Sagrario Pascual

Functional Iron Oxide Magnetic Nanoparticles with Hyperthermia‐Induced Drug Release Ability by Using a Combination of Orthogonal Click Reactions

Click and drug: A combination of orthogonal click reactions is employed for the preparation of functional iron oxide nanoparticles (IONPs) that show unprecedented hyperthermia-induced drug release through a magnetically stimulated retro-Diels-Alder (rDA) process. Magnetic stimulation induces sufficient local energy in close proximity to the cycloadduct to initiate the rDA process

Introducing the Azlactone Functionality into Polymers through Controlled Radical Polymerization: Strategies and Recent Developments

Polymers containing the highly reactive azlactone group have emerged as a powerful platform useful in various application areas. This Highlight summarizes recent developments in the field of azlactone-derived polymers made in our group using controlled radical polymerizations (ATRP and RAFT) and ‘click’ chemistry methodology (thiol-Michael addition), leading to well defined reactive polymers.

Stable azlactone-functionalized nanoparticles prepared from thermoresponsive copolymers synthesized by RAFT polymerization

A new class of stable azlactone-functionalized thermoresponsive nanoparticles have been synthesized and characterized. Such particles are based on well-defined copolymers of poly(N-isopropylacrylamide) (PNIPAM), poly(N,N-dimethylacrylamide) (PDMA) and poly(2-vinyl-4,4-dimethylazlactone) (PVDM) copolymers synthesized using reversible addition–fragmentation chain transfer (RAFT) polymerization. A well-defined PNIPAM macromolecular RAFT agent and a PDMA macromolecular RAFT agent of low polydispersities (PDIs = 1.04–1.12) were used to mediate the copolymerizations of DMA/VDM and of NIPAM/VDM, respectively, resulting in copolymers of Mn ranging from 19 500 g mol−1 to 64 600 g mol−1 and PDIs ranging from 1.04 to 1.20. Depending on the number-average polymerization degrees of NIPAM, DMA and VDM, lower critical solution temperatures (LCSTs) ranging from 36 °C to 44 °C were measured. Two block copolymers PNIPAM46-b-P(VDM6-co-DMA65) and PDMA23-b-P(VDM10-co-NIPAM46) have a LCST that occurs at the physiological temperature. Above the LCST, the resulting nanoparticles were covalently stabilized by reacting a diamine with azlactone rings. The size exclusion chromatography (SEC) analyses revealed that all unimers are incorporated into the core-crosslinked structures and into the shell-crosslinked structures. This new strategy of crosslinking nanoparticles based on thermoresponsive copolymers is of particular interest as it is highly efficient. The azlactone groups remaining in core-crosslinked nanoparticles are suitable to react with dansylhydrazine as shown by SEC analysis using UV detection.

Thermoresponsive block copolymers containing reactive azlactone groups and their bioconjugation with lysozyme

Thermoresponsive block copolymers based on poly(ethylene oxide) (PEO) and poly(N-isopropyl acrylamide) (PNIPAM) containing azlactone groups along the backbone and at the chain-end of the macromolecular chain were synthesized by statistically reversible addition–fragmentation chain transfer (RAFT) copolymerization and by using a combination of RAFT polymerization and thiol–ene Michael addition. Well-defined poly(ethylene oxide)-b-poly(2-vinyl-4,4-dimethylazlactone-co-N-isopropyl acrylamide) (PEO-b-P(VDM-co-NIPAM)) block copolymers and azlactone-terminated poly(ethylene oxide)-b-poly(N-isopropyl acrylamide) (PEO-b-PNIPAM-VDM) diblock copolymers with low polydispersity indices (PDIs ≤ 1.10) were prepared and fully characterized by 1H NMR spectroscopy, FT-IR spectroscopy, and SEC. Such PEO-b-P(VDM-co-NIPAM) block copolymers and azlactone-terminated PEO-b-PNIPAM block copolymers present tunable lower critical solution temperature (LCST) depending on PEO, PNIPAM, and PVDM molar ratios. The reactivity of the PEO44-b-P(VDM20-co-NIPAM80) copolymer (Mn,NMR = 14 200 g mol−1, PDI = 1.08) and of the PEO44-b-PNIPAM101-VDM copolymer (Mn,NMR = 13 700 g mol−1, PDI = 1.08) was studied with lysozyme as a model protein. A bioconjugate with a higher apparent molecular weight was obtained with the PEO44-b-P(VDM20-co-NIPAM80) copolymer in comparison with the one obtained using the PEO44-b-PNIPAM101-VDM copolymer as shown by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). The results suggest promising applications of azlactone-functionalized polymers within the field of bioconjugation.

Synthesis of thermoresponsive oxazolone end-functional polymers for reactions with amines using thiol-Michael addition “click” chemistry

Well-defined poly(N-isopropylacrylamide) (PNIPAM) polymers with an oxazolone ring at the chain end have been synthesized by combining controlled radical polymerization and thiol-Michael addition “click” chemistry. First, PNIPAM was synthesized using reversible addition–fragmentation chain transfer (RAFT) polymerization to afford polymers of controlled molecular weight and molecular weight distribution (Mn (1H NMR) = 3200 g mol−1; PDISEC = 1.05). The chain end was quantitatively converted to a thiol by aminolysis. Then, the functional monomer vinyl azlactone (VDM) was quantitatively “clicked” onto the chain end using a thiol-Michael addition reaction. The polymers were reacted with a model amine in order to demonstrate the potential of these polymers for bioconjugation.

