XPS study of one-dimensional compounds: TiS3

X-Ray photoelectron spectra of TiS₃ with a one-dimensional structure were measured. TiS₃ may be regarded as Ti⁴⁺(S₂)^2?S^2? with pairs of S atoms (S₂) and isolated S atoms. The spectra of the sulfur core-levels are assigned by comparison with those of TiS₂, where all S atoms are largely separated. The binding energy of the S₂ pairs is found to be 1.4 eV higher than that of the isolated S atoms, which is consistent with the larger negative charge of the isolated atoms. The structures of the valence band of TiS₃ are discussed in terms of a molecular orbital scheme for the S₂ pairs.     

Addition reactions of cyclooctatetraene with 1,3-diphenylisobenzofuran the benzene ring as dienophile in a [4+2] cycloaddition reaction

Addition reactions of cyclooctatetraene with 1,3-diphenylisobenzofuran resulted in the formation of three 1:1 cycloadducts, 1, 2, and 3, and a 1:2 cycloadduct, 4. Single crystal x-ray analysis established 3 to be a cage compound formed by an unprecedented [4+2] cycloaddition reaction of 1 in which the double bond of the benzene moiety acted as the dienophile.     

Effect of explicit cationic size and valence constraints on the phase stability of 1:2 B-site-ordered perovskite ruthenates

The related parameters of cation size and valence that control the crystallization of Sr(3)CaRu(2)O(9) into a 1:2 B-site-ordered perovskite structure were explored by cationic substitution at the strontium and calcium sites and by the application of high pressure. At ambient pressures, Sr(3)MRu(2)O(9) stoichiometries yield multiphasic mixtures for M = Ni(2+), Mg(2+), and Y(3+), whereas pseudocubic perovskites result for M = Cu(2+) and Zn(2+). For A-site substitutions, an ordered perovskite structure results for Sr(3-x)Ca(x)CaRu(2)O(9), with 0 相似文献   

Asymmetric skeletal rearrangement of symmetrically alpha,alpha-disubstituted alpha-amino aldehydes: a new entry to optically active alpha-hydroxy ketones

A unique asymmetric skeletal rearrangement of symmetrically alpha,alpha-disubstituted alpha-amino aldehydes has been accomplished for the first time using a chiral organoaluminum Lewis acid 1. For instance, treatment of (S)-2,2'-bis(trifluoromethanesulfonylamino)-1,1'-binaphthyl with Me3Al (1.0 equiv) in toluene at room temperature for 15 min and at 110 degrees C for an additional 15 min produced (S)-1, and a subsequent reaction with alpha -amino aldehyde 2a (R = CH2Ph) at -78 degrees C for 4 h and at -40 degrees C for 12 h resulted in the smooth rearrangement to the zwitterionic iminium intermediate A, which furnished the alpha-hydroxy ketone 3a (R = CH2Ph) in 93% isolated yield with 95% ee (S) after acidic hydrolysis. This result, together with other representative examples, clearly demonstrates the effectiveness of the present method for the hitherto difficult asymmetric synthesis of acyloins. Furthermore, we found that the treatment of the in situ generated A with DIBAH afforded the corresponding anti amino alcohol exclusively without loss of enantiomeric excess. Our approach casts light on the previously unexplored yet potential utility of alpha-amino aldehydes as synthetic building blocks and also provides a new entry to optically active alpha-hydroxy ketones and 1,2-amino alcohols.     

Antioxidant effects of hydroxybenzalacetones on peroxynitrite-induced lipid peroxidation in red blood cell membrane ghost and SOS response in Salmonella typhimurium TA4107/pSK1002

Antioxidant activity of a series of hydroxybenzalacetones was determined against peroxynitrite-induced lipid peroxidation in red blood cell membrane and SOS response through DNA damage in bacterial cells. Hydroxybenzalacetone derivatives with hydroxy, methoxy, ethoxy or methyl substitution were analyzed and found to be more effective than the water-soluble vitamin E analogue Trolox. The inhibitory effect against lipid peroxidation correlated well to that against the SOS response, which is dependent on decomposition of peroxynitrite by hydroxybenzalacetones outside of the cell membrane. The antioxidant activity was shown to correlate well with the electric parameter sigma+. Electron-donating substituents with more negative sigma+ values increased the potencies. The result suggests that hydroxybenzalacetones with more electron-donating substituents will protect tissue more effectively against oxidative stress.     

