Slow Ligand Research Articles

An Aptamer-Based Hydrogel Sensing Platform Enabling Low Micromolar Detection of Small Molecules Using Low Sample Volumes.

Poor fluorescence recovery at low analyte dosages and slow ligand binding kinetics are critical challenges currently limiting the use of aptamer-functionalized hydrogels for sensing small molecules. In this paper, we report an adenosine-responsive hydrogel sensor that integrates FRET-signaling aptamer switches into in situ-gelling thin-film hydrogels. The hydrogel sensor is able to entrap a high proportion of the sensing probes (>70% following vigorous washing), delay nucleolytic degradation, stabilize weak aptamer complexes to improve hybridization affinity and suppress fluorescence background, and provide high sensitivity in biological fluids (i.e., undiluted human serum). Furthermore, the developed hydrogel sensors were able to achieve low limits of detection (5.3 μM in buffer and 8.8 μM in serum) within 4 min of exposure to the sample, with signal generation requiring only 20 μL/well of analyte sample. The physical nature of the aptamer encapsulation allows this approach to accommodate virtually any small-molecule aptamer, avoiding the need for covalent anchoring and the complex modification of nucleic acid sequences typically required for effective aptamer-based molecular recognition.

Tris buffer-accelerated ligand exchange rate for instant fluorescence detection of trivalent chromium ion

Functional nucleic acids (FNAs) have attracted a lot of attention for the rapid detection of metal ions. Cr3+ is one of the major heavy metal ions in natural waters. Due to the slow ligand exchange rate of Cr3+, the FNA-based Cr3+ sensors require long assay times, limiting the on-site applications. In this study, we report that the good's buffers containing amino and polyhydroxy groups greatly increase the ligand exchange rate of Cr3+. Using EDTA as a model coordinate ligand, the Tris buffer (100 mM, pH 7.0) showed the best acceleration effect among the eight buffers. It improved the rate constant ∼20-fold, shorten the half-time 19-fold, and lowered the activation energy ∼70% at 40 °C. The Tris buffer was then applied for sensor based on the Cr3+-binding induced fluorescence quenching of fluorescein (FAM)-labeled and single-stranded DNA (ssDNA), which shortened the assay time from 1 h to 1 min. The Tris buffer also ∼100% enhanced the fluorescence intensity of FAM, achieving the 11.4-fold lower limit of detection (LOD = 6.97 nM, S/N = 3). By the combination use of the Tris buffer and ascorbic acid, the strong interference from Cu2+, Pb2+, and Fe3+ suffered in many previous reported Cr3+ sensors was avoided. The practical application of the sensor for the detection of Cr3+ spiked in the real water samples were demonstrated with high recovery percentages. The Tris buffer could be applied for other metal ions with slow ligand exchange rate (such as V2+, Co3+ and Fe2+) to solve diverse issues such as long assay time and low synthesis yield of metal complexes, without the need of heating treatment.

Einbau von (Bioaktiven) Äquatorialen Liganden in Platin(IV)-Komplexe.

