Non-aqueous capillary electrophoresis of the positional isomers of a sulfated monosaccharide

A non-aqueous capillary electrophoresis (NACE) method coupled to indirect absorbance detection has been developed for the separation of the three positional isomers of monosulfated fucose. The optimized electrolyte was composed of 12 mM ethanolamine, 2 mM trimesic acid buffer in a methanol-ethanol (1:1, v/v) mixture. As the retained electrolyte entails no separating agent other than the pH buffer, the NACE separation of the positional isomers has been ascribed mainly to selective ion-pairing with the electrolyte counter-ion and the possibility of a selective solvation effect in the alcohol mixture. In the absence of pure isomeric standards, peak identification was completed by MS and NMR spectroscopy and selective enzymatic desulfation. This method should be of interest for the structure elucidation of monosulfated fucose-based polysaccharides and for the screening of sulfoesterase of unknown activity.     

Plasma-chemical decomposition of methane during diamond synthesis

Using a mass spectrometric sampling method, we have observed the decomposition of CH₄ in an rf plasma usedfor diamond deposition. The gas samples were extracted through an orifice located downstream of the plasma zone and analyzed online. For the experiments a dilute mixture of H₂ and CH₄ containing 0.1–3% CH₄ has been used. CH₄ is converted to C₂H₂ and C₂H₄ quantitatively. Small amounts of heavier hydrocarbons are formed. A comparison of the experimental results with a recent kinetic model treating a purely thermal environment is made and the differences between our experiment and the model are explained. The role of acetylene as a species formed in an atmosphere rich in atomic hydrogen is proposed. The electron impact dissociation process is suggested as the rare-determining step in the plasma-chemical decomposition of methane.     

Bildung siliciumorganischer Verbindungen. LVI. Reaktionen Si- und C-chlorierter 1,3,5-Trisilapentane mit CH3MgCl

Formation of Organosilicon Compounds. LVI. Reactions of Si- and C-Chlorinated 1,3,5-Trisilapentanes with CH₃MgCl (Cl₃Si? CCl₂)₂SiCl₂ (1) reacts with an excess of meMgCl (me = CH₃) forming me₃Si? C?C? Sime₃ (2), Sime₄, H₂C?C(Sime₃)[CH(Sime₃)₂] (3) as main products and (me₃Si)₂C? CH(Sime₃) and as by-products. The cleavage reaction of (1) to (2) and (3) does not occur when the meMgCl-concentration is lowered. The reaction is started by the formation of a GRIGNARD reagent at a CCl-group in compound (1). Cl₃Si? CCl₂? SiCl₂? CH₂? SiCl₃ forms with ; me₃Si? CCl₂? SiCl₂? CHCl? SiCl₃ forms (me₃Si)₂C?CH(Sime₃). A reaction sequence is given.     

Bildung und Reaktionen P-funktioneller Phosphane

Formation and Reaction of P-functional Phosphanes The reaction of (me₃Si)₂PLi · 2 THF a (me = CH₃) with PCl₃ b at ?78°C via the intermediate (me₃Si)₂P? PCl₂ 1 yields [(me₃Si)₂P]₂PCl 2 and [(me₃Si)₂P]₂P? P(Sime₃)₂ 3 . By addition of me₃CLi c to the reaction mixture of a and b (molar ratio a:b:c (molar ratio a:b:c = 1:1:1) at ?60°C, 2 is formed as a main product, which reacts on to yield [(me₃Si)₂P]₂PH 4 (white crystals, mp = 73°C). By reactions of a:b:c in a molar ratio of 1:1:2 the cyclotetraphosphane (me₃C)₃ (me₃Si)P₄ 7 is accessible, and the additional formation of (me₃Si)₂PLi · 2 THF, (me₃Si)₃P and Li₃P₇ · 3 THF 13 was detected. Warming (me₃Si)₂P? PCl(Cme₃) 5 to 20°C produces cis- and trans-cyclotetraphosphanes (me₃Si)₂(me₃C)₂P₄. By running the reaction of a and b at ?78°C and adding me₃CLi only after 24 h, additionally to (me₃Si)₂P? PH Cme₃) and (me₃Si)₃P also (me₃Si)₂P? P(Cme₃)? P(Cme₃)? P (Sime₃)₂ is obtained, which is formed by metallation of (me₃Si)₂P? PCl(Cme₃) with me₃CLi and by further reaction of the intermediate (me₃Si)₂P? PLi(Cme₃) with (me₃Si)₂P? PCl(Cme₃). The reaction of (me₃Si₃)P with PCl₃ at ?78°C only yields (me₃Si)₂P? PCl₂ 1 and me₃SiCl. On addition of me₃CLi (?78°C, molar ratio = 1:1:1) preferrably 2 and (me₃Si)₂P? PCl(Cme₃) are formed, whereas after warming the mixture to 20°C, 4 and (me₃Si)₂P? PH(Cme₃) are found to be the main products. These reactions are induced by the cleavage of 1 by means of me₃CLi, and by the formation of (me₃Si)₂PLi and me₃C? PCl₂.     

