Thymol as Starting Material for the Development of a Biobased Material with Enhanced Antimicrobial Activity: Synthesis, Characterization, and Potential Application.

A biobased material, polythymol (PTF), was prepared using thymol, a monoterpene obtained from the essential oil of Thymus vulgaris (Lamiaceae), as a starting material with the aim of enhancing the antimicrobial properties of this natural product. Initially, different processes were performed in order to optimize the reaction conditions to obtain a macromolecule with a high purity and yield. PTF was characterized using different techniques, such as NMR, infrared, UV-Vis, and thermogravimetric analyses. The antimicrobial activity of both PTF and thymol was evaluated against different microorganisms, including S. aureus, E. coli, P. aeruginosa, and C. albicans. The obtained MIC values showed a higher potential for PTF than the monomer thymol-for example, against S. aureus (500 and 31.5 µg·mL-1 for thymol and PTF, respectively). Therefore, the obtained results show that the polymerization of thymol afforded more active biomaterial than the starting monomeric antimicrobial compound (thymol), suggesting that PTF is an important biomaterial.

Evaluation of the effects in cellular membrane models of antitrypanosomal poly-thymolformaldehyde (PTF) using Langmuir monolayers.

The polymerization of bioactive compounds may be interesting because the supramolecular structures formed can boost biological action on microorganism membranes. In the present work, poly-thymolformaldehyde (PTF) activity, prepared by condensation of thymol and formaldehyde, was evaluated against trypomastigote forms of Trypanosoma cruzi and related with the physicochemical changes provided by the incorporation of the compound in protozoan cell membrane models. PTF exhibited an EC50 value of 23.4 µg/mL and no toxicity against mammalian cells (CC50 > 200 µg/mL). To understand the molecular action of PTF as an antiprotozoal candidate, this compound was incorporated in Langmuir monolayers of dipalmitoylphosphatidylglycerol (DPPG) as a model for parasite cell membranes. PTF shifted DPPG surface pressure-area isotherms to higher areas, indicating its incorporation in the lipid films. Additionally, it changed the thermodynamic, compressional, structural, and morphological properties of the floating monolayers, decreasing the collapse pressure, reducing the surface elasticity, and segregating molecules at the interface, forming domains with different reflectivities. Infrared spectroscopy showed that the lipid films with PTF presented an increased rate of gauche/all-trans conformers for the methylene groups from the acyl chains, indicating molecular disorder. Therefore, these results show that PTF alters the physicochemical properties of DPPG monolayers as a model for protozoa cell membranes, which can enhance the comprehension of the parasitic action of PTF against T. cruzi.

Optical and Thermal Stability of Oligofluorene/Rubber Luminescent Blend.

This paper proposes to obtain homogeneous and stable blends of oligo(9,9-dioctylfluorene)-co-phenylene (OF), a conjugated oligomer with strong tendency of formation of excimers in the solid state, and nitrile rubber (NBR). This rubber protection reduces the formation of polymer excimers in the films. The fluorene oligomer was synthesized via Suzuki reaction and incorporated in the nitrile rubber. The films were formed by spin coating and casting techniques on the proportions of 1, 5, 10, 20 and 50 % (w/w) of OF in the nitrile rubber (NBR). The structural, optical and thermal properties of the films were evaluated with infrared, UV-Vis, fluorescence and thermogravimetry, respectively. The nitrile rubber proved to be essential for the preparation of homogeneous and stable films, since it was not possible to obtain films with only fluorene using the above-mentioned techniques. Furthermore, luminescent properties of OF are unchanged and the excimers formation in the solid state decrease suggesting the efficiency of nitrile rubber as the matrix for making films.

Investigation of the conformational changes of a conducting polymer in gas sensor active layers by means of polarization-modulation infrared reflection absorption spectroscopy (PM-IRRAS).

