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1.
1H-nmr spectra for a series of Boc-L -(Met)n-OMe (n = 2–9) homo-oligopeptides have been observed in the helix-supporting solvent trifluoroethanol (TFE) at millimolar concentrations. Interfering solvent peaks were eliminated using two decoupling frequencies to selectively remove the methylene and hydroxyl protons of the solvent. Comparisons with specifically α-deuterated homo-oligopeptides gave complete assignments of the NH region of the Boc-Metn-OMe oligomers up to the heptapeptide. Analysis of chemical shifts, coupling constants, and temperature dependence of chemical shifts suggests that up to the hexapeptide, similar structures exist in deuterochloroform and TFE. In contrast, nmr parameters at the heptapeptide for several internal residues differ in these solvents. These results suggest that a C7 to α-helix transition may occur in TFE as the chain length of the methionine oligopeptides increases. 相似文献
2.
Hazime Sait Ryoko Tabeta Fernando Formaggio Marco Crisma Claudio Toniolo 《Biopolymers》1988,27(10):1607-1617
High-resolution solid-state 13C-nmr spectra of two series of fully protected oligopeptides, Z-(Aib)n-OMe (n = 3?8) and Z-(Aib)n-L-Leu-(Aib)2-OMe (n = 0?5), were recorded to gain insight into main-chain length dependence for 310-helix formation. We found that all the oligopeptides examined adopt an incipient or a fully developed 310-helical structure, as judged from the characteristic splitting of the Cβ signals as well as the conformation-dependent displacements of the Cα and C?O peaks. 相似文献
3.
A series of L -methionine oligomers [BOC-(Met)n-OMe] (n = 2–7) and the corresponding diastereomeric di- and tripeptides were synthesized using the mixed anhydride method. Oligomers prepared in this manner were optically pure and were obtained in reasonable yield. Preliminary optical examination of the peptides suggests that secondary structures may begin forming in the pentamer or hexamer in trifluoroethanol. BOC-(Met)4-OMe and BOC-(Met)5-OMe were also synthesized using an insoluble resin containing BOC-L -methionine as the nitrophenol active ester. 相似文献
4.
Vibrational CD (VCD) and ir absorption data are reported for a series of films of Boc-(L -Ala)n-OMe homo-oligopeptides (n = 3–7) in the amide I and A regions. The data evidenced a sharp change between n = 3 and n = 4, which parallels the onset of β-structure formation, and another between n = 5 and n = 6, which parallels the full development of β-structure. This represents the first report of the application of VCD to oligopeptide conformation. The data resembled earlier reported film VCD studies of higher-molecular-weight polypeptides of known β-structure. 相似文献
5.
Yu. A. Lazarev V. M. Lobachov B. A. Grishkovski V. A. Shibnev V. S. Grechishko M. P. Finogenova N. G. Esipova V. N. Rogulenkova 《Biopolymers》1978,17(5):1215-1233
Oligotripeptides Z-(Gly-Pro-Pro)n-OMe (n = 1,2,…,8), Z-Gly-Pro_Pro-Gly-Pro-Gly-OMe, Z-Gly-Pro-Pro-Gly-Pro-Gly-Gly-Pro-Pro-OMe, Z-Gly-Pro-Pro-(Gly-Pro-Gly)2-Gly-Pro-Pro-OMe, and Z-(Gly-Pro-Ala)n-OMe (n = 1,2,…,4) were synthesized step-by-step and then studied by means of x-ray diffraction, ir spectroscopy, the kinetics of hydrogen-deuterium exchange of peptide groups, and circular dichroism,. Different stages in the formation of a triple helix in Z-(Gly-Pro-Pro)n-OMe were revealed during the chain elongation. In the solid state, at the first stage a conformation of the polyproline II-type is formed in the tripeptide and in the second stage a triple helical complex appears in the hexapeptide. Interpeptide hydrogen bonds in this complex are still of low order. At further stages an ordered set of interpeptide hydrogen bonds is gradually formed. It is shown that the degree of order of interpeptide H bonds depends on the length of the molecular chain, the amino acid composition, and residue sequence in the triplets. 相似文献
6.
