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211.
This review details ion chromatography developments and related applications, mainly in the field of environmental analysis, gained by the evolution in the science and technology for new stationary phases. Unconventional approaches to ion chromatographic separations are also outlined. 相似文献
212.
Concetta De Stefano Claudia Foti Ottavia Giuffrè Graziella Signorino 《Journal of solution chemistry》1998,27(7):655-662
Thermodynamic parameters, G°, H° and TS° are reported for the formation of proton amine–hexacyanoferrate(II) complexes, in aqueous solution, at 25°C. H° were determined by the temperature dependence of formation constants and/ or by direct calorimetry in aqueous solution, at T = 25°C. Enthalpy changes for the reaction HiAi+ + Hj Fe(CN)
6
j-4
= AFe (CN)6H
i+j
i+j-4
(where A = methylamine, ethylenediamine, and tetraethylenepentamine) are quite low and the main contribution to the stability of these complexes arises from the entropic term, as expected for electrostatic interactions. When j = 0, the formation entropy is linearly dependent on i according to the simple equation TS° = 13.4 i kJ-mol–1. 相似文献
213.
Mabilia R Cecinato A Tomasi Scianò MC Di Palo V Possanzini M 《Annali di chimica》2004,94(9-10):733-740
Exhaust emissions from a recent model heavy-duty diesel vehicle (city bus) in a chassis dynamometer were measured during a transient driving cycle. Particle-bound polycyclic aromatic hydrocarbons (PAHs) and gaseous carbonyls, substances that create health hazards and are, as yet, unregulated were collected, the former on filters and the latter on dinitrophenylhydrazine (DNPH)-coated silica cartridges and analysed by GC-MS and HPLC, respectively. PAH emission rates decreased with the number of benzene fused rings. They averaged 0.2 mg km(-1) for a total of 11 PAHs ranging from fluoranthene to benzo(ghi)perylene. Fluoranthene and pyrene accounted for 90% of total PAHs. The sum of emission rates of C1 approximately C6 carbonyls averaged 174 mg km(-1), even if formaldehyde alone represented approximately 70% of the total carbonyl mass, followed by acetaldehyde (13%). Results obtained were compared with emission data reported in previous studies. 相似文献
214.
De Stefano C Gianguzza A Piazzese D Sammartano S 《Analytical and bioanalytical chemistry》2005,383(4):587-596
Acid–base behaviour of a commercial sodium alginate extracted from brown seaweed (Macrocystis pyrifera) has been investigated at different ionic strengths (0.1≤I/mol l?1≤1.0) and in different supporting electrolytes (Et4NI, NaCl, KCl, LiCl, NaCl+MgCl2), with the aim of examining the influence of ionic medium on the proton-binding capacity and of quantifying the strength of interaction with light metal ions in the perspective of speciation studies in natural aqueous systems. Potentiometric ([H+]-glass electrode) and titration calorimetric data were expressed as a function of the dissociation degree (α) using different models (Henderson–Hasselbalch modified, Högfeldt three parameters and linear equations). The dependence on ionic strength of the protonation constants was taken into account by a modified specific interaction theory model. Differences among different media were explained in terms of the interaction between polyanion and metal cations of the supporting electrolytes. Quantitative information on the proton-binding capacity, together with the stabilities of different species formed, is reported. Protonation thermodynamic parameters, at α=0.5, are log K H=3.686±0.005, ΔG 0=?21.04±0.03 kJ mol?1, ΔH 0=4.8±0.2 kJ mol?1 and TΔS 0=35.7±0.3 kJ mol?1, at infinite dilution. Protonation enthalpies indicate that the main contribution to proton binding arises from the entropy term. A strict correlation between ΔG and TΔS was found, TΔS=?9.5–1.73 ΔG. Results are reported in light of building up a chemical complexation model of general validity to explain the binding ability of naturally occurring polycarboxylate polymers and biopolymers. Speciation profiles of alginate in the presence of sodium and magnesium ions, naturally occurring cations in natural waters, are also reported. 相似文献
215.
