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1.
J Org Chem ; 85(3): 1513-1524, 2020 Feb 07.
Artigo em Inglês | MEDLINE | ID: mdl-31769989

RESUMO

Peptides are well-known to play a fundamental therapeutic role and to represent building blocks for numerous useful biomaterials. Stabilizing their active 3D-structure by appropriate modifications remains, however, a challenge. In this study, we have expanded the available literature information on the conformational propensities of a promising backbone change of a terminally blocked δ-amino acid residue, a dipeptide mimic, by replacing its central amide moiety with an (E) Cß═Cγ alkene unit. Specifically, we have examined by DFT calculations, X-ray diffraction in the crystalline state, and FT-IR absorption/NMR spectroscopies in solution the extended vs folded preferences of analogues of this prototype system either unmodified or possessing single or multiple methyl group substituents on each of its four -CH2-CH═CH-CH2- main-chain carbon atoms. The theoretical and experimental results obtained clearly point to the conclusion that increasing the number of adequately positioned methylations will enhance the preference of the original sequence to fold, thus opening interesting perspectives in the design of conformationally constrained peptidomimetics.

2.
J Magn Reson ; 309: 106621, 2019 12.
Artigo em Inglês | MEDLINE | ID: mdl-31669794

RESUMO

In frozen biological media and molecular glasses only restricted motions exist; because of the weakness and disorder of intermolecular bonds these motions may have stochastic nature. Electron spin echo (ESE) spectroscopy of spin-labeled molecules allows detecting their restricted stochastic rotations (stochastic molecular librations). As in molecular disordered media motions may be highly cooperative, it would be desirable to investigate their spectroscopic manifestation also in the systems where cooperative effects would be certainly ruled out. In this work, ESE of spin-labeled molecules adsorbed on inorganic SiO2 surface was investigated in a wide temperature range. The rate of motion-induced spin relaxation was found to become measurable above 130 K, increasing with temperature and attaining then a saturating behavior with a well-defined maximum near 250 K. For two types of molecules differing remarkably in their size and polarity (a small highly-polar nitroxide radical and a large spin-labeled peptide), quite similar results were obtained. This saturating behavior was quantitatively reproduced in simulations within a simple model of jump between two close orientations. Comparison with experiment allowed estimate that at 250 K the correlation time of the motion τc is of the order of several tens of nanoseconds and the angle α between two orientations is around 0.02 rad. As the found saturating behavior is a property of individual motions, for any other molecular system an excess of the spin relaxation rate above the maximum found here for adsorbed molecules may be ascribed to cooperative motions. Comparison with literature data on molecular systems of different origin has shown that effects of cooperativity indeed are present and, moreover, may be very essential.

3.
Phys Chem Chem Phys ; 21(41): 23217, 2019 Oct 24.
Artigo em Inglês | MEDLINE | ID: mdl-31602454

RESUMO

Correction for 'An EPR study of ampullosporin A, a medium-length peptaibiotic, in bicelles and vesicles' by Marco Bortolus et al., Phys. Chem. Chem. Phys., 2016, 18, 749-760.

4.
Chem Sci ; 10(28): 6908-6914, 2019 Jul 28.
Artigo em Inglês | MEDLINE | ID: mdl-31391913

RESUMO

The unique abilities of homo-oligo-adamantyl peptides to adopt α- and γ-turn conformations are demonstrated by X-ray diffraction, and NMR and FT-IR absorption spectroscopies. Assembled by an Ugi multiple component reaction strategy, N α-formyl-adamantyl tripeptide iso-propyl and tert-butyl amides are respectively found to adopt an isolated α-turn and an incipient γ-helix conformation by X-ray diffraction crystallography. The shortest example of a single α-turn with ideal geometry is observed in the crystalline state. In solution both peptides predominantly assume γ-helical structures.

