Discrete <i>O</i>‑Lactate and β‑Alkoxybutyrate Aluminum Pyridine–Bis(naphtholate) Complexes: Models for Mechanistic Investigations in the Ring-Opening Polymerization of Lactides and β‑Lactones

Methyl aluminum­(III) complexes {ONO^SiR3}­AlMe (SiR₃ = SiPh₃ (<b>2a</b>), SiMe₂<i>t</i>Bu (<b>2b</b>)) were synthesized by reaction of AlMe₃ with pyridine–bis­(naphthol) proligands {ONO^SiR3}­H₂ (<b>1a</b>,<b>b</b>) having bulky <i>o</i>-SiR₃ substituents on the naphthol groups. Complexes <b>2a</b>,<b>b</b> were converted into the Al isopropoxide, <i>O</i>-lactate, and β-alkoxybutyrate complexes {ONO^SiR3}­AlOR′ (R′ = <i>i</i>Pr (<b>3a</b>), (<i>S</i>)-CH­(Me)­CO₂<i>i</i>Pr (<b>4a</b>,<b>b</b>), (<i>R</i>)-CH­(Me)­CH₂CO₂Me (<b>5a</b>), <i>rac</i>-CH­(CF₃)­CH₂CO₂Et (<b>6a</b>)) by reaction with the corresponding alcohol and α- and β-hydroxy esters R′OH. C–<i>H</i>···π close contacts between the SiPh₃ phenyl groups and hydrogens of the methine, methylene, and alkyl ester groups were evidenced by X-ray diffraction studies (for <b>2a</b> and <b>4a</b>–<b>6a</b>) and by solution NMR. In contrast to the case for (<i>S</i>)-<b>4b</b>, (<i>S</i>)-<b>4a</b> interacts reversibly with racemic lactide (<i>rac</i>-LA) in toluene-<i>d</i>₈ at 20 °C, discriminating the l and d monomers, yet without forming isolable six-coordinated adducts. NMR monitoring of the reaction of (<i>S</i>)-<b>4a</b> with l-LA in CD₂Cl₂ at room temperature allowed identifying the propagation product <b>7a</b>, as a result of propagation being faster than insertion. The same propagating species formed upon reaction of (<i>S</i>)-<b>4a</b> with l-LA in toluene-<i>d</i>₈ at 80 °C. Conversely, the reaction of (<i>R</i>)-<b>5a</b> and l-LA in CD₂Cl₂ eventually allowed catching the very first insertion product <b>8a</b>. These observations imply that insertion of LA proceeds more easily into a six-membered Al β-alkoxybutyrate species than into a five-membered Al <i>O</i>-lactate species

Discrete <i>O</i>‑Lactate and β‑Alkoxybutyrate Aluminum Pyridine–Bis(naphtholate) Complexes: Models for Mechanistic Investigations in the Ring-Opening Polymerization of Lactides and β‑Lactones

Methyl aluminum­(III) complexes {ONO^SiR3}­AlMe (SiR₃ = SiPh₃ (<b>2a</b>), SiMe₂<i>t</i>Bu (<b>2b</b>)) were synthesized by reaction of AlMe₃ with pyridine–bis­(naphthol) proligands {ONO^SiR3}­H₂ (<b>1a</b>,<b>b</b>) having bulky <i>o</i>-SiR₃ substituents on the naphthol groups. Complexes <b>2a</b>,<b>b</b> were converted into the Al isopropoxide, <i>O</i>-lactate, and β-alkoxybutyrate complexes {ONO^SiR3}­AlOR′ (R′ = <i>i</i>Pr (<b>3a</b>), (<i>S</i>)-CH­(Me)­CO₂<i>i</i>Pr (<b>4a</b>,<b>b</b>), (<i>R</i>)-CH­(Me)­CH₂CO₂Me (<b>5a</b>), <i>rac</i>-CH­(CF₃)­CH₂CO₂Et (<b>6a</b>)) by reaction with the corresponding alcohol and α- and β-hydroxy esters R′OH. C–<i>H</i>···π close contacts between the SiPh₃ phenyl groups and hydrogens of the methine, methylene, and alkyl ester groups were evidenced by X-ray diffraction studies (for <b>2a</b> and <b>4a</b>–<b>6a</b>) and by solution NMR. In contrast to the case for (<i>S</i>)-<b>4b</b>, (<i>S</i>)-<b>4a</b> interacts reversibly with racemic lactide (<i>rac</i>-LA) in toluene-<i>d</i>₈ at 20 °C, discriminating the l and d monomers, yet without forming isolable six-coordinated adducts. NMR monitoring of the reaction of (<i>S</i>)-<b>4a</b> with l-LA in CD₂Cl₂ at room temperature allowed identifying the propagation product <b>7a</b>, as a result of propagation being faster than insertion. The same propagating species formed upon reaction of (<i>S</i>)-<b>4a</b> with l-LA in toluene-<i>d</i>₈ at 80 °C. Conversely, the reaction of (<i>R</i>)-<b>5a</b> and l-LA in CD₂Cl₂ eventually allowed catching the very first insertion product <b>8a</b>. These observations imply that insertion of LA proceeds more easily into a six-membered Al β-alkoxybutyrate species than into a five-membered Al <i>O</i>-lactate species

Multitask Imidazolium Salt Additives for Innovative Poly(l‑lactide) Biomaterials: Morphology Control, Candida spp. Biofilm Inhibition, Human Mesenchymal Stem Cell Biocompatibility, and Skin Tolerance

Candida species have great ability to colonize and form biofilms on medical devices, causing infections in human hosts. In this study, poly­(l-lactide) films with different imidazolium salt (1-<i>n</i>-hexadecyl-3-methylimidazolium chloride (<b>C</b>_<b>16</b><b>MImCl</b>) and 1-<i>n</i>-hexadecyl-3-methylimidazolium methanesulfonate (<b>C</b>_<b>16</b><b>MImMeS</b>)) contents were prepared, using the solvent casting process. Poly­(l-lactide)-imidazolium salt films were obtained with different surface morphologies (spherical and directional), and the presence of the imidazolium salt in the surface was confirmed. These films with different concentrations of the imidazolium salts <b>C</b>_<b>16</b><b>MImCl</b> and <b>C</b>_<b>16</b><b>MImMeS</b> presented antibiofilm activity against isolates of Candida tropicalis, Candida parapsilosis, and Candida albicans. The minor antibiofilm concentration assay enabled one to determine that an increasing imidazolium salt content promoted, in general, an increase in the inhibition percentage of biofilm formation. Scanning electron microscopy micrographs confirmed the effective prevention of biofilm formation on the imidazolium salt containing biomaterials. Lower concentrations of the imidazolium salts showed no cytotoxicity, and the poly­(l-lactide)-imidazolium salt films presented good cell adhesion and proliferation percentages with human mesenchymal stem cells. Furthermore, no acute microscopic lesions were identified in the histopathological evaluation after contact between the films and pig ear skin. In combination with the good morphological, physicochemical, and mechanical properties, these poly­(l-lactide)-based materials with imidazolium salt additives can be considered as promising biomaterials for use in the manufacturing of medical devices