Polycyclic aromatic hydrocarbons and their oxygenated derivatives in urban aerosol: levels, chemical profiles, and contribution to PM2.5 oxidative potential.

The concentrations of polycyclic aromatic hydrocarbons (PAHs) and quinones, a subgroup of oxygenated PAHs (oxy-PAHs), were measured in PM2.5 samples collected during warm (May-June 2019) and cold (February-March 2020) seasons in the city of Bologna, Italy. Total PAHs concentration was nearly double in winter (6.58 ± 1.03 ng m-3) compared with spring (3.16 ± 0.53 ng m-3), following the trend of the PM2.5 mass concentration. Molecular diagnostic ratios suggested that, together with traffic, biomass burning was the dominant emission source contributing to the peaks of concentration of PM2.5 registered in the cold season. Quinone level was constant in both seasons, being 1.44 ± 0.24 ng m-3, that may be related to the increased secondary formation during warm season, as confirmed by the higher Σoxy-PAHs/ΣPAHs ratio in spring than in winter. The oxidative potential (OP) of the PM2.5 samples was assessed using acellular dithiothreitol (DTT) and ascorbic acid (AA) assays. The obtained responses showed a strong seasonality, with higher volume-normalized (OPV) values in winter than in spring, i.e., OPVDTT: 0.32 ± 0.15 nmol min-1 m-3 vs. 0.08 ± 0.03 nmol min-1 m-3 and OPVAA: 0.72 ± 0.36 nmol min-1 m-3 vs. 0.28 ± 0.21 nmol min-1 m-3. Both OPVDTT and OPVAA responses were significantly associated with total PAHs, as a general descriptor of redox-active PAH derivatives, associated with co-emission from burning sources or secondary atmospheric oxidation of parent PAHs. Otherwise, only winter OPVDTT responses showed a significant correlation with total Æ©oxy-PAHs concentration.

Historical Changes in Seasonal Aerosol Acidity in the Po Valley (Italy) as Inferred from Fog Water and Aerosol Measurements.

Acidity profoundly affects almost every aspect that shapes the composition of ambient particles and their environmental impact. Thermodynamic analysis of gas-particle composition datasets offers robust estimates of acidity, but they are not available for long periods of time. Fog composition datasets, however, are available for many decades; we develop a thermodynamic analysis to estimate the ammonia in equilibrium with fog water and to infer the pre-fog aerosol pH starting from fog chemical composition and pH. The acidity values from the new method agree with the results of thermodynamic analysis of the available gas-particle composition data. Applying the new method to historical (25 years) fog water composition at the rural station of San Pietro Capofiume (SPC) in the Po Valley (Italy) suggests that the aerosol has been mildly acidic, with its pH decreasing by 0.5-1.5 pH units over the last decades. The observed pH of the fog water also increased 1 unit over the same period. Analysis of the simulated aerosol pH reveals that the aerosol acidity trend is driven by a decrease in aerosol precursor concentrations, and changes in temperature and relative humidity. Currently, NOx controls would be most effective for PM2.5 reduction in the Po valley both during summer and winter. In the future, however, seasonal transitions to the NH3-sensitive region may occur, meaning that the NH3 reduction policy may become increasingly necessary.

Effect of filter extraction solvents on the measurement of the oxidative potential of airborne PM2.5.

Solvent extraction of PM2.5 samples collected on the filter is a preliminary step for assessing the PM2.5 oxidative potential (OP) using cell-free assays, as the dithiothreitol (DTT) and the ascorbic acid (AA) assays. In this study, we evaluated the effect of the solvent choice by extracting ambient PM2.5 samples with different solvents: methanol, as organic solvent, and two aqueous buffers, i.e., phosphate buffer (PB) and Gamble's solution (G), as a lung fluid surrogate solution. Both the measured volume-based OPVDTT and OPVAA responses varied for the different extraction methods, since methanol extraction generated the lowest values and phosphate buffer the highest. Although all the tested solvents produced intercorrelated OPVDTT values, the phosphate buffer resulted the most useful for OPDTT assessment, as it provided the most sensible measure (nearly double values) compared with other extractions. The association of the measured OPV values with PM chemical composition suggested that oxidative properties of the investigated PM2.5 samples depend on both transition metals and quinones, as also supported by additional experimental measurements on standard solutions of redox-active species.

