Long-term diffusive samplers for the indoor air quality evaluation

Three kinds of diffusion samplers, conceived to perform long-term samplings in indoor sites are illustrated in this work. Two of them, in part deriving from the previous "Analyst for VOC" device, extend the field of application up to the semi-volatile organic compounds (SVOC), PAHs and nicotine in particular. A third device, which employs a basic barium hydroxide solution as an absorbing medium, is proposed for the determination of carbon dioxide levels which indicate the air change quality in the indoor sites. Laboratory and field experiments, performed in order to assess the reliability of the proposed devices, are shown. A monthly monitoring campaign, performed at three private apartments in Rome and its outskirts highlights that the indoor pollution levels are a complex function of various concurrent and opposite factors, like external air pollution, internal sources, air change rate and sink effect of surfaces, which contribute to depletion phenomena through adsorption and/or decomposition processes.     

Air monitoring of volatile aromatic compounds by means of long-term exposure diffusive samplers

Results obtained by using "Analyst", a long-term diffusive sampler, in some monitoring campaigns, performed for the determination of benzene and the volatile aromatic pollutants, in five cities of the Italian Umbria Region and at the city of Forlì, are presented and discussed. First results of an inter comparison between the "Analyst" and "radial-type" diffusive samplers, carried out by the Regional Agency for the Ambient Protection (ARPA) of Forlì, point out substantial advantages with the long-time sampling devices.     

Modeling acid and cationic catalysis on the reactivity of duocarmycins

Several catalyzed alkylation reactions of 9-methyladenine by a model [CPI, cyclopropa[c]pyrrolo[3,2-e]indol-4(5H)-one (1)] of duocarmycin anticancer drugs have been compared to the uncatalyzed reaction in gas phase and in water solvent bulk, using density functional theory at the B3LYP level with the 6-31+G(d,p) basis set and C-PCM solvation model. The effect on the CPI reactivity induced by water, formic and phosphoric acids (general acid catalysis), H3O+ (specific acid catalysis), sodium, and ammonium cation complexation (cationic catalysis) has been investigated. The calculations indicate that the specific acid catalysis and the catalysis induced by sodium cation complexation are strong in the gas phase, but solvation reduces them dramatically by electrostatic effects. The specific acid catalysis is still operative, but strongly reduced in water solution, where the reaction barrier is reduced by 8.6 kcal mol(-1) in comparison to the uncatalyzed reaction. The general acid catalysis induced by phosphoric acid (-7.3 kcal mol(-1)) and the catalysis induced by Na+ and NH4+ complexation become competitive, with a catalytic effect of -3.6 and -4.1 kcal mol(-1) in water, respectively. With the specific acid catalysis, the high acidity (low pK(a) value) of the conjugated acid of CPI (CPIH+), computed in water solution using both C-PCM (pK(a) = +2.6) and PCM-B3LYP/6-31+G(d,p) (pK(a) = +2.4) solvation models, suggests that the catalytic effects induced by NH4+ complexation could become more important than the specific acid catalysis and the general catalysis by H3PO4 under physiological conditions, due to concentration effects of the catalysts.     

Modeling of overloaded gradient elution of nociceptin/orphanin FQ in reversed-phase liquid chromatography

The Reversed-phase (RP) gradient elution chromatography of nociceptin/orphanin FQ (N/OFQ), a neuropeptide with many biological effects, has been modeled under linear and non-linear conditions. In order to do this, the chromatographic behavior has been studied under both linear and nonliner conditions under isocratic mode at different mobile phase compositions--ranging from 16 to 19% (v/v) acetonitrile (ACN) in aqueous trifluoracetic acid (TFA) 0.1% (v/v)-on a C-8 column. Although the range of mobile phase compositions investigated was quite narrow, the retention factor of this relatively small polypeptide (N/OFQ is a heptadecapeptide) has been found to change by more than 400%. In these conditions, gradient operation resulted thus to be the optimum approach for non-linear elution. As the available amount of N/OFQ was extremely reduced (only a few milligrams), the adsorption isotherms of the peptide, at the different mobile phase compositions examined, have been measured through the so-called inverse method (IM) on a 5 cm long column. The adsorption data at different mobile phase compositions have been fitted to several models of adsorption. The dependence of the isotherm parameters on the mobile phase composition was modeled by using the linear solvent strength (LSS) model and a generalized Langmuir isotherm that includes the mobile phase composition dependence. The overloaded gradient separation of N/OFQ has been modeled by numerically solving the equilibrium-dispersive (ED) model of chromatography under a selected gradient elution mode, on the basis of the previously determined generalized Langmuir isotherm. The agreement between theoretical calculations and experimental overloaded band profiles appeared reasonably accurate.     

