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101.
Francesco Crea Concetta De Stefano Giuseppe Manfredi Silvio Sammartano 《Journal of solution chemistry》2012,41(7):1240-1253
The interaction between adenosine-5??-triphosphate (ATP) and some aromatic amines (L), namely 1,2-phenylenediamine, 2-(2,4-diaminophenoxy)ethanol, 4-N-(2-hydroxyethyl)2,4-diaminoanisole, 4,5-diamino-1-N-(2-hydroxyethyl)pyrazole and 1,3-bis(2,4-diaminophenoxy) propane, was studied at T=298.15 K and I=0.06 mol?L?1 in NaCl aqueous solution. For all of the investigated systems, the formation of [(ATP)(L)H i ](i?4) species (i=1 to n+2; n=maximum protonation degree of the amine) with high yields (60?C80?%) were found. The ionic strength and temperature dependences of the complex formation constants were studied using semiempirical equations. The sequestering ability of the aromatic amines toward ATP was defined by calculating the pL50 parameter (the total ligand concentration, as ?log10 C L, able to bind 50?% of ATP). The dependence of pL50 on pH, ionic strength and temperature is reported. Moreover, it was found that the overall formation constants are reasonably linearly dependent on the number of protons in the complex species. Comparison with the stability of the species of analogous systems, such as ATP?Caliphatic amines and pyrophosphate?Caliphatic amines, is reported. For all these systems a fairly linear dependence was found of the formation constants on the basicity of the amines. 相似文献
102.
Maria Concetta Bruzzoniti Rosa Maria De Carlo Sonia Fiorilli Barbara Onida Corrado Sarzanini 《Journal of chromatography. A》2009,1216(29):5540-5547
The retention properties of a SBA-15 mesoporous silica functionalized with –(CH2)3COOH groups, synthesized by a co-condensation route, were investigated for the ion chromatography of different cationic species. A systematic study on the effect of different eluent compositions containing non-complexing (methanesulfonic acid) or complexing (oxalic or pyridine-2,6-dicarboxylic acids) eluents, in the presence of organic modifiers (CH3CN, CH3OH, CH3NH2) on the retention of cations (Li+, Na+, K+, Ca2+, Mg2+, Sr2+, Ba2+, NH4+, Cu2+, Ni2+, Zn2+, Cd2+, Co2+, Pb2+, Fe3+) chosen as model analytes and for their environmental importance, allowed us to elucidate the mechanisms (cation-exchange or complexation) involved in the retention on the SBA-15 phase. For the first time separations of cations on SBA-15 based stationary phases are investigated, providing the basis for further development of mesoporous silica chemistry for in-flow ion-exchange applications. 相似文献
103.
Maria Concetta Bruzzoniti Dorota Korte Kobylinska Corrado Sarzanini 《Analytica chimica acta》2010,665(1):69-73
A flow injection method has been developed for determination of silver. The method is based on a reduction reaction with sodium borohydride which leads to the formation of a colloidal species which is monitored at a wavelength of 390 nm.The reaction variables flow rate, sodium borohydride concentration and pH, which affect sensitivity, were investigated and their effects were established using a two-levels, three-factor experimental design. Further optimization of manifold variables (reaction coil and injection volume) allowed us to determine silver in the range 0.050-5.0 mg L−1 with a minimum detectable concentration of 0.050 mg L−1. Silver is added, as biocide, to drinking water for spacecrafts. The chemical species of silver, present in this kind of sample, were characterized by a procedure based on the selective retention of Ag+ onto a 2.2.2. cryptand based substrate followed by determination of the non-bound and bound (after elution) Ag+ by the FIA method. The method optimized was applied to a drinking water sample provided for the launch with the Automated Transfer Vehicle (ATV) module Jule Verne to the International Space Station (March 9, 2008). 相似文献
104.
Protonation constants of carbonate were determined in tetramethylammonium chloride (Me4NClaq 0.1 ≤ I/mol kg−1 ≤ 4) and tetraethylammonium iodide (Et4NIaq 0.1 ≤ I/mol kg−1 ≤ 1) by potentiometric ([H+]-glass electrode) measurements. Dependence of protonation constants on ionic strength was taken into account by modified specific ion interaction theory (SIT) and by Pitzer models. Literature data on the protonation of carbonate in NaClaq (0.1 ≤ I/mol kg−1 ≤ 6) were also critically analysed. Both protonation constants of carbonate follow the trend Et4NI > Me4NCl > NaCl. An ion pair formation model designed to take into account the different protonation behaviours of carbonate in different supporting electrolytes was also evaluated. 相似文献
105.
