Immobilized DNA aptamers as target-specific chiral stationary phases for resolution of nucleoside and amino acid derivative enantiomers

Recently, we described the use of a DNA aptamer as a new target-specific chiral stationary phase (CSP) for the separation of oligopeptide enantiomers (Michaud, M.; Jourdan, E.; Villet, A.; Ravel, A.; Grosset, C.; Peyrin, E. J. Am. Chem. Soc. 2003, 125, 8672). However, from a practical point of view, it was fundamental to extend the applicability of such target-specific aptamer CSP to the resolution of small (bioactive) molecule enantiomers. In this paper, immobilized DNA aptamers specifically selected against D-adenosine and L-tyrosinamide were used to resolve the enantiomers by HPLC, using microbore columns. At 20 degrees C, the adenosine enantioseparation was similar to that classically reported with imprinted CSPs (approximately 3.5) while a very high enantioselectivity was observed for the tyrosinamide enantiomers (the nontarget enantiomer was essentially nonretained on the CSP). The influence of temperature on solute binding and chiral discrimination was analyzed. The binding enthalpic contributions were determined from linear van't Hoff plots. Very large DeltaH values were obtained for the target enantiomers (-71.4 +/- 0.7 kJ/mol for D-adenosine and -139.4 +/- 2.0 kJ/mol for L-tyrosinamide). Such values were consistent with the formation of a tight complex between these analytes and the aptamer CSPs. This work demonstrates that target-specific aptamer CSPs constitute a powerful tool for the resolution of small (bioactive) molecule enantiomers.     

Resilience of super users’ mental models of enterprise-wide systems

Research on information system training has focused primarily on methods, while neglecting the effects of interruption intervals between training and system implementation. This empirical study examines the resilience of accurate mental models of an enterprise-wide system in a large health care facility. Accurate mental models were shown to withstand the passage of time and resulted in superior field performance following a crash conversion. Consistent with prior experimental research, certain types of learners were more likely to acquire these sounder mental models. In large organisations where the simultaneous training of users on a complex system is virtually impossible, scheduling is an important facet of the training paradigm. The main practical implications of this study involve the development of: (1) training programmes emphasising performance on far-transfer tasks, (2) training schedules designed to minimise knowledge erosion, and (3) criteria for selecting highly capable super users.     

Eco-friendly TiO2–AC Photocatalyst for the Selective Photooxidation of 4-Chlorophenol

The influence of surface pH of activated carbon on selectivity of TiO₂ during the photooxidation of 4-chlorophenol on UV-irradiation was studied. Chlorine substitution by p-hydroxylation yielding hydroquinone in equilibrium with benzoquinone and o-hydroxylation to 4-chlorocathecol were detected as the main intermediates in the photooxidation of 4CP. Changes in surface pH of carbons from basic to closely neutral induce a remarkably increase in the production of 4-chlorocatechol by a factor of 22 on TiO₂–AC in comparison of TiO₂ alone. A mechanism of interaction between both solids is proposed to explain changes both in photoactivity and photoselectivity of TiO₂. In conclusion, results showed that TiO₂–AC can be used as an alternative green photocatalyst in organic synthesis.     

Isolation and characterization of inositol sphingophospholipids from Phytophthora parasitica Dastur

Several inositol sphingophospholipids (ISPL) were isolated from mycelia of Phytophthora parasitica Dastur, a phytopathogenic fungus of carnation. The ISPL structures were determined by fast atom bombardment. All ISPL consisted of ceramides linked to inositol phosphate. We investigated the effect of growth conditions on the ISPL produced in four different media that are commonly used for fungal cultures. We showed that P. parasitica Dastur synthesized four major classes of compounds with molecular weights of M_r=751, 807, 835, and 849 containing the 16:1 base and the 16:0 or 20:0 or 22:0 or 22h:1 N-acyl group. The relative abundance of the different ISPL is dependent on growth conditions. This work is dedicated to the memory of Professor G. Michel.     

High-Temperature, High-Pressure X-ray Investigation of Dicalcium Silicate

Energy-dispersive X-ray powder diffraction experiments have been investigated at high temperature and room pressure, and at high pressure and room temperature, starting from either γ- or β-Ca₂SiO₄. High-temperature studies were performed up to 1980 K, using a versatile heating cell. The high-temperature phase transformations previously described were reexamined. Volume and linear thermal expansions were measured for each Ca₂SiO₄ polymorph, γ, β, α';_L,α';_H, and α. Volume thermal expansion increases with increasing temperature except for α';_H, whose thermal expansion tends to decrease at elevated temperature. High-pressure investigations were performed in the 0–15 GPa pressure range, using a diamond anvil cell, with silicon oil as the pressure-transmitting medium. The value of the room-pressure bulk modulus K₀ , assuming a second-order BirchMurnaghan equation of state with K'₀= 4, is 140(8) GPa for γ-Ca₂SiO₄. The γ olivine form exhibits anisotropic compression, with the c axis as the most compressible. From such in situ high-pressure X-ray investigations, the γ-→Ca₂SiO₄ phase transformation induced by cold compression is clearly evidenced and extends from 2 to about 5 GPa.     