Virender K. Sharma Fabien Casteran Frank J. Millero Concetta De Stefano 《Journal of solution chemistry》2002,31(10):783-792
The sulfur-containing biomolecule, cysteine has a role in physiological and natural environment because of its strong interactions with metals. To understand these interactions of metals with cysteine, one needs reliable dissociation constants for the protonated cysteine species [
CH(CH2SH)COOH; H3B+]. The values of dissociated constants, p
, for protonated cysteine species (H3B+ H+ + H2B, K
1; H2B H+ + HB–,K
2; HB– H+ + B2–,K
3) were determined from potentiometric measurements in NaCl solutions as a function of ionic strength, 0.5–6.0 mol-(kgH2O)–1 and between 5, and 45°C. The equations
were fitted to the results with a standard errors of the fits of 0.116, 0.057, and 0.093 for
,
, and
, respectively. The
results were used to determine new Pitzer parameters (0, 1, and C) for the interactions of Na+ and Cl– with cysteine species. These coefficients can be used to make reasonable estimates of the activity coefficients of the cysteine species and
for the dissociation of cysteine in physiological and natural waters containing mostly NaCl. 相似文献
216.
Alessandro De Robertis Concetta De Stefano Grazia Patane Silvio Sammartano 《Journal of solution chemistry》1993,22(10):927-940
Protonation constants of triethylenetetramine (trien) and tetraethylenepentamine (tetren) were determined, in NaCl aqueous solutions, at different ionic strengths, at 25°C, using the the pH-metric technique. The behavior of protonation constants as a function of ionic strength can be explained by a model which takes into account the formation of the species AH
q
Cl
p
[A=amine; q=1...4, p=1,2 (trien); q=1...5, p=1.3 (tetren)]. 相似文献
217.
Giuseppina Negri Concetta Kascheres Albert J. Kascheres 《Journal of heterocyclic chemistry》2004,41(4):461-491
Enaminoketones and esters are gaining increased interest, particularly cyclic‐β‐enaminoesters, which are known as important intermediates for the synthesis of heterocycles and natural products, because the enantioselective preparation of highly functionalized compounds is of central importance in synthetic chemistry. Enaminones are versatile synthetic intermediates that combine the ambident nucleophilicity of enamines with the ambident eletrophilicity of enones. Enaminoketones and enaminonitriles have proven to be versatile building blocks for the synthesis of various heterocycles such as pyridine, pyrimidine and pyrrole deriva tives. Enaminones systems have “enone” character, and may act as acceptors in both 1,2 and 1,4‐additions. In this way the enaminone serves as a scaffold for annulation, and can gain access to systems such as pyrroles indolizidines, quinolizidines and perhydroindoles, all of which are common motifs in alkaloid structures. Enaminones are frequently employed as building blocks for the preparation of a variety of bicyclic compounds of biological interest and have been recently recognized as potential anticonvulsant compounds. Since a large number of developments in the use of enaminones in heterocyclic synthesis have occurred, a review of the recent developments in the synthetic approaches, covering the literature since 1995 until 2004, to these interesting molecules and their useful chemical transformations and biological activity can be considered of considerable value. 相似文献
218.
Pier G. Daniele Alessandro De Robertis Concetta De Stefano Antonio Gianguzza Silvio Sammartano 《Journal of solution chemistry》1991,20(5):495-515
Protonation constants of o-phosphate were studied potentiometrically, using the (H+)-glass electrode in aqueous NaCl, KCl and tetraethylammonium iodide solutions, at 0IIM and 10T50°C. The differences found in the protonation constants for different salt solutions are explained by a complex formation model. The formation of the species MPO
4
2–
, MHPO
4
–
, MH2PO
4
0
, M2PO
4
–
and M2HPO
4
0
(M=Na+, K+) is hypothesized. In mixed NaCl-KCl solutions, it is possible to find the mixed metal species NaKPO
4
–
and NaKHPO
4
0
. Ionic strength and temperature dependence parameters are reported for all species. The relevance of Na+ and K+ complexes is discussed in connection with speciation problems of natural fluids, such as marine water and urine. 相似文献
219.
220.
Paola Cardiano S. Sergi Concetta De Stefano S. Ioppolo P. Piraino 《Journal of Thermal Analysis and Calorimetry》2008,91(2):477-485
The ancient mortars of the monastery of San Filippo di Fragalà in Frazzanò, the first Basilian-Norman center in Sicily, have
been studied and classified by means of ICP, HPLC, TG-DTA, XRD and thin sections analysis. A new very simple method to evaluate
the hydraulic properties of the mortars, based on the combination of analytical and thermogravimetric data, is also reported.
The HPLC investigations indicate that the monastery is only partially involved in decay phenomena due to the action of soluble
salts. 相似文献