AbstractPlatin(IV)‐Prodrugs sind aufgrund ihrer erhöhten Tumorselektivität und geringeren Nebenwirkungen äußerst interessante Alternativen zu Platin(II)‐Antitumortherapeutika. Im Gegensatz zur gängigen Theorie haben wir kürzlich beobachtet, dass äquatoriale Liganden von z. B. Oxaliplatin(IV)‐Komplexen unter Bildung von [(DACH)Pt(OHeq)2(OAcax)2] hydrolysiert werden können. In der hier vorgestellten Arbeit untersuchten wir die Reaktivität und synthetische Verwendbarkeit dieses Komplexes, als Vorstufe für die Entwicklung neuartiger Platin(IV)‐Komplexe, welche mit herkömmlichen Methoden nicht zugänglich sind. Tatsächlich war es möglich die äquatorialen Hydroxidoliganden z. B. durch ein oder zwei monodentate Biotin‐Liganden, die unter Standardmethoden oxidiert werden würden, zu ersetzen. Die gebildeten Komplexe erwiesen sich als sehr stabil und zeigten auch nach der Reduktion eine langsame Ligandenfreisetzung, eine ideale Eigenschaft für lang zirkulierende zielgerichtete Strategien. Daraufhin wurden zwei Platin(IV)‐Komplexe mit äquatorialen Maleimiden, für die Bindung an Serumalbumin als natürlichen Nanocarrier, synthetisiert. Die Komplexe zeigten im Vergleich zu Oxaliplatin eine stark verlängerte Plasmahalbwertszeit und eine deutlich verbesserte Antitumoraktivität in vivo. Zusammenfassend ermöglicht diese neu entwickelte Syntheseplattform den einfachen und gezielten Einbau äquatorialer Liganden in Platin(IV)‐Komplexe. Des Weiteren können verschiedene (bioaktive) Einheiten koordiniert werden, wodurch sogar zielgerichtete dreifach‐wirksame Platin(IV)‐Prodrugs mit nur einem Platinzentrum möglich wären.

Insertion of (Bioactive) Equatorial Ligands into Platinum(IV) Complexes.

Platinum(IV) prodrugs are highly interesting alternatives to platinum(II) anticancer therapeutics due to their increased tumor selectivity and reduced side effects. In contrast to the established theory, we recently observed that the equatorial ligand(s) of e.g. oxaliplatin(IV) complexes can be hydrolyzed with formation of [(DACH)Pt(OHeq )2 (OAcax )2 ]. In the work presented here, we investigated the reactivity and synthetic usability of this complex to be exploited as a precursor for the development of novel platinum(IV) complexes, not able to be synthesized by conventional protocols. Indeed, we could substitute the equatorial hydroxido ligand(s) e.g. by one or two monodentate biotin ligands (which would be oxidized under standard methods). The formed complexes turned out to be very stable with slow ligand release after reduction, ideal for long-circulating tumor-targeting strategies. Therefore, two platinum(IV) complexes with equatorial maleimides, capable of exploiting serum albumin as a natural nanocarrier, were synthesized as well. The complexes showed massively prolonged plasma half-life and distinctly improved anticancer activity in vivo compared to oxaliplatin. Taken together, the newly developed synthetic platform allows the simple and specific insertion of equatorial ligands into platinum(IV) complexes. This will enable the attachment of three different (bioactive) moieties generating targeted triple-action platinum(IV) prodrugs within one single platinum complex.

Probing the Nitrite Reductase Activity of Heme-Copper Respiratory Oxidase

Heme-copper oxidases, in particular cytochrome ba 3, is capable of reducing NO to N2O and oxidizing CO to CO2, although with a low activity. Despite the very low (20%) overall sequence homology to other structurally known cytochrome c oxidases, the four redox centers of cytochrome ba 3 display high similarity with those of other oxidases. Extensive studies, at ambient temperatures, have shown that the heme a 3-CuB binuclear center of fully reduced (FR) and mixed valence (MV) cytochrome ba 3 is subjected to peculiar thermodynamic and kinetic properties, with significant deviations, relative to the mesophilic aa 3-type oxidases. These properties include an increased hydrophobicity, a high affinity of CuB for exogenous ligands such as CO (K > 104 M-1) and a slow intramolecular ligand transfer to heme a 3 (k = 8 s-1). As a result, cytochrome ba 3 is the only documented oxidase where the binding of CO to CuB is exergonic and accounts for 25-30% of the total enzyme concentration. Furthermore, the proximal and the distal environment of heme a 3 shows a high structural flexibility evidenced from the multiple heme a 3 Fe2+-CO conformers detected in both the FR and MV forms of the enzyme. Time-resolved step-scan FTIR studies showed that after photolysis of CO from heme a 3 2+ the ligand is almost quantitatively transferred to CuB 1+ and the transiently formed CuB 1+-CO complex exhibits an unusual long lifetime of 20 ms (pD 8.50). In addition, the midpoint redox potentials of hemes b and a 3 have been reported in three different studies being inverted, with values of 210/213 and 430/285 mV (versus Normal Hydrogen Electrode (NHE)), respectively. Resonance Raman and FTIR studies of the ligand binding properties of heme-copper oxidases will be presented.References. Discrete Ligand Binding and Electron Transfer Properties of ba 3-Cytochrome c Oxidase from Thermus thermophilus: Evolutionary Adaption to Low Oxygen and ...C Koutsoupakis, T Soulimane, C. Varotsis Accounts of chemical research 52 (5), 1380-139, 2019. The structure of a ferrous heme-nitro species in the binuclear heme a3/CuB center of ba 3-cytochrome c oxidase as determined by resonance Raman spectroscopy Loullis, MR Noor, T Soulimane, E Pinakoulaki Chemical Communications 51 (2), 286-289, 2015.

