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1.
We discuss role of partially gravitating scalar fields, scalar fields whose energy–momentum tensors vanish for a subset of dimensions, in dynamical compactification of a given set of dimensions. We show that the resulting spacetime exhibits a factorizable geometry consisting of usual four-dimensional spacetime with full Poincaré invariance times a manifold of extra dimensions whose size and shape are determined by the scalar field dynamics. Depending on the strength of its coupling to the curvature scalar, the vacuum expectation value (VEV) of the scalar field may or may not vanish. When its VEV is zero the higher-dimensional spacetime is completely flat and there is no compactification effect at all. On the other hand, when its VEV is nonzero the extra dimensions get spontaneously compactified. The compactification process is such that a bulk cosmological constant is utilized for curving the extra dimensions. 相似文献
2.
A new enantioselective synthesis of furan‐2‐yl amines and amino acids is described, in which the key step is the oxazaborolidine‐catalyzed enantioselective reduction of O‐benzyl (E)‐ and (Z)‐furan‐2‐yl ketone oximes to the corresponding chiral amines. The chirality of the furan‐2‐yl amines is fully controlled by the appropriate choice of the geometrical isomer of the O‐benzyl oxime. Oxidation of the furan ring furnished amino acids in high yields. 相似文献
3.
Mustafa Odabaolu idem Albayrak Reit
zkanca Fatma Zehra Aykan Peter Lonecke 《Journal of Molecular Structure》2007,840(1-3):71-89
Some new substituted polyhydroxy azo–azomethine compounds were prepared by reaction of tris(hydroxymethyl)aminomethane with (E)-2-hydroxy-5-(phenyldiazenyl) benzaldehyde and its substituted derivatives. The structures of azo and azo–azomethine compounds were determined by IR, UV–vis, 1H NMR and 13C NMR spectroscopic techniques, and/or X-ray diffraction studies. According to IR spectra, all azo–azomethine compounds adopt keto form in solid state. UV–vis analysis has shown the presence of keto–enol tautomerism in solution for all azo–azomethine compounds, except that for nitro substituted derivative, enol form is dominantly favored in solution. At the same time, above mentioned derivative compounds were studied in vitro for their antimicrobial properties. Among the phenylazosalicylaldehyde series compound tested, 4-phenylazosalicylaldehyde, 4-(3-chlorophenylazo)salicylaldehyde, 4-(2-chlorophenylazo)salicylaldehyde, 4-(4-fluorophenylazo)salicylaldehyde, 4-(3-chlorophenylazo)salicylaldehyde and 4-(4-ethylphenylazo)salicylaldehyde showed a weak antimicrobial activity only against gram positive bacteria. On the contrary, phenylazosalicylaldehyde series compounds were reacted tris(hydroxmethyl)aminomethane, that exhibited a strong antimicrobial activity against gram positive bacteria, yeast and mould. Moreover, while the 2-{[1,3-dihydroxy-2-(hydroxymethyl)propan-2-ylimino]methyl}phenol did not show an inhibition on tested microorganism, the addition of phenyldiazine groups to 2-{[1,3-dihydroxy-2-(hydroxymethyl)propan-2-ylimino]methyl}phenol resulted in a strong increases in antimicrobial activity. 相似文献
4.
Fatma I. Khattab M. M. Amer Nagiba Y. M. Hassan 《Journal of Thermal Analysis and Calorimetry》1982,25(2):367-375
Some sulphonamides are evaluated by means of thermal analysis. Use is made of their characteristic endothermic DTA peaks (melting peaks), where the area changes linearly with variations in the amount of sulphonamides. The method is suitable for the determination of 30–100 mg of sulphathiazole, sulphisomidine, sulphaguanidine, sulphacetamide sodium and sulphamethoxypyridazine with reasonable accuracy. As for sulphisoxazole, two peaks are used for its determination: an endothermic one to determine 30–100 mg, and an exothermic one to determine 6–30 mg.
Zusammenfassung Einige Sulphonamide wurden durch thermische Analyse bestimmt, wobei von der linearen Abhängigkeit der Fläche der charakteristischen endothermen DTA-Peaks (Schmelzpeaks) von der Menge der Sulphonamide Gebrauch gemacht wurde. Mit der Methode können 30–100 mg Sulphathiazol, Sulphisoimidin, Sulphaguanidin, Natrium-Sulphacetamid und Sulphamethoxypyridazin mit ausreichender Genauigkeit bestimmt werden. Bei der Bestimmung von Sulphisooxazol wurde ein endothermer Peak für Mengen von 30–100 mg und ein exothermer für geringere Mengen von 6–30 mg herangezogen.
. - ( ), . 30–100 , , , . , — 30 100 , — 6 30 .相似文献
5.
