Search results for "MR"
showing 10 items of 3001 documents
INTERACTIONS OF ORGANOTIN(IV) HALIDES WITH REDUCED GLUTATHIONE IN AQUEOUS-SOLUTION
1993
Abstract Glutathione (GSH) is a compound extremely common among many living organisms in which it plays a fundamental role in the processes of detoxification. Also, organotin(IV) derivatives are more and more commonly used in technological processes or as antitumor drugs. So it seemed interesting to investigate the possible interactions between GSH and organotin compounds in water. Particularly, it has been studied because of its role in the organic radicals linked to the tin center on the stoichiometry and the structure of the adducts. Information was obtained following the reaction between Me n SnCl 4-n (n = 1 to 3) and GSH by Mossbauer and NMR spectroscopies on the assumption that change…
Complexes of Tungsten(VI) with Mucic Acid: a Spectrophotometric and Polarimetric Study in Aqueous Solution
1986
Abstract Spectrophotometric work on mucic acid-W(VI) system shows the formation of three different oxoanion complexes in aqueous solution; their stability is dependent upon pH. One of the complexes is monomeric tungstodimucate and the other two are 2/2 species. An anomalous cryoscopic behaviour, similar to that of W(VI) tartaric system, has been observed for the dimeric complex formed at higher pH. The stoichiometries and conditional dissociation constants have been polarimetrically determined by means of competitive reactions between the mucic and tartaric ligands. 1 H and 13 C NMR spectra have been interpreted for the similar complex species of both mucic and tartaric acids.
Synthesis, Characterization, and X-ray Crystal Structures of Cyclam Derivatives. 8. Thermodynamic and Kinetic Appraisal of Lead(II) Chelation by Octa…
2005
En route toward the development of hybrid organic−inorganic extracting materials incorporating lead-selective chelators and their implementation in water purification processes, the lead(II) binding properties of three N-carbamoylmethyl-substituted 1,4,8,11-tetraazacyclotetradecanes (cyclams) have been fully investigated by spectroscopic (IR, UV−vis, MALDI-TOF MS, 1H and 13C NMR), X-ray crystallographic, potentiometric, and kinetic methods. Solution NMR studies revealed that the Pb2+ ion is entrapped in a molecular cage constituted by the four macrocyclic nitrogen and four amidic oxygen atoms. Protonation and lead binding constants determined in aqueous solution were shown to be linearly de…
Dendritic octa-CMPO derivatives of calix[4]arenes
2004
Abstract Calix[4]arenes substituted at the narrow or wide rim by eight carbamoylmethyl-phosphine oxide (CMPO) functions in a dendritic manner were synthesised and studied in extraction of Eu 3+ and Am 3+ from aqueous nitric acid into o -nitrophenylhexyl ether. 1 H NMR relaxivity titrations for a wide rim octa-CMPO reveal the clear formation of a solvent-free 1:2 ligand/metal complex, while the wide rim tetra-CMPO formed oligomeric complexes under similar conditions.
Dielectric Behavior of Aqueous Solutions of α,β-Poly(aspartyl hydrazide) and α,β-Poly(N-hydroxyethyl aspartamide): An Investigation of the Structural…
1994
The dielectric properties of aqueous solutions of α,β-poly(aspartyl hydrazide) (PAHy) and of α,β-poly( N-hydroxyethyl aspartamide) (PHEA) were measured at 25 ° C in the frequency range of 100 MHz to 15 GHz using a time domain reflection method (TDR). Single time relaxation processes were found at 2 GHz and 15 GHz, respectively. The low frequency dispersion was inter preted in terms of the dynamics of polymeric segments based on the dielectric relaxation strength and the relaxation time. The high frequency process which is attributed to the rotational relaxation of water, indicated that water mole cules surrounding the polymeric backbone and in the pure state have a similar rotational behav…
Ti(iv)-amino triphenolate complexes as effective catalysts for sulfoxidation
2010
C 3 -symmetric Ti (IV) amino triphenolate complexes efficiently catalyze, without previous activation and in excellent yields, the oxidation of sulfides at room temperature, using both CHP and the more environment friendly aqueous hydrogen peroxide as terminal oxidants, with catalyst loadings down to 0.01%. The Ti(IV) catalysts and the intermediate Ti(IV)-peroxo complexes have been characterized in solution by 1H NMR and ESI-MS techniques and via density functional studies.
Reaction pathways of glucose oxidation by ozone under acidic conditions.
2009
The ozonation of d-glucose-1-(13)C, 2-(13)C, and 6-(13)C was carried out at pH 2.5 in a semi-batch reactor at room temperature. The products present in the liquid phase were analyzed by GC-MS, HPAEC-PAD, and (13)C NMR spectroscopy. Common oxidation products of glucose have also been submitted to identical ozonation conditions. For the first time, a pentaric acid was identified and its formation quantitatively correlated to the loss of C-6 of glucose in the form of carbon dioxide. Potential mechanisms for the formation of this pentaric acid are discussed. The well-accepted pathway involving the anomeric position in glucose, gluconic acid, arabinose, and carbon dioxide is reinvestigated. The …
Identification of Bioactive Compounds in Polar and Nonpolar Extracts of Araujia sericifera
2017
Abstract Araujia sericifera is a native perennial, climbing laticiferous shrub from South America that is currently naturalized in many other countries. Previous data describe promising properties for A. sericifera, but no systematic study of its bioactive compounds and possible medicinal applications has been conducted to date. In the present study, aerial parts of A. sericifera (leaves, stems, and fruits) were explored by combining GC-MS and NMR spectroscopy analysis for both nonpolar (hexane) and polar (methanol) extracts. The hexanic extracts contained high amounts of pentacyclic triterpenes including two new metabolites, 3-tigloyl germanicol (18) and 3-tigloyl lupeol (19). The methanol…
Chemical characterization of organic residues on Late Roman amphorae from shipwrecks off the coast of Marsala (Trapani, Italy)
2021
Abstract Organic residues were extracted from thirty-three different types of Roman and Late Antique amphorae retrieved from underwater contexts in the custody of the Archaeological Museum “Baglio Anselmi” of Marsala in Sicily. The samples were analysed using GC-MS and 1H NMR, finding biomarkers of plant oils (including saturated and unsaturated fatty acids, alcohols and alkanes present in plant waxes) were identified in seven samples. The biomarkers for Pinaceae spp., used for making pitch, were identified in one sample. The results obtained shed light on the function of different types of North African amphorae, traditionally interpreted as containers for olive oil, wine and fish sauce, p…
New organotin(IV) complexes with L-Arginine,Nα-t-Boc-L-Arginine and L-Alanyl-L-Arginine.Synthesis, structural investigations and cytotoxic activity
2010
Abstract Novel diorganotin(IV) derivatives of l -Arginine (HArg), N α -( tert -Butoxycarbonyl)- l -Arginine (Boc–Arg–OH) and l -Ala- l -Arg (H 2 Ala–Arg), H 2 NC( NH)NH(CH 2 ) 3 CH(NHR′)CO 2 H, where R′ = H in HArg, R′ = C(O)OC(CH 3 ) 3 in Boc–Arg–OH, R′ = H 2 NCH(CH 3 )CO in H 2 Ala–Arg and triorganotin(IV) derivatives of Boc–Arg–OH have been synthesized and structurally characterized. The complexes were investigated by FT-IR and 119 Sn Mossbauer in the solid state and by 1 H, 13 C, 119 Sn and 1 H– 1 H COSY NMR spectroscopy, in solution. The spectroscopic characterization leading to the proposed molecular structures was accomplished on the basis of these experiments. l -Arginine appears to…