The structures of the N-terminal domain of Ascaris hemoglobin and of several mutants have been determined at 2.2 A resolution. This perienteric hemoglobin from a parasitic nematode has an exceptionally high affinity for oxygen. It is an octameric protein containing two similar heme-binding domains per subunit. The recombinant monomelic N-tem1inal heme-binding domain (D 1) retains full oxygen avidity. Its structure reveals a ch';racteiistic globin fold. A strong hydrogen bond between tyrosine B 10 and the ligand distal oxygen, combined with a weak hydrogen bond between glutamine E7 and the proximal oxygen, grip the ligand in the bmdmg pocket. A third hydrogen bond between these t-vvo amino acids appears to stabilize the structure. Mutation of B 10 Y->L increases the oxygen dissociation rate of D l about 500 fold. Aninitial difference Fomier indicated negative density at the site of tvrosine B l 0, consistent with substitution by leucine: refinement ~f the model indicated little additional change in structure, confinning the importance of the strong hydrogen bond of the tyrosine hydroxyl to dioxygen. Mutation ofE7 Q->L increases the oxvgen off-rate 5-fold. Analysis of this mutant shows a slight reducti~I~ of the E7 side chain volume and the elimination of the hydrogen bonds both to the oxygen and the tyrosine. In addition, there appears to be a slight reorientation of the heme group toward the mutated side chain and a l.3A movement of the FG loop toward the exposed edge of the heme group. Mutation ofE7 Q->N increases the oxygen off-rate 50-fold. The mutated E7 Asn is too far from the oxyg~n to form a hydrogen bond, but a hydrogen bond to the B 10

Ruthenium-bipyridine complexes of molecular clips selfassemble in water to form scroll-and cigar-like nanostructures.

The step‐wise reaction of the cationic complex [(tpa)RhI(ethene)]+ (tpa=N,N,N‐tri(2‐pyridylmethyl)amine) with H2O2 and NH4+/MeCN gives a metallacyclic amide [Eq. (a)]. This new mode of C−N bond formation from a coordinated olefin might offer new possibilities for transition metal catalyzed amidation of olefins.

As ignificant amount of attention has been given to the design and synthesis of co-crystals by both industry and academia because of its potential to change am olecules physicochemical properties.Y et, difficulties arise when searching for adequate combinations of molecules (or coformers) to form co-crystals,h ampering the efficient exploration of the targetss olid-state landscape.T his paper reports on the application of ad ata-driven co-crystal prediction method based on two types of artificial neural network models and cocrystal data present in the Cambridge Structural Database.The models accept pairs of coformers and predict whether ac ocrystal is likely to form. By combining the output of multiple models of both types,o ur approach shows to have excellent performance on the proposed co-crystal training and validation sets,and has an estimated accuracy of 80 %for molecules for which previous co-crystallization data is unavailable.

The bulky ligands L(X)- (L(X) = (2,6-C6H3X2)NC(Me)CHC(Me)N(2,6-C6H3X2), X =Cl, Me) can be used to generate fluxional mononuclear arene complexes [L(X)Rh(eta4-arene)] (arene = benzene, toluene, m-xylene, mesitylene), which for X = Me disproportionate to fluxional dinuclear complexes [[L(Me)Rh]2(anti-mu-arene)]. For both mononuclear and dinuclear complexes, steric interactions do not stop the fluxionality but govern the preferred orientation of the methyl-substituted arenes, thus allowing indirect determination of the static NMR parameters. For the mu-arene complexes, two distinct types of fluxionality are proposed on the basis of calculations: ring rotation and metal shift. In the solid state, the toluene complex has an eta4(1,2,3,4):eta4(3,4,5,6)-bridged structure; the NMR analysis indicates that the benzene and m-xylene complexes have similar structures. The mesitylene complex, however, has an unprecedented eta3(1,2,3):eta3(3,4,5)-bridged structure, which is proposed to correspond to the transition state for arene rotation in the other cases. Steric factors are thought to be responsible for this reversal of stabilities.