Air-equilibrated Water Research Articles

A new large-volume equilibration method for high-precision measurements of dissolved noble gas stable isotopes.

Noble gases are widely used as physically based climate proxies, notably in dissolved water samples as tracers of past recharge temperature in groundwater and air-sea gas exchange processes in seawater. Recent advances in measuring large-volume samples of dissolved noble gas isotopic ratios at high precision have expanded the range of climate parameters that can be interpreted. We build on prior methods for measuring noble gas stable isotopes at high precision with a new large-volume equilibration (LVE) method wherein sample gases are equilibrated in the sample flask between the dissolved phase and the headspace. The original dissolved gas composition is determined by measuring the headspace gases and correcting for the equilibrium dissolved gas content of the discarded water using known solubilities and fractionation factors. We evaluate the accuracy and precision of this method with air-equilibrated water standards of known noble gas composition. Replicate air-equilibrated water standards and field measurements demonstrate that the LVE method achieves comparable precision to prior methods, with major advantages of measuring the Ne content as a constraint on excess air and allowing for long-term sample storage. Isotope ratios measured with the LVE method in replicate samples were consistent between two laboratories, and LVE elemental noble gas abundances agreed closely with replicate samples measured using established copper-tube methods and static noble gas mass spectrometry. The new LVE method enables reconstruction of past water table depths at ±1m precision along with excess air, recharge temperature, and age and hydrogeochemical indicators. It has wide application to investigating climate signals and physical gas exchange processes in groundwater and seawater.

Properties of Blisters Formed on Polymer Films and Differentiating them from Nanobubbles/Nanodrops.

When studying surface nanobubbles on film-coated substrates, a class of bubble-like domains called blisters are probably forming at the solid-liquid interface together with nanobubbles. This may easily lead to a misunderstanding of the characteristics and applications of surface nanobubbles and thus continue to cause problems within the nanobubble community. Therefore, how to distinguish surface nanobubbles from blisters is a problem. Herein, the morphology and properties of blisters are investigated on both smooth and nanopitted polystyrene (PS) films in degassed water. The morphology and contact angle of blisters are similar to those of surface nanobubbles. However, blisters were observed to be punctured under the tip-blister interaction and be torn broken by an atomic force microscope tip during the process of scanning. At the same time, nanopits on the surface of blisters that formed on a pitted PS film can be seen clearly. These provide direct and visual evidence for distinguishing blisters from surface nanobubbles. In addition, surface nanobubbles and blisters on smooth and pitted PS films in air-equilibrated water are studied. No punctured surface nanobubble was observed, and the force curves obtained on surface nanobubbles and the change in height of blisters and surface nanobubbles under a large scanning force show that surface nanobubbles are much softer than blisters.

Dynamics and emissions of N2O in groundwater: A review.

This work reviews the concentrations, the dynamics and the emissions of nitrous oxide (N2O) in groundwater. N2O is an important greenhouse gas (GHG) and the primary stratospheric ozone depleting substance. The major anthropogenic source that contributes to N2O generation in aquifers is agriculture because the use of fertilizers has led to the widespread groundwater contamination by inorganic nitrogen (N) (mainly nitrate, NO3-). Once in the aquifer, this inorganic N is transported and affected by several geochemical processes that produce and consume N2O. An inventory of dissolved N2O concentrations is presented and the highest concentration is about 18.000 times higher than air-equilibrated water (up to 4004μg N L-1). The accumulation of N2O in groundwater is mainly due to denitrification and to lesser extent to nitrification. Their occurrence depend on the geochemical (e.g., NO3-, dissolved oxygen, ammonium and dissolved organic carbon) as well as hydrogeological parameters (e.g., groundwater table fluctuations and aquifer permeability). The coupled understanding of both parameters is necessary to gain insight on the dynamics and the emissions of N2O in groundwater. Overall, groundwater indirect N2O emissions seem to be a minor component of N2O emissions to the atmosphere. Further research might be devoted to evaluate the groundwater contribution to the indirect emissions of N2O because this will help to better constraint the N2O global budget and, consequently, the N budget.

Vapor and Gas-Bubble Growth Dynamics around Laser-Irradiated, Water-Immersed Plasmonic Nanoparticles.

