Proton Magnetic Resonance and the Helix–Coil Transition

Bradbury, E. Morton; Crane‐Robinson, Colyn; Goldman, Howard; Rattle, H. W. E.

doi:10.1038/217812a0

Cited by 77 publications

(29 citation statements)

References 13 publications

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“…6). The α-CH resonance signal of the PBLG main chain was known to give a peak at 3.95 ppm ascribed to the α-helix conformation, while giving an apparent lowfield shift on going from the helix to the random coil form [17]. From signal areas based on α-helix and random coil forms, the helix contents were evaluated and summarized in TaTable 1 Helix content of PBLG(n)SS and PBLG(n)SS-Au particles in CHCl 3 based on 1 ble 1, together with data on PBLG(50)SS and PBLG(50)SSAu and from FTIR analyses.…”

Section: Secondary Structures Of Pblg Segmentsmentioning

confidence: 99%

Preparation of helical peptide monolayer-coated gold nanoparticles

Higashi

Kawahara

Niwa

2005

Journal of Colloid and Interface Science

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Section: Secondary Structures Of Pblg Segmentsmentioning

confidence: 99%

Preparation of helical peptide monolayer-coated gold nanoparticles

Higashi

Kawahara

Niwa

2005

Journal of Colloid and Interface Science

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“…Numerous reports have appeared showing that under certain circumstances many polypeptides exhibit NMR spectra with double peaks from NH and a-CH protons (2)(3)(4)(5)(6)(7)(8). The doubling of peaks was attributed initially by Ferretti to the coexistence of helical and random-coil structures in solution, in spite of the fact that dynamic measurements indicate that the average rate of the helix to coil transition (0.1-10 Asec) is extremely rapid on the NMR time scale (9)(10)(11)(12).…”

mentioning

confidence: 99%

Apparent Helix-Coil Transition for Poly(L-Alanine) as Measured by Nuclear Magnetic Resonance

Goodman¹,

Toda²,

Ueyama³

1973

Proc. Natl. Acad. Sci. U.S.A.

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The previous contention by several groups that double peaks that arise in NMR spectra from NH and a-CH protons of poly L-alanines are caused by the coexistence of helical and random-coil structures in solution is disputed.Numerous reports have appeared showing that under certain circumstances many polypeptides exhibit NMR spectra with double peaks from NH and a-CH protons (2-8). The doubling of peaks was attributed initially by Ferretti to the coexistence of helical and random-coil structures in solution, in spite of the fact that dynamic measurements indicate that the average rate of the helix to coil transition (0.1-10 Asec) is extremely rapid on the NMR time scale (9-12). Such rates should lead to a single averaged peak. Explanations for the doubled peaks have been offered based on polydispersity (13), slow nucleation of the transition (14), and protonation of the peptide bonds (15). Scheraga and his coworkers (16) speculated that the a-helix peak should not be observable because of dipolar broadening. They suggested that double peaks arise from specific, slowly exchanging solvations of random-coil species in mixed solvents containing acids such as trifluoroacetic acid (CF3COOH). Recently, Bradbury and his associates (17) assigned the double peaks to the a-helix and random coils on the basis of comparisons of the areas for a-CH with the side-chain peaks. The Bradbury group concludes that rapid exchange between a-helix and random coil takes place, with the double peaks arising from polydispersity. NMR spectra of poly(L-alanine) were analyzed by Jardetzky (3), Bradbury (18), and Ferretti (3) and their associates. The second two groups found double peaks for the a-CH at 220 MHz. One peak at 4.5 ppm was attributed to the a-helix, while the other peak at 4.7 ppm was assigned to the random-coil conformation of the polypeptide chain.In this paper, we present results indicating that the double peaks seen for poly(L-alanine) may not arise from the helix to coil transition, and that the above explanations may not apply to the observed phenomena. We believe the lowfield peak arises from the a-CH of oligomeric peptides. The high-field peak represents a single averaged peak of helix and random coil. We performed measurements using a 220-MHz Varian spectrometer and very low concentrations of L-alaninederived peptides, necessitating time-averaging to improve the signal-to-noise ratios in solvents composed of deuterochloro- form (CDC13) and CF3COOH. We varied the molecular weight of the polymers, sample concentrations, solvent compositions, and temperature at which the experiments were performed. Although the spectra do not exhibit good signal-to-noise ratios (even after time-averaging), we were able to obtain clear and interpretable results.Double peakst at about 4.6 and 4.3 ppm are observed for poly(L-alanine)i-[average degree of polymerization (DP)37], as is shown in Fig. 1

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“…The C a H proton signals in NMR spectra are useful for characterizing the conformation of PBLG. [17][18][19][20][21] Figure 2 shows Figure 3 shows vol% TFA dependence of the extent of the helical fraction based on the C a H peak areas (f H ¼P H /(P H +P C )) for the PBLG 55 -N-PS 160 , PBLG 55 -N-PS 320 and PBLG 310 -N-PS 320 block copolymers. For comparison, the f H values for the corresponding PBLG homopolymers, PBLG 55 and PBLG 310 , are also plotted in the figure.…”

Section: Resultsmentioning

confidence: 99%

“…[16][17][18][19][20][21] Although the helix-coil transformation of PBLG in a PBLG/PS block copolymer in solution was studied using small-angle neutron scattering, 22 the effects of molecular weight and the peptide terminus to which the PS is attached remain unclear. As PBLG block copolymers are often used as drug-delivery carriers and gene vectors, 23 further study of the conformational behavior is required.…”

Section: Introductionmentioning

confidence: 99%

Helix–coil transformation of poly(γ-benzyl-L-glutamate) with polystyrene attached to the N or C terminus in trifluoroacetic acid–chloroform mixtures

Itoh

Hatanaka

Ihara

et al. 2011

Polym J

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The helix-coil transformations of block copolymers composed of poly(c-benzyl-L-glutamate) (PBLG) and polystyrene (PS), in which PS was attached to either the N terminus (PBLG n -N-PS m ) or the C terminus (PS n -C-PBLG m ) of PBLG, were investigated in trifluoroacetic acid (TFA)-chloroform mixtures with TFA concentrations in the range of 0.7-10 vol%. The helical content (f H ) estimated from 1 H nuclear magnetic resonance measurements indicated that the PBLG segment in PBLG 55 -N-PS 160 underwent a gradual helix-coil transformation from f H ¼1 to f H ¼0.75 over the range of 3.6-5.7 vol% TFA and then a drastic transformation to f H ¼0 at 9.5 vol% TFA, in a manner similar to that of the PBLG 55 homopolymer. In PS 120 -C-PBLG 55 , the helical deformation of the PBLG segment was observed by adding a very small amount of TFA (0.7-3.6 vol%), followed by gradual and drastic transformations at higher TFA concentrations. The results indicate that the conformational stability of the C terminus in a PBLG chain differs from that of the N terminus. Transformations of PBLG/PS block copolymers with various molecular weights and compositions were also studied.

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Proton Magnetic Resonance and the Helix–Coil Transition

Cited by 77 publications

References 13 publications

Preparation of helical peptide monolayer-coated gold nanoparticles

Preparation of helical peptide monolayer-coated gold nanoparticles

Apparent Helix-Coil Transition for Poly(L-Alanine) as Measured by Nuclear Magnetic Resonance

Helix–coil transformation of poly(γ-benzyl-L-glutamate) with polystyrene attached to the N or C terminus in trifluoroacetic acid–chloroform mixtures

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