Chemical Stabilization of Hexanal Molecules by Inclusion as Guests of Nanoporous-Crystalline Syndiotactic Polystyrene Crystals

Salicylic Acid Release from Syndiotactic Polystyrene Staple Fibers

Films and fibers of syndiotactic polystyrene (sPS), being amorphous or exhibiting nanoporous crystalline (NC) or dense crystalline phases, were loaded with salicylic acid (SA), a relevant non-volatile antimicrobial molecule. In the first section of the paper, sPS/SA co-crystalline (CC) δ form is characterized, mainly by wide angle X-ray diffraction (WAXD) patterns and polarized Fourier transform infrared (FTIR) spectra. The formation of sPS/SA δ CC phases allows the preparation of sPS fibers even with a high content of the antibacterial guest, which is also retained after repeated washing procedures at 65 °C. A preparation procedure starting from amorphous fibers is particularly appropriate because involves a direct formation of the CC δ form and a simultaneous axial orientation. The possibility of tuning drug amount and release kinetics, by simply selecting suitable crystalline phases of a commercially available polymer, makes sPS fibers possibly useful for many applications. In particular, fibers with δ CC forms, which retain SA molecules in their crystalline phases, could be useful for antimicrobial textiles and fabrics. Fibers with the dense γ form which easily release SA molecules, because they are only included in their amorphous phases, could be used for promising SA-based preparations for antibacterial purposes in food processing and preservation and public health. Finally, using a cell-based assay system and antibacterial tests, we investigated the cellular activity, toxicity and antimicrobial properties of amorphous, δ CC forms and dense γ form of sPS fibers loaded with different contents of SA.

Segregation of Benzoic Acid in Polymer Crystalline Cavities

Benzoic acid (BA) and its derivatives are very attractive because of their pharmacological properties, such as antioxidant, radical-regulating, antiviral, antitumor, anti-inflammatory, antimicrobial and antifungal. Syndiotactic polystyrene (sPS) and poly(2,6-dimethyl-1,4-phenylene)oxide (PPO) films exhibiting co-crystalline phases with BA were prepared and characterized by WAXD, FTIR and polarized FTIR measurements. The FTIR measurements clearly showed that BA was present mainly as a dimer in the crystalline channels of the ε form of sPS as well as in the α form of PPO, as generally occurs not only in the solid state but also in organic dilute solutions. BA was instead present as isolated molecules in the crystalline cavities of the δ form of sPS. In fact, the FTIR spectra of BA guest molecules exhibited vibrational peaks close to those of BA in its vapor phase. Hence, the nanoporous-crystalline δ form of sPS not only avoids additive aggregation but also leads to the separation of dimeric molecules and the segregation of monomeric BA.

Molecular Features Behind Formation of α or β Co-Crystalline and Nanoporous-Crystalline Phases of PPO

Guest molecular features determining the formation of α and β phases of poly(2-6-dimethyl-1,4-phenylene) oxide (PPO) are explored by collecting literature data and adding many new film preparations, both by solution casting and by guest sorption in amorphous films. Independently of the considered preparation method, the α-form is favored by the hydrophobic and bulky guest molecules, while the hydrophilic and small guest molecules favor the β-form. Furthermore, molecular modeling studies indicate that the β-form inducer guests establish stronger dispersive interactions with the PPO units than the α-form inducer guests. Thus, the achievement of co-crystalline (and derived nanoporous crystalline) α- and β-forms would result from differences in energy gain due to the host–guest interactions established at the local scale.

Monomeric and Dimeric Carboxylic Acid in Crystalline Cavities and Channels of Delta and Epsilon Forms of Syndiotactic Polystyrene

Delta (δ) and epsilon (ε) co-crystalline forms of syndiotactic polystyrene with a carboxylic acid guest were obtained by sorption of liquid hexanoic acid in syndiotactic polystyrene films exhibiting delta and epsilon nanoporous-crystalline forms. The characterization study is facilitated by axially stretched syndiotactic polystyrene films, used both for polarized FTIR spectra and for WAXD fiber patterns. Particularly informative are two carbonyl-stretching FTIR peaks, attributed to monomeric and dimeric hexanoic acid. The dichroism of these carbonyl peaks indicates that both delta and epsilon phases are able to include hexanoic acid as isolated guest molecules, while only the epsilon phase is also able to include dimeric hexanoic acid molecules in its crystalline channels. The inclusion of both isolated and dimeric hexanoic acid species in the epsilon form crystalline channels produces extremely fast hexanoic acid uptakes by syndiotactic polystyrene epsilon form films.

Axial Orientation of Co-Crystalline Phases of Poly(2,6-Dimethyl-1,4-Phenylene)Oxide Films

Films exhibiting co-crystalline (CC) phases between a polymer host and low-molecular-mass guest molecules are relevant for many applications. As is usual for semi-crystalline polymers, axially oriented films can give relevant information on the crystalline structure, both by Wide Angle X-ray diffraction fiber patterns and by polarized Fourier-transform infrared spectroscopy. Axially oriented CC phases of poly(2,6-dimethyl-1,4-phenylene)oxide (PPO) with 1,3,5-trimethylbenzene (mesitylene) can be simply obtained by the stretching of CC PPO films. In fact, due to the plasticization effect of this highly boiling guest, PPO orientation can occur in a stretching temperature range (170-175 °C) nearly 50 °C lower than that generally needed for PPO films (220-230 °C). This low stretching temperature range allows avoidance of polymer oxidation, as well as formation of the mesomorphic dense γ PPO phase. Axially oriented CC phases of PPO with toluene, i.e., with a more volatile guest, can be instead obtained by the stretching (in the same low temperature range: 170-175 °C) of CC PPO blend films with polystyrene.

The Influence of Film and Storage on the Phenolic and Antioxidant Properties of Red Raspberries (Rubus idaeus L.) cv. Erika

In this paper, the effect of the packaging material and storage method on red raspberries produced at Reggio Calabria (Italy) was studied. For this purpose, the fruits were stored immediately after harvest in different conditions: in the fridge at 1 °C and in the freezer at -20 °C, using different packaging materials, two new patented films (nanoactive A) and (nanoactive B), one common packaging film (polyethylene terephthalate), and other fruits were left without any packaging material. Chemical parameters were analysed at harvest to have the initial characteristics without any conditioned storage and to distinguish the post-harvest effect on the fruits, then daily for storage in the fridge and monthly for storage in the freezer. The aims of our project were first to determine the qualitative characterization of these red raspberries, the optimization of their shelf-life during time in the fridge or freezer, using the different types of packaging materials and finally to highlight the usefulness of the new patented packaging materials. Nanoactive A film showed the best shelf-life in the fridge, and after 14 days the values, given as mg/100 g fresh weight, were: total phenolics (166.70), monomeric anthocyanin content (50.82), flavonoids (24.64), ascorbic acid (32.42), and 1, 1-diphenyl-2-picrylhydrazyl (DPPH) assay (95.93).