Gerardo Zaragoza-Galán

Synthesis and Characterization of Novel Pyrene-Dendronized Porphyrins Exhibiting Efficient Fluorescence Resonance Energy Transfer: Optical and Photophysical Properties

A novel series of pyrene dendronized porphyrins bearing two and four pyrenyl groups (Py(2)-TMEG1 and Py(4)-TMEG2) were successfully synthesized. First and second generation Fréchet type dendrons (Py(2)-G1OH and Py(4)-G2OH) were prepared from 1-pyrenylbutanol and 3,5-dihydroxybenzyl alcohol. These compounds were further linked to a trimesitylphenylporphyrin containing a butyric acid spacer via an esterification reaction to obtain the desired products. Dendrons and dendronized porphyrins were fully characterized by FTIR and (1)H NMR spectroscopy and their molecular weights were determined by matrix-assisted laser desorption ionization time of flight mass spectrometry. Their optical and photophysical properties were studied by absorption and fluorescence spectroscopies. The formation of dynamic excimers was detected in the pyrene-labeled dendrons, with more excimer being produced in the higher generation dendron. The fluorescence spectra of the pyrene dendronized porphyrins exhibited a significant decrease in the amount of pyrene monomer and excimer emission, jointly with the appearance of a new emission band at 661 nm characteristic of porphyrin emission, an indication that fluorescence resonance energy transfer (FRET) occurred from one of the excited pyrene species to the porphyrin. The FRET efficiency was found to be almost quantitative ranging between 97% and 99% depending on the construct. Model Free analysis of the fluorescence decays acquired with the pyrene monomer, excimer, and porphyrin core established that only residual pyrene excimer formation in the dendrons could occur before FRET from the excited pyrene monomer to the ground-state porphyrin core.

Fréchet-type dendrons bearing azobenzene units and flexible oligo(ethylene glycol) spacers: synthesis, characterization, thermal and optical properties

In this study, we report the synthesis and characterization of a novel series of first- and second-generation Fréchet-type dendrons bearing amino-nitro, amino-methoxy and amino-butyl substituted azobenzene units and tetra(ethylene glycol) spacers. These compounds were fully characterized by FTIR, 1H and 13C NMR spectroscopies, and their molecular weights were determined by MALDITOF. The thermal properties of the obtained dendrons were studied by thermogravimetric analysis and differential scanning calorimetry and their optical properties by absorption spectroscopy in solution. Molecular calculations were performed in order to determine the dipole moment of these molecules. Some of the dendrons showed a liquid crystalline behaviour, which was studied by light polarized microscopy as a function of the temperature in order to determine the transition temperatures and the structure of the mesophase.

Luminescent polythiophenes-containing porphyrin units: synthesis, characterization, and optical properties

A novel thiophene monomer containing a meso-tetraphenylporphyrin (MTPP) unit linked via an alkyl spacer was synthesized and characterized. This monomer was copolymerized in the presence of 3-dodecylthiophene (MDT) in different ratios MTPP: MDT (1:2, 1:4, and 1:6), using FeCl3 as oxidizing agent, to give the corresponding copolymers (CP12, CP14, and CP16). In addition, MTPP and MDT were also homopolymerized under the same reaction conditions to give homopolymers PTPP and PDT, respectively. The obtained compounds were characterized by FTIR and 1H NMR spectroscopy. The optical properties of the polymers were studied by absorption and fluorescence spectroscopy in THF solution. All polymers exhibited the typical absorption bands of the porphyrin: a Soret band at λ = 422 nm and four Q-bands between λ = 500–700 nm. Moreover, an additional band was observed at λ = 328 nm, due to the polythiophene backbone. CP14 and CP16 showed intense emission in the region between λ  = 550–800 nm.

Synthesis and characterization of novel polymers bearing fluorescein units: thermal and optical properties

In this work, we report the synthesis and characterization of four novel series of copolymers bearing fluorescein moieties. Two monomers: fluorescein methacrylate and dimethacrylate were prepared and were copolymerized in the presence of four different acrylic monomers bearing oligo(ethylene glycol) segments: ethylene glycol phenyl ether acrylate, ethylene glycol phenyl ether methacrylate, poly(ethylene glycol) methyl ether acrylate (Mn = 475 g/mol), and poly(ethylene glycol) methyl ether methacrylate (Mn = 480 g/mol). The obtained copolymers were fully characterized by Fourier Transform Infrared Spectroscopy (FTIR) and Proton Nuclear Magnetic Resonance (1H NMR) spectroscopy. Their thermal properties were determined by thermogravimetric analysis and differential scanning calorimetry, and their optical properties were studied by absorption and fluorescence spectroscopy in solution and in solid state.

Pyrene-Fullerene C60 Dyads as Light-Harvesting Antennas

A series of pyrene-fullerene C60 dyads bearing pyrene units (PyFC12, PyFPy, Py2FC12 and PyFN) were synthesized and characterized. Their optical properties were studied by absorption and fluorescence spectroscopies. Dyads were designed in this way because the pyrene moeities act as light-harvesting molecules and are able to produce “monomer” (PyFC12) or excimer emission (PyFPy, Py2FC12 and PyFN). The fluorescence spectra of the dyads exhibited a significant decrease in the amount of pyrene monomer and excimer emission, without the appearance of a new emission band due to fullerene C60. The pyrene fluorescence quenching was found to be almost quantitative, ranging between 96%–99% depending on the construct, which is an indication that energy transfer occurred from one of the excited pyrene species to the fullerene C60.

