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Polyamidoamine hydrogels prepared by the radical post-polymerization of α,ω-bisacrylamide-terminated M-AGM oligomers, in turn obtained by the polyaddition of 4-aminobutylguanidine with N,N’-methylenebisacrylamide, were reinforced with raw silk fibers, which can establish covalent bonds with the polyamidoamine matrix via reaction of the amine groups in the lysine residues with the acrylamide terminals of the M-AGM oligomer. Silk/M-AGM membranes were prepared by impregnating silk mats with M-AGM aqueous solutions and subsequent crosslinking by UV irradiation. The guanidine pendants of the M-AGM units imparted the ability to form strong but reversible interactions with oxyanions, including the highly toxic chromate ions. The potential of the silk/M-AGM membranes to purify Cr(VI)-contaminated water down to the drinkability level, that is, below 50 ppb, was tested by performing sorption experiments both in static (Cr(VI) concentration 20–2.5 ppm) and flow conditions (Cr(VI) concentration 10–1 ppm). After static sorption experiments, the Cr(VI)-loaded silk/M-AGM membranes could easily be regenerated via treatment with a 1 M sodium hydroxide solution. Dynamic tests performed using two stacked membranes and a 1 ppm Cr(VI) aqueous solution reduced Cr(VI) concentration down to 4 ppb. Remarkably, the use of renewable sources, the environmentally friendly preparation process, and the goal achieved meet eco-design requirements.

Polyamidoamines (PAAs) are biocompatible and biodegradable polymers with a huge potential as biomaterials for pharmaceutical applications. They are obtained by the step-wise aza-Michael polyaddition of bifunctional or multifunctional amines with bisacrylamides in water. To the best of our knowledge, no synthetic protocols leading to hyperbranched PAAs as well as PAA microgels have been published so far. To fill this gap, a statistical approach was established in this work to fine-tune the aza-Michael polyaddition stoichiometry when a multifunctional co-monomer (bf) is added to a mixture of bifunctional monomers with complementary functions (a2 + b2), possibly even in presence of a monofunctional co-monomer (b1), for obtaining either microgels or hyperbranched polymers by a one-pot reaction. For this purpose, two new equations, obtained by reworking the classic Flory–Stockmayer equations, were successfully applied to the synthesis of different model systems, obtaining biocompatible microgels with tunable size distribution (200–500 nm) and properly designed end-chains in a simple and straightforward way. The same mathematical approach allowed us to empirically evaluate the actual number of active reactive functions of the co-monomers. A number of selected systems, being evaluated for their cytotoxicity in vitro, proved highly cytocompatible and, therefore, endowed with great potential for pharmaceutical and medical applications.

A novel polyamidoamine (M-PCASS) bearing a disulfide group and two phosphonate groups per repeat unit was obtained by reacting N,N′-methylenebisacrylamide with a purposely designed bis-sec-amine monomer, namely, tetraethyl(((disulfanediylbis(ethane-2,1-diyl))bis(azanediyl))bis(ethane-2,1-diyl))bis(phosphonate) (PCASS). The aim was to ascertain whether the introduction of phosphonate groups, well-known for inducing cotton charring in the repeat unit of a disulfide-containing PAA, increased its already remarkable flame retardant efficacy for cotton. The performance of M-PCASS was evaluated by different combustion tests, choosing M-CYSS, a polyamidoamine containing a disulfide group but no phosphonate groups, as a benchmark. In horizontal flame spread tests (HFSTs), M-PCASS was a more effective flame retardant than M-CYSS at lower add-ons with no afterglow. In vertical flame spread tests, the only effect was afterglow suppression with no self-extinguishment even at add-ons higher than in HFSTs. In oxygen-consumption cone calorimetry tests, M-PCASS decreased the heat release rate peak of cotton by 16%, the CO2 emission by 50%, and the smoke release by 83%, leaving a 10% residue to be compared with a negligible residue for untreated cotton. Overall, the set of results obtained envisage that the newly synthesized phosphonate-containing PAA M-PCASS may be suitable for specific applications as flame retardant, where smoke suppression or reduction of total gas released is a key requirement.

Hydrophilic cyclodextrin nanosponges were prepared by the oxo-Michael polyaddition in an aqueous solution at pH > 10 of α-, β-, and γ-cyclodextrin with 1,4-bisacryloylpiperazine or 2,2-bisacrylamidoacetic acid. These nanosponges and, for comparison purposes, their precursor cyclodextrins were tested as sorbents of o-toluidine, a carcinogenic wastewater contaminant, by monitoring the depletion of o-toluidine from a 10−4 M (10 ppm) aqueous solutions. To this aim, an innovative analytical procedure was used: The voltammetric peak currents of o-toluidine in linear sweep voltammetry experiments were registered using multi-walled carbon nanotubes-modified glassy carbon electrodes. The experimental sorption curves fitted a mono-exponential kinetic model, and the residual o-toluidine was 0.16 ppm, one order of magnitude lower than those of all other sorbents reported so far. The sorption capacities ranged from 88 to 199 µmol g−1 (10–21.3 mg g−1), equal to or higher than those of the parent cyclodextrins. All nanosponges were completely regenerated by extracting with methanol. After regeneration, the sorption capacity slightly improved, suggesting a rearrangement of the nanosponge network. Overall, it may be reasonably concluded that the cyclodextrin nanosponges reported in this paper warrant potential as o-toluidine exhaustive sorbents.

Strategies for endosomal escape and access to the cell nucleus are highly sought for nanocarriers to deliver their load efficiently following endocytosis. In this work, we have studied the uptake and intracellular trafficking of a polycationic polyamidoamine (PAA) endowed with a luminescent Ru complex, Ru-PhenAN, that shows unique trafficking to the cell nucleus. Live cell imaging confirmed the capacity of this polymer to access the nucleus, excluding artifacts due to cell fixation, and clarified that the mechanism of escape is light-triggered and relies on the presence of the Ru complexes and their capacity to absorb light and act as photosensitizers for singlet oxygen production. These results open up the possibility to use PAA-ruthenium complexes for targeted light-triggered delivery of genetic material or drugs to the cytosol and nucleus.

