Tadao Hayakawa

Synthesis and conformational study of poly(l-β-3,4-dihydroxyphenyl-α-alanine)

Abstract High molecular weight poly( l -β-3,4-dihydroxyphenyl-α-alanine) has been synthesized. Both optical rotatory dispersion and circular dichroism spectra of the polypeptide are anomalous and give little information about its conformation. From the total results obtained by a study of the optical rotation, nuclear magnetic resonance and infra-red absorption, poly( l -β-3,4-dihydroxyphenyl-α-alanine) is most probably right-handed helical in trimethyl phosphate, methanol or water/trimethyl phosphate ( 1:1 v v ) mixed solvents below pH 10.4. It is in the random coil structure in dimethyl sulphoxide or water/trimethyl phosphate mixed solvents above pH 11. The transition midpoint is pH 10.6 in water/trimethyl phosphate mixed solvents. The results were compared with those of poly( l -tyrosine).

VIBRATIONAL CIRCULAR DICHROISM OF PROLINE-CONTAINING OLIGOPEPTIDES

Vibrational circular dichroism (VCD) and infrared absorption spectra in the amide A region of blocked oligopeptides containing proline have been obtained in apolar organic solvents in order to clarify the characteristic VCD for the intramolecularly hydrogen-bonded NH stretching involved in the turn structures of peptide chains as well as the intermolecularly hydrogen-bonded NH stretching in associated molecules. The γ-turn with the intramolecularly hydrogen-bonded C7 conformation exhibits a characteristic positive VCD band at about 3330 cm−1 in dilute solutions of Piv-Pro-NHMe and Ac-Pro-NHMe. The intramolecularly hydrogen-bonded NH stretching in the type II β-turn with C10 conformation gives rise to a positive VCD band at 3345 cm−1 for Piv-Pro-Gly-NHMe. The Gly NH group of Piv-Pro-Gly-OMe and Ac-Pro-Gly-OMe in dilute solutions assumes C7C5 conformation stabilized by a bifurcated three-center intramolecular hydrogen bond and exhibits a positive VCD band near 3300 cm−1 at a lower frequency than the intermolecularly hydrogen-bonded band. All the peptides studied give a characteristic negative—positive bisignate couplet from the high wavenumber side for the intermolecularly hydrogen-bonded NH stretching band at high concentrations.

Catalytic actions of synthetic polypeptides: 2. stereoselective inhibition of ascorbic acid oxidation by the basic polypeptide-copper (II) complexes

Abstract The oxidation of l -ascorbic acid and d -isoascorbic acid by the poly( l -lysine) (PLL), poly( d -lysine) (PDL), poly( l -ornithine), poly( l -arginine) and poly( l -histidne) Cu(II) complexes in phosphate buffer has been investigated. Most polypeptide-Cu(II) complexes showed an inhibitory effect. However, a comparison of the initial velocities of the enantiomeric polypeptide Cu(II) complexes gave the stereoselectivity indices ( V O ) PDL cu/( V O ) PLL-Cu = 2.8 on l -ascorbic acid and 1.8 on d -isoascorbic acid at pH 5. At alkaline pH, the reverse was found for the stereoselective oxidation. At pH 10.5, the indices were calculated to be 0.7 on both ascorbic acids.

Improved synthetic method and conformation studies of polymers and copolymers of l-β-3,4-dihydroxyphenyl-α-alanine with l-glutamic acid

Abstract Eight different copolymers of l -β-3,4-dihydroxyphenyl-α-alanine ( l -Dopa) and l -glutamic acid with high degrees of polymerization have been synthesized by the treatment of a series of copoly (O,O′- dimethyl- l -Dopa , γ-benzyl- l -glutamate) with boron tribromide in chloroform. The conformation of poly( l -Dopa) has been established to be a right-handed helix in trimethyl phosphate on the basis of the following observations. The [ θ ] 222 and b 0 values of the copolymers were almost linear with composition in trimethyl phosphate. The linear relationship between the rotation properties and composition indicates that poly( l -Dopa) has the same helical sense as that of poly( l -glutamic acid) which is a right-handed α-helix.

Circular dichroism of poly(β-benzyl-l-aspartate) films in the α, β and ω conformations

The conformations of poly(β-benzyl l-aspartate) (PBLA) in film were studied by means of circular dichroism (c.d.). Films of PBLA show c.d. which is related to the benzyl chromophores of this polypeptide. The magnitude and sign of the c.d. of the benzyl chromophores depend on the conformation i.e. α-helix, ω-helix or β-form. The aromatic c.d. of the left-handed α-helix or the left-handed ω-helix is negative in sign, and that of the β-form is positive in sign. The absolute magnitude of the c.d. of PBLA is much larger in the ω-helical conformation than in the α-helical or the β-conformations. In the left-handed α-helical PBLA (α-PBLA), the positive dichroism band of the n−π∗ peptide electronic transition is observed at about 226 nm. When the α-PBLA is converted to the left-handed ω-helical PBLA (ω-PBLA), the band at 226 nm shifts to 224 nm, and its magnitude becomes much smaller. In the β-form PBLA (β-PBLA), this band is negative in sign and observed at 223 nm. The absolute magnitude of the c.d. relative to this electronic transition follows the order: β-form < ω-helix < α-helix.

