Analytical performances of a DNA-ligand system using time-resolved fluorescence for the determination of ochratoxin A in wheat

The analytical performances of a novel DNA-ligand system using the time-resolved fluorescence (TRF) response of ochratoxin A (OTA)-terbium-DNA aptamer interaction were tested for the quantitative determination of OTA in wheat. Wheat was extracted with acetonitrile/water (60:40, v/v) followed by clean-up through affinity columns containing a DNA-aptamer-based oligosorbent. Then, OTA was detected by TRF spectroscopy after reaction with a terbium fluorescent solution containing the DNA-aptamer probe. The entire procedure was performed in less than 30 min, including sample preparation, and allowed analysis of several samples simultaneously with a 96-well microplate reader. The average recovery from samples spiked with 2.5-25 μg kg(-1) OTA was 77%, with a relative standard deviation lower than 6% and a quantification limit of 0.5 μg kg(-1). Comparative analyses of 29 naturally contaminated (up to 14 μg kg(-1)) wheat samples using the aptamer-affinity column/TRF method or the immunoaffinity column/high-performance liquid chromatography method showed good correlation (r = 0.985) in the range tested. The trueness of the aptamer-based method was additionally assessed by analysis of two quality control wheat materials for OTA. The DNA-ligand system is innovative, simple and rapid, and can be used to screen large quantities of samples for OTA contamination at levels below the EU regulatory limit with analytical performances satisfying EU criteria for method acceptability.     

High-frequency hearing in phocid and otariid pinnipeds: an interpretation based on inertial and cochlear constraints (L)

Audiograms in air and underwater, determined by previous workers for four pinniped species, two eared seals (Otariidae) and two phocids (Phocidae), are supplemented here by measurements on their middle ear ossicular mass, enabling mechanistic interpretations of high-frequency hearing and audiogram differences. Otariid hearing is not largely affected by the medium (air/water). This indicates that cochlear constraints limit high-frequency hearing in otariids. Phocids, however, have massive middle ear ossicles, and underwater hearing has radically shifted towards higher frequencies. This suggests that the high-frequency hearing of phocids in air is constrained by ossicle inertia.     

Unusual high exposure to ultraviolet-C radiation

UV radiation is known to cause acute and chronic eye and skin damage. The present case report describes a 90 min accidental exposure to UV-C radiation of 26 medical school students. Germicidal lamps were lit due to a malfunctioning of the timer system. Several hours after irradiation exposure, all subjects reported the onset of ocular symptoms, subsequently diagnosed as photokeratitis, and skin damage to the face, scalp and neck. While the ocular symptoms lasted 2-4 days, the sunburn-like condition produced significant erythema followed by deep skin exfoliation. The irradiation was calculated to be approximately 700 mJ cm(-2) absorbed energy, whereas the actual radiation emitted by the lamps was 0.14 mW cm(-2) (the radiometric measurements confirmed these calculi, because the effective irradiance measured from the height of the autopsy table to about 1 m under the UV-C lamp varied from 0.05 to 0.25 mW cm(-2)) but, more likely, the effective irradiance, according to skin phototype and symptoms, was between 50 and 100 mJ cm(-2). The ocular and skin effects produced by such a high irradiation (largely higher than that accepted by the American Conference of Governmental Industrial Hygienists [ACGIH] threshold limit values [TLVs]) appeared reversible in a relatively short time.     

Fundamental solution and sharp L p estimates for Laplace operators in the contact complex of Heisenberg groups

Abstract In this paper we construct a fundamental solution for the Laplace operator on the contact complex in Heisenberg groups (Rumin’s complex) relying on the notion of currents in given recently by Franchi, Serapioni and Serra Cassano. This operator is of order 2 on k intrinsic forms for k≠ n, but is of order 4 on n intrinsic forms. As an application, we prove sharp L^p a priori estimates for horizontal derivatives. Keywords: Heisenberg groups, Differential forms, Currents, Laplace operators, Fundamental solution Mathematics Subject Classification (2000): 43A80, 58A10, 58A25, 35A08     

Protein aggregation and misfolding: good or evil?

