Well-defined homopolypeptides, copolypeptides, and hybrids of Poly(l-proline)

l-Proline is the only, out of 20 essential, amino acid that contains a cyclized substituted α-amino group (is formally an imino acid), which restricts its conformational shape. The synthesis of well-defined homo- and copolymers of l-proline has been plagued either by the low purity of the monomer or the inability of most initiating species to polymerize the corresponding N-carboxy anhydride (NCA) because they require a hydrogen on the 3-N position of the five-member ring of the NCA, which is missing. Herein, highly pure l-proline NCA was synthesized by using the Boc-protected, rather than the free amino acid. The protection of the amine group as well as the efficient purification method utilized resulted in the synthesis of highly pure l-proline NCA. The high purity of the monomer and the use of an amino initiator, which does not require the presence of the 3-N hydrogen, led for the first time to well-defined poly(l-proline) (PLP) homopolymers, poly(ethylene oxide)-b-poly(l-proline), and poly(l-proline)-b-poly(ethylene oxide)-b-poly(l-proline) hybrids, along with poly(γ-benzyl-l-glutamate)-b-poly(l-proline) and poly(Boc-l-lysine)-b-poly(l-proline) copolypeptides. The combined characterization (NMR, FTIR, and MS) that results for the l-proline NCA revealed its high purity. In addition, all synthesized polymers exhibit high molecular and compositional homogeneity

Influence of polymer molar mass and mixture stoichiometry on polyelectrolyte complexes of poly(l-arginine) and Poly(l-glutamic acid)

Poly(l-arginine) (PARG) and poly(l-glutamic acid) (PLGA) homopolypeptides were custom synthesized by precision N-carboxyanhydride ring-opening polymerization methods with two molar masses, matched for pairs of cationic and anionic polypeptides (degrees of polymerization n = 100 and n = 500). The conformations of the homopolypeptides were probed using circular dichroism (CD) and FTIR spectroscopy which revealed the presence of mainly polyproline II (PPII) conformation. Small-angle X-ray scattering (SAXS) showed concentration-dependent polyelectrolyte peaks and form factor with high q scaling due to the excluded volume behaviour of the wormlike chains. We then examined polyelectrolyte complexation in mixtures of pairs of PARG and PLGA polypeptides with matched molar masses. Precipitation was generally observed and the structures of precipitates, supernatant and resuspended precipitates were investigated using CD, SAXS and cryo-TEM. These revealed that, contrary to prior suggestions in the literature, the precipitates contain mostly polypeptides in a PPII-like conformation, and there is only a minimal β-sheet content (which is enhanced upon drying the sample during preparation for certain measurements). The precipitates have a fractal-like structure as revealed by cryo-TEM and SAXS. Our findings on the structure of polypeptide complex precipitates contribute to the understanding of phase separation of polyelectrolyte complexes and coacervation and may shed light on the formation of inter-cellular bodies of proteins and peptides such as Lewy and other inclusion bodies

Proyecto Vainica: valoración e intervención nutricional e insuficiencia cardiaca

Desde el comienzo del milenio diversos estudios muestran la “paradoja de la obesidad en pacientes con insuficiencia cardiaca”. Existe una epidemiología inversa: la obesidad predispone para desarrollar enfermedades cardiovasculares e insuficiencia cardiaca, pero un índice de masa corporal elevado mejora la supervivencia a dos y cinco años. Esta paradoja se ha extendido con posterioridad, a otras enfermedades de carácter crónico y ha sido un tema controvertido en la comunidad científica. Posteriormente, diversos estudios han ido migrando la orientación, relacionando el pronóstico no con el índice de masa corporal en sí, sino con el estado nutricional y el adelgazamiento no intencionado. De modo que el foco de interés está ahora en el estado nutricional de los pacientes y no en su índice de masa corporal. El peso –y por tanto el índice de masa corporal- es un parámetro cambiante en los pacientes con insuficiencia cardiaca, ya que por la naturaleza de su patología, pueden presentar un volumen hídrico aumentado y son susceptibles a descompensaciones edemo-asciticas. Los episodios de descompensación son habitualmente tratados con diuréticos, con el objetivo de eliminar el exceso de líquido, lo que hace que el peso fluctúe rápidamente, a expensas de la reducción del exceso de volumen hídrico. No existe consenso o marcador universalmente aceptado para definir la malnutrición. Por ello, coexisten múltiples métodos de cribado y valoración nutricional. No destacándose ninguno como “gold estándar”..

