Alessandra Operamolla

Enhancing the Light Harvesting Capability of a Photosynthetic Reaction Center by a Tailored Molecular Fluorophore

Light machine: The simplest photosynthetic protein able to convert sunlight into other energy forms is covalently functionalized with a tailored organic dye to obtain a fully functional hybrid complex that outperforms the natural system in light harvesting and conversion ability.

Bioconjugation of hydrogen-bonded organic semiconductors with functional proteins

We demonstrate the direct bioconjugation of hydrogen-bonded organic semiconductors with two different complex functional proteins in an aqueous environment. The representative semiconductors are epindolidione and quinacridone, materials used in devices in the form of vacuum-evaporated polycrystalline films. First, these molecules in thin films react spontaneously with N-hydroxysuccinimide functionalized linkers: disuccinimidyl suberate and succinimidyl biotinate. The suberate linker is then used to covalently bind the Rhodobacter sphaeroides reaction centre (RC), the key photoenzyme for conversion of light into electrical charges in photosynthetic bacteria. Similarly, the biotin linker is used to bridge streptavidin to the surface of the hydrogen-bonded semiconductor film. Multiple-reflection infrared spectroscopy, water contact angle measurements, and atomic force microscopy are used to verify surface functionalization. The presence and functional integrity of the immobilized proteins are demonstrated by specific experiments: a charge recombination kinetics assay in the case of the RC, and photoluminescence measurements for quantum dot-labelled streptavidin. As key results of our work, we have shown that upon bioconjugation, the semiconductors preserve their favourable electrical properties: as evidenced by photoconductor devices operating under water sensitized by the RC, and thin film transistor measurements before and after bioconjugation. These are enabling steps for using hydrogen-bonded semiconductors as platforms for multifunctional bioelectronics devices.

Self-assembly of mono- and bidentate oligoarylene thiols onto polycrystalline Au.

Four thiolated oligoarylene molecules (i) 4-methoxy-terphenyl-4″-methanethiol (MTM), (ii) 4-methoxy-terphenyl-3″,5″-dimethanethiol (MTD), (iii) 4-nitro-terphenyl-4″-methanethiol (NTM), and (iv) 4-nitro-terphenyl-3″,5″-dimethanethiol (NTD) were synthesized and self-assembled as monolayers (SAMs) on polycrystalline Au electrodes of organic field-effect transistors (OFETs). SAMs were characterized by contact angle and AC/DC electrochemical measurements, whereas atomic force microscopy was used for imaging the pentacene films grown on the coated electrodes. The electrical properties of functionalized OFETs, the electrochemical SAMs features and the morphology of pentacene films were correlated to the molecular organization of the thiolated oligoarylenes on Au, as calculated by means of the density functional theory. This multi-methodological approach allows us to associate the systematic replacement of the SAM anchoring head group (viz. methanethiol and dimethanethiol) and/or terminal tail group (viz. nitro-, -NO2, and methoxy, -OCH3) with the change of the electrical features. The dimethanethiol head group endows SAMs with higher resistive features along with higher surface tensions compared with methanethiol. Furthermore, the different number of thiolated heads affects the kinetics of Au passivation as well as the pentacene morphology. On the other hand, the nitro group confers further distinctive properties, such as the positive shift of both threshold and critical voltages of OFETs with respect to the methoxy one. The latter experimental evidence arise from its electron-withdrawing capability, which has been verified by both DFT calculations and DC electrochemical measurements.

''Garnishing'' the photosynthetic bacterial reaction center for bioelectronics

The photosynthetic reaction center is an extraordinarily efficient natural photoconverter, which can be ideally used in combination with conducting or semiconducting interfaces to produce electrical signals in response to absorption of photons. The actual applicability of this protein in bioelectronic devices critically depends on the finding of (a) suitable deposition methods enabling controlled addressing and precise orientation of the protein on electrode interfaces and (b) chemical manipulation protocols able to tune and enhance protein light absorption in specific or broader spectral regions. Literature reports several examples of approaches to fulfill these requirements, which have faced in different ways the fundamental issues of assembling the biological component and non-natural systems, such as electrode surfaces and artificial light harvesting components. Here we present a short overview of the main methods reported to accomplish both the objectives by properly “garnishing” the photosynthetic reaction center (RC) via chemical modifications.