Quercetin, 6-bromoquercetin (3), and 8-bromoquercetin (4) undergo H/D exchange at 6- and 8-positions, in acetone-d6 and methanol-d4, catalyzed by acids and bases. The base-catalyzed process is faster, and in acetone-d6 the half-lives of H-8 and H-6 are 56.5 and 48.6 h, respectively. A high regioselectivity at the position 8 of quercetin is observed under acid-catalysis in both solvents but in methanol-d4 regioselectivity is retained even under base-catalysis. On the other hand, 6,8-dibromoquercetin (2), 4 and 6,8-dibromo-2′-hydroxyquercetin (5) manifest the ability of exchanging bromine with hydrogen (or deuterium) under acid-catalysis in acetone and other enolizable ketones (e.g., methyl ethyl ketone, acetylacetone, and isophorone). These bromophenols release bromine from their 8-position only, in a slow bromination process that likely involves their protonated form (arenium ion I) as brominating agent and the enol of the above ketones as Br-acceptor. The arenium ion I of these bromophenols is expected to be a powerful electrophile and its formation is most likely to be rate-determining. 相似文献
106.
Abstract The phase behaviour of blends of poly(ethylene oxide) (PEO) with the liquid crystal p-azoxyanisole (PAA) has been studied by differential scanning calorimetry and optical microscopy. This system exhibits partial miscibility of the components in the molten state (at temperatures above 337 K). The melting temperature and enthalpy of the PAA phase has been found to depend on the blend composition, whereas the melting behaviour of the polymer phase remains quite unaltered. The occurrence of the PAA nematic phase, dispersed within an isotropic liquid phase, has been observed at high concentrations of liquid crystal. The morphology of the blends in the solid state changes largely with the PAA content, depending on the solubility of the components in the liquid phase. 相似文献
107.
Giuseppe CremonesiPiero Dalla Croce Alessandra ForniMaddalena Gallanti Concetta La Rosa 《Tetrahedron》2011,67(16):2925-2933
Enantiomerically pure, 3-methyl- or 3-ethoxycarbonyl-substituted (5S)- and (5R)-5-acetyl-2-isoxazolines were obtained from the corresponding racemic mixtures by means of an enzymatic reduction with baker’s yeast, followed by the separation of the enantiopure syn- and anti-alcohols and oxidation of the alcohol group. The reaction between these ketones and (2R)-Schöllkopf’s bislactim ether azaenolate was studied: using (5S)- and (5R)-3-methyl derivatives, two diastereoisomeric adducts were obtained in good yield and stereoselectivity, whereas reaction with the (5S)- and (5R)-3-ethoxycarbonyl derivatives led to a complex mixture of products. Subsequent controlled hydrolysis of the pyrazine ring led to β-(3-methyl-4,5-dihydro-isoxazol-5-yl)-l-threonines methyl ester together with the corresponding (R)-valine dipeptides. 相似文献
108.
There have been many studies of the fragmentation of metastable ions in the field-free regions of sector mass spectrometers.1 Such ions have a lower internal energy than do ions fragmenting in the source. As a result, their reactions are often more sensitive to 相似文献
109.
Daniela Giardina‐Papa Francesco Paolo Intini Giovanni Natile Concetta Pacifico 《Acta Crystallographica. Section C, Structural Chemistry》2012,68(11):m300-m302
The title compound, [PtCl(C3H7NO)2(C18H15P)]Cl·H2O or trans‐[PtCl{Z‐HN=C(Me)OMe}2(PPh3)]Cl·H2O, crystallizes from an acetone solution of isomeric trans‐[PtCl{E‐HN=C(Me)OMe}2(PPh3)]Cl. The two HN=C(Me)OMe ligands show typical π‐bond delocalization over the N—C—O group [Cini, Caputo, Intini & Natile (1995). Inorg. Chem. 34 , 1130–1137] and have the unprecedented Z–anti configuration. The relative orientation of the imino ether ligands is head‐to‐tail. 相似文献
110.
Dr. Concetta Avitabile Dr. Carlo Diaferia Dr. Valentina Roviello Dr. Davide Altamura Dr. Cinzia Giannini Dr. Luigi Vitagliano Dr. Antonella Accardo Prof. Alessandra Romanelli 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(65):14850-14857
Studies carried out in recent decades have revealed that the ability to self-assemble is a widespread property among biomolecules. Small nucleic acid moieties or very short peptides are able to generate intricate assemblies endowed with remarkable structural and spectroscopic properties. Herein, the structural/spectroscopic characterization of aggregates formed by nucleobases and peptide nucleic acid (PNA)–peptide conjugates are reported. At high concentration, all studied nucleobases form aggregates characterized by previously unreported fluorescence properties. The conjugation of these bases, as PNA derivatives, to the dipeptide Phe–Phe leads to the formation of novel hybrid assemblies, which are characterized by an amyloid-like association of the monomers. Although these compounds share the same basic cross-β motif, the nature and number of PNA units have an important impact on both the level of structural order and the intrinsic fluorescence of the self-assembled nanostructure. 相似文献