The synthess of 18 co-oligopeptides of L -methionine and glycine is reported. A series of oligomers, Boc-Gly-Metn-OMe (n = 1–6), and six hexamers-containing five methionyl and one glycyl residue were synthesized using the mixed anhydride procedure. Polarimetric studies give evidence that oligomers in the Boc-Gly-Metn-Ome series are essentially disordered in hexafluoroacetone sesquihydrate but begin forming secondry structures at n > 4 in trifluorethanol. Difference in the molar rotation values found for the six hexamers in hexafluoroacetone sesquihydrate may indicate that these compounds, while primirily disordered, are present in slightly different conformations. 相似文献
7.
The conventionally protected oligopeptides of the two homologous series Boc-(L -Ile)n-OMe and Boc-(D -aIle)n-OMe (n = 2–6) were synthesized in a standard stepwise fashion and their uv and CD spectra in 2,2,2-trifluoroethanol, and solid-state ir spectra were investigated. In addition, two oligomeric products derived from the NCAs of L -isoleucine and of D -allo-isoleucine and having a DP of 20 and 12, respectively, were studied in the solid state by x-ray and ir. No substantial differences between the properties of the diastereomeric oligomers in the solid state were noticed, a β-structure being very likely at least for the Boc-protected hexapeptides and the higher oligomers. In contrast, differences were observed between the spectroscopic properties of the diastereomeric oligopeptides, and especially of the hexapeptides, in trifluoroethanol solution. The different properties of the hexapeptides in solution were related to the existence, in the case of Boc-(L -Ile)6-OMe, of soluble molecular aggregates in which the peptide chains assume the β-conformation. These results provide an additional example of the influence of the configuration of asymmetric carbon atoms of the side chains on the conformational properties of peptide molecules in solution. 相似文献
8.
Andr Aubry Daniel Bayeul Hans Brückner Norbert Schiemann Ettore Benedetti 《Journal of peptide science》1998,4(8):502-510
Ac-(Aib-Ala)3-OH (a protected segment of the peptaibols gliodeliquescin and paracelsin), Z-Leu-Aib-Val-Aib-Gly-OtBu (a segment of [Leu]7-gliodeliquescin), Z-Val-Aib-Aib-Gln-OtBu (a common segment of alamethicin, paracelsin, and hypelcin), and Ac-Aib-Pro-(Aib-Ala)2-OMe and Z-Aib-Pro-(Aib-Ala)2-OMe, which represent differently Nα-protected 1–6 segments of alamethicin and hypelcin, have been synthesized by solution methods. The crystal-state conformations of these five Aib-containing peptides have been determined by X-ray diffraction analysis. We have confirmed that the 310-helical structure is preferentially adopted by Aib-rich short peptides. An experimentally unambiguous proof for the 310→α-helix conversion has been provided by the two differently N-blocked -Aib-Pro-(Aib-Ala)2-OMe hexapeptides. The β-bend ribbon conformation, commonly observed in the (Aib-Pro)n sequential oligopeptides, is not found in the -Aib-Pro-Aib-Ala-Aib-Ala- sequence. As expected on the basis of the l -configuration of the Cα-monoalkylated residues, a right-handed helix screw sense was found in all peptides investigated. © 1998 European Peptide Society and John Wiley & Sons, Ltd. 相似文献
9.
An apolar synthetic octapeptide, Boc-(Ala-Aib)4-OMe, was crystallized in the triclinic space group P1 with cell dimensions a = 11.558 Å, b = 11.643 Å, c = 9.650 Å, α = 120.220°, β = 107.000°, γ = 90.430°, V = 1055.889 Å3, Z = 1, C34H60O11N8·H2O. The calculated crystal density was 1.217 g/cm3 and the absorption coefficient ? was 6.1. All the intrahelical hydrogen bonds are of the 310 type, but the torsion angles, ? and ψ, of Ala(5) and Ala(7) deviate from the standard values. The distortion of the 310-helix at the C-terminal half is due to accommodation of the bulky Boc group of an adjacent peptide in the nacking. A water molecule is held between the N-terminal of one peptide and the C-terminal of the other. The oxygen atom of water forms hydrogen bonds with N (1) -H and N (2) -H, which are not involved in the intrahelical hydrogen bonds. The hydrogen atoms of water also formed hydrogen bonds with carbonyl oxygens of the adjacent peptide molecule. On the other hand, 1H-nmr analysis revealed that the octapeptide took an α-helical structure in a CD3CN solution. The longer peptides, Boc-(Ala-Aib)6-OMe and Boc-(Ala-Aib)8-OMe, were also shown to take an α-helical structure in a CD3CN solution. An α-helical conformation of the hexadecapeptide in the solid state was suggested by x-ray analysis of the crystalline structure. Thus, the critical length for transition from the 310- to α-helix of Boc-(Ala-Aib)n-OMe is 8. © 1993 John Wiley & Sons, Inc. 相似文献
10.
