Synthesis of (-)-ilimaquinone via a radical decarboxylation and quinone addition reaction

[reaction: see text] A stereoselective synthesis of (-)-ilimaquinone (4) is presented. The synthetic strategy is based on a novel radical decarboxylation and quinone addition methodology that produces quinone 7 from reaction of thiohydroxamic acid derivative 8 with benzoquinone (9). Final functionalization of 7 to ilimaquinone (4) is achieved by exploring the electronic effects of the residual thiopyridyl group.     

Synthesis and thermal cyclization of an enediyne-sulfonamide

The synthesis of an enediyne sulfonamide by alkylidene carbene rearrangement is reported. The compound cyclizes thermally to give the Bergman product, which was prepared independently for comparison. Like other σ-acceptor substituents at the enediyne alkyne termini, such as fluoride, oxonium or ammonium groups, the sulfonamide moiety enhances the reactivity for thermal Bergman cyclization as shown by the cyclization kinetic of the title compound.     

Darstellung,struktur und eigenschaften des dreikernigen titankomplexes (π-C2H5)2TiClOTi(π-C5H5)ClOTiCl(π-C5H5)2·CHCl3

The trinuclear titanium(IV) complex (π-C₅H₅)₂TiClOTi(π-C₅H₅)ClOTiCl(π-C₅H₅)₂ · CHCl₃ is formed by hydrolysis of (π-C₅H₅)₂TiCl₂ at pH > 3.5 and can be isolated in the crystalline state from the reaction of (π-C₅H₅)₂TiCl₂ with Ag₂O and water in chloroform. Its structure is determined by X-ray analysis.     

Spectroscopy of hydrothermal reactions, 19: pH and salt dependence of decarboxylation of α‐alanine at 280–330°C in an FT‐IR spectroscopy flow reactor

The spontaneous decarboxylation of 0.5 m aqueous α‐alanine solutions as a function of pH (1–9 at 320°C, where neutrality is approximately 6) was determined with a flow reactor at 280–330°C and 275 bar by FT‐IR spectroscopy. The kinetics for the cationic and anionic forms have not been previously reported. The rate constants for the cationic form [CH₃(NH₃⁺)CHCO₂H], the anionic form [CH₃(NH₂)CHCO₂^?], and the zwitterion form [CH₃(NH₃⁺)CHCO₂^?] were obtained and followed the first‐order rate law. The rate of decarboxylation of the zwitterion is three times greater than that of the cationic and anionic forms in the temperature and pH ranges of study. The corresponding Arrhenius parameters were determined and compared with previously reported data. The addition of KCl (1 and 2 m) at the natural pH of α‐alanine resulted in a reduction of the decarboxylation rate, suggesting that the transition state is less polar than the zwitterion and/or that the activity of the zwitterion has been reduced. The α‐alanine solution is therefore somewhat more robust in solutions of high ionic strength, such as seawater, than it is in pure water. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 271–277, 2002     

Arsenidostannate mit Arsen-analogen [SnAs]-Schichten: Darstellung und Struktur von Na[Sn2As2], Na0,3Ca0,7[Sn2As2], Na0,6Sr0,6[Sn2As2], Na0,6Ba0,4[Sn2As2] und K0,3Sr0,7[Sn2As2]

Arsenidostannates with [SnAs] Nets Isostructural to Grey Arsenic: Synthesis and Crystal Structure of Na[Sn₂As₂], Na_0.3Ca_0.7[Sn₂As₂], Na_0.4Sr_0.6[Sn₂As₂], Na_0.6Ba_0.4[Sn₂As₂], and K_0.3Sr_0.7[Sn₂As₂] The metallic lustrous compounds Na[Sn₂As₂], Na_0.3Ca_0.7[Sn₂As₂], Na_0.4Sr_0.6[Sn₂As₂], Na_0.6Ba_0.4[Sn₂As₂] and K_0.3Sr_0.7[Sn₂As₂] were prepared from melts of mixtures of the elements. The compounds crystallize in the trigonal system (space group R3 m, No. 166, Z = 3) with lattice constants see in “Inhaltsübersicht”. The structures are isotypic to Sr[Sn₂As₂] containing puckered [SnAs] nets which are stacked with a sequence of six layers. The E(I)/E(II) atoms are located between each second [SnAs] layer in trigonal antiprismatic interstices formed by As atoms. In the resulting [Sn₂As₂] double layers the _∞²[SnAs] nets are stacked in such a way that additional Sn—Sn contacts arise.     