Source-related components of fine particulate matter and risk of adverse birth outcomes in Northern Italy.

BACKGROUND/AIM: The aim of the present study was to assess the association between PM2.5, its sources, and preterm birth (PTB), low birth weight (LBW), and small for gestational age (SGA) in a large open residential cohort (Supersito Project in the Emilia-Romagna Region - Northern Italy). METHODS: We collected 2012-2014 pregnancy and childbirth data from Birth Assistance Certificates and selected the pregnancies of interest. PTBs (gestational age < 37 weeks), LBW (weight < 2500 g), and SGA (newborns weighing ≤ 10th age and pregnancy week-specific percentile) were considered. Three-year measurements of daily concentrations and constituents of PM2.5 were available at four sites and were analyzed through a source apportionment approach identifying 6 sources (traffic, biomass burning, oil combustion, anthropogenic mix, and two secondary factors). Exposure to PM2.5 and sources was calculated at address level. Using logistic regression models, associations between exposure and outcomes were derived, applying single-pollutant and two-pollutant models, to verify the independent effect of each source. RESULTS: The study included 23,708 neonates born to 23,415 women, among whom 1,311 PTB, 424 LBW, and 1,354 SGA occurred. PTB was the only outcome associated with PM2.5 mass (OR 1.03, 95% CI 1.002-1.058 per 1 µg/m3). Traffic, oil combustion and secondary sulfates and organics showed independent effects on PTB. Exposure to secondary nitrates was associated with a lower risk of PTB. There was no association between LBW or SGA and source-specific PM2.5 components or the residual PM2.5 related to all other sources. CONCLUSION: This study found an association between PTB and PM2.5. Traffic, secondary sulfates, and organic and oil combustion were the sources with most consistent association.

Higher health effects of ambient particles during the warm season: The role of infiltration factors.

A large number of studies have shown much higher health effects of particulate matter (PM) during the warm compared to the cold season. In this paper we present the results of an experimental study carried out in an unoccupied test apartment with the aim of understanding the reasons behind the seasonal variations of the health effects due to ambient PM2.5 exposure. Measurements included indoor and outdoor PM2.5 mass and chemical composition as well as particle size distribution of ultrafine particles. Monitoring campaigns were carried out during summer and winter following a ventilation protocol developed to replicate typical occupant behaviour according to a questionnaire-based survey. Our findings showed that seasonal variation of the relationship between ambient and indoor mass concentrations cannot entirely explain the apparent difference in PM toxicity between seasons and size distribution and chemical composition of particles were identified as other possible causes of changes in the apparent PM toxicity. A marked decrease of ultrafine particles (<100 nm) passing from outdoors to indoors was observed during winter; this resulted in higher indoor exposure to nanoparticles (<50 nm) during summer. With regards to the chemical composition, a pooled analysis showed infiltration factors of chemical species similar to that obtained for PM2.5 mass with values increasing from 0.73 during winter to 0.90 during summer and few deviations from the pooled estimates. In particular, significantly lower infiltration factors and sink effect were found for nitrates and ammonium during winter. In addition, a marked increase in the contribution of indoor and outdoor sulfates to the total mass was observed during summer.

Vertical variation of PM2.5 mass and chemical composition, particle size distribution, NO2, and BTEX at a high rise building.

Substantial efforts have been made in recent years to investigate the horizontal variability of air pollutants at regional and urban scales and epidemiological studies have taken advantage of resulting improvements in exposure assessment. On the contrary, only a few studies have investigated the vertical variability and their results are not consistent. In this study, a field experiment has been conducted to evaluate the variation of concentrations of different particle metrics and gaseous pollutants on the basis of floor height at a high rise building. Two 15-day monitoring campaigns were conducted in the urban area of Bologna, Northern Italy, one of the most polluted areas in Europe. Measurements sites were operated simultaneously at 2, 15, 26, 44 and 65 m a.g.l. Several particulate matter metrics including PM2.5 mass and chemical composition, particle number concentration and size distribution were measured. Time integrated measurement of NO2 and BTEX were also included in the monitoring campaigns. Measurements showed relevant vertical gradients for most traffic related pollutants. A monotonic gradient of PM2.5 was found with ground-to-top differences of 4% during the warm period and 11% during the cold period. Larger gradients were found for UFP (∼30% during both seasons) with a substantial loss of particles from ground to top in the sub-50 nm size range. The largest drops in concentrations for chemical components were found for Elemental Carbon (-27%), iron (-11%) and tin (-36%) during winter. The ground-to-top decline of concentrations for NO2 and benzene during winter was equal to 74% and 35%, respectively. In conclusion, our findings emphasize the need to include vertical variations of urban air pollutants when evaluating population exposure and associated health effects, especially in relation to some traffic related pollutants and particle metrics.

