•A new sequence, DAMAT, for magic-angle hopping/turning experiments is described.•DAMAT incorporates the double-acquisition method to enhance the S/N ratio.•DAMAT realizes better S/N and has several favorable features.The double-acquisition scheme for efficient data collection of hypercomplex data (the States method) of a two-dimensional experiment is adopted to magic-angle hopping (MAH) and magic-angle turning (MAT) experiments, which are powerful methods to measure the principal values of the chemical shift anisotropy (CSA) in a powder sample. It is shown that the double acquisition MAT (DAMAT) sequence realizes the S/N ratio comparable to or better than those of other variants of the MAH/MAT sequences. In addition, we show that DAMAT has preferable features that there are no spinning sidebands in the indirect dimension, and no spectral shearing is necessary.

Pradimicin A (PRM-A) is a unique natural product that recognizes d-mannopyranoside (Man) in the presence of Ca2+ ion. Although the Man binding geometry of PRM-A is largely understood, the molecular basis of Man recognition has yet to be established because of the lack of information regarding Ca2+ binding geometry. In this work, to examine the Ca2+ binding site of PRM-A, we performed a solid-state nuclear magnetic resonance experiment using 111Cd2+ as a surrogate probe for Ca2+. Evaluation of 13C–111Cd distances in the [PRM-A/111Cd2+] complexes by rotational-echo double resonance (REDOR) and 111Cd frequency selective REDOR (FSR) revealed that PRM-A binds 111Cd2+ at the anthraquinone moiety, which contradicts the previous hypothesis of the alanine moiety being the Ca2+ and Cd2+ binding sites of PRM-A. The distances between Cd2+ and the carbon atoms at the binding site of PRM-A were found to be 3.5 ± 0.2 Å. Importantly, Man binding was shown not to alter the distances, indicating that [PRM-A/Ca2+] and [PRM-A/Ca2+/Man] complexes have similar Ca2+ binding geometries. This study provides an important clue to understanding the molecular basis of Man recognition of PRM-A.

To investigate local structures of left-handed α-helix (αL) and left-handed ω-helix (ωL), the principal values (δ11, δ22, and δ33) of the 13C chemical shift anisotropy (CSA) tensors of the main-chain carbonyl (C═O) carbons in poly(β-benzyl l-aspartate) were determined by 13C switching-angle sample-spinning solid-state NMR. Further, the observed CSA tensor values for αR, αL, and ωL are compared with those obtained by quantum chemical calculation for a model peptide. Although the isotropic chemical shifts of the C═O carbons in αR, αL, and ωL lie within ±2 ppm, the δ22 values, whose axis is close to the direction of the hydrogen bond (C═O···H–N), are markedly different. In contrast to the relation established for the δ22 values in various αR helices, that is, an increase of the hydrogen-bond length leads to an upfield shift of δ22, the δ22 values for αL and ωL show a downfield shift for the longer hydrogen-bond length.

Proton multiple-quantum (MQ) spin-counting experiment has been employed to study arrangement of hydrogen atoms in 9 Å/11 Å natural/synthetic tobermorites. Even though all tobermorite samples give similar characterless, broad static-powder 1H NMR spectra, their MQ spin-counting spectra are markedly different; higher quanta in 11 Å tobermorite do not grow with the MQ excitation time, while those in 9 Å one do. A statistical analysis of the MQ results recently proposed [26] is applied to show that hydrogens align in 9 Å tobermorite one dimensionally, while in 11 Å tobermorite they exist as a cluster of 5–8 hydrogen atoms.

•We propose a novel cross-polarization (CP) sequence under magic-angle spinning.•Like in COMPOZER, polarization transfer occurs between Z magnetizations.•The sequence is tolerant of RF field inhomogeneity and Hartmann–Hahn mismatch.•It retains these merits characteristic of COMPOZER, and still works under MAS.We propose a cross polarization (CP) sequence effective under magic-angle spinning (MAS) which is tolerant to RF field inhomogeneity and Hartmann–Hahn mismatch. Its key feature is that spin locking is not used, as CP occurs among the longitudinal (Z) magnetizations modulated by the combination of two pulses with the opposite phases. We show that, by changing the phases of the pulse pairs synchronized with MAS, the flip–flop term of the dipolar interaction is restored under MAS.Download high-res image (215KB)Download full-size image

A novel statistical approach for analyzing 1H multiple-quantum (MQ) spin dynamics in so-called spin-counting solid-state NMR experiments is presented. The statistical approach is based on the percolation theory with Monte Carlo methods and is examined by applying it to the experimental results of three solid samples having unique hydrogen arrangement for 1–3 dimensions: the n-alkane/d-urea inclusion complex as a one-dimensional (1D) system, whose 1H nuclei align approximately in 1D, and magnesium hydroxide and adamantane as a two-dimensional (2D) and a three-dimensional (3D) system, respectively. Four lattice models, linear, honeycomb, square and cubic, are used to represent the 1H arrangement of the three samples. It is shown that the MQ dynamics in adamantane is consistent with that calculated using the cubic lattice and that in Mg(OH)2 with that calculated using the honeycomb and the square lattices. For n-C20H42/d-urea, these 4 lattice models fail to express its result. It is shown that a more realistic model representing the 1H arrangement of n-C20H42/d-urea can describe the result. The present approach can thus be used to determine 1H arrangement in solids.

