Hideki Etori

FT-IR spectra of glycine oligomers

Abstract Fourier transform infrared spectra were revisited for glycine oligomers (trimer through hexamer) and polyglycine. Oligomers precipitated from aqueous solutions with acetone existed in the planar zigzag conformation similar to polyglycine I. Infrared spectra for the helical conformation similar to polyglycine II were also obtained for glycine pentamer and hexamer.

Aggregation of polyene antibiotics as studied by electronic absorption and circular dichroism spectroscopies

Abstract The self-association of amphotericin B and hamycin, the heptaene polyene antibiotics, was observed in alcoholic solutions on addition of increasing amounts of water at a studied antibiotics concentration of 1 × 10 −5 M. An increase in the aggregation was noticed in methanolic solutions at and above 65–70% (vol. %) water content. The antibiotics were found to be aggregated at and above 85% water content in propanol. The increased water content required to initiate the aggregation in propanol was related to the more hydrophobic nature of the latter. The aggregation of antibiotics was hindered by the addition of Triton X-100, a non-ionic detergent, at a concentration of 0.5%. The self-association of amphotericin B and hamycin was observed at concentrations of 5 × 10 −7 and 1 × 10 −7 M respectively, in phosphate-buffered saline as detected by the presence of an excitonic doublet in their circular dichroism (CD) spectra. The aggregation was found to be enhanced while the concentration increased up to the studied concentration of 5 × 10 −5 M. The polyene antibiotics existed as monomers in dimethyl sulfoxide(DMSO) at concentrations of 1 × 10 −7 −4.3 × 10 −2 M and 1 × 10 −7 −1 × 10 −2 M for amphotericin B and hamycin respectively, as revealed by their concentration-independent CD spectra.

Vibrational Spectroscopic Evidence for the Associated-Anion Promotion of the Helical Structure of N-Acylglycine Oligomers

Vibrational spectroscopic evidence for conformational change of the anions of N-acylglycine oligomers (trimers, tetramers, and pentamers) in aqueous solution is reported. The infrared absorption spectra of sample solutions diluted below the critical micelle concentration (cmc) can be explained by the coexistence of several conformations containing the polyglycine I-like extended form and the polyglycine II-like helix. However, above the cmc the infrared bands arising from the polyglycine II-like helix are intensified. This result is due to preferential stabilization of the helical structure, promoted by intermolecular association of the anions. The helical structure is also stable in the hydrophobic environment of micelles.

Vibrational spectra of N-acylglycine oligomers and the long N-acyl chain effect

Trimers, tetramers and pentamers of N-acylglycine oligomer acid types with various acyl chains, their potassium or sodium salts, and their N-deuterated salts have been prepared. The vibrational spectra of these molecules have been measured and compared with those of polyglycine I (PGI; extended β form) and polyglycine II (PGII; helical form). Only a conformation similar to PGII exists in the solid state for these compounds. The long acyl chains induce a further PGII-like structure in the NH⋯OC and peptide skeletons. This effect is reflected markedly in the NH and ND stretching, amide I and II and low-frequency regions.

Vibrational spectroscopic analysis of N-acyl-l-alanine oligomers and β-sheet structure promoted by the long acyl chains

Abstract Trimers and tetramers of N- acyl- l -alanine oligomer acid types with various acyl chains (acetyl, butanoyl, hexanoyl and octanoyl groups), their potassium (K) salts and their benzylesters have been synthesized. The vibrational spectra of these oligomers have been measured and compared with those of α-helical and β-sheet poly( l -alanine). A conformation similar to β-poly( l -alanine) was found in the solid state for these oligopeptides. The long acyl chains induce a further β-sheet structure in the hydrogen bonding of the peptide skeleton. This effect is reflected by noticeable changes in the NH stretching, amide-characteristic vibrational modes and low frequency regions.

Raman scattering study of N-acyl-l-alanine oligomer salts: Stabilization of the α-helical structure promoted by micellization

Abstract N -acyl- l -alanine oligomer potassium salts (CH 3 (CH 2 ) n CO(NHCH(CH 3 )CO) m O − K + , n =0, 2, 4, 6 and 8, m =3 and 4) have been synthesized. Raman spectroscopic evidence for a conformational change of the oligomer anions in aqueous solution is reported. The Raman scattering spectra of sample solutions diluted below the critical micelle concentration (cmc) are accounted for by postulating the coexistence of several conformations containing the α -helix, β -sheet, and β -turn structures. Above the cmc, the Raman bands for the amide I, III and skeletal stretch modes which are characteristic of an α -helix become more intense and this result is ascribed to preferential stabilization of the helical structure, promoted by intermolecular association of oligomer anions.

Vibrational spectra of N-acetylglycine oligomersPart 2.—Raman scattering study ofselectively C-deuteriated oligomers with polyglycine I- and II-typestructures

Selectively C-deuteriated N-acetylglycine trimer and tetramer acid types have been synthesized, and their two crystalline modifications, solid-A and solid-B [which correspond in structure to polyglycine (PG) II and I, respectively] have been prepared. Raman scattering spectra have been measured for a series of these glycine oligomers, and the CH 2 - and CD 2 -characteristic modes have been investigated in detail. Assignment of the CH 2 -characteristic bands to each CH 2 group in the oligomers has been carried out successfully. In particular, the results obtained from the CD 2 stretch region show that N- and C-terminal glycine residues for the PGI- and PGII-type trimers and tetramers are all in very similar environments and that the glycine residues which are sandwiched between the two terminal residues are also in a similar environment for both the trimers and the tetramers.

13C and 2H NMR studies of N-acetylglycine oligomer ethyl esters (residue number, n=3–9) and selectively C-deuteriated oligomer acid types (n=3, 4): Intermolecular hydrogen-bonding distance and segmental mobility

N-Acetylglycine oligomer ethyl esters (residue number, n=3–9) and selectively C-deuteriated oligomer acid types (n=3, 4) have been synthesized. Two crystalline modifications, the A- and B-series [which correspond to polyglycine (PG) II and I in structure, respectively] have been prepared. For the two series of oligomers, the intermolecular hydrogen-bond distance (R N···O ) and segmental mobility were evaluated using 13 C CP MAS and 2 H NMR spectra. The results showed that the R N···O values for the A- and B-series of oligomer ethyl esters closely correspond to those of PGII and PGI, respectively, and that for the two series of C-deuteriated oligomers segmental mobilities of the CH 2 groups of both the N- and C-terminal residues are more restricted than those of the methylenes sandwiched between the terminal residues.