Pinalysa Cosma

Development of a novel enzyme/semiconductor nanoparticles system for biosensor application

Abstract Nanosized semiconductor crystals can increase efficiency of photochemical reactions and can be effectively coupled to biomolecular units, such as enzyme, to generate novel photoelectrochemical systems. In this work, nanocrystalline CdS has been synthesized by using a microemulsive system and immobilised by self-assembling on a gold electrode in order to prepare, combined with formaldehyde dehydrogenase (FDH) enzyme, a biological-inorganic hybrid able to perform catalytic oxidation of formaldehyde. The preliminary results indicate that quantum-sized CdS layer on gold, in close contact with the enzyme, is an effective photoactive material to replace the NAD+/NADH role as charge transfer in the enzymatic reaction.

Spectroscopic and electrochemical characterization of chlorophyll a in different water + organic solvent mixtures

Abstract Triangular-sweep adsorption voltammetry and absorption and fluorescence spectroscopy are employed in the study of chlorophyll a hydration and aggregation in binary mixtures of water with acetone, dimethylformamide (DMF) and acetonitrile (ACN). From the variation of the relative intensities and positions of the polarographic and spectroscopic peaks with the composition of the solvent, it is concluded that the organic solvates of Chl a are completely converted to Chl a·2 H2O at a water mole fraction χH2O ⪢ 0.66. A further shift in the equilibrium towards the dimerization of Chl a·2 H2O is observed at χH2O ⪢ 0.75. The lower water content and Chl a concentration required for aggregation in DMF and ACN compared with that required in acetone is discussed in terms of the bulk properties of the binary solvent mixtures.

9,10-Ter-anthrylene-ethynylene: a new molecular architecture for solution processed anthracene-based thin film transistors

This study deals with the properties of a new molecular architecture for organic thin film transistors obtained by introducing 10-decylanthr-9-yl-ethynyl moieties at the anthracene 9,10 positions. The resulting structure, formally a ter-anthrylene-ethynylene (D3ANT), is stable and endowed with sufficient solubility to guarantee the formation of good quality films. The molecule was characterised by 1H NMR, mass spectrometry, IR, UV–vis and photoluminescence both in solution and in the solid state. Cyclic voltammetry measurements, combined with solution UV–vis, permitted the evaluation of HOMO and LUMO energy levels. A series of D3ANT-based OTFT devices were built both in bottom and top contact configurations by a spin coating technique. Top contact OTFT devices exhibited the best semiconducting characteristics, showing an average mobility of 1.2 × 10−2 cm2 V−1 s−1 with on–off ratios higher then 104, while the highest mobility obtained was 0.055 cm2 V−1 s−1. AFM thin-film characterization showed evidence of a granular structure. High-resolution STM images of D3ANT monolayers adsorbed on Au(111) and HOPG reveal highly-ordered self-organized domains with molecules lying flat on the substrates, but, remarkably, no reflections were recorded by out-of plane GIXRD of spin coated films on SiO2.

Formation of chlorophyll a photoreactive dimers in alcoholic mixtures: spectroscopic and electrochemical study

Abstract Chlorophyll a (Chl a ) aggregation in alcohol was examined as a function of the type of alcohol, Chl a concentration and water content. The sample preparation procedure was observed to play an important role in determining whether the dihydrate dimer or the monohydrate dimer was formed. The characterization of the different species formed in alcohol on addition of water was carried out using absorption, fluorescence and circular dichroism spectroscopic techniques. The results were confirmed by adsorptive stripping cathodic voltammetry and differential pulse polarography.

Aggregation processes and photophysical properties of chlorophyll a in aqueous solutions modulated by the presence of cyclodextrins

In the present paper we report the preliminary results on the behaviour of chlorophyll a (Chl a), the main photosynthetic amphiphilic pigment of green plants, in water and aqueous solutions of cyclodextrins (α-cyclodextrin, hydroxypropyl-β-cyclodextrin, heptakis(2,6-di-O-methyl)-β-cyclodextrin and hydroxypropyl-γ-cyclodextrin). In particular our study was aimed to understand the influence of CDs on solubility and aggregation of Chl a in water and to get information on the interactions between different cyclodextrins and the pigment. The role played by different CDs in affecting the photoactivity of the chlorophyll, with particular attention to the quantum yield of the singlet oxygen production, has been also discussed. The study was carried out by using different spectroscopic (UV–Vis, fluorescence, circular dichroism, time resolved absorption and luminescence) and calorimetric (ITC) techniques.

