ABSTRACT Concept Building artificial photosynthetic molecular machines capable of exploiting sola... more ABSTRACT Concept Building artificial photosynthetic molecular machines capable of exploiting solar energy for photocatalysis and electrical energy production, has attracted considerable interest in recent years [1]. Photosynthetic reaction centers (RC) are the Nature's solar batteries, converting light energy into chemical potential in the photosynthetic membrane, thereby assuring carbon reduction in cells. The photoconversion efficiency of the primary charge separation step in RC, close to unit, is pushing efforts of the scientific community toward artificial photosynthesis. We propose here the concept of an hybrid organic-biologic system formed by tailored organic fluorophores acting as covalently bound antenna to the RC protein scaffold. The hybrid functions like the natural system and is capable of extending the useful range of visible wavelengths for energy photoconversion. Motivations and Objectives Ideal biomimetic systems must efficiently harvest sunlight and effectively converting it into a stable charge-separated state, with a sufficiently long lifetime to allow ancillary chemistry to take place. However the combination of these requirements has not, thus far, been fully attained. Recently, fluorescent quantum dots (QDs) have been proposed as artificial antennas [2] as the first example of efficient transfer of excitation energy from QDs to RC, but few information on the duration of the charge-separated state and protein stability were given. Herein we propose to bioconjugate organic fluorophores, belonging to the aryleneethynylenes (AE) class, and used as antenna to the RC, synthetizing an hybrid system whose biological core maintains the conversion efficiency of the natural system. AE dyes have been designed and synthesized [3] to fulfill the spectroscopic, chemical, and steric requirements for such bioconjugation. Results and Discussion AE dyes were covalently and selectively bioconjugated to specific lysine residues of the photosynthetic RC. The resulting hybrid system is capable of absorbing light and efficiently performing photo- conversion in a wavelength range where the non-conjugated protein does not absorb [4]. The energy collected by the attached fluorophore is efficiently transferred, via FRET mechanism, to the protein pigments, and eventually used for the enzymatic activity, which outperforms the natural system. Diffraction data, collected at synchrotron facilities, obtained by the crystallization of the bioconjugated protein, confirm the hypothesis that functionalized lysines are within the Förster distance for efficient energy transfer. References [1] P. Maroti, M.Trotta in CRC Handbook of Organic Photochemistry and Photobiology, 3rd ed, Boca Raton, FL, 2012 [2] I. Nabiev, A. Rakovich et al., Angew. Chem. Int. Ed., 49 (2010), 7217–7221 [3] A. Operamolla, R. Ragni et al., Curr. Org. Synth., 9 (2012), 150-62 [4] F. Milano, R.R. Tangorra et al., Angew. Chem. Int. Ed., 51 (2012), 11019 – 11023
The Reaction Centers (RCs) of photosynthetic organisms are efficient billion-of-years optimized p... more The Reaction Centers (RCs) of photosynthetic organisms are efficient billion-of-years optimized photoenzimes for conversion of absorbed light into charge separated states. Combination of such effective photoenzimes with π-conjugated molecules appears an intriguing strategy to obtain a new generation of versatile bio-optoelectronic materials for applications ranging from photoconversion to photocatalysis and sensing. We present here the design and synthesis of hybrid bio-organic photosynthetic complexes by combination of the Reaction Center of the photosynthetic bacterium Rhodobacter Sphaeroides R26 with tailored molecular semiconductors. The organic molecules can act as antennas to extend the light harvesting capability of the Reaction Center, thus enhancing its photoconversion performances [1], but can be also used for charge transfer processes to external electron/hole acceptors. We have developed protocols to synthesize tailored bio-organic complexes, exhibiting optimized interac...
ABSTRACT Covalent functionalization of reduced graphene oxide (rGO) with the photosynthetic react... more ABSTRACT Covalent functionalization of reduced graphene oxide (rGO) with the photosynthetic reaction center (RC) from Rhodobacter sphaeroides R26 via click chemistry reaction has been performed. The hybrid system was characterized by flash photolysis and infrared spectroscopy and the RC was found to retain its photoactivity and structural integrity. The strategy is applicable for the fabrication of hybrid bio-electronic devices capable of absorbing and converting solar energy.
