Detection and memory of nonracemic molecules by a racemic host polymer film
ABSTRACT Robust syndiotactic polystyrene films, presenting a suitable nanoporous host crystalline phase, are able to transfer, amplify, and memorize the chirality of nonracemic low-molecular-mass molecules. In fact, after temporary exposure to volatile nonracemic guests, the polymer films present intense induced circular dichroism (ICD) phenomena. These ICD phenomena are associated with the temporary formation of polymer/guest cocrystalline phases.
- SourceAvailable from: Michele Giordano
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- "The occurrence of transfer and amplification of chiral information is particularly relevant for solid polymer films, since they could have in principle applications in chirooptical devices and data storage systems. Recently, is has been reported that non-racemic s-PS films are able to detect, amplify and memorize the chirality of several volatile organic molecules [123,124]. "
ABSTRACT: Chemical sensors are generally based on the integration of suitable sensitive layers and transducing mechanisms. Although inorganic porous materials can be effective, there is significant interest in the use of polymeric materials because of their easy fabrication process, lower costs and mechanical flexibility. However, porous polymeric absorbents are generally amorphous and hence present poor molecular selectivity and undesired changes of mechanical properties as a consequence of large analyte uptake. In this contribution the structure, properties and some possible applications of sensing polymeric films based on nanoporous crystalline phases, which exhibit all identical nanopores, will be reviewed. The main advantages of crystalline nanoporous polymeric materials with respect to their amorphous counterparts are, besides a higher selectivity, the ability to maintain their physical state as well as geometry, even after large guest uptake (up to 10-15 wt%), and the possibility to control guest diffusivity by controlling the orientation of the host polymeric crystalline phase. The final section of the review also describes the ability of suitable polymeric films to act as chirality sensors, i.e., to sense and memorize the presence of non-racemic volatile organic compounds.Sensors 12/2009; 9(12):9816-57. DOI:10.3390/s91209816 · 2.05 Impact Factor
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ABSTRACT: Thermal transitions of the three crystalline phases (γ, δ, and) of syndiotactic polystyrene (s-PS), presenting s(2/1)2 helices, have been compared by X-ray diffraction, differential scanning calorimetry (DSC), and dynamic-mechanical analyses. These analyses have been conducted on crystalline (δ and) films, obtained by similar solvent sorption and desorption procedures, starting from a same γ-form film. The Fourier transform Infrared (FTIR) spectra of the three films have also been compared. The obtained results indicate that the recently discovered -phase, as the already known δ-phase, is transformed in γ-phase by heating above 100 °C. However, the f γ transition occurs directly without the formation, for intermediate temperatures, of a helical mesomorphic phase, as instead observed for the δ f γ transition. DSC studies and FTIR measurements also suggest that the crystalline packing of the -form could be rather similar to that one of the γ-form.Macromolecules 12/2007; 40(26). DOI:10.1021/ma071640q · 5.93 Impact Factor
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ABSTRACT: Guest-induced transitions from α and γ phases of syndiotactic polystyrene (s-PS) toward cocrystalline and nanoporous phases, and related guest-induced orientation phenomena, have been investigated by X-ray diffraction. Guests, being able to induce cocrystal formation in amorphous s-PS samples, are able to induce room-temperature cocrystal formation from γ and α form films, only if their vapor pressure is higher than 20 and 60 Torr, respectively. Guest-induced recrystallizations of unoriented γ form films generally lead to unoriented cocrystalline and δ form films, while chloroform-induced recrystallization leads to cocrystalline and ε form films with perpendicular orientation of chain axes. On the other hand, guest-induced recrystallizations of unoriented α form films generally lead to oriented cocrystalline and derived δ form films. In particular, recrystallizations of unoriented α form films by room-temperature sorption of trichloroethylene and CHCl3 lead to films with (002) uniplanar and (2̅10) uniplanar orientations, i.e., with chain axes perpendicular and parallel to the film plane, respectively. The new procedures to prepare nanoporous films with different uniplanar orientations present substantial advantages with respect to the procedures already described in the literature.Macromolecules 04/2008; 41(7). DOI:10.1021/ma7026275 · 5.93 Impact Factor