New insights in the slow ligand exchange reaction between Cr(III)-EDTA and Fe(III), and direct analysis of free and complexed EDTA in tannery wastewaters by liquid chromatography - Tandem mass spectrometry

EDTA and soluble Cr(III) are usually both present in wastewaters coming from treatment plants handling tannery effluents. A well-established method to determine EDTA is based on the conversion of free and complexed EDTA into its Fe(III) complex. This procedure gives inconsistent data when Cr(III)-EDTA is present. This fact was here demonstrated by studying the kinetics of the exchange reaction between Fe(III) and Cr(III)-EDTA at 90 °C and various pH values, from acidic to neutral. The reaction is very slow (several weeks); the slow kinetics of conversion of Cr(III)-EDTA to Fe(III)-EDTA is even more accentuated at room temperature and the low concentrations of reactants in wastewaters. The presence of EDTA complexes of Fe(III) and Cr(III) was demonstrated in industrial effluents and wastewaters by developing a selective method based on liquid chromatography-tandem mass spectrometry (LC-MS/MS), which was able to detect free and complexed EDTA at concentration levels <1 μM. A systematic underestimation of the EDTA expressed as Fe(III) complex was demonstrated in samples containing Cr(III)-EDTA. Cr(III)-EDTA was identified for the first time as a component of wastewater samples at a concentration level of about 2 μM and turned out to be an inert species that significantly contributes to the final soluble Cr amount. This study gives new insights into the inertness of Cr(III) toward metal exchange equilibria of EDTA complexes, resolves a bias in the analysis of total EDTA in samples containing Cr(III)-EDTA, allowing the direct determination of free and complexed EDTA by LC-MS.

Slow lactate gluconate exchange in calcium complexes during precipitation from supersaturated aqueous solutions

Saturated solutions of calcium l-lactate in water or in deuterium oxide continuously dissolve calcium l-lactate by addition of solid sodium d-gluconate and become strongly supersaturated in calcium d-gluconate due to no or slow precipitation. The quantification of total dissolved calcium allied with the calcium complexes equilibrium constants allowed an ion speciation, which shows an initial non-thermal and spontaneous supersaturation of more than a factor of 50 at 25 °C only slowly decreasing after initiation of precipitation of calcium d-gluconate after a lag phase of several hours. A mathematical model is proposed, based on numerical solution of coupled differential equations of dynamics of l-lactate and d-gluconate exchange during the lag phase for precipitation and during precipitation. A slow exchange of l-lactate coordinated to calcium with d-gluconate is indicated with a time constant of 0.20 h−1 in water and of 0.15 h−1 in deuterium oxide and a kinetic deuterium/hydrogen isotope effect of 1.25. Such spontaneous non-thermal supersaturation and slow ligand exchange with a pseudo first order equilibration process with a half-life of 3.5 h in water for calcium hydroxycarboxylates can help to understand the higher calcium bioavailability from calcium hydroxycarboxylates compared to simple salts.