E. Benedetti B. Di Blasio V. Pavone C. Pedone A. Santini M. Crisma G. Valle C. Toniolo 《Biopolymers》1989,28(1):175-184
The crystal-state molecular structures of five linear Ac3c homo-oligopeptides to the tetramer were determined by x-ray diffraction. The oligomers are H-(Ac3c)2-OMe, Fmoc-(Ac3c)2-OMe MeOH, Ac-(Ac3c)2-OMe, pBrBz-(Ac3c)3-OMe · H2O, and t-Boc-(Ac3c)4-OMe · 2H2O. The results indicate the propensity of the tri- and tetrapeptides to fold into type I β-bends and distorted 310-helices, respectively, in partial contrast to Aib, Ac5c, and Ac6c homo-peptides of comparable main-chain length, where regular type III β-bends and 310-helical structures were found. When the influence of the constraints produced by the intramolecular H bonds of the C10-type is absent, other less common structural features may be observed. The average geometry of the cyclopropyl group of the Ac3c residue is found to be asymmetric and the N? Cα? C′ bond angle significantly expanded from the regular tetrahedral value. 相似文献
11.
The CD spectra of the peptides Boc-X-(Aib-X)n-OMe (n = 1, 2, 3) and Boc-(Aib-X)5-OMe, where X = L -Ala or L -Val have been examined in several solvents. The X = Ala and Val peptides behave similarly in all solvents, suggesting that the Aib residues dominate the folding preferences of these peptides. The decapeptides adopt helical conformations in methanol and trifluoroethanol, with characteristic negative CD bands at 222 and 205 nm. In the heptapeptides, similar spectra with reduced intensities are observed. Comparison with nmr studies suggest that estimates of helical content in oligopeptides by CD methods may lead to erroneous conclusions. The pentapeptides yield solvent-dependent spectra indicative of conformational perturbations. Peptide association in dioxane results in an unusual spectrum with a single negative band at 210 nm for the decapeptides. Disaggregation is induced by the addition of methanol or water to dioxane solutions. Aggregation of the heptapeptides is less pronounced in dioxane, suggesting that a critical helix length may be necessary to promote association stabilized by helix dipole–dipole interactions. 相似文献
12.
Studies on hydration are important for better understanding of structure and function of nucleic acids. We compared the hydration of self-complementary DNA, RNA and 2′-O-methyl (2′-OMe) oligonucleotides GCGAAUUCGC, (UA)6 and (CG)3 using the osmotic stressing method. The number of water molecules released upon melting of oligonucleotide duplexes, ΔnW, was calculated from the dependence of melting temperature on water activity and the enthalpy, both measured with UV thermal melting experiments. The water activity was changed by addition of ethylene glycol, glycerol and acetamide as small organic co-solutes. The ΔnW was 3–4 for RNA duplexes and 2–3 for DNA and 2′-OMe duplexes. Thus, the RNA duplexes were hydrated more than the DNA and the 2′-OMe oligonucleotide duplexes by approximately one to two water molecules depending on the sequence. Consistent with previous studies, GC base pairs were hydrated more than AU pairs in RNA, whereas in DNA and 2′-OMe oligonucleotides the difference in hydration between these two base pairs was relatively small. Our data suggest that the better hydration of RNA contributes to the increased enthalpic stability of RNA duplexes compared with DNA duplexes. 相似文献
13.
The possibility of selectively reducing the number of β-helical structures theoretically possible for a D ,L -alternating peptide by using a N-methyl group as conformational constraint is considered. Some 1H-nmr data regarding Boc(L -Nle-D -Nle)3-L -Nle-D -MeNle -L -Nle-D -Nle-L -Nle-OMe (I), its formyl analogue (II), and the pentadecapeptide Boc(D -Leu-L -Leu)5-D -MeLeu -(L -Leu-D -Leu)2-OMe (III) are presented. It is shown that these alternating stereocooligopeptides with a N-methyl group in the (n ? 3) (I and II) or (n ? 4) position (III) differ drastically in their behavior from the corresponding nonmethylated compounds. In chloroform, I and II form predominantly ↑↓ β7.2-helices and III forms almost exclusively ↑↓ β5.6 or ↑↓ β7.2-helices. The helices are in every case those having the maximum possible number of interchain H bonds. 相似文献
14.
