High-molar-mass silsesquioxanes (SSQO) based on (3-glycidoxypropyl)trimethoxysilane (GPMS) and (3-methacryloxypropyl)trimethoxysilane (MPMS) were synthesized. The hydrolytic condensation of GPMS was performed using HCOOH (0.1 N) as catalyst, keeping the molar ratio H 2O/Si ) 3. A first step was performed in tetrahydrofuran (THF) at 50°C, followed by a second step in diglycidyl ether of bisphenol A (DGEBA), where temperature was increased in steps up to 140°C. The hydrolytic condensation of MPMS was performed in bulk with HCOOH 98%, at T ) 50 or 70°C, using molar ratios of HCOOH/Si ) 3 or 6. Homogeneous solutions were obtained for both silanes. The reaction was followed by size exclusion chromatography (SEC), and final products were characterized by matrix-assisted ultraviolet laser desorption/ionization time-of-flight mass spectrometry (UV-MALDI-TOF MS), FTIR, and 1 H and 29 Si NMR. Molar-mass distributions showed the presence of clusters corresponding to products formed in different generations. With the aid of UV-MALDI-TOF MS, the different species present in every cluster could be identified for one of the silsesquioxanes derived from MPMS. During the initial stage of the hydrolytic condensation, species with 7-12 Si atoms were produced. They mainly consisted of incompletely condensed polyhedra (species with 1-3 OH per molecule) and ladder-type structures (species with 4 OH per molecule). Species with more OH groups were condensed with a higher probability, giving place to a second generation of products. This process accounts for the presence of a cluster of species with 14-24 Si atoms and the enrichment of the first cluster in the more condensed structures (T 7(OH), T8(OH)2, and T9(OH)). Third and fourth generations of condensation products were also present. Structures of different species may be depicted as combinations of incompletely condensed polyhedra with ladder fragments.

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The polycondensation of [3-(methacryloxy)propyl]trimethoxysilane was performed in bulk, using 98 wt % formic acid (molar ratio HCOOH/Si ) 3 or 6), at 50 or 70°C, for periods of time of up to 1 month. The resulting silsesquioxanes (SSOs) were characterized by 1 H NMR, FTIR, SEC, UV-MALDI-TOF MS (linear, reflector, and post-source decay modes), and ESI-TOF MS. The residual concentrations of Si-OCH3 groups, and generated CH3OH and HCOOCH3, were quantitatively monitored by 1 H NMR during the initial stage of the synthesis. After 2 days of reaction at 50°C, or about 6 h at 70°C, the resulting SSO mainly contained residual Si-OH groups with only traces of Si-OCH3 groups, as was also confirmed by FTIR and UV-MALDI-TOF MS in the reflector mode. After this time, the polycondensation continued slowly during storage at room temperature, basically through Si-OH + Si-OH reactions. The average fraction of intramolecular cycles increased continuously during the polycondensation. An average value, f av ) 0.81, was found for species containing 6-24 Si atoms in a typical reaction product. This evidenced the presence of species with relatively closed structures. In MS/MS spectra, fragmentation of one or more ester groups attached to Si atoms was observed, following a McLafferty rearrangement. The addition of water to the initial formulation (about 3:1 H2O/Si molar ratio) led to a slower polycondensation rate and to a decrease of the average fraction of intramolecular cycles (formation of more open structures). Therefore, the use of 98 wt % formic acid was useful to synthesize SSOs containing a higher fraction of intramolecular cycles than those resulting from conventional formulations.

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The development and characterization of a bacteriocin-containing polyethylene-based film is described, incorporating lactocin 705 and lactocin AL705, produced by Lactobacillus curvatus CRL705, and nisin. Three different procedures to obtain lactocin 705 and AL705 solution were evaluated, with the partially purified aqueous bacteriocin solution showing the highest inhibitory activity against indicator strains (Lactobacillus plantarum CRL691 and Listeria innocua 7). Pouch contact, soaking and a contact method were compared for incorporating bacteriocins onto PE-based films. Contact between the PE film and bacteriocin solution was the most effective, resulting in a more uniform distribution of bacteriocins on the film surface and using less active solution. The minimal inhibitory concentration of bacteriocin solution was 267 AU cm(-3) (lactocin 705) and 2133 AU cm(-3) (lactocin AL705), while the minimal contact time was 1 h. When relative inhibition area for antilisterial activity of the active films was compared, those treated with L. curvatus CRL705 bacteriocins displayed higher inhibitory activity than nisin-treated films. Functional properties of active PE-films containing lactocin 705 and AL705 showed no differences compared with non-active control films. Bacteriocin-active PE-based films are shown to be highly effective in inhibiting growth of Listeria. The potential use of commercially available packaging films as bacteriocins carriers may benefit active-packaging systems.

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