Polyamidoamines (PAAs) are multifunctional polymers prepared from prim- or sec-amines by Michael-type polyaddition with bisacrylamides. The reaction is preferably carried out at room temperature in water and without added catalysts or organic solvents. The reaction is specific. The presence in the starting monomers of additional functions, leaving apart amine, thiol and phosphine groups, does not interfere with the polymerization process. Consequently, PAAs are a polymer class endowed with unusual structural versatility. Moreover, at pH > 7 they are hydrolytically degradable in aqueous media to harmless products mostly consisting of β-amino-propionic acids. Many PAAs are remarkably biocompatible notwithstanding their polycationic nature. These properties allow to prepare multifunctional polymeric structures suitable for many diversified applications in biotechnology, such as drug carriers, transfection promoters, antiviral and antimalarial agents, hydrogels scaffolds for tissue engineering. The objective of this paper is to fully report the PAA chemistry and the studied biotechnological applications of a vast PAA library.

The aza-Michael polyaddition of L-arginine and N,N′-methylene-bis-acrylamide gives the biocompatible and easily cell-internalized polyamidoamine ARGO7. By controlled synthesis, two ARGO7 oligomers, namely a trimer and a pentamer, bearing acrylamide terminal units, were obtained as precursors of the β-cyclodextrin-end-terminated oligomers P3 and P5, which have been shown to encapsulate curcumin at both pH 7.4 and 4.5. After lyophilization, P3- and P5-curcumin complexes gave stable water solutions. The apparent solubility of encapsulated curcumin was in the range 20–51 μg mL−1, that is, three orders of magnitude higher than the water solubility of free curcumin (0.011 μg mL−1). The drug release profiles showed induction periods both at pH levels 4.5 and 7.4, suggesting a diffusive release mechanism, as confirmed by kinetic studies. The release rate of curcumin was higher at pH 7.4 than at pH 4.5 and, in both cases, it was higher for the P5 complex. Encapsulated curcumin was more photostable than the free drug. Molecular mechanics and molecular dynamics simulations explain at atomistic level the formation of aggregates due to favorable van der Waals interactions. The drug molecules interact with the external surface of carriers or form inclusion complexes with the β-cyclodextrin cavities. The aggregate stability is higher at pH 4.5.

The hitherto known polyamidoamines (PAAs) are not suitable as structural materials because they are usually water-soluble or swellable in water. This paper deals with the synthesis and characterization of semi-crystalline hydrophobic PAAs (H-PAAs) by combining different bis-sec-amines with bis-acrylamides obtained from C6–C12 bis-prim-amines. H-PAAs were initially obtained in a solution of benzyl alcohol, a solvent suitable for both monomers and polymers. Their number average molecular weights, M¯n, which were determined with 1H-NMR by evaluating the percentage of their terminal units, varied from 6000 to &gt, 10,000. The solubility, thermal properties, ignitability and water resistance of H-PAAs were determined. They were soluble in organic solvents, semi-crystalline and thermally stable. The most promising ones were also prepared using a bulk process, which has never been previously reported for PAA synthesis. In the form of films, these H-PAAs were apparently unaffected by water. The films underwent tensile and wettability tests. They showed similar Young moduli (260–263 MPa), whereas the maximum stress and the stress at break depended on the number of methylene groups of the starting bis-acrylamides. Their wettability was somewhat higher than that of common Nylons. Interestingly, none of the H-PAAs considered, either as films or powders, ignited after prolonged exposure to a methane flame.

This paper aims at elucidating the degradation mechanism of linear polyamidoamines (PAAs) in water. PAAs are synthesized by the aza-Michael polyaddition of prim-monoamines or bis-sec-amines with bisacrylamides. Many PAAs are water-soluble and have potential for biotechnological applications and as flame-retardants. PAAs have long been known to degrade in water at pH &ge, 7, but their degradation mechanism has never been explored in detail. Filling this gap was necessary to assess the suitability of PAAs for the above applications. To this aim, a small library of nine PAAs was expressly synthesized and their degradation mechanism in aqueous solution studied by 1H-NMR in different conditions of pH and temperature. The main degradation mechanism was in all cases the retro-aza-Michael reaction triggered by dilution but, in some cases, hints were detected of concurrent hydrolytic degradation. Most PAAs were stable at pH 4.0, all degraded at pH 7.0 and 9.0. Initially, the degradation rate was faster at pH 9.0 than at pH 7.0, but the percent degradation after 97 days was mostly lower. In most cases, at pH 7.0 the degradation followed first order kinetics. The degradation rates mainly depended on the basicity of the amine monomers. More basic amines acted as better leaving groups.

D- and L-arginine-based polyamidoamino acids, called D- and L-ARGO7, retain the chirality and acid/base properties of the parent -amino acids and show pH-dependent self-structuring in water. The ability of the ARGO7 chiral isomers to selectively interact with chiral biomolecules and/or surfaces was studied by choosing sodium deoxycholate (NaDC) as a model chiral biomolecule for its ability to self-assembly into globular micelles, showing enantio-selectivity. To this purpose, mixtures of NaDC with D-, L- or D,L-ARGO7, respectively, in water were analysed by circular dichroism (CD) spectroscopy and small-angle neutron scattering (SANS) at different levels of acidity expressed in terms of pD and concentrations. Differences in the CD spectra indicated chiral discrimination for NaDC/ARGO7 mixtures in the gel phase (pD 7.30) but not in the solution phase (pD 9.06). SANS measurements confirmed large scale structural perturbation induced by this chiral discrimination in the gel phase yet no modulation of the structure in the solution phase. Together, these techniques shed light on the mechanism by which ARGO7 stereoisomers modify the morphology of NaDC micelles as a function of pH. This work demonstrates chirality-dependent interactions that drive structural evolution and phase behaviour of NaDC, opening the way for designing novel smart drug delivery systems.

