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

Amphiphilic polypeptides: synthesis, characterization and self-assembly in aqueous solutions

In this dissertation we study the synthesis, characterization and self-assembly ofamphiphilic polypeptides in aqueous solutions, using the ring-opening polymerizationtechnique as long as high vacuum techniques for the purification of all the chemicalsinvolved (reagents, solvents). For the preparation of well-defined polypeptides, thepurification of the initial monomers (N-carboxy anhydrides) is of paramount importance.As regards the polypeptides, we synthesized linear block copolypeptides of ΑΒ type thatboth adopt a-helices, hybrid block polypeptides of ΑΒ type, consisting of poly(ethyleneoxide) and poly(L-proline), hybrid triblock polypeptides of ΑΒA type, with poly(ethyleneoxide) as the middle block and poly(L-lysine), poly(L-proline) or poly(L-glutamic acid) asthe side blocks, as long as hybrid triblock polypeptides of ΑΒC type, star hybridpolypeptides, consisting of poly(ethylene oxide) and poly(L-proline) and polypeptidesgrafted on carbon nanotubes. The polymers were characterized with different spectroscopic methods (FTIR, NMR,SEC, TGA, UV-Vis), while as regards their self-assembly, we examined their behavior inaqueous solutions (CD, TEM) and in the solid state, in both short-range order (WAXS,XRD) and long-range order (SAXS). Finally, it is important to be mentioned that all thepolymers synthesized in this dissertation, had potential applications as models(molecular rulers), as silk mimetics (high mechanical properties) and very interestingbio-applications (kidney stones, drug carriers for cancer therapy).SUBJECT AREA: polymersKEYWORDS: amphiphilic polypeptides, Ν-carboxy anhydrides, self-assembly, water,bio-applicationsΣε αυτή τη διατριβή μελετούμε τα αμφίφιλα πολυπεπτίδια ως προς την σύνθεση, τονχαρακτηρισμό και την αυτοοργάνωση τους σε υδατικά διαλύματα, με χρήση τεχνικώνπολυμερισμού διάνοιξης δακτυλίου των Ν-καρβοξυ ανυδριτών των αντίστοιχωναμινοξέων, καθώς και τεχνικές υψηλού κενού για τον καθαρισμό των αντιδραστηρίωνκαι των διαλυτών. Για την σύνθεση καλά καθορισμένων πολυπεπτιδίων, αμιγών καιυβριδικών, διαπιστώθηκε ότι είναι απαραίτητος ο καλός καθαρισμός των αρχικώνπρόδρομων μονομερών (Ν-καρβοξυ ανυδρίτες αμινοξέων).Ως προς τα πολυπεπτίδια, συνθέσαμε γραμμικά κατά συστάδες συμπολυπεπτίδια πουσχηματίζουν α-έλικες του τύπου ΑΒ, υβριδικά κατά συστάδες πολυπεπτίδιαπολυ(αιθυλενοξειδίου)-πολυ(L-προλίνης) του τύπου ΑΒ, υβριδικά τρισυσταδικάπολυπεπτίδια του τύπου ΑΒΑ με πολυ(αιθυλενοξείδιο) ως μεσαία συστάδα καιπλευρικές συστάδες: πολυ(L-λυσίνη), πολυ(L-προλίνη), πολυ(L-γλουταμικό οξύ), καθώςεπίσης και υβριδικά τρισυσταδικά πολυπεπτίδια του τύπου ΑΒC, αστεροειδήσυμπολυμερή πολυ(στυρενίου)-πολυ(L-προλίνης) και εμβολιασμένα πολυπεπτίδια πάνω σε νανοσωλήνες.Oλα τα πολυμερή χαρακτηρίστηκαν με πληθώρα φασματοσκοπικών τεχνικών (FTIR,NMR, SEC, TGA, UV-Vis), ενώ ως προς την αυτοοργάνωση τους, εξετάσαμε τηνσυμπεριφορά τους σε υδατικά διαλύματα (CD, TEM) και την αυτοοργάνωση τους σεστερεά κατάσταση, τόσο σε επίπεδο μοναδιαίας κυψελίδας (WAXS, XRD) όσο και σεοργάνωση μεγάλης κλίμακας (SAXS). Τέλος, είναι σημαντικό να αναφερθεί ότι όλα ταπολυμερή που συντέθηκαν στην διδακτορική αυτή διατριβή, βρήκαν εφαρμογές είτε ωςμοντέλα (μοριακός χάρακας), είτε ως μιμητές μεταξιού (αυξημένες μηχανικές ιδιότητες),ενώ ορισμένα είχαν σπουδαίες βιο-εφαρμογές (πέτρα στα νεφρά, φορείς αντικαρκινικώνφαρμάκων)

Ligand-Specific Nano-Contrast Agents Promote Enhanced Breast Cancer CT Detection at 0.5 mg Au

For many cancer types, being undetectable from early symptoms or blood tests, or often detected at late stages, medical imaging emerges as the most efficient tool for cancer screening. MRI, ultrasound, X-rays (mammography), and X-ray CT (CT) are currently used in hospitals with variable costs. Diagnostic materials that can detect breast tumors through molecular recognition and amplify the signal at the targeting site in combination with state-of-the-art CT techniques, such as dual-energy CT, could lead to a more precise detection and assist significantly in image-guided intervention. Herein, we have developed a ligand-specific X-ray contrast agent that recognizes α5β1 integrins overexpressed in MDA-MB-231 breast cancer cells for detection of triple (−) cancer, which proliferates very aggressively. In vitro studies show binding and internalization of our nanoprobes within those cells, towards uncoated nanoparticles (NPs) and saline. In vivo studies show high retention of ~3 nm ligand-PEG-S-AuNPs in breast tumors in mice (up to 21 days) and pronounced CT detection, with statistical significance from saline and iohexol, though only 0.5 mg of metal were utilized. In addition, accumulation of ligand-specific NPs is shown in tumors with minimal presence in other organs, relative to controls. The prolonged, low-metal, NP-enhanced spectral-CT detection of triple (−) breast cancer could lead to breakthrough advances in X-ray cancer diagnostics, nanotechnology, and medicine