Tetrakis(4-pyridyl)porphyrin Supramolecular Complexes with Cyclodextrins in Aqueous Solution

Abstract The formation of inclusion complexes of hydroxypropyl-β-cyclodextrin, heptakis(2,6-di-O-methyl)-β-cyclodextrin and heptakis(2,3,6-tri-O-methyl)-β-cyclodextrin with 5,10,15,20-tetrakis(4-pyridyl)porphyrin (TpyP) has been studied in aqueous buffer solution (phosphate buffer pH = 7 and I = 0.01 M) to give a structural and spectroscopic characterization of a new class of potential sensitizers for photodynamic therapy. The interaction was investigated by a combination of UV/Vis absorption, fluorescence anisotropy, time-resolved fluorescence and circular dichroism. The experimental results point to the presence of the pigment in water in a monomeric complexed form. The fluorescence anisotropy measurements suggest that TpyP forms 1:1 complexes with heptakis(2,3,6-tri-O-methyl)-β-cyclodextrin and hydroxypropyl-β-cyclodextrin, while 1:2 complexes are obtained with heptakis(2,6-di-O-methyl)-β-cyclodextrin.

Electroactive layer-by-layer plasmonic architectures based on Au nanorods.

Nanostructured films based on Au nanorods (NRs) have been obtained by layer-by-layer (LbL) assembly driven by electrostatic interaction between metal nanoparticles and polyelectrolytes. Multilayer films have been fabricated by using LbL assembly of poly(sodium styrenesulfonate) (PSS) and positively charged Au NRs on a polyelectrolyte-modified substrate. The effect of fabrication parameters, including the nature of the substrate, the polyelectrolyte initial anchoring layer, and the number of layers has been investigated by means of UV-vis absorbance spectroscopy and atomic force microscopy (AFM). The results demonstrated the dependence of morphology and plasmonic features in the multilayered nanostructured architectures from the nature of the anchoring polyelectrolyte on the substrate, the number of layers, and the kind of NR mutual assembly. In addition, a study of the electrochemical activity at the solid/liquid interface has been carried out in order to assess charge transport through the NR multilayer by using two molecular probes in solution, namely, potassium ferricyanide, a common and well-established redox mediator with reversible behavior, and cytochrome C, a robust model redox protein. The presented systematic study of the immobilization of Au NRs opens the venue to several application areas, such as (bio)chemical sensing.

Fluoro-functionalization of vinylene units in a polyarylenevinylene for polymer solar cells

A low band-gap copolymer PDTBTFV alternating bis-thienyl-(bis-alkoxy)-benzothiadiazole blocks with difluorovinylene units and its non-fluorinated counterpart PDTBTV have been synthesized and characterized as donor materials in bulk heterojunction (BHJ) solar cells with PCBM as the acceptor. The solar cells with the fluorinated polymer show better photovoltaic performances than those recorded with the non-fluorinated material. Comparative spectroscopic and computational studies, together with morphological, electrical and optical characterization of thin films, have been carried out to shed light on the reasons for the improvement of performances as induced by the double bond fluorination. Our study introduces the fluorinated double bond as a new conjugated unit in donor polymers for BHJ solar cells.

The effects of increasing NaCl concentration on the stability of inclusion complexes in aqueous solution

Equilibrium constants and standard molar enthalpies of reaction were determined by titration calorimetry for the reaction of 1-butanol with 2-hydroxypropyl-b-cyclodextrin (HP-b-CD) in aqueous solution at different concentrations of NaCl (0-1.9 M). The standard molar free energy and entropy changes associated to the complexation were calculated from the corresponding equilibrium constants, K, and standard enthalpies determined experimentally. In NaCl solutions the inclusion complexes ButOH/HP-b-CD are more stable than in water and their stability increases at increasing NaCl concentration; otherwise, the standard molar enthalpy associated to the formation of the complexes does not change with the increasing of salt concentration. The dependence of K on NaCl concentration were used to evaluate the number of water molecules displaced from the hydration shells of HP-b-CD and ButOH in forming complexes.

Photochemical sensitisation process at photosynthetic pigments/Q-sized colloidal semiconductor hetero-junctions

Abstract Electrodes based on Q-sized ZnO and TiO2, synthesised by non-hydrolytic routes, were prepared and characterised. The nanostructured electrodes were modified with photosynthetic pigments, namely, chlorophyll a, carotenoids and their mixture, to probe the photochemical sensitisation process. The photocurrent response of the hetero-junctions and the current–potential (I–V) characteristics of the sensitised electrodes are presented for different dyes. The Q-sized semiconductor sensitised electrodes showed different behaviour when compared to correspondent commercial oxides. Co-sensitisation acted by chlorophyll a and carotenoids on nanostructured electrodes was found to greatly enhance the photocurrent generation.