New ammonium surfactant-stabilized rhodium(0) colloidal suspensions: influence of novel counter-anions on physico-chemical and catalytic properties

Novel anionic species, such as hydrogen carbonate (HCO(3)(?)), fluoride (F(?)), triflate (CF(3)SO(3)(?)), tetrafluoroborate (BF(4)(?)) and chloride (Cl(?)) were investigated as new partners of water soluble N,N-dimethyl-N-cetyl-N-(2-hydroxyethyl) ammonium salts, used as a protective agent of rhodium colloids. The effect of the surfactant polar head on the micellar behavior, size and morphology of the nanospecies was studied by adapted physico-chemical experiments (surface tension measurements, dynamic light scattering, thermogravimetric and TEM analyses) and discussed in terms of strong or weak stabilization of the growing nanoparticles surface. Finally, the influence of the nanoenvironment generated by the surfactant with various counter-anions was evaluated via the hydrogenation of aromatics.     

Fe3O4 nanoparticle-supported copper(I) pybox catalyst: magnetically recoverable catalyst for enantioselective direct-addition of terminal alkynes to imines

An Fe(3)O(4) nanoparticle-supported copper(I) pybox catalyst, which exhibits excellent reactivity and yields products with good enantioselectivity, was developed. As a proof of concept, six optically active propargyl amines were obtained in excellent yields. The catalyst can be magnetically removed and recycled easily six times without a decrease in activity or enantioselectivity.     

Development of an efficient protein phosphatase-based colorimetric test for okadaic acid detection

Okadaic acid (OA), responsible for gastrointestinal problems, inhibits protein phosphatase 2A (PP2A). Therefore, the inhibition exerted by the toxin on PP2A could be used to detect the presence of OA in aqueous solution and in shellfish sample.In this work, two commercial PP2As (from ZEU Immunotec and Millipore) and one produced by molecular engineering (from GTP Technology) were tested. Enzymes were used in solution and also immobilized within a polymeric gel. In solution, best performances were obtained using PP2A purchased from ZEU Immunotec (Spain). OA was detected in aqueous solution in concentration as low as 0.0124 μg L⁻¹ using the enzyme from ZEU Immunotec whereas the detection limits were 0.47 μg L⁻¹ and 0.123 μg L⁻¹ with PP2As from Millipore and GTP Technology, respectively. Considering that the immobilization step contributes to stabilize the PP2A activity, enzymes were entrapped within a photopolymer and an agarose gel. These different polymeric matrices were optimized, tested and compared. Agarose gel seems to be a good alternative to the photopolymer largely used in our group. For instance, the IC₅₀ value obtained with the test based on PP2A from ZEU Immunotec immobilized within an agarose gel was 1.98 μg L⁻¹. This value was 1.8-fold lower than those obtained with the photopolymer test using the same enzyme. The proposed test is sensitive, fast and does not require expensive equipment. To evaluate the efficiency of the assay, PP inhibition tests based on PP2A from ZEU Immunotec in solution or immobilized within a gel were used for OA detection in contaminated shellfish.     

An easily accessible Re-based catalyst for the selective conversion of methanol: evidence for an unprecedented active site structure through combined operando techniques

Heterogeneous Re/SiO(2) catalysts prepared using a one pot sol-gel synthesis were found to display high activity in the direct, selective methanol conversion to methylal, which is correlated to an unprecedented rhenium oxide structure.     

Recent progress in SERS biosensing

This perspective gives an overview of recent developments in surface-enhanced Raman scattering (SERS) for biosensing. We focus this review on SERS papers published in the last 10 years and to specific applications of detecting biological analytes. Both intrinsic and extrinsic SERS biosensing schemes have been employed to detect and identify small molecules, nucleic acids, lipids, peptides, and proteins, as well as for in vivo and cellular sensing. Current SERS substrate technologies along with a series of advancements in surface chemistry, sample preparation, intrinsic/extrinsic signal transduction schemes, and tip-enhanced Raman spectroscopy are discussed. The progress covered herein shows great promise for widespread adoption of SERS biosensing.     

Symbolic Drawings Reveal Changes in Preservice Teacher Mathematics Attitudes After a Mathematics Methods Course

A new method of analyzing mathematics attitudes through symbolic drawings, situated within the field of Jungian‐oriented analytical psychology, was applied to 52 preservice elementary teachers before and after a mathematics methods course. In this triangulation mixed methods design study, pretest images related to past mathematics experiences drawn by prospective teachers were 63.2% negative in tone, and listed associated emotions were 60.4% negative; on the posttest these changed significantly to 72.1% positive images, with 70.5% positive associated emotions. The qualitative analysis of images and preservice teacher interpretations of them indicate that mathematics anxiety decreased and motivation changed from extrinsic to intrinsic as a result of the course. Pretest images and interpretations focused primarily on grades, unhappiness, time and pressure, struggle, and lack of success. Posttest images and interpretations revealed (a) greater understanding of mathematical concepts through use of concrete materials; (b) greater engagement in mathematics through interesting activities and discourse with peers; and (c) a sense of accomplishment from teaching practicum lessons. Because the drawing exercise helped students connect with their previously unconscious images of mathematics, thereby helping to shift the mathematics anxiety complex toward a more positive affective state, it is recommended that these activities be part of mathematics methods courses.     

Fourier analysis,correlation functions and nonadiabatic electron transfer: Wavepackets and exact representations

Summary We investigate the validity of several common approximations in the analysis of nonadiabatic intramolecular electron transfer rate constants. Utilizing the Fourier representation of the golden rule form, we study the evolution of the vibrational correlation function that represents the density-of-states-weighted Franck-Condon factor. In particular, we test the validity of the perturbation theoretic golden rule form and of the Gaussian wavepacket representation for the vibrational wavefunctions against numerically exact quantum mechanical propagations. Although specific cases are found in which both of these break down, for a wide range of conditions (including anharmonic behavior and frequency changes), both the Gaussian wavepacket representation and the golden rule are excellent approximations.     

A new diatomics-in-molecules study of Li3 and Li4

The diatomics-in-molecules method, with an improved triplet diatomic curve for Li₂, is employed in a reexamination of the stability of Li₃ and Li₄ species. Results are compared to other theoretical and experimental values.     

Homotopy Algorithm for Optimal Control Problems with a Second-order State Constraint

This paper deals with optimal control problems with a regular second-order state constraint and a scalar control, satisfying the strengthened Legendre-Clebsch condition. We study the stability of structure of stationary points. It is shown that under a uniform strict complementarity assumption, boundary arcs are stable under sufficiently smooth perturbations of the data. On the contrary, nonreducible touch points are not stable under perturbations. We show that under some reasonable conditions, either a boundary arc or a second touch point may appear. Those results allow us to design an homotopy algorithm which automatically detects the structure of the trajectory and initializes the shooting parameters associated with boundary arcs and touch points.