Microbubbles produced by exposing water-immersed metallic nanoparticles to resonant light play an important role in emerging and efficient plasmonic-enhanced processes for catalytic conversion, solar energy harvesting, biomedical imaging, and cancer therapy. How do these bubbles form, and what is their gas composition? In this paper, the growth dynamics of nucleating bubbles around laser-irradiated, water-immersed Au plasmonic nanoparticles are studied to determine the exact origin of the occurrence and growth of these bubbles. The microbubbles' contact angle, footprint diameter, and radius of curvature were measured in air-equilibrated water (AEW) and degassed water (DGW) with fast imaging. Our experimental data reveals that the growth dynamics can be divided into two regimes: an initial bubble nucleation phase (regime I, < 10 ms) and, subsequently a bubble growth phase (regime II). The explosive growth in regime I is identical for AEW and DGW due to the vaporization of water. However, the slower growth in regime II is distinctly different for AEW and DGW, which is attributed to the uptake of dissolved gas expelled from the water around the hot nanoparticle. Our scaling analysis reveals that the bubble radius scales with time as R(t) ∝ t1/6 for both AEW and DGW in the initial regime I, whereas in the later regime II it scales as R(t) ∝ t1/3 for AEW and is constant for perfectly degassed water. These scaling relations are consistent with the experiments.

Using noble gas ratios to determine the origin of ground ice

Argon, krypton and xenon have different solubilities in water, meaning their ratios in water are different from those in atmospheric air. This characteristic is used in a novel method to distinguish between ice bodies which originate from the compaction of snow (i.e. buried snow banks, glacial ice) vs. ice which forms from the freezing of groundwater (i.e. pingo ice). Ice which forms from the compaction of snow has gas ratios similar to atmospheric air, while ice which forms from the freezing of liquid water is expected to have gas ratios similar to air-equilibrated water. This analysis has been conducted using a spike dilution noble gas line with gas extraction conducted on-line. Samples were mixed with an aliquot of rare noble gases while being melted, then extracted gases are purified and cryogenically separated. Samples have been analysed from glacial ice, buried snow bank ice, intrusive ice, wedge ice, cave ice and two unknown ice bodies. Ice bodies which have formed from different processes have different gas ratios relative to their formation processes.

Cryogenic separation of an oxygen-argon mixture in natural air samples for the determination of isotope and molecular ratios.

The separation and purification of oxygen-argon mixtures are critical in the high-precision analysis of Δ(17) O and δ(O2 /Ar) for geochemical applications. At present, chromatographic methods are used for the separation and purification of oxygen-argon mixtures or pure oxygen, but these methods require the use of high-purity helium as a carrier gas. Considerable interest has been expressed in the development of a helium-free cryogenic separation of oxygen-argon mixtures in natural air samples. The precise and simplified cryogenic separation of oxygen-argon mixtures from natural air samples presented here was made possible using a single 5A (30/60 mesh) molecular sieve column. The method involves the trapping of eluted gases using molecular sieves at liquid nitrogen temperature, which is associated with isotopic fractionation. We tested the proposed method for the determination of isotopic fractionations during the gas exchange between water and atmospheric air at equilibrium. The dependency of fractionation was studied at different water temperatures and for different methods of equilibration (bubbling and stirring). Isotopic and molecular fractionations during gas desorption from molecular sieves were studied for different amounts and types of molecular sieves. Repeated measurements of atmospheric air yielded a reproducibility (±SD) of 0.021 ‰, 0.044 ‰, 15 per meg and 1.9 ‰ for δ(17) O, δ(18) O, Δ(17) O and δ(O2 /Ar) values, respectively. We applied the method to determine equilibrium isotope fractionation during gas exchange between air and water. Consistent δ(18) O and Δ(17) O results were obtained with the latest two studies, whereas there was a significant difference in δ(18) O values between seawater and deionized water. We have revised a helium-free, cryogenic separation of oxygen-argon mixtures in natural air samples for isotopic and molecular ratio analysis. The use of a single 13X (1/8" pellet) molecular sieve yielded the smallest isotopic and molecular fractionations, and this fractionation by molecular sieves can be corrected by the amount of molecular sieve used in the experiment. The reproducibility of the method was tested by the measurement of the oxygen isotope ratios of dissolved oxygen at equilibrium with atmospheric air. We confirmed that the choice of methods for making air-equilibrated water was not related to the magnitude of isotope fractionation, whereas there was a difference between seawater and deionized water.

