Xanthomonins I–III: A New Class of Lasso Peptides with a Seven‐Residue Macrolactam Ring

Lasso peptides belong to the class of ribosomally synthesized and post‐translationally modified peptides. Their common distinguishing feature is an N‐terminal macrolactam ring that is threaded by the C‐terminal tail. This lasso fold is maintained through steric interactions. The isolation and characterization of xanthomonins I–III, the first lasso peptides featuring macrolactam rings consisting of only seven amino acids, is now presented. The crystal structure of xanthomonin I and the NMR structure of xanthomonin II were also determined. A total of 25 variants of xanthomonin II were generated to probe different aspects of the biosynthesis, stability, and fold maintenance. These mutational studies reveal the limits such a small ring imposes on the threading and show that every plug amino acid larger than serine is able to maintain a heat‐stable lasso fold in the xanthomonin II scaffold.     

Cs4[Sc6C]Cl13 und Cs4[Pr6(C2)]I13 — zwei Beispiele für das fehlende Bindeglied bei der Verknüpfung der Baueinheiten [M6Z]XX

Cs₄[Sc₆C]Cl₁₃ and Cs₄[Pr₆(C₂)]I₁₃ — Two Examples for the Missing Link in the Connectivity of [M₆Z]X X Building Units Cs₄[Sc₆C]Cl₁₃ (tetragonal, I4₁/amd, a = 1 540.5(4), c = 1 017.9(7) pm, c/a = 0.661, Z = 4, R = 0.038, R_w = 0.026) and Cs₄[Pr₆(C₂)]I₁₃ (a = 1 804.9(3), c = 1 259.5(3) pm, c/a = 0.698, R = 0.106, R_w = 0.068) are obtained as green-black and blue-black single crystals with brass-like metallic lustre through metallothermic reduction of ScCl₃ and PrI₃, respectively, with cesium in the presence of carbon in sealed tantalum containers. The, overall, isotypic compounds contain isolated [Sc₆C] and [Pr₆(C₂)] clusters, respectively, that are surrounded by 18 halide (X) ligands (12 Xⁱ and 6 X^a; X = Cl or I). The connection is carried out via the motif [M₆Z]XXXX (M = Sc and Pr; Z = C and C₂, respectively) and is thereby the missing link of the motifs of connection for the composition A_x[M₆Z]X₁₃. Analogous interconnection of [TiO₆] octahedra is found in the anatase-type of structure of TiO₂.     

Monoxidised Sulfur and Selenium Derivatives of 1,8‐Bis(diphenylphosphino)naphthalene: Synthesis and Coordination Chemistry

Treatment of 1,8‐bis(diphenylphosphino)naphthalene (dppn, 1 ) with stoichiometric amounts of sulfur or selenium in toluene at 80 °C selectively afforded the diphosphine monochalcogenides 1‐Ph₂P(C₁₀H₆)‐8‐P(:S)Ph₂ (dppnS, 2 a ) and 1‐Ph₂P(C₁₀H₆)‐8‐P(:Se)Ph₂ (dppnSe, 2 b ). The ³¹P{¹H} NMR spectrum of 2 b showed an unusually large ⁵J(P–Se) value, which indicates a significant through‐space coupling component. The monosulfide acted as a bidentate P,S‐ligand towards platinum(II) ( 3 a ), whereas the corresponding monoselenide complex ( 3 b ′) lost elemental selenium with formation of the previously reported complex [PtCl₂(dppn)‐P,P′] ( 3 ). Treatment of dppnSe with [(nor)Mo(CO)₄] (nor = norbornadiene) led to formation of [(dppnSe)Mo(CO)₄‐P,Se] ( 3 b ). Solutions of the latter slowly deposited Se with formation of [(dppn)Mo(CO)₄‐P,P′] ( 4 ) which was also obtained by independent synthesis from 1 and [(nor)Mo(CO)₄]. All isolated new compounds were characterised by a combination of ³¹P, ¹H, ¹³C and ⁷⁷Se ( 2 b ) NMR spectroscopy, IR spectroscopy, mass spectrometry and elemental analysis. Single‐crystal X‐ray structure determinations were performed for dppnSe ( 2 b ), [PtCl₂(dppnS)‐P,S] ( 3 a ), [(dppnSe)Mo(CO)₄‐P,Se] ( 3 b ) and [(dppn)Mo(CO)₄‐P,P′] ( 4 ). In 2 b steric effects cause the naphthalene ring to be distorted and force the phosphorus atoms by 65 and 59 pm to opposite sides of the best naphthalene plane. In the metal complexes 3 a , 3 b and 4 the phosphino‐phosphinochalcogenyl systems act as bidentate ligands through the P and the chalcogen atoms. The naphthalene systems are again distorted. The two independent molecules of 4 differ in their conformations.     

Bonding in a borylene complex investigated by photoionization and dissociative photoionization

The borylene complex [(OC)(5)Cr=B=N(SiMe(3))(2)] has been investigated by using threshold photoelectron-photoion coincidence spectroscopy with synchrotron radiation. The ionization energy of the parent complex and the 0?K appearance energies of the sequential CO loss channels have been determined. The derived bond-dissociation energies are used to discuss bonding and energetics in this compound.     

On the structure of amorphous calcium carbonate--a detailed study by solid-state NMR spectroscopy

The calcium carbonate phases calcite, aragonite, vaterite, monohydrocalcite (calcium carbonate monohydrate), and ikaite (calcium carbonate hexahydrate) were studied by solid-state NMR spectroscopy ( (1)H and (13)C). Further model compounds were sodium hydrogencarbonate, potassium hydrogencarbonate, and calcium hydroxide. With the help of these data, the structure of synthetically prepared additive-free amorphous calcium carbonate (ACC) was analyzed. ACC contains molecular water (as H 2O), a small amount of mobile hydroxide, and no hydrogencarbonate. This supports the concept of ACC as a transient precursor in the formation of calcium carbonate biominerals.     

Terahertz spectroscopy of oxygen, O2, in its Σg and Δ electronic states : THz Spectroscopy of O2

High precision rotational spectra of isotopic oxygen O₂ (with or ) in its electronic ground state have been measured in selected frequency regions between 0.4 and 2.0 THz. The main isotopic species, , was also investigated in its first excited electronic state . The new data, analyzed together with previous measurements, yielded improved spectroscopic parameters.