A portable device enabling fluorescent-to-electric resistant transduction for selective Cr3+ detection based on its slow ligand bind kinetics

Using simple and commonly available devices for signal reading has attracted much attention recently for DNA-based sensors. Most previous works focused on electrochemical or colorimetric signals. In this work, a portable device was structured by simple electronic and 3D-printed components to convert fluorescence signal to electric resistance with reading by a multimeter. To demonstrate its application, we took advantage of the slow ligand bind kinetics of Cr3+ to promote DNA adsorption on metal oxide nanoparticles (MONPs). Nanoceria (CeO2), screened from a total of 13 kinds of MONPs, possesses high specificity for Cr3+ from other metal ions. EDTA can mask other metal ions, while it cannot bind Cr3+ quickly so that Cr3+ promotes DNA adsorption and thus fluorescence quenching. The linear range is from 0 to 2 μM Cr3+ with a LOD of 0.02 μM. Using common electronic components and the 3D-printed miniaturized device, the sensor to transfer fluorescence to electric resistant signal was also measured by a digital multimeter. In this case, the LOD is about 1 μM Cr3+. Such a strategy may provide a simple and general approach for fluorescent portable device fabrication and may find applications for other onsite sensing applications.

Electrochemical Investigation of the Hydrogen Evolution Reaction on Electrodeposited Films of Cr(OH)3 and Cr2O3 in Mild Alkaline Solutions

The hydrogen evolution reaction (HER) from water reduction is the main cathodic reaction in the sodium chlorate process. The reaction typically takes place on electrodes covered with a Cr(III) oxide-like film formed in situ by reduction of sodium dichromate in order to avoid reduction of hypochlorite and thereby increase the selectivity for the HER. However, the chemical structure of the Cr(III) oxide-like film is still under debate. In the present work, the kinetics of the HER were studied using titanium electrodes covered with electrodeposited Cr(OH)3 or Cr2O3, which were characterized by means of scanning electron microscopy (SEM), energy-dispersive x-ray spectroscopy (EDX), x-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. A clear difference in the morphology of the deposited surfaces was obtained, and the structure could be revealed with Raman spectroscopy. The kinetics for the HER were investigated using potentiodynamic and potentiostatic techniques. The results show that the first electron transfer is rate limiting and that the activity decreases in the order Cr2O3@Ti > bare Ti > Cr(OH)3@Ti. The low activity obtained for Cr(OH)3@Ti is discussed in terms of the involvement of structural water in the HER and the slow ligand exchange rate for water in Cr(III) complexes, while the high activity obtained for Cr2O3@Ti is rationalized by a surface area effect in combination with reduction of surface water and water in solution.Graphical ᅟ

Site-Selective Labeling of Chromium(III) as a Quencher on DNA for Molecular Beacons.

Molecular beacons typically use organic molecules or nanomaterials as quenchers. Many transition-metal ions have excellent fluorescence quenching ability, and the aim of this study was to recruit them as small quenchers in DNA detection. Cr3+ has a slow ligand exchange rate, forming stable adducts with DNA. With its strong fluorescence quenching ability, the site-specific labeling of Cr3+ on DNA to form a new type of molecular beacon was investigated. The kinetics of quenching by Cr3+ were measured for single- and double-stranded DNA as a function of salt concentration, pH, and Cr3+ ion concentration. The goal was to achieve a selective reaction with the single-stranded but not double-stranded regions. The reaction mechanism was also probed by adding adenosine triphosphate, revealing two Cr3+ -binding modes: fast but unstable, and slow but stable. A partially complementary duplex was designed with a short polyguanine overhang, which, under optimal conditions, enabled selective labeling of the overhanging region with Cr3+ . The resulting sequence was tested as a molecular beacon with a detection limit of 0.3 nm DNA and a saturated fluorescence enhancement of fivefold. With a 13-nucleotide target DNA, the single mismatch discrimination of the beacon was 22-fold. This study demonstrates the possibility of forming useful Cr3+ adducts with DNA. Such adducts are not only useful for developing biosensors but also for constructing new materials.

Homochiral Self-Sorted and Emissive IrIII Metallo-Cryptophanes.