To establish a relationship between the secondary structure of a peptide and the quadrupolar coupling of its amide 14N, we examined 14N quadrupolar couplings for eight different polypeptide samples, each of whose secondary structure (α-helix or β-sheet) is known. The 14N quadrupolar coupling is estimated from indirect observation of a 14N overtone resonance under magic-angle spinning. From the observed indirect 14N overtone spectra and calculated 14N quadrupolar couplings for model molecules by using ab initio calculation (Gaussian03), it is shown that the quadrupolar coupling for the α-helix is larger than that for the β-sheet by a few 100 kHz irrespective of the kind of amino acid residues examined (Ala, Val, Leu).

To examine noisy nuclear-magnetic resonance (NMR) spectra, we have developed a novel signal analysis method based on phase correlation between the NMR signal and the excitation pulse. The new phase-covariance analysis is compatible with the conventional signal accumulation, and successful de-noising is demonstrated.

In most solid-state NMR experiments, cross-polarization is an essential step to detect low-γ nuclei such as 13C and 15N. In this study, we present a new cross-polarization scheme using spin-locks composed of composite 0° pulses in the RF channels of high-γ and low-γ nuclei to establish the Hartmann–Hahn match. The composite 0° pulses with no net nutation-angle{(2π)X − (2π)−X − (2π)Y − (2π)−Y −}n applied simultaneously to both high-γ (I) and low-γ (S  ) nuclei create an effective heteronuclear dipolar Hamiltonian Hd(0)=d2(2IZSZ+IXSX+IYSY), which is capable of transferring the Z-component of the I spin magnetization to the Z-component of the S spin magnetization. It also retains a homonuclear dipolar coupling Hamiltonian that enables the flip–flop transfer among abundant spins. While our experimental results indicate that the new pulse sequence, called composite zero cross-polarization (COMPOZER-CP) performs well on adamantane, it is expected to be more valuable to study semi-solids like liquid crystalline materials and model lipid membranes. Theoretical analysis of COMPOZER-CP is presented along with experimental results. Our experimental results demonstrate that COMPOZER-CP overcomes the RF field inhomogeneity and Hartmann–Hahn mismatch for static solids. Experimental results comparing the performance of COMPOZER-CP with that of the traditional constant-amplitude CP and rampCP sequences are also presented in this paper.

The thermodynamic characteristics associated with conformational change of poly(β-benzyl l-aspartate) (PBLA) in the solid state are studied by using 13C high-resolution solid-state NMR. PBLA was chosen because four different conformations, i.e., the right-handed (αR-) and left-handed α-helices (αL-helix), left-handed ω-helix (ωL-helix), and antiparallel β-sheet (β-sheet), can be prepared separately, and the thermally induced transition occurs among them. In this work, we analyze spectral changes due to conformational transformation of PBLA and determine the enthalpic and entropic changes associated with the transformation of αR-helix to other conformations; the enthalpic change ΔH per residue becomes ca. 1.4 kJ mol−1, and the entropic change ΔS per residue becomes ca. 3.5 J K−1 mol−1. With using these ΔH and ΔS values, we show that the observed transition curve can be reproduced by a simple statistical model.

A compensation method based on reference deconvolution is developed to obtain high-resolution NMR spectra under an unstable magnetic field. It is shown that the applicability of the original deconvolution method is limited for small fluctuation, and a process what may be called phase reconstruction is proposed to compensate large field fluctuation. We demonstrate the method using a probe with a coil that can generate a fluctuation field artificially. A high-resolution 1H NMR spectrum of ethylbenzene was obtained under the unstable field after compensation with this method.

A novel statistical approach for analyzing 1H multiple-quantum (MQ) spin dynamics in so-called spin-counting solid-state NMR experiments is presented. The statistical approach is based on the percolation theory with Monte Carlo methods and is examined by applying it to the experimental results of three solid samples having unique hydrogen arrangement for 1–3 dimensions: the n-alkane/d-urea inclusion complex as a one-dimensional (1D) system, whose 1H nuclei align approximately in 1D, and magnesium hydroxide and adamantane as a two-dimensional (2D) and a three-dimensional (3D) system, respectively. Four lattice models, linear, honeycomb, square and cubic, are used to represent the 1H arrangement of the three samples. It is shown that the MQ dynamics in adamantane is consistent with that calculated using the cubic lattice and that in Mg(OH)2 with that calculated using the honeycomb and the square lattices. For n-C20H42/d-urea, these 4 lattice models fail to express its result. It is shown that a more realistic model representing the 1H arrangement of n-C20H42/d-urea can describe the result. The present approach can thus be used to determine 1H arrangement in solids.

To examine noisy nuclear-magnetic resonance (NMR) spectra, we have developed a novel signal analysis method based on phase correlation between the NMR signal and the excitation pulse. The new phase-covariance analysis is compatible with the conventional signal accumulation, and successful de-noising is demonstrated.