Production of Antibodies and Development of Specific Polarization Fluoroimmunoassay for Acetochlor

Specific polyclonal antibodies towards acetochlor (2-chloro- N -(ethoxymethyl)- N -(2-ethyl-6-methylphenyl)acetamide) were obtained from rabbits immunized against a 3-mercaptopropionic acid derivative of acetochlor, covalently attached to bovine serum albumin. A polarization fluoroimmuoassay (PFIA) based on these antibodies was developed and optimized to detect acetochlor in water samples. The optimized PFIA had a detection limit of 9 µg/L, linear working range from 50 to 5500 µg/L and within-assay coefficient of variation less than 4%. Cross-reactivity studies demonstrated that these antibodies are capable of specific detection of acetochlor amongst structurally related chloroacetanilide herbicides. Assay cross-reactivity values were: alachlor 0%, metolachlor 2.4%, propachlor 0%, butachlor 0.2% and dimethachlor 0.5%. Five organic solvents commonly used in sample extraction were evaluated for their effect on acetochlor PFIA performance, and methanol and ethanol were found to be compatible with the assay up to 10% v/v.     

Well‐Defined Molecular Magnesium Hydride Clusters: Relationship between Size and Hydrogen‐Elimination Temperature

A new tetranuclear magnesium hydride cluster, [{ NN ‐(MgH)₂}₂], which was based on a N? N‐coupled bis‐β‐diketiminate ligand ( NN ^2?), was obtained from the reaction of [{ NN ‐(MgnBu)₂}₂] with PhSiH₃. Its crystal structure reveals an almost‐tetrahedral arrangement of Mg atoms and two different sets of hydride ions, which give rise to a coupling in the NMR spectrum (J=8.5 Hz). To shed light on the relationship between the cluster size and H₂ release, the thermal decomposition of [{ NN ‐(MgH)₂}₂] and two closely related systems that were based on similar ligands, that is, an octanuclear magnesium hydride cluster and a dimeric magnesium hydride species, have been investigated in detail. A lowering of the H₂‐desorption temperature with decreasing cluster size is observed, in line with previously reported theoretical predictions on (MgH₂)_n model systems. Deuterium‐labeling studies further demonstrate that the released H₂ solely originates from the oxidative coupling of two hydride ligands and not from other hydrogen sources, such as the β‐diketiminate ligands. Analysis of the DFT‐computed electron density in [{ NN ‐(MgH)₂}₂] reveals a counterintuitive interaction between two formally closed‐shell H^? ligands that are separated by 3.106 Å. This weak interaction could play an important role in H₂ desorption. Although the molecular product after H₂ release could not be characterized experimentally, DFT calculations on the proposed decomposition product, that is, the low‐valence tetranuclear Mg(I) cluster [( NN ‐Mg₂)₂], predict a structure with two almost‐parallel, localized Mg? Mg bonds. As in a previously reported β‐diketiminate Mg^I dimer, the Mg? Mg bond is not characterized by a bond critical point, but instead displays a local maximum of electron density midway between the atoms, that is, a non‐nuclear attractor (NNA). Interestingly, both of the NNAs in [( NN ‐Mg₂)₂] are connected through a bond path that suggests that there is bonding between all four Mg^I atoms.     

Unzipping Nucleoside Channels by Means of Alcohol Disassembly

Gold nanoparticles capped with simple adenosine derivatives can form colloidal aggregates in nonpolar solvents. Theoretical calculations indicate the formation of organic channels by the supramolecular assembly of the nanoparticles by means of hydrogen bonds between the adenine moieties. The aggregates were only negligibly sensitive to nPrOH, iPrOH, and tBuOH, whereas some showed a similar response to MeOH and EtOH, and others showed high selectivity toward MeOH. DNA nucleoside derivatives (1‐(2‐deoxy‐β‐D ‐ribofuranosyl)‐5‐methyluracil and 2′,3′‐O‐isopropylideneadenosine) as well as thymine and other aromatic compounds such as pyrene derivatives (pyrene, 1‐chloropyrene, 1‐hydroxypyrene, (1‐pyrenyl)methanol, and 2‐hydroxynapthalene) did not induce disassembly of the nanoparticle aggregates. Data suggest that the nucleoside channels allow access to alcohols according to their size, and an efficient interaction between the alcohol and the adenine units destabilizes the hydrogen bonds, which eventually leads to nanoparticle disassembly.     

