Pyruvate formate-lyase (also called formate acetyltransferase; EC 2.3.1.54; PFI .) catalyses the thiolytic cleavage of pyruvate by CoA, yielding acetyl-CoA and formate. This reaction is the key step in the glucose-fermentation route in Escherichziz coli and various other bacteria. Operationally, it resembles the (B-keto)thiolase reaction of the fatty-acid degradation cycle. The mechanism of pyruvate formate-lyase, however, is fundamentally different, since the carbon-carbon bond of its substrate is cleaved homolytically rather than heterolytically. This property emerged with the discovery of a protein-based radical in the active enzyme form [ 11. The unpaired spin has recently been assigned to C-2 of (;lyi" [ 2 ] .The radical is produced by a postribosomal hydrogen-atom abstraction that is catalysed by PFI, activase using adenosylmethionine (AdoMet) and reduced flavodoxin as co-substrates [ 11. A separate reaction that quenches the protein radical in PFI, is catalysed by the multifunctional AdhE protein and is initiated when anaerobic cells are shifted to positive redox potentials [3].Metabolic aspects of PFI, interconversion between inactive (E) and active (Em) forms and the genetic/transcriptional background of the system have already been reviewed 141. This review will focus on enzyme-catalytic structure/function properties.

The development of a synthetic approach to a C3v -symmetric tris-salicylaldehyde based on triptycene is presented. The tris-salicylaldehyde is a versatile precursor for porous molecular materials, as demonstrated in the [4+4] condensation reaction with a triptycene triamine to form a molecular shape-persistent porous cube. The amorphous material of the molecular porous cube shows a very high surface area of 1014 m(2)  g(-1) (BET model) and a high uptake of CO2 (18.2 wt % at 273 K and 1 bar). Furthermore, during the multistep synthesis of the tris-salicylaldehyde precursor, a relatively rare (twofold) addition of the aryne to the anthracene in the 1,4- and 1,4,5,8-positions have been found during a Diels-Alder reaction, as proven by X-ray structure analysis.

In recent years, interest in shape‐persistent organic cage compounds has steadily increased, not least because dynamic covalent bond formation enables such structures to be made in high to excellent yields. One often used type of dynamic bond formation is the generation of an imine bond from an aldehyde and an amine. Although the reversibility of the imine bond formation is advantageous for high yields, it is disadvantageous for the chemical stability of the compounds. Amide bonds are, in contrast to imine bonds much more robust. Shape‐persistent amide cages have so far been made by irreversible amide bond formations in multiple steps, very often accompanied by low yields. Here, we present an approach to shape‐persistent amide cages by exploiting a high‐yielding reversible cage formation in the first step, and a Pinnick oxidation as a key step to access the amide cages in just three steps. These chemically robust amide cages can be further transformed by bromination or nitration to allow post‐functionalization in high yields. The impact of the substituents on the gas sorption behavior was also investigated.

Chiral self-sorting is intricately connected to the complicated chiral processes observed in nature and no artificial systems of comparably complexity have been generated by chemists.H owever,o nly af ew examples of purely organic molecules have been reported so far,w here the selfsorting process could be controlled. Herein, we describe the chiral self-sorting of large cubic [8+ +12] salicylimine cage compounds based on ac hiral TBTQ precursor.O ut of 23 possible cage isomers only the enantiopure and am eso cage were observed to be formed, whichhave been unambiguously characterized by single crystal X-raydiffraction. Furthermore, by careful choice of solvent the formation of meso cage could be controlled. With internal diameters of d in = 3.3-3.5 nm these cages are among the largest organic cage compounds characterizedand show very high specific surface areas up to approx. 1500 m 2 g À1 after desolvation.

In recent years the interest of shape-persistent organic cage compounds synthesized by dynamic covalent chemistry (DCC) has risen, because these cages are potentially interesting for gas sorption or -separation. One such reaction in DCC is the condensation of boronic acids with diols to form boronic esters. Most interestingly, the variety of geometries and sizes for boronic ester cages is much lower than that of, for example, imine-based cages. Here, a small series of shape-persistent [4+6] tetrahedral boronic ester cages is introduced. One cage has a high specific surface area of 511 m g and selectively adsorbs ethane over ethylene and acetylene.