Transition to adulthood as a parent-youth project: Governance transfer, career promotion, and relational processes.

This study determined how youth (ages 17-21) and their parents jointly constructed and acted on goals and strategies pertinent to the transition to adulthood. Twenty parent-youth dyads were followed over an 8-month period using the qualitative action-project method. Data included their joint conversations, video recall of internal processes, self-monitoring logs, and researcher telephone monitoring. Detailed and repeated analysis of elements, functional steps, and goals resulted in the identification of an explicit joint project for each dyad that the participants saw as pertinent to the transition to adulthood. These projects referred broadly to the youth development of identity and social inclusion in the adult world and included the specific projects of career promotion, governance transfer, and parent-youth relational processes. The findings illustrate the complexity of the transition-to-adulthood process as well as its joint construction by parent and youth. Implications for practice include identifying and following the joint parent-youth transition project. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Local pH variation as an initial step in bacterial surface-sensing and biofilm formation

The development of surface-associated layers of matrix-embedded microbial populations, called biofilms, is a serious problem in many medical and industrial settings. These contaminations are difficult to eradicate because of the high resistance level acquired by the cells in their particular environment. From the very beginning of the colonization process, modifications of gene expression are observed and could, at least partially, explain biofilm resistance. In order to develop anti-biofilm molecules and surface treatments, it is of pivotal importance to identify the physico-chemical parameters which activate the sensor systems of pioneering microbes when they come into contact with a surface. The aim of our study was to examine the pH variations in the local micro-environment created between the cell layer and the surface after bacteria adhesion. Using an ion-sensitive field effect transistor (ISFET), as a substratum, colonized by a curli hyperproducing strain known to form biofilms, we observed that the evolution of the pH change was significantly different in the micro-compartment in contact with the electrochemical sensor compared to that within the liquid phase.     

Adaptive gain and delay mismatch cancellation for LINC transmitter

Linear amplification with Nonlinear Component (LINC) transmitter architecture is an efficient solution for high efficiency amplification of signals. Nonetheless, this solution suffers both from gain impairment and delay mismatch between the two signal paths. Indeed, a mismatch in propagation time between the paths degrades the quality of the transmit signal but also disrupts the convergence of the gain correction algorithm resulting in a degradation of its performance. In this paper, we present an adaptive algorithm based on a gradient descent formulation for the identification and correction of these delays. We also demonstrate its effectiveness when applied prior to the gain adjustment procedure. The identification approach is preferred here, to ensure monitoring facilities.     

In‐situ Remediation of Hydrogen Fluoride During a Detonation Event

Hydrogen fluoride (HF) is a known product from the combustion or detonation of explosives formulated with fluoropolymer binder systems. This presents the user with elevated risk levels during unintended combustion events or detonations in confined situations. In an effort to remediate the production of HF, calcium disilicide (CaSi₂) was added to explosive formulations and the amount of HF formed was monitored. Viton A/calcium disilicide mixtures were made and the thermal decomposition characteristics studied using thermal gravimetric/differential thermal analysis (TG/DTA). The activation energy ranged from 145–190 kJ mol⁻¹, indicative of C F scission in the Viton A binder prior to calcium fluoride formation. An energetic formulation was prepared which consisted of approximately a 5/3 mass ratio of Viton A/CaSi₂. Combustion calorimetry in oxygen and air, and subsequent analysis of the residues using X‐ray diffraction (XRD) showed evidence of calcium fluoride (CaF₂) formation. The decrease in HF formation was determined by trapping off gases and subsequent analysis in anion exchange chromatography of combustion and detonation products. Upon introduction of calcium disilicide into the formulation, a small decrease in HF formation was observed along with appearance of calcium fluoride and free Si in the residue. Such products are consistent with the mechanism following a general decomposition path of 2F⁻+CaSi₂→CaF₂+2Si. Under detonation conditions, the decomposition path followed nearly the same route with a net ca. 30 % decrease in HF formation, but with a portion of the silicon oxidizing slightly further to SiO₂.