Self-assembly of telechelic tyrosine end-capped PEO and poly(alanine) polymers in aqueous solution

The self-assembly in aqueous solution of three novel telechelic conjugates comprising a central hydrophilic polymer and short (trimeric or pentameric) tyrosine end-caps has been investigated. Two of the conjugates have a central poly(oxyethylene) (polyethylene oxide, PEO) central block with different molar masses. The other conjugate has a central poly(l-alanine) (PAla) sequence in a purely amino-acid based conjugate. All three conjugates self-assemble into β-sheet based fibrillar structures, although the fibrillar morphology revealed by cryogenic-TEM is distinct for the three polymers—in particular the Tyr5-PEO6k-Tyr5 forms a population of short straight fibrils in contrast to the more diffuse fibril aggregates observed for Tyr5-PEO2k-Tyr5 and Tyr3-PAla-Tyr3. Hydrogel formation was not observed for these samples (in contrast to prior work on related systems) up to quite high concentrations, showing that it is possible to prepare solutions of peptide–polymer-peptide conjugates with hydrophobic end-caps without conformational constraints associated with hydrogelation. The Tyr5-PEO6k-Tyr5 shows significant PEO crystallization upon drying in contrast to the Tyr5-PEO2k-Tyr5 conjugate. Our findings point to the remarkable ability of short hydrophobic peptide end groups to modulate the self-assembly properties of polymers in solution in model peptide-capped “associative polymers”. Retention of fluidity at high conjugate concentration may be valuable in potential future applications of these conjugates as bioresponsive or biocompatible materials, for example exploiting the enzyme-responsiveness of the tyrosine end-group

Self-assembly of a model amphiphilic oligopeptide incorporating an arginine headgroup

The self-assembly in aqueous solution of the alanine-rich peptide A12R2 containing twelve alanine residues and two arginine residues has been investigated. This oligomeric peptide was synthesized via NCA-polymerization methods. The surfactant-like peptide is found via FTIR to form antiparallel dimers which aggregate into twisted fibrils, as revealed by cryogenic-transmission electron microscopy. The fibril substructure is probed via detailed X-ray scattering experiments, and are uniquely comprised of twisted tapes only 5 nm wide, set by the width of the antiparallel A12R2 dimers. The packing of the alanine residues leads to distinct “b-sheet” spacings compared to those for amyloid-forming peptides. For this peptide, b-sheet structure coexists with some a-helical content. These ultrafine amyloid fibrils present arginine at high density on their surfaces, and this may lead to applications in nanobiotechnology

Synthesis and characterization of model 4-miktoarm star co- and quaterpolymers

The synthesis of well-defined, nearly monodisperse, 4-miktoarm (from the Greek word μικτος meaning mixed) star co- and quaterpolymers of the A2B2 and ABCD types, is described. A is polystyrene, B polybutadiene, C polyisoprene, and D poly(4-methylstyrene). The synthetic approach involves the reaction of tetrachlorosilane with the active chain end centers of the first arm under conditions unfavorable to chain coupling or linking, followed by a stoichiometric addition (titration) of the living polymer of the second or the third arm, and finally by an excess of the living polymer of the last arm. The sequence of addition of the different living polymers and the monitoring of the progress of the linking reaction by size-exclusion chromatography (SEC) are the key for successful synthesis. Characterization was carried out by SEC, low-angle laser light scattering, laser differential refractometry, membrane and vapor pressure osmometry, and NMR spectroscopy. © 1993, American Chemical Society. All rights reserved

Synthesis of a model 3-miktoarm star terpolymer

The synthesis of a well-defined, near monodisperse, star terpolymer with three different arms, i.e., polyisoprene, polystyrene, and polybutadiene, is described. The synthetic approach involves the reaction of polyisoprenyllithium with an excess of methyltrichlorosilane followed, after removed of the excess of methyltrichlorosilane, by a stoichiometric addition (titration) of polystyrillithium and finally by a small excess of polybutadienyllithium. The sequence of the addition of the different living polymers is very critical. After linking, the excess of the polybutadienyllithium was terminated with methanol and removed by fractionation. Characterization was carried out by size-exclusion chromatography, low-angle laser light scattering, laser differential refractometry, osmometry, and NMR and UV spectroscopy. © 1992, American Chemical Society. All rights reserved

Smart Materials from Living Polypeptides

Attempts to synthesize well-defined polypeptides by the ring-opening polymerization (ROP) of α-amino acid N-carboxyanhydrides (NCAs) with primary amines have been plagued, for more than 50 years, by unwanted side reactions. Recently, we have employed high vacuum techniques (HVT) to create living conditions for the amino-initiated ROP of NCAs (γ-benzyl L-glutamate, ε-Z L-lysine, proline, etc.). With this approach, a wide variety of novel block copolypeptides, having controlled molecular and architectural characteristics have been synthesized in ∼100% yields. The same holds for hybrid-polypeptides (chimeras), only that the initiating amino group is attached to a conventional macromolecule rather than to a small molecule. Along these synthetic lines, a series of novel amphiphilic triblock copoly-peptides, poly(L-lysine)-b-poly(γ-benzyl-L-glutamate)-b-poly(L- lysine), were synthesized. Due to the macromolecular architecture of the tribock copolypeptides and the rigid nature of the poly(γ-benzyl-L-glutamate) middle block, the formation of bilayers was favored, and vesicles formed in water at neutral pH over the entire compositional range. Compared to other vesicular structures derived from conventional polymers, these polypeptidic vesicles possess the unique feature of being stimuli-responsive to pH and temperature (smart materials). In the presence of deoxyguanosine monophosphate, a multilevel self-assembly of the triblock copolypeptides in water was observed. © 2009 Springer Science+Business Media B.V

