11 research outputs found

    Electrochemical Synthesis of Unnatural Amino Acids Embedding 5- and 6‑Membered Heteroaromatics

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    Using a commercially available potentiostat, the electrochemical synthesis of unnatural amino acids bearing heteroaromatics on the lateral chain has been accomplished. This strategy exploits the side-chain decarboxylative arylation of aspartic/glutamic acid, a reaction that becomes challenging with electron-rich coupling partners such as 5- and 6-membered heteroaromatics. These rings are underrepresented in unnatural amino acids, therefore allowing a wider exploration of the chemical space, given the abundance of the aryl bromides employable in this reaction

    Electrochemical Synthesis of Unnatural Amino Acids Embedding 5- and 6‑Membered Heteroaromatics

    No full text
    Using a commercially available potentiostat, the electrochemical synthesis of unnatural amino acids bearing heteroaromatics on the lateral chain has been accomplished. This strategy exploits the side-chain decarboxylative arylation of aspartic/glutamic acid, a reaction that becomes challenging with electron-rich coupling partners such as 5- and 6-membered heteroaromatics. These rings are underrepresented in unnatural amino acids, therefore allowing a wider exploration of the chemical space, given the abundance of the aryl bromides employable in this reaction

    Glucose and Lactate Miniaturized Biosensors for SECM-Based High-Spatial Resolution Analysis: A Comparative Study

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    With the aim of developing miniaturized enzymatic biosensors suitable for <i>in vitro</i> diagnostic applications, such as monitoring of metabolites at single cell level, glucose and lactate biosensors were fabricated by immobilizing enzymes (glucose oxidase and lactate oxidase, respectively) on 10 μm Pt ultramicroelectrodes. These electrodes are meant to be employed as probes for scanning electrochemical microscopy (SECM), which is a unique technique for high-spatial-resolution electrochemical-based analysis. The use of enzymatic moieties improves sensitivity, time scale response, and information content of the microprobes; however, protein immobilization is a key step in the biosensor preparation that greatly affects the overall performance. A crucial aspect is the miniaturization of the sensing, preserving their sensitivity. In this work, we investigated the most common enzyme immobilization techniques. Several fabrication routes are reported and the main figures of merit, such as sensitivity, detection limit, response time, reproducibility, spatial resolution, biosensor efficiency, permeability, selectivity, and the ability to block electro-active interfering species, are investigated and compared. With the intent of using the microprobes for <i>in vitro</i> functional imaging of single living cells, we carefully evaluate the spatial resolution achieved by our modified electrodes on 2D SECM imaging. Metabolic activity of single MCF10A cells were obtained by monitoring the glucose concentrations in close proximity of single living cell, using the UME-based biosensor probes prepared. A voltage-switch approach was implemented to disentangle the topographical contribution of the cells enabling quantitative measurements of cellular uptakes

    Electrochemical Polymerization of Allylamine Copolymers

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    We describe for the first time the electro-oxidative synthesis and passivating properties of surface films of poly­(allylamine) and copolymers of allylamine and diallylamine. Cyclic voltammetry and impedance spectra show that the films exhibit high charge-transfer resistance and that the addition of diallylamine causes improvements in the compactness and stability toward swelling of the films when compared to both allylamine and diallyamine, leading to coatings with high charge-transfer resistance up to 70 MΩ. We also show that removing oxygen before the polymerization further improves the films’ passivating properties

    Numerical Simulation of Doped Silica Nanoparticle Electrochemiluminescence

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    In the present work we numerically simulated the electrogenerated chemiluminescence (ECL) from a Ru­(bpy)<sub>3</sub><sup>2+</sup>-doped silica nanoparticle (Ru-DSNP) in buffer containing tripropylamine (TPrA). An experimental study reported from Zanarini et al. showed that ECL intensity for the Ru-DSNP/TPrA system exhibits two emission waves, while the potential of the working electrode is swept in the positive direction. The first ECL wave with a peak at ∼0.9 V (vs Ag|AgCl) is triggered by TPrA oxidation and is governed by the deprotonation equilibrium of TPrA cation radical (TPrA<sup>•+</sup> = TPrA<sup>•</sup> + H<sup>+</sup>). We present a model for the description of the first ECL wave, which also takes into consideration the influence on the deprotonation equilibrium of the electrode surface functionality. This model indicated that the detachment of a Ru-DSNP (initially bound to the electrode surface via alkylthiols linkers) from the electrode surface and the subsequent electrode surface oxidation facilitate the radical deprotonation on the electrode surface causing the ECL quenching. The second ECL wave having its peak at ∼1.2 V is triggered by direct Ru­(bpy)<sub>3</sub><sup>2+</sup> oxidation. We modeled the second ECL wave as related to the electron hopping mechanism between Ru­(bpy)<sub>3</sub><sup>2+</sup> labels inside the Ru-DSNP. The results of the numerical simulations indicate that electrode surface functionality modification, which occurs during potential sweep, and the electron hopping mechanism between Ru­(bpy)<sub>3</sub><sup>2+</sup> labels play important roles in defining the Ru-DSNP/TPrA ECL signal

    Heterogeneous Crystallization of Proteins: Is it a Prenucleation Clusters Mediated Process?