This paper reports on synthesis, acid–base properties, and self-structuring in water of a chiral polyamidoamino acid, M-l-Gln, obtained from the polyaddition of N,N′-methylenebisacrylamide with l-glutamine, with the potential of establishing hydrogen bonds through its prim-amide pendants. The M-l-Gln showed pH-responsive circular dichroism spectra, revealing ordered conformations. Structuring was nearly insensitive to ionic strength but sensitive to denaturing agents. The NMR diffusion studies were consistent with a population of unimolecular nanoparticles thus excluding aggregation. The M-l-Gln had the highest molecular weight and hydrodynamic radius among all polyamidoamino acids described. Possibly, transient hydrogen bonds between l-glutamine molecules and M-l-Gln growing chains facilitated the polyaddition reaction. Theoretical modeling showed that M-l-Gln assumed pH-dependent self-ordered coil conformations with main chain transoid arrangements reminiscent of the protein hairpin motif owing to intramolecular dipole moments and hydrogen bonds. The latter were most numerous at the isoelectric point (pH 4.5), where they mainly involved even topologically distant main chain amide N–H and side chain amide C=O brought to proximity by structuring. Hydrogen bonds at pH 4.5 were also suggested by variable temperature NMR. The 2D NOESY experiments at pH 4.5 confirmed the formation of compact structures through the analysis of the main chain/side chain hydrogen contacts, in line with MD simulations.

This paper reports on synthesis, acid&ndash, base properties, and self-structuring in water of a chiral polyamidoamino acid, M-l-Gln, obtained from the polyaddition of N,N&rsquo, methylenebisacrylamide with l-glutamine, with the potential of establishing hydrogen bonds through its prim-amide pendants. The M-l-Gln showed pH-responsive circular dichroism spectra, revealing ordered conformations. Structuring was nearly insensitive to ionic strength but sensitive to denaturing agents. The NMR diffusion studies were consistent with a population of unimolecular nanoparticles thus excluding aggregation. The M-l-Gln had the highest molecular weight and hydrodynamic radius among all polyamidoamino acids described. Possibly, transient hydrogen bonds between l-glutamine molecules and M-l-Gln growing chains facilitated the polyaddition reaction. Theoretical modeling showed that M-l-Gln assumed pH-dependent self-ordered coil conformations with main chain transoid arrangements reminiscent of the protein hairpin motif owing to intramolecular dipole moments and hydrogen bonds. The latter were most numerous at the isoelectric point (pH 4.5), where they mainly involved even topologically distant main chain amide N&ndash, H and side chain amide C=O brought to proximity by structuring. Hydrogen bonds at pH 4.5 were also suggested by variable temperature NMR. The 2D NOESY experiments at pH 4.5 confirmed the formation of compact structures through the analysis of the main chain/side chain hydrogen contacts, in line with MD simulations.

Linear polyamidoamines (PAAs) derived from the polyaddition of natural α-amino acids and N,N′-methylene bis(acrylamide) are intumescent flame retardants for cotton. Among them, the glycine-derived M-GLY extinguished the flame in horizontal flame spread tests at 4% by weight add-on. This paper reports on an extensive study aimed at understanding the molecular-level transformations of M-GLY-treated cotton upon heating in air at 300 °C, 350 °C and 420 °C. Thermogravimetric analysis (TGA) identified different thermal-oxidative decomposition stages and, coupled to Fourier transform infrared spectroscopy, allowed the volatile species released upon heating to be determined, revealing differences in the decomposition pattern of treated and untreated cotton. XPS analysis of the char residues of M-GLY-treated cotton revealed the formation of aromatic nanographitic char at lower temperature with respect to untreated cotton. Raman spectroscopy of the char residues provided indications on the degree of graphitization of treated and untreated cotton at the three reference temperatures. Solid state 13C nuclear magnetic resonance spectroscopy (NMR) provided information on the char structure as a function of the treatment temperature, clearly indicating that M-GLY favors the carbonization of cotton with the formation of more highly condensed aromatic structures.

In this paper, bioinspired polyamidoamines (PAAs) were synthesized from N,N′-methylenebisacrylamide and nine natural α-amino acids: L-alanine, L-valine, L-leucine (M-LEU), L-histidine, L-serine, L-asparagine, L-glutamine (M-GLN), L-aspartic acid and L-glutamic acid (M-GLU) and their performance as flame retardants (FRs) for cotton were determined. The aim was to ascertain if the ability to protect cotton from fire by the process of intumescing, previously found for the glycine-derived M-GLY, was a general feature of α-amino acid-derived PAAs. None of the PAAs ignited by flame impingement, apart from M-LEU, which burned for a few seconds leaving 93% of residue. All of them formed carbon- and oxygen-rich, porous chars with a graphitic structure in the air at 350 °C, as revealed by X-ray photoelectron spectroscopy. All samples were tested as FRs for cotton by horizontal flame spread tests. At a 5% add-on, M-GLU and M-GLN extinguished the flame. The same results were obtained with all the other PAAs at a 7% add-on. The α-amino acid residues influenced the FR performance. The most effective were those that, by heating, were most suitable for producing thermally stable cyclic aromatic structures. All PAA-treated cotton samples, even when burning, left significant residues, which, according to scanning electron microscopy analysis, maintained the original cotton texture.

AGMA1, a prevailingly cationic, guanidine-bearing, linear, amphoteric polyamidoamine is an effective siRNA condensing agent. Here two AGMA1 samples of different molecular weight, i.e. AGMA1–5 and AGMA1–10 were evaluated as siRNA condensing agents and transfection promoters. AGMA1–10 formed stable polyplexes with a size lower than 50 nm and positive zeta potential. AGMA1–5 polyplexes were larger, about 100 nm in size. AGMA1–10 polyplexes, but not AGMA1–5 proved to be an effective intracellular siRNA carrier, able to trigger gene silencing in Hela and PC3 cell lines without eliciting cytotoxic effects. AGMA1–10 knocked down AKT-1 expression upon transfection with an AKT-1 specific siRNA. The polyplex entry mechanism was investigated and was mediated by macropinocytosis. In conclusion, AGMA1 has potential as an efficient, non-toxic tool for the intracellular delivery of siRNA and warrants further investigation.