5.
Chembiochem ; 20(16): 2141-2150, 2019 08 16.
Artigo em Inglês | MEDLINE | ID: mdl-31125169

RESUMO

Trichogin GA IV is a short peptaibol with antimicrobial activity. This uncharged, but amphipathic, sequence is aligned at the membrane interface and undergoes a transition to an aggregated state that inserts more deeply into the membrane, an assembly that predominates at a peptide-to-lipid ratio (P/L) of 1:20. In this work, the natural trichogin sequence was prepared and reconstituted into oriented lipid bilayers. The 15 N NMR chemical shift is indicative of a well-defined alignment of the peptide parallel to the membrane surface at P/Ls of 1:120 and 1:20. When the P/L is increased to 1:8, an additional peptide topology is observed that is indicative of a heterogeneous orientation, with helix alignments ranging from around the magic angle to perfectly in-plane. The topological preference of the trichogin helix for an orientation parallel to the membrane surface was confirmed by attenuated total reflection FTIR spectroscopy. Furthermore, 19 F CODEX experiments were performed on a trichogin sequence with 19 F-Phe at position 10. The CODEX decay is in agreement with a tetrameric complex, in which the 19 F sites are about 9-9.5 Šapart. Thus, a model emerges in which the monomeric peptide aligns along the membrane surface. When the peptide concentration increases, first dimeric and then tetrameric assemblies form, made up from helices oriented predominantly parallel to the membrane surface. The formation of these aggregates correlates with the release of vesicle contents including relatively large molecules.

6.
J Pept Sci ; 25(5): e3165, 2019 May.
Artigo em Inglês | MEDLINE | ID: mdl-30916858

RESUMO

α-Amino acid residues with a ϕ,ψ constrained conformation are known to significantly bias the peptide backbone 3D structure. An intriguing member of this class of compounds is (αMe)Aze, characterized by an Nα -alkylated four-membered ring and Cα -methylation. We have already reported that (S)-(αMe)Aze, when followed by (S)-Ala in the homochiral dipeptide sequential motif -(S)-(αMe)Aze-(S)-Ala-, tends to generate the unprecedented γ-bend ribbon conformation, as formation of a regular, fully intramolecularly H-bonded γ-helix is precluded, due to the occurrence of a tertiary amide bond every two residues. In this work, we have expanded this study to the preparation and 3D structural analysis of the heterochiral (S)-Ala/(R)-(αMe)Aze sequential peptides from dimer to hexamer. Our conformational results show that members of this series may fold in type-II ß-turns or in γ-turns depending on the experimental conditions.


Assuntos
Alanina/química , Ácido Azetidinocarboxílico/química , Oligopeptídeos/química , Oligopeptídeos/síntese química , Ressonância Magnética Nuclear Biomolecular , Conformação Proteica , Difração de Raios X
7.
Biochim Biophys Acta Biomembr ; 1861(2): 524-531, 2019 02 01.
Artigo em Inglês | MEDLINE | ID: mdl-30550880

RESUMO

The antimicrobial action of peptides in bacterial membranes is commonly related to their mode of self-assembling which results in pore formation. To optimize peptide antibiotic use for therapeutic purposes, a study on the concentration dependence of self-assembling process is thus desirable. In this work, we investigate this dependence for peptaibol trichogin GA IV (Tric) in the 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) model membrane in the range of peptide concentrations between 0.5 and 3.3 mol%. Pulsed double electron-electron resonance (PELDOR) applied on spin-labeled peptide analogs highlights the onset of peptide dimerization above a critical peptide concentration value, namely ~ 2 mol%. Electron spin echo (ESE) envelope modulation (ESEEM) for D2O-hydrated bilayers shows that dimerization is accompanied by peptide re-orientation towards a trans-membrane disposition. For spin-labeled stearic acids (5-DSA) in POPC bilayers, the study of ESE decays and ESEEM in the presence of a deuterated peptide analog indicates that above the critical peptide concentration the 5-DSA molecules are attracted by peptide molecules, forming nanoclusters. As the 5-DSA molecules represent a model for the behavior of fatty acids participating in bacterial membrane homeostasis, such capturing action by Tric may represent an additional mechanism of its antibiotic activity.


