Helical conformations, internal motion, and helix sense reversal in polyisocyanates and the preferred helix sense of an optically active polyisocyanate

Lifson, Shneior; Felder, Clifford E.; Green, Mark M.

doi:10.1021/ma00042a015

Cited by 109 publications

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“…N p=O N p=O (10) with N LL w(N,p)=l Actual calculations were performed by using eq 7 through eq 9 with appropriate values chosen for uM,l ( = uM), v, and [exJm for appropriately generated random copolymers and taking the averages. The results were also used with eq 10 along with an appropriate w(N,p) to calculate [ti] for statistical copolymers.…”

Section: Type 1 Polymersmentioning

confidence: 99%

Molecular Mechanisms for the Optical Activities of Polyisocyanates Induced by Intramolecular Chiral Perturbations

Sato

Teŕamoto

et al. 1997

Polym J

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ABSTRACT:Molecular mechanisms were proposed to account for extraordinary optical activities of polyisocyanates containing chiral moieties (chiral monomer or initiator fragment) reported by Green et al. and by Okamoto et al., where the polyisocyanate molecule was modeled by a helical chain consisting of an alternating sequence of right-handed and left-handed helices with helix reversals in between. Theoretical predictions based on this model were consistent with remarkable dependence of optical rotation on monomer composition for random copolyisocyanates of chiral and achiral monomers and enantiomorphous copolymers and chain length dependence of optical rotation for achiral polyisocyanates with a chiral initiator fragment on the chain end. The helix reversal was shown to be the key factor for all the cases and more frequent for aromatic sidechain polymer poly(m-methyl phenyl isocyanate) than for aliphatic side chain polymers such as poly(butyl and hexyl isocyanate)s.KEY WORDS Chiral / Optical Activity / Polyisocyanate / Helical Conformation / Helix Reversal / Statistical Mechanics / Copolymer / Amide bonds of partial double-bond nature in a polyisocyanate chain tend to be coplanar, but they are distorted in a helical conformation due to steric interactions between the main chain and side chains. 1 -1° For this reason the global conformation of the polymer chain is well modeled by wormlike chains. 7 -9 • 11 -18 However the sense of the helix is not determined for an achiral polyisocyanate because both the right-handed and lefthanded helices are symmetric. This symmetry is broken by a subtle chiral perturbation within a given molecule and this molecule becomes optical active. [19][20][21][22][23][24][25] showed that incorporation of a very small amount of chiral monomers into an achiral polyisocyanate in a random fashion gives rise to remarkable optical activity, which increases disproportionately with the mole fraction of chiral monomer. A similar disproportionate change in optical activity has been found in copolymers of enantiomorphous isocyanates (R-S copolymers). 25 On the other hand Okamoto and collaborators 26 • 27 introduced a chiral perturbation into polyisocyanate chains in a different way; they synthesized polyisocyanates with chiral initiators, which were attached to a chain end, and showed that those polyisocyanates exhibited optical activity changing remarkably with length and temperature. The present study was motivated by these findings and tries to explore the molecular mechanisms behind the optical activities in these particular polymers. Green et al. 20 called chiral entities sergeants and achiral entities soldiers. Thus we here deal with sergeants-soldiers polymers. Theoretically these polyisocyanates are regarded as typical linear cooperative systems just as chiral polyisocyanates and a-helical polypeptides. Therefore we analyze their conformational properties including optical activity by the well-established statistical mechanical procedures based on the matrix method. 28 -30 A preliminary...

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Section: Type 1 Polymersmentioning

confidence: 99%

Molecular Mechanisms for the Optical Activities of Polyisocyanates Induced by Intramolecular Chiral Perturbations

Sato

Teŕamoto

et al. 1997

Polym J

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“…In particular, for a racemic compound interacting with a helical polymer, we derived the ratio of the two adsorbed enantiomer species: the results obtained in Eqs. (11), (14), and (14) can be applied to experimental results to estimate microscopic parameters such as the chemical potentials µ ± , the amine coupling J 2 , or the polymer-amine interaction h 1 . Several HPLC experiments estimate the capacity and separation factors (related to the retention times) of chiral amines interacting with chiral poly-6 and poly-7 used as a molecular sieve [6].…”

Section: Discussionmentioning

confidence: 99%

Chiral molecule adsorption on helical polymers

D’Orsogna

Chou

2004

Phys. Rev. E

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We present a lattice model for helicity induction on an optically inactive polymer due to the adsorption of exogenous chiral amine molecules. The system is mapped onto a one-dimensional Ising model characterized by an on-site polymer helicity variable and an amine occupancy one. The equilibrium properties are analyzed at the limit of strong coupling between helicity induction and amine adsorption and that of non-interacting adsorbant molecules. We discuss our results in view of recent experimental results.