Reaction of hydroxylamine with 5-aminooxazoles. A new route to isoxazoles

The nucleophilic attack of hydroxylamine at the 5 position of 2-aryl-4-trifluoroacetyl-5-amino-oxazoles leads to a mixture of stereoisomeric isoxazolines. Dehydration of these isomeric isoxazolines in the presence of trifluoroacetic anhydride gives 3-amino-4-acylamino-5-trifluoromethylisoxazoles. The structures and spectroscopic data of these compounds are discussed.     

Bildung siliciumorganischer Verbindungen. 89. Selektive Photobromierung von Si-methylierten Carbosilanen

Formation of Organosilicon Compounds. 89. Selective Photobromination of Si-methylated Carbosilanes A selective photobromination of the C atoms in the skeleton of Si-methylated carbosilanes is reported. (me₃Si? CH₂)₂Sime₂ reacts to me₃Si? CBr₂? Sime₂? CH₂? Sime₃ in good yields (me = CH₃); the second CH₂ group is considerably slower brominated. Photobromination of (me₂Si? CH₂)₃ consecutively yields a and b . Also from (me₂Si? CH₂)₄ the derivative with one CBr₂ group is accessible. Bromination of tertiary CH groups is highly preferred; this is shown by the selective formation of c . The C-bromination of SiBr-substituted carbosilanes is significantly more difficult; nevertheless (Brme₂Si)₂CH₂ selectively forms (Brme₂Si)₂CBr₂. Brme₂Si? CH₂? Sime₂? CH₂? Sime₃ forms Brme₂Si? CH₂? Sime₂? CBr₂? Sime₃, i. e., only the CH₂ group non-adjacent to SiBr is attacked. The formation of CHBr groups could not be detected. Higher temperatures and longer reaction times increase the formation of polymers.     

Bildung siliciumorganischer Verbindungen. LI. Reaktionen verschieden chlorierter 1,3,5-Trisila-cyclohexane mit CHMgCl und ihre 29SiNMR-Spektren

Formation of Organosilicon Compounds. LI. Reactions of Various Chlorinated 1.3.5-Trisilacyclohexanes with CH₃MgCl and their ²⁹SiNMR Spectra The reaction of (a) with meMgCl starts with the formation of a Grignard compound of (a) and forms (c) via (b). The reaction sequence will be described. The ring contraction of the six-membered ringsystem is also observed with compound (d) leading to (e), whereas (f) reacts to (g), the ringsystem being maintained. No ring-contraction is observed when investigating the reactions of the derivatives containing Si? H- and C? Cl-groups. Compound (i) gives rise to (j), (k) to (l) whereas cleavage occurs with (m) and (n) does not react under the conditions applied. According to the PMR and ²⁹SiNMR spectra, the polarity of the Si? Cl-bond decreases in the compounds containing Si? Cl and CCl-groups by increasing the number of CCl₂ groups. In the compounds containing Si? H and C? Cl-groups the polarity of the Si? H-bond increases with the degree of chlorination at the C-atom. By that, the different chemical behaviour can be understood. The preparations of the starting compounds are described.     