Synthesis of a Functionalized Benzofuran as a Synthon for Salvianolic Acid C Analogues as Potential LDL Antioxidants

A palladium mediated synthesis of a common synthon for the syntheses of antioxidant analogues of naturally occurring salvianolic acids is presented. The synthetic route may be used to obtain analogues with a balanced lipophilicity/hydrophilicity which may result in potentially interesting LDL antioxidants for the prevention of cardiovascular diseases.

Design of novel luminescent porphyrins bearing donor–acceptor groups

In this work, we report the synthesis and characterization of a novel series of porphyrins, some of them bearing donor-acceptor groups. meso-substituted free-base porphyrins:5-(4-amino-phenyl)-10,15,20-triphenylporphyrin (TPPNH2) and 5-(4-acetamidophenyl)-10,15,20-triphenylporphyrin (TPPNHAc), as well as their tribromo (Br3TPPNH2 and Br3TPPNHAc) and trimethylsilyl-substituted homologs (TMS3TPPNH2 and TMS3TPPNHAc were synthesized and characterized. The optical properties of all compounds have been studied by absorption and fluorescence spectroscopy. Theoretical calculations were performed in order to recognize the optimized geometry and the correlation with the optical properties. On the other hand, an azobenzene containing porphyrin (TPPN2PhC14H29) was also prepared to study the influence of the trans-cis photoisomerization on its optical properties. Almost all porphyrin derivatives exhibited a Soret band at ca. λ = 419–422 nm followed by four Q-bands in the range between 500–700 nm. Besides, these porphyrins showed two emission bands located at ca. λ = 654 nm and 714 nm with different intensities, depending on the substituents. The relative quantum yields were calculated for these compounds with respect to the most emissive species.

Biopolymers from Waste Biomass — Extraction, Modification and Ulterior Uses

The residues coming from woodlands and agricultural exploitation constitute the most abundant biomass available on earth. Its importance as a source of renewable energy has grown in addition to the environmental impact. Biomass waste is a lignocellulosic feedstock which contains three main biopolymers: cellulose, hemicel‐ lulose and lignin. It could be utilized for the production of a number of value-added products due to their chemical composition, but it is necessary to efficiently recover the valuable biopolymer as intact as possible by different processing techniques.For different applications, the principal objective of pre-treatment is to keep the cellu‐ lose intact, meanwhile hemicellulose and lignin are removed. The yields of the frac‐ tions depend on the pre-treatment method, which is the most expensive step in biomass conversion. Traditionally, cellulose is obtained by kraft, sulphite and soda treatments. These methods are non-environmentally friendly and generate huge quantities of toxic wastes. Recently developed models considering the environmen‐ tal laws encourage the sustainable processing of biomass into value-added prod‐ ucts. The use of ionic liquids as new solvents for biomass waste and organosolv processes is reviewed, which are used to obtain cellulose. One of the possible appli‐ cations of cellulose is membrane synthesis, which has been reported for other bio‐ mass materials, such as sugarcane bagasse, mango seed and newspaper. In this chapter, some green pre-treatment methods, different sustainable routes for cellu‐ lose modification and some of the results obtained on membrane development based on waste biomass are discussed.

Lipase catalyzed epoxidation of fatty acid methyl esters derived from unsaturated vegetable oils in absence of carboxylic acid

Nowadays the industrial chemistry reactions rely on green technologies. Enzymes as lipases are increasing its use in diverse chemical processes. Epoxidized fatty acid methyl esters obtained from transesterification of vegetable oils have recently found applications as polymer plasticizer, agrochemical, cosmetics, pharmaceuticals and food additives. In this research article, grapeseed, avocado and olive oils naturally containing high percents of mono and poly unsaturations were used as starting materials for the production of unsaturated fatty acid methyl esters. The effect of lauric acid as an active oxygen carrier was studied on epoxidation reactions where unsaturated fatty acid methyl esters were converted to epoxy fatty acid methyl esters using immobilized Candida antarctica Lipase type B as catalyst and hydrogen peroxide as oxygen donor at mild temperature and pressure conditions. After this study it was confirmed by 1H NMR, 13C NMR and GC–MS that the addition of lauric acid to the enzymatic reaction is unnecessary to transform the alkenes in to epoxides. It was found that quantitative conversions were possible in despite of a carboxylic acid absence.

Synthesis, characterization and optical properties of novel dendronized azo-dyes containing a fullerene C60 unit and well-defined oligo(ethylene glycol) segments

Herein, we report the preparation and characterization of a novel series of dendronized azo-dyes containing a fullerene C60 unit and well-defined oligo(ethylene glycol) spacers. The azobenzene units present in these dyes were substituted in the 4′-position with different functional groups (–H, –OCH3, –C4H9, –CN and –NO2). The optical properties of these compounds were studied by absorption spectroscopy as a function of the dipole moment of the azobenzene moieties. All fullerene C60-azobenzene derivatives exhibited trans–cis photoisomerization and photoprotonation under irradiation with UV-light. The results were compared to those obtained with their precursor azo-dyes without fullerene C60. It was found that the presence of the fullerene unit significantly quenches the photoisomerization yield, whereas the photoprotonation was not affected by the presence of this chromophore.