Selectivity of purine alkylation by a quinone methide. Kinetic or thermodynamic control?

The alkylation reaction of 9-methyladenine and 9-methylguanine (as prototype substrates of deoxy-adenosine and -guanosine), by the parent o-quinone methide (o-QM), has been investigated in the gas phase and in aqueous solution, using density functional theory at the B3LYP/6-311+G(d,p) level. The effect of the medium on the reactivity, and on the stability of the resulting adducts, has been investigated by using the C-PCM solvation model to assess which adduct arises from the kinetically favorable path, or from an equilibrating process. The calculations indicate that the most nucleophilic site of the methyl-substituted nucleobases in the gas phase is the guanine oxygen atom (O(6)) (DeltaG()(gas) = 5.6 kcal mol(-)(1)), followed by the adenine N1 (DeltaG)(gas) = 10.3 kcal mol(-)(1)), while other centers exhibit a substantially lower nucleophilicity. The bulk effect of water as a solvent is the dramatic reduction of the nucleophilicity of both 9-methyladenine N1 (DeltaG)(solv) = 14.5 kcal mol(-)(1)) and 9-methylguanine O(6) (DeltaG)(solv) = 17.0 kcal mol(-)(1)). As a result there is a reversal of the nucleophilicity order of the purine bases. While O(6) and N7 nucleophilic centers of 9-methylguanine compete almost on the same footing, the reactivity gap between N1 and N7 of 9-methyladenine in solution is highly reduced. Regarding product stability, calculations predict that only two of the adducts of o-QM with 9-methyladenine, those at NH(2) and N1 positions, are lower in energy than reactants, both in the gas phase and in water. However, the adduct at N1 can easily dissociate in water. The adducts arising from the covalent modification of 9-methylguanine are largely more stable than reactants in the gas phase, but their stability is markedly reduced in water. In particular, the oxygen alkylation adduct becomes slightly unstable in water (DeltaG(solv) = +1.4 kcal mol(-)(1)), and the N7 alkylation product remains only moderately more stable than free reactants (DeltaG(solv) = -2.8 kcal mol(-)(1)). Our data show that site alkylations at the adenine N1 and the guanine O(6) and N7 in water are the result of kinetically controlled processes and that the selective modification of the exo-amino groups of guanine N2 and adenine N6 are generated by thermodynamic equilibrations. The ability of o-QM to form several metastable adducts with purine nucleobases (at guanine N7 and O(2), and adenine N1) in water suggests that the above adducts may act as o-QM carriers.     

An investigation of some homo- and heterobinuclear complexes of copper(II) and nickel(II) with pyridine-2-aldoxime

The reactions between copper(II) or nickel(II) with thecis-pyridine-2-aldoxime complexes of the same metal ions have been investigated by spectrophotometric measurements. The homo and heterobinuclear chelates involved have been isolated as the chlorides and characterized by spectroscopic and thermoanalytical techniques. The first decomposition step is not dependent on the furnace atmosphere (N₂ or O₂) and is accompanied by a large exothermic effect (DSC curves in N₂). TG curves show that binuclear complexes are generally slightly less stable than the respective mononuclear complexes but, in the case of [Cu(NiL₂)Cl₂(H₂O)₂], the complexation of copper(II) gives rise a drastic decrease of its thermal stability.

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Zusammenfassung Die Reaktionen zwischen Kupfer(II) und Nickel(II) mit den cis-Pyridin-2-aldoxim-Komplexen der gleichen Metallionen wurden spektrophotometrisch untersucht. Die homo- und heterobinuklearen Chelate wurden als Chloride isoliert und durch spektroskopische und thermoanalytische Methoden charakterisiert. Der erste Zersetzungsschritt ist unabhängig von der Ofenatmosphäre (N₂ oder O₂) und ist stark exotherm (s. DSC-Kurven in Abb. 1). Die TG-Kurven lassen erkennen, dass zweikernige Komplexe im allgemeinen etwas weniger stabil als die entsprechenden einkernigen Komplexe sind, im Falle von [Cu(NiL₂)Cl₂(H₂O)₂], aber die Anlagerung von Liganden an das Kupfer zu einer drastischen Verminderung der Stabilität führt.