Is particulate air pollution at the front door a good proxy of residential exposure?

The most advanced epidemiological studies on health effects of air pollution assign exposure to individuals based on residential outdoor concentrations of air pollutants measured or estimated at the front-door. In order to assess to what extent this approach could cause misclassification, indoor measurements were carried out in unoccupied rooms at the front and back of a building which fronted onto a major urban road. Simultaneous measurements were also carried out at adjacent outdoor locations to the front and rear of the building. Two 15-day monitoring campaigns were conducted in the period June-December 2013 in a building located in the urban area of Bologna, Italy. Particulate matter metrics including PM2.5 mass and chemical composition, particle number concentration and size distribution were measured. Both outdoor and indoor concentrations at the front of the building substantially exceeded those at the rear. The highest front/back ratio was found for ultrafine particles with outdoor concentration at the front door 3.4 times higher than at the rear. A weak influence on front/back ratios was found for wind direction. Particle size distribution showed a substantial loss of particles within the sub-50 nm size range between the front and rear of the building and a further loss of this size range in the indoor data. The chemical speciation data showed relevant reductions for most constituents between the front and the rear, especially for traffic related elements such as Elemental Carbon, Iron, Manganese and Tin. The main conclusion of the study is that gradients in concentrations between the front and rear, both outside and inside the building, are relevant and comparable to those measured between buildings located in high and low traffic areas. These findings show high potential for misclassification in the epidemiological studies that assign exposure based on particle concentrations estimated or measured at subjects' home addresses.

Characteristics and major sources of carbonaceous aerosols in PM2.5 in Emilia Romagna Region (Northern Italy) from four-year observations.

The concentrations of organic and elemental carbon in PM2.5 aerosol samples were measured in two sites of Emilia Romagna (Po Valley, Northern Italy) in eight campaigns during different seasons from 2011 to 2014. Strong seasonality was observed with the highest OC concentrations during the cold periods (≈ 5.5 µg m(-3)) and the lowest in the warm months (≈ 2.7 µg m(-3)) as well as with higher EC levels in fall/winter (≈ 1.4 µg m(-3)) in comparison with spring/summer (≈ 0.6 µg m(-3)). Concerning spatial variability, there were no statistically significant difference (p<0.05) between OC concentrations at the two sampling sites in each campaign, while the EC values were nearly twofold higher levels at the urban site than those at the rural one. Specific molecular markers were investigated to attempt the basic apportionment of OC by discriminating between the main emission sources of primary OC, such as fossil fuels burning - including traffic vehicle emission - residential wood burning, and bio-aerosol released from plants and microorganisms, and the atmospheric photo-oxidation processes generating OCsec. The investigated markers were low-molecular-weight carboxylic acids - to describe the contribution of secondary organic aerosol - anhydrosugars - to quantify primary emissions from biomass burning - bio-sugars - to qualitatively estimate biogenic sources - and Polycyclic Aromatic Hydrocarbons - to differentiate among different combustion emissions. Using the levoglucosan tracer method, contribution of wood smoke to atmospheric OC concentration was computed. Wood burning accounts for 33% of OC in fall/winter and for 3% in spring/summer. A clear seasonal trend is also observed for the impact of secondary processes with higher contribution in the warm seasons (≈ 63%) in comparison with that in colder months (≈ 33%), that is consistent with enhanced solar radiation in spring/summer.

Stoichiometric diversity of Ni(II) metallacrowns with ß-alaninehydroxamic acid in aqueous solution.

