Functionalization of Si(1 0 0) with ferrocene derivatives via “click” chemistry

We prepared ferrocene-modified silicon surfaces through a three-step procedure consisting of the photochemical anchoring of 11-bromo-1-undecene on H-Si(1 0 0), followed by treatment with NaN₃ and by a reaction with ethynylferrocene via azide-alkyne Huisgen cycloaddition reaction, also known as “click” chemistry. The advantages of this approach are multiple: the synthetic approach is flexible, provided a CC tethering arm is present on the molecule of interest; a self-assembled hydrocarbon chain can guarantee a good coverage and resistance to the further synthetic steps; the redox centers are located at the outer surface, where a good contact with the electrolyte becomes possible. We have monitored the progression of the reaction steps by XPS, and characterized the resulting new hybrid on Si by electrochemical methods. The presence and chemical nature of the redox species covalently attached to the SAM on Si has been evaluated by XPS, while the overall coverage has been calculated by CV measurements. A reversible electrochemical response has been evidenced for the hybrids and the progressive ageing followed at thousands of oxidation-reduction cycles.     

Nucleic acid amplification of individual molecules in a microfluidic device

A microfluidic device was developed that enabled rapid polymerase chain reaction (PCR) analysis of individual DNA molecules. The device combined a means for accessing samples serially from a microtiter plate, channels for assembling eight parallel PCR reactions, and integrated resistive heaters for rapid thermocycling (>5 degrees C/s heating, >7 degrees C/s cooling) of samples as they flowed continuously through PCR channels. Amplification was monitored by fluorescence detection of Taqman probes. The long, narrow channels (10 microm x 180 microm x 40 mm) allowed sufficient separation between neighboring DNA templates to enable amplification of discreet DNA molecules. The functionality of the device was demonstrated by reproducibly amplifying a 2D6.6 CYP450 template and distinguishing between wild-type and mutant sequences using Taqman probes. A comparison of the rate of individual amplification events to the expected Poisson distribution confirmed that the device could reliably analyze individual DNA molecules. This work establishes the feasibility of rapid, single-molecule interrogation of nucleic acids.     

Dynamic infrared study of polyphenylene sulfide using planar array infrared spectroscopy

Planar array infrared (PA-IR) spectroscopy was used to study polyphenylene sulfide (PPS) at room temperature during the application of a sinusoidal elastic deformation. All of the intensity in the dynamic spectra was contained within the in-phase spectrum, which was expected since the measurements were carried out at room temperature, far below the glass transition temperature. The contributions of chain orientation, sample thinning, and stress-induced band shifts were separated in the dynamic spectra. It was found that the effects of chain orientation and sample thinning canceled each other out. Stress-induced band shifts far below the spectral resolution, on the order of 0.01 cm(-1), were quantified and used to calculate the stress optical coefficients and mode Gruneisen parameters for PPS.     

Influence of the crack morphology on the fatigue crack growth rate: A continuously-kinked crack model based on fractals

Threshold condition and rate of fatigue crack growth appear to be significantly affected by the degree of deflection of cracks. In the present paper, the reduction of the fatigue crack growth rate for a so-called ‘periodically-kinked crack’ as compared to that for a straight counterpart is quantified via the Paris–Erdogan law modified according to some simple theoretical arguments. It is shown that such a reduction increases as the value of the kinking angle increases. Then, a so-called ‘continuously-kinked crack’ (the kink length tends to zero) is considered and modelled as a self-similar invasive fractal curve. The sequence of kinking angles in the crack is such that the fatigue crack path is ‘on average’ straight. Using the Richardson’s expression for self-similar fractals, the fractal dimension of the crack is expressed as a function of the kinking angle. It is shown that the fatigue crack growth rate in the Paris range depends not only on the above fractal dimension and in turn on the kinking angle, but also, in an explicit fashion, on the crack length. Some experimental results related to concrete and showing a crack size effect on the fatigue crack growth rate are analysed.     

Count-rate analysis from clinical scans in PET with LSO detectors

The purpose of optimising the acquisition parameters in positron emission tomography is to improve the quality of the diagnostic images. Optimisation can be done by maximising the noise equivalent count rate (NECR) that in turn depends on the coincidence rate. For each bed position the scanner records coincidences and singles rates. For each patient, the true, random and scattered coincidences as functions of the single count rate(s) are determined by fitting the NEMA (National Electrical Manufacturers Association) 70 cm phantom count rate curves to measured clinical points. This enables analytical calculation of the personalised PNECR [pseudo NECR(s)] curve, linked to the NECR curve. For central bed positions, missing activity of approximately 70% is estimated to get maximum PNECR (PNECR(max)), but the improvement in terms of signal-toz-noise ratio would be approximately 15%. The correlation between patient weight and PNECR(max) is also estimated to determine the optimal scan duration of a single bed position as a function of patient weight at the same PNEC. Normalising the counts at PNECR(max) for the 70 kg patient, the bed duration for a 90 kg patient should be 230 s, which is approximately 30% longer. Although the analysis indicates that the fast scanner electronics allow using higher administered activities, this would involve poor improvement in terms of NECR. Instead, attending to higher bed duration for heavier patients may be more useful.     