MODEL MIKTOARM STAR CO-, TER AND QUATERPOLYMERS. SYNTHESIS- CHARACTERIZATION-PROPERTIES

MODEL MIKTOARM STAR POLYMERS OF THE TYPE A2B, A2B2, ABC AND ABCD WERE SYNTHESIZED AND CHARACTERIZED, WHERE A IS POLYSTYRENE, B IS POLYISOPRENE, C IS POLYBUTADIENE AND D IS POLY (4-METHYL STYRENE). THE MORPHOLOGICAL STUDY OF THE A2B COPOLYMERS REVEALED THAT THE PHASE BOUNDARIES OF THE COMPOSITION ARE DIFFERENT FROM THOSE OF THE CORRESPONDING AB COPOLYMERS. ALSO, THE DILUTE SOLUTION PROPERTIES OF THE A2B COPOLYMERS HAS SHOWN THAT THEIR DIMENSIONS ARE LARGER THAN THE THEORETICALLY CALCULATED ONES. THIS IS DUE TO THEIR MACROMOLECULAR ARCHITECTURE.ΠΑΡΑΣΚΕΥΑΣΤΗΚΑΝ ΚΑΙ ΧΑΡΑΚΤΗΡΙΣΤΗΚΑΝ ΠΡΟΤΥΠΑ ΜΙΚΤΟΚΛΩΝΑ ΑΣΤΕΡΟΕΙΔΗ ΠΟΛΥΜΕΡΗ ΤΟΥΤΥΠΟΥ Α2Β, Α2Β2, ABC ΚΑΙ ABCD, ΟΠΟΥ Α ΠΟΛΥΣΤΥΡΕΝΙΟ, Β ΠΟΛΥΙΣΟΠΡΕΝΙΟ, C ΠΟΛΥΒΟΥΤΑΔΙΕΝΙΟ ΚΑΙ D ΠΟΛΥ(4-ΜΕΘΥΛΟ-ΣΤΥΡΕΝΙΟ). Η ΜΟΡΦΟΛΟΓΙΚΗ ΜΕΛΕΤΗ ΤΩΝ ΣΥΜΠΟΛΥΜΕΡΩΝ Α2Β ΕΔΕΙΞΕ ΟΤΙ ΟΙ ΠΕΡΙΟΧΕΣ ΣΥΣΤΑΣΗΣ ΣΤΙΣ ΟΠΟΙΕΣ ΕΜΦΑΝΙΖΟΝΤΑΙ ΟΙ ΔΙΑΦΟΡΕΣ ΜΙΚΡΟΔΟΜΕΣ ΕΙΝΑΙ ΔΙΑΦΟΡΕΤΙΚΕΣ ΑΠΟ ΤΙΣ ΑΝΤΙΣΤΟΙΧΕΣ ΤΩΝ ΠΟΛΥΜΕΡΩΝ ΑΒ. ΕΠΙΣΗΣ ΟΙ ΔΙΑΣΤΑΣΕΙΣ ΤΟΥΣ ΣΕ ΑΡΑΙΑ ΔΙΑΛΥΜΑΤΑ ΕΙΝΑΙ ΑΥΞΗΜΕΝΕΣ ΣΕ ΣΧΕΣΗ ΜΕ ΤΙΣ ΘΕΩΡΗΤΙΚΑ ΥΠΟΛΟΓΙΣΜΕΝΕΣ. ΑΥΤΟ ΟΦΕΙΛΕΤΑΙ ΣΤΗ ΜΑΚΡΟΜΟΡΙΑΚΗ ΑΡΧΙΤΕΚΤΟΝΙΚΗ ΤΩΝ ΣΥΜΠΟΛΥΜΕΡΩΝ ΑΥΤΩΝ

Well-defined linear multiblock and branched polypeptides by linking chemistry

The synthesis of linear multiblock copolypeptides along with three-arm star homo- and copolypeptides was investigated. The precursors along with the final copolypeptides were characterized by membrane osmometry and size exclusion chromatography (SEC) featuring a two-angle laser scattering (TALLS) detector. In both methods, the measurements were performed at 60°C and the solvent was a 0.1N LiBr solution in N,N'-dimethylformamide (DMF). It was concluded that the livingness of the polypeptides under high-vacuum (HV) conditions can be preserved indefinitely and this allows the use of coupling chemistry for the synthesis of homo- and copolypeptides with a wide variety of macromolecular architectures