The complex-formation equilibria of the system Ni(II)/ß-alaninehydroxamic acid (ß-AlaHA, LH) have been studied in solution by using potentiometry, calorimetry, ESI mass spectrometry and UV-Visible spectrophotometry. A series of mononuclear and polynuclear species have been identified at different pH and for different Ni(II)/ligand ratios. Among the polymetallic species, we have identified the 12-metallacrown-4 (12-MC-4) species [Ni5(LH(-1))4](2+), which is analogous to the previously characterized [Cu5(LH(-1))4](2+) 12-MC-4 complex, and which corresponds to the metallacrown complex predicted by the Metallacrown Structural Paradigm. Besides this species, we have very unexpectedly identified in solution three other polynuclear species, corresponding to the stoichiometries [Ni4(LH(-1))4], [Ni5(LH(-1))5] and [Ni6(LH(-1))6]. A metallacrown with the same stoichiometry as [Ni5(LH(-1))5] containing α-AlaHA as the ligand has been previously reported, while the other two species are new for the speciation systems of Cu(II) or Ni(II) aminohydroxamic acids. Intriguingly, all the three latter stoichiometries correspond to those of vacant 12-MC-4, 15-MC-5 or 18-MC-6 species. The thermodynamic parameters related to their formation in solution are discussed, together with the speciation of the mononuclear complexes, on the basis of the structural and thermodynamic information available on metallacrowns.

GC/MS analysis of water-soluble organics in atmospheric aerosol: optimization of a solvent extraction procedure for simultaneous analysis of carboxylic acids and sugars.

The main goal of the present study was to develop a procedure for the simultaneous GC/MS analysis of a wide range of water-soluble organic compounds (WSOCs, mainly dicarboxylic acids and sugars) in atmospheric aerosol as chemical markers of atmospheric processes. The response surface methodology, including central composite design, was applied to systematically investigate and optimize the operating conditions of a solvent extraction method as the most widely used procedure for determining WSOCs in particulate matter (PM) samples. A solvent mixture of methanol/dichloromethane (90:10) and a volume of 10 ml were the optimum conditions that permit the simultaneous analysis of 30 target WSOCs, including dicarboxylic acids and sugars. Recoveries and limits of detection were determined for a standard mixture containing target analytes, and they varied from 79 to 103 % and 0.3 to 1 ng m(-3), respectively. The optimized procedure was used for the analysis of field PM filters and demonstrated its feasibility in detecting several important environmental WSOCs.

Seasonal variation and source estimation of organic compounds in urban aerosol of Augsburg, Germany.

This study reports a general assessment of the organic composition of the PM(2.5) samples collected in the city of Augsburg, Germany in a summer (August-September 2007) and a winter (February-March 2008) campaign of 36 and 30 days, respectively. The samples were directly submitted to in-situ derivatisation thermal desorption gas chromatography coupled with time of flight mass spectrometry (IDTD-GC-TOFMS) to simultaneously determine the concentrations of many classes of molecular markers, such as n-alkanes, iso- and anteiso-alkanes, polycyclic aromatic hydrocarbons (PAHs), oxidized PAHs, n-alkanoic acids, alcohols, saccharides and others. The PCA analysis of the data identified the contributions of three emission sources, i.e., combustion sources, including fossil fuel emissions and biomass burning, vegetative detritus, and oxidized PAHs. The PM chemical composition shows seasonal trend: winter is characterized by high contribution of petroleum/wood combustion while the vegetative component and atmospheric photochemical reactions are predominant in the hot season.

GC-MS analysis of water-soluble organics in atmospheric aerosol: response surface methodology for optimizing silyl-derivatization for simultaneous analysis of carboxylic acids and sugars.

This paper describes the development of a derivatization procedure - silylation using N,O-bis(trimethylsilyl)-trifluoroacetamide (BSTFA) - for the simultaneous GC-MS analysis of a wide range of water-soluble organics in atmospheric aerosols. The reaction operating conditions were optimized using the response surface methodology (RSM) including central composite design (CCD) in order to achieve the highest response for a large number of dicarboxylic acids and sugars. The factors considered were: (i) reaction temperature (50-90°C), (ii) the reaction duration (60-120 min), (iii) reagent concentrations (10-100% of the total solution volume) and (iv) pyridine concentration (0-50% of the derivatization reagent). On the basis of RSM and experimental evidence, the optimum derivatization conditions were defined as reaction temperature of 75°C, reaction duration of 70 min, BSTFA reagent concentration of 55% and pyridine concentration of 35%. The optimized protocol was extended to a broader range of 22 target analytes that are relevant chemical markers, i.e., 15 carboxylic acids and 7 sugars. In addition, the applicability of the optimized procedure was verified in environmental matrices from PM filters collected under different conditions, i.e., different seasons (summer vs. winter), different sampling sites (urban vs. rural), different particle size dimensions (PM(2.5) vs. PM(1)).

