Search results for "Spectrum analysis"
showing 10 items of 287 documents
A New Major Triterpene Saponin from the Roots of Cucurbita foetidissima
2000
Foetidissimoside B (1), a novel triterpene saponin, was isolated from the roots of Cucurbita foetidissima. Based on spectroscopic data, especially direct and long-range heteronuclear 2D NMR analysis and on chemical transformations, the structure of 1 was elucidated as 3-O-beta-D-glucuronopyranosyl-echinocystic acid 28-O-beta-D-glucopyranosyl-(1-->3)-beta-D-xylopyranosyl(1-->3)-[beta- D-xylopyranosyl (1-->4)]-alpha-L-rhamnopyranosyl-(1-->2)-alpha-L-arabinopyranoside . Compound 1 did not show any ability to potentiate in vitro cisplatin cytotoxicity in a human colon cancer cell line.
Melampolides from Enydra anagallis
2001
The investigation of an Argentine collection of Enydra anagallis afforded sesquiterpene lactones of the melampolide type two of which were previously known. Their structures were elucidated by spectroscopic methods. Fil: Bardon, Alicia del Valle. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto de Química del Noroeste. Universidad Nacional de Tucumán. Facultad de Bioquímica, Química y Farmacia. Instituto de Química del Noroeste; Argentina Fil: Cardona, Luis. Universidad de Valencia; España Fil: Cartagena, Elena. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. In…
Joziknipholones A and B: The First Dimeric Phenylanthraquinones, from the Roots ofBulbine frutescens
2007
From the roots of the African plant Bulbine frutescens (Asphodelaceae), two unprecedented novel dimeric phenylanthraquinones, named joziknipholones A and B, possessing axial and centrochirality, were isolated, together with six known compounds. Structural elucidation of the new metabolites was achieved by spectroscopic and chiroptical methods, by reductive cleavage of the central bond between the monomeric phenylanthraquinone and -anthrone portions with sodium dithionite, and by quantum chemical CD calculations. Based on the recently revised absolute axial configuration of the parent phenylanthraquinones, knipholone and knipholone anthrone, the new dimers were attributed to possess the P-co…
Synthesis, properties, antitumor and antibacterial activity of new Pt(II) and Pd(II) complexes with 2,2′-dithiobis(benzothiazole) ligand
2017
Mono- and binuclear Pt(II) and Pd(II) complexes with 2,20-dithiobis(benzothiazole) (DTBTA) ligand are reported. [Pt(DTBTA)(DMSO)Cl]Cl∙CHCl3 (1) and [Pd2(m-Cl)2(DTBTA)2]Cl2 (2) have been synthesized and structurally characterized by elemental analysis, IR, 1H and 13C NMR spectroscopy, MS spectrometry and the content of platinum and palladium was determined using a flame atomic spectrometer. Two different coordination modes of 1 and 2 complexes were found; in both complexes, the coordination of Pt(II) and Pd(II) ions involves the N(3) atoms of the ligand but the binuclear complex 2, is a cis-chloro-bridged palladium complex. Evaluation of their in vitro antitumor activity against two human tu…
CO2 Fixation by Cu2+ and Zn2+ complexes of a terpyridinophane aza receptor. Crystal structures of Cu2+ complexes, pH-metric, spectroscopic, and elect…
2006
The synthesis of the terpyridinophane-type polyamine 2,6,9,12,16-pentaaza[17]-(5,5' ')-cyclo-(2,2':6',2' ')-terpyridinophane heptahydrobromide tetrahydrate (L.7HBr.4H2O) is described. L presents six protonation constants with values in the range 9.21-3.27 logarithmic units. L interacts with Cu2+ and Zn2+ forming in both cases, neutral, protonated, and hydroxylated mono- and binuclear complexes whose constants have been calculated by potentiometry in 0.15 M NaClO4 at 298.1 K. The crystal structures of the compounds [Cu(HL-carb)(H2O)](ClO4)3.2H2O (1) and [Cu2(H2L)(CO3)]2(ClO4)8.9H2O (2) have been solved by X-ray diffraction. In 1, the metal center presents square pyramidal geometry. The base …
Formation of New η5-Rhodium(III) Complexes from η5-Rh(I) Rhodacarborane-Containing Charge-Compensated Ligands
2004
