Distance Teaching in Chemistry: Opportunities and Limitations.

Remote teaching in the tertiary education sector is a relatively common practice, and the implementation of digital solutions in chemistry teaching offers many new opportunities and tools. A survey was conducted after 3 months of emergency remote teaching linked to the COVID-19 pandemic and showed that half of the students estimated it was difficult to study remotely, and reported they had to invest more time compared to classroom teaching, which led to a drop in motivation. Professors also noted that the time necessary to invest in order to produce digital teaching content was enormous. Massive open online laboratories (MOOLs) and process simulators are interesting tools, but practical lab work and related know-how cannot fully be replaced by digital techniques. Finally, it appeared that the professor-student interaction is very important in the distance-learning process, and that a high level of pedagogical (inter)activity is mandatory to maintain motivation and better quality of teaching and learning.

Reduction of ferricytochrome c catalyzed by optically active chromium(III) complexes.

The reduction rates of horse heart ferricytochrome c by amalgamated zinc or by electrolysis at fixed potential on a mercury pool as the cathode have been measured in a buffered solution at pH 7.5 by absorption spectrophotometry. In both cases, the reaction was strongly accelerated by the presence of the optically active complexes Lambda-[Cr(III)((S,S)-promp)H(2)O](+) (H(2)promp = N,N'-[(pyridine-2,6-diyl)bis(methylene)]-bis[(S)-proline]), Delta-[Cr(III)((R,R)-alamp)H(2)O](+) (H(2)alamp = N,N'-[(pyridine-2,6-diyl)bis(methylene)]-bis[(R)-alanine]) and Lambda-[Cr(III)((S,S)-alamp)(H(2)O)(2)](+). These were shown to undergo reversible one-electron reduction to the corresponding labile chromium(II) species by cyclic voltammetry (CV), although the diaquo Lambda-[Cr(III)((S,S)-alamp)(H(2)O)(2)](+) compound behaved differently than the two others. The cyclic voltammogram evidenced a strong catalytic reduction wave below -1.1 V/SHE overlapping with the Cr(3+)/Cr(2+) couple, which has been attributed to the catalytic reduction of hydroxonium ions to molecular hydrogen. Although stable in the second time range as demonstrated by CV, the chromium(II) complexes exist in solution only as short-lived species in the absence of protein and are rapidly reoxidized to the initial trivalent state, thus preventing their isolation even under anaerobic conditions. However, their lifetime was found to be long enough to catalyze the reduction of the ferric heme moiety of cytochrome c according to an electron-transfer-mediated reaction. Both chemical and electrochemical processes were found to follow zero-order kinetics. It could therefore be safely concluded that the rate-determining step is associated to the electron transfer from transient chromium(II) complexes to the protein and not to the in situ generation of the metallic reducing agent.

The proton complex of a diaza-macropentacycle: structure, slow formation, and chirality induction by ion pairing with the optically active 1,1'-binaphthyl-2,2'-diyl phosphate anion.

The protonation of a sterically crowded [N2S6] macropentacycle (1) with 1 equiv of CF3SO3H in CDCl3 is slow and gives the singly (oo(+) [1 x H](+)) and doubly (o(+)o(+) [1 x 2H](2+)) protonated forms as kinetic products, the i(+)o form of [1 x H](+) being the thermodynamic product. i(+)o [1 x H](+) is C3 helically chiral in the solid state and in solution. The barrier to racemization (DeltaG(double dagger)) of the [1 x H](+) propeller is >71 kJ mol(-1). The ammonium proton is encapsulated in the tetrahedral coordination sphere provided by the endo (i) nitrogen bridgehead atom and the three proximal thioether sulfurs, which makes [1 x H](+) a proton complex. Use of the optically active acid (R)-(-)- or (S)-(+)-1,1'-binaphthyl-2,2'-diyl hydrogen phosphate (BNPH) in chloroform allowed us to induce a significant diastereomeric excess (24% de), which produced a detectable ICD. The de was decreased in acetone-d6 (10%), suggesting that the sense of chirality of [1 x H](+) is controlled by ion-pair interactions. Detailed NMR studies allowed us to locate the chiral anion on the endo side of [1 x H](+), in the cavity lined by endo t-Bu groups, and to establish that the rate of anion exchange in [1 x H][(S,R)-(+/-)-BNP] was higher than the rate of propeller inversion of [1 x H](+).

Electron-transfer-mediated binding of optically active cobalt(III) complexes to horse heart cytochrome c.

Optically active cobalt(II) complexes are used as reducing agents in the electron-transfer reaction involving horse heart cytochrome c. Analysis of the circular dichroism (CD) spectra of reaction products indicates that the corresponding cobalt(III) species of both enantiomers of [CoII(alamp)] (H2alamp=N,N'-[(pyridine-2,6-diyl)bis(methylene)]-bis[alanine]) are partly attached to the protein during electron transfer by coordination to an imidazole unit of one of the histidine residues. His-26 and His-33 are both solvent exposed, and the results suggest that one of these histidine residues acts as a bridge in the electron transfer to and from the haem iron of cytochrome c. The reaction is enantioselective: the ratio of the relative reactivity at 15 degrees C is 2.9 in favour of the R,R-enantiomer. A small induced CD activity in the haem chromophore reveals that some structural changes in the protein occur consecutively with the binding of the cobalt(III) complex.