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    Several studies have shown that heterogeneous agents are able to reduce required starting protein concentration and induction time for crystallization. However, in many cases, the molecular mechanism by which heterogeneous agents promote the nucleation is still unclear, although examples of epitaxial crystallization have been reported. Here, a set of focused crystallization trials, together with a review of the literature data, point out that the process of heterogeneous nucleation can be described by a nonclassical mechanism. We suppose that due to concentration fluctuations, unstable prenucleation aggregates homogeneously form in solution in conditions of low supersaturation, when the chemistry of solution favors this event. Then heterogeneous substrates stabilize prenucleation clusters by nonspecific interactions and trigger the nucleation event. This concept applied to proteins, but also to any colloidal system where the ordered assembly is governed by weak interactions, highlights the importance of the chemistry of the solution as a key parameter to achieve nucleation, even in the presence of heterogeneous nucleants

    Variable Doping Induces Mechanism Swapping in Electrogenerated Chemiluminescence of Ru(bpy)<sub>3</sub><sup>2+</sup> Core–Shell Silica Nanoparticles

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    The impact of nanotechnology on analytical science is hardly overlooked. In the search for ever-increasing sensitivity in biomedical sensors, nanoparticles have been playing a unique role as, for instance, ultrabright labels, and unravelling the intimate mechanisms which govern their functioning is mandatory for the design of ultrasentitive devices. Herein, we investigated the mechanism of electrogenerated chemiluminescence (ECL) in a family of core–shell silica–PEG nanoparticles (DDSNs), variously doped with a Ru­(bpy)<sub>3</sub><sup>2+</sup> triethoxysilane derivative, and displaying homogeneous morphological, hydrodynamic, and photophysical properties. ECL experiments, performed in the presence of 2-(dibutylamino)­ethanol (DBAE) as coreactant, showed two parallel mechanisms of ECL generation: one mechanism (I) which involves exclusively the radicals deriving from the coreactant oxidation and a second one (II) involving also the direct anodic oxidation of the Ru­(II) moieties. The latter mechanism includes electron (hole) hopping between neighboring redox centers as evidenced in our previous studies and supported by a theoretical model we have recently proposed. Quite unexpectedly, however, we found that the efficiency of the two mechanisms varies in opposite directions within the DDSNs series, with mechanism I or mechanism II prevailing at low and high doping levels, respectively. Since mechanism II has an intrinsically lower efficiency, the ECL emission intensity was also found to grow linearly with doping only at relatively low doping levels while it deviates negatively at higher ones. As the ζ-potential of DDSNs increases with the doping level from negative to slightly positive values, as a likely consequence of the accumulating cationic charge within the silica core, we attributed the observed change in the ECL generation mechanism along the DDSN series to a modulation of the electrostatic and hydrophobic/hydrophilic interactions between the DDSNs and the radical cationic species involved in the ECL generation. The results we report therefore show that the ECL intensity of a nanosized system cannot be merely incremented acting on doping, since other parameters come into play. We think that these results could serve as valuable indications to design more efficient ECL nano- and microsized labels for ultrasensitive bioanalysis

    New Approaches toward Ferrocene–Guanine Conjugates: Synthesis and Electrochemical Behavior

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    Different substituted ferrocene–guanine conjugates were prepared, and their electrochemical behavior was investigated. A new approach for the introduction of ferrocene in guanine’s 9-position through a quite effective S<sub>N</sub>1-type reaction was disclosed. The electrochemical behavior of the various derivatives can be used as standard for the quantification and analysis of DNA strands

    Efficient Photoinduced Charge Separation in a BODIPY–C<sub>60</sub> Dyad

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    A donor–acceptor dyad composed of a BF<sub>2</sub>-chelated dipyrromethene (BODIPY) and a C<sub>60</sub> fullerene has been newly synthesized and characterized. The two moieties are linked by direct addition of an azido substituted BODIPY on the C<sub>60</sub>, producing an imino–fullerene–BODIPY adduct. The photoinduced charge transfer process in this system was studied by ultrafast transient absorption spectroscopy. Electron transfer toward the fullerene was found to occur selectively exciting both the BODIPY chromophore at 475 nm and the C<sub>60</sub> unit at 266 nm on a time scale of a few picoseconds, but the dynamics of charge separation was different in the two cases. Eletrochemical studies provided information on the redox potentials of the involved species and spectroelectrochemical measurements allowed to unambiguously assign the absorption band of the oxidized BODIPY moiety, which helped in the interpretation of the transient absorption spectra. The experimental studies were complemented by a theoretical analysis based on DFT computations of the excited state energies of the two components and their electronic couplings, which allowed identification of the charge transfer mechanism and rationalization of the different kinetic behavior observed by changing the excitation conditions

    Highly Sensitive Electrochemiluminescent Nanobiosensor for the Detection of Palytoxin

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    Marine toxins appear to be increasing in many areas of the world. An emerging problem in the Mediterranean Sea is represented by palytoxin (PlTX), one of the most potent marine toxins, frequently detected in seafood. Due to the high potential for human toxicity of PlTX, there is a strong and urgent need for sensitive methods toward its detection and quantification. We have developed an ultrasensitive electrochemiluminescence-based sensor for the detection of PlTX, taking advantage of the specificity provided by anti-PlTX antibodies, the good conductive properties of carbon nanotubes, and the excellent sensitivity achieved by a luminescence-based transducer. The sensor was able to produce a concentration-dependent light signal, allowing PlTX quantification in mussels, with a limit of quantification (LOQ = 2.2 μg/kg of mussel meat) more than 2 orders of magnitude more sensitive than that of the commonly used detection techniques, such as LC-MS/MS
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