Metallacrowns of Ni(II) with α-aminohydroxamic acids in aqueous solution: beyond a 12-MC-4, an unexpected (vacant?) 15-MC-5.

Growing attention has been devoted in the recent years to a class of metallamacrocycles known as metallacrowns (MCs). They are structural analogues of crown ethers where the methylene bridges have been substituted by coordinative bonds formed by a transition metal ion ("ring" metal) and a nitrogen atom. The cavity of the metallacrown can accommodate an additional metal ion ("core" metal) either identical or different from the ring metal, thus forming a homo- or hetero-metallic MC. The most studied ring metal ion is certainly Cu(2+) and the aminohydroxamic acids have proved to be very suitable ligands to form MCs. The behavioural analogies between Cu(2+) and Ni(2+) in forming complexes, along with recent literature data in the solid state, prompted us to investigate the possible MC formation between Ni(2+) and both (S)-α-alaninehydroxamic acid and (S)-valinehydroxamic acid, in aqueous solution. Two metallacrowns, a 12-MC-4 and an unexpected 15-MC-5 have been detected by potentiometry and confirmed by ESI-MS results. Their structures are discussed on the basis of potentiometric, calorimetric, spectroscopic data and DFT calculations. The existence of a vacant 15-MC-5 species in solution can be put forward for the first time, making the present metal/ligand systems very interesting for their potential applications in cation recognition and separation. Finally, the crystal structure of the binary complex K[NiL(2)H(-1)]·5/3 H(2)O of (S)-α-alaninehydroxamic acid (LH) is also reported.

2D autocovariance function for comprehensive analysis of two-way GC-MS data matrix: application to environmental samples.

This paper describes a signal processing method for comprehensive analysis of the large data set generated by hyphenated GC-MS technique. It is based on the study of the 2D autocovariance function (2D-EACVF) computed on the raw GC-MS data matrix, extending the procedure previously developed for 1D to 2D signals. It appears specifically promising for GC-MS investigation, in particular to single out ordered patterns in complex data: such patterns can be simply identified by visual inspection from deterministic peaks in the 2D-EACVF plot. A case of order along the retention time axis (x=t(R)) is represented by a horizontal sequence of peaks, located at the same interdistance Δt(R)=b(x), e.g., b(x) is the CH(2) retention time increment between subsequent terms of an homologous series. The order along the fragment mass axis (y=m/z) contains information on analyte fragmentation patterns. Deterministic peaks appear in the 2D-EACVF plot at Δm/z values corresponding to the most abundant ion fragments - dominating fragments in MS spectrum - or to ions generated by repetitive loss of the same ion fragment, i.e., Δm/z=14 amu produced by the [CH(2)]() group loss in n-alkanes. Method applicability was tested by processing GC-MS data of organic extracts of atmospheric aerosol samples: attention is focused on identifying and characterizing homologous series of organics, i.e., n-alkanes and n-alkanoic acids, since they are considered molecular tracers able to track the origin and fate of different organics in the environment.

Thermodynamics of self-assembly of copper(II) 15-metallacrown-5 of Eu(III) or Gd(III) with (S)-alpha-alaninehydroxamic acid in aqueous solution.

