Synthese und Charakterisierung von Quecksilbercyanamid

Synthesis and Characterisation of Mercury Cyanamide HgCN₂ was prepared by double conversion of HgCl₂ with sodium cyanamide in aqueous solution. Its crystal structure has been determined using X‐ray powder data and refined by combined profile fits using X‐ray and neutron diffraction data (Pbca, Z = 8, a = 10.4851(1), b = 6.5138(1), c = 6.8929(1) Å; R_p (X‐ray) = 6.15%; R_p (neutrons) = 2.33; 2.43%). The cyanamide‐anion is bent (172.4(7)°), which has been confirmed by vibrational spectroscopy. Mercury and carbon form zigzag chains. Not including nitrogen, the structure is related to the MnP‐structure type.     

A Multifunctional Magnetic Material under Pressure

Fe^II(Metz)₆](Fe^IIIBr₄)₂ (Metz=1‐methyltetrazole) is one of the rare systems combining spin‐crossover and long‐range magnetic ordering. A joint neutron and X‐ray diffraction and magnetometry study allows determining its collinear antiferromagnetic structure, and shows an increase of the Néel temperature from 2.4 K at ambient pressure, to 3.9 K at 0.95 GPa. Applied pressure also enables a full high‐spin to low‐spin switch at ambient temperature.     

New Structural Motif for Carboxylic Acid Perhydrolases

Some serine hydrolases also catalyze a promiscuous reaction— reversible perhydrolysis of carboxylic acids to make peroxycarboxylic acids. Five X‐ray crystal structures of these carboxylic acid perhydrolases show a proline in the oxyanion loop. Here, we test whether this proline is essential for high perhydrolysis activity using Pseudomonas fluorescens esterase (PFE). The L29P variant of this esterase catalyzes perhydrolysis 43‐fold faster (k_cat comparison) than the wild type. Surprisingly, saturation mutagenesis at the 29 position of PFE identified six other amino acid substitutions that increase perhydrolysis of acetic acid at least fourfold over the wild type. The best variant, L29I PFE, catalyzed perhydrolysis 83‐times faster (k_cat comparison) than wild‐type PFE and twice as fast as L29P PFE. Despite the different amino acid in the oxyanion loop, L29I PFE shows a similar selectivity for hydrogen peroxide over water as L29P PFE (β₀=170 vs. 160 M ^?1), and a similar fast formation of acetyl‐enzyme (140 vs. 62 U mg^?1). X‐ray crystal structures of L29I PFE with and without bound acetate show an unusual mixture of two different oxyanion loop conformations. The type II β‐turn conformation resembles the wild‐type structure and is unlikely to increase perhydrolysis, but the type I β‐turn conformation creates a binding site for a second acetate. Modeling suggests that a previously proposed mechanism for L29P PFE can be extended to include L29I PFE, so that an acetate accepts a hydrogen bond to promote faster formation of the acetyl‐enzyme.     

The stuffed framework structure of SrP2N4: challenges to synthesis and crystal structure determination

SrP2N4 was obtained by high-pressure high-temperature synthesis utilizing the multianvil technique (5 GPa, 1400 degrees C) starting from mixtures of phosphorus(V) nitride and strontium azide. SrP2N4 turned out to be isotypic with BaGa(2)O(4) and is closely related to KGeAlO(4). The crystal structure (SrP2N4, a=17.1029(8), c=8.10318(5) A, space group P6(3) (no. 173), V=2052.70(2) A3, Z=24, R(F2)=0.0633) was solved from synchrotron powder diffraction data by applying a combination of direct methods, Patterson syntheses, and difference Fourier maps adding the unit cell information derived from electron diffraction and symmetry information obtained from 31P solid-state NMR spectroscopy. The structure of SrP2N4 was refined by the Rietveld method by utilizing both neutron and synchrotron X-ray powder diffraction data, and has been corroborated additionally by 31P solid-state NMR spectroscopy by employing through-bond connectivities and distance relations.     

The Structure of 2‐[(1S)‐(+)‐10‐camphorsulfonamino]‐6‐aminopyridine in the Solid State and in Solution; Unprecedented Cocrystallization of Four Stereoisomers

The solid and solution structures of a new optically active aminopyridine compound, 2‐[(1S)‐(+)‐10‐camphorsulfonamino]‐6‐aminopyridine [(S)‐csaap], 1 , are reported. Crystal data: space group P2₁, a = 8.9729 (5), b = 10.9447 (6), c = 36.693 (2) Å, β = 96.435 (1)°, V = 3580.8 (3) ų, Z = 8, R₁ = 0.0673 and wR₂ = 0.1600 with I > 2σ(I). This chiral compound shows an unprecedented cocrystallization of four stereoisomers, which are characterized by X‐ray crystallography and NMR spectroscopy.