Detection of a biomarker for Alzheimer's disease from synthetic and clinical samples using a nanoscale optical biosensor

A nanoscale optical biosensor based on localized surface plasmon resonance (LSPR) spectroscopy has been developed to monitor the interaction between the antigen, amyloid-beta derived diffusible ligands (ADDLs), and specific anti-ADDL antibodies. Using the sandwich assay format, this nanosensor provides quantitative binding information for both antigen and second antibody detection that permits the determination of ADDL concentration and offers the unique analysis of the aggregation mechanisms of this putative Alzheimer's disease pathogen at physiologically relevant monomer concentrations. Monitoring the LSPR-induced shifts from both ADDLs and a second polyclonal anti-ADDL antibody as a function of ADDL concentration reveals two ADDL epitopes that have binding constants to the specific anti-ADDL antibodies of 7.3 x 10(12) M(-1) and 9.5 x 10(8) M(-1). The analysis of human brain extract and cerebrospinal fluid samples from control and Alzheimer's disease patients reveals that the LSPR nanosensor provides new information relevant to the understanding and possible diagnosis of Alzheimer's disease.     

Glycol-based sol-gel process for the fabrication of ferroelectric PZT thin films

A new sol-gel system using ethylene glycol was developed for the fabrication of PZT thin films with compositions near the morphotropic phase boundary Pb(Zr_0.52Ti_0.48)O₃. Ethylene glycol was used as both a chelating agent and a solvent to replace the highly toxic methoxyethanol used in previous formulations. Thin films were deposited by spin coating the solutions onto platinized silicon substrates. Films were completely crystallized by about 600°C and contained the ferroelectric perovskite phase. A dielectric constant of about 750–800 at 1 KHz was obtained for thin films of 0.3 µm thickness. The hysteresis measurements revealed a remanent polarization of 15 mC/cm² with a coercive field of 60 kV/cm.     

Metalations—XVI : Polylithiation at benzylic positions

Metalation of mesitylene with butyllithium in hexane in the presence of tetramethylethylenediamine yields mono-, di- and trilithiated benzylic compounds (1–5), characterized as their silylated derivatives. Dilithiation occurred partly at the same but preferentially at different methyls. The symmetrical tris-1,3,5-(lithiomethylene)benzene was the main product. Similar metalation occurred with m-xylene. o-Xylene gave also dilithiated products, but at a slower rate, and p-xylene gave slowly and exclusively the gem-dilithio-derivative.The results were explained by greater stabilization of polylithio derivatives with charges all on the starred carbons of the conjugated system, rather than those with charges uniformly dispersed on all carbons. CNDO/2 calculations of the energy of the anions account only partially for the order of stability of most of the studied compounds, but a good correlation between this experimental order and the energies of the lithium compounds was found.     

ROTATIONAL DIFFUSION OF RHODAMINE 6G IN HUMAN BLOOD SERUM

Abstract —The time-dependent rotational relaxation of Rhodamine 6G in fresh and dried human blood serum was investigated using picosecond phasefluorometry. Measurements were also carried out in aqueous solutions of amino acids, glucose, urea, and bovine serum albumin to evaluate our model for the interactions. It is shown that the distribution of Rhodamine 6G between the aqueous and the protein phase of the blood serum strongly depends on protein concentration and temperature.