A continuous flow isotope ratio mass spectrometry method for high precision determination of dissolved gas ratios and isotopic composition

Dissolved gas ratios and isotopic compositions provide essential information about the biological and physical mechanisms influencing N2, O2, and Ar in aquatic systems. Current methods available are either limited by overall cost, labor‐intensive sample collection and analysis, or insufficient precision. Here, we present a new highly accurate and robust method for sample collection and subsequent simultaneous measurement of the dissolved gas ratios (N2/Ar and O2/Ar) and isotopic compositions (δ15N2 and δ18O2) in seawater. The relatively simple sampling procedure using low cost materials enables collection of hundreds to more than a thousand discrete samples on a single research cruise. Samples can be preserved and stored at room temperature and maintain their integrity for many months. Laboratory analysis employs an on‐line extraction system coupled to a multi‐collector isotope ratio mass spectrometer (IRMS). A continuous flow of He carrier gas completely degasses the sample, and passes through the preparation and purification system before entering the IRMS for analysis. The use of this continuous He carrier permits short analysis times (less than 8 min per sample) as compared with current high‐precision methods. In addition to reference gases, calibration is achieved using air‐equilibrated water standards of known temperature and salinity. Assessment of reference gas injections, air equilibrated standards, as well as samples collected in the field shows the accuracy and precision of this new method to be equal to or better than current standard techniques.

Reproducibility and accuracy of noble gas measurements on water samples in the microlitre range

In order to derive meaningful noble gas temperatures (NGTs) from speleothem fluid inclusions, precise and accurate measurements of noble gas concentrations on very small water samples are necessary. To optimise these measurements and their reliability, an investigation of the reproducibility and accuracy of the analytical procedure is essential. Water equilibrated with air under controlled conditions was filled into copper capillaries to produce small (about 1 μL) air-equilibrated water samples (so-called μAEWs). As speleothem samples, the μAEWs were opened in a crusher and the released noble gases analysed with an electron ionisation sector field mass spectrometer run in static mode. For better comparability with speleothem samples, a defined amount of air was added to the noble gases derived from one group of μAEWs. The reproducibility of the experimental procedure was found to be better than 2.2% for all relevant noble gases. Within these uncertainties, the measured noble gas concentrations of μAEWs agree with expectations. The corresponding NGTs reproduce within 0.5°C and deviate by less than 1°C from the equilibration temperature. In the case of air addition, the air to water ratio was determined accurately and, excluding one outlier, the NGTs were determined with a reproducibility and accuracy well below 1°C. The results show that the used measurement procedure is generally suitable to reveal major climatic temperature changes, for which an overall NGT error of less than 1°C is desirable, from very small water samples as obtained from speleothem fluid inclusions.

Highly luminescent Tb(III) macrocyclic complex based on a DO3A hosting unit and an appended carboxylated N,C-pyrazolylpyridine antenna

Abstract The synthesis of a new ligand based on a DO3A moiety (DO3A = 1,4,7,10 tetraaza cyclododecane -1,4,7-triacetic acid) as a hosting agent for the lanthanide ions and an appended chromophoric unit N , C -pyrazolylpyridine core functionalized by a carboxylic acid in the 3-position of the pyrazole ring was reported. The luminescence properties of the 1/1 Eu(III) and Tb(III) corresponding complexes were investigated in air-equilibrated water and deuterated water (Tris buffer, pH 7.4) at 298 and 77 K. High luminescence lifetime ( τ = 2.30 ms), quantum yield ( Φ = 45%) and efficiency for the sensitized emission ( η sens = 60%) were observed for the terbium complex. A detailed study of the steps originating from light absorption at the chromophore unit and leading to lanthanide-centred emission was reported.

Photocatalytic reduction of vanadium(V) in TiO2 suspension: Chemometric optimization and application to wastewaters

The photocatalytic reduction of V(V) to V(IV) over TiO2 in aqueous solution is presented. Experiments were undertaken on air-equilibrated water spiked with V(V) (0.6–20mgL−1), under UV-A or solar light. A chemometric study was performed to optimize the reduction yield, by considering the most important variables recognized to affect the photocatalytic process. Among pH, irradiation time and catalyst concentration, the two latter proved to be determinant. The good yields achieved (up to 98%), along with the possibility of working in aerated solution, make this procedure simple, rapid and efficient. Although a deep insight on the photochemical mechanisms was beyond our scope, the role of electron donors was investigated, proving the efficiency of 2-propanol, citric acid and formic acid in the acceleration and improvement of V(V) conversion. After irradiation, total vanadium and aqueous V(V) and V(IV) after solid-phase separation on Chelex-100 resin, were determined by inductively coupled plasma optical emission spectroscopy (ICP-OES). The procedure was applied to contaminated wastewaters, combining remediation and possible vanadium recovery as V(IV).