Assuntos
Antibacterianos/farmacologia , Ácidos Graxos/química , Bicamadas Lipídicas/química , Lipopeptídeos/farmacologia , Peptídeos/farmacologia , Sequência de Aminoácidos , Dimerização , Espectroscopia de Ressonância de Spin Eletrônica , Fosfatidilcolinas/química , Ácidos Esteáricos/química , Água/química
8.
Chempluschem ; 84(11): 1688-1696, 2019 11.
Artigo em Inglês | MEDLINE | ID: mdl-31943881

RESUMO

The influence of conformational dynamics on the self-assembly process of a conformationally constrained analogue of the natural antimicrobial peptide Trichogin GA IV was analysed by spectroscopic methods, microscopy imaging at nanometre resolution, and molecular dynamics simulations. The formation of peptide films at the air/water interface and their deposition on a graphite or a mica substrate were investigated. A combination of experimental evidence with molecular dynamics simulation was used to demonstrate that only the fully developed helical structure of the analogue promotes formation of ordered aggregates that nucleate the growth of micrometric rods, which give rise to homogenous coating over wide regions of the hydrophilic mica. This work proves the influence of helix flexibility on peptide self-organization and orientation on surfaces, key steps in the design of bioinspired organic/inorganic hybrid materials.


Assuntos
Silicatos de Alumínio/química , Grafite/química , Lipopeptídeos/química , Nanoestruturas/química , Sequência de Aminoácidos , Microscopia de Força Atômica , Simulação de Dinâmica Molecular , Propriedades de Superfície , Água/química , Difração de Raios X
9.
Org Biomol Chem ; 16(42): 7947-7958, 2018 10 31.
Artigo em Inglês | MEDLINE | ID: mdl-30318540

RESUMO

Unlike the extensively investigated relationship between the peptide ß-bend ribbon and its prototypical 310-helix conformation, the corresponding relationship between the narrower γ-bend ribbon and its regular γ-helix counterpart still remains to be studied, as the latter 3D-structures have not yet been experimentally authenticated. In this paper, we describe the results of the first characterization, both in the crystal state and in solution, of the γ-bend ribbon conformation using X-ray diffraction and FT-IR absorption, electronic CD and 2D-NMR spectroscopies applied to an appropriate set of synthetic, homo-chiral, sequential dipeptide oligomers based on (S)-Ala and the known γ-bend inducer, Cα-tetrasubstituted, N-alkylated α-amino acid residue (S)-Cα-methyl-azetidine-carboxylic acid.

10.
J Phys Chem B ; 122(24): 6305-6313, 2018 06 21.
Artigo em Inglês | MEDLINE | ID: mdl-29792795

RESUMO

Peptide self-assembly is ubiquitous in nature. It governs the organization of proteins, controlling their folding kinetics and preserving their structural stability and bioactivity. In this connection, model oligopeptides may give important insights into the molecular mechanisms and elementary forces driving the formation of supramolecular structures. In this contribution, we show that a single residue substitution, that is, Aib (α-aminoisobutyric acid) in place of Ala at position 4 of an -(l-Ala)5-homo-oligomer, strongly alters the aggregation process. In particular, this process is initiated by the formation of small peptide clusters that promote aggregation on the nanometer scale and, through a hierarchical self-assembly, lead to mesoscopic structures of micrometric dimensions. Furthermore, we show that the use of the well-established Langmuir-Blodgett technique represents an effective strategy for coating extended areas of inorganic substrates by densely packed peptide layers, thus paving the way for application of peptide films as templates for biomineralization, biocompatible coating of surfaces, and scaffolds for tissue engineering.