Polarization-Modulation Infrared Reflection Absorption Spectroscopy (PM-IRRAS) was employed to observe the changes in the molecular conformation of poly(2-phenyl-1,4-xylylene) (PPPX) films that occurred after exposure to organic solvent vapors. The PPPX films were supported on solid matrixes by casting, spin-coating, and Langmuir-Blodgett (LB) techniques. The results show that the polymer is sensitive to the solvent vapors, which affect some of the vibration dipole moments, as detected by PM-IRRAS. The sensitivity depends on the method employed to immobilize the polymer, with more significant changes in films formed using techniques that result in a less systematically organized conformation. This feature enables the use of surface vibration spectroscopy to detect organic solvent vapors and may be applied in an artificial nose.

Mixing alternating copolymers containing fluorenyl groups with phospholipids to obtain Langmuir and Langmuir-Blodgett films.

The control of molecular architectures may be essential to optimize materials properties for producing luminescent devices from polymers, especially in the blue region of the spectrum. In this Article, we report on the fabrication of Langmuir-Blodgett (LB) films of polyfluorene copolymers mixed with the phospholipid dimyristoyl phosphatidic acid (DMPA). The copolymers poly(9,9-dioctylfluorene)-co-phenylene (copolymer 1) and poly(9,9-dioctylfluorene)-co-quaterphenylene) (copolymer 2) were synthesized via Suzuki reaction. Copolymer 1 could not form a monolayer on its own, but it yielded stable films when mixed with DMPA. In contrast, Langmuir monolayers could be formed from either the neat copolymer 2 or when mixed with DMPA. The surface pressure and surface potential measurements, in addition to Brewster angle microscopy, indicated that DMPA provided a suitable matrix for copolymer 1 to form a stable Langmuir film, amenable to transfer as LB films, while enhancing the ability of copolymer 2 to form LB films with enhanced emission, as indicated by fluorescence spectroscopy. Because a high emission was obtained with the mixed LB films and since the molecular-level interactions between the film components can be tuned by changing the experimental conditions to allow for further optimization, one may envisage applications of these films in optical devices such as organic light-emitting diodes (OLEDs).

Light emitting diodes containing Langmuir-Blodgett films of copolymer of a poly(p-phenylene-vinylene) derivative and poly(octaneoxide).

The properties of Langmuir and Langmuir-Blodgett (LB) films from a block copolymer with polyethylene oxide and phenylene-vinylene moieties are reported. The LB films were successfully transferred onto several types of substrates, with sufficient quality to allow for evaporation of a metallic electrode on top of the LB films to produce polymer light emitting diodes (PLEDs). The photoluminescence and electroluminescence spectra of the LB film and device were similar, featuring an emission at ca. 475 nm, from which we could infer that the emission mechanisms are essentially the same as in poly(p-phenylene) derivatives. Analogously to other PLEDs the current versus voltage characteristics of the LB-based device could be explained with the Arkhipov model according to which charge transport occurs among localized sites. The implications for nanotechnology of the level of control that may be achieved with LB devices will also be discussed.

Solid-state NMR study of Na versus K doping of para-phenylene oligomers.

13C solid-state nuclear magnetic resonance (NMR) experiments were performed on p-terphenyl, p-quaterphenyl, and p-sexiphenyl either in their pristine or doped with alkali metals form. The 13C NMR spectra of doped materials show new resonances by comparison with pristine compounds. For the K-doped materials, these resonances appear in the 90-135 ppm range, while for Na-doped materials, they are observed in the larger 20-150 ppm range. It suggests that the interaction between the alkali ions and the oligomers depends on the nature of the alkali. It is corroborated by 13C NMR experiments after exposure to air that show different behaviors. As expected, air exposure of K-doped samples restores the pristine spectra. This is not the case for Na doping, where the signature of the doped material persists even after exposure to air. In the latter case, some 13C resonances can be assigned to sp3 hybridized carbons and to the quinoid group. It suggests that Na doping induces a polymerization of the oligophenylenes.

Easy synthesis of phenyl oligomers using a Ni complex.

In this work are described the syntheses of p-sexiphenyl and p-octiphenyl starting from 4-bromo-p-terphenyl and 4-bromo-p-quaterphenyl, respectively, by using a nickel complex in the presence of bipyridine with DMF as solvent. This type of synthesis was shown to give an improved yield as well as easy preparation and purification of these phenylene oligomers.