A series of new Rh(I) half-sandwich complexes of formula [3,3-(PPh 3 ) 2 -8-L-closo-3,1,2-RhC 2 B 9 H 1 0 )] (L = SMe 2 (2a), SEt 2 (2b), S(CH 2 ) 4 (2c), SEtPh (2d)) and [1-Me-3,3-(PPh 3 ) 2 -8-L-closo-3,1,2-RhC 2 B 9 H 9 )] (L = SMe 2 (2e), SEt 2 (2f)) have been prepared by reaction of the respective monoanionic charge-compensated ligands [10-L-nido-7,8-C 2 B 9 H 1 0 ] - and [7-Me-10-L-7,8-C 2 B 9 H 9 ] - with [RhCl(PPh 3 ) 3 ]. Complex [3,3-(cod)-8-SMe2-closo-3,1,2-RhC 2 B 9 H 1 0 ] (3) has also been prepared by reaction of K[10-SMe 2 -nido-7,8-C 2 B 9 H 1 0 ] with [RhCl(cod)] 2 . Rh(I) complexes 2a-d may be easily oxidized to the corresponding Rh(III) complexes 4a-d under N 2 atmosphere…
Spectroscopic and conformational properties of size-fractions separated from a lignite humic acid
2007
Abstract A lignite humic acid (HA) was fractionated by preparative high performance size-exclusion chromatography (HPSEC) in seven different size-fractions. The size-fractions were characterized by cross polarization (CP) magic angle spinning (MAS) 13 C NMR spectroscopy and a further analytical HPSEC elution under UV and fluorescence detection. The alkyl hydrophobic components mainly distributed in the largest molecular-size-fraction, whereas the amount of oxidized carbons increased with decreasing size of fractions. Cross polarization time ( T CH ) and proton spin-lattice relaxation time in the rotating frame ( T 1 ρ (H)) were measured from variable contact time (VCT) experiments. The bulk…
Effect of water on glass transition in starch/sucrose matrices investigated through positron annihilation lifetime spectroscopy: a new approach
2011
Glass transition is studied through positron annihilation lifetime spectroscopy (PALS) in maize starch matrices containing 10 (batch STS10) and 20 (STS20) w/w% sucrose, as a function of temperature (T) and water content (c(w)). To circumvent important losses of water upon heating while recording the PALS spectra, a new method is developed: instead of a series of measurements of τ(3), the triplet positronium lifetime, at different T, the latter is kept constant and the series relates to c(w), which is left to decrease at a constant rate. Similarly to the changes in τ(3) with T, the τ(3)vs. c(w) plots obtained show a smooth linear increase until a break, denoting the occurrence of glass trans…
Characterization of a sucrose/starch matrix through positron annihilation lifetime spectroscopy: unravelling the decomposition and glass transition p…
2010
The triplet state of positronium, o-Ps, is used as a probe to characterize a starch-20% w/w sucrose matrix as a function of temperature (T). A two-step decomposition (of sucrose, and then starch) starts at 440 K as shown by a decrease in the o-Ps intensity (I(3)) and lifetime (τ(3)), the latter also disclosing the occurrence of a glass transition. Upon sucrose decomposition, the matrix acquires properties (reduced size and density of nanoholes) that are different from those of pure starch. A model is successfully established, describing the variations of both I(3) and τ(3) with T and yields a glass transition temperature, T(g) = (446 ± 2) K, in spite of the concomitant sucrose decomposition…
Electrochemical impedance spectroscopy of polyelectrolyte multilayer modified gold electrodes: influence of supporting electrolyte and temperature.
2005
Electrochemical impedance spectroscopy and cyclic voltammetry are employed to characterize poly(styrenesulfonate)/poly(allylamine hydrochloride) multilayers assembled onto cysteamine-modified gold surfaces. The influence of the supporting electrolyte and temperature on the impedance response is studied because of both its practical interest and the need to test further the capillary membrane model recently developed by Barreira et al. [J. Phys. Chem. B 2004, 108, 17973]. The results obtained are interpreted quite satisfactorily in terms of this model, thus providing additional support to its usefulness for the description of ionic transport through polyelectrolyte multilayers. It is observe…