Bis(trimethylphosphine)silver(I) hexafluorophosphate

In the title two‐coordinate silver compound, [Ag(C₃­H₉­P)₂]­PF₆, the cation has crystallographically imposed mirror symmetry, and approximates very closely to m (D_3d) symmetry with fully staggered methyl groups in the solid state. The Ag atom has a nearly linear coordination geometry, with a P—Ag—P angle of 178.70 (4)°. The Ag—P bond lengths are 2.3746 (12) and 2.3783 (12) Å, which are ­significantly longer than the Au—P bond length of 2.304 (1) Å in the analogous two‐coordinate gold cation. The lack of intra­molecular steric effects within the present cations containing tri­methyl­phosphine (cone angle 118°), compared with those in known cations containing trimesityl­phosphine (cone angle 212°), provides a better comparison of M—P distances and thus more conclusive evidence that Au really is smaller than Ag.     

A spectrophotometric method for the determination of nitrite

Nitrite reacts with dichromate quantitatively under suitable conditions of temperature and acid concentration. A linear relationship was found to exist between nitrite concentration and the absorbance at 580 nm of the chromium (III) species produced. This was used to determine the nitrite. The influence of a number of ions on the determination of nitrite was investigated; up to 100-fold excess nitrate has no influence on the determination of nitrite.     

Molecular Replacement Studies of Cucurmosin from Cucurbita Moschata:Structure Homology with Trichosanthin

1 INTRODUCTION Many plants contain proteins that are capable of inactivating ribosomes and therefore are called ribosome-inactivating proteins or RIPs[1]. RIPs are RNA N-glycosidases that inactivate ribosomes through a site-specific deadenylation of the large ribosomal RNA[2, 3]. RIPs are also capable of inactivating many nonribosomal nucleic acid substrates and can be considered as polynucleotide: adenosine glycosidases[4～6]. There are two types of RIPs: type I, single chain pr…     

Reaction of Silver Metaborate with Trimethyltin Bromide

The reaction between trimethyltin bromide and silvermetaboratc leads to the formation of trimethyltin metaborate, (CH₃)₃SnBO₂, and AgBr. The properties of the isolated new trimethyltin metaborate have also been studied. U.V. and I.R. spectra of (CH₃)₃SnBO₂ has also been recorded.     

Synthesis of mesocyclic and macrocyclic polythioethers using the cesium dithiolate technique

The mesocyclic trithioethers, 1,4,7-trithiacyclodecane, 1,4,7-trithiacycloundecane, 1,4,8-trithiacycloundecane, and 1,5,9-trithiacyclododecane; the mesocyclic trithioether ketones, 1,4,7-trithiacyclodecan-9-one; 1,4,8-trithiacycloundecan-6-one, and 1,5,9-trithiacyclododecan-3-one; and the mesocyclic trithioether alcohols, 1,4,7-trithiacyclodecan-9-ol, 1,4,8-trithiacycloundecan-6-ol, and 1,5,9-trithiacyclododecan-3-ol, have been synthesized using the cesium dithiolate technique. In some cases, the corresponding macrocyclic hexathioether was isolated from the reaction mixture in addition to the mesocyclic trithioether; 1,4,7,11,14,17-hexathiacycloeicosane, 1,4,7,11,14,17-hexathiacycloeicosan-9,19-dione, 1,4,7,12,15,18-hexathiacyclodocosane, and 1,5,9,13,17,21-hexathiacyclotetracosane. Single-crystal X-ray structures have been determined for 1,5,9-trithiacyclododecan-3-ol and 1,4,7,12,15,18-hexathiacyclodocosane. For 1,5,9-trithiacyclododecane-3-ol, the compound crystallizes in the monoclinic space group, C2/c, with a = 10.5926( 9 ) Å, b = 15.582(2) Å, c = 13.6015(8) Å, β = 98.186(6)⁰, Z = 8, and R = 0.038. The macrocycle, 1,4,7,12,15,18-hexathiacyclodocosane, crystallizes in the orthorhombic space group, Pbca, with a = 21.406(5) Å, b = 9.810(2) Å, c = 10.225(2) Å, Z = 4, and R = 0.020.     

A second generation dendrimer incorporating nine S2N2-donor macrocycles and its palladium(II) complex

A new second generation dendrimer incorporating nine S2N2-donor macrocyclic units that bind nine Pd(II) cations is reported.     

Analysis of the ketosynthase-chain length factor heterodimer from the fredericamycin polyketide synthase

The pentadecaketide fredericamycin has the longest carbon chain backbone among polycyclic aromatic polyketide antibiotics whose biosynthetic genes have been sequenced. This backbone is synthesized by the bimodular fdm polyketide synthase (PKS). Here, we demonstrate that the bimodular fdm PKS as well as its elongation module alone synthesize undecaketides and dodecaketides. Thus, unlike other homologs, the fdm ketosynthase-chain length factor (KS-CLF) heterodimer does not exclusively control the backbone length of its natural product. Using sequence- and structure-based approaches, 48 CLF multiple mutants were engineered and analyzed. Unexpectedly, the I134F mutant was unable to turn over but could initiate and partially elongate the polyketide chain. This unprecedented mutant suggests that the KS-CLF heterodimer harbors an as yet uncharacterized chain termination mechanism. Together, our findings reveal fundamental mechanistic differences between the fdm PKS and its well-studied homologs.