Four linear terarylene molecules (i) 4-nitro-terphenyl-4′′-
methanethiol (NTM), (ii) 4-nitro-terp... more Four linear terarylene molecules (i) 4-nitro-terphenyl-4′′- methanethiol (NTM), (ii) 4-nitro-terphenyl-3′′,5′′-dimethanethiol (NTD), (iii) ([1,1′;4′,1′′] terphenyl-3,5-diyl)methanethiol (TM), and (iv) ([1,1′;4′,1′′] terphenyl-3,5-diyl)dimethanethiol (TD) have been synthesized and their self- assembled monolayers (SAMs) have been obtained on polycrystalline gold. NTM and NTD SAMs have been characterized by X-ray photoelectron spectroscopy, Kelvin probe measurements, electrochemistry, and contact angle measurements. The terminal nitro group (−NO2) is irreversibly reduced to hydroxylamine (−NHOH), which can be reversibly turned into nitroso group (−NO). The direct comparison between NTM/ NTD and TM/TD SAMs unambiguously shows the crucial influence of the nitro group on electrowetting properties of polycrystalline Au. The higher grade of surface tension related to NHOH has been successfully exploited for basic operations of digital μ-fluidics, such as droplets motion and merging.
A new set of linear oligoarylene thiol molecules, namely (40-(Thiophen-2-yl)Biphenyl-3,5-diyl) Di... more A new set of linear oligoarylene thiol molecules, namely (40-(Thiophen-2-yl)Biphenyl-3,5-diyl) Dimethanethiol (TBD), (40-(Thiophen-2-yl)Biphenyl-4-yl)Methanethiol (TBM) and ([1,10;40,100] Terphenyl-3,5-diyl)Dimethanethiol (TD), were synthesized and used for functionalizing the polycrystalline gold electrodes. Such molecules differ for the number of anchoring groups (TBM vs. TBD) and the terminal rings (TD vs. TBD). As shown by electrochemical measurements, they form homogeneous and pinholes-free self-assembly monolayers (SAMs) when deposited on the gold electrode. Moreover, the wettability of the functionalized surface and the morphological changes of pentacene films grown on SAMs were investigated by contact angle and atomic force microscopy, respectively. OTFT has been used as organic gauge for investigating the metal–SAM–organic semiconductor structure. Charge carriers mobility, threshold voltage, contact resistance were measured in both air and vacuum to assess the influence of the anchoring groups and the terminal rings to the transistor performance. Although these SAMs do not show an improvement of mobility due to an increase of contact resistance, they allow a better modulation of the current flowing across the electrode–organic semiconductor (OS) interface, pointing out the structural differences between the three SAMs in terms of resistance drop combined with the critical voltage.
Various chiral non-racemic b-ketosulfoxides, a class of compounds frequently used in asymmetric s... more Various chiral non-racemic b-ketosulfoxides, a class of compounds frequently used in asymmetric synthesis, were prepared in good yields by tert-butyl hydroperoxide oxidation of the corresponding sulfides in the presence of a complex between titanium and (S,S)-hydrobenzoin. The ee values of almost all of the purified products were >98%. As ascertained by X-ray analysis and/ or by NMR spectroscopy, the use of the (S,S)-form of the ligand led to aryl b-ketosulfoxides with (RS)-configuration and to methyl phenacyl sulfoxide with the (SS)-configuration. Some of the aryl ketosulfoxides were subjected to reduction with DIBAL-H/ZnCl2 and the corresponding b-sulfinylalcohols with an (R,RS)-configuration produced.
Organic-based Chemical and Biological Sensors, 2007
ABSTRACT Organic thin film transistor (OTFT) sensors are capable of fast, sensitive and reliable ... more ABSTRACT Organic thin film transistor (OTFT) sensors are capable of fast, sensitive and reliable detection of a variety of analytes. They have been successfully tested towards many chemical and biological "odor" molecules showing high selectivity, and displaying the additional advantage of being compatible with plastic technologies. Their versatility is based on the possibility to control the device properties, from molecular design up to device architecture. Here phenylene-thiophene based organic semiconductors functionalized with ad hoc chosen side groups are used as active layers in sensing OTFTs. These materials, indeed, combine the detection capability of organic molecules (particularly in the case of bio-substituted systems) with the electronic properties of the conjugated backbone. A new OTFT structure including Langmuir-Schäfer layer by layer organic thin films is here proposed to perform chemical detection of organic vapors, including vapor phase chiral molecules such as citronellol vapors, with a detection limit in the ppm range. Thermally evaporated α6T based OTFT sensors are used as well to be employed as standard system in order to compare sensors performances.
