3 research outputs found
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<sup>SiR3</sup>}AlMe (SiR<sub>3</sub> = SiPh<sub>3</sub> (<b>2a</b>), SiMe<sub>2</sub><i>t</i>Bu (<b>2b</b>)) were synthesized
by reaction of AlMe<sub>3</sub> with pyridine–bis(naphthol)
proligands {ONO<sup>SiR3</sup>}H<sub>2</sub> (<b>1a</b>,<b>b</b>) having bulky <i>o</i>-SiR<sub>3</sub> 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<sup>SiR3</sup>}AlOR′
(R′ = <i>i</i>Pr (<b>3a</b>), (<i>S</i>)-CH(Me)CO<sub>2</sub><i>i</i>Pr (<b>4a</b>,<b>b</b>), (<i>R</i>)-CH(Me)CH<sub>2</sub>CO<sub>2</sub>Me (<b>5a</b>), <i>rac</i>-CH(CF<sub>3</sub>)CH<sub>2</sub>CO<sub>2</sub>Et (<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 SiPh<sub>3</sub> 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><sub>8</sub> 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 CD<sub>2</sub>Cl<sub>2</sub> 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><sub>8</sub> at
80 °C. Conversely, the reaction of (<i>R</i>)-<b>5a</b> and l-LA in CD<sub>2</sub>Cl<sub>2</sub> 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<sup>SiR3</sup>}AlMe (SiR<sub>3</sub> = SiPh<sub>3</sub> (<b>2a</b>), SiMe<sub>2</sub><i>t</i>Bu (<b>2b</b>)) were synthesized
by reaction of AlMe<sub>3</sub> with pyridine–bis(naphthol)
proligands {ONO<sup>SiR3</sup>}H<sub>2</sub> (<b>1a</b>,<b>b</b>) having bulky <i>o</i>-SiR<sub>3</sub> 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<sup>SiR3</sup>}AlOR′
(R′ = <i>i</i>Pr (<b>3a</b>), (<i>S</i>)-CH(Me)CO<sub>2</sub><i>i</i>Pr (<b>4a</b>,<b>b</b>), (<i>R</i>)-CH(Me)CH<sub>2</sub>CO<sub>2</sub>Me (<b>5a</b>), <i>rac</i>-CH(CF<sub>3</sub>)CH<sub>2</sub>CO<sub>2</sub>Et (<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 SiPh<sub>3</sub> 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><sub>8</sub> 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 CD<sub>2</sub>Cl<sub>2</sub> 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><sub>8</sub> at
80 °C. Conversely, the reaction of (<i>R</i>)-<b>5a</b> and l-LA in CD<sub>2</sub>Cl<sub>2</sub> 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><sub><b>16</b></sub><b>MImCl</b>) and 1-<i>n</i>-hexadecyl-3-methylimidazolium methanesulfonate (<b>C</b><sub><b>16</b></sub><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><sub><b>16</b></sub><b>MImCl</b> and <b>C</b><sub><b>16</b></sub><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