Gold nanoparticles are elective candidate for cancer therapy. Current efforts are devoted to developing innovative methods for their synthesis. Besides, understanding their interaction with cells have become increasingly important for their clinical application. This work aims to describe a simple approach for the synthesis of extra-small gold nanoparticles for breast cancer therapy. In brief, a biocompatible and biodegradable polyamidoamine (named AGMA1-SH), bearing 20%, on a molar basis, thiol-functionalized repeat units, is employed to stabilize and coat extra-small gold nanospheres of different sizes (2.5, 3.5, and 5 nm in gold core), and to generate a nanoplatform for the link with Trastuzumab monoclonal antibody for HER2-positive breast cancer targeting. Dynamic light scattering, transmission electron microscopy, ultraviolet visible spectroscopy, X-ray powder diffraction, circular dichroism, protein quantification assays are used for the characterization. The targeting properties of the nanosystems are explored to achieve enhanced and selective uptake of AGMA1-SH-gold nanoparticles by in vitro studies against HER-2 overexpressing cells, SKBR-3 and compared to HER-2 low expressing cells, MCF-7, and normal fibroblast cell line, NIH-3T3. In vitro physicochemical characterization demonstrates that gold nanoparticles modified with AGMA1-SH are more stable in aqueous solution than the unmodified ones. Additionally, the greater gold nanoparticles size (5-nm) is associated with a higher stability and conjugation efficiency with Trastuzumab, which retains its folding and anticancer activity after the conjugation. In particular, the larger Trastuzumab functionalized nanoparticles displays the highest efficacy (via the pro-apoptotic protein increase, anti-apoptotic components decrease, survival-proliferation pathways downregulation) and internalization (via the activation of the classical clathrin-mediated endocytosis) in HER-2 overexpressing SKBR-3 cells, without eliciting significant effects on the other cell lines. The use of biocompatible AGMA1-SH for producing covalently stabilized gold nanoparticles to achieve selective targeting, cytotoxicity and uptake is completely novel, offering an important advancement for developing new anticancer conjugated-gold nanoparticles.

In this work, we report the synthesis of [Ru(phen)3 2+]-based complexes and their use as photosensitizers for photodynamic therapy (PDT), a treatment of pathological conditions based on the photoactivation of bioactive compounds, which are not harmful in the absence of light irradiation. Of these complexes, Ru-PhenISA and Ru-PhenAN are polymer conjugates containing less than 5%, (on a molar basis), photoactive units. Their performance is compared with that of a small [Ru(phen)3 2+] compound, [Ru(phen)2BAP](OTf)2 (BAP = 4-(4′-aminobutyl)-1,10-phenanthroline, OTf = triflate anion), used as a model of the photoactive units. The polymer ligands, PhenISA and PhenAN, are polyamidoamines with different acid-base properties. At physiological pH, the former is zwitterionic, the latter moderately cationic, and both intrinsically cytocompatible. The photophysical characterizations show that the complexation to macromolecules does not hamper the Ru(phen)3 2+ ability to generate toxic singlet oxygen upon irradiation, and phosphorescence lifetimes and quantum yields are similar in all cases. All three compounds are internalized by HeLa cells and can induce cell death upon visible light irradiation. However, their relative PDT efficiency is different: the zwitterionic PhenISA endowed with the Ru-complex lowers the PDT efficiency of the free complex, while conversely, the cationic PhenAN boosts it. Flow cytometry demonstrates that the uptake efficiency of the three agents reflects the observed differences in PDT efficacy. Additionally, intracellular localization studies show that while [Ru(phen)2BAP](OTf)2 remains confined in vesicular structures, Ru-PhenISA localization is hard to determine due to the very low uptake efficiency. Very interestingly, instead, the cationic Ru-PhenAN accumulates inside the nucleus in all treated cells. Overall, the results indicate that the complexation of [Ru(phen)2BAP](OTf)2 with a cationic polyamidoamine to give the Ru-PhenAN complex is an excellent strategy to increase the Ru-complex cell uptake and, additionally, to achieve accumulation at the nuclear level. These unique features together make this compound an excellent photosensitizer with very high PDT efficiency.

Polyamidoamino acids (PAACs) are synthetic polymers prepared by the polyaddition of bisacrylamides with natural &alpha, amino acids, which in the process maintain both their chirality and their amphoteric nature. This polymerization process is slow, but has the merits of taking place in water and of neither involving protection/de-protection steps nor releasing by-products. However, it leads to polydisperse polymers and, using &alpha, amino acids mixtures, random copolymers. This paper presents a step-by-step polyaddition process leading to homo- and copolymeric PAACs with controlled sequences and controlled molecular weights. It exploits the much different rates of the two Michael addition steps of NH2 of &alpha, amino acids with acrylamides, and the low solubility in organic solvents of the &alpha, amino acid addition products. As a proof of principle, the controlled synthesis of the PAAC from l-arginine and N,N&prime, methylenebisacrylamide was performed up to a monodisperse product with 11 monomeric units and molecular weight 1840. This synthetic procedure was also tested with l-alanine. All intermediates were isolated and characterized. Noticeably, all of them were &alpha, &omega, difunctionalized with either acrylamides or sec-amines and were, in fact, building blocks with potential for preparing complex macromolecular architectures. In a first instance, copolymers with controlled sequences of amidoamine- and amidoamino acid units were prepared.

