A new route to spirooxindoles

[reaction: see text]Reaction of indole amides 5 with tributylstannane gave spiroindolenines 9 which are readily converted into spiropyrrolidinyloxindoles. This tricyclic system is found in a number of interesting natural products.     

Kinetics of thermal depolymerization of trimethylsiloxy end-blocked polydimethylsiloxane and polydimethylsiloxane-N-phenylsilazane copolymer

The thermal degradation of Me₃SiO end-blocked polydimethylsiloxane (eb-PDMS) and polydimethylsiloxane-N-phenylsilazane (eb-PDMS–NPhSz) copolymer was studied. For both polymers relative degree of polymerization (DP /DP ₀) as a function of conversion (1 – W/W₀) data were obtained. For eb-PDMS the results were consistent with a mechanism involving a rate determining random siloxane bond cleavage initiation step followed by a rapid and complete depropagation of the active fragments evolving volatile cyclic oligomers. Rate constants (k) for initiation were obtained at four temperatures from plots of DP ^?1 vs. time. An Arrhenius activation energy of approximately 80 kcal/mol was determined and is consistent with a SiOSi scission transition state. The degradation of eb-PDMS–NPhSz appears to follow the same depolymerization process evolving cyclic oligomers. Although DP /DP ₀ vs. C data suggest a random cleavage–complete depolymerization mechanism, an Arrhenius plot suggests a more complex degradation mechanism. The role of impurities as degradation catalysts is discussed.     

Substituted γ-lactones: On the structural elucidation of the reaction products from 4-aroyl-3-hydroxy-2(5H)-furanones and 1,2-diamines

The reaction pathway of 4-aroyl-3-hydroxy-2(5H)-furanones 1 with diamines depends on the nature of the amine as well as on the applied reaction conditions. Thus, the reaction of 1a-d with 5,6-diamino-1,3-dimethyluracil 5 led to the formation of two isomeric Schiff bases 7a-d and 8a-d . Conversely type 1 compounds reacted with 4,5-diaminopyrimidine 9 or 2,3-diaminopyridine 10 to form the mono acid-base adducts 11a and 11b respectively. When type 1 compounds were reacted with aliphatic diamines 13a-d or p-phenylenediamine and p-xylenediamine, respectively also an immediate formation of acid-base adducts 15a-f was observed. The reaction of a number of O-methylated type 1 compounds with 1,2-ethylenediamine afforded the novel seven-membered ring compounds 18a-d in good yields. The analogous reaction of O-alkylated 1a with o-phenylenediamine 2 or 2,3-diaminonaphthalene gave the expected tricyclic ring systems 19 or 20 .     

Analysis of transient membrane protein interactions by single-molecule diffusional mobility shift assay

Various repertoires of membrane protein interactions determine cellular responses to diverse environments around cells dynamically in space and time. Current assays, however, have limitations in unraveling these interactions in the physiological states in a living cell due to the lack of capability to probe the transient nature of these interactions on the crowded membrane. Here, we present a simple and robust assay that enables the investigation of transient protein interactions in living cells by using the single-molecule diffusional mobility shift assay (smDIMSA). Utilizing smDIMSA, we uncovered the interaction profile of EGFR with various membrane proteins and demonstrated the promiscuity of these interactions depending on the cancer cell line. The transient interaction profile obtained by smDIMSA will provide critical information to comprehend the crosstalk among various receptors on the plasma membrane.Subject terms: Fluorescence imaging, Super-resolution microscopy, Single-molecule biophysics     

Solid state synthesis of copper(I) thiotungstate cluster compounds at low heating temperatures. Crystal structures of [(n-Bu)4N]3-[WS4Cu3Cl3Br] and [Et4N]4[WS4Cu4I6]

Summary Reaction of [NH₄]₂[WS₄] with CuX (X = Cl or I) and R₄NX (R = Et or n-Bu) in the solid state gave two new bimetallic compounds with W:Cu compositions from 1:3 to 1:4. Compound (1), [(n-Bu)₄N]₃[WS₄Cu₃Cl₃Br], crystallizes in the hexagonal space group R3c with a = 17.051(5), c = 38.372(5) Å, V = 9661.8 ų, Z = 6. The cluster anion of (1) comprises a cubane-like cluster core [WS₃Cu₃Br] of C₃ symmetry with a Cl atom attached to each of the three Cu atoms and one terminal sulphido ligand attached to the W atom. Compound (2), [Et₄N]₄[WS₄Cu₄I₆], crystallizes in the monoclinic space group C2/m with a = 29.702(6), b = 12.7887(5), c = 15.327(3)Å, = 99.69(2), V = 5738.1 ų, Z = 4. In the cluster anion of (2), four edges of the WS₄ core are coordinated by four Cu atoms, giving a WS₄Cu₄ aggregate of approximate C_2V symmetry.     