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“…Then the backbone of PHIC takes the Schmueli-TraubRosenheck 17 8 3 helix, 16,[18][19][20] and the equilibrium conformational behavior of its helix axis (without consideration of the torsion) may be well described by the (original 9 ) KP chain with…”

Section: Hw Theorymentioning

confidence: 99%

“…It is seen that the theory gives almost a quantitative explanation of the experimental results within experimental error. We then find the hydrodynamic diameter d of the KP cylinder having the same hydrodynamic volume as the discrete generalized KP chain to be equal to 19 18 respectively. It is pertinent to make here a remark on the assumption of ¼ 0.…”

Section: Hw Theorymentioning

confidence: 99%

Nuclear Magnetic Relaxation of Poly(n-hexyl isocyanate) in Dilute Solution. Effects of Chain Stiffness

Nakatsuji

Yoshizaki

Yamakawa

2005

Polym J

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ABSTRACT:The spin-lattice relaxation time T 1 , spin-spin relaxation time T 2 , and nuclear Overhauser enhancement NOE were determined from nuclear magnetic relaxation measurements on five well-fractionated samples of poly-(n-hexyl isocyanate) in the range of weight-average molecular weight M w from 1:65 Â 10 4 to 5:71 Â 10 4 in n-hexane at 25 C. It is found that T 1 increases and T 2 decreases monotonically with increasing M w in the range of M w examined, As is well known, the spin-lattice relaxation time T 1 , spin-spin relaxation time T 2 , and nuclear Overhauser enhancement NOE for 13 C nuclei may be expressed in terms of time-correlation functions of components of the dyadic of the internuclear vector 13 C! 1 H from a 13 C nucleus to a bonded 1 H one if we simply assume that the nuclear magnetism of 13 C relaxes only due to the heteronuclear dipolar interaction.1,2 We have made so far experimental studies of T 1 and NOE for backbone 13 C of typical flexible polymers such as atactic polystyrene, 3 atactic poly-(methyl methacrylate), 4 isotactic poly(methyl methacrylate), 5 and atactic poly(-methylstyrene). 6 In the case of flexible polymers, tumbling motions of repeat units are hardly coupled with the entire chain motion, so that values of T 1 , T 2 , and NOE are almost independent of the molecular weight M except for oligomers with very small M. In the case of semiflexible polymers, on the other hand, the former motions may be considered to be coupled with the latter even in the range of rather large M, and therefore the dependence of T 1 , T 2 , and NOE on M must be different from that for flexible polymers. Unfortunately, however, such literature data for typical semiflexible polymers are not available except those obtained by Budd et al. 7 for T 1 and T 2 for poly(-benzyl L-glutamate) (PBLG). In the present paper, therefore, we examine experimentally the dependence on M of T 1 , T 2 , and also NOE for poly(n-hexyl isocyanate) (PHIC) as another example of semiflexible polymers. We note that DuPré and Wang 8 have determined T 1 , T 2 , and NOE for a PHIC sample with the weight-average molecular weight M w ¼ 3:39 Â 10 4 , and therefore have not examined the dependence of these quantities on M w .PHIC is a typical semiflexible polymer whose molecular characterization has almost completely been done by an analysis of dilute solution properties on the basis of the Kratky-Porod (KP) wormlike chain model. 9,10 Specifically, the KP model parameters for PHIC, i.e., the static stiffness parameters À1 , the shift factor M L as defined as the molecular weight per unit contour length of the KP chain, and the hydrodynamic diameter d, have been determined rather unambiguously.11 Thus, from a comparison of present experimental data with the theory previously 12 developed for the generalized KP chain [a special case of the helical wormlike (HW) chain] 10 by the use of the established values of the KP model parameters, 11 we may verify its validity. This is the main purpose of the present paper.A remark should be made ...

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Helical conformations, internal motion, and helix sense reversal in polyisocyanates and the preferred helix sense of an optically active polyisocyanate

Cited by 109 publications

References 0 publications

Molecular Mechanisms for the Optical Activities of Polyisocyanates Induced by Intramolecular Chiral Perturbations

Molecular Mechanisms for the Optical Activities of Polyisocyanates Induced by Intramolecular Chiral Perturbations

Chiral molecule adsorption on helical polymers

Nuclear Magnetic Relaxation of Poly(n-hexyl isocyanate) in Dilute Solution. Effects of Chain Stiffness

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