Chiral polyamidoamino acids were obtained by polyaddition of N,N&rsquo, methylenebisacrylamide with d-, d,l- and l-tryptophan (M-d-Trp, M-d,l-Trp and M-l-Trp). l-tryptophan/glycine copolymers, M-G-l-Trp5, M-G-l-Trp10, M-G-l-Trp20 and M-G-l-Trp40, were prepared from l-tryptophan/glycine mixtures. These polymers were amphoteric, with acid-base properties similar to those of the parent amino acids. The l-tryptophan/glycine copolymers with high glycine content were water soluble in the pH range 2-12. M-G-l-Trp40 showed a solubility gap centred at pH 4.5 and all tryptophan homopolymers were soluble only at pH &gt, 7. Dynamic light scattering measurements performed in their solubility ranges, namely 2-11 M-G-l-Trp5, M-G-l-Trp10 and M-G-l-Trp20 and 7-11 for M-G-l-Trp40, M-d-Trp, M-l-Trp and M-d,l-Trp, showed that the size of all samples did not significantly vary with pH. Both M-l-Trp and M-G-l-Trp copolymers showed pH-dependent circular dichroism spectra in the wavelength interval 200&ndash, 280 nm, revealing structuring. All samples were fluorescent. Their emission spectra were unstructured and, if normalized for their tryptophan content, almost superimposable at the same pH, providing evidence that only tryptophan governed the photoluminescence properties. Changing pH induced in all cases a slight shift of the emission wavelength maximum ascribed to the modification of the microenvironment surrounding the indole ring induced by different protonation degrees.

Chiral polyamidoamino acids were obtained by polyaddition of N,N’-methylenebisacrylamide with d-, d,l- and l-tryptophan (M-d-Trp, M-d,l-Trp and M-l-Trp). l-tryptophan/glycine copolymers, M-G-l-Trp5, M-G-l-Trp10, M-G-l-Trp20 and M-G-l-Trp40, were prepared from l-tryptophan/glycine mixtures. These polymers were amphoteric, with acid-base properties similar to those of the parent amino acids. The l-tryptophan/glycine copolymers with high glycine content were water soluble in the pH range 2-12. M-G-l-Trp40 showed a solubility gap centred at pH 4.5 and all tryptophan homopolymers were soluble only at pH > 7. Dynamic light scattering measurements performed in their solubility ranges, namely 2-11 M-G-l-Trp5, M-G-l-Trp10 and M-G-l-Trp20 and 7-11 for M-G-l-Trp40, M-d-Trp, M-l-Trp and M-d,l-Trp, showed that the size of all samples did not significantly vary with pH. Both M-l-Trp and M-G-l-Trp copolymers showed pH-dependent circular dichroism spectra in the wavelength interval 200–280 nm, revealing structuring. All samples were fluorescent. Their emission spectra were unstructured and, if normalized for their tryptophan content, almost superimposable at the same pH, providing evidence that only tryptophan governed the photoluminescence properties. Changing pH induced in all cases a slight shift of the emission wavelength maximum ascribed to the modification of the microenvironment surrounding the indole ring induced by different protonation degrees.

We present multifunctional, biocompatible and biodegradable magnetic nanovectors based on different polyamidoamine (PAA) polymers tailored with different diagnostic and therapeutic properties. Using maghemite nanoparticles with average size 15.5 +/- 2.8 rim prepared by thermal decomposition, superparamagnetic nanovectors were obtained by coating the nanoparticles with synthetic polymers of PM. These have a segmented copolymer structure, and bear PAA segments containing different amount of carboxyl groups per repeating units together with PEG segments. These copolymers are thought to combine the binding properties of the carboxylated PM segments to inorganic nanoparticles, with the stealth properties of the PEG ones. The magnetic, hyperthermal and relaxometric properties of the synthesized samples were investigated. Magnetic measurements revealed that the samples are superparamagnetic at room temperature and the overall magnetic behavior is not affected by the functionalization process. Calorimetric measurements demonstrated a good heating efficiency at alternating magnetic field parameters below the human tolerability threshold (SAR of ca. 70 W/g at 260 Hz and 10.8 kA/m). H-1-NMR relaxivities were relevant compared to the values of the commercial contrast agents over the whole investigated frequency range.

This paper reports on synthesis, acid–base properties and pH-dependent structuring in water of d-, l- and d,l-ARGO7, bioinspired polymers obtained by polyaddition of the corresponding arginine stereoisomers with N,N′-methylenebis(acrylamide). The circular dichroism spectra of d- and l-ARGO7 showed a peak at 228 nm and quickly and reversibly responded to pH changes, but were nearly unaffected by temperature, ionic strength, and denaturating agents. Theoretical modeling studies of L-ARGO7 showed that it assumed a folded structure. Intramolecular interactions led to transoid arrangements of the main chain reminiscent of the protein hairpin motif. Torsion angles showed a quite similar distribution at pH 6 and 14 consistent with the similarity of the CD spectra from pH 6 upward.

This paper reports on the development of montmorillonite (MMT)-reinforced hydrogels, based on a peptidomimetic polyamidoamine carrying guanidine pendants (AGMA1), as substrates for the osteo-induction of osteoblast precursor cells. AGMA1 hydrogels of various degrees of crosslinking responded favourably to MMT reinforcement, giving rise to composite hydrogels with shear storage modulus G', when fully swollen in water, up to 200 kPa, i.e. 20 times higher than the virgin hydrogels and of the same order or higher than other hydrogel-based composites proposed for orthopaedic applications. This significant improvement was ascribed to the effective interpenetration between the polymer matrix and the inorganic filler. AGMA1-MMT hydrogels, when evaluated as scaffolds for the osteogenic differentiation of mouse calvaria-derived pre-osteoblastic MC3T3-E1 cells, proved able to support cell adhesion and proliferation and clearly induced differentiation towards the osteoblastic phenotype, as indicated by different markers. In addition, AGMA1-MMT hydrogels proved completely degradable in aqueous media at pH 7.4 and did not provide any evidence of cytotoxicity. The experimental evidence suggests that AGMA1-MMT composites definitely warrant potential as scaffolds for osteoblast culture and bone grafts. Copyright © 2016 John Wiley & Sons, Ltd.

