Continuous flow enzyme-catalyzed polymerization in a microreactor

Enzymes immobilized on solid supports are increasingly used for greener, more sustainable chemical transformation processes. Here, we used microreactors to study enzyme-catalyzed ring-opening polymerization of ε-caprolactone to polycaprolactone. A novel microreactor design enabled us to perform these heterogeneous reactions in continuous mode, in organic media, and at elevated temperatures. Using microreactors, we achieved faster polymerization and higher molecular mass compared to using batch reactors. While this study focused on polymerization reactions, it is evident that similar microreactor based platforms can readily be extended to other enzyme-based systems, for example, high-throughput screening of new enzymes and to precision measurements of new processes where continuous flow mode is preferred. This is the first reported demonstration of a solid supported enzyme-catalyzed polymerization reaction in continuous mode.     

Three types of mathematical representational translations: Comparing empirical and theoretical results

Previous research has investigated the representational translation practices of high school students, high school teachers, and college preservice teachers in various mathematical contexts including linear functions. Findings from qualitative research has frequently led to new notions about participant work and understanding. Many quantitative research has investigated the degree to which some in these populations correctly perform these translations. However, it seems that only infrequently have empirical research investigated findings from qualitative studies and vice versa, and findings regarding one population are rarely compared with findings of another population. This study (a) empirically explores the frequency of success of preservice teachers (N = 80) regarding representational translations in the context of linear functions, (b) quantifies results from previous qualitative, literature‐based research regarding high school students and teachers, and (c) quantitatively compares the results. This study demonstrates that some mathematical representational translations are more difficult than others.     

Acyclic stereoselection. 27. Simple diastereoselection in the lewis acid mediated reactions of enolsilanes with aldehydes.

The Lewis acid mediated reactions of enolsilanes 1–11 with benzaldehyde and isobutyraldehyde have been investigated. With the exception of compound 4, essentially no stereoselectivity is observed.     

The refractive index enhancement at Eg in narrow-gap semiconductors: comparison between the interband absorption edge and the oscillator model

A comparison is made between the refractive index enhancement near the M₀-type absorption edge in direct narrow-gap semiconductors and the dispersive structure of a Lorentz oscillator. Phenomenologically, both absorptive structures can be described by three parameters, and the analogy between both models concerning n(E) is discussed. Examples for the predicted dependencies are given. With increasing energy gap the n(E) enhancement becomes related to discrete excitonic bands rather than to free-to-free transitions, thereby undergoing a spectral shift from energies above gap to energies below gap.     

Theoretical calculation of the potential curves of the states of HF below 14 eV

Potential energy curves obtained through extensive ab initio configuration interaction calculations are reported for the states of HF below 14 eV as well as that for the ground state of HF⁺. Agreement with ultraviolet absorption data is obtained to within 0.2 eV. The disagreement between the reported UV absorption and electron scattering data is examined.     

Membrane admittance measurements under computer control

The application of the elegant Fourier transform method of Smith et al.^3,4 to measurements on ultrathin, “black” lipid membrane is described. A digital computer generates a waveform containing many frequencies, applies it to the measurement cell containing an artificial, ultrathin membrane, collects the resulting electrical response, extracts the cell admittance by a substitution method, and facilitates subsequent numerical data analysis. The performance of the instrument is illustrated.