The equilibria of self-assembly of 15-metallacrown-5 (15-MC-5) complexes of Cu(2+) and (S)-alpha-alaninehydroxamic acid (alpha-Alaha, HL) with the lanthanide (Ln) ions Eu(3+) or Gd(3+) in aqueous solution are described. The binary Ln(3+)/alpha-Alaha systems were first studied by potentiometric and calorimetric in-cell titrations; the latter technique allowed us to define the most suitable speciation model. On the contrary, because the kinetics of formation of the Ln(3+) 15-MC-5 complexes is slow, their stability constants were determined by out-of-cell (batch) potentiometric titrations. Two 15-MC-5 complexes are formed with both Eu(3+) and Gd(3+), namely, {Ln[Cu(5)L(5)H(-5)]}(3+) and {Ln[Cu(5)L(5)H(-5)](OH)}(2+), with the latter being the hydroxo species of the former. The acidity of the former to give the hydroxo species is remarkably high (log K = 4.40-4.69). Moreover, our potentiometric and spectrophotometric investigations clearly indicate that the hydroxide ion is coordinated to the central Ln ion, as was reported for several 15-MC-5 in the solid state. The formation of {Ln[Cu(5)L(5)H(-5)]}(3+) starts at ca. pH 3.5, which converts at ca. pH 4.5 into the {Ln[Cu(5)L(5)H(-5)](OH)}(2+) species, which predominates up to pH 7, where a purple precipitate occurs. The coexistence of both 15-MC-5 species and the copper(II) 12-MC-4 species of alpha-Alaha ([Cu(5)L(4)H(-4)](2+)) was observed under appropriate experimental conditions (pH and ligand and metal concentrations). A complete ESI-MS investigation of the Ln(3+)/Cu(2+)/alpha-Alaha system at different pH's confirmed the formation of the two 15-MC-5 species. The 15-MC-5 stability constants were employed to quantitatively evaluate the solution behavior of Ln(III) MCs regarding their integrity, ligand substitution, and transmetalation processes. In particular, EDTA or DOTA, added in equimolar amounts, should not appreciably interfere with the MC integrity, as found in previous experimental investigations, although it is expected that at higher amounts of EDTA, the MC should be disrupted. Our results also demonstrate that an excess of alpha-aminohydroxamate does not interfere with the integrity of the MC, and the disappearance of the CD spectra upon addition of the R enantiomer to 15-MC-5 containing the S enantiomer is due to a very rapid ligand exchange with formation of all possible isomers with no selectivity. The stability of the 15-MC-5 complexes in the presence of transferrin, serum albumin, or an excess of Zn(2+) is also discussed. With regards to the latter metal ion, we found that the MCs are stable toward Gd(3+)/Zn(2+) transmetalation. although the presence of a phosphate buffer promotes the disruption of the MC scaffold by formation of stable Gd(3+)/phosphate species.

GC-MS analysis of low-molecular-weight dicarboxylic acids in atmospheric aerosol: comparison between silylation and esterification derivatization procedures.

This paper describes methods for the determination of low-molecular-weight (LMW) dicarboxylic acids in atmospheric aerosols as important chemical tracers for source apportionment of aerosol organics and for studying atmospheric processes leading to secondary organic aerosol formation. The two derivatization procedures most widely used in GC analysis of dicarboxylic acids were compared: esterification using BF(3)/alcohol reagent and silylation using N,O-bis(trimethylsilyl)-trifluoroacetamide (BSTFA). The advantages and drawbacks of the two methods are investigated and compared in terms of (1) precision and accuracy of the results and (2) sensitivity and detection limit of the procedure. The comparative investigation was performed on standard solutions containing target C(3)-C(9) dicarboxylic acids and on experimental particulate matter (PM) samples. Attention was focused on low-volume sampling devices that collect small amounts of sample for organic speciation. The results show that, overall, both the techniques appear suitable for the analysis of LMW dicarboxylic acids in atmospheric aerosols since they provide low detection limits (< or = 4 ng m(-3)) and satisfactory reproducibility (RSD% < or = 15%). Between them, BSTFA should be the reagent of choice under the most limiting conditions of PM filters collected by low-volume air samplers: It provides determination of all the target C(3)-C(9) dicarboxylic acids with lower detection limits (< or = 2 ng m(-3)) and higher reproducibility (RSD% < or = 10%).

Copper(II) coordination outside the tandem repeat region of an unstructured domain of chicken prion protein.