The radical polymerization of 1-vinylpyrrolidin-2-one (NVP) in poly(lactic-co-glycolic acid) (PLGA) 50:50 at 100 °C leads to amphiphilic PLGA-g-PVP copolymers. Their composition is determined by FT-IR spectroscopy. Thermogravimetric analyses agree with FT-IR determinations. Saponification of the PLGA-g-PVP polyester portion allows isolating the PVP side chains and measuring their molecular weight, from which the average chain transfer constant (CT) of the PLGA units is estimated. The MALDI-TOF spectra of PVP reveal the presence at one chain end of residues of either glycolic acid- or lactic acid- or lactic/glycolic acid dimers, trimers and one tetramer, the other terminal being hydrogen. This unequivocally demonstrates that grafting occurred. Accordingly, the orthogonal solvent pair ethyl acetate—methanol, while separating the components of PLGA/PVP intimate mixtures, fails to separate pure PVP or PLGA from the reaction products. All PLGA-g-PVP and PLGA/PLGA-g-PVP blends, but not PLGA/PVP blends, give long-time stable dispersions in water. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 1919–1928

This paper reports on synthesis, acid-base properties and self-structuring in water of chiral polyamidoamino acids (PAACs) obtained by polyaddition of N,N&prime, methylenebisacrylamide with l-alanine, l-valine and l-leucine (M-l-Ala, M-l-Val, M-l-Leu) with potential for selective interactions with biomolecules. The polymers maintained the acid-base properties of amino acids. In water, the circular dichroism spectra of PAACs revealed pH-dependent structuring in the range 3&ndash, 11 and in the wavelength interval 200&ndash, 280 nm. Taking as reference the values at pH 3, the differential molar ellipticities were plotted in the pH interval 3&ndash, 11. Sigmoidal curves were obtained presenting inflection points at pH 8.1, 6.8 and 7.3 for M-l-Ala, M-l-Val and M-l-Leu, respectively, corresponding to the amine half-ionization. Theoretical modeling showed that PAACs assumed stable folded conformations. Intramolecular interactions led to transoid arrangements of the main chain reminiscent of protein hairpin motif. Oligomers with ten repeat units had simulated gyration radii consistent with the hydrodynamic radii obtained by dynamic light scattering.

A synthetic strategy was established for decorating and stabilizing superparamagnetic iron oxide nanoparticles (SPIONs) with a zwitterionic linear polyamidoamine (PAA). The strategy was successfully tested with a PAA coded ISA23 previously found endowed with interesting biological properties, such as biocompatibility, degradability in aqueous media and stealth-like properties when injected in test animals. A post-synthetic functionalization with catechol-bearing moieties of a preformed PAA was successfully carried out. ISA23 was obtained by polyaddition reactions of methyl-piperazine and 2,2-bis(acrylamidoacetic) acid. It was functionalized using nitrodopamine and 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide as coupling agent, to randomly form amide bonds with 17% of ISA23 carboxylic groups (ISA23-ND). SPIONs were prepared by a thermal decomposition synthesis in 1-octadecene with oleic acid, and then transferred in water by two distinct ligand exchange procedures: i) the direct displacement of oleate molecules from SPION surface by ISA23 in a biphasic (n-hexane/water) environment; ii) the two-step method involving an intermediate small molecule, tetramethylammonium hydroxide, used as a transient transfer agent, which was in turn exchanged with ISA23-ND in a second exchange step occurring in water. The two-step procedure provided a SPION@PAA nanocomposite more stable than that obtained by the one-step procedure in the presence of an applied external magnetic field. ATR-FTIR spectroscopy, ζ-potential and thermogravimetric analysis (TGA) showed the presence of the ISA23 on the SPION surface. In particular, TGA showed that the ISA23-ND amount on the NPs accounted for 26% of the overall nanocomposite mass. The nanocomposite size was determined by both TEM (21.1±2.9 nm) and DLS measurements (hydrodynamic size 100±28 nm). SPION@ISA23-ND were re-suspended after lyophilization reverting to their pristine dimensions. The SPION@ISA23-ND adsorption of BSA in water, considered as the first stage of phagocytosis, was very low, suggesting that ISA23 could impart stealthiness to SPION@ISA23-ND. 1H-NMR relaxivity measurements showed an r2 value of 158 s-1 mmol-1 L (vs 100 s-1 mmol-1L for Endorem®) at relevant clinical fields for magnetic resonance imaging (from 0.2 to 1.5 T). SPION@ISA23-ND was tested on HeLa cells and their internalization was visualized by reflectance microscopy. Finally, with the aim of prepare a new dual magneto-optical system, a synthetic procedure to decorate SPION@ISA23-ND with a fluorescent dye was devised, even though the emission intensity of the resultant conjugate was lower than expected, possibly due to luminescence quenching caused by the closeness of emitting moieties to the SPION surface.

Bioinspired polyamidoamines containing disulfide-groups in the main chain (SS-PAAs), prepared by Michael polyaddition of 2,2-bis(acrylamido)acetic acid with l -cystine (B-CYSS) and of N,N′-bis(acryloyl- l -cystine) with either glycine or 2-methylpiperazine (BACYSS-GLY and BACYSS-MP), were investigated as intumescent surface-confined flame retardants for cotton textiles. The main purpose was to ascertain if the presence of disulfide functions in the repeat units imparted superior flame retardant properties compared with sulfur-deprived polyamidoamines whose efficacy were previously demonstrated. In horizontal flame spread tests, at 18% add-on both BACYSS-GLY and BACYSS-MP inhibited ignition; at 12% add-on BACYSS-GLY extinguished flame, whereas BACYSS-MP burnt completely leaving substantial carbonaceous residues. In vertical flame spread tests, both BACYSS-GLY and BACYSS-MP burnt completely leaving substantial residues up to at least 18% add-on. At 12% add-on B-CYSS inhibited ignition in both horizontal- and vertical flame spread tests. In the latter test, only limited afterglow was observed. Scanning electron microscopy (SEM), thermogravimetric and cone calorimetric analyses were consistent with these results. In particular, thermogravimetric analyses showed at 750 °C high residues in nitrogen (28–54%) and only moderately lower residues in air (19–48%). In cone calorimetry tests, all tested SS-PAAs increased time to ignition, decreased peak of heat release rate and effective heat of combustion of cotton. All samples remarkably reduced CO and CO2 yields. SEM micrographs of combustion residues of all SS-PAAs treated cotton fabrics presented diffused intumescent bubbles.