Oligoindole-based foldamers with a helical conformation induced by chloride

As a new type of foldamers, oligoindoles containing 4, 6, and 8 indole rings were synthesized, and their folding properties were characterized by a combination of 1H NMR techniques and UV/visible titration experiments. When chloride was added, the NH signals of the oligoindoles were downfield shifted as a result of hydrogen-bond formation, and the aromatic signals were upfield shifted by stacking between two indoles. Moreover, the ROESY experiment provided definitive NOE evidence for the helical stacking in the presence of chloride. Finally, the UV/visible titration experiments demonstrated that the oligoindoles formed 1:1 complexes with chloride, and the association constants greatly increased with increasing the number of the indole NHs. These observations are all consistent with the fact that oligoindoles adopt a helical conformation when complexed with chloride by hydrogen-bonding interactions.     

Density functional study of lithium-aromatic sandwich compounds and their crystals

Using density functional theory, we have theoretically studied the formation of neutral lithium-aromatic complexes R-nLi and R-nLi-R, where R is benzene, naphthalene, or pyrene. We first find that the maximum number of lithium atoms n in the complexes increases with the size of R. In addition, pyrene favors the sandwich compound R-4Li-R over R-4Li more than three times that of the corresponding tendency for benzene, strongly suggesting the possible existence of oligomer (R-4Li)x. We have also investigated energetics and band structures of infinite one-dimensional crystals of R-nLi, finding them metallic. Detailed analysis of the electronic structure shows that all these observations are related to the strong electrostatic interaction among the species, which is originated from the charge transfer from Li atoms to the aromatic rings. In addition, it is shown that the pyrene crystal is mechanically stable with respect to deformation. This also suggests the possibility of its existence, which, in turn, holds potential application in lithium storage in respect to its large Li/C ratio.     

Neutron diffraction study of [H(4)Co(4)(C(5)Me(4)Et)(4)], a tetrahedral metal cluster complex with four face-bridging hydride ligands

A single-crystal neutron diffraction analysis of the cluster complex [H(4)Co(4)(C(5)Me(4)Et)(4)] was carried out on the new quasi-Laue diffractometer VIVALDI at the Institut Laue-Langevin. The structure consists of four face-bridging hydrides attached to a tetrahedral cobalt metal core. Average distances and angles in the core of the molecule are as follows: Co-Co = 2.571(8), Co-C = 2.158(6), Co-H = 1.749(7), H.H = 2.366(9) A; Co-H-Co = 94.6(3), H-Co-H = 85.1(3) degrees. The hydride ligands are located off the Co-Co-Co planes by an average distance of 0.923(8) A. It is suggested that the dimensions of the HCo(3) fragments found in this molecule provide reasonable estimates for analogous distances and angles associated with chemisorbed H atoms situated on the 3-fold hollows of a cobalt surface. Crystallographic details: space group P2(1)/a (monoclinic); a = 21.979(2), b = 10.924(1), c = 34.406(2) A; beta = 90.81(1) degrees; Z = 8. Final agreement factor: R(F) = 0.099 for 3779 reflections [I > 2sigma(I)] collected at 20 K.     

Photoreactions of benzosilacyclobutenes with carbonyl compounds. SH2 reaction on SiC bond by triplet carbonyl compounds

Photoreaction of 2,3-benzo-1,1-diphenyl(or dimethyl)-1-sila-2-cyclobutene with an aldehyde or ketone results in 1:1 cycloadduct of [4+2] type, the formation of which is accountd for in terms of S_H2 process, i.e., attack of a triplet carbonyl compound on the silicon of the benzosilacyclobutene.     

XPS analysis of the effect of Pt addition to Pd catalysts for complete benzene oxidation

Pt-Pd bimetallic catalysts were prepared in order to develop and investigate catalysts having excellent activity and stability for benzene destruction. The effect of Pt addition to Pd catalysts is studied by XPS analysis. This revised version was published online in August 2006 with corrections to the Cover Date.