Takuo Ozaki

Hydrogen-bonding structural study of solid peptides and polypeptides containing a glycine residue by 17O NMR spectroscopy

Abstract Static 17 O NMR spectra of polyglycines I and II and glycylglycine peptides in the solid state were measured by the cross polarization technique. By computer simulations of these spectra, three NMR parameters (quadrupolar coupling constant ( e 2 qQ / h ), electric field gradient asymmetry parameter (η Q ), and chemical shift (δ)) were determined. From these results, it was found that as the hydrogen bond length decreased, the e 2 qQ / h value decreased. Furthermore, the principal values of the 17 O chemical shift tensor for both the peptides and polypeptides moved upfield with a decrease in the hydrogen bond length. From these experimental findings, it was clarified that 17 O NMR spectroscopy can provide a useful means of elucidating the hydrogen-bonding structure in solid peptides and polypeptides.

Hydrogen-bonding effect on 15N NMR chemical shifts of the glycine residue of oligopeptides in the solid state as studied by high-resolution solid-state NMR spectroscopy

Abstract High-resolution 15 N NMR spectra of a variety of solid oligopeptides (X-Gly-Gly) containing glycine residues have been measured, of which the crystal structures had already been determined by X-ray diffraction. The experimental 15 N chemical shifts of the glycine residues were plotted against the N⋯O hydrogen bond length and the NH bond length in the type hydrogen bond form, respectively. It was found that the decrease of the NH bond length leads to a linear increase in 15 N shielding, but there is no clear relationship between the 15 N chemical shifts and the N⋯O separation. Further, 15 N chemical shift calculations were carried out using a model compound, by the FPT-INDO method, in order to further understand the nature of the hydrogen bond. The calculated results reasonably explain the experimental ones.

A Survey of Trace Elements in Pteridophytes

Concentration of 11 trace elements (Ca, Sc, Cr, Fe, Co, Zn, Rb, Cs, Ba, La, and Ce) in 96 pteridophytes (fern and fern ally species) was determined by instrumental neutron activation analysis to evaluate a concentration range for each element and also to find species characteristic in the uptake of trace elements. Asplenium trichomanes was found to accumulate Sc, Cr, and Co to the highest concentrations among 96 pteridophytes. The highest concentration of Ca and Zn was observed for Asplenium obscurum. The other Pteridophytes exhibited only one element whose concentration was the highest. A positive correlation was found between the concentrations of Fe and Sc, and also between the concentrations of Cr and Co. The remarkable accumulation of lanthanides (La and Ce) was observed mainly in diversifying genera (Polystichum and Dryopteris in Dryopteridaceae, Diplazium in Woodsiaceae, and Asplenium in Aspleniaceae).

17O NMR chemical shifts and quadrupole coupling constants in solid poly(L-alanine)s determined using a high-speed MAS technique

Abstract The solid-state 17 O NMR spectra of L-alanine-residue containing polypeptides were measured by magic-angle spinning (MAS) at 25 kHz. NMR parameters such as the chemical shift, quadrupolar coupling constant and asymmetry parameter are obtained from the spectra. The relationship between the hydrogen-bonded structure and these NMR parameters is clarified. The hydrogen-bonding structures are related to the quadrupolar coupling constants and the chemical shift values.

Hydrogen-bonded structure and 13C NMR chemical shift tensor of amino acid residue carbonyl carbons of peptides and polypeptides in the crystalline state. Part I

Abstract 13 C chemical shift tensor components ( δ 11 δ 22 and δ 33 ) of glycine (Gly), l -valine (Val), l -leucine (Leu), and l -asparagine (Asp) residue carbonyl carbons (C  O) of peptides and polypeptides covering a wide range of hydrogen-bond lengths ( R N…O ) in the crystalline state have been measured by slow magic-angle-spinning solid-state 13 C NMR. From these experiments, it is found that δ 22 , which lies approximately along the amide C  O bond, moves linearly downfield with a decrease in R N…O and the slope and intercept of the variation of δ 22 against R N…O depend on the amino acid residue. Using this relationship, the R N…O values for polypeptides were determined by observation of the δ 22 of the guest Gly residue incorporated into host polypeptides. δ 11 , and δ 33 are found to be insensitive to the change in R N…O and amino acid residues. Moreover, it is found that the sum of δ 11 and δ 33 is almost constant (337.5 ± 3.5 ppm) and is independent of the amino acid residue. The quantum-chemical calculation on the 13 C shielding constant for a peptide model compound was carried out by the finite perturbation theory within the INDO framework. This calculation acceptably explains the experimental results.

Hydrogen bond length and 15N NMR chemical shift of the glycine residue of some oligopeptides in the solid state

Abstract CP-MAS and CP-static 15 N NMR spectra were measured for a variety of solid oligopeptides containing the glycine residue, the crystal structures of which had already been determined by X-ray diffraction. From the results of the observed 15 N chemical shifts, it was found that the isotropic 15 N chemical shifts (σ iso ) of the glycine residues move downfield with a decrease of hydrogen bond lengths ( R N⋯O ) between the nitrogen and oxygen atoms in the amide groups, and that the pricipal value of σ 33 moves linearly downfield with a decrease of R N⋯O . There is no relationship between the principal value of σ 11 or σ 22 and R N⋯O . This indicates that such a linear downfield shift of σ 33 contributes predominantly to the downfield shift σ iso . Quantum chemical calculations of the 15 N shielding constant for the model compounds were carried out by the FPT-INDO method, and the relationship between 15 N chemical shift and R N⋯O discussed.