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- -2- . - , . ( ) , -, . , , , , [Cu(NiL₂)Cl₂(H₂O)₂], .

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This work was carried out with financial support by MPI National Project.     

The molecular mechanics of valinomycin. I. Energy minimization calculations on the uncomplexed ionophore

We have used energy minimization calculations to study a number of conformations of uncomplexed valinomycin. In certain cases, x-ray diffraction atomic coordinates were used directly as input coordinates, while in other cases, conformations were found by altering the x-ray coordinates prior to minimization. Five calculated conformations are reported along with their relative energies. The conformation found theoretically to be the most stable is in agreement with earlier, cruder calculations, but does not correspond to the predominant conformation observed in nonpolar solvents. A possible rationale is presented.     

Direct evidence for muonium radicals in water solutions

The precession frequencies of muonium in a molecular radical state have been observed by μSR technique in diluted solutions of 2,6-dihydroxy-5-methyl-pyrimidine (thymine) in water. The conditions for the observation of the radicals are discussed in terms of the interdependent roles played by the chemical reaction time for muonium and by the external magnetic field. A comparison with the known ESR data on solid thymine confirms that the observed product of the muonium's reaction is an adduct radical with an hyperfine interaction reduced to 7% ± 1% of the muonium value     

Binuclear chelates of diethylenetriamine-Pentaacetic acid with chromium(III) and oxovanadium(IV) ions

The reactions of diethylenetriaminepentaacetic acid (DTPA=H₅L) or chromium(III)-DTPA, a ‘chelating agent’, with oxovanadium(IV) were investigated in aqueous solution by potentiometric methods. Homo- and hetero-binuclear species were evidenced as well as mixed complexes with hydrogen or hydroxide ions. The stability constants for these equilibria were calculated in 1.0 mol 1^?1 NaClO₄ solution at 20?C. The mononuclear (VO)H₃L·H₂O and the heterobinuclear (VO)CrL·5H₂O complexes were also obtained as solid compounds and were characterized by IR spectroscopy and thermoanalytical techniques (TG and DSC).     

Spectral and thermal studies of copper(II) complexes of 3- and 4-pyridinealdoxime

Copper(II) complexes of 3- and 4-pyridinealdoxime have been prepared and analyzed by spectroscopic (ir and diffuse reflectance) and thermoanalytical (TG, DTG and DTA) techniques. For both these systems, only species with metal: organic ligand: chloride ratio of 122 were found, and the organic ligand appears as a neutral molecule. The spectral data suggest a polymeric structure where the copper(II) ions are in a distorted octahedral environment.The thermal decompositions occur through the reduction of copper(II) to copper(I) and the conversion of the residual organic ligand into acid amide, as found for dihydrogenbis(pyridine-2-aldoxime) copper(II) chloride, but the initial decomposition temperatures are slightly increased, giving rise to the thermal stability sequence:

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Zusammenfassung Kupfer(II)-Komplexe von 3- und 4-Pyridinaldoxim wurden hergestellt und spektroskopisch (IR und diffuse Reflexion) sowie thermoanalytisch (TG, DTG und DTA) analysiert. Für beide Systeme wurden nur Species mit einem Metall:Ligand:Chlorid-Verhältnis von 122 gefunden. Der organische Ligand liegt als neutrales Molekül vor. Die Spektren deuten auf eine polymère Struktur hin, in der die Kupfer(II)-Ionen in einer verzerrten oktaedrischen Koordination vorliegen. Die thermischen Zersetzungen verlaufen über die Reduktion von Cu(II) zu Cu(I) und die Umwandlung des verbleibenden organischen Liganden in Säureamid, wie für Dihydrogen-bis(pyridin-2-aldoxim)-kupfer(II)-chlorid gefunden wurde, aber die Temperaturen des Beginns der Zersetzung und damit die thermische Stabilität steigen in der Reihenfolge [Cu(Py₄-CHNOH)₂Cl₂][Cu(Py₃-CHNOH)₂Cl₂]>[Cu(Py₂-CHNOH)₂]Cl₂ etwas an.

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(, ) ( ) 3- 4- . 122, . , . -( -2-)- . , , , : Cu(4-Py-CHNOH)₂Cl₂Cu(3-Py-CHNOH)₂Cl₂>Cu(2-Py-CHNOH)₂Cl₂.