Assuntos
Nanoestruturas/química , Oligopeptídeos/química , Ar , Ácidos Aminoisobutíricos/química , Microscopia de Força Atômica , Simulação de Dinâmica Molecular , Oligopeptídeos/metabolismo , Estrutura Secundária de Proteína , Espectrometria de Fluorescência , Água/química
11.
Phys Chem Chem Phys ; 20(5): 3592-3601, 2018 Jan 31.
Artigo em Inglês | MEDLINE | ID: mdl-29340383

RESUMO

The antimicrobial action of the peptide antibiotic alamethicin (Alm) is commonly related to peptide self-assembling resulting in the formation of voltage-dependent channels in bacterial membranes, which induces ion permeation. To obtain a deeper insight into the mechanism of channel formation, it is useful to know the dependence of self-assembling on peptide concentration. With this aim, we studied Alm F50/5 spin-labeled analogs in a model 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) membrane, for peptide-to-lipid (P/L) ratios varying between 1/1500 and 1/100. Pulsed electron-electron double resonance (PELDOR) spectroscopy reveals that even at the lowest concentration investigated, the Alm molecules assemble into dimers. Moreover, under these conditions, electron spin echo envelope modulation (ESEEM) spectroscopy of D2O-hydrated membranes shows an abrupt change from the in-plane to the trans-membrane orientation of the peptide. Therefore, we hypothesize that dimer formation and peptide reorientation are concurrent processes and represent the initial step of peptide self-assembling. By increasing peptide concentration, higher oligomers are formed. A simple kinetic model of equilibrium among monomers, dimers, and pentamers allows for satisfactorily describing the experimental PELDOR data. The inter-label distances in the oligomers obtained from PELDOR experiments become better resolved with increasing P/L ratio, thus suggesting that the supramolecular organization of the higher-order oligomers becomes more defined.


Assuntos
Alameticina/química , Bicamadas Lipídicas/química , Alameticina/metabolismo , Sequência de Aminoácidos , Dimerização , Espectroscopia de Ressonância de Spin Eletrônica , Cinética , Bicamadas Lipídicas/metabolismo , Fosfatidilcolinas/química , Marcadores de Spin , Água/química
12.
Biopolymers ; 2017 Nov 11.
Artigo em Inglês | MEDLINE | ID: mdl-29127716

RESUMO

In this work, an extensive set of spectroscopic and biophysical techniques (including FT-IR absorption, CD, 2D-NMR, fluorescence, and CW/PELDOR EPR) was used to study the conformational preferences, membrane interaction, and bioactivity properties of the naturally occurring synthetic 14-mer peptaibiotic chalciporin A, characterized by a relatively low (≈20%), uncommon proportion of the strongly helicogenic Aib residue. In addition to the unlabeled peptide, we gained in-depth information from the study of two labeled analogs, characterized by one or two residues of the helicogenic, nitroxyl radical-containing TOAC. All three compounds were prepared using the SPPS methodology, which was carefully modified in the course of the syntheses of TOAC-labeled analogs in view of the poorly reactive α-amino function of this very bulky residue and the specific requirements of its free-radical side chain. Despite its potentially high flexibility, our results point to a predominant, partly amphiphilic, α-helical conformation for this peptaibiotic. Therefore, not surprisingly, we found an effective membrane affinity and a remarkable penetration propensity. However, chalciporin A exhibits a selectivity in its antibacterial activity not in agreement with that typical of the other members of this peptide class.