Several organometallic methods are used to synthesize π-conjugated molecules and polymers with al... more Several organometallic methods are used to synthesize π-conjugated molecules and polymers with alternating thiophene-dialkoxyphenylene units in the conjugated backbone. Here we describe our approaches to the synthesis of materials based on the dialkoxyphenylenethienylene structural motif via palladium catalyzed cross-coupling reactions of organomagnesium or organoboron reagents with aryl halides. The properties of the resulting compounds and their applications in (opto)electronic devices (organic field effect transistors, resistive gas sensors, field effect chiral sensors, photoelectrochemical cells and bulk-heterojunction solar cells) are also discussed, highlighting the role of the synthetic logic in the design of multifunctional organic materials.
The reconstitution of the integral membrane protein photosynthetic reaction center (RC) in polyme... more The reconstitution of the integral membrane protein photosynthetic reaction center (RC) in polymersomes, i.e. artificial closed vesicles, was achieved by the micelle-to-vesicle transition technique, a very mild protocol based on size exclusion chromatography often used to drive the incorporation of proteins contemporarily to liposome formation. An optimized protocol was used to successfully reconstitute the protein in a fully active state in polymersomes formed by the tri-block copolymers PMOXA22-PDMS61-PMOXA22. The RC is very sensitive to its solubilizing environment and was used to probe the positioning of the protein in the vesicles. According to charge-recombination experiments and to the enzymatic activity assay, the RC is found to accommodate in the PMOXA22 region of the polymersome, facing the water bulk solution, rather than in the PDMS61 transmembrane-like region. Furthermore, polymersomes were found to preserve protein integrity efficiently as the biomimetic lipid bilayers but show a much longer temporal stability than lipid based vesicles.
L'interesse del mondo scientifico ed industriale nei confronti di sistemi in grado di immagaz... more L'interesse del mondo scientifico ed industriale nei confronti di sistemi in grado di immagazzinare la luce solare e convertirla in una opportuna forma di energia è in netto aumento negli ultimi anni.[1] I candidati naturali in grado di svolgere tali compiti sono i sistemi fotosintetici, le cui proprietà di assorbimento della luce, selezionate dalla natura nel corso dell'evoluzione, sono però complesse da riprodurre in dispositivi artificiali. La sintesi chimica mette oggi a disposizione diverse molecole che possono essere convenientemente sfruttate per migliorare e modulare le caratteristiche spettroscopiche di questi sistemi naturali. Grazie a tali molecole è possibile ottenere sistemi ibridi capaci di assorbire la luce e convertirla in uno stato di separazione di carica stabile. A tal proposito, un fluoroforo organico (AE) appartenente alla famiglia degli arilenietinileni, coniugato in maniera covalente a residui di lisina del centro di reazione fotosintentico (RC), è sta...