Synthesis and Biological Evaluation of CTP Synthetase Inhibitors as Potential Agents for the Treatment of African Trypanosomiasis

Acivicin analogues with an increased affinity for CTP synthetase (CTPS) were designed as potential new trypanocidal agents. The inhibitory activity against CTPS can be improved by increasing molecular complexity, by inserting groups able to establish additional interactions with the binding pocket of the enzyme. This strategy has been pursued with the synthesis of α‐amino‐substituted analogues of Acivicin and N1‐substituted pyrazoline derivatives. In general, there is direct correlation between the enzymatic activity and the in vitro anti‐trypanosomal efficacy of the derivatives studied here. However, this cannot be taken as a general rule, as other important factors may play a role, notably the ability of uptake/diffusion of the molecules into the trypanosomes.     

Confocal ultrafast pump-probe spectroscopy: a new technique to explore nanoscale composites

This article is devoted to the exploration of the benefits of a new ultrafast confocal pump-probe technique, able to study the photophysics of different structured materials with nanoscale resolution. This tool offers many advantages over standard stationary microscopy techniques because it directly interrogates excited state dynamics in molecules, providing access to both radiative and non-radiative deactivation processes at a local scale. In this paper we present a few different examples of its application to organic semiconductor systems. The first two are focussed on the study of the photophysics of phase-separated polymer blends: (i) a blue-emitting polyfluorene (PFO) in an inert matrix of PMMA and (ii) an electron donor polythiophene (P3HT) mixed with an electron acceptor fullerene derivative (PCBM). The experimental results on these samples demonstrate the capability of the technique to unveil peculiar interfacial dynamics at the border region between phase-segregated domains, which would be otherwise averaged out using conventional pump-probe spectroscopy. The third example is the study of the photophysics of isolated mesoscopic crystals of the PCBM molecule. Our ultrafast microscope could evidence the presence of two distinctive regions within the crystals. In particular, we could pinpoint for the first time areas within the crystals showing photobleaching/stimulated emission signals from a charge-transfer state.     

Antibody phage display libraries: contributions to oncology

Since the advent of phage display technology, dating back to 1985, antibody libraries displayed on filamentous phage surfaces have been used to identify specific binders for many different purposes, including the recognition of tumors. Phage display represents a high-throughput technique for screening billions of random fusion antibodies against virtually any target on the surface or inside cancer cells, or even soluble markers found in patient serum. Many phage display derived binders targeting important tumor markers have been identified. Selection directed to tumoral cells' surfaces lead to the identification of unknown tumoral markers. Also the improvement of methods that require smaller amounts of cells has opened the possibility to use this approach on patient samples. Robust techniques combining an antibody library displayed on the phage surface and protein microarray allowed the identification of auto antibodies recognized by patient sera. Many Ab molecules directly or indirectly targeting angiogenesis have been identified, and one of them, ramucirumab, has been tested in 27 phase I-III clinical trials in a broad array of cancers. Examples of such antibodies will be discussed here with emphasis on those used as probes for molecular imaging and other clinical trials.     

Increasing the X-ray Diffraction Power of Protein Crystals by Dehydration: The Case of Bovine Serum Albumin and a Survey of Literature Data

Serum albumin is one of the most widely studied proteins. It is the most abundant protein in plasma with a typical concentration of 5 g/100 mL and the principal transporter of fatty acids in plasma. While the crystal structures of human serum albumin (HSA) free and in complex with fatty acids, hemin, and local anesthetics have been characterized, no crystallographic models are available on bovine serum albumin (BSA), presumably because of the poor diffraction power of existing hexagonal BSA crystals. Here, the crystallization and diffraction data of a new BSA crystal form, obtained by the hanging drop method using MPEG 5K as precipitating agent, are presented. The crystals belong to space group C2, with unit-cell parameters a = 216.45 Å, b = 44.72 Å, c = 140.18 Å, β = 114.5°. Dehydration was found to increase the diffraction limit of BSA crystals from ~8 Å to 3.2 Å, probably by improving the packing of protein molecules in the crystal lattice. These results, together with a survey of more than 60 successful cases of protein crystal dehydration, confirm that it can be a useful procedure to be used in initial screening as a method of improving the diffraction limits of existing crystals.