13.
J Org Chem ; 82(19): 10033-10042, 2017 10 06.
Artigo em Inglês | MEDLINE | ID: mdl-28858505

RESUMO

The intrinsically blue-colored Ullman imidazolinyl nitronyl nitroxide (NN) mono-radicals have found various applications, in particular as spin probes and organic magnetic materials. Here, we present the solution-phase synthesis, extensive characterization, and conformational analysis of the first peptidomimetics with two pendant, chiral nitronyl nitroxide free radical units. Two (R)-Aic(NN) residues, where Aic(NN) is 2-amino-5-nitronylnitroxide-indan-2-carboxylic acid, have been inserted at positions i and i+3 of the pentapeptide Boc-(R)-Aic(NN)-(Ala)2-(R)-Aic(NN)-Ala-OMe and the hexapeptide Boc-[Ala-(R)-Aic(NN)-Ala]2-OMe as well. The two compounds were obtained in good yields and high purities. Thanks to a combination of several spectroscopic techniques (IR absorption, NMR, VCD, and EPR) we gained clear evidence that both compounds adopt a right-handed 310-helical conformation with both nitronyl nitroxide pendants positioned on the same side of the helix. This peptidomimetic/free radical system is a potentially excellent template for the preparation of a set of appropriate analogs with exciting applications in the area of host-guest organic chemistry, or to spectroscopically evaluate in-depth the intramolecular exchange interactions in this type of probe.

14.
Soft Matter ; 13(23): 4231-4240, 2017 Jun 14.
Artigo em Inglês | MEDLINE | ID: mdl-28509927

RESUMO

Two appropriately functionalized nucleobases, thymine and adenine, have been covalently linked at the N- and C-termini, respectively, of two α-aminoisobutyric acid-rich helical peptide foldamers, aiming at driving self-assembly through complementary recognition. A crystal-state analysis (by X-ray diffraction) on the shorter, achiral foldamer 1 unambiguously shows that adeninethymine base pairing, through Watson-Crick intermolecular H-bonding, does take place between either end of each peptide molecule. In the crystals, π-stacking between base pairs is also observed. Evidence for time-dependent foldameroldamer associations for the longer, chiral foldamer 2 in solution is provided by circular dichroism measurements. The self-assembly of foldamer 2, through living supramolecular polymerization, eventually leads to the formation of twisted fibers. Such a supramolecular organization can be affected by addition of either pristine adenine or thymine, that acts as a "terminator" by selectively matching a pairing nucleobase at one end of the foldamer. The co-assembly of foldamer 2 with a porphyrin-derivatized thymine, under appropriate experimental conditions, leads to the formation of vesicles which, in turn, can be converted to the fiber morphology by changing the environmental polarity. Conversely, dendrimeric, star polymer-like microstructures are generated when the supramolecular assembly of foldamer 2 is seeded by adenine-capped gold nanoparticles.

15.
J Phys Chem B ; 121(17): 4379-4387, 2017 05 04.
Artigo em Inglês | MEDLINE | ID: mdl-28422504

RESUMO

We address the interpretation, via an integrated computational approach, of the experimental continuous-wave electron paramagnetic resonance (cw-EPR) spectra of a complete set of conformationally highly restricted, stable 310-helical peptides from hexa- to nonamers, each bis-labeled with nitroxide radical-containing TOAC (4-amino-1-oxyl-2,2,6,6-tetramethylpiperidine-4-carboxylic acid) residues. The usefulness of TOAC for this type of analysis has been shown already to be due to its cyclic piperidine side chain, which is rigidly connected to the peptide backbone α-carbon. The TOAC α-amino acids are separated by two, three, four, and five intervening residues. This set of compounds has allowed us to modulate both the radical···radical distance and the relative orientation parameters. To further validate our conclusion, a comparative analysis has been carried out on three singly TOAC-labeled peptides of similar main-chain length.


Assuntos
Óxidos N-Cíclicos/química , Óxidos de Nitrogênio/química , Peptídeos/química , Teoria Quântica , Espectroscopia de Ressonância de Spin Eletrônica , Marcadores de Spin
16.
J Pept Sci ; 23(2): 104-116, 2017 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-28054413