Crystal violet combined with Merocyanine 540 for the ex vivo purging of hematopoietic stem cell grafts

The purpose of this study was to determine in a preclinical purging model, how effective crystal violet-mediated photodynamic therapy (CV-PDT) is against solid tumor and drug-resistant mutant tumor cells, and if certain limitations of CV-PDT can be overcome by using crystal violet (CV) in combination with the membrane-active photosensitizer, Merocyanine 540 (MC540). When used under conditions that preserved an adequate fraction of normal human granulocyte/macrophage progenitors (CFU-GM), CV-PDT failed to achieve meaningful reductions of DU145 prostate, H69 small cell lung cancer, and MDA-MB-435S breast cancer cells. Melphalan-resistant L1210/L-PAM1, adriamycin-resistant P388/ADR, and adriamycin-resistant HL-60/ADR leukemia cells were markedly less sensitive to CV-PDT than their wild-type counterparts, whereas cisplatin-resistant H69/CDDP cells were more sensitive than wild-type H69 cells. Sequential exposure to MC540- and CV-PDT under conditions that preserved an adequate fraction (73% and 29%, respectively) of normal CD34-positive hematopoietic stem cells and granulocyte/macrophage progenitors was highly effective against H69 (99.997% reduction) and H69/CDDP (99.999% reduction) cells, but ineffective against HL-60/ADR, MDA-MB-435S, and DU145 cells. CV thus shows only limited promise as a single-modality purging agent. However, in certain situations, clinically meaningful tumor cell depletions can be obtained by using CV in combination with a second photosensitizer such as MC540.     

Bildung siliciumorganischer Verbindungen. 70 [1]. Reaktionen Si-fluorierter 1,3,5-Trisilapentane mit CH3MgCl und LiCH3

Formation of Organosilicon Compounds. 70. Reactions of Si-fluorinated 1,3,5-Trisilapentanes with CH₃MgCl and LiCH₃ F₃Si? CCl₂? SiF₂? CH₂? SiF₃ 3 reacts with meMgCl. (me = Ch₃ starting with a Si-methylation and not with a C-metallation as in the corresponding Si- and C-chlorinated compounds, e. g. (Cl₃Si? CCl₂)₂SiCl₂ [2]. A CCl-hydrogenation is observed too, which in the case of F₃Si? CCl₂? SiF₂? CHCl? SiF₃ 4 gives meS₃Si? CCl₂? Sime₂? CH₂? Sime₃. (F₃Si? CCl₂)_{2 5} reacts with meMgCl to form preferentially 1,2-Disilapropanes by cleaving a Si? Cbond. The isolation of F₃Si? CCl₂H and meF₂Si? CCl₂? SiF₂me allows to locate the bond where 5 is cleaved at the beginning of the reaction. With meLi 5 reacts to form mainly me₃Si? C?C? Sime₃, showing that in the reaction of meLi, being a stronger reagent than meMgCl, and 5 a C-metallation occurs, following the same mechanism as in the reaction with (Cl₃Si? CCl₂)₂)SiCl₂ [2]. The reaction conditions for the synthesis of Si-fluroinated and C-chlorinated 1,3,5-Trisilapentanes in a 0.1 mol scale are reported. N.m.r. data of all investigated compounds are tabulated.     

Overhauser shift in single crystals of FA2PF6

The shift ΔB_ov of the ESR line due to the saturation of the NMR of hyperfine-coupled nuclei (Overhauser shift) was measured for single crystals of the organic conductor (FA₂)^±PF₆^?. ΔB_ov is proportional to AP, where A is the average hyperfine interaction between the conduction electrons and the nuclei in resonance and P is the dynamic nuclear polarization. The proton spin relaxation times were measured from the time dependence of the Overhauser shift, ΔB_ov(t), after rf pulses.