Stability of Interfacial Nanobubbles

Interfacial nanobubbles (INBs) on a solid surface in contact with water have drawn widespread research interest. Although several theoretical models have been proposed to explain their apparent long lifetimes, the underlying mechanism still remains in dispute. In this work, the morphological evolution of INBs was examined in air-equilibrated and partially degassed water with the use of atomic force microscopy (AFM). Our results show that (1) INBs shrank in the partially degassed water while they grew slightly in the air-equilibrated water, (2) the three-phase boundary of the INBs was pinned during the morphological evolution of the INBs. Our analyses show that (1) the lifetime of INBs was sensitive to the saturation level of dissolved gases in the surrounding water, especially when the concentration of dissolved gases was close to saturation, and (2) the pinning of the three-phase boundary could significantly slow down the kinetics of both the growth and the shrinkage of the INBs. We developed a one-dimensional version of the Epstein-Plesset model of gas diffusion to account for the effect of pinning.

Dissolved gases in frozen basal water from the NGRIP borehole: implications for biogeochemical processes beneath the Greenland Ice Sheet

Little information exists on biogeochemical transformations in aquatic ecosystems beneath polar ice sheets (i.e., water-saturated sediments, streams, rivers, and lakes) and their role in global elemental cycles. Subglacial environments may represent important sources of atmospheric CO2 and/or CH4 during deglaciation, thus acting as amplifiers in the climate system. However, the role of subglacial environments in global climate processes has been difficult to assess given the absence of biogeochemical data from the basal zones of inland polar ice sheets. Here, we report on the concentrations of CO2, CH4, and H2 in samples of refrozen basal water recovered at a depth of ~3,042 meters below the surface during the North Greenland Ice Core Project (NGRIP). CH4 and H2 concentrations in the NGRIP samples were approximately 60- and 700-fold higher, respectively, relative to air-equilibrated water, whereas CO2 was ~fivefold lower. Metabolic pathways such as (1) methanogenesis, (2) organic matter fermentation, carboxydotrophic, and/or methylotrophic activity, and (3) CO2 fixation provide plausible biotic explanations for the observed CH4, H2, and CO2 concentrations, respectively.

Oxygen as a Driver of Early Arthropod Micro-Benthos Evolution

BackgroundWe examine the physiological and lifestyle adaptations which facilitated the emergence of ostracods as the numerically dominant Phanerozoic bivalve arthropod micro-benthos.Methodology/Principal FindingsThe PO2 of modern normoxic seawater is 21 kPa (air-equilibrated water), a level that would cause cellular damage if found in the tissues of ostracods and much other marine fauna. The PO2 of most aquatic breathers at the cellular level is much lower, between 1 and 3 kPa. Ostracods avoid oxygen toxicity by migrating to waters which are hypoxic, or by developing metabolisms which generate high consumption of O2. Interrogation of the Cambrian record of bivalve arthropod micro-benthos suggests a strong control on ecosystem evolution exerted by changing seawater O2 levels. The PO2 of air-equilibrated Cambrian-seawater is predicted to have varied between 10 and 30 kPa. Three groups of marine shelf-dwelling bivalve arthropods adopted different responses to Cambrian seawater O2. Bradoriida evolved cardiovascular systems that favoured colonization of oxygenated marine waters. Their biodiversity declined during intervals associated with black shale deposition and marine shelf anoxia and their diversity may also have been curtailed by elevated late Cambrian (Furongian) oxygen-levels that increased the PO2 gradient between seawater and bradoriid tissues. Phosphatocopida responded to Cambrian anoxia differently, reaching their peak during widespread seabed dysoxia of the SPICE event. They lacked a cardiovascular system and appear to have been adapted to seawater hypoxia. As latest Cambrian marine shelf waters became well oxygenated, phosphatocopids went extinct. Changing seawater oxygen-levels and the demise of much of the seabed bradoriid micro-benthos favoured a third group of arthropod micro-benthos, the ostracods. These animals adopted lifestyles that made them tolerant of changes in seawater O2. Ostracods became the numerically dominant arthropod micro-benthos of the Phanerozoic.Conclusions/SignificanceOur work has implications from an evolutionary context for understanding how oxygen-level in marine ecosystems drives behaviour.