ABSTRACT Concept Building artificial photosynthetic molecular machines capable of exploiting sola... more ABSTRACT Concept Building artificial photosynthetic molecular machines capable of exploiting solar energy for photocatalysis and electrical energy production, has attracted considerable interest in recent years [1]. Photosynthetic reaction centers (RC) are the Nature's solar batteries, converting light energy into chemical potential in the photosynthetic membrane, thereby assuring carbon reduction in cells. The photoconversion efficiency of the primary charge separation step in RC, close to unit, is pushing efforts of the scientific community toward artificial photosynthesis. We propose here the concept of an hybrid organic-biologic system formed by tailored organic fluorophores acting as covalently bound antenna to the RC protein scaffold. The hybrid functions like the natural system and is capable of extending the useful range of visible wavelengths for energy photoconversion. Motivations and Objectives Ideal biomimetic systems must efficiently harvest sunlight and effectively converting it into a stable charge-separated state, with a sufficiently long lifetime to allow ancillary chemistry to take place. However the combination of these requirements has not, thus far, been fully attained. Recently, fluorescent quantum dots (QDs) have been proposed as artificial antennas [2] as the first example of efficient transfer of excitation energy from QDs to RC, but few information on the duration of the charge-separated state and protein stability were given. Herein we propose to bioconjugate organic fluorophores, belonging to the aryleneethynylenes (AE) class, and used as antenna to the RC, synthetizing an hybrid system whose biological core maintains the conversion efficiency of the natural system. AE dyes have been designed and synthesized [3] to fulfill the spectroscopic, chemical, and steric requirements for such bioconjugation. Results and Discussion AE dyes were covalently and selectively bioconjugated to specific lysine residues of the photosynthetic RC. The resulting hybrid system is capable of absorbing light and efficiently performing photo- conversion in a wavelength range where the non-conjugated protein does not absorb [4]. The energy collected by the attached fluorophore is efficiently transferred, via FRET mechanism, to the protein pigments, and eventually used for the enzymatic activity, which outperforms the natural system. Diffraction data, collected at synchrotron facilities, obtained by the crystallization of the bioconjugated protein, confirm the hypothesis that functionalized lysines are within the Förster distance for efficient energy transfer. References [1] P. Maroti, M.Trotta in CRC Handbook of Organic Photochemistry and Photobiology, 3rd ed, Boca Raton, FL, 2012 [2] I. Nabiev, A. Rakovich et al., Angew. Chem. Int. Ed., 49 (2010), 7217–7221 [3] A. Operamolla, R. Ragni et al., Curr. Org. Synth., 9 (2012), 150-62 [4] F. Milano, R.R. Tangorra et al., Angew. Chem. Int. Ed., 51 (2012), 11019 – 11023
The Reaction Centers (RCs) of photosynthetic organisms are efficient billion-of-years optimized p... more The Reaction Centers (RCs) of photosynthetic organisms are efficient billion-of-years optimized photoenzimes for conversion of absorbed light into charge separated states. Combination of such effective photoenzimes with π-conjugated molecules appears an intriguing strategy to obtain a new generation of versatile bio-optoelectronic materials for applications ranging from photoconversion to photocatalysis and sensing. We present here the design and synthesis of hybrid bio-organic photosynthetic complexes by combination of the Reaction Center of the photosynthetic bacterium Rhodobacter Sphaeroides R26 with tailored molecular semiconductors. The organic molecules can act as antennas to extend the light harvesting capability of the Reaction Center, thus enhancing its photoconversion performances [1], but can be also used for charge transfer processes to external electron/hole acceptors. We have developed protocols to synthesize tailored bio-organic complexes, exhibiting optimized interac...
ABSTRACT Covalent functionalization of reduced graphene oxide (rGO) with the photosynthetic react... more ABSTRACT Covalent functionalization of reduced graphene oxide (rGO) with the photosynthetic reaction center (RC) from Rhodobacter sphaeroides R26 via click chemistry reaction has been performed. The hybrid system was characterized by flash photolysis and infrared spectroscopy and the RC was found to retain its photoactivity and structural integrity. The strategy is applicable for the fabrication of hybrid bio-electronic devices capable of absorbing and converting solar energy.
Four linear terarylene molecules (i) 4-nitro-terphenyl-4′′-
methanethiol (NTM), (ii) 4-nitro-terp... more Four linear terarylene molecules (i) 4-nitro-terphenyl-4′′- methanethiol (NTM), (ii) 4-nitro-terphenyl-3′′,5′′-dimethanethiol (NTD), (iii) ([1,1′;4′,1′′] terphenyl-3,5-diyl)methanethiol (TM), and (iv) ([1,1′;4′,1′′] terphenyl-3,5-diyl)dimethanethiol (TD) have been synthesized and their self- assembled monolayers (SAMs) have been obtained on polycrystalline gold. NTM and NTD SAMs have been characterized by X-ray photoelectron spectroscopy, Kelvin probe measurements, electrochemistry, and contact angle measurements. The terminal nitro group (−NO2) is irreversibly reduced to hydroxylamine (−NHOH), which can be reversibly turned into nitroso group (−NO). The direct comparison between NTM/ NTD and TM/TD SAMs unambiguously shows the crucial influence of the nitro group on electrowetting properties of polycrystalline Au. The higher grade of surface tension related to NHOH has been successfully exploited for basic operations of digital μ-fluidics, such as droplets motion and merging.