The racemic ligands (±)‐tris(isonicotinoyl)‐cyclotriguaiacylene (L1), or (±)‐tris(4‐pyridyl‐methyl)‐cyclotriguaiacylene (L2) assemble with racemic (Λ,Δ)‐[Ir(ppy)2(MeCN)2]+, in which ppy=2‐phenylpyridinato, to form [{Ir(ppy)2}3(L)2]3+ metallo‐cryptophane cages. The crystal structure of [{Ir(ppy)2}3(L1)2]⋅3BF4 has MM‐ΛΛΛ and PP‐ΔΔΔ isomers, and homochiral self‐sorting occurs in solution, a process accelerated by a chiral guest. Self‐recognition between L1 and L2 within cages does not occur, and cages show very slow ligand exchange. Both cages are phosphorescent, with [{Ir(ppy)2}3(L2)2]3+ having enhanced and blue‐shifted emission when compared with [{Ir(ppy)2}3(L1)2]3+.

Impacts of Surface Site Coordination on Arsenate Adsorption: Macroscopic Uptake and Binding Mechanisms on Aluminum Hydroxide Surfaces.

Aluminum hydroxides play important roles in regulating the fate and transport of contaminants and nutrients in soils and aquatic systems. Like many metal oxides, these minerals display surface functional groups in a series of coordination states, each of which may differ in its affinity for adsorbates. The distribution of functional group types varies among distinct surfaces of aluminum hydroxides, and we thus hypothesize that the adsorption behavior and mechanisms will show a dependence on particle morphology. To test this hypothesis, we investigate arsenate adsorption on two aluminum hydroxide polymorphs with distinct particle morphologies, gibbsite [γ-Al(OH)3] and bayerite [α-Al(OH)3], at pH 4 and 7. Synthetic gibbsite platelets expose large (001) basal surfaces predicted to be terminated by doubly coordinated functional groups (>Al2OH). In contrast, synthetic bayerite microrods display mainly edge surfaces (parallel to the c axis) containing abundant singly coordinated functional groups (>AlOH2). Macroscopic adsorption studies show that gibbsite adsorbs less arsenate per unit surface area than bayerite at both pH values and suggest that two surface complexes form on each material. Similar electrokinetic behavior is displayed at the same relative coverages of arsenate, suggesting that similar reactive surface groups (>AlOH2) control the surface charging on both particles. EXAFS spectroscopy shows that there is no variation in arsenate surface speciation on a given mineral with surface coverage or pH. Whereas bidentate binuclear inner-sphere species are the dominant complexes present, the EXAFS result suggest that outer-sphere species also occur on both minerals, with a greater abundance on gibbsite. This binding mode likely involves adsorption to >Al2OH sites, which have a slow ligand exchange rate that inhibits inner-sphere binding. These results demonstrate that adsorption mechanisms and capacity, even when normalized for specific surface area, vary with metal oxide particle morphology because of the distribution of distinct functional groups.

Cr(3+) Binding to DNA Backbone Phosphate and Bases: Slow Ligand Exchange Rates and Metal Hydrolysis.

The interaction between chromium ions and DNA is of great interest in inorganic chemistry, toxicology, and analytical chemistry. Most previous studies focused on in situ reduction of Cr(VI), producing Cr(3+) for DNA binding. Recently, Cr(3+) was reported to activate the Ce13d DNAzyme for RNA cleavage. Herein, the Ce13d is used to study two types of Cr(3+) and DNA interactions. First, Cr(3+) binds to the DNA phosphate backbone weakly through reversible electrostatic interactions, which is weakened by adding competing inorganic phosphate. However, Cr(3+) coordinates with DNA nucleobases forming stable cross-links that can survive denaturing gel electrophoresis condition. The binding of Cr(3+) to different nucleobases was further studied in terms of binding kinetics and affinity by exploiting carboxyfluorescein-labeled DNA homopolymers. Once binding takes place, the stable Cr(3+)/DNA complex cannot be dissociated by EDTA, attributable to the ultraslow ligand exchange rate of Cr(3+). The binding rate follows the order of G > C > T ≈ A. Finally, Cr(3+) gradually loses its DNA binding ability after being stored at neutral or high pH, attributable to hydrolysis. This hydrolysis can be reversed by lowering the pH. This work provides a deeper insight into the bioinorganic chemistry of Cr(3+) coordination with DNA, clarifies some inconsistency in the previous literature, and offers practically useful information for generating reproducible results.