Establishing constraints on groundwater ages with 36Cl, 14C, 3H, and noble gases: A case study in the eastern Paris basin, France

Groundwaters from the Tithonian/Kimmeridgian, Oxfordian and Upper Dogger aquifers, within the eastern part of the Paris basin (France), were characterised using 3H, 14C and 36Cl, and noble gases tracers, to evaluate their residence times and determine their recharge period. This information is an important prerequisite to evaluating the confinement properties of the Callovo-Oxfordian clay formation sandwiched between the Oxfordian aquifer and the Dogger aquifer, currently being investigated by the French nuclear waste management agency (Andra) for radioactive waste disposal. Data presented in this paper are used to test 4 hypotheses : (1) The Oxfordian limestone is isolated from the overlying Tithonian/Kimmeridgian surface aquifer. This first hypothesis is supported by the presence of measurable 3H activities in groundwaters from the surface aquifer (6–11 TU), and by its absence in groundwaters derived from deeper aquifers (<3 TU), as well as by geochemical data from earlier studies. (2) The Callovo-Oxfordian clay sequence in the vicinity of the URL serves as an effective barrier to advective flow and transport between the underlying Upper Dogger aquifer and the overlying Oxfordian limestone aquifer. This second hypothesis is supported by relatively low concentrations of Cl (3.5–78 mg L−1), Na (15–145 mg L−1), Br (0.08–0.4 mg L−1) and 4Herad (0.2–2.3 ccSTP g−1) and slightly higher 36Cl/Cl ratios (2.7–59 × 10−15 at at−1) in groundwaters from the Oxfordian aquifer, compared to those from the Upper Dogger aquifer (345–4027 mgCl L−1; 402–2390 mgNa L−1, 1.8–22.2 mgBr L−1, 1.6–37.2 ccSTP He g−1, 1–5 × 10−15 at 36Cl at−1 Cl). (3) Groundwaters from the Oxfordian aquifer, in the vicinity of URL are pre-Holocene, with residence times exceeding 10 ka. Geochemical and isotopic lines of evidence for this hypothesis include: (a) δ13C values measured on Oxfordian aquifer waters that are close to δ13C of the aquifer matrix, reflecting strong isotopic exchange over several thousand years; (b) noble-gas temperatures that indicate recharge temperatures between 3 and 8.6 °C, lower by 2–7 °C than the modern average temperature in this area; (c) radiogenic 4He concentrations between 0.16 × 10−5 and 2.3 × 10−5 ccSTP g−1 of water, about 2–3 orders of magnitude greater than the 4He concentration of air-equilibrated water. (4) Groundwater residence time for the Upper Dogger aquifer in the vicinity of the URL probably exceed several hundred thousand years. Such long residence times are indicated by the accumulation of radiogenic He-up to 37 × 10−5 ccSTP g−1 assuming a closed system. Primary contributors to uncertainties in interpretation of the data presented in this paper are the lack of : –well-defined 36Cl/Cl input ratio; –knowledge about the 4Herad sources for Oxfordian and Dogger aquifers; –knowledge about transport processes occurring through the Dogger aquifer, and the extensive dilution of initial 14C activities by dissolution/exchange with aquifer matrix. Overall, however, although the data presented in this paper remain semi-quantitative due to inevitable intrinsic limitations of the methods, none contradict the hypotheses of long residence times and aquifer isolation in the vicinity of the URL.

Characterization of the hydroperoxyl/superoxide anion radical (HO 2[rad]/O 2[rad]−) formed from the photolysis of immobilized TiO 2 in a continuous flow

In this study, the steady-state concentrations of HO 2 /O 2 − formed from the photocatalysis of immobilized TiO 2 were investigated quantitatively by using the kinetic method with a continuous flow injection. In air-equilibrated water, the concentration of HO 2 /O 2 − was typically 1.01 (±0.08) × 10 −9 M at pH 5.80 in the absence of buffers. The reduction of O 2 by photo-induced electrons (e cb −) was increased by the concentration of O 2 (from 0 to 0.38 mM). However, in the presence of buffer anions the concentration of HO 2 /O 2 − was gradually decreased by increasing pH. This indicates that the suppression of HO 2 /O 2 − in the presence of buffer ions is attributed to the blocking of active sites of the immobilized TiO 2 photocatalyst and to certain processes, that is, the reaction between HO 2 /O 2 − and OH (and/or h vb +). Furthermore, the concentration of HO 2 /O 2 − increased with the increasing concentrations of H 2O 2 and oxalate, and then on the further addition of H 2O 2 (>10 mM) and oxalate (>2 mM), the concentration of HO 2 /O 2 − reached steady values. These results strongly suggest that HO 2 /O 2 − formed on TiO 2 photocatalysis migrates into the water bulk, and this study can contribute significantly to the body of knowledge regarding HO 2 /O 2 − at very low levels.