An improved capillary electrophoresis method for in vitro monitoring of the challenging early steps of Aβ1–42 peptide oligomerization: Application to anti‐Alzheimer's drug discovery

We report an improved CE method to monitor in vitro the self‐assembly of monomeric amyloid β‐peptide (42 amino acids amyloid β‐peptide, Aβ_1–42) and in particular the crucial early steps involved in the formation of the neurotoxic oligomers. In order to start the kinetics from the beginning, sample preparation was optimized to provide samples containing exclusively the monomeric form. The CE method was also improved using a dynamic coating and by reducing the separation distance. Using this method, the disappearance of the monomer as well as the progressive formation of four species during the self‐assembly process can now be monitored and quantified over time. The hydrodynamic radius of the species present at the initial kinetics step was estimated around 1.8 nm by Taylor dispersion analysis while SDS‐PAGE analyses showed the predominance of the monomer. These results confirmed that the Aβ_1–42 species present at this initial time was the monomer. Methylene blue, an anti‐Alzheimer disease candidate, was then evaluated. In spite of an oligomerization inhibition, the enhanced disappearance of the Aβ_1–42 monomer provoked by methylene blue was demonstrated for the first time. This method, allowing the monomeric and smallest oligomeric species to be monitored, represents a new accurate and precise way to evaluate compounds for drug discovery.     

Surface and Structural Properties of Gold Nanoparticles and Their Biofunctionalized Derivatives in Aqueous Electrolytes Solution

Gold nanoparticles reduced by sodium citrate (d ～ 10 nm) and purchased gold colloid particles (d ～ 500 nm) were examined and compared. The properties of both gold particles and their biofunctionalized derivatives with L-cysteine and L-glutathione were studied in the presence of sodium nitrate. The structural investigations indicated an aggregated inner structure.

The isoelectric points of pure gold, citrate reduced gold, and functionalized gold were measured and compared. The low isoelectric point of pure gold/water interface was explained by considering the distribution and accumulation of H⁺ and OH^? ions within the interfacial water layer, being more pronounced for OH^? ions.      

Size does matter! Label-free detection of small molecule–protein interaction

This review is focused on methods for detecting small molecules and, in particular, the characterisation of their interaction with natural proteins (e.g. receptors, ion channels). Because there are intrinsic advantages to using label-free methods over labelled methods (e.g. fluorescence, radioactivity), this review only covers label-free techniques. We briefly discuss available techniques and their advantages and disadvantages, especially as related to investigating the interaction between small molecules and proteins. The reviewed techniques include well-known and widely used standard analytical methods (e.g. HPLC-MS, NMR, calorimetry, and X-ray diffraction), newer and more specialised analytical methods (e.g. biosensors), biological systems (e.g. cell lines and animal models), and in-silico approaches.     

Grain shape influence on semiconducting metal oxide based gas sensor performance: modeling versus experiment

A model for sensing with semiconducting metal oxide (SMOX)-based gas sensors was developed which takes the effect of the shape of the grains in the sensing layers into account. Its validity is limited to materials in which the grains of the SMOX sensing layer are large enough to have an undepleted bulk region (large grains). This means that in all experimental conditions, the SMOX properties ensure that the influence of surface phenomena is not extended to the whole grain. The model takes the surface chemistry and its impact on the electrical properties of the sensing material into consideration. In this way, it relates the sensor signal—defined as the relative change of the sensor’s conductance—directly to the concentration of the target gas and also exhibits meaningful chemical parameters, such as the type of reactive oxygen species, the reaction constants, and the concentration of adsorption sites. The validity of the model is confirmed experimentally by applying it to data gathered by measuring homemade sensors in relevant conditions.     

Pyrene-Capped CdSe@ZnS Nanoparticles as Sensitive Flexible Oxygen Sensors in Non-Aqueous Media

A flexible, highly sensitive sensor of oxygen in non-aqueous solvents is described. It consists of CdSe/ZnS nanoparticles decorated with a considerable number of pyrene units, thus making the formation of the pyrene excimer possible. The emission of the pyrene excimer and that of the nanoparticle are suitably separated from each other and also from the excitation wavelength. This sensor can be applied as a ratiometric oxygen sensor by using the linear response of the pyrene excimer lifetime combined with the linear response of the nanoparticle excited state lifetime. This nanohybrid has been assayed in seven media with different dielectric constants and viscosities over the whole oxygen concentration range. In addition, the sensor versatility provides an easy way for monitoring oxygen diffusion through systems.