Eight linear polyamidoamines (PAAs) prepared by polyaddition of amines to bisacrylamides are investigated as intumescent surface-confined flame retardants for cotton textiles. The structure of the amine-derived subunits governs their performances. In ignitability tests, aminoacid-deriving PAAs exposed to direct flame for 10 s do not burn, but produce carbonaceous crusts sheltering the underneath sample apparently intact. PAAs carrying guanidine pendants partially volatilize without burning. 2-Methylpiperazine-derived PAAs burn completely. Thermogravimetric analyses show that in air at ≥400 °C all PAAs leave substantial char residues that oxidize at >500 °C. Horizontal flame spread tests on PAA-impregnated cotton stripes show flame extinction for add-ons ranging from 4 to 20%, apart from 2-methylpiperazine-deriving PAAs that never extinguish flame but slow down flame propagation leaving a substantial residue. In vertical flame spread tests, no PAA induces flame extinguishment at add-ons up to 20%, but all PAA-treated fabrics leave significant residues. In cone calorimetry tests, all PAAs increase the time to ignition and decrease the peak of heat release rate and the effective heat of combustion. Most PAAs remarkably reduce the release of CO and CO 2 . After the above tests the combustion residues of PAA-treated cotton fabrics present intumescent bubbles. All results indicate that PAAs warrant potential as effective surface-confined intumescent flame retardants.

Purpose: This study aimed to further explore the mechanisms behind the ability of certain linear polyamidoamines (PAAs) to transfect cells with minimal cytotoxicity. Methods: The transfection efficiency of DNA complexed with a PAA of a molecular weight over 10 kDa or 25 kDa branched polyethyleneimine (BPEI) was compared in A549 cells using a luciferase reporter gene assay. The impact of endo/lysosomal escape on transgene expression was investigated by transfecting cells in presence of bafilomycin A1 or chloroquine. Cytotoxicity caused by the vectors was evaluated by measuring cell metabolic activity, lactate dehydrogenase release, formation of reactive oxygen species and changes in mitochondrial membrane potential. Results: The luciferase activity was 3-fold lower after transfection with PAA polyplexes than with BPEI complexes at the optimal polymer to nucleotide ratio (RU:Nt). However, in contrast to BPEI vectors, PAA polyplexes caused negligible cytotoxic effects. The transfection efficiency of PAA polyplexes was significantly reduced in presence of bafilomycin A1 while chloroquine enhanced or decreased transgene expression depending on the RU:Nt. Conclusions: PAA polyplexes displayed a pH-dependent endo/lysosomal escape which was not associated with cytotoxic events, unlike observed with BPEI polyplexes. This is likely due to their greater interactions with biological membranes at acidic than neutral pH.

Photosensitizers belonging to the boron-dipyrromethenes (BODIPYs) class were recently found endowed with good efficacy in the antibacterial photodynamic therapy (aPDT) against both Gram-positive and Gram-negative bacteria. In this paper, we report on the remarkable adjuvant effect exerted in this respect by linear polyamidoamines (PAAs), a family of moderately basic polymers obtained by Michael-type polyaddition of amines to bisacrylamides. Three different PAAs (AGMA1, BP-AGMA, and BP-DMEDA) were studied, testing for each two different molecular weight samples (8000 and 24000 Da). At nontoxic concentrations (1 or 10 µg mL-1) all PAAs remarkably improved the killing efficacy of BODIPY upon irradiation with a green LED device (range: from 480 to 580 nm with λmax = 525 nm) up to an energy rate of 16.6 J cm-2. A 6–7 log unit decrease in bacteria survival was observed with concentrations of BODIPY of 1.0 and 0.1 µM in the case of Escherichia coli and Staphylococcus aureus, respectively. The one-way analysis of variance (ANOVA) was used to evaluate the statistical significance of different treatments (n ≥ 3). Thus, the PAA-photosensitizer combination warrants potentially as a new, effective, and mild method of killing bacteria. Moreover, the antibacterial treatment here reported might be successfully applied to defeat the bacterial resistance often encountered with many antibacterial drugs owing to the double action of this two-component treatment.

Glucocorticoids are widely prescribed in treatment of rheumatoid arthritis, asthma, systemic lupus erythematosus, lymphoid neoplasia, skin and eye inflammations. However, well-documented adverse effects offset their therapeutic advantages. In this work, novel nano-hydrogels for the sustained delivery of dexamethasone were designed to increase both bioavailability and duration of the administered drug and reducing the therapeutic dose. Hydrogels are soft materials consisting of water-swollen cross-linked polymers to which the insertion of cyclodextrin (CD) moieties adds hydrophobic drug-complexing sites. Polyamidoamines (PAAs) are biocompatible and biodegradable polymers apt to create CD moieties in hydrogels. In this work, β or γ-CD/PAA nanogels have been developed. In vitro studies showed that a pretreatment for 24–48 h with dexamethasone-loaded, β-CD/PAA nanogel (nanodexa) inhibits adhesion of Jurkat cells to human umbilical vein endothelial cells (HUVEC) in conditions mimicking inflammation. This inhibitory effect was faster and higher than that displayed by free dexamethasone. Moreover, nanodexa inhibited COX-2 expression induced by PMA+A23187 in Jurkat cells after 24–48 h incubation in the 10−8–10−5 M concentration range, while dexamethasone was effective only at 10−5 M after 48 h treatment. Hence, the novel nanogel-dexamethasone formulation combines faster action with lower doses, suggesting the potential for being more manageable than the free drug, reducing its adverse side effects.