A new set of linear oligoarylene thiol molecules, namely (40-(Thiophen-2-yl)Biphenyl-3,5-diyl) Di... more A new set of linear oligoarylene thiol molecules, namely (40-(Thiophen-2-yl)Biphenyl-3,5-diyl) Dimethanethiol (TBD), (40-(Thiophen-2-yl)Biphenyl-4-yl)Methanethiol (TBM) and ([1,10;40,100] Terphenyl-3,5-diyl)Dimethanethiol (TD), were synthesized and used for functionalizing the polycrystalline gold electrodes. Such molecules differ for the number of anchoring groups (TBM vs. TBD) and the terminal rings (TD vs. TBD). As shown by electrochemical measurements, they form homogeneous and pinholes-free self-assembly monolayers (SAMs) when deposited on the gold electrode. Moreover, the wettability of the functionalized surface and the morphological changes of pentacene films grown on SAMs were investigated by contact angle and atomic force microscopy, respectively. OTFT has been used as organic gauge for investigating the metal–SAM–organic semiconductor structure. Charge carriers mobility, threshold voltage, contact resistance were measured in both air and vacuum to assess the influence of the anchoring groups and the terminal rings to the transistor performance. Although these SAMs do not show an improvement of mobility due to an increase of contact resistance, they allow a better modulation of the current flowing across the electrode–organic semiconductor (OS) interface, pointing out the structural differences between the three SAMs in terms of resistance drop combined with the critical voltage.
Various chiral non-racemic b-ketosulfoxides, a class of compounds frequently used in asymmetric s... more Various chiral non-racemic b-ketosulfoxides, a class of compounds frequently used in asymmetric synthesis, were prepared in good yields by tert-butyl hydroperoxide oxidation of the corresponding sulfides in the presence of a complex between titanium and (S,S)-hydrobenzoin. The ee values of almost all of the purified products were >98%. As ascertained by X-ray analysis and/ or by NMR spectroscopy, the use of the (S,S)-form of the ligand led to aryl b-ketosulfoxides with (RS)-configuration and to methyl phenacyl sulfoxide with the (SS)-configuration. Some of the aryl ketosulfoxides were subjected to reduction with DIBAL-H/ZnCl2 and the corresponding b-sulfinylalcohols with an (R,RS)-configuration produced.
Organic-based Chemical and Biological Sensors, 2007
ABSTRACT Organic thin film transistor (OTFT) sensors are capable of fast, sensitive and reliable ... more ABSTRACT Organic thin film transistor (OTFT) sensors are capable of fast, sensitive and reliable detection of a variety of analytes. They have been successfully tested towards many chemical and biological "odor" molecules showing high selectivity, and displaying the additional advantage of being compatible with plastic technologies. Their versatility is based on the possibility to control the device properties, from molecular design up to device architecture. Here phenylene-thiophene based organic semiconductors functionalized with ad hoc chosen side groups are used as active layers in sensing OTFTs. These materials, indeed, combine the detection capability of organic molecules (particularly in the case of bio-substituted systems) with the electronic properties of the conjugated backbone. A new OTFT structure including Langmuir-Schäfer layer by layer organic thin films is here proposed to perform chemical detection of organic vapors, including vapor phase chiral molecules such as citronellol vapors, with a detection limit in the ppm range. Thermally evaporated α6T based OTFT sensors are used as well to be employed as standard system in order to compare sensors performances.
Several organometallic methods are used to synthesize π-conjugated molecules and polymers with al... more Several organometallic methods are used to synthesize π-conjugated molecules and polymers with alternating thiophene-dialkoxyphenylene units in the conjugated backbone. Here we describe our approaches to the synthesis of materials based on the dialkoxyphenylenethienylene structural motif via palladium catalyzed cross-coupling reactions of organomagnesium or organoboron reagents with aryl halides. The properties of the resulting compounds and their applications in (opto)electronic devices (organic field effect transistors, resistive gas sensors, field effect chiral sensors, photoelectrochemical cells and bulk-heterojunction solar cells) are also discussed, highlighting the role of the synthetic logic in the design of multifunctional organic materials.