Protein aggregation and misfolding have important implications in an increasing number of fields ranging from medicine to biology to nanotechnology and material science. The interest in understanding this field has accordingly increased steadily over the last two decades. During this time the number of publications that have been dedicated to protein aggregation has increased exponentially, tackling the problem from several different and sometime contradictory perspectives. This review is meant to summarize some of the highlights that come from these studies and introduce this topical issue on the subject. The factors that make a protein aggregate and the cellular strategies that defend from aggregation are discussed together with the perspectives that the accumulated knowledge may open.     

Explaining the length threshold of polyglutamine aggregation

The existence of a length threshold, of about 35 residues, above which polyglutamine repeats can give rise to aggregation and to pathologies, is one of the hallmarks of polyglutamine neurodegenerative diseases such as Huntington's disease. The reason why such a minimal length exists at all has remained one of the main open issues in research on the molecular origins of such classes of diseases. Following the seminal proposals of Perutz, most research has focused on the hunt for a special structure, attainable only above the minimal length, able to trigger aggregation. Such a structure has remained elusive and there is growing evidence that it might not exist at all. Here we review some basic polymer and statistical physics facts and show that the existence of a threshold is compatible with the modulation that the repeat length imposes on the association and dissociation rates of polyglutamine polypeptides to and from oligomers. In particular, their dramatically different functional dependence on the length rationalizes the very presence of a threshold and hints at the cellular processes that might be at play, in vivo, to prevent aggregation and the consequent onset of the disease.     

The Shapes of Sulfonamides: A Rotational Spectroscopy Study

Benzenesulfonamides are a class of molecules of extreme interest in the biochemical field because many of them are active against a variety of diseases. In this work, the pharmacophoric group benzensulfonamide, its derivatives para-toluensulfonamide and ortho-toluensulfonamide, and the bioactive molecule sulfanilamide, were investigated using rotational spectroscopy to determine their conformations and the influence of different substituents on their structures. For all species, the hyperfine structure due to the ¹⁴N atom was analyzed, and this provided crucial information for the unambiguous identification of the observed conformation of all molecules. In addition, for ortho-toluensulfonamide, the vibration–rotation hyperfine structure related to the methyl torsion was analyzed, and the methyl group rotation barrier was determined. For benzensulfonamide, partial r_S and r₀ structures were established from the experimental rotational constants of the parent and two deuterated isotopic species. In all compounds except ortho-toluensulfonamide, the amino group of the sulfonamide group lies perpendicular to the benzene plane with the aminic hydrogens eclipsing the oxygen atoms. In ortho-toluensulfonamide, where weak attractive interactions occur between the nitrogen lone pair and the methyl hydrogen atoms, the amino group lies in a gauche orientation, retaining the eclipsed configuration with respect to the SO₂ frame. A comparison of the geometrical arrangements found in the PDB database allowed us to understand that the bioactive conformations are different from those found in isolated conditions. The conformations within the receptor are reached with an energy cost, which is balanced by the interactions established in the receptor.     

Single-Molecule Two-Color Coincidence Detection of Unlabeled alpha-Synuclein Aggregates

Protein misfolding and aggregation into oligomeric and fibrillar structures is a common feature of many neurogenerative disorders. Single-molecule techniques have enabled characterization of these lowly abundant, highly heterogeneous protein aggregates, previously inaccessible using ensemble averaging techniques. However, they usually rely on the use of recombinantly-expressed labeled protein, or on the addition of amyloid stains that are not protein-specific. To circumvent these challenges, we have made use of a high affinity antibody labeled with orthogonal fluorophores combined with fast-flow microfluidics and single-molecule confocal microscopy to specifically detect α-synuclein, the protein associated with Parkinson's disease. We used this approach to determine the number and size of α-synuclein aggregates down to picomolar concentrations in biologically relevant samples.     

ChemInform Abstract: Fullerene‐Like III—V Clusters: A Density Functional Theory Prediction.

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