Linear polyamidoamines containing disulphide groups (SS-PAAs) were prepared by polyaddition of L-cystine with 2,2-bisacrylamidoacetic acid (B-CYSS), N,N′-methylenebisacrylamide (M-CYSS) and 1,4-bisacryloylpiperazine (BP-CYSS). They were evaluated as flame retardants for cotton, alone or with cellulose-derived nano-graphene oxide (nGO) carbon dots, to assess whether, due to their potential as radical scavengers, the latter would improve the already good performance of SS-PAAs. In vertical flame spread tests (VFST), cotton treated with 1% nGO burned as quickly as cotton, whereas B-CYSS, M-CYSS and BP-CYSS extinguished the flame at add-ons ≥ 12, 16 and 20%, respectively. Probably, the gaseous products of SS-PAA thermal degradation quenched the radicals involved in oxidation. Cotton treated with 8, 12 and 15%, respectively, of B-CYSS, M-CYSS and BP-CYSS burned completely, but further addition of 1% nGO either inhibited ignition or shortly extinguished the flame, demonstrating synergism between the two components. Synergism was confirmed by assessing the synergism effectiveness parameter for the residual mass fraction (RMF) and by comparing the calculated and experimental TG curves in air for the cotton/SS-PAA-nGO systems. In cone calorimetry tests, the presence of nGO did not improve the already good performances of SS-PAAs, supporting the hypothesis that the action of both takes place in the gas phase.

A linear amphoteric poly(amidoamino acid), L-ARGO7, is prepared by Michael-type polyaddition of L-arginine with N,N'-methylenebisacrylamide. Chain-extension of acrylamide end-capped L-ARGO7 oligomers with piperazine leads to high-molecular-weight copolymers in which L-arginine maintains its absolute configuration. Acid/base properties of L-ARGO7 polymers show isolectric points of ≈ 10 and positive net average charges per repeating unit at pH = 7.4 from 0.25 to 0.40. These arginine-rich synthetic polymers possibly share some of the unique biological properties of polyarginine cell-permeating peptides. In vitro tests with mouse embryo fibroblasts balb/3T3 clone A31 show that L-ARGO7 polymers are endowed with effective cell internalization ability combined with minimal cytotoxicity.

The initial steps of viral infections are mediated by interactions between viral proteins and cellular receptors. Blocking the latter with high-affinity ligands may inhibit infection. DC-SIGN, a C-type lectin receptor expressed by immature dendritic cells and macrophages, mediates human immunodeficiency virus (HIV) infection by recognizing mannose clusters on the HIV-1 gp120 envelope glycoprotein. Mannosylated glycodendrimers act as HIV entry inhibitors thanks to their ability to block this receptor. Previously, an amphoteric, but prevailingly cationic polyamidoamine named AGMA1 proved effective as infection inhibitor for several heparan sulfate proteoglycan-dependent viruses, such as human papilloma virus HPV-16 and herpes simplex virus HSV-2. An amphoteric, but prevailingly anionic PAA named ISA23 proved inactive. It was speculated that the substitution of mannosylated units for a limited percentage of AGMA1 repeating units, while imparting anti-HIV activity, would preserve the fundamentals of its HPV-16 and HSV-2 infection inhibitory activity. In this work, four biocompatible linear PAAs carrying different amounts of mannosyl-triazolyl pendants, Man-ISA7, Man-ISA14, Man-AGMA6.5 and Man-AGMA14.5, were prepared by reaction of 2-(azidoethyl)-α-D-mannopyranoside and differently propargyl-substituted AGMA1 and ISA23. All mannosylated PAAs inhibited HIV infection. Both Man-AGMA6.5 and Man-AGMA14.5 maintained the HPV-16 and HSV-2 activity of the parent polymer, proving broad-spectrum, dual action mode virus infection inhibitors.

This paper reports on the synthesis and physico-chemical, mechanical, and biological characterization of two sets of poly(amidoamine) (PAA) hydrogels with potential as scaffolds for in vivo peripheral nerve regeneration. They are obtained by polyaddition of piperazine with N,N'-methylenebis(acrylamide) or 1,4-bis(acryloyl)piperazine with 1,2-diaminoethane as cross-linking agent and exhibit a combination of relevant properties, such as mechanical strength, biocompatibility, biodegradability, ability to induce adhesion and proliferation of Schwann cells (SCs) preserving their viability. Moreover, the most promising hydrogels, that is those deriving from 1,4-bis(acryloyl)piperazine, allow the in vitro growth of the sensitive neurons of the dorsal root ganglia, thus getting around a critical point in the design of conduits for nerve regeneration.

This article reports on a simple and straightforward preparation method of poly(amidoamine)s (PAAs) with hetero-difunctional chain ends as well as of several up to now hardly obtainable PAA derivatives of biotechnological interest, such as for instance PAAs of controlled molecular weight and narrow polydispersity mono-functionalized at one end with an acrylamide group, PAAs with star-like molecular architecture, graft-PAA-protein conjugates, “tadpole-like” PAA conjugates with hydrophobic moieties able to self assemble into nanoparticles in aqueous media. The key step was to design suitable building blocks consisting of hetero-difunctional dimers (HDDs). In particular, the HDDs considered were the mono-addition products of bis-sec-amines and bisacrylamides expected to give PAAs of proven biomedical potential and were obtained as hydrochlorides or trifluoroacetates. In this form, they could be indefinitely kept dormant at 0–5 °C in the dry state, whereas at room temperature and in aqueous media, they polymerized at pH > 7.5. The preparation of the above-cited PAA derivatives did not necessarily involve the preliminary synthesis of hetero-difunctional PAAs but was directly achieved by one-pot polymerization of HDDs in the presence of the substrates of interest. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012