Fabrication of Highly Transparent and Flexible NanoMesh Electrode via Self‐assembly of Ultrathin Gold Nanowires

Transparent electrodes simultaneously require high electrical conductivity and high optical transparency, which have been achieved with mesh metal structures. However, most currently fabricated micro‐ and nanoelectronic devices are produced via top‐down lithography methods. Here, a bottom‐up self‐assembly approach to fabricate mesh electrode using ultrathin gold nanowires (AuNWs) at the air/water interface is reported. Slow partial ligand removal during the aging process is the key for the formation of such self‐assembled mesh structures. The resulting mesh film has a typical mesh pore size of 8–52 μm, with a sheet resistance of ≈40 times smaller than our previously reported nonmeshed AuNWs electrodes under similar optical transmittance. Our self‐assembled mesh electrodes are mechanically flexible, easily transferrable to a variety of substrates, and also patternable by marker pen lithography or cutting machine lithography, and washable, and can be directly used for touch screen and flexible interconnects for light‐emitting devices. The entire fabrication process is under ambient conditions without the need for any special equipment. These attributes indicate the potential applications of self‐assembled gold mesh electrodes in flexible solar cells, touch screen displays, and wearable electronics.

Fast and Slow Ligand Exchange at the Surface of Colloidal Gold Nanoparticles

Applications of gold nanoparticles often demand that the particle’s ligand shell is modified after particle formation. Obviously, there is a great need for a molecular understanding of this process which is often not accessible in situ. Here, we have applied second-harmonic light scattering (SHS) to investigate the ligand exchange at the surface of colloidal gold nanoparticles in situ and in real time. We demonstrate that the ligand exchange at the surface of citrate-covered Au nanoparticles with 3-mercapto-1-propanesulfonate (MPS) must be described by a fast (<100 s) and a slow reaction process (<23 min), which can be attributed to MPS adsorption on low- and high-coordinated Au surface sites. Using a modified Langmuir isotherm, the average Gibbs free energy of adsorption ΔG (−46 kJ/mol) and the surface coverage Γ (∼3.5 μmol/m2) for MPS on Au nanoparticles were determined. The latter was found to be much smaller compared to planar gold surfaces which points to coadsorption of MPS with citrate on high-coordinated sites, i.e., Au terraces. On more reactive low-coordinated Au sites, i.e., edge sites, citrate is easily replaced by MPS. In fact, we find that a substantial portion (49%) of the surface-adsorbed MPS is present on these low-coordinated sites.

ChemInform Abstract: Recent Advances in Osmium‐Catalyzed Hydrogenation and Dehydrogenation Reactions

AbstractReview: 39 refs.

Dimeric 1:2 adduct of β,β′-bis(diphenylphosphino)porphyrin with silver(I) chloride

A 2,18-bis(diphenylphosphino)porphyrin ligand undergoes complexation with silver(I) chloride to afford a stable phosphine-silver complex. X-ray crystallographic analysis of the complex revealed a dimeric structure of a 1:2 adduct of the diphosphine and silver(I) chloride, where each phosphorus atom coordinates a silver atom. The four AgCl units construct a distorted cubic cluster with small metallophilic interaction. Variable temperature 31 P NMR study exhibited a slow ligand exchange process between 107 Ag and 109 Ag at high temperature.

