motions. The theory explains the sudden change in dielectric loss with composition for copolymers of y-methyl L-glutamate and yp-chlorobenzyl L-glutamate. The ranges of cooperative side-chain motion for these copolymers were estimated to be about II side chains. This value was compared with each of those of polymer blends of poly(y-methyl L-glutamate) and poly(y-p-chlorobenzyl L-glutamate). Differences in dielectric property between the copolymer and the polymer blend are explained by the effective freevolume on the basis of these models. Characteristics of cooperative interactions in chain motions of poly(a-amino acid)s and amorphous polymers were discussed.KEY WORDSCooperative properties of molecular motion are of importance in understanding the dynamical behavior of macromolecules 1 -3 and small molecules as well. 4 -6 It has been well established that the glass-rubber relaxation of conventional amorphous polymers is caused by cooperative motions of the main chain. 7 -9 On the other hand, the side-chain motion has been considered to be less cooperative.7·8·10 It has been reported that the side-chain relaxation of a-helical poly(a-amino acid) in the solid state resembles the glass-rubber relaxation of conventional amorphous polymersY-14 Side chains of y-methyl L-glutamate (MLG) and y-benzyl L-glutamate (BLG) in the copolymer of MLG and BLG undergo cooperative motions and show a single side-chain relaxation.U However, the cooperativity of the side-chain motion of poly(a-amino acid) seems to be less significant than that of the main-chain motion in conventional amorphous polymers. 15In our previous paper ,1 5 the dielectric properties of copolymers of MLG and y-p-chlorobenzyl Lglutamate (pClBLG) in the solid state were reported. We found that the dielectric properties did not change smoothly but rather abruptly with composition. Two side-chain relaxations related to MLG and pClBLG side-chains, respectively, were observed for copolymers with mole fractions of pClBLG ranging from 0.1 to 0.5. The value of the dielectric loss related to MLG side-chains was much smaller than that expected from the mole fraction of MLG residues in the copolymer. Thus, we suggest that the relaxation due to MLG side-chains in the copolymer is caused not by a single MLG sidechain, but by clusters of MLG side-chains larger than a certain critical size. In a cluster smaller than the critical size, the motion is severely restricted because of the interaction with pClBLG side-chain. This cooperative property of the side-chain motion has not as yet been discussed in detail.In the present paper, we present models to explain the cooperative property of the side-chain motion together with some theoretical considerations on the experimental results. Furthermore, we show dielectric data for blends of...

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Nuclear Magnetic Resonance Relaxation Study of Poly(γ-benzyl L-glutamate) Side-Chain Mobility in Helix-Coil Transition

Cited by 10 publications

References 3 publications

Molecular Motions of Poly(γ-monosubstituted-benzyl D-glutamate) in the Solid State

Molecular Motions of Poly(γ-monosubstituted-benzyl D-glutamate) in the Solid State

Stiff Chain Polymer Lyotropic Liquid Crystals

Cooperative Interaction on Side-Chain Motion of Poly(α-amino acid)

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