Functional metallomacrocycle derivatives and their polymers. Part 23. Biaxially orientated Langmuir–Blodgett films of substituted metallophthalocyanines

Soluble metallophthalocyanine compounds (M = NiII or CuII) with alkyloxycarbonyl groups substituted at either the 2 or 3 position of the benzene ring (alkyl = 1- or 2-octyl, or 1-decyl) were synthesized by the reaction of the corresponding metallophthalocyaninetetracarboxyl chlorides with the alkyl alcohols, and monolayers were formed at a water–air interface. All compounds formed stable monolayers at surface pressures higher than ca. 15 mNm–1. In the Langmuir–Blodgett films built up from monolayers of the compounds on Pyrex substrates, the orientation of the phthalocyanine rings was shown to be biaxial from the one-dimensional orientation of the phthalocyanine stacked columns, observed by measurement of polarized visible absorption spectra.

Conformation of polyamino acids containing fluorine

Abstract The conformation of poly(γ-4-fluoro-benzyl- l -glutamate) (F-PBLG) and poly(γ-4-trifluoromethyl-benzyl- l -glutamate) (CF 3 -PBLG) was investigated. Circular dichroism (c.d.), infra-red (i.r.) spectra and X-ray analysis indicated that the secondary structure of F-PBLG and CF 3 -PBLG was α-helical both in the solid state and in chloroform solution, similar to PBLG, while it was random coil in trifluoroacetic acid (TFA) and dichloroacetic acid (DCA). In the chloroform-TFA solvent system, these polypeptides changed their conformation from helix to coil; the minimum TFA concentrations required for helix-coil transition were 10–12% in CF 3 -PBLG, 14% in F-PBLG and 12–13% in PBLG. The results suggest that CF 3 groups have a pronounced effect on the stability of α-helical structure of these polypeptides. The helix-coil transition of the polypeptides was accompanied by a perturbation of 19 F nuclear magnetic resonance chemical shift.

Circular dichroism studies of complexes of sequential histidine polypeptides with methyl orange

Abstract The induced circular dichroism (c.d.) spectra of poly( l -histidine) and sequential histidine polypeptide-dye complexes were measured. Two dichroic bands associated with the blue shifted absorption shoulder of methyl orange at around 370 nm were observed by complex formation between the polypeptides and the dye. Induced c.d. arose from the dye bound to the polypeptide in random coil structure, the optimal pH being 4.1. Added sodium chloride decreases the intensity of the induced c.d. Intramolecular interaction was assumed from the relationship between the concentrations of the polypeptide-dye complex and the intensities of the induced c.d. The intensity of the induced c.d. decreases with increasing distance between the intramolecular histidine residues. The induced c.d. spectrum of the poly( l -histidine)-dye complex shows the irreversible thermal change when heating.

Synthesis and conformational studies of polymers and copolymers of O,O′-dimethyl-l-β-3,4-dihydroxyphenyl-α-alanine with γ-benzyl-l-glutamate

Eight different copolymers of O,O′-dimethyl-l-β-3,4-dihydroxyphenyl-α-alanine (O,O′-dimethyl-l-Dopa) and γ-benzyl-l-glutamate with degrees of polymerization of 320-80 have been synthesized by the N-carboxyanhydride method. From the results obtained by a study of the optical rotatory dispersion and circular dichroism for the copolymer series, the conformation of poly(O,O′-dimethyl-l-Dopa) is a right-handed helix in helicogenic solvents such as chloroform, dioxane or 2-chloroethanol. Copolymers containing less than 50 mol % glutamate show a circular dichroism peak at 285 nm suggesting stacking of aromatic groups in the side chain. Poly(O,O′-dimethyl-l-Dopa) is in the random coil structure in trifluoroacetic acid or hexafluoroacetone. The results were compared with those of poly(O,O′-dicarbobenzoxy-l-Dopa) and poly(l-Dopa).

Studies of polymers and copolymers of O,O′-dicarbobenzoxy-l-β-3,4-dihydroxyphenyl-l-alanine with γ-benzyl-l- and d-glutamates

Abstract The synthesis of ten different copolymers of O,O′- dicarbobenzoxy- l -β-3,4,- dihydroxyphenyl -α- alanine ( O,O′- dicarbobenzoxy- l -Dopa ) and γ-benzyl- l - and d -glutamates with degree of polymerization of 40–270 is described. It has been concluded that poly (O,O′- dicarbobenzoxy- l -Dopa ) and poly(γ-benzyl- l -glutamate) exist as helices with the opposite sense of twist in dioxane on the basis of the following observations. The copolymers of O,O′- dicarbobenzoxy- l -Dopa with γ-benzyl- l -glutamate show a linear variation of circular dichroism properties with composition in methylene dichloride, whereas the copolymers do not in dioxane. The results for the copolymers with γ-benzyl- d -glutamate are the reverse in dioxane and methylene dichloride.