An alternative interpretation of the ultracold methylhydroxycarbene rearrangement mechanism: cooperative effects.

Recent studies have reported surprising results related to the rearrangement of carbenes under ultracold conditions, making use of sophisticated models of quantum tunnelling to explain the observed phenomena. Here, we demonstrate that a methylhydroxycarbene (H3C-C-OH) rearrangement is possible by making changes in molecularity (i.e., through cooperative effects), owing to intermolecular hydrogen bond/H-transfer. The model used for accomplishing these changes in molecularity suggests the occurrence of two chemical species during the rearrangement and preferential formation of acetaldehyde. We propose an alternative interpretation for the methylhydroxycarbene rearrangement, as well as for a bimolecular isomerization mechanism for acetaldehyde formation with an activation barrier, Ea, of +0.25 kcal mol(-1), relative to 1a' (−8.06 kcal mol(-1) relative to 1a); this barrier is lower than that required by H-tunnelling as proposed by Schreiner et al. We also note that the mechanism for obtaining vinyl alcohol leads to the simultaneous formation of acetaldehyde through an Ea of +13.53 kcal mol(-1), relative to 1a (+0.93 kcal mol(-1) relative to 1b), again confirming the predominant presence of acetaldehyde.

3,4-Methylenedioxypyrovalerone (MDPV) Sensing Based on Electropolymerized Molecularly Imprinted Polymers on Silver Nanoparticles and Carboxylated Multi-Walled Carbon Nanotubes.

3,4-methylenedioxypyrovalerone (MDPV) is a harmful and controlled synthetic cathinone used as a psychostimulant drug and as sport-enhancing substance. A sensor was developed for the direct analysis of MDPV by transducing its oxidation signal by means of an electropolymerized molecularly imprinted polymer (e-MIP) built in-situ on the screen-printed carbon electrode's (SPCE) surface previously covered with multi-walled carbon nanotubes (MWCNTs) and silver nanoparticles (AgNPs). Benzene-1,2-diamine was used as the functional monomer while the analyte was used as the template monomer. Each step of the sensor's development was studied by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) in a solution containing ferricyanide, however no redox probe was required for the actual MDPV measurements. The interaction between the poly(o-phenylenediamine) imprinted polymer and MDPV was studied by density-functional theory (DFT) methods. The SPCE-MWCNT-AgNP-MIP sensor responded adequately to the variation of MDPV concentration. It was shown that AgNPs enhanced the electrochemical signal by around a 3-fold factor. Making use of square-wave voltammetry (SWV) the developed sensor provided a limit of detection (LOD) of 1.8 µmol L-1. The analytical performance of the proposed sensor paves the way to the development of a portable device for MDPV on-site sensing to be applied in forensic and doping analysis.