Alterations in Rubisco activity and in stomatal behavior induce a daily rhythm in photosynthesis of aerial leaves in the amphibious-plant Nuphar lutea

Nuphar lutea is an amphibious plant with submerged and aerial foliage, which raises the question how do both leaf types perform photosynthetically in two different environments. We found that the aerial leaves function like terrestrial sun-leaves in that their photosynthetic capability was high and saturated under high irradiance (ca. 1,500 mumol photons m(-2) s(-1)). We show that stomatal opening and Rubisco activity in these leaves co-limited photosynthesis at saturating irradiance fluctuating in a daily rhythm. In the morning, sunlight stimulated stomatal opening, Rubisco synthesis, and the neutralization of a night-accumulated Rubisco inhibitor. Consequently, the light-saturated quantum efficiency and rate of photosynthesis increased 10-fold by midday. During the afternoon, gradual closure of the stomata and a decrease in Rubisco content reduced the light-saturated photosynthetic rate. However, at limited irradiance, stomatal behavior and Rubisco content had only a marginal effect on the photosynthetic rate, which did not change during the day. In contrast to the aerial leaves, the photosynthesis rate of the submerged leaves, adapted to a shaded environment, was saturated under lower irradiance. The light-saturated quantum efficiency of these leaves was much lower and did not change during the day. Due to their low photosynthetic affinity for CO(2) (35 muM) and inability to utilize other inorganic carbon species, their photosynthetic rate at air-equilibrated water was CO(2)-limited. These results reveal differences in the photosynthetic performance of the two types of Nuphar leaves and unravel how photosynthetic daily rhythm in the aerial leaves is controlled.

Luminescence properties and solution dynamics of lanthanide complexes composed by a macrocycle hosting site and naphthalene or quinoline appended chromophore

The two-component ligand systems 1 and 2 which contain 1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid ( DO3A) as the hosting unit for the lanthanide cations, and naphthalene (which is devoid of any chelating ability) or quinoline units, respectively, as chromophores, were synthesized. The 1:1 complexes with Gd 3+, Eu 3+ and Tb 3+ have been studied in aqueous solution. Relaxometric properties for Gd · 1 indicate that two water molecules ( q = 2) are in the first coordination sphere of the metal ion whereas for Gd · 2, q < 2 is found. For Gd · 1, these results indicate that the naphthalene unit is not coordinated to the metal centre; for the case of quinoline, reasons for the lower hydration state are discussed. In case of Eu · 1, Tb · 1, Eu · 2, and Tb · 2 the absorption and luminescence spectra, the overall luminescence efficiencies, and the metal-centred lifetimes, were obtained both in water and deuterated water. The coordination features of these complexes were explored by comparing their luminescence properties, resulting in hydration state q = 2 and 1.4 for the cases of the complexes of 1 and 2, respectively. Use of the photophysical parameters in air-equilibrated water allowed the determination of the ligand-to-cation energy transfer efficiency, Φ EnT, leading to the overall emission sensitization process. For Eu · 1, and Eu · 2, we found Φ EnT = 0.034 and 0.078, respectively, supporting that also a non-coordinating chromophore like naphthalene, case of ligand 1, can transfer excitation energy to the metal centre.

Solution medium effects on the photochemical degradation of pyrene in water

Poly-aromatic hydrocarbons (PAHs), carcinogenic compounds ubiquitous in the environment, are readily degraded photochemically. Understanding the kinetics and mechanisms of their photochemical degradation is important in assessing their overall toxicity. Here we have measured the photo-oxidation rate of pyrene in aqueous solution as a function of environmentally relevant solution media. The degradation rate of pyrene is 0.268 min −1 in air-equilibrated water at pH 8. Degradation appears to require water and is dependant on oxygen concentrations, ionic strength and the concentration of humic acid in solution. Rates decrease as oxygen concentrations decrease, reaching a rate of 0.0424 min −1 in argon-purged solutions. Degradation increases as ionic strength increases and decreases as humic acid concentration increases. Rates will vary by as much as an order of magnitude over the range of environmental ionic strengths and humic acid concentrations. Mechanistic studies showed the formation of the 1-hydroxypyrene intermediate, consistent with a previously proposed mechanism in the literature that proceeds via electron transfer from excited singlet state pyrene to oxygen.