Combined potentiometric, calorimetric and spectroscopic methods were used to investigate the Cu(2+) binding ability and coordination behaviour of some peptide fragments related to the neurotoxic region of chicken Prion Protein. The systems studied were the following protein fragments: chPrP(106-114), chPrP(119-126), chPrP(108-127), chPrP(105-127) and chPrP(105-133).The complex formation always starts around pH 4 with the coordination of an imidazole nitrogen, followed by the deprotonation and binding of amide nitrogens from the peptidic backbone. At neutral pH, the {N(im), 3N(-)} binding mode is the preferred one. The amide nitrogens participating in the binding to the Cu(2+) ion derive from residues from the N-terminus side, with the formation of a six-membered chelate ring with the imidazolic side chain.Comparison of thermodynamic data for the two histydyl binding domains (around His-110 and His-124), clearly indicates that the closest to the hexarepeat domain (His-110) has the highest ability to bind Cu(2+) ions, although both of them have the same coordination mode. Conversely, in the case of the human neurotoxic peptide region, between the two binding sites, located at His-96 and His-111, the farthest from the tandem repeat region is the strongest one. Finally, thermodynamic data show that chicken peptide is a distinctly better ligand for coordination of copper ions with respect to the human fragment.

CuII binding sites located at His-96 and His-111 of the human prion protein: thermodynamic and spectroscopic studies on model peptides.

The prion protein (PrP) is a Cu(2+)-binding cell-surface glycoprotein. Using PrP peptide fragments, by means of potentiometric, spectroscopic and thermodynamic techniques, we have shown that Cu(2+) ions bind to the region comprising His-96, His-111 and the octarepeat domain within residues 60-91. Cu(2+) may bind in different modes, which strongly depend both on His position within the peptide sequence and on the adjacent residues. We have used a series of protected oligopeptides having His at the C- or the N-terminus, inducing different binding modes to amide nitrogens around the His residue, either towards the N- or C-terminus. His imidazole acts as an anchoring site for Cu(2+) and then binding to ionized amide nitrogens follows. When it is directed towards the C-terminus the formation of a less stable seven-membered chelate ring with a {N(im), N(-)} binding mode occurs. When coordination goes towards the N-terminus the thermodynamically more stable six-membered chelate ring is formed. NMR data suggest that both the coordination modes are possible for the model peptides; however, the thermodynamic measurements show that they only slightly differ in energy and the influence of the adjacent amino acid residues can address the coordination toward the C- or the N-terminus.

Copper(II) 12-metallacrown-4 complexes of alpha-, beta- and gamma-aminohydroxamic acids: a comparative thermodynamic study in aqueous solution.

A complete thermodynamic study of the protonation and Cu(II) complex formation equilibria of a series of alpha- and beta-aminohydroxamic acids in aqueous solution was performed. The thermodynamic parameters obtained for the protonation of glycine-, (S)-alpha-alanine-, (R,S)-valine-, (S)-leucine-, beta-alanine- and (R)-aspartic-beta-hydroxamic acids were compared with those previously reported for gamma-amino- and (S)-glutamic-gamma-hydroxamic acids. The enthalpy/entropy parameters calculated for the protonation microequilibria of these three types of ligands are in very good agreement with the literature values for simple amines and hydroxamic acids. The pentanuclear complexes [Cu5L4H(-4)]2+ contain the ligands acting as (NH2,N-)-(O,O-) bridging bis-chelating and correspond to 12-metallacrown-4 (12-MC-4) which are formed by self-assembly between pH 4 and 6 with alpha-aminohydroxamates (HL), while those with beta- and gamma-derivatives exist in a wider pH range (4-11). The stability order of these metallomacrocycles is beta- >> alpha- > gamma-aminohydroxamates. The formation of 12-MC-4 with alpha-aminohydroxamates is entropy-driven, and that with beta-derivatives is enthalpy-driven, while with gamma-GABAhydroxamate both effects occur. These results are interpreted on the basis of specific enthalpies or entropy contributions related to chelate ring dimensions, charge neutralization and solvation-desolvation effects. The enthalpy/entropy parameters of 12-MC-4 with alpha-aminohydroxamic acids considered are also dependent on the optical purity of the ligands. Actually, that with (R,S)-valinehydroxamic acid presents an higher entropy and a lower enthalpy value than those of enantiopure ligands, although the corresponding stabilities are almost equivalent. Moreover, DFT calculations are in agreement with a more exothermic enthalpy found for metallacrowns with enantiomerically pure ligands.