Facile aqueous synthesis and stabilization of nearly monodispersed gold nanospheres by poly(L -proline)

A facile strategy is developed to synthesize Au nanoparticles (Au-NPs) using water-soluble poly(L-proline) (PLP). The synthesized NPs were characterized by TEM, FTIR and NMR spectroscopy, thermogravimetric analysis, and circular dichroism. It was found that PLP has a "dual" role as an efficient reductant of Au(III) and simultaneously as a stabilizing agent of Au-NPs. The influence of PLP molecular weight, temperature, initial Au(III) concentration, and Au(III)/PLP molar ratio on the size and dispersity of Au-NPs is examined. It was found that the unique extended secondary structure of PLP II resulted in the facile formation of highly crystalline Au-NPs in water at a very low Au(III)/PLP molar ratio. These Au-NPs have the smallest dimensions and size distributions among NPs synthesized so far by polymeric materials in aqueous media, and exhibit enduring colloidal stability. Therefore, by utilizing biocompatible and benign materials in water, we managed to obtain Au-NPs, so as the final product is ready-to-use for biomedical applications. © 2013 Wiley Periodicals, Inc

Thermoresponsive and Mechanical Properties of Poly(l‑proline) Gels

Gelation of the left helical N-substituted homopolypeptide poly­(l-proline) (PLP) in water was explored, employing rheological and small-angle scattering studies at different temperatures and concentrations in order to investigate the network structure and its mechanical properties. Stiff gels were obtained at 10 wt % or higher at 5 °C, the first time gelation has been observed for homopolypeptides. The secondary structure and helical rigidity of PLP has large structural similarities to gelatin but as gels the two materials show contrasting trends with temperature. With increasing temperature in D₂O, the network stiffens, with broad scattering features of similar correlation length for all concentrations and molar masses of PLP. A thermoresponsive transition was also achieved between 5 and 35 °C, with moduli at 35 °C higher than gelatin at 5 °C. The brittle gels could tolerate strains of 1% before yielding with a frequency-independent modulus over the observed range, similar to natural proline-rich proteins, suggesting the potential for thermoresponsive or biomaterial-based applications

Complexation-Driven Mutarotation in Poly(l-proline) Block Copolypeptides

Novel poly(l-lysine)-block-poly(l-proline) (PLL-b-PLP)-based materials with all PLP helical conformers, i.e., PLP II and the rare PLP I are here reported. Electrostatic supramolecular complexation of the adjacent cationic PLL with anionic molecules bearing DNA analogue H-bonding functionalities, such as deoxyguanosine monophosphate (dGMP), preserves the extended PLP II helix, and the complexed molecule is locked and held in position by orthogonal shape-persistent hydrogen-bonded dGMP ribbons and their extended π-stacking. The branched anionic surfactant dodecylbenzenesulfonic acid (DBSA) on the other hand, introduces periodicity frustration and interlayer plasticization, leading to a reversed mutarotation to the more compact PLP I helix by complexation, without external stimuli, and is here reported for the first time. We foresee that our findings can be used as a platform for novel molecularly adaptive functional materials, and could possibly give insight in many proline-related transmembrane biological functions. © 2015 American Chemical Society

Surface initiated ring-opening polymerization of l-proline N-carboxy anhydride from single and multi walled carbon nanotubes

Ring-opening surface initiated polymerization of l-proline N-carboxyanhydride was performed from amine functionalized single (SWNTs) and multi walled carbon nanotubes (MWNTs). The primary amines were grafted on the surfaces via a well-studied Diels-Alder cycloaddition. The initiator attachment helped the debundling of carbon nanotubes as shown by atomic force microscopy (AFM) studies where only small aggregates were observed. Thermogravimetric analysis revealed high wt% of grafted polyproline on the carbon nanotubes surface after the ring-opening polymerization. AFM studies showed a rather uniform layer of grafted polyproline from both MWNTs and SWNTs. The grafting of PLP on the surface was also verified by FTIR and Raman spectroscopy as well as 1H NMR in CDCl3/d-TFA. The polyproline grafted carbon nanotubes (CNTs) were readily dissolved in organic solvents in contrast to the insoluble pristine and amine-functionalized CNTs. © 2013 Elsevier Ltd. All rights reserved

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. © 2011 American Chemical Society

Complexation-Driven Mutarotation in Poly(l‑proline) Block Copolypeptides

Novel poly­(l-lysine)-<i>block</i>-poly­(l-proline) (PLL-<i>b</i>-PLP)-based materials with all PLP helical conformers, i.e., PLP II and the rare PLP I are here reported. Electrostatic supramolecular complexation of the adjacent cationic PLL with anionic molecules bearing DNA analogue H-bonding functionalities, such as deoxyguanosine monophosphate (dGMP), preserves the extended PLP II helix, and the complexed molecule is locked and held in position by orthogonal shape-persistent hydrogen-bonded dGMP ribbons and their extended π-stacking. The branched anionic surfactant dodecylbenzenesulfonic acid (DBSA) on the other hand, introduces periodicity frustration and interlayer plasticization, leading to a reversed mutarotation to the more compact PLP I helix by complexation, without external stimuli, and is here reported for the first time. We foresee that our findings can be used as a platform for novel molecularly adaptive functional materials, and could possibly give insight in many proline-related transmembrane biological functions