Efficient synthesis of 2-modified 1alpha,25-dihydroxy-19-norvitamin D3 with Julia olefination: high potency in induction of differentiation on HL-60 cells

Six novel 2-substituted analogues of 1alpha,25-dihydroxy-19-norvitamin D(3), 6a,b-8a,b, were efficiently synthesized utilizing (-)-quinic acid as the A-ring precursor. The C2-modified A-rings were prepared as 4-alkylated (3R,5R)-3,5-dihydroxycyclohexanones 12-15 from (-)-quinic acid based on radical allylation at the C4 position of methyl (-)-quinicate. The new type of the CD-ring coupling partner 23 was synthesized from 25-hydroxy Grundmann's ketone 19 to apply to the modified Julia olefination to construct a diene unit between the A-ring and the CD-ring. The coupling yields, including a deprotection step, were 47-62%. After the separation of the diastereomers based on C2 stereochemistry, the structure (2alpha or 2beta) was determined by (1)H NMR experiments and compared to DeLuca's 2-methyl- and 2-ethyl-1alpha,25-dihydroxy-19-norvitamin D(3). Thus, the synthesized 2alpha-(3-hydroxypropyl)-1alpha,25-dihydroxy-19-norvitamin D(3) (8a) showed almost the same potency in binding to the bovine thymus vitamin D receptor (VDR) as the natural hormone 1, while its beta-isomer 8b had only a 3% affinity. Both 2alpha-allyl- and 2alpha-propyl-1alpha,25-dihydroxy-19-norvitamin D(3) (6a and 7a) and their 2beta-analogues (6b and 7b) possessed a weak affinity for the VDR. The strong VDR ligand 8a was ca. 36-fold more potent in induction of HL-60 cell differentiation than 1, and interestingly, even the weaker ligand 8b showed a 6.7-fold higher potency in the cell differentiation activity than that of 1.     

Conformationally controlled (entropy effects), stereoselective vibrational quenching of singlet oxygen in the oxidative cleavage of oxazolidinone-functionalized enecarbamates through solvent and temperature variations

On photooxygenation (methylene blue as sensitizer) of E/Z enecarbamates, equipped with the oxazolidinone chiral auxiliary, the oxidative cleavage of the alkenyl functionality releases the enantiomerically enriched methyldesoxybenzoin (MDB) product. The extent (% ee) as well as the sense (R vs S) of the stereoselectivity in the MDB formation depends on the choice of the alkene configuration; the efficacy of stereocontrol may be tuned by appropriate solvent and temperature conditions. Highlighted is the finding that the formation of the preferred MDB enantiomer (R or S) depends for the E isomer on the chosen solvent and temperature, but not for the corresponding Z isomer. The activation parameters for the various solvents disclose that differential entropy effects (ΔΔS^‡) dominate the conformationally more flexible E diastereomers. As mechanistic rationale for this unprecedented conformationally imposed stereochemical behavior, we propose the competitive action of stereoselective vibrational quenching of the attacking singlet oxygen by the enecarbamate versus sterically controlled stereoselective oxidative cleavage of its double bond.     

Extraction behaviour of copper(II) and silver(I) with a thiacrown ether carboxylic acid, 2-(3,6,10,13-tetrathiacyclotetradec-1-oxy)hexanoic acid

The extraction behaviour of copper(II) and silver(I) with 2-(3,6,10,13-tetrathiacyclotetradec-1-oxy)hexanoic acid (TTCTOHA) was investigated at 25+/-0.1 degrees C and ionic strength of 0.1. The value of the logarithmic distribution coefficient, logK(DR) of TTCTOHA between octan-1-ol and aqueous phases was determined to be 4.13. Copper(II) was extracted with TTCTOHA into octan-1-ol as CuL(2), where L represents the anionic species of TTCTOHA. The logarithmic extraction constant, logK(ex(10)), was determined at -7.42. Silver(I) was extracted with TTCTOHA into octan-1-ol as AgL and Ag(2)L(2). The logarithmic distribution constant, logK(DC), of AgL was estimated to be 0.49. On the other hand, silver(I) was extracted into 1,2-dichloroethane as AgL and the logarithmic extraction constant, logK(ex(10)), was determined to be -2.24.     

High performance liquid chromatography post-column chemiluminescence determination of sulfonamide residues in milk at low concentration levels using bis[4-nitro-2-(3,6,9-trioxadecyloxycarbonyl)phenyl] oxalate as chemiluminescent reagent

The determination of seven sulfonamides by means of HPLC with chemiluminescence detection is proposed for the first time. The analytes are derivatized with fluorescamine, separated and subsequently they participate in the post-column chemiluminescence (CL) peroxyoxalate system using imidazole as a catalyst. Among the different peroxyoxalates tested, bis[4-nitro-2-(3,6,9-trioxadecyloxycarbonyl)phenyl] oxalate provides higher sensitivities and stabilities, avoiding precipitation problems. A rigorous optimization of the significant variables by means of experimental designs has been developed in order to reconcile the chromatographic conditions with the CL reaction. The method provides detection limits in the low microgl(-1) range and has been satisfactorily applied to the analysis of spiked raw milk samples.     

Syntheses and biological activities of renin inhibitors containing statine analogues

Syntheses and biological activities of dipeptide renin inhibitors that contain statine analogues are described. The key steps of the synthetic approach to dipeptide renin inhibitors are the asymmetric synthesis of 2(R)-substituted-3-aminocarbonylpropionic acids and the diastereoselective syntheses of (3S,4S)-statine analogues. These inhibitors (2,14-40) inhibited human renin in the 3-140 nM range. Inhibitor ES 6864 (2) was found to be a highly potent inhibitor of human renin (IC50: 4.6 x 10(-9) M) and showed high enzyme specificity. Oral administration of ES 6864 at 3 mg/kg to conscious, sodium-depleted marmosets inhibited plasma renin activity (PRA) more than 80% after 1 h.