A HIGH RESOLUTION 13C NMR STUDY OF SOLID POLY (β-BENZYL-l-ASPARTATE) BY THE CROSS POLARIZATION-MAGIC ANGLE SPINNING METHOD. DISTINCTION OF THE RIGHT-HANDED α-HELIX, LEFT-HANDED α-HELIX, ω-HELIX, AND β-SHEET FORMS BY CONFORMATION-DEPENDENT 13C CHEMICAL SHIFTS
Abstract:High resolution 13C NMR spectra of solid poly(β-benzyl-l-aspartate) taking the right-handed α-helix, left-handed α-helix, ω-helix, and β-sheet conformations were recorded by the cross polarization-magic angle spinning method. 13C chemical shifts of the right-handed α-helix form were significantly displaced as compared with those of the left-handed α-helix and ω-helix forms.
“…For [Asp*(OBzl)] n -2, the 13 C chemical shift values were observed at 172.5 (CO (amide and ester)), 51.5 (C α ), and 34.5 ppm (C β ), which are characteristic of the α L -helix form. These values are in good agreement with those obtained for films cast from chloroform solution . For [Asp*(OBzl)] n -3, the 13 C chemical shift values of the CO (amide and ester), C α , and C β signals are 172.1, 51.8, and 34.1 ppm, respectively, which are characteristic of the ω L -helix form.…”
Section: Resultssupporting
confidence: 87%
“…Figure shows 67.80 MHz 13 C CP-MAS NMR spectra of [Asp*(OBzl)] n adopting four different kinds of conformations (α R -helix, α L -helix, ω L -helix, and β-sheet forms). The assignment of the peaks for each carbon was determined on the basis of reference data reported previously. , The 13 C isotropic chemical shifts determined from these spectra are listed in Table . 1 The 67.80 MHz 13 C CP-MAS NMR spectra of [Asp*(OBzl)] n with (a) α R -helix, (b) α L -helix, (c) ω L -helix, and (d) β-sheet forms in the solid state.…”
The relationship between the 15N isotropic chemical shift (δ
iso) or 15N chemical shift tensor
components (δ
11, δ
22, and δ
33) and the main-chain conformationsuch as the right-handed α-helix (αR-helix), left-handed α-helix (αL-helix), left-handed ω-helix (ωL-helix), and antiparallel β-sheet (β-sheet)
forms of 15N-labeled poly(β-benzyl l-aspartate) [Asp*(OBzl)]
n
in the solid statewas studied using solid-state 15N NMR methods. We have found that the δ
iso and δ
22 of Asp*(OBzl) residue were significantly
displaced depending upon conformation: δ
iso (αR-helix, 98.9; αL-helix, 96.8; ωL-helix, 96.3; β-sheet, 100.0
ppm) and δ
22 (αR-helix, 52.8; αL-helix, 48.3; ωL-helix, 47.4; β-sheet, 56.4 ppm). Thus, it became apparent
that the δ
iso and δ
22 are very useful barometers for the conformational analysis, especially for the
determination of the helical sense of [Asp*(OBzl)]
n
in the solid state.
“…For [Asp*(OBzl)] n -2, the 13 C chemical shift values were observed at 172.5 (CO (amide and ester)), 51.5 (C α ), and 34.5 ppm (C β ), which are characteristic of the α L -helix form. These values are in good agreement with those obtained for films cast from chloroform solution . For [Asp*(OBzl)] n -3, the 13 C chemical shift values of the CO (amide and ester), C α , and C β signals are 172.1, 51.8, and 34.1 ppm, respectively, which are characteristic of the ω L -helix form.…”
Section: Resultssupporting
confidence: 87%
“…Figure shows 67.80 MHz 13 C CP-MAS NMR spectra of [Asp*(OBzl)] n adopting four different kinds of conformations (α R -helix, α L -helix, ω L -helix, and β-sheet forms). The assignment of the peaks for each carbon was determined on the basis of reference data reported previously. , The 13 C isotropic chemical shifts determined from these spectra are listed in Table . 1 The 67.80 MHz 13 C CP-MAS NMR spectra of [Asp*(OBzl)] n with (a) α R -helix, (b) α L -helix, (c) ω L -helix, and (d) β-sheet forms in the solid state.…”
The relationship between the 15N isotropic chemical shift (δ
iso) or 15N chemical shift tensor
components (δ
11, δ
22, and δ
33) and the main-chain conformationsuch as the right-handed α-helix (αR-helix), left-handed α-helix (αL-helix), left-handed ω-helix (ωL-helix), and antiparallel β-sheet (β-sheet)
forms of 15N-labeled poly(β-benzyl l-aspartate) [Asp*(OBzl)]
n
in the solid statewas studied using solid-state 15N NMR methods. We have found that the δ
iso and δ
22 of Asp*(OBzl) residue were significantly
displaced depending upon conformation: δ
iso (αR-helix, 98.9; αL-helix, 96.8; ωL-helix, 96.3; β-sheet, 100.0
ppm) and δ
22 (αR-helix, 52.8; αL-helix, 48.3; ωL-helix, 47.4; β-sheet, 56.4 ppm). Thus, it became apparent
that the δ
iso and δ
22 are very useful barometers for the conformational analysis, especially for the
determination of the helical sense of [Asp*(OBzl)]
n
in the solid state.