RESUMO

The role of the conformationally constrained α-aminoisobutyric acid (Aib) residue in the aggregation and self-assembly properties of oligopeptides is discussed, critically reviewing our recent work in the field. In this connection, three significant case studies are presented: (i) aggregation propensity of Aib homo-oligopeptides of different length; (ii) perturbation of the conformational and aggregation properties of Ala-based pentapeptides by a single Aib versus Ala substitution; and (iii) build up of self-assembled monolayers formed by Aib homo-hexapeptide building blocks. The peptides investigated were all functionalized by a fluorescent probe, that is, a naphthyl group in the first case-study and a pyrenyl group in the other two, with the aim at applying optical spectroscopy techniques and evaluating the relevance of aromatic interactions in the aggregation process. Microscopy techniques at nanometric resolution and results of molecular dynamics simulations are also presented to analyze how the conformational properties of the peptide building blocks would affect the morphology of the peptide aggregates from the nanoscale to the mesoscale. Copyright © 2017 European Peptide Society and John Wiley & Sons, Ltd.


Assuntos
Ácidos Aminoisobutíricos/química , Oligopeptídeos/química , Agregados Proteicos , Sequência de Aminoácidos , Corantes Fluorescentes/química , Ligação de Hidrogênio , Microscopia de Força Atômica , Simulação de Dinâmica Molecular , Sondas Moleculares/química , Estrutura Secundária de Proteína , Soluções , Espectrometria de Fluorescência
17.
Biopolymers ; 108(1)2017 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-27404945

RESUMO

In this study, we performed a detailed literature survey of the ɛ-turn in peptides and proteins. This three-dimensional structural feature is characterized by an eleven-membered pseudo-cycle closed by an intramolecular backbone…backbone H-bond. Interestingly, in this motif the direction of the N-H…O = C H-bond runs opposite to that of the much more popular and extensively investigated α-, ß-, and γ-turns. We did not authenticate unequivocally the ɛ-turn main-chain reversal topology in any linear short peptide. However, it is frequently observed in small cyclic peptides formed by four, five, and six amino acid residues with stringent geometric requirements. Rather surprisingly, ɛ-turns do occur in proteins, although to a relatively moderate extent, as an isolated feature or in the turn segment of hairpin motifs based on two antiparallel, pleated ß-strands. Moreover, the ɛ-turn may also host not only the seven-membered, intramolecularly H-bonded, pseudo-cycle termed γ-turn, either of the classic or inverse type, but also one (or even two) cis peptide bond(s) or a ß-bulge conformation. Based on their ϕ, ψ backbone torsion angles, we were able to classify the protein ɛ-turns in six different families. Conformational energy computations using the DFT methodology were also performed on the ɛ-turns adopted by the amino acid triplet -Gly-Gly-Gly- (Gly is the most commonly found residue at each of the three positions in our analysis of proteins). Again, in this computational study, six families of turns were identified, but only some of them resemble rather closely those extracted from our investigation on proteins.


Assuntos
Peptídeos/química , Sequência de Aminoácidos , Cristalografia por Raios X , Ligação de Hidrogênio , Isomerismo , Espectroscopia de Ressonância Magnética , Oligopeptídeos/química , Peptídeos Cíclicos/química , Estrutura Secundária de Proteína , Proteínas/química
18.
Biopolymers ; 108(1)2017 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-27623395

RESUMO

Trichogin GA IV is a short-length (10-amino acid long), mostly hydrophobic, peptaibiotic with an N-terminal fatty acyl chain and a C-terminal 1,2-amino alcohol. A cardinal role of the terminal moieties in the cytotoxic activity of trichogin has been recently found. Previously, peptide orientation and dynamics of trichogin analogs in the membrane were studied using methyl ester derivatives. Therefore, in the present work we synthesized several trichogin analogs with naturally occurring terminal groups to verify whether these moieties have any effect on peptide-membrane interaction. These trichogin analogs, both neutral and carrying a positively charged Lys residue, bear the nitroxide-containing α-amino acid TOAC to study them using EPR spectroscopy. Vesicles were used to investigate orientation and penetration depth of the peptide at room temperature. Bicelles were employed to evaluate the order, dynamics, and orientation of the peptide at a near physiological temperature. In addition, the position of the N-terminal 1-octanoyl chain in the membrane was studied by labeling it with a nitroxide. The secondary structure of the peptides in vesicles was studied by CD spectroscopy showing that they adopt a mostly α-helical structure. In vesicles, the analogs insert below the lipid headgroups with the helix axis oriented parallel to the membrane surface at a peptide-to-lipid (P:L) ratio of 1:100. The presence of the single, positively charged Lys residue does not alter the orientation adopted by the peptides. In bicelles at P:L ratios 1:100 and 1:60, the peptide adopts a transmembrane orientation characterized by a very low orientational order, whereas at a 1:15 P:L ratio it severely disrupts the membrane. Our data shows that overall orientation and insertion in model membranes of the native trichogin GA IV are strictly comparable to those of its methyl ester analogs previously examined.


