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.     

A systematic experimental study of the vO—H…O and vO—D…O in bands of the H bonds of HCOOH and DCOOD crystals

The lineshape of the band corresponding to the stretching vibration v_O—H…O of the H atom in the H bonds of HCOOH crystals (and v_O—D…O in DCOOD crystals) is studied at various temperatures ranging from liquid helium temperature to?25°C. The complex structure of this band is analyzed in terms of elementary bands and a decomposition of the spectrum is proposed. This decomposition will be theoretically analyzed in a subsequent article.     

Anharmonicities of the vO---H…O and vO---D…O vibrations in formic acid crystals

The integrated transition probability, centre of gravity and mean square of the v_O---H…O (IR) band in formic acid crystal are calculated, assuming that the v_O---H…O vibration is ruled by a potential showing several kinds of anharmonicities: it is basically a Morse-type potential whose force constant at the origin and anharmonicity constant depend on a parameter representing the coordinate of a slow vibration. Besides these two anharmonicities (Morse + coupling with a slow vibration) we include in this potential a term representing resonance coupling between two H-bonds (or Fermi resonance with other vibrations of the molecule). We also include in the dipolar moment electrical anharmonicity. By comparison of the calculated results with the corresponding experimental quantities measured for the v_O---H…O and v_O---D…O bands of HCOOH, HCOOD, DCOOH and DCOOD crystals, as described in the preceding article, we can evaluate the orders of magnitude of these different anharmonic contributions, which are found to be all important. A discussion is given of this kind of approach.     

Reactivity of fluorostyrenes in cationic polymerization

Reactivity ratios relative for cationic copolymerization of three fluorostyrenes and styrene were studied. The values of r₁ and r₂ for various experimental conditions were determined. The influence of the nature of the solvent and of the polymerization temperature were studied in particular. Relative activation entropies and enthalpies were determined, and an isokinetic relationship was found for 2-, 3-, and 4-fluorostyrenes. There is a fairly linear correlation between the C8 chemical shift and the values of 1/r₂. All the experimental reactivities were correlated with the quantum chemistry parameters. From this correlation, interaction with C8 and also with C7 and F, was found to be possible, depending on the nature of the monomer.     

Synthese et etude de poly(ester-seq-ether)—III. Etude cinetique de la polycondensation d'oligomeres difonctionnels et de leurs modeles

The kinetics of the bulk catalysed and uncatalysed polycondensations of oligomeric ωω′ dihydroxy polyethers and ωω′ diacid polyesters are studied. A model reaction (condensation of octadecanoic acid with 1-octadecanol) is studied under the same conditions. For the model, without catalyst, the reaction order depends on the pressure. When a protonic catalyst is present, the reaction is second order and in the presence of Ti(OBu)₄ the overall order is 1 with respect to the reactants and 0.5 with respect to the catalyst. These results are compared to those of previous workers. For the oligomers, in the absence of added catalyst, the reaction is second order with respect to the acid and first order with respect to the alcohol; in the presence of Ti(OBu)₄, the reaction is first order with respect to the reactants. The rate constants and the activation enthalpies are reported.