The reconstitution of the integral membrane protein photosynthetic reaction center (RC) in polyme... more The reconstitution of the integral membrane protein photosynthetic reaction center (RC) in polymersomes, i.e. artificial closed vesicles, was achieved by the micelle-to-vesicle transition technique, a very mild protocol based on size exclusion chromatography often used to drive the incorporation of proteins contemporarily to liposome formation. An optimized protocol was used to successfully reconstitute the protein in a fully active state in polymersomes formed by the tri-block copolymers PMOXA22-PDMS61-PMOXA22. The RC is very sensitive to its solubilizing environment and was used to probe the positioning of the protein in the vesicles. According to charge-recombination experiments and to the enzymatic activity assay, the RC is found to accommodate in the PMOXA22 region of the polymersome, facing the water bulk solution, rather than in the PDMS61 transmembrane-like region. Furthermore, polymersomes were found to preserve protein integrity efficiently as the biomimetic lipid bilayers but show a much longer temporal stability than lipid based vesicles.
L'interesse del mondo scientifico ed industriale nei confronti di sistemi in grado di immagaz... more L'interesse del mondo scientifico ed industriale nei confronti di sistemi in grado di immagazzinare la luce solare e convertirla in una opportuna forma di energia è in netto aumento negli ultimi anni.[1] I candidati naturali in grado di svolgere tali compiti sono i sistemi fotosintetici, le cui proprietà di assorbimento della luce, selezionate dalla natura nel corso dell'evoluzione, sono però complesse da riprodurre in dispositivi artificiali. La sintesi chimica mette oggi a disposizione diverse molecole che possono essere convenientemente sfruttate per migliorare e modulare le caratteristiche spettroscopiche di questi sistemi naturali. Grazie a tali molecole è possibile ottenere sistemi ibridi capaci di assorbire la luce e convertirla in uno stato di separazione di carica stabile. A tal proposito, un fluoroforo organico (AE) appartenente alla famiglia degli arilenietinileni, coniugato in maniera covalente a residui di lisina del centro di reazione fotosintentico (RC), è sta...
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Papers by Omar Hassan Omar
methanethiol (NTM), (ii) 4-nitro-terphenyl-3′′,5′′-dimethanethiol (NTD),
(iii) ([1,1′;4′,1′′] terphenyl-3,5-diyl)methanethiol (TM), and (iv) ([1,1′;4′,1′′]
terphenyl-3,5-diyl)dimethanethiol (TD) have been synthesized and their self-
assembled monolayers (SAMs) have been obtained on polycrystalline gold.
NTM and NTD SAMs have been characterized by X-ray photoelectron
spectroscopy, Kelvin probe measurements, electrochemistry, and contact angle
measurements. The terminal nitro group (−NO2) is irreversibly reduced to
hydroxylamine (−NHOH), which can be reversibly turned into nitroso group (−NO). The direct comparison between NTM/ NTD and TM/TD SAMs unambiguously shows the crucial influence of the nitro group on electrowetting properties of polycrystalline Au. The higher grade of surface tension related to NHOH has been successfully exploited for basic operations of digital μ-fluidics, such as droplets motion and merging.
methanethiol (NTM), (ii) 4-nitro-terphenyl-3′′,5′′-dimethanethiol (NTD),
(iii) ([1,1′;4′,1′′] terphenyl-3,5-diyl)methanethiol (TM), and (iv) ([1,1′;4′,1′′]
terphenyl-3,5-diyl)dimethanethiol (TD) have been synthesized and their self-
assembled monolayers (SAMs) have been obtained on polycrystalline gold.
NTM and NTD SAMs have been characterized by X-ray photoelectron
spectroscopy, Kelvin probe measurements, electrochemistry, and contact angle
measurements. The terminal nitro group (−NO2) is irreversibly reduced to
hydroxylamine (−NHOH), which can be reversibly turned into nitroso group (−NO). The direct comparison between NTM/ NTD and TM/TD SAMs unambiguously shows the crucial influence of the nitro group on electrowetting properties of polycrystalline Au. The higher grade of surface tension related to NHOH has been successfully exploited for basic operations of digital μ-fluidics, such as droplets motion and merging.