Langmuir-Schaefer films for aligned carbon nanotubes functionalized with a conjugate polymer and photoelectrochemical response enhancement.

Single-walled carbon nanotubes (SWCNTs) were suspended in 1,2-dichloroethane by noncovalent functionalization with a low-band-gap conjugated polymer 1 alternating dialkoxyphenylene-bisthiophene units with benzo[c][2,1,3]thiadiazole monomeric units. The suspended 1/SWCNT blend was transferred onto different solid substrates by the Langmuir-Schaefer deposition method, resulting in films with a high percentage of aligned nanotubes. Photoelectrochemical characterization of 1/SWCNT thin films on indium-tin oxide showed the benefits of SWCNT alignment for photoconversion efficiency.

Mono/bidentate thiol oligoarylene-based self-assembled monolayers (SAMs) for interface engineering

A new set of linear oligoarylene thiol molecules, namely (4′-(Thiophen-2-yl)Biphenyl-3,5-diyl)Dimethanethiol (TBD), (4′-(Thiophen-2-yl)Biphenyl-4-yl)Methanethiol (TBM) and ([1,1′;4′,1′′]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.

Synthesis of Functionalized Aryleneethynylene Oligomers and Polymers for Organic Electronics by Pd-Catalyzed Coupling Reactions

In this article we discuss synthetic routes to organic conjugated oligomers and polymers bearing triple C-C bonds that have been recently developed in our laboratories, based on Pd-catalyzed Csp-Csp 2 coupling reactions. Experimental protocols have been tuned to face synthetic challenges such as the presence in the main conjugated backbone of multifunctional substituents or uncommon conju- gated units. The relevance of the obtained products in terms of properties and applications is also shortly mentioned.

Synthetic Antenna Functioning As Light Harvester in the Whole Visible Region for Enhanced Hybrid Photosynthetic Reaction Centers.

The photosynthetic reaction center (RC) from the Rhodobacter sphaeroides bacterium has been covalently bioconjugated with a NIR-emitting fluorophore (AE800) whose synthesis was specifically tailored to act as artificial antenna harvesting light in the entire visible region. AE800 has a broad absorption spectrum with peaks centered in the absorption gaps of the RC and its emission overlaps the most intense RC absorption bands, ensuring a consistent increase of the protein optical cross section. The covalent hybrid AE800-RC is stable and fully functional. The energy collected by the artificial antenna is transferred to the protein via FRET mechanism, and the hybrid system outperforms by a noteworthy 30% the overall photochemical activity of the native protein under the entire range of visible light. This improvement in the optical characteristic of the photoenzyme demonstrates the effectiveness of the bioconjugation approach as a suitable route to new biohybrid materials for energy conversion, photocatalysis, and biosensing.

Pd-Catalyzed Thiophene–Aryl Coupling Reaction via C–H Bond Activation in Deep Eutectic Solvents

Direct arylation of 5-octylthieno[3,4-c]pyrrole-4,6-dione with a series of functionalized aryl iodides via C-H bond activation is demonstrated in a deep eutectic solvent made of choline chloride and urea in non-anhydrous conditions and without exclusion of air. This is the first demonstration of a thiophene-aryl coupling via direct arylation in deep eutectic solvents.

Iron-Catalyzed Cross-Coupling Reaction of Aryl Grignard Reagents with bis(2-bromovinyl)benzenes

Fe(acac)3 has been used as the catalyst in cross-coupling reactions of aryl Grignard reagents with 1,4-bis(2- bromovinyl)benzenes affording bis(2-arylvinyl)benzenes. Effects of alkoxy substituents on both reactants and of the temperature on the reaction outcome are investigated.