Solid-state NMR measurements have been reported for four peptides derived from beta-amyloid peptide Abeta(1-42): Abeta(1-40), Abeta(10-35), Abeta(16-22), and Abeta(34-42). Of these, the first two are predicted to be amphiphilic and were reported to form parallel beta-sheets, whereas the latter two peptides appear nonamphiphilic and adopt an antiparallel beta-sheet organization. These results suggest that amphiphilicity may be significant in determining fibril structure. Here, we demonstrate that acylation of Abeta(16-22) with octanoic acid increases its amphiphilicity and changes the organization of fibrillar beta-sheet from antiparallel to parallel. Electron microscopy, Congo Red binding, and one-dimensional 13C NMR measurements demonstrate that octanoyl-Abeta(16-22) forms typical amyloid fibrils. Based on the stability of monolayers at the air-water interface, octanoyl-Abeta(16-22) is more amphiphilic than Abeta(16-22). Measurements of 13C-13C and 15N-13C nuclear magnetic dipole-dipole couplings in isotopically labeled fibril samples, using the constant-time finite-pulse radiofrequency-driven recoupling (fpRFDR-CT) and rotational echo double resonance (REDOR) solid-state NMR techniques, demonstrate that octanoyl-Abeta(16-22) fibrils are composed of parallel beta-sheets, whereas Abeta(16-22) fibrils are composed of antiparallel beta-sheets. These data demonstrate that amphiphilicity is critical in determining the structural organization of beta-sheets in the amyloid fibril. This work also shows that all amyloid fibrils do not share a common supramolecular structure, and suggests a method for controlling the structure of amyloid fibrils.
“…PBLA samples with various secondary structures can be obtained by heat treatment with different temperatures. 41 This has been demonstrated by real-time temperature-variable 13 C CP-MAS NMR measurements. 53 It was seen that PBLA takes the a R -helix form at room temperature, and by elevating the temperature, the a R -helix form is gradually changed to the o L -helix form and, at the same time, slightly to the b-sheet form.…”
Section: Conformation-dependent Nmr Chemical Shifts Of Peptides and Pmentioning
confidence: 93%
“…[35][36][37][38]40 Here, it is seen that the C a and C ¼ O peaks of the a-helix form are all displaced downfield with respect to those of the b-sheet form, consistent with the experimental data of (Ala) n . Furthermore, the 13 41 It is shown that the absolute 13 C chemical shifts of the C a and C b carbons are affected by the chemical structure of the individual amino-acid residues and can be used effectively for conformational studies of the particular amino acid residues in polypeptides and proteins. However, the C ¼ O chemical shifts do not seem to be affected by the residue structure and thus can be used to determine the main-chain conformation.…”
Section: Conformation-dependent Nmr Chemical Shifts Of Peptides and Pmentioning
Studies on the NMR methodology for characterizing the structure of polymers and biopolymers based on the understanding of the NMR chemical shift/structure correlation using solution-state and solid-state NMR experiments, the development of the NMR chemical shift theory and their combination have been reviewed. Polymer Journal (2012) 4 and Johnsen and Tessmar 5 independently reported a very important discovery for polymer science: the a-CH 3 signals in the 1 H NMR spectrum of poly(methyl methacrylate)s with different tacticities in chloroform solution appear at different chemical shift positions, in which the three splitting signals were assigned to the rr, mr and mm triads from upfield on the basis of sophisticated and reasonable experiments, where m and r are the meso and racemic dyads, respectively. Since that time, NMR spectroscopy has been well recognized to be the most powerful method available for characterizing the structures of polymers. This means that the chemical shift (chemical shielding), as one of the important NMR parameters, 6 can be meaningfully used for the structural characterization of polymers.With such a foundation, the sophisticated understanding and development of the NMR chemical shift/structure correlation for the structural characterization of polymers and biopolymers have been implemented as one of our research programs. In this review, it is shown by the author and his colleagues that understanding the NMR chemical shift/structure correlation provides a powerful methodology for the structural characterization of polymers and biopolymers based on the sophisticated development of solution-state and solid-state NMR experiments, the development of NMR chemical shift theory, and their combination. 7,8 THE CONCEPT OF THE NMR CHEMICAL SHIFT/STRUCTURE CORRELATION A polymer chain has an enormous number of chemical bonds. In the solution state, the NMR chemical shifts of polymers are generally the averaged values over all of the possible conformations because of the rapid interconversions by rotation around the chemical bonds. However, in solids, the chemical shifts are often characteristic of specific conformations because of strongly restricted rotation around the bonds. 7,8 The NMR chemical shift is affected by a change in the electronic structure caused by the conformational change. Solid-state NMR chemical shifts, therefore, provide useful information about the electronic structure of a polymer chain and multiple polymer chains with a fixed structure. Furthermore, the complete chemical shift tensor components can often be determined because the chemical shift is, in principle, the second-rank tensor quantity. The complete chemical shift tensor components (the chemical shift anisotropy) of polymers and biopolymers provide information about the local symmetry of the electron cloud around the nucleus, and therefore, provide much more detailed knowledge about the conformation associated with electronic structure compared with the averaged chemical shift. To completely understand the NMR ch...
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