Addition of p-azido-L-phenylalanine to the genetic code of Escherichia coli

We report the selection of a new orthogonal aminoacyl tRNA synthetase/tRNA pair for the in vivo incorporation of a photocrosslinker, p-azido-l-phenylalanine, into proteins in response to the amber codon, TAG. The amino acid is incorporated in good yield with high fidelity and can be used to crosslink interacting proteins.     

Stereoselective reductase-catalysed deoxygenation of sulfoxides in aerobic and anaerobic bacteria

Direct and indirect evidence, of unexpected stereoselective reductase-catalysed deoxygenations of sulfoxides, was found. The deoxygenations proceeded simultaneously, with the expected dioxygenase-catalysed asymmetric sulfoxidation of sulfides, during some biotransformations with the aerobic bacterium Pseudomonas putida UV4. Stereoselective reductase-catalysed asymmetric deoxygenation of racemic alkylaryl, dialkyl and phenolic sulfoxides was observed, without evidence of the reverse sulfoxidation reaction, using anaerobic bacterial strains. A purified dimethyl sulfoxide reductase, obtained from the intact cells of the anaerobic bacterium Citrobacter braakii DMSO 11, yielded, from the corresponding racemates, enantiopure alkylaryl sulfoxide and thiosulfinate samples.     

Clar valence bond representation of pi-bonding in carbon nanotubes

The application of the Clar aromatic sextet valence bond (VB) model to extended, defect-free single-walled carbon nanotubes (CNTs) with roll-up vectors (m, n) provides a real space model of their electronic structure. If m - n = 3k, where k is an integer, then all pi-electrons can be represented by aromatic sextets, and the CNT is fully benzenoid; the converse is also true. Since m - n = 3k is known to be a necessary criterion for conductivity in CNTs, only fully benzenoid CNTs are metallic, and only potentially metallic CNTs are fully benzenoid. This behavior contrasts with that of planar polycyclic aromatic hydrocarbons, in which the fully benzenoid structures are known to have large HOMO-LUMO gaps. For CNTs that are not fully benzenoid, e.g., m - n = 3k + l, where l = 1 or 2 and k is an integer, a seam of double bonds wraps about an otherwise benzenoid CNT at the chiral angle - 60 degrees or the chiral angle, respectively. Nucleus-independent chemical shift calculations on hydrogen-terminated CNT segments support this, and show that the magnetic manifestation of aromatic sextets is not due to electron correlation. The resonance hybrid of the Clar VB structures corresponds to patterns occasionally observed in scanning tunneling microscopy images of CNTs.     

Formation of ti(28) ln cages, the highest nuclearity polyoxotitanates (ln=la, ce)

The solvothermal reactions of Ti(OEt)(4) with LnCl(3) (Ln=La, Ce) produced new Ti(28) Ln cages, in which the Ln(3+) ions are coordinated within a metallocrown arrangement, which represents the highest nuclearity cages of this type.     

Secondary metabolites produced by fungi derived from a microbial mat encountered in an iron-rich natural spring

A collection of fungal isolates was obtained from a complex microbial mat, which occupied an iron-rich freshwater spring that feeds into Clear Creek, Golden, Colorado, USA. Two of the fungal isolates, a Glomeromycete (possibly Entrophospora sp.) and a Dothideomycete (possibly Phaeosphaeria sp.), were investigated for bioactive secondary metabolites. In total, six new compounds consisting of clearanols A-E (5, 6, 10-12) and disulochrin (7) were purified and their structures were determined. Disulochrin exhibited modest antibacterial activity against methicillin-resistant Staphylococcus aureus, whereas clearanol C showed weak inhibitory activity against Candida albicans biofilm formation.     

Thermal effects on energetics and dynamics in water cluster anions (H2O)n(-)

The electron binding energies and relaxation dynamics of water cluster anions (H(2)O)(n)(-) (11 ≤ n ≤ 80) formed in co-expansions with neon were investigated using one-photon and time-resolved photoelectron imaging. Unlike previous experiments with argon, water cluster anions exhibit only one isomer class, the tightly bound isomer I with approximately the same binding energy as clusters formed in argon. This result, along with a decrease in the internal conversion lifetime of excited (H(2)O)(n)(-) (25 ≤ n ≤ 40), indicates that clusters are vibrationally warmer when formed in neon. Over the ranges studied, the vertical detachment energies and lifetimes appear to converge to previously reported values.     

Exceptionally strong multiphoton-excited blue photoluminescence and lasing from ladder-type oligo(p-phenylene)s

We report the synthesis and investigation of multiphoton absorption properties of a novel series of diphenylamino-end-capped ladder-type oligo(p-phenylene)s which exhibit greatly enhanced and efficient multiphoton (from two- to five-photon) upconverted blue photoluminescence with which the record-high intrinsic three-photon absorption cross-section of 4.56 × 10(-76) cm(6) s(2) in the femtosecond regime has been obtained. Exceptionally efficient two- to five-photon-excited lasing in the blue region has also been demonstrated in which the highest two-photon-excited lasing efficiency of 0.34% has been achieved.     

Manganese carbonyl fluorides: are they viable molecules?

The mononuclear Mn(CO)(5)X and binuclear Mn(2)(CO)(8)(μ-X)(2) manganese carbonyl halides have long been known for the halogens Cl, Br, and I. However, the corresponding manganese carbonyl fluorides (X = F) remain unknown. The structures and thermochemistry of such manganese carbonyl fluorides and their decarbonylation products have now been investigated using density functional theory. In all cases singlet structures were found to have lower energies than the corresponding triplet structures. The expected octahedral structure is predicted for Mn(CO)(5)F. Decarbonylation of Mn(CO)(5)F is predicted to give trigonal bipyramidal Mn(CO)(4)F with equatorial fluorine. Further, decarbonylation gives tetrahedral Mn(CO)(3)F. All of the binuclear Mn(2)(CO)(n)F(2) structures (n = 8, 7, 6) are predicted to have a central Mn(2)F(2) unit with two bridging F atoms, a non-bonding Mn···Mn distance of ~3.1 ?, and exclusively terminal CO groups. The thermochemistry of these manganese carbonyl fluorides indicates that they are viable species. This suggests that the failure to date to synthesize the simple manganese carbonyl fluorides arises from a lack of a suitable synthetic method rather than from the instability of the desired products.