Nermin Biricik Cezmi Kayan Zhaofu Fei Paul J. Dyson ?smail Özdemir 《Inorganica chimica acta》2010,363(5):1039-1047
Four new bis(phosphino)amine ligands (Ph2P)2N-C6H3-R, where R = 3,5-OMe (1), 2,5-OMe (2), 2,4-OMe (3) or 3,4-OMe (4), were prepared via aminolysis of the corresponding dimethoxyanilines with 2 equiv. of diphenylphosphine chloride in the presence of triethyl amine. Oxidation of these ligands with aqueous H2O2, elemental S8 or Se powder afforded the corresponding chalcogen oxides 1a-4a, sulfides 1b-4b and selenides 1c-4c in good yields. Reaction of 1-4 with [MCl2(cod)] (M = Pt, Pd; cod = cycloocta-1,5-diene) in equimolar ratios afforded cis-[MCl2{(Ph2P)2N-C6H3-R}] (M = Pt; R = 3,5-OMe 1d, R = 2,5-OMe 2d, R = 2,4-OMe 3d, and R = 3,4-OMe 4d. M = Pd; R = 3,5-OMe 1e, R = 2,5-OMe 2e, R = 2,4-OMe 3e, and R = 3,4-OMe 4e). Similarly, reaction of [Cu(CH3CN)4]PF6 with the 1-4 in 1:2 ratio gave [Cu{(Ph2P)2N-C6H3-R}2]PF6 (R = 3,5-OMe 1f, 2,5-OMe 2f, 2,4-OMe 3f and 3,4-OMe 4f). All new compounds were fully characterized by spectroscopy and elemental analysis and the molecular structures of seven representative compounds were determined by single-crystal X-ray crystallography. In addition, the palladium complexes were investigated as pre-catalysts in C-C coupling reactions. 相似文献
15.
Anthony A. Ribeiro Robert P. Saltman Murray Goodman Manfred Mutter 《Biopolymers》1982,21(11):2225-2239
The use of 1H-nmr spectroscopy is demonstrated to be a useful analytical method to characterize the structure of synthetic peptides attached to soluble, macromolecular polyoxyethylene (POE) supports in the liquid-phase method (LPM) of peptide synthesis. We report an extensive 360-MHz 1H-nmr study of POE-bound homo-oligo-L -methionine peptides. A combination of high field and selective saturation or Redfield pulse methods allows resolution of individual backbone NH and α-CH resonances of dilute peptides in the presence of strong resonances from macromolecular POE and/or protonated solvents. The nmr spectra for the POE-bound peptides in CDCl3 are qualitatively similar to those of the low-molecular-weight Boc-L -Metn-OMe peptide esters. This corroborates other observations that POE has little effect on peptide stucture. The backbone α-CH region of peptides is overlapped by signals from the terminal oxyethylene group of POE, but the peptide side-chain and low-field backbone NH resonances are well resolved. In trifluoroethanol the Boc-(L -Met)n-NH-POE heptamer and octamer adopt the right-handed α-helical structure, and the present nmr studies provide evidence for two strong intramolecular hydrogen bonds to stabilize the helices. In water, the N-deblocked derivatives, (L -Met)n-NH-POE oligomers adopt β-sheet structure and manifest well-resolved nonequivalent NH resonances with 6–7 Hz 3JNH-CH coupling constants. 相似文献
16.
The circular dichroism of a series of L -methionine oligopeptides [BOC-(Met)n-OMe] was examined in trifluoroethanol and hexafluoroacetone sesquihydrate. The results indicate that the trimer through the hexamer exists predominantly in disordered conformations in these solvents. An abrupt change in the CD pattern at the heptamer in trifluoroethanol suggests that L -methionine oligopeptides begin forming helices at this chain length. 相似文献
17.