In this study, a rapid pre-concentration procedure, which employs powdered activated carbon as a clean-up and pre-concentration material, is described for the gas chromatographic analysis of N-nitrosodiethylamine (NDEA) and N-nitrosodimethylamine (NDMA) in aqueous solutions. It was found that powdered activated carbon is suitable for the adsorption of volatile N-nitrosamine compounds from aqueous solutions. Adsorption efficiency with spiked beer samples (alcohol content 5% v/v) was found to be 80.5% (NDMA) and 89.4% (NDEA) and recovery of extraction from activated carbon was calculated as 82.1% (NDMA) and 89.7% (NDEA), respectively. The effect of 100µgmL–1 of tannic acid on the adsorption was also studied, and no significant effect on the adsorption and extraction of volatile N-nitrosamine compounds was found. 相似文献
6.
A one-step synthesis of 5-alkoxypyrrole-3-phosphonates is presented starting from suitable α-cyanomethyl-β-ketophosphonates. The key step in the synthesis involves a one-pot addition and heteroannulation sequence. The zinc perchlorate-catalyzed addition of alcohols to the nitrile carbon of α-cyanomethyl-β-ketophosphonates followed by annulation furnished 5-alkoxypyrrole-3-phosphonates. The addition-annulation process is carried out in the presence of water and 4,5-dihydro-5-oxo-1H-pyrrole-3-phosphonates (pyrrolinones) are obtained in good yields. 相似文献
7.
4,4-Bis(chloroacetyl)diphenylmethane has been prepared from ClCH2COCl and Ph2CH2. 4,4-Methylenebis(phenylglyoxylohydroximoyl chloride has also been obtained. Four new substituted 4,4-bis(alkylaminoisonitrosoacetyl)diphenylmethanes (ligands) have been prepared from 4,4-methylenebis(phenylglyoxylohydroximoyl chloride) and the corresponding amines. The NiII, CuII and CoII complexes of these ligands were prepared and their structures were identified using AAS, i.r., 1H-n.m.r. spectral data, elemental analyses and magnetic susceptibility measurements. 相似文献
8.
A new iridoid glucoside, verproside (2) , has been isolated from Veronica officinalis L. and its structure has been established to be 6-O-protocatechuoylcatalpol. 相似文献
9.
Fatma Alper 《Journal of organometallic chemistry》2006,691(12):2734-2738
Pentacarbonylpyrazinetungsten(0), (CO)5W(pyz), is not stable in solution in polar solvents such as acetone or dichloromethane and undergoes conversion to a bimetallic complex, (CO)5W(pyz)W(CO)5 plus free pyrazine. These three species exist at equilibrium. Using the quantitative 1H NMR spectroscopy, the equilibrium constant could be determined to be Keq = (5.9 ± 0.8) × 10−2 at 25 °C. Introducing a second pyrazine ligand into the molecule does not stabilize the complex, as cis-W(CO)4(pyz)2 was found to be less stable than W(CO)5(pyz) and, therefore, could not be isolated. However, introducing trimethylphosphite as a donor ligand into the complex leads to the stabilization of the carbonyl-pyrazine-metal(0) complexes, as shown by the synthesis of cis-W(CO)4[P(OCH3)3](pyz). This complex could be isolated from the reaction of the photogenerated W(CO)4[P(OCH3)3](tetrahydrofuran) with trimethylphosphite upon mixing for 2 h at 10 °C in tetrahydrofuran and characterized by elemental analysis, IR, MS, 1H, 13C, and 31P NMR spectroscopy. 相似文献
10.
Eker F Griebenow K Schweitzer-Stenner R 《Journal of the American Chemical Society》2003,125(27):8178-8185
Determination of the precise solution structure of peptides is of utmost importance to the understanding of protein folding and peptide drugs. Herein, we have measured the UV circular dichroism (UVCD) spectra of tri-alanine dissolved in D(2)O, H(2)O, and glycerol. The results clearly show the coexistence of a polyproline II or 3(1)-helix and a somewhat disordered flat beta-strand conformation, in complete agreement with recent predictions from spectroscopic data (Eker et al. J. Am. Chem. Soc. 2002, 124, 14 330-14 341). A thermodynamic analysis revealed that enthalpic contributions of about 11 and 17 kJ/mol stabilize polyproline II in D(2)O and H(2)O, respectively, but at room temperature they are counterbalanced by entropic contributions, which clearly favor the more disordered beta-strand conformation. It is hypothesized that this delicate balance is the reason for the variety of structural propensities of amino acid residues in the absence of nonlocal interactions. The isotope effect yielding a higher occupation of polyproline II in H(2)O with respect to D(2)O strongly suggests that a hydrogen-bonding network involving the peptide and water molecules in the hydration shell plays a major role in stabilizing this conformation. The equilibrium between polyproline II and beta-strand is practically maintained in glycerol, which suggests that glycerol can substitute water as stabilizing solvent for the polyproline II conformation. We also measured the UVCD spectra of tri-valine and tri-lysine (both at acidic pD) in D(2)O and found them to adopt a flat beta-strand and left-handed turn structure, respectively, in accordance with recent analyses of vibrational spectroscopy data. Generally, the present study adds substantial evidence to the notion that the so-called random coil state of peptides is much more structured than generally assumed. 相似文献