Bimodal System (Luminophore and Paramagnetic Contrastophore) Derived from Ln(III) Complexes Based on a Bipyridine-Containing Macrocyclic Ligand

The synthesis of a new 15-membered polyaza-macrocyclic ligand L3H3, which is based on a 2,2'-bipyridine moiety and a diethylenetriaminetriacetic acid core, is reported. The lanthanide chelates of this octadentate ligand were programmed for bimodal probes, luminescent agents (Sm, Eu, Tb, Dy), and magnetic resonance imaging agents (Gd3+). The neutral 1:1 complexes with these Ln3+ ions were prepared and studied in aqueous solution by luminescence and NMR techniques. The main photophysical characteristics of these complexes (i.e., the absorption and luminescence spectra, the metal-centered lifetimes, and the overall luminescence yields, Phi) were measured. In addition, the role played by nonradiative pathways (vibrational energy transfer involving coordinated water molecules, involvement of ligand-to-metal charge-transfer excited states, or metal --> ligand back transfer) is discussed. The L3.Eu and L3.Tb complexes show very bright luminescence when photoexcited from the lowest-energy absorption band of the bipyridine chromophore. The luminescence quantum yields in an air-equilibrated water solution at room temperature are 0.10 and 0.21, respectively, despite the presence of one water molecule in the first coordination sphere of the metal ion. NMR data show that L3.Gd contains also one H2O molecule in the inner sphere. The proton longitudinal relaxivity, r1, of this complex is 3.4 s(-1) mM(-1) (0.47 T, 310 K) and the rotational correlation time, tau(R), is 57 ps (310 K). These values are comparable to those of the clinically used Gd-DTPA. Interestingly, the water exchange rate between the coordination site and the bulk solvent is slow (tau(M) = 3.5 micros at 310 K). The presence of water molecules in the second sphere and in rapid exchange with the solvent is discussed. Finally, it was found by luminescence and NMR experiments that these lanthanide complexes are stable versus transmetalation by several cations (especially Ca2+ and Zn2+) at physiological pH and have no interaction with blood proteins.

Visible and Near-Infrared Intense Luminescence from Water-Soluble Lanthanide [Tb(III), Eu(III), Sm(III), Dy(III), Pr(III), Ho(III), Yb(III), Nd(III), Er(III)] Complexes

The synthesis of a new ligand (1) containing a single phenanthroline (phen) chromophore and a flexibly connected diethylenetriamine tetracarboxylic acid unit (DTTA) as a lanthanide (Ln) coordination site is reported [1 is 4-[(9-methyl-1,10-phenantrol-2-yl)methyl]-1,4,7-triazaheptane-1,1,7,7-tetraacetic acid]. From 1, an extended series of water-soluble Ln.1 complexes was obtained, where Ln is Eu(III), Tb(III), Gd(III), Sm(III), Dy(III), Pr(III), Ho(III), Yb(III), Nd(III), and Er(III). The stoichiometry for the association was found 1:1, with an association constant K(A) > or = 10(7) s(-1) as determined by employing luminescence spectroscopy. The luminescence and photophysical properties of the series of lanthanide complexes were investigated in both H2O and D2O solutions. High efficiencies for the sensitized emission, phi(se), in air-equilibrated water were observed for the Ln.1 complexes of Eu(III) and Tb(III) in the visible region (phi(se) = 0.24 and 0.15, respectively) and of Sm(III), Dy(III), Pr(III), Ho(III), Yb(III), Nd(III), and Er(III) in the vis and/or near-infrared region [phi(se) = 2.5 x 10(-3), 5 x 10(-4), 3 x 10(-5), 2 x 10(-5), 2 x 10(-4), 4 x 10(-5), and (in D2O) 4 x 10(-5), respectively]. For Eu.1 and Tb.1, luminescence data for water and deuterated water allowed us to estimate that no solvent molecules (q) are bound to the ion centers (q = 0). Luminescence quenching by oxygen was investigated in selected cases.