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61.
We have re-examined the problem of the interaction of melanins with metal ions. Metal ions are normal constituents of the
pigment, but in some cases they can be related to pathologies, mainly at the level of the skin (Cu2+ and Fe3+) and of the central nervous system (Fe2+ and Mn2+). Our approach has been based on the mechanisms of adsorption on the particle surface, by the use of theoretical adsorption
isotherms and kinetic models. Although this analysis doesn’t give detailed information on the specific sites involved, it
is useful to better characterize the surface behaviour of the colloidal melanin. The results obtained demonstrate that the
affinity of melanin for metal ions is very high, comparable to the most efficient materials employed in decontamination and
recovery techniques. Moreover, our results demonstrate that three-parameters models, such as Langmuir-Freundlich, Redlich-Peterson
and Tóth equations, fit the experimental data with great accuracy and that the adsorption follows pseudo-second-order kinetics. 相似文献
62.
Grazia Cafeo Dr. Franz H. Kohnke Prof. Luca Valenti Andrew J. P. White Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(36):11593-11600
10α,20α‐Bis(4‐nitrophenyl)calix[4]pyrrole ( 1 ) forms 1:1 complexes with anions of selected aromatic hydroxy acids in which the host orientation within the guest is controlled by a change in the pH value. Some bis‐anionic guests, including those obtained from 4‐hydroxybenzoic acid, 1,4‐ and 1,3‐benzenedicarboxylic acids, induce the self‐assembly of molecular capsules involving two molecules of the receptor. 1H NMR data and solid‐state structures of the 1:1 complex of 1 with p‐C6H4(COOH)(COO?)+NMe4 and the 2:1 capsule [( 1 )2m‐C6H4(COO?)2(+NMe4)2] provide structural details in solution and in the solid state. 相似文献
63.
64.
The self-assembly of a thymine nucleotide-calixarene hybrid (1) in CDCl3 as a solvent was investigated. FT-IR, ESI-MS, 1H and DOSY-NMR spectra evidenced that compound 1 (ammonium or sodium salt) self-assembles in a triangular trimeric supramolecule by thymine-thymine hydrogen bonding. The saline form is crucial for the arrangement in the cyclic trimer as the protonation of the nucleotide phosphate groups leads the assembly toward a dimeric species. 相似文献
65.
The electronic properties of a single layer (SL) of pentacene molecules are investigated by high-resolution UV photoemission and near-edge X-ray absorption spectroscopy in different configurations of the SL, either standing up on an aromatic self-assembled monolayer or planar on a bare Cu(001) substrate. The weakly interacting pentacene molecules in the standing-up SL present a semiconducting character, and the empty states distribution reflects that of gas-phase pentacene, while the planar pentacene-Cu system shows a metallic interface with redistribution of the empty molecular states. The highest-occupied molecular orbital lineshape in the weakly interacting SL shows a double structure, attributed to two nonequivalent molecules in the ordered configuration. 相似文献
66.
A GC-MS investigation is conducted on the double bass "Panormus", property of Conservatorio di Musica "Vincenzo Bellini" in Palermo. The most important components of the varnish (fatty acids) and of the glue (proteinaceous amino acids), with which the musical instrument was treated in the past, are determined. The analyses are carried out by prior derivatization of fatty acids by acidic methanol and of amino acids by acidic methanol and trifluoroacetic anhydride (TFAA). Analytes identification is achieved by direct comparison with several reference materials and the use of a digitized library. 相似文献
67.
Castelli F Sarpietro MG Rocco F Ceruti M Cattel L 《Journal of colloid and interface science》2007,313(1):363-368
The stability and bioavailability of anticancer agents, such as gemcitabine, can be increased by forming prodrugs. Gemcitabine is rapidly deaminated to the inactive metabolite (2('),2(')-difluorodeoxyuridine), thus to improve its stability a series of increasingly lipophilic gemcitabine prodrugs linked through the 4-amino group to valeroyl, lauroyl, and stearoyl acyl chains were synthesized. Studies of monolayer properties are important to improve understanding of biological phenomena involving lipid/gemcitabine or lipid/gemcitabine derivative interactions. The interfacial behavior of monolayers constituted by DMPC plus gemcitabine or lipophilic gemcitabine prodrugs at increasing molar fractions was studied at the air/water interface at temperatures below (10 degrees C) and above (37 degrees C) the lipid phase transition. The effect of the hydrophobic chain length of gemcitabine derivatives on the isotherm of pure DMPC was investigated by surface tension measurement, and the results are reported as molar fractions as a function of mean molecular area per molecule. The results show that the compounds interact with DMPC producing mixed monolayers that are subject to an expansion effect, depending on the prodrug chain length. The results give useful hints of the interaction of these prodrugs with biological membranes and increase knowledge on the incorporation site of such compounds, as a function of their lipophilicity, in a lipid carrier; they may lead to improved liposomal formulation design. 相似文献
68.
69.
Maria Grazia Sarpietro Sara Ottimo Maria Chiara Giuffrida Dorotea Micieli Francesco Castelli 《Thermochimica Acta》2009,495(1-2):149-154
The interaction of eicosapentaenoic acid, a polyunsaturated fatty acid belonging to the omega-3 class, with biomembrane models represented by multilamellar or unilamellar vesicles made of dimyristoylphosphatidylcholine was monitored by means of differential scanning calorimetry technique. The calorimetric analysis of vesicle prepared in the presence of increasing molar fraction of eicosapentaenoic acid was carried out to show its maximum interaction with biomembrane models evaluating the effects of eicosapentaenoic acid on the biomembrane models thermotropic parameters (transition temperature and enthalpy variation). Furthermore, in order to detect the influence of the presence of hydrophilic or lipophilic media on the entity of the compound absorption by the biomembrane models, kinetic experiments were carried out.The results indicate that eicosapentaenoic acid strongly interacts with the biomembrane models depressing the transition temperature and the enthalpy variation. Eicosapentaenoic acid is absorbed by the biomembrane models and the absorption is affected by the used medium; in fact a bigger absorption happens in the presence of a lipophilic medium. 相似文献
70.
The 10α,20α-bis(4-nitrophenyl)-calix[4]pyrrole 2 can act as a topologically selective protecting group in the O-alkylation and acylation of polyphenolic polycyclic aromatic compounds thanks to the regioselective formation of phenolate-type complexes. Remarkably, the host-guest interaction with the anionic reagents is sufficiently strong and kinetically slow to produce a high degree of selectivity. 相似文献