Mechanistic study of PFOS adsorption on kaolinite and montmorillonite

Adsorption of perfluorooctane sulfonate (PFOS) on clay minerals is pivotal in the fate and transport of PFOS in the environment. Understanding the PFOS adsorption mechanisms, however, presents challenges, especially in the presence of natural organic substances. In this study, the adsorption mechanism of PFOS on kaolinite and montmorillonite, with and without humic acids (HA), were investigated using batch experiments, ATR-FTIR spectroscopy, zeta potential, NEXAFS, and XRD. The results showed that PFOS had a higher adsorption capacity on kaolinite than on montmorillonite, both with a rapid formation of an outer-sphere complex followed by a slow ligand exchange reaction with the elimination of adsorbed H2O molecules. In addition to nonspecific hydrophobic and electrostatic interactions, specific chemisorption also exists between sulfonate group of PFOS and hydroxyl group on surfaces of clay minerals. The HA coating on clay materials inhibited PFOS adsorption due to its occupation of adsorption sites and increased electrostatic repulsion. The insights gained from this study improve our understanding on the mechanism of multilateral forces on PFOS adsorption at the molecular level.

From trigonal bipyramidal to platonic solids: self-assembly and self-sorting study of terpyridine-based 3D architectures.

Using a series of tritopic 2,2':6',2″-terpyridine (tpy) ligands constructed on adamantane, three discrete 3D metallo-supramolecular architectures were assembled, i.e., trigonal bipyramidal, tetrahedron, and cube. The self-assembly used tritopic ligands as corner directing units and metal ions as glue units at the edge. The angles of the linkers between adamantane and tpy head play a critical role in guiding the assembled structures, which have the general formula of M3nL2n, where M denotes metal ion and L denotes ligand. All complexes were fully characterized by (1)H, (13)C NMR, diffusion-ordered NMR spectroscopy, ESI-MS, and traveling-wave ion mobility-mass spectrometry. The binary mixtures of LA and LC or LB and LC underwent a self-sorting process that led to the self-assembly of discrete 3D structures. The self-sorting behavior is solely based on the angles precoded within the arm of tritopic ligands. Moreover, kinetic study of preassembled cube and tetrahedron demonstrated a slow ligand exchange process toward a statistical mixture of hetero tetrahedrons with LA and LB.

Dissolved copper speciation in the Tasman Sea, SW Pacific Ocean

The speciation of copper (Cu) in seawater is dominated by organic complexation but the sources, distribution and nature of these natural organic ligands remain unclear. The spatial distribution and character of organic copper binding ligands at two sites in the Tasman Sea were investigated using competitive ligand exchange adsorptive cathodic stripping voltammetry, utilising salicylaldoxime as the competing ligand. The first station was located in the oligotrophic north Tasman Sea and was contrasted with a second, mesotrophic, station in the south of the region where sampling coincided with a coccolithophore bloom. The northern P1 site (0–3000m) was characterised by detection of a single, strong, class of ligand with a uniformly distributed conditional stability constant (log K′CuL=12.97±0.26). At the two shallowest depths of the southern P3 site (13 and 28m), two ligands were detected. A single, stronger, ligand was detected at all other depths for this site. Below 120m, conditional stability constants at the southern P3 site (0–3500m) were uniformly distributed (log K′CuL=13.32±0.21). At both stations, ligand concentrations usually exceeded the total dissolved Cu concentration and mirrored the bio-intermediate Cu profile at depth. Dissolved Cu was more than 99% complexed by organic ligands at all depths except one, when dissolved Cu concentration exceeds the dissolve ligand concentration. The variability in ligand concentrations was greatest in the top 0–50m at the northern P1 site and 0–80m at the southern site. Based on a combination of phototrophic cell counts and biomarker pigment concentrations, the source of organic Cu-binding ligands in the north Tasman Sea is thought to be from cyanobacterial production, namely Synechococcus spp which dominates in the region. The detection of two organic Cu binding ligand classes at the southern P3 station indicates a more complex Cu-binding ligand pool in the surface waters. At this site, the ligands are likely sourced from cyanobacteria and eukaryotes, namely coccolithophores. At the northern P1 station only, a relationship between the proportion of unbound ligand available and the dissolved oxygen concentration was obtained. Given the simpler ligand pool dynamics of the northern station relative to the south, this relationship may reveal that complexation of organic Cu-binding ligands is important to prevent or slow ligand degradation in the deep sea.