Hydrogen-bonding effect on 13C NMR chemical shifts of amino acid residue carbonyl carbons of some peptides in the crystalline state

Abstract 13 C cross polarization-magic angle spinning NMR spectra were measured for a series of peptides containing l -valine, l -leucine and l -aspartic acid residues, for which the crystal structures were already determined by X-ray diffraction, in order to investigate the relationship between hydrogen-bond lengths ( R N…O ) and 13 C chemical shifts of amide carbonyl carbons in the peptides. From these experimental results, it was found that the isotropic 13 C chemical shifts ( δ iso ) of the amino acid residues move linearly downfield with a decrease in R N…O within the hydrogen-bonded length range considered here and also shown in our previous work on glycine and l -alanine residues as expressed by δ iso ( ppm ) = a − bR N…O ( A ) where a and b are 215.4 (ppm) and 14.2 (ppm A −1 ) for the l -valine residue, 202.2 (ppm) and 10.0 (ppm A −1 ) for the l -leucine residue, and 199.0 (ppm) and 9.6 (ppm A −1 ) for the l -aspartic acid residue, respectively. Using these relations, the R N…O values of some polypeptides in the crystalline state were determined through the observation of the amide carbonyl carbon chemical shifts. These values were compared with those determined by the X-ray diffraction method. Furthermore, quantum-chemical calculation of the 13 C shielding constant for a model compound was carried out by the finite perturbation theory INDO method in order to ascertain the 13 C shielding behavior in the formation of hydrogen bonds.

Hydrogen-bonded structure and NMR parameters of oxygen-17 labeled poly(L-alanine)s as studied by solid state oxygen-17 NMR spectroscopy

Abstract 17O-labeled poly(L-alanine)s with different degrees of polymerization were synthesized. These poly(L-alanine)s take an α-helix form and a β-sheet form. Solid state 17O NMR spectra of these polymers were measured at different frequencies. By comparing the obtained spectrum and theoretical simulation, the NMR parameters, such as the quadrupolar coupling constant and chemical shift tensor components, were determined. The relationship between the hydrogen-bonded structure and the NMR parameters was elucidated in relation to the main-chain conformation. In addition, these results were compared with those of polyglycine as reported previously, and the feature of 17O NMR behavior of these polypeptides, associated with the hydrogen-bonded structure, was discussed.

Sorption behavior of europium(III) and curium(III) on the cell surfaces of microorganisms

Summary We investigated the association of europium(III) and curium(III) with the microorganisms Chlorella vulgaris, Bacillus subtilis, Pseudomonas fluorescens, Halomonas sp., Halobacterium salinarum, and Halobacterium halobium . We determined the kinetics and distribution coefficients (Kd) for Eu(III) and Cm(III) sorption at pH 3-5 by batch experiments, and evaluated the number of water molecules in the inner-sphere (NH₂O) and the degree of strength of ligand field (RE/M) for Eu(III) by time-resolved laser-induced fluorescence spectroscopy (TRLFS). Exudates from C. vulgaris, Halomonas sp., and H. halobium had an affinity for Eu(III) and Cm(III). The log Kd of Eu(III) and Cm(III) showed that their sorption was not fully due to the exchange with three protons on the functional groups on cell surfaces. The halophilic microorganisms (Halomonas sp., Halobacterium salinarum, H. halobium) showed almost no pH dependence in log Kd, indicating that an exchange with Na+ on the functional groups was involved in their sorption. The Δ NH₂O(=9-NH₂O) for Eu(III) on C. vulgaris was 1-3, while that for the other microorganisms was over 3, demonstrating that the coordination of Eu(III) with C. vulgaris was predominantly an outer-spherical process. The RE/M for Eu(III) on halophilic microorganisms was 2.5-5, while that for non-halophilic ones was 1-2.5. This finding suggests that the coordination environment of Eu(III) on the halophilic microorganisms is more complicated than that on the other three non-halophilic ones.

Association mechanisms of Europium(III) and Curium(III) with Chlorella vulgaris.

The association of Europium(III) (Eu[III]) and Curium(III) (Cm[III]) with Chlorella vulgaris and with cellulose was studied by a batch method and time-resolved laser-induced fluorescence spectroscopy (TRLFS). The kinetics study performed by the batch method showed that maximum adsorption of Eu(III) and Cm(III) on C. vulgaris was attained within 3 min of contact; afterward, the percentage adsorption decreased with time due to chelation of the ions with exudates released from C. vulgaris with a strong affinity for Eu(III) and Cm(III). The TRLFS revealed that the short-term adsorption of Eu(III) on C. vulgaris was attributable to its coordination with cellulose on the algal cell wall. However, Eu(III) coordinated with the functional groups of cellulose very weakly despite the large distribution coefficients observed. These results indicate that the reactions, both at the cells surfaces through adsorption and in solution phases through chelation with the exudates, are important in estimating the behavior of Eu(III) and Cm(III) in aqueous environments.