Synthesis of New Polyamides from Natural Monomers: L-Malic acid and L-Lysine

The synthesis of new polyamides from two natural compounds L-malic acid and L-lysine was carried out via the active ester polycondensation method (pentafluorophenyl ester). The hydroxyl and carboxylic side groups were orthogonally protected as tert-butyl ether and benzyl ester, respectively. High molecular masses (reaching 25 000 g/mol) were obtained at 60°C in tetrahydrofuran for fully protected polyamide. This polymer was soluble in chloroform. Total regeneration of hydroxyl groups was carried out in trifluoroacetic acid. Regeneration of the carboxylic group by hydrogenolysis led to a polyamide, soluble in Tris buffer solution (pH = 7.4). The polyamides bearing free hydroxyl and carboxyl groups were water-soluble.

Synthesis and characterization of high grafting density bottle-brush poly(oxa)norbornene-g-poly(ε-caprolactone)

Poly(e-caprolactone)-based (oxa)norbornene macromonomers with two poly(e-caprolactone) (PCL) chains on the polymerizable entity were synthesized through organocatalyst mediated ring-opening polymerization (ROP) in high yields, with excellent control over molecular weights (from 2800 to 11 000 g mol−1) and dispersities (ĐM < 1.26). Ring-opening metathesis polymerization (ROMP) of these macromonomers was carried out using the very active, fast-initiating Grubbs’ second generation catalyst and the fast-initiating, fast-propagating Grubbs’ third generation catalyst. High grafting density poly(oxa)norbornene-g-PCLs were obtained with a backbone length between 10 and 100 repeating units and a graft length between 10 and 48 while retaining a narrow distribution of molecular weights, leading to comb or brush copolymers according to the lengths of the backbone and graft chains. Thermal analyses show a higher stability of the bottle-brush poly(oxa)norbornene-g-PCLs compared to their PCL-based (oxa)norbornene macromonomers together with a weaker crystallinity resulting from steric hindrance.

Amine-Reactive Polymers Synthesized by RAFT Polymerization Using an Azlactone Functional Trithiocarbonate RAFT Agent

A new azlactone-derived trithiocarbonate is prepared and used as a chain-transfer agent to mediate the reversible addition-fragmentation chain transfer (RAFT) polymerization of styrene, ethyl acrylate, and N-isopropyl acrylamide. Well-defined polymers with controlled molecular weights (M(n) = 1000-7000 g mol(-1) ) and narrow molecular weight distributions (PDI = 1.05-1.10) are thus obtained that retain the azlactone functionality at the chain end. The ability of the resulting end-functionalized polymers to react quantitatively at room temperature with a stoichiometric amount of amino groups with retention of the thiocarbonylthio moiety is ascertained by using 4-fluorobenzylamine and allylamine.

Investigation of the effects of various parameters on the synthesis of oligopeptides in aqueous solution

Abstract Oligomerization efficiency of amino acids in aqueous solution has been compared under different conditions (temperature, activating agent, etc.) using 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) and 1,1 ′ -carbonyldiimidazole (CDI) as coupling agents. Glycine (H 2 N–CH 2 –COOH) and α-alanine (H 2 N–CH(CH 3 )–COOH) were chosen as α-amino acids and β-alanine (H 2 N–CH 2 –CH 2 –COOH) as the β-amino acid. The coupling reaction between EDC and glycine was shown to occur but does not go to completion either at ambient temperature or at 70 °C. The presence of a carboxylic activating agent such as N -hydroxysuccinimide improves the EDC-mediated coupling reaction, and the amino acid structure (α- or β-) was shown to have an influence on the oligomerization efficiency, with β-alanine polymerisation being more efficient. These findings are explained by reference to the reaction mechanism.

Sol–gel reversible metallo-supramolecular hydrogels based on a thermoresponsive double hydrophilic block copolymer

A well-defined poly(N,N-dimethylacrylamide)-b-poly(N-isopropylacrylamide-co-2-vinyl-4,4-dimethylazlactone) thermoresponsive double hydrophilic block copolymer bearing a terpyridine entity (Tpy-PDMA-b-P(NIPAM-co-VDM)) was synthesized by successive RAFT polymerizations. An amphiphilic macro-chain transfer agent bearing a terpyridine moiety (Tpy-PDMA-CTA) was synthesized and used for the preparation of a double hydrophilic block copolymer (Tpy-PDMA-b-P(NIPAM-co-VDM)) by RAFT dispersion polymerization. The RAFT dispersion polymerization of water-soluble monomers showed good control over the molar mass and dispersity, as characterized by size exclusion chromatography (SEC) and 1H-NMR spectroscopy. Complexation in the presence of metal ions (Fe2+) and self-assembly of the Tpy-PDMA-b-P(NIPAM-co-VDM) copolymer in diluted solution (0.5% w/v) were investigated. The formation of dynamic metallo-supramolecular flower-like micelles was demonstrated by UV-Vis spectrophotometry and dynamic light scattering (DLS). The effect of the addition of Fe2+ ions to a concentrated solution (8% w/v) of the Tpy-PDMA-b-P(NIPAM-co-VDM) copolymer at low temperature was investigated and the thermal profile of the metallic bis-terpyridine complex ([Fe(Tpy-PDMA-b-P(NIPAM-co-VDM))2]2+) has been studied by differential scanning calorimetry (DSC). The influence of temperature on the aqueous solution (8% w/v) of the ([Fe(Tpy-PDMA-b-P(NIPAM-co-VDM))2]2+) metallic complex was investigated by rotational rheometry. The results show that the self-assembly of the thermoresponsive block of the metallic bis-terpyridine complex formed a dynamic hydrogel with a sol–gel thermoreversible transition.