Evaristo Peggion Manlio Palumbo Gian Maria Bonora Claudio Toniolo 《Bioorganic chemistry》1974,3(2):125-132
The conformations of a series of l-phenylalanine oligomers having the general formula BOC-(Phe)n-OMe (n = 1–9) were investigated by circular dichroism in a number of solvent systems. These studies indicate that in trifluoroethanol and in hexafluoroisopropanol these oligomers probably form β-associated conformations beginning at the hexamer. 相似文献
18.
As model peptides of collagen, (Pro-Pro-Gly)n (n = 10, 12, 14, and 15) and (Pro-Pro-Gly)n(Ala-Pro-Gly)m(Pro-Pro-Gly)n (2n + m = 15; m = 1, 3, and 5) were synthesized by the solid-phase method. The final products were pure when checked by high-voltage paper electrophoresis and by amino acid analysis. Elemental composition was also examined. 相似文献
19.
The water-soluble poly(1-vinyl-2-ethylimidazole) quaternized with ethyl bromide and lauryl bromide was prepared; lauryl group content, 8.8 mol% (L-9), 28.9 mol% (L-29), and 40.9 mol% (L-41). The λmax value of methyl orange near 460 nm shifted to shorter wavelengths (417–433 nm) in the aqueous solution of L-29 and L-41, and the intrinsic viscosity of L-29 was more than ten times smaller than that of L-9. The rate and equilibrium constants (k? and K) for addition of cyanide ion to the N-substituted 3-carboxamidopyridinium ions were studied at 30°C, where N-substituents employed were n-propyl, n-hexyl, benzyl, 2,6-dichlorobenzyl, and n-lauryl. The kinetic parameters for n-lauryl-3-carboxamidopyridinium were markedly increased in the presence of L-29 and L-41 and with increasing polymer concentrations (84-fold for k? and 7800-fold for K), especially at low ionic strength, whereas L-9 decelerated the addition reaction. These distinct behaviors mean that L-29 and L-41 are classified as micellelike polymers and L-9 as a polyelectrolytelike polymer. However, L-29 depressed the rate of the forward reaction for benzyl-3-carboxamidopyridinium, acting like a simple polyelectrolyte. Therefore, the polymer micelle can provide both the microenvironments characteristic of polyelectrolytes and micelles, depending on the hydrophobicity of substrates. 相似文献
20.
The ability of oligodesoxyribonucleotides of various chain lengths to form complexes has been compared with that of oligoribonucleotides. Four series of oligonucleotidcs were prepared and investigated, i.e., dCn at acid pH versus rCn, dAn and dTn versus. rAn and rUn at neutral pH. The results indicate that in dilute solution, the formation of complexes is greatly facilitated in the case of desoxyoligomers and occurs for shorter oligomere than in the corresponding ribooligomers. The spectrophotometric titration of deoxyribooligo C indicates the appearance of two pK values in the 4–5 pH region characteristic of the double-stranded form, which occurs for much shorter dCn than rCn. The circular dichroism (CD.) spectra of deoxycytidylies in dilute solution starting from the trimer are conservative, characteristic of the double-stranded helical form of poly C at acid pH. In contrast, the CD spectra of a series of corresponding ribo Cn, under identical conditions is of nonconservative character similar to that of the single-stranded form of poly C at neutral pH, but differs in the band position. This spectrum is called intermediate. Only at higher concentrations of oligonucleotidcs (i.e., 10?3Minstead of 10?4M) does the circular dichroism spectrum of longer ribocytidylics assume conservative character. Thermal denaturation of deoxycytidylces at acid pH are strongly dependent on chain length and concentration, its one would expect for a cooperative helix-coil transition. The circular dichroism spectra measured at different temperatures shows one isosbestic point. In dilute solution, the standard-state enthalpy change found was 5–6 kcal/mole for higher oligomers (dC7). These properties are all in agreement with a structural transition from the d-Cn double-stranded form to a coil for n > 3. Studies of dAn and dTn in solutions of high ionic strength at low temperature indicate that complex formation occurs already at the level of trimer and for high oligomers. Under identical conditions a complex between rAn and rUn is detected only for oligomers longer than the hexamer. The nature of the “intermediate” form of oligoribo C at acid pH and low temperature was investigated by sedimentation and circular dichroism. A model of rCn is proposed of linear molecules which are partially double-stranded and partially single-stranded, which probably are slowly rearranged by “slippage” into a regular-double-stranded helical form. 相似文献