Assuntos
Bicamadas Lipídicas/química , Lipopeptídeos/química , Sequência de Aminoácidos , Dicroísmo Circular , Espectroscopia de Ressonância de Spin Eletrônica , Interações Hidrofóbicas e Hidrofílicas , Bicamadas Lipídicas/metabolismo , Lipopeptídeos/síntese química , Lipopeptídeos/metabolismo , Lipossomos/química , Lipossomos/metabolismo , Estrutura Secundária de Proteína , Temperatura
19.
J Pept Sci ; 23(4): 346-362, 2017 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-28004461

RESUMO

We performed the solution-phase synthesis of a set of model peptides, including homo-oligomers, based on the 2-aminoadamantane-2-carboxylic acid (Adm) residue, an extremely bulky, highly lipophilic, tricyclic, achiral, Cα -tetrasubstituted α-amino acid. In particular, for the difficult peptide coupling reaction between two Adm residues, we took advantage of the Meldal's α-azidoacyl chloride approach. Most of the synthesized Adm peptides were characterized by single-crystal X-ray diffraction analyses. The results indicate a significant propensity for the Adm residue to adopt γ-turn and γ-turn-like conformations. Interestingly, we found that a -CO-(Adm)2 -NH- sequence is folded in the crystal state into a regular, incipient γ-helix, at variance with the behavior of all of the homo-dipeptides from Cα -tetrasubstituted α-amino acids already investigated, which tend to adopt either the ß-turn or the fully extended conformation. Our density functional theory conformational energy calculations on the terminally blocked homo-peptides (n = 2-8) fully confirmed the crystal-state data, strongly supporting the view that this rigid Cα -tetrasubstituted α-amino acid residue is largely the most effective building block for γ-helix induction, although to a limited length (anti-cooperative effect). Copyright © 2016 European Peptide Society and John Wiley & Sons, Ltd.


Assuntos
Peptídeos/química , Cristalografia por Raios X , Modelos Moleculares , Peptídeos/síntese química , Conformação Proteica , Teoria Quântica , Soluções
20.
J Pept Sci ; 23(2): 155-161, 2017 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-27862690

RESUMO

A symmetrical dipeptide-based diacetylene system (DAs) was found to be able to self-assemble in dichloromethane and to form a compact fiber network which resulted in a stable organogel. As a consequence of the organogel formation, we explored the possibility to run a light-induced topochemical polymerization. This is a typical reaction of ordered diacetylene moieties taking advantage from their organized packing mode resulting from fiber formation. Evidence for the generation of peptide-based polydiacetylenes is provided by Raman, UV-Vis, and CD spectroscopies and a set of microscopic techniques. Finally, we succeeded in processing a polymeric composite by use of the electrospinning technique, starting from a mixture of a dipeptide-based diacetylene and polymethyl methacrylate. Copyright © 2016 European Peptide Society and John Wiley & Sons, Ltd.


Assuntos
Dipeptídeos/química , Polímeros/química , Polimetil Metacrilato/química , Poli-Inos/química , Técnicas Eletroquímicas , Géis , Luz , Processos Fotoquímicos , Polímero Poliacetilênico , Polimerização
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