Light Activation for the Versatile and Accurate Kinetic Analysis of Disassembly of Self‐Immolative Spacers

Three procedures that rely on photoactivation are introduced to accurately analyze the disassembly kinetics of a collection of self‐immolative spacer groups within the window 10^?2–10³ s. Our results are relevant for deriving quantitative structure–property relationships. In particular, we have been able to access 20 ms temporal resolution, which made possible the measurement of the shortest ever reported disassembly time for an activated self‐immolative spacer.     

A practical approach to new (5Z) 2-alkylthio-5-arylmethylene-1-methyl-1,5-dihydro-4H-imidazol-4-one derivatives

A practical protocol for the preparation of (5Z)-2-alkylthio-5-arylmethylene-1-methyl-1,5-dihydro-4H-imidazol-4-one derivatives is reported. The new compounds were obtained in good yield and stereoselectivity in two steps, namely a solvent-free Knoevenagel condensation under microwave irradiation, followed by an S-alkylation reaction with various halogenoalkanes.     

Detection of DNA damage in yolk-sac larvae of the Japanese Medaka, Oryzias latipes, by the comet assay

This study was set up to determine the suitability of the early life stage (ELS) alkaline comet assay for the detection of DNA strand breaks induced by genotoxicants in whole organism. This assay was performed on cells of medaka 2 days posthatch (dph). An efficient procedure for cell dissociation using enzymatic and mechanical digestion was developed. This protocol ensures 80% viability of cells and low DNA damage background. Cells from 2 dph medaka larvae were exposed in vitro to model genotoxicants, hydrogen peroxide, cadmium, and fluoranthene, followed by comet assay analysis. Results show a significant increase in the percentage of DNA damage of dissociated cells by all the tested compounds when compared to controls. The assay was also performed in vivo on medaka larvae (2 dph) exposed for 24 h to waterborne cadmium or fluoranthene. Significant induction of DNA damage levels were observed following larvae exposure to cadmium and fluoranthene at concentrations of 0.1 and 50 μM, respectively. This study demonstrates that cells of embryo life stage medaka respond to known DNA damaging agents and that the ELS comet assay may be a useful biomarker to detect DNA strand breakage in whole body of pluricellular organism induced by a range of agents. This technique may provide a sensitive, nonspecific endpoint of genotoxicity as part of ELS toxicity test.     

Autocatalyses

Autocatalysis is a fundamental concept, used in a wide range of domains. From the most general definition of autocatalysis, that is, a process in which a chemical compound is able to catalyze its own formation, several different systems can be described. We detail the different categories of autocatalyses and compare them on the basis of their mechanistic, kinetic, and dynamic properties. It is shown how autocatalytic patterns can be generated by different systems of chemical reactions. With the notion of autocatalysis covering a large variety of mechanistic realizations with very similar behaviors, it is proposed that the key signature of autocatalysis is its kinetic pattern expressed in a mathematical form.     

Opto-electronic properties of blue phosphorene oxide with and without oxygen vacancies

Blue phosphorene is an attractive nanomaterial that exhibits some remarkable optoelectronic properties. Various studies have verified its ability to adsorb gaseous compounds and, in particular, to dissociate O₂, forming covalent bonds between phosphorus and oxygen atoms. These covalent bonds could be the reason behind the oxidation reaction that affects the blue phosphorene in normal room conditions. Theoretically, it has been demonstrated that the blue phosphorene oxide (BPO) is just as stable as the blue phosphorene. Given that metallic oxides are widely used as catalyzers and gas sensors, this opens the possibility of the BPO being presented as a gas sensor as well. For all the above, in this work the optoelectronic properties of BPO were studied, along with the generation of the oxygen vacancies. The investigation was performed within the density functional theory (DFT). In the study of the oxygen vacancy, the formation energy was calculated, and the results are similar to the formation energies of oxygen vacancies in other known oxides. It was found that the BPO with a single vacancy has a favorable energetic stability. The characterization of the vacancy is achieved using the electronic structure and the optical response. Additionally, the analysis of the adsorption of a hydrogen atom on the BPO, and the subsequent formation of hydroxide is presented.     

Synthesis of Phosphorus Containing Polymers by Phase Transfer Catalysis (PTC). II. Experimental Design for Polycondensation in Liquid-Vapor System

Abstract

The simultaneous influence of four factors [reaction time (I), temperature (T), base concentration (c). molar ratio of the reagents (r)] on the yield (q) and on the inherent viscosity (qIv) of the product has been studied for the liquid-vapor system pol ycondensation of cyclohexyldichlorophosphonate (CDP) with bisphenol A (BA) by second order central composite circumscribed design. For a reasonable domain of the parameters [t = 30 ÷ 70 min., T = 20 ÷ 60 °C, c = 1 ÷ 5 mol/l, r = 1 ÷ 3.5 mol(CDP)/mol(BA)], designing the experiments, the η and η_iv values where determined in 31 synthesis (7 center points were used). In order to model the response (hyper)surfaces for η and η_iv, second order equations with interaction terms were used. Analyzing these model equations, T and c appear to be the most important factors, but acting in opposite way. Higher T resulted in greater yield and inherent viscosity. In the above defined domain the hypersurface of η presents a saddle point. From the sequential inspection of the dependence of η and η_iv on the different parameter pairs, using contour plots and 3D-plots [see for example the attached figure for the yield fimction of factors x2 (T) and x3 (c)] optimum conditions can be deduced for the desired good yield and great inherent viscosity. These are: long reaction time (70 min), high temperature (60 °C), low base concentration (1 mol/l) and high to moderate CDP excess.     

Interlocked optimization and fast gradient algorithm for a seismic inverse problem

We give a nonlinear inverse method for seismic data recorded in a well from sources at several offsets from the borehole in a 2D acoustic framework. Given the velocity field, approximate values of the impedance are recovered. This is a 2D extension of the 1D inversion of vertical seismic profiles [18]. The inverse problem generates a large scale undetermined ill-conditioned problem. Appropriate regularization terms render the problem well-determined. An interlocked optimization algorithm yields an efficient preconditioning. A gradient algorithm based on the adjoint state method and domain decomposition gives a fast parallel numerical method. For a realistic test case, convergence is attained in an acceptable time with 128 processors.     

Heterogeneous diffusion in a reversible gel

We introduce a microscopically realistic model of a physical gel and use computer simulations to study its static and dynamic properties at thermal equilibrium. The phase diagram comprises a sol phase, a coexistence region ending at a critical point, a gelation line determined by geometric percolation, and an equilibrium gel phase unrelated to phase separation. The global structure of the gel is homogeneous, but the stress is only supported by a fractal network. The gel dynamics is highly heterogeneous and we propose a theoretical model to quantitatively describe dynamic heterogeneity in gels. We elucidate several differences between the dynamics of gels and that of glass formers.     

Efficient measurement of linear susceptibilities in molecular simulations: application to aging supercooled liquids

We propose a novel method to measure time-dependent linear susceptibilities in molecular simulations, which does not require the use of nonequilibrium simulations, subtraction techniques, or fluctuation-dissipation theorems. The main idea is an exact reformulation of linearly perturbed quantities in terms of observables accessible in a single unperturbed trajectory. We apply these ideas to supercooled liquids in a nonequilibrium aging regime. We show that previous work had underestimated deviations from fluctuation-dissipation